Efficient quantum circuit implementation of quantum walks
International Nuclear Information System (INIS)
Douglas, B. L.; Wang, J. B.
2009-01-01
Quantum walks, being the quantum analog of classical random walks, are expected to provide a fruitful source of quantum algorithms. A few such algorithms have already been developed, including the 'glued trees' algorithm, which provides an exponential speedup over classical methods, relative to a particular quantum oracle. Here, we discuss the possibility of a quantum walk algorithm yielding such an exponential speedup over possible classical algorithms, without the use of an oracle. We provide examples of some highly symmetric graphs on which efficient quantum circuits implementing quantum walks can be constructed and discuss potential applications to quantum search for marked vertices along these graphs.
Quantum teleportation for continuous variables and related quantum information processing
International Nuclear Information System (INIS)
Furusawa, Akira; Takei, Nobuyuki
2007-01-01
Quantum teleportation is one of the most important subjects in quantum information science. This is because quantum teleportation can be regarded as not only quantum information transfer but also a building block for universal quantum information processing. Furthermore, deterministic quantum information processing is very important for efficient processing and it can be realized with continuous-variable quantum information processing. In this review, quantum teleportation for continuous variables and related quantum information processing are reviewed from these points of view
Efficient quantum walk on a quantum processor
Qiang, Xiaogang; Loke, Thomas; Montanaro, Ashley; Aungskunsiri, Kanin; Zhou, Xiaoqi; O'Brien, Jeremy L.; Wang, Jingbo B.; Matthews, Jonathan C. F.
2016-01-01
The random walk formalism is used across a wide range of applications, from modelling share prices to predicting population genetics. Likewise, quantum walks have shown much potential as a framework for developing new quantum algorithms. Here we present explicit efficient quantum circuits for implementing continuous-time quantum walks on the circulant class of graphs. These circuits allow us to sample from the output probability distributions of quantum walks on circulant graphs efficiently. We also show that solving the same sampling problem for arbitrary circulant quantum circuits is intractable for a classical computer, assuming conjectures from computational complexity theory. This is a new link between continuous-time quantum walks and computational complexity theory and it indicates a family of tasks that could ultimately demonstrate quantum supremacy over classical computers. As a proof of principle, we experimentally implement the proposed quantum circuit on an example circulant graph using a two-qubit photonics quantum processor. PMID:27146471
Regression relation for pure quantum states and its implications for efficient computing.
Elsayed, Tarek A; Fine, Boris V
2013-02-15
We obtain a modified version of the Onsager regression relation for the expectation values of quantum-mechanical operators in pure quantum states of isolated many-body quantum systems. We use the insights gained from this relation to show that high-temperature time correlation functions in many-body quantum systems can be controllably computed without complete diagonalization of the Hamiltonians, using instead the direct integration of the Schrödinger equation for randomly sampled pure states. This method is also applicable to quantum quenches and other situations describable by time-dependent many-body Hamiltonians. The method implies exponential reduction of the computer memory requirement in comparison with the complete diagonalization. We illustrate the method by numerically computing infinite-temperature correlation functions for translationally invariant Heisenberg chains of up to 29 spins 1/2. Thereby, we also test the spin diffusion hypothesis and find it in a satisfactory agreement with the numerical results. Both the derivation of the modified regression relation and the justification of the computational method are based on the notion of quantum typicality.
Efficient quantum circuits for Szegedy quantum walks
International Nuclear Information System (INIS)
Loke, T.; Wang, J.B.
2017-01-01
A major advantage in using Szegedy’s formalism over discrete-time and continuous-time quantum walks lies in its ability to define a unitary quantum walk by quantizing a Markov chain on a directed or weighted graph. In this paper, we present a general scheme to construct efficient quantum circuits for Szegedy quantum walks that correspond to classical Markov chains possessing transformational symmetry in the columns of the transition matrix. In particular, the transformational symmetry criteria do not necessarily depend on the sparsity of the transition matrix, so this scheme can be applied to non-sparse Markov chains. Two classes of Markov chains that are amenable to this construction are cyclic permutations and complete bipartite graphs, for which we provide explicit efficient quantum circuit implementations. We also prove that our scheme can be applied to Markov chains formed by a tensor product. We also briefly discuss the implementation of Markov chains based on weighted interdependent networks. In addition, we apply this scheme to construct efficient quantum circuits simulating the Szegedy walks used in the quantum Pagerank algorithm for some classes of non-trivial graphs, providing a necessary tool for experimental demonstration of the quantum Pagerank algorithm. - Highlights: • A general theoretical framework for implementing Szegedy walks using quantum circuits. • Explicit efficient quantum circuit implementation of the Szegedy walk for several classes of graphs. • Efficient implementation of Szegedy walks for quantum page-ranking of a certain class of graphs.
Efficient quantum circuits for Szegedy quantum walks
Loke, T.; Wang, J. B.
2017-07-01
A major advantage in using Szegedy's formalism over discrete-time and continuous-time quantum walks lies in its ability to define a unitary quantum walk by quantizing a Markov chain on a directed or weighted graph. In this paper, we present a general scheme to construct efficient quantum circuits for Szegedy quantum walks that correspond to classical Markov chains possessing transformational symmetry in the columns of the transition matrix. In particular, the transformational symmetry criteria do not necessarily depend on the sparsity of the transition matrix, so this scheme can be applied to non-sparse Markov chains. Two classes of Markov chains that are amenable to this construction are cyclic permutations and complete bipartite graphs, for which we provide explicit efficient quantum circuit implementations. We also prove that our scheme can be applied to Markov chains formed by a tensor product. We also briefly discuss the implementation of Markov chains based on weighted interdependent networks. In addition, we apply this scheme to construct efficient quantum circuits simulating the Szegedy walks used in the quantum Pagerank algorithm for some classes of non-trivial graphs, providing a necessary tool for experimental demonstration of the quantum Pagerank algorithm.
Numerical multistep methods for the efficient solution of quantum mechanics and related problems
International Nuclear Information System (INIS)
Anastassi, Z.A.; Simos, T.E.
2009-01-01
In this paper we present the recent development in the numerical integration of the Schroedinger equation and related systems of ordinary differential equations with oscillatory solutions, such as the N-body problem. We examine several types of multistep methods (explicit, implicit, predictor-corrector, hybrid) and several properties (P-stability, trigonometric fitting of various orders, phase fitting, high phase-lag order, algebraic order). We analyze the local truncation error and the stability of the methods. The error for the Schroedinger equation is also presented, which reveals the relation of the error to the energy. The efficiency of the methods is evaluated through the integration of five problems. Figures are presented and analyzed and some general conclusions are made. Code written in Maple is given for the development of all methods analyzed in this paper. Also the subroutines written in Matlab, that concern the integration of the methods, are presented.
International Nuclear Information System (INIS)
Banai, M.
1983-11-01
A quantum relativity theory formulated in terms of Davis' quantum relativity principle is outlined. The first task in this theory as in classical relativity theory is to model space-time, the arena of natural processes. It is argued that the quantum space-time models of Banai introduced in an earlier paper is formulated in terms of Davis' quantum relativity. Then it is shown that the recently proposed classical relativistic quantum theory of Prugovecki and his corresponding classical relativistic quantum model of space-time open the way to introduce in a consistent way the quantum space-time model (the 'canonically quantized Minkowski space') proposed by Banai earlier. The main new aspect of the quantum mechanics of the quantum relativistic particles is, in this model of space-time, that it provides a true mass eigenvalue problem and, that the excited mass states of such particles can be interpreted as classifically relativistic (massive) quantum particles ('elementary particles'). The question of field theory over quantum relativistic models of space-time is also discussed. Finally, it is suggested that 'quarks' should be considered as quantum relativistic particles. (author)
Efficiency of fermionic quantum distillation
Energy Technology Data Exchange (ETDEWEB)
Herbrych, Jacek W. [Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Feiguin, Adrian E. [Northeastern Univ., Boston, MA (United States); Dagotto, Elbio R. [Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Heidrich-Meisner, F. [Ludwig-Maximilians-Univ. Munchen, Munchen (Germany)
2017-09-13
Here, we present a time-dependent density-matrix renormalization group investigation of the quantum distillation process within the Fermi-Hubbard model on a quasi-one-dimensional ladder geometry. The term distillation refers to the dynamical, spatial separation of singlons and doublons in the sudden expansion of interacting particles in an optical lattice, i.e., the release of a cloud of atoms from a trapping potential. Remarkably, quantum distillation can lead to a contraction of the doublon cloud, resulting in an increased density of the doublons in the core region compared to the initial state. As a main result, we show that this phenomenon is not limited to chains that were previously studied. Interestingly, there are additional dynamical processes on the two-leg ladder such as density oscillations and self-trapping of defects that lead to a less efficient distillation process. An investigation of the time evolution starting from product states provides an explanation for this behavior. Initial product states are also considered since in optical lattice experiments, such states are often used as the initial setup. We propose configurations that lead to a fast and efficient quantum distillation.
Quantum entanglement helps in improving economic efficiency
International Nuclear Information System (INIS)
Du Jiangfeng; Ju Chenyong; Li Hui
2005-01-01
We propose an economic regulation approach based on quantum game theory for the government to reduce the abuses of oligopolistic competition. Theoretical analysis shows that this approach can help government improve the economic efficiency of the oligopolistic market, and help prevent monopoly due to incorrect information. These advantages are completely attributed to the quantum entanglement, a unique quantum mechanical character
Quantum entanglement helps in improving economic efficiency
Du, Jiangfeng; Ju, Chenyong; Li, Hui
2005-02-01
We propose an economic regulation approach based on quantum game theory for the government to reduce the abuses of oligopolistic competition. Theoretical analysis shows that this approach can help government improve the economic efficiency of the oligopolistic market, and help prevent monopoly due to incorrect information. These advantages are completely attributed to the quantum entanglement, a unique quantum mechanical character.
Quantum autoencoders for efficient compression of quantum data
Romero, Jonathan; Olson, Jonathan P.; Aspuru-Guzik, Alan
2017-12-01
Classical autoencoders are neural networks that can learn efficient low-dimensional representations of data in higher-dimensional space. The task of an autoencoder is, given an input x, to map x to a lower dimensional point y such that x can likely be recovered from y. The structure of the underlying autoencoder network can be chosen to represent the data on a smaller dimension, effectively compressing the input. Inspired by this idea, we introduce the model of a quantum autoencoder to perform similar tasks on quantum data. The quantum autoencoder is trained to compress a particular data set of quantum states, where a classical compression algorithm cannot be employed. The parameters of the quantum autoencoder are trained using classical optimization algorithms. We show an example of a simple programmable circuit that can be trained as an efficient autoencoder. We apply our model in the context of quantum simulation to compress ground states of the Hubbard model and molecular Hamiltonians.
An efficient quantum algorithm for spectral estimation
Steffens, Adrian; Rebentrost, Patrick; Marvian, Iman; Eisert, Jens; Lloyd, Seth
2017-03-01
We develop an efficient quantum implementation of an important signal processing algorithm for line spectral estimation: the matrix pencil method, which determines the frequencies and damping factors of signals consisting of finite sums of exponentially damped sinusoids. Our algorithm provides a quantum speedup in a natural regime where the sampling rate is much higher than the number of sinusoid components. Along the way, we develop techniques that are expected to be useful for other quantum algorithms as well—consecutive phase estimations to efficiently make products of asymmetric low rank matrices classically accessible and an alternative method to efficiently exponentiate non-Hermitian matrices. Our algorithm features an efficient quantum-classical division of labor: the time-critical steps are implemented in quantum superposition, while an interjacent step, requiring much fewer parameters, can operate classically. We show that frequencies and damping factors can be obtained in time logarithmic in the number of sampling points, exponentially faster than known classical algorithms.
Modern canonical quantum general relativity
Thiemann, Thomas
2007-01-01
This is an introduction to the by now fifteen years old research field of canonical quantum general relativity, sometimes called "loop quantum gravity". The term "modern" in the title refers to the fact that the quantum theory is based on formulating classical general relativity as a theory of connections rather than metrics as compared to in original version due to Arnowitt, Deser and Misner. Canonical quantum general relativity is an attempt to define a mathematically rigorous, non-perturbative, background independent theory of Lorentzian quantum gravity in four spacetime dimensions in the continuum. The approach is minimal in that one simply analyzes the logical consequences of combining the principles of general relativity with the principles of quantum mechanics. The requirement to preserve background independence has lead to new, fascinating mathematical structures which one does not see in perturbative approaches, e.g. a fundamental discreteness of spacetime seems to be a prediction of the theory provi...
Efficient networks for quantum factoring
International Nuclear Information System (INIS)
Beckman, D.; Chari, A.N.; Devabhaktuni, S.; Preskill, J.
1996-01-01
We consider how to optimize memory use and computation time in operating a quantum computer. In particular, we estimate the number of memory quantum bits (qubits) and the number of operations required to perform factorization, using the algorithm suggested by Shor [in Proceedings of the 35th Annual Symposium on Foundations of Computer Science, edited by S. Goldwasser (IEEE Computer Society, Los Alamitos, CA, 1994), p. 124]. A K-bit number can be factored in time of order K 3 using a machine capable of storing 5K+1 qubits. Evaluation of the modular exponential function (the bottleneck of Shor close-quote s algorithm) could be achieved with about 72K 3 elementary quantum gates; implementation using a linear ion trap would require about 396K 3 laser pulses. A proof-of-principle demonstration of quantum factoring (factorization of 15) could be performed with only 6 trapped ions and 38 laser pulses. Though the ion trap may never be a useful computer, it will be a powerful device for exploring experimentally the properties of entangled quantum states. copyright 1996 The American Physical Society
Conditional efficient multiuser quantum cryptography network
International Nuclear Information System (INIS)
Xue Peng; Li Chuanfeng; Guo Guangcan
2002-01-01
We propose a conditional quantum key distribution scheme with three nonorthogonal states. Combined with the idea presented by Lo et al. (H.-K. Lo, H. F. Chau, and M. Ardehali, e-print arXiv: quant-ph/0011056), the efficiency of this scheme is increased to tend to 100%. Also, such a refined data analysis guarantees the security of our scheme against the most general eavesdropping strategy. Then, based on the scheme, we present a quantum cryptography network with the addition of a device called ''space optical switch.'' Moreover, we give out a realization of a quantum random number generator. Thus, a feasible experimental scheme of this efficient quantum cryptography network is completely given
Efficient multiparty quantum-secret-sharing schemes
International Nuclear Information System (INIS)
Xiao Li; Deng Fuguo; Long Guilu; Pan Jianwei
2004-01-01
In this work, we generalize the quantum-secret-sharing scheme of Hillery, Buzek, and Berthiaume [Phys. Rev. A 59, 1829 (1999)] into arbitrary multiparties. Explicit expressions for the shared secret bit is given. It is shown that in the Hillery-Buzek-Berthiaume quantum-secret-sharing scheme the secret information is shared in the parity of binary strings formed by the measured outcomes of the participants. In addition, we have increased the efficiency of the quantum-secret-sharing scheme by generalizing two techniques from quantum key distribution. The favored-measuring-basis quantum-secret-sharing scheme is developed from the Lo-Chau-Ardehali technique [H. K. Lo, H. F. Chau, and M. Ardehali, e-print quant-ph/0011056] where all the participants choose their measuring-basis asymmetrically, and the measuring-basis-encrypted quantum-secret-sharing scheme is developed from the Hwang-Koh-Han technique [W. Y. Hwang, I. G. Koh, and Y. D. Han, Phys. Lett. A 244, 489 (1998)] where all participants choose their measuring basis according to a control key. Both schemes are asymptotically 100% in efficiency, hence nearly all the Greenberger-Horne-Zeilinger states in a quantum-secret-sharing process are used to generate shared secret information
Relating quantum discord with the quantum dense coding capacity
Energy Technology Data Exchange (ETDEWEB)
Wang, Xin; Qiu, Liang, E-mail: lqiu@cumt.edu.cn; Li, Song; Zhang, Chi [China University of Mining and Technology, School of Sciences (China); Ye, Bin [China University of Mining and Technology, School of Information and Electrical Engineering (China)
2015-01-15
We establish the relations between quantum discord and the quantum dense coding capacity in (n + 1)-particle quantum states. A necessary condition for the vanishing discord monogamy score is given. We also find that the loss of quantum dense coding capacity due to decoherence is bounded below by the sum of quantum discord. When these results are restricted to three-particle quantum states, some complementarity relations are obtained.
Relating quantum discord with the quantum dense coding capacity
International Nuclear Information System (INIS)
Wang, Xin; Qiu, Liang; Li, Song; Zhang, Chi; Ye, Bin
2015-01-01
We establish the relations between quantum discord and the quantum dense coding capacity in (n + 1)-particle quantum states. A necessary condition for the vanishing discord monogamy score is given. We also find that the loss of quantum dense coding capacity due to decoherence is bounded below by the sum of quantum discord. When these results are restricted to three-particle quantum states, some complementarity relations are obtained
Quantum decoherence and interlevel relations
Crull, Elise M.
Quantum decoherence is a dynamical process whereby a system's phase relations become delocalized due to interaction and subsequent entanglement with its environment. This delocalization, or decoherence, forces the quantum system into a state that is apparently classical (or apparently an eigenstate) by prodigiously suppressing features that typically give rise to so-called quantum behavior. Thus it has been frequently proposed by physicists and philosophers alike that decoherence explains the dynamical transition from quantum behavior to classical behavior. Statements like this assume the existence of distinct realms, however, and the present thesis is an exploration of the metaphysical consequences of quantum decoherence motivated by the question of the quantum-to-classical transition and interlevel relations: if there are in-principle "classical" and "quantum" levels, what are the relations between them? And if there are no such levels, what follows? Importantly, the following philosophical investigations are carried out by intentionally leaving aside the measurement problem and concerns about particular interpretations of quantum mechanics. Good philosophical work, it is argued, can be done without adopting a specific interpretational framework and without recourse to the measurement problem. After introducing the physics of decoherence and exploring the four canonical models applied to system-environment interactions, it is argued that, ontologically speaking, there exist no levels. This claim---called the "nontological thesis"---exposes as ill-posed questions regarding the transition from the quantum regime to the classical regime and reveals the inappropriateness of interlevel relations (like reduction, supervenience and emergence) operating within metaphysical frameworks. The nontological thesis has further important consequences regarding intralevel relations: not only are there no meaningful ways to carve the world into levels, but there are no meaningful
Efficient quantum computing with weak measurements
International Nuclear Information System (INIS)
Lund, A P
2011-01-01
Projective measurements with high quantum efficiency are often assumed to be required for efficient circuit-based quantum computing. We argue that this is not the case and show that the fact that they are not required was actually known previously but was not deeply explored. We examine this issue by giving an example of how to perform the quantum-ordering-finding algorithm efficiently using non-local weak measurements considering that the measurements used are of bounded weakness and some fixed but arbitrary probability of success less than unity is required. We also show that it is possible to perform the same computation with only local weak measurements, but this must necessarily introduce an exponential overhead.
International Nuclear Information System (INIS)
Rovelli, C.
1996-01-01
I suggest that the common unease with taking quantum mechanics as a fundamental description of nature (the open-quotes measurement problemclose quotes) could derive from the use of an incorrect notion, as the unease with the Lorentz transformations before Einstein derived from the notion of observer-independent time. I suggest that this incorrect notion that generates the unease with quantum mechanics is the notion of open-quotes observer-independent stateclose quotes of a system, or open-quotes observer-independent values of physical quantities.close quotes I reformulate the problem of the open-quotes interpretation of quantum mechanicsclose quotes as the problem of deriving the formalism from a set of simple physical postulates. I consider a reformulation of quantum mechanics in terms of information theory. All systems are assumed to be equivalent, there is no observer-observed distinction, and the theory describes only the information that systems have about each other; nevertheless, the theory is complete
Efficient quantum circuits for one-way quantum computing.
Tanamoto, Tetsufumi; Liu, Yu-Xi; Hu, Xuedong; Nori, Franco
2009-03-13
While Ising-type interactions are ideal for implementing controlled phase flip gates in one-way quantum computing, natural interactions between solid-state qubits are most often described by either the XY or the Heisenberg models. We show an efficient way of generating cluster states directly using either the imaginary SWAP (iSWAP) gate for the XY model, or the sqrt[SWAP] gate for the Heisenberg model. Our approach thus makes one-way quantum computing more feasible for solid-state devices.
Quantum physics and relational ontology
Energy Technology Data Exchange (ETDEWEB)
Cordovil, Joao [Center of Philosophy of Sciences of University of Lisbon (Portugal)
2013-07-01
The discovery of the quantum domain of reality put a serious ontological challenge, a challenge that is still well present in the recent developments of Quantum Physics. Physics was conceived from an atomistic conception of the world, reducing it, in all its diversity, to two types of entities: simple, individual and immutable entities (atoms, in metaphysical sense) and composite entities, resulting solely from combinations. Linear combinations, additive, indifferent to the structure or to the context. However, the discovery of wave-particle dualism and the developments in Quantum Field Theories and in Quantum Nonlinear Physical, showed that quantum entities are not, in metaphysical sense, neither simple, nor merely the result of linear (or additive) combinations. In other words, the ontological foundations of Physics revealed as inadequate to account for the nature of quantum entities. Then a fundamental challenge arises: How to think the ontic nature of these entities? In my view, this challenge appeals to a relational and dynamist ontology of physical entities. This is the central hypothesis of this communication. In this sense, this communication has two main intentions: 1) positively characterize this relational and dynamist ontology; 2) show some elements of its metaphysical suitability to contemporary Quantum Physics.
Fast, efficient error reconciliation for quantum cryptography
International Nuclear Information System (INIS)
Buttler, W.T.; Lamoreaux, S.K.; Torgerson, J.R.; Nickel, G.H.; Donahue, C.H.; Peterson, C.G.
2003-01-01
We describe an error-reconciliation protocol, which we call Winnow, based on the exchange of parity and Hamming's 'syndrome' for N-bit subunits of a large dataset. The Winnow protocol was developed in the context of quantum-key distribution and offers significant advantages and net higher efficiency compared to other widely used protocols within the quantum cryptography community. A detailed mathematical analysis of the Winnow protocol is presented in the context of practical implementations of quantum-key distribution; in particular, the information overhead required for secure implementation is one of the most important criteria in the evaluation of a particular error-reconciliation protocol. The increase in efficiency for the Winnow protocol is largely due to the reduction in authenticated public communication required for its implementation
Quantum information and relativity theory
International Nuclear Information System (INIS)
Peres, Asher; Terno, Daniel R.
2004-01-01
This article discusses the intimate relationship between quantum mechanics, information theory, and relativity theory. Taken together these are the foundations of present-day theoretical physics, and their interrelationship is an essential part of the theory. The acquisition of information from a quantum system by an observer occurs at the interface of classical and quantum physics. The authors review the essential tools needed to describe this interface, i.e., Kraus matrices and positive-operator-valued measures. They then discuss how special relativity imposes severe restrictions on the transfer of information between distant systems and the implications of the fact that quantum entropy is not a Lorentz-covariant concept. This leads to a discussion of how it comes about that Lorentz transformations of reduced density matrices for entangled systems may not be completely positive maps. Quantum field theory is, of course, necessary for a consistent description of interactions. Its structure implies a fundamental tradeoff between detector reliability and localizability. Moreover, general relativity produces new and counterintuitive effects, particularly when black holes (or, more generally, event horizons) are involved. In this more general context the authors discuss how most of the current concepts in quantum information theory may require a reassessment
Introducing Relativity into Quantum Chemistry
Li, Wai-Kee; Blinder, S. M.
2011-01-01
It is not often realized by chemists that the special theory of relativity is behind several aspects of quantum chemistry. The Schrdinger equation itself is based on relations between space-time and energy-momentum four vectors. Electron spin is, of course, the most obvious manifestation of relativity. The chemistry of some heavy elements is…
Efficient quantum computing using coherent photon conversion.
Langford, N K; Ramelow, S; Prevedel, R; Munro, W J; Milburn, G J; Zeilinger, A
2011-10-12
Single photons are excellent quantum information carriers: they were used in the earliest demonstrations of entanglement and in the production of the highest-quality entanglement reported so far. However, current schemes for preparing, processing and measuring them are inefficient. For example, down-conversion provides heralded, but randomly timed, single photons, and linear optics gates are inherently probabilistic. Here we introduce a deterministic process--coherent photon conversion (CPC)--that provides a new way to generate and process complex, multiquanta states for photonic quantum information applications. The technique uses classically pumped nonlinearities to induce coherent oscillations between orthogonal states of multiple quantum excitations. One example of CPC, based on a pumped four-wave-mixing interaction, is shown to yield a single, versatile process that provides a full set of photonic quantum processing tools. This set satisfies the DiVincenzo criteria for a scalable quantum computing architecture, including deterministic multiqubit entanglement gates (based on a novel form of photon-photon interaction), high-quality heralded single- and multiphoton states free from higher-order imperfections, and robust, high-efficiency detection. It can also be used to produce heralded multiphoton entanglement, create optically switchable quantum circuits and implement an improved form of down-conversion with reduced higher-order effects. Such tools are valuable building blocks for many quantum-enabled technologies. Finally, using photonic crystal fibres we experimentally demonstrate quantum correlations arising from a four-colour nonlinear process suitable for CPC and use these measurements to study the feasibility of reaching the deterministic regime with current technology. Our scheme, which is based on interacting bosonic fields, is not restricted to optical systems but could also be implemented in optomechanical, electromechanical and superconducting
Parallel state transfer and efficient quantum routing on quantum networks.
Chudzicki, Christopher; Strauch, Frederick W
2010-12-31
We study the routing of quantum information in parallel on multidimensional networks of tunable qubits and oscillators. These theoretical models are inspired by recent experiments in superconducting circuits. We show that perfect parallel state transfer is possible for certain networks of harmonic oscillator modes. We extend this to the distribution of entanglement between every pair of nodes in the network, finding that the routing efficiency of hypercube networks is optimal and robust in the presence of dissipation and finite bandwidth.
Quantum Efficiency of Hybrid Photon Detectors for the LHCb RICH
Lambert, R W
2008-01-01
The production of Hybrid Photon Detectors to be used as the single-photon sensors for the RICH detectors of the LHCb experiment has recently finished. We present the quantum efficiency measurements of the entire sample of 550 tubes. The manufacturer has succeeded in consistently improving the quantum efficiency of the employed S20-type multi-alkali photocathode above our expectations, by a relative 27 % integrated over the energy spectrum. We also report measurements of the vacuum quality using the photocurrent of the device as a monitor for possible vacuum degradation.
Quantum relativity theory and quantum space-time
International Nuclear Information System (INIS)
Banai, M.
1984-01-01
A quantum relativity theory formulated in terms of Davis' quantum relativity principle is outlined. The first task in this theory as in classical relativity theory is to model space-time, the arena of natural processes. It is shown that the quantum space-time models of Banai introduced in another paper is formulated in terms of Davis's quantum relativity. The recently proposed classical relativistic quantum theory of Prugovecki and his corresponding classical relativistic quantum model of space-time open the way to introduce, in a consistent way, the quantum space-time model (the quantum substitute of Minkowski space) of Banai proposed in the paper mentioned. The goal of quantum mechanics of quantum relativistic particles living in this model of space-time is to predict the rest mass system properties of classically relativistic (massive) quantum particles (''elementary particles''). The main new aspect of this quantum mechanics is that it provides a true mass eigenvalue problem, and that the excited mass states of quantum relativistic particles can be interpreted as elementary particles. The question of field theory over quantum relativistic model of space-time is also discussed. Finally it is suggested that ''quarks'' should be considered as quantum relativistic particles. (author)
Modern Canonical Quantum General Relativity
Thiemann, Thomas
2008-11-01
Preface; Notation and conventions; Introduction; Part I. Classical Foundations, Interpretation and the Canonical Quantisation Programme: 1. Classical Hamiltonian formulation of general relativity; 2. The problem of time, locality and the interpretation of quantum mechanics; 3. The programme of canonical quantisation; 4. The new canonical variables of Ashtekar for general relativity; Part II. Foundations of Modern Canonical Quantum General Relativity: 5. Introduction; 6. Step I: the holonomy-flux algebra [P]; 7. Step II: quantum-algebra; 8. Step III: representation theory of [A]; 9. Step IV: 1. Implementation and solution of the kinematical constraints; 10. Step V: 2. Implementation and solution of the Hamiltonian constraint; 11. Step VI: semiclassical analysis; Part III. Physical Applications: 12. Extension to standard matter; 13. Kinematical geometrical operators; 14. Spin foam models; 15. Quantum black hole physics; 16. Applications to particle physics and quantum cosmology; 17. Loop quantum gravity phenomenology; Part IV. Mathematical Tools and their Connection to Physics: 18. Tools from general topology; 19. Differential, Riemannian, symplectic and complex geometry; 20. Semianalytical category; 21. Elements of fibre bundle theory; 22. Holonomies on non-trivial fibre bundles; 23. Geometric quantisation; 24. The Dirac algorithm for field theories with constraints; 25. Tools from measure theory; 26. Elementary introduction to Gel'fand theory for Abelean C* algebras; 27. Bohr compactification of the real line; 28. Operatir -algebras and spectral theorem; 29. Refined algebraic quantisation (RAQ) and direct integral decomposition (DID); 30. Basics of harmonic analysis on compact Lie groups; 31. Spin network functions for SU(2); 32. + Functional analytical description of classical connection dynamics; Bibliography; Index.
Relativistic quantum metrology: exploiting relativity to improve quantum measurement technologies.
Ahmadi, Mehdi; Bruschi, David Edward; Sabín, Carlos; Adesso, Gerardo; Fuentes, Ivette
2014-05-22
We present a framework for relativistic quantum metrology that is useful for both Earth-based and space-based technologies. Quantum metrology has been so far successfully applied to design precision instruments such as clocks and sensors which outperform classical devices by exploiting quantum properties. There are advanced plans to implement these and other quantum technologies in space, for instance Space-QUEST and Space Optical Clock projects intend to implement quantum communications and quantum clocks at regimes where relativity starts to kick in. However, typical setups do not take into account the effects of relativity on quantum properties. To include and exploit these effects, we introduce techniques for the application of metrology to quantum field theory. Quantum field theory properly incorporates quantum theory and relativity, in particular, at regimes where space-based experiments take place. This framework allows for high precision estimation of parameters that appear in quantum field theory including proper times and accelerations. Indeed, the techniques can be applied to develop a novel generation of relativistic quantum technologies for gravimeters, clocks and sensors. As an example, we present a high precision device which in principle improves the state-of-the-art in quantum accelerometers by exploiting relativistic effects.
Pure sources and efficient detectors for optical quantum information processing
Zielnicki, Kevin
Over the last sixty years, classical information theory has revolutionized the understanding of the nature of information, and how it can be quantified and manipulated. Quantum information processing extends these lessons to quantum systems, where the properties of intrinsic uncertainty and entanglement fundamentally defy classical explanation. This growing field has many potential applications, including computing, cryptography, communication, and metrology. As inherently mobile quantum particles, photons are likely to play an important role in any mature large-scale quantum information processing system. However, the available methods for producing and detecting complex multi-photon states place practical limits on the feasibility of sophisticated optical quantum information processing experiments. In a typical quantum information protocol, a source first produces an interesting or useful quantum state (or set of states), perhaps involving superposition or entanglement. Then, some manipulations are performed on this state, perhaps involving quantum logic gates which further manipulate or entangle the intial state. Finally, the state must be detected, obtaining some desired measurement result, e.g., for secure communication or computationally efficient factoring. The work presented here concerns the first and last stages of this process as they relate to photons: sources and detectors. Our work on sources is based on the need for optimized non-classical states of light delivered at high rates, particularly of single photons in a pure quantum state. We seek to better understand the properties of spontaneous parameteric downconversion (SPDC) sources of photon pairs, and in doing so, produce such an optimized source. We report an SPDC source which produces pure heralded single photons with little or no spectral filtering, allowing a significant rate enhancement. Our work on detectors is based on the need to reliably measure single-photon states. We have focused on
Efficient Multiphoton Generation in Waveguide Quantum Electrodynamics
González-Tudela, A.; Paulisch, V.; Kimble, H. J.; Cirac, J. I.
2017-05-01
Engineering quantum states of light is at the basis of many quantum technologies such as quantum cryptography, teleportation, or metrology among others. Though, single photons can be generated in many scenarios, the efficient and reliable generation of complex single-mode multiphoton states is still a long-standing goal in the field, as current methods either suffer from low fidelities or small probabilities. Here we discuss several protocols which harness the strong and long-range atomic interactions induced by waveguide QED to efficiently load excitations in a collection of atoms, which can then be triggered to produce the desired multiphoton state. In order to boost the success probability and fidelity of each excitation process, atoms are used to both generate the excitations in the rest, as well as to herald the successful generation. Furthermore, to overcome the exponential scaling of the probability of success with the number of excitations, we design a protocol to merge excitations that are present in different internal atomic levels with a polynomial scaling.
Modern Canonical Quantum General Relativity;
International Nuclear Information System (INIS)
Kiefer, Claus
2008-01-01
The open problem of constructing a consistent and experimentally tested quantum theory of the gravitational field has its place at the heart of fundamental physics. The main approaches can be roughly divided into two classes: either one seeks a unified quantum framework of all interactions or one starts with a direct quantization of general relativity. In the first class, string theory (M-theory) is the only known example. In the second class, one can make an additional methodological distinction: while covariant approaches such as path-integral quantization use the four-dimensional metric as an essential ingredient of their formalism, canonical approaches start with a foliation of spacetime into spacelike hypersurfaces in order to arrive at a Hamiltonian formulation. The present book is devoted to one of the canonical approaches-loop quantum gravity. It is named modern canonical quantum general relativity by the author because it uses connections and holonomies as central variables, which are analogous to the variables used in Yang-Mills theories. In fact, the canonically conjugate variables are a holonomy of a connection and the flux of a non-Abelian electric field. This has to be contrasted with the older geometrodynamical approach in which the metric of three-dimensional space and the second fundamental form are the fundamental entities, an approach which is still actively being pursued. It is the author's ambition to present loop quantum gravity in a way in which every step is formulated in a mathematically rigorous form. The formal Leitmotiv of loop quantum gravity is background independence. Non-gravitational theories are usually quantized on a given non-dynamical background. In contrast, due to the geometrical nature of gravity, no such background exists in quantum gravity. Instead, the notion of a background is supposed to emerge a posteriori as an approximate notion from quantum states of geometry. As a consequence, the standard ultraviolet divergences of
Quantum mechanics from general relativity
International Nuclear Information System (INIS)
Sachs, M.
1986-01-01
A generalization of quantum mechanics is demonstrated in the context of general relativity, following from a generally covariant field theory of inertia. Nonrelativistically, the formalism corresponds with linear quantum mechanics. In the limit of special relativity, nonlinearity remains and several new features are derived: (1) Particle-antiparticle pairs do not annihilate; an exact bound state solution is derived corresponding with all experimental facts about annihilation/creation - which, in approximation, gives the blackbody radiation spectrum for a sea of such pairs. (2) A result is proven, without approximation, that is physically equivalent to the Pauli exclusion principle - which, in linear approximation, gives the totally antisymmetrised many-body wave function and Fermi-Dirac statistics. (3) The hydrogen spectrum is derived, including the Lamb shifts, in agreement with experiment; new results are found for high energy electron-proton scattering. (4) Finally, several applications to the elementary particle domain are demonstrated, in agreement with results from experimental high energy physics. (Auth.)
Quantum information and general relativity
International Nuclear Information System (INIS)
Peres, A.
2004-01-01
The Einstein-Podolsky-Rosen paradox (1935) is reexamined in the light of Shannon's information theory (1948). The EPR argument did not take into account that the observers' information was localized, like any other physical object. General relativity introduces new problems: there are horizons which act as on-way membranes for the propagation of quantum information, in particular black holes which act like sinks. (Abstract Copyright [2004], Wiley Periodicals, Inc.)
Quantum information and general relativity
Energy Technology Data Exchange (ETDEWEB)
Peres, A. [Technion, Israel Institute of Technology, Haifa (Israel)
2004-12-01
The Einstein-Podolsky-Rosen paradox (1935) is reexamined in the light of Shannon's information theory (1948). The EPR argument did not take into account that the observers' information was localized, like any other physical object. General relativity introduces new problems: there are horizons which act as on-way membranes for the propagation of quantum information, in particular black holes which act like sinks. (Abstract Copyright [2004], Wiley Periodicals, Inc.)
Quantum information and general relativity
Peres, Asher
2004-01-01
The Einstein-Podolsky-Rosen paradox (1935) is reexamined in the light of Shannon's information theory (1948). The EPR argument did not take into account that the observers' information was localized, like any other physical object. General relativity introduces new problems: there are horizons which act as one-way membranes for the propagation of quantum information, in particular black holes which act like sinks.
Quantum information and general relativity
Peres, A.
2004-11-01
The Einstein-Podolsky-Rosen paradox (1935) is reexamined in the light of Shannon's information theory (1948). The EPR argument did not take into account that the observers' information was localized, like any other physical object. General relativity introduces new problems: there are horizons which act as on-way membranes for the propagation of quantum information, in particular black holes which act like sinks.
Highly Efficient Spontaneous Emission from Self-Assembled Quantum Dots
DEFF Research Database (Denmark)
Johansen, Jeppe; Lund-Hansen, Toke; Hvam, Jørn Märcher
2006-01-01
We present time resolved measurements of spontaneous emission (SE) from InAs/GaAs quantum dots (QDs). The measurements are interpreted using Fermi's Golden Rule and from this analysis we establish the parameters for high quantum efficiency.......We present time resolved measurements of spontaneous emission (SE) from InAs/GaAs quantum dots (QDs). The measurements are interpreted using Fermi's Golden Rule and from this analysis we establish the parameters for high quantum efficiency....
Pulsed homodyne Gaussian quantum tomography with low detection efficiency
Esposito, M.; Benatti, F.; Floreanini, R.; Olivares, S.; Randi, F.; Titimbo, K.; Pividori, M.; Novelli, F.; Cilento, F.; Parmigiani, F.; Fausti, D.
2014-04-01
Pulsed homodyne quantum tomography usually requires a high detection efficiency, limiting its applicability in quantum optics. Here, it is shown that the presence of low detection efficiency (<50%) does not prevent the tomographic reconstruction of quantum states of light, specifically, of Gaussian states. This result is obtained by applying the so-called ‘minimax’ adaptive reconstruction of the Wigner function to pulsed homodyne detection. In particular, we prove, by both numerical and real experiments, that an effective discrimination of different Gaussian quantum states can be achieved. Our finding paves the way to a more extensive use of quantum tomographic methods, even in physical situations in which high detection efficiency is unattainable.
Pulsed homodyne Gaussian quantum tomography with low detection efficiency
International Nuclear Information System (INIS)
Esposito, M; Benatti, F; Randi, F; Titimbo, K; Pividori, M; Parmigiani, F; Fausti, D; Floreanini, R; Olivares, S; Novelli, F; Cilento, F
2014-01-01
Pulsed homodyne quantum tomography usually requires a high detection efficiency, limiting its applicability in quantum optics. Here, it is shown that the presence of low detection efficiency (<50) does not prevent the tomographic reconstruction of quantum states of light, specifically, of Gaussian states. This result is obtained by applying the so-called ‘minimax’ adaptive reconstruction of the Wigner function to pulsed homodyne detection. In particular, we prove, by both numerical and real experiments, that an effective discrimination of different Gaussian quantum states can be achieved. Our finding paves the way to a more extensive use of quantum tomographic methods, even in physical situations in which high detection efficiency is unattainable
Efficient one-way quantum computations for quantum error correction
International Nuclear Information System (INIS)
Huang Wei; Wei Zhaohui
2009-01-01
We show how to explicitly construct an O(nd) size and constant quantum depth circuit which encodes any given n-qubit stabilizer code with d generators. Our construction is derived using the graphic description for stabilizer codes and the one-way quantum computation model. Our result demonstrates how to use cluster states as scalable resources for many multi-qubit entangled states and how to use the one-way quantum computation model to improve the design of quantum algorithms.
Computationally Efficient Nonlinear Bell Inequalities for Quantum Networks
Luo, Ming-Xing
2018-04-01
The correlations in quantum networks have attracted strong interest with new types of violations of the locality. The standard Bell inequalities cannot characterize the multipartite correlations that are generated by multiple sources. The main problem is that no computationally efficient method is available for constructing useful Bell inequalities for general quantum networks. In this work, we show a significant improvement by presenting new, explicit Bell-type inequalities for general networks including cyclic networks. These nonlinear inequalities are related to the matching problem of an equivalent unweighted bipartite graph that allows constructing a polynomial-time algorithm. For the quantum resources consisting of bipartite entangled pure states and generalized Greenberger-Horne-Zeilinger (GHZ) states, we prove the generic nonmultilocality of quantum networks with multiple independent observers using new Bell inequalities. The violations are maximal with respect to the presented Tsirelson's bound for Einstein-Podolsky-Rosen states and GHZ states. Moreover, these violations hold for Werner states or some general noisy states. Our results suggest that the presented Bell inequalities can be used to characterize experimental quantum networks.
Duality quantum algorithm efficiently simulates open quantum systems
Wei, Shi-Jie; Ruan, Dong; Long, Gui-Lu
2016-01-01
Because of inevitable coupling with the environment, nearly all practical quantum systems are open system, where the evolution is not necessarily unitary. In this paper, we propose a duality quantum algorithm for simulating Hamiltonian evolution of an open quantum system. In contrast to unitary evolution in a usual quantum computer, the evolution operator in a duality quantum computer is a linear combination of unitary operators. In this duality quantum algorithm, the time evolution of the open quantum system is realized by using Kraus operators which is naturally implemented in duality quantum computer. This duality quantum algorithm has two distinct advantages compared to existing quantum simulation algorithms with unitary evolution operations. Firstly, the query complexity of the algorithm is O(d3) in contrast to O(d4) in existing unitary simulation algorithm, where d is the dimension of the open quantum system. Secondly, By using a truncated Taylor series of the evolution operators, this duality quantum algorithm provides an exponential improvement in precision compared with previous unitary simulation algorithm. PMID:27464855
Efficient multiuser quantum cryptography network based on entanglement.
Xue, Peng; Wang, Kunkun; Wang, Xiaoping
2017-04-04
We present an efficient quantum key distribution protocol with a certain entangled state to solve a special cryptographic task. Also, we provide a proof of security of this protocol by generalizing the proof of modified of Lo-Chau scheme. Based on this two-user scheme, a quantum cryptography network protocol is proposed without any quantum memory.
Efficient universal quantum channel simulation in IBM's cloud quantum computer
Wei, Shi-Jie; Xin, Tao; Long, Gui-Lu
2018-07-01
The study of quantum channels is an important field and promises a wide range of applications, because any physical process can be represented as a quantum channel that transforms an initial state into a final state. Inspired by the method of performing non-unitary operators by the linear combination of unitary operations, we proposed a quantum algorithm for the simulation of the universal single-qubit channel, described by a convex combination of "quasi-extreme" channels corresponding to four Kraus operators, and is scalable to arbitrary higher dimension. We demonstrated the whole algorithm experimentally using the universal IBM cloud-based quantum computer and studied the properties of different qubit quantum channels. We illustrated the quantum capacity of the general qubit quantum channels, which quantifies the amount of quantum information that can be protected. The behavior of quantum capacity in different channels revealed which types of noise processes can support information transmission, and which types are too destructive to protect information. There was a general agreement between the theoretical predictions and the experiments, which strongly supports our method. By realizing the arbitrary qubit channel, this work provides a universally- accepted way to explore various properties of quantum channels and novel prospect for quantum communication.
High Efficiency Colloidal Quantum Dot Phosphors
Energy Technology Data Exchange (ETDEWEB)
Kahen, Keith
2013-12-31
The project showed that non-Cd containing, InP-based nanocrystals (semiconductor materials with dimensions of ~6 nm) have high potential for enabling next-generation, nanocrystal-based, on chip phosphors for solid state lighting. Typical nanocrystals fall short of the requirements for on chip phosphors due to their loss of quantum efficiency under the operating conditions of LEDs, such as, high temperature (up to 150 °C) and high optical flux (up to 200 W/cm2). The InP-based nanocrystals invented during this project maintain high quantum efficiency (>80%) in polymer-based films under these operating conditions for emission wavelengths ranging from ~530 to 620 nm. These nanocrystals also show other desirable attributes, such as, lack of blinking (a common problem with nanocrystals which limits their performance) and no increase in the emission spectral width from room to 150 °C (emitters with narrower spectral widths enable higher efficiency LEDs). Prior to these nanocrystals, no nanocrystal system (regardless of nanocrystal type) showed this collection of properties; in fact, other nanocrystal systems are typically limited to showing only one desirable trait (such as high temperature stability) but being deficient in other properties (such as high flux stability). The project showed that one can reproducibly obtain these properties by generating a novel compositional structure inside of the nanomaterials; in addition, the project formulated an initial theoretical framework linking the compositional structure to the list of high performance optical properties. Over the course of the project, the synthetic methodology for producing the novel composition was evolved to enable the synthesis of these nanomaterials at a cost approximately equal to that required for forming typical conventional nanocrystals. Given the above results, the last major remaining step prior to scale up of the nanomaterials is to limit the oxidation of these materials during the tens of
Quantum mechanics, relativity and casuality
International Nuclear Information System (INIS)
Tati, T.
1976-01-01
In quantum mechanics, the state is prepared by a measurement on a spacelike surface sigma. What is that determine the surface sigma on which the measurement prepares the stae. It si considered either a mechanism proper to the measuring process (apparatus) or a universal property of space-time. In the former case, problems arise, concerning casuality or conservation of probability due to the fact that the velocity of reduction of a wave packet is considered to exceed the light velocity. The theory of finite degree of freedom proposed previously belongs to the latter case. In this theory, the surface sigma is restricted to the hyper-plane perpendicular to a universal time-like vector governing casual relations. An experimental to discriminate between the above-mentioned two cases and to test the existence of the universal timelike vector is proposed
Quantum mechanics, relativity and causality
International Nuclear Information System (INIS)
Tati, Takao.
1975-07-01
In quantum mechanics, the state is prepared by a measurement on a space-like surface sigma. What is that determines the surface sigma on which the measurement prepares the state It is considered either a mechanism proper to the measuring process (apparatus) or a universal property of space-time. In the former case, problems arise, concerning causality or conservation of probability due to that the velocity of reduction of wave-packet is considered to exceed the light velocity. The theory of finite degree of freedom proposed previously belongs to the latter case. In this theory, the surface sigma is restricted to the hyper-plane perpendicular to a universal time-like vector governing causal relations. We propose an experiment to discriminate between the above-mentioned two cases and to test the existence of the universal time-like vector. (auth.)
Quantum efficiency and oscillator strength of site-controlled InAs quantum dots
DEFF Research Database (Denmark)
Albert, F.; Stobbe, Søren; Schneider, C.
2010-01-01
We report on time-resolved photoluminescence spectroscopy to determine the oscillator strength (OS) and the quantum efficiency (QE) of site-controlled InAs quantum dots nucleating on patterned nanoholes. These two quantities are determined by measurements on site-controlled quantum dot (SCQD...
Quantum efficiency and oscillator strength of site-controlled InGaAs quantum dots
DEFF Research Database (Denmark)
Albert, F.; Schneider, C.; Stobbe, Søren
2010-01-01
We report on time-resolved photoluminescence spectroscopy to determine the oscillator strength (OS) and the quantum efficiency (QE) of site-controlled In(Ga)As quantum dots nucleating on patterned nanoholes. These two quantities are determined by measurements on site-controlled quantum dot (SCQD...
Quantum entanglement and special relativity
International Nuclear Information System (INIS)
Nishikawa, Yoshihisa
2008-01-01
Quantum entanglement was suggested by Einstein to indicate that quantum mechanics was incomplete. However, against Einstein's expectation, the phenomenon due to quantum entanglement has been verified by experiments. Recently, in quantum information theory, it has been also treated as a resource for quantum teleportation and so on. In around 2000, it is recognized that quantum correlations between two particles of one pair state in an entangled spin-state are affected by the non-trivial effect due to the successive Lorentz transformation. This relativistic effect is called the Wigner rotation. The Wigner rotation has to been taken into account when we observe spin-correlation of moving particles in a different coordinate frame. In this paper, first, we explain quantum entanglement and its modification due to the Wigner rotation. After that, we introduce an extended model instead of one pair state model. In the extended model, quantum entanglement state is prepared as a superposition state of various pair states. We have computed the von Neumann entropy and the Shannon entropy to see the global behavior of variation for the spin correlation due to the relativistic effect. We also discuss distinguishability between the two particles of the pair. (author)
A general theory of quantum relativity
International Nuclear Information System (INIS)
Minic, Djordje; Tze, C.-H.
2004-01-01
The geometric form of standard quantum mechanics is compatible with the two postulates: (1) the laws of physics are invariant under the choice of experimental setup and (2) every quantum observation or event is intrinsically statistical. These postulates remain compatible within a background independent extension of quantum theory with a local intrinsic time implying the relativity of the concept of a quantum event. In this extension the space of quantum events becomes dynamical and only individual quantum events make sense observationally. At the core of such a general theory of quantum relativity is the three-way interplay between the symplectic form, the dynamical metric and non-integrable almost complex structure of the space of quantum events. Such a formulation provides a missing conceptual ingredient in the search for a background independent quantum theory of gravity and matter. The crucial new technical element in our scheme derives from a set of recent mathematical results on certain infinite-dimensional almost Kahler manifolds which replace the complex projective spaces of standard quantum mechanics
Efficient quantum secure communication with a publicly known key
International Nuclear Information System (INIS)
Li Chunyan; Li Xihan; Deng Fuguo; Zhou Hongyu
2008-01-01
This paper presents a simple way for an eavesdropper to eavesdrop freely the secret message in the experimental realization of quantum communication protocol proposed by Beige et al (2002 Acta Phys. Pol. A 101 357). Moreover, it introduces an efficient quantum secure communication protocol based on a publicly known key with decoy photons and two biased bases by modifying the original protocol. The total efficiency of this new protocol is double that of the original one. With a low noise quantum channel, this protocol can be used for transmitting a secret message. At present, this protocol is good for generating a private key efficiently. (general)
Quantum Theory finally reconciled with Special Relativity
Tommasini, Daniele
2001-01-01
In 1935 Einstein, Podolsky and Rosen (EPR) pointed out that Quantum Mechanics apparently implied some mysterious, instantaneous action at a distance. This paradox is supposed to be related to the probabilistic nature of the theory, but since deterministic alternatives involving "Hidden Variables" hardly agree with the experiments, the scientific community is now accepting this ``quantum nonlocality" as if it were a reality. However, I have argued recently that Quantum Electrodynamics is free ...
Quantum efficiency of InAs/InP nanowire heterostructures grown on silicon substrates
International Nuclear Information System (INIS)
Anufriev, Roman; Chauvin, Nicolas; Bru-Chevallier, Catherine; Khmissi, Hammadi; Naji, Khalid; Gendry, Michel; Patriarche, Gilles
2013-01-01
Photoluminescence (PL) quantum efficiency (QE) is experimentally investigated, using an integrating sphere, as a function of excitation power on both InAs/InP quantum rod nanowires (QRod-NWs) and radial quantum well nanowires (QWell-NWs) grown on silicon substrates. The measured values of the QE are compared with those of the planar analogues such as quantum dash and quantum well samples, and found to be comparable for the quantum well structures at relatively low power density. Further studies reveal that the values of QE of the QRod-NWs and QWell-NWs are limited by the low quality of the InP NW structure and the quality of radial quantum well, respectively. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Quasi-Resonant Absorption for Quantum Efficiency Improvement in Detectors
National Aeronautics and Space Administration — Quasi-resonant absorption has been demonstrated to enhance the quantum efficiency of devices across the spectrum, but specifically it is a challenge in the UV...
Quantum efficiency and thermal emittance of metal photocathodes
Directory of Open Access Journals (Sweden)
David H. Dowell
2009-07-01
Full Text Available Modern electron beams have demonstrated the brilliance needed to drive free electron lasers at x-ray wavelengths with major advances occurring since the invention of the photocathode gun and the realization of emittance compensation. These state-of-the-art electron beams are now becoming limited by the intrinsic thermal emittance of the cathode. In both dc and rf photocathode guns details of the cathode emission physics strongly influence the quantum efficiency and the thermal emittance. Therefore improving cathode performance is essential to increasing the brightness of beams. It is especially important to understand the fundamentals of cathode quantum efficiency and thermal emittance. This paper investigates the relationship between the quantum efficiency and the thermal emittance for metal cathodes using the Fermi-Dirac model for the electron distribution. We use a consistent theory to derive the quantum efficiency and thermal emittance, and compare our results to those of others.
The Quantum Efficiency and Thermal Emittance of Metal Photocathodes
International Nuclear Information System (INIS)
Dowell, D.
2009-01-01
Modern electron beams have demonstrated the brilliance needed to drive free electron lasers at x-ray wavelengths, with the principle improvements occurring since the invention of the photocathode gun. The state-of-the-art normalized emittance electron beams are now becoming limited by the thermal emittance of the cathode. In both DC and RF photocathode guns, details of the cathode emission physics strongly influence the quantum efficiency and the thermal emittance. Therefore improving cathode performance is essential to increasing the brightness of beams. It is especially important to understand the fundamentals of cathode quantum efficiency and thermal emittance. This paper investigates the relationship between the quantum efficiency and the thermal emittance of metal cathodes using the Fermi-Dirac model for the electron distribution. We derive the thermal emittance and its relationship to the quantum efficiency, and compare our results to those of others
Energy Technology Data Exchange (ETDEWEB)
Netzel, Carsten; Hoffmann, Veit; Wernicke, Tim; Knauer, Arne; Weyers, Markus [Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany); Kneissl, Michael [Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany); Institut fuer Festkoerperphysik, Technische Universitaet Berlin, Hardenbergstrasse 36, 10623 Berlin (Germany)
2010-07-15
To determine relevant processes affecting the internal quantum efficiency in GaInN quantum well structures, we have studied the temperature and excitation power dependent photoluminescence intensity for quantum wells with different well widths on (0001) c-plane GaN and for quantum wells on nonpolar (11-20) a-plane GaN. In thick polar quantum wells, the quantum confined Stark effect (QCSE) causes a stronger intensity decrease with increasing temperature as long as the radiative recombination dominates. At higher temperatures, when the nonradiative recombination becomes more important, thick polar quantum wells feature a lower relative intensity decrease than thinner polar or nonpolar quantum wells. Excitation power dependent photoluminescence points to a transition from a recombination of excitons to a bimolecular recombination of uncorrelated charge carriers for thick polar quantum wells in the same temperature range. This transition might contribute to the limitation of nonradiative recombination by a reduced diffusivity of charge carriers. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Direct determination of quantum efficiency of semiconducting films
Faughnan, B.W.; Hanak, J.J.
Photovoltaic quantum efficiency of semiconductor samples is determined directly, without requiring that a built-in photovoltage be generated by the sample. Electrodes are attached to the sample so as to form at least one Schottky barrier therewith. When illuminated, the generated photocurrent carriers are collected by an external bias voltage impressed across the electrodes. The generated photocurrent is measured, and photovoltaic quantum efficiency is calculated therefrom.
Efficient Luminescence from Perovskite Quantum Dot Solids
Kim, Younghoon; Yassitepe, Emre; Voznyy, Oleksandr; Comin, Riccardo; Walters, Grant; Gong, Xiwen; Kanjanaboos, Pongsakorn; Nogueira, Ana F.; Sargent, Edward H.
2015-01-01
© 2015 American Chemical Society. Nanocrystals of CsPbX3 perovskites are promising materials for light-emitting optoelectronics because of their colloidal stability, optically tunable bandgap, bright photoluminescence, and excellent photoluminescence quantum yield. Despite their promise, nanocrystal-only films of CsPbX3 perovskites have not yet been fabricated; instead, highly insulating polymers have been relied upon to compensate for nanocrystals' unstable surfaces. We develop solution chemistry that enables single-step casting of perovskite nanocrystal films and overcomes problems in both perovskite quantum dot purification and film fabrication. Centrifugally cast films retain bright photoluminescence and achieve dense and homogeneous morphologies. The new materials offer a platform for optoelectronic applications of perovskite quantum dot solids.
Efficient Luminescence from Perovskite Quantum Dot Solids
Kim, Younghoon
2015-11-18
© 2015 American Chemical Society. Nanocrystals of CsPbX3 perovskites are promising materials for light-emitting optoelectronics because of their colloidal stability, optically tunable bandgap, bright photoluminescence, and excellent photoluminescence quantum yield. Despite their promise, nanocrystal-only films of CsPbX3 perovskites have not yet been fabricated; instead, highly insulating polymers have been relied upon to compensate for nanocrystals\\' unstable surfaces. We develop solution chemistry that enables single-step casting of perovskite nanocrystal films and overcomes problems in both perovskite quantum dot purification and film fabrication. Centrifugally cast films retain bright photoluminescence and achieve dense and homogeneous morphologies. The new materials offer a platform for optoelectronic applications of perovskite quantum dot solids.
Peng, Hu-Ping; Fang, Mao-Fa; Yu, Min; Zou, Hong-Mei
2018-03-01
We study the influences of quantum coherence on the positive work and the efficiency of quantum heat engine (QHE) based on working substance of two-qubit Heisenberg model under a constant external magnetic field. By using analytical and numerical solution, we give the relation expressions for both the positive work and the efficiency with quantum coherence, and in detail discuss the effects of the quantum coherence on the positive work and the efficiency of QHE in the absence or presence of external magnetic field, respectively.
Peng, Hu-Ping; Fang, Mao-Fa; Yu, Min; Zou, Hong-Mei
2018-06-01
We study the influences of quantum coherence on the positive work and the efficiency of quantum heat engine (QHE) based on working substance of two-qubit Heisenberg model under a constant external magnetic field. By using analytical and numerical solution, we give the relation expressions for both the positive work and the efficiency with quantum coherence, and in detail discuss the effects of the quantum coherence on the positive work and the efficiency of QHE in the absence or presence of external magnetic field, respectively.
Quantum interferences reconstruction with low homodyne detection efficiency
Energy Technology Data Exchange (ETDEWEB)
Esposito, Martina; Randi, Francesco [Universita degli studi di Trieste, Dipartimento di Fisica, Trieste (Italy); Titimbo, Kelvin; Zimmermann, Klaus; Benatti, Fabio [Universita degli studi di Trieste, Dipartimento di Fisica, Trieste (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, Trieste (Italy); Kourousias, Georgios; Curri, Alessio [Sincrotrone Trieste S.C.p.A., Trieste (Italy); Floreanini, Roberto [Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, Trieste (Italy); Parmigiani, Fulvio [Universita degli studi di Trieste, Dipartimento di Fisica, Trieste (Italy); Sincrotrone Trieste S.C.p.A., Trieste (Italy); University of Cologne, Institute of Physics II, Cologne (Germany); Fausti, Daniele [Universita degli studi di Trieste, Dipartimento di Fisica, Trieste (Italy); Sincrotrone Trieste S.C.p.A., Trieste (Italy)
2016-12-15
Optical homodyne tomography consists in reconstructing the quantum state of an optical field from repeated measurements of its amplitude at different field phases (homodyne data). The experimental noise, which unavoidably affects the homodyne data, leads to a detection efficiency η<1. The problem of reconstructing quantum states from noisy homodyne data sets prompted an intense scientific debate about the presence or absence of a lower homodyne efficiency bound (η>0.5) below which quantum features, like quantum interferences, cannot be retrieved. Here, by numerical experiments, we demonstrate that quantum interferences can be effectively reconstructed also for low homodyne detection efficiency. In particular, we address the challenging case of a Schroedinger cat state and test the minimax and adaptive Wigner function reconstruction technique by processing homodyne data distributed according to the chosen state but with an efficiency η>0.5. By numerically reproducing the Schroedinger's cat interference pattern, we give evidence that quantum state reconstruction is actually possible in these conditions, and provide a guideline for handling optical tomography based on homodyne data collected by low efficiency detectors. (orig.)
Quantum theory and Einstein's general relativity
International Nuclear Information System (INIS)
Borzeszkowski, H.H.v.; Treder, H.J.
1984-01-01
The paper concerns Einstein's general relativity, wave mechanics and the quantization of Einstein's gravitation equations. The principle of equivalence and its association with both wave mechanics and quantum gravity, is discussed. (U.K.)
High Quantum Efficiency OLED Lighting Systems
Energy Technology Data Exchange (ETDEWEB)
Shiang, Joseph [General Electric (GE) Global Research, Fairfield, CT (United States)
2011-09-30
The overall goal of the program was to apply improvements in light outcoupling technology to a practical large area plastic luminaire, and thus enable the product vision of an extremely thin form factor high efficiency large area light source. The target substrate was plastic and the baseline device was operating at 35 LPW at the start of the program. The target LPW of the program was a >2x improvement in the LPW efficacy and the overall amount of light to be delivered was relatively high 900 lumens. Despite the extremely difficult challenges associated with scaling up a wet solution process on plastic substrates, the program was able to make substantial progress. A small molecule wet solution process was successfully implemented on plastic substrates with almost no loss in efficiency in transitioning from the laboratory scale glass to large area plastic substrates. By transitioning to a small molecule based process, the LPW entitlement increased from 35 LPW to 60 LPW. A further 10% improvement in outcoupling efficiency was demonstrated via the use of a highly reflecting cathode, which reduced absorptive loss in the OLED device. The calculated potential improvement in some cases is even larger, ~30%, and thus there is considerable room for optimism in improving the net light coupling efficacy, provided absorptive loss mechanisms are eliminated. Further improvements are possible if scattering schemes such as the silver nanowire based hard coat structure are fully developed. The wet coating processes were successfully scaled to large area plastic substrate and resulted in the construction of a 900 lumens luminaire device.
Unitary Quantum Relativity. (Work in Progress)
Finkelstein, David Ritz
2017-01-01
A quantum universe is expressed as a finite unitary relativistic quantum computer network. Its addresses are subject to quantum superposition as well as its memory. It has no exact mathematical model. It Its Hilbert space of input processes is also a Clifford algebra with a modular architecture of many ranks. A fundamental fermion is a quantum computer element whose quantum address belongs to the rank below. The least significant figures of its address define its spin and flavor. The most significant figures of it adress define its orbital variables. Gauging arises from the same quantification as space-time. This blurs star images only slightly, but perhaps measurably. General relativity is an approximation that splits nature into an emptiness with a high symmetry that is broken by a filling of lower symmetry. Action principles result from self-organization pf the vacuum.
Energy entanglement relation for quantum energy teleportation
Energy Technology Data Exchange (ETDEWEB)
Hotta, Masahiro, E-mail: hotta@tuhep.phys.tohoku.ac.j [Department of Physics, Faculty of Science, Tohoku University, Sendai 980-8578 (Japan)
2010-07-26
Protocols of quantum energy teleportation (QET), while retaining causality and local energy conservation, enable the transportation of energy from a subsystem of a many-body quantum system to a distant subsystem by local operations and classical communication through ground-state entanglement. We prove two energy-entanglement inequalities for a minimal QET model. These relations help us to gain a profound understanding of entanglement itself as a physical resource by relating entanglement to energy as an evident physical resource.
Special relativity at the quantum scale.
Directory of Open Access Journals (Sweden)
Pui K Lam
Full Text Available It has been suggested that the space-time structure as described by the theory of special relativity is a macroscopic manifestation of a more fundamental quantum structure (pre-geometry. Efforts to quantify this idea have come mainly from the area of abstract quantum logic theory. Here we present a preliminary attempt to develop a quantum formulation of special relativity based on a model that retains some geometric attributes. Our model is Feynman's "checker-board" trajectory for a 1-D relativistic free particle. We use this model to guide us in identifying (1 the quantum version of the postulates of special relativity and (2 the appropriate quantum "coordinates". This model possesses a useful feature that it admits an interpretation both in terms of paths in space-time and in terms of quantum states. Based on the quantum version of the postulates, we derive a transformation rule for velocity. This rule reduces to the Einstein's velocity-addition formula in the macroscopic limit and reveals an interesting aspect of time. The 3-D case, time-dilation effect, and invariant interval are also discussed in term of this new formulation. This is a preliminary investigation; some results are derived, while others are interesting observations at this point.
Special relativity at the quantum scale.
Lam, Pui K
2014-01-01
It has been suggested that the space-time structure as described by the theory of special relativity is a macroscopic manifestation of a more fundamental quantum structure (pre-geometry). Efforts to quantify this idea have come mainly from the area of abstract quantum logic theory. Here we present a preliminary attempt to develop a quantum formulation of special relativity based on a model that retains some geometric attributes. Our model is Feynman's "checker-board" trajectory for a 1-D relativistic free particle. We use this model to guide us in identifying (1) the quantum version of the postulates of special relativity and (2) the appropriate quantum "coordinates". This model possesses a useful feature that it admits an interpretation both in terms of paths in space-time and in terms of quantum states. Based on the quantum version of the postulates, we derive a transformation rule for velocity. This rule reduces to the Einstein's velocity-addition formula in the macroscopic limit and reveals an interesting aspect of time. The 3-D case, time-dilation effect, and invariant interval are also discussed in term of this new formulation. This is a preliminary investigation; some results are derived, while others are interesting observations at this point.
Maximally efficient protocols for direct secure quantum communication
Energy Technology Data Exchange (ETDEWEB)
Banerjee, Anindita [Department of Physics and Materials Science Engineering, Jaypee Institute of Information Technology, A-10, Sector-62, Noida, UP-201307 (India); Department of Physics and Center for Astroparticle Physics and Space Science, Bose Institute, Block EN, Sector V, Kolkata 700091 (India); Pathak, Anirban, E-mail: anirban.pathak@jiit.ac.in [Department of Physics and Materials Science Engineering, Jaypee Institute of Information Technology, A-10, Sector-62, Noida, UP-201307 (India); RCPTM, Joint Laboratory of Optics of Palacky University and Institute of Physics of Academy of Science of the Czech Republic, Faculty of Science, Palacky University, 17. Listopadu 12, 77146 Olomouc (Czech Republic)
2012-10-01
Two protocols for deterministic secure quantum communication (DSQC) using GHZ-like states have been proposed. It is shown that one of these protocols is maximally efficient and that can be modified to an equivalent protocol of quantum secure direct communication (QSDC). Security and efficiency of the proposed protocols are analyzed and compared. It is shown that dense coding is sufficient but not essential for DSQC and QSDC protocols. Maximally efficient QSDC protocols are shown to be more efficient than their DSQC counterparts. This additional efficiency arises at the cost of message transmission rate. -- Highlights: ► Two protocols for deterministic secure quantum communication (DSQC) are proposed. ► One of the above protocols is maximally efficient. ► It is modified to an equivalent protocol of quantum secure direct communication (QSDC). ► It is shown that dense coding is sufficient but not essential for DSQC and QSDC protocols. ► Efficient QSDC protocols are always more efficient than their DSQC counterparts.
Quantum engine efficiency bound beyond the second law of thermodynamics.
Niedenzu, Wolfgang; Mukherjee, Victor; Ghosh, Arnab; Kofman, Abraham G; Kurizki, Gershon
2018-01-11
According to the second law, the efficiency of cyclic heat engines is limited by the Carnot bound that is attained by engines that operate between two thermal baths under the reversibility condition whereby the total entropy does not increase. Quantum engines operating between a thermal and a squeezed-thermal bath have been shown to surpass this bound. Yet, their maximum efficiency cannot be determined by the reversibility condition, which may yield an unachievable efficiency bound above unity. Here we identify the fraction of the exchanged energy between a quantum system and a bath that necessarily causes an entropy change and derive an inequality for this change. This inequality reveals an efficiency bound for quantum engines energised by a non-thermal bath. This bound does not imply reversibility, unless the two baths are thermal. It cannot be solely deduced from the laws of thermodynamics.
The Relation between Classical and Quantum Electrodynamics
Directory of Open Access Journals (Sweden)
Mario Bacelar Valente
2011-01-01
Full Text Available Quantum electrodynamics presents intrinsic limitations in the description of physical processes that make it impossible to recover from it the type of description we have in classical electrodynamics. Hence one cannot consider classical electrodynamics as reducing to quantum electrodynamics and being recovered from it by some sort of limiting procedure. Quantum electrodynamics has to be seen not as an more fundamental theory, but as an upgrade of classical electrodynamics, which permits an extension of classical theory to the description of phenomena that, while being related to the conceptual framework of the classical theory, cannot be addressed from the classical theory.
Internal quantum efficiency enhancement of GaInN/GaN quantum-well structures using Ag nanoparticles
DEFF Research Database (Denmark)
Iida, Daisuke; Fadil, Ahmed; Chen, Yuntian
2015-01-01
We report internal quantum efficiency enhancement of thin p-GaN green quantumwell structure using self-assembled Ag nanoparticles. Temperature dependent photoluminescence measurements are conducted to determine the internal quantum efficiency. The impact of excitation power density on the enhance......We report internal quantum efficiency enhancement of thin p-GaN green quantumwell structure using self-assembled Ag nanoparticles. Temperature dependent photoluminescence measurements are conducted to determine the internal quantum efficiency. The impact of excitation power density...
Efficient generation of photonic entanglement and multiparty quantum communication
Energy Technology Data Exchange (ETDEWEB)
Trojek, Pavel
2007-09-15
This thesis deals largely with the problem of efficient generation of photonic entanglement with the principal aim of developing a bright source of polarization-entangled photon pairs, which meets the requirements for reliable and economic operation of quantum communication prototypes and demonstrators. Our approach uses a cor-related photon-pair emission in nonlinear process of spontaneous parametric downconversion pumped by light coming from a compact and cheap blue laser diode. Two alternative source configurations are examined within the thesis. The first makes use of a well established concept of degenerate non-collinear emission from a single type-II nonlinear crystal and the second relies on a novel method where the emissions from two adjacent type-I phase-matched nonlinear crystals operated in collinear non-degenerate regime are coherently overlapped. The latter approach showed to be more effective, yielding a total detected rate of almost 10{sup 6} pairs/s at >98% quantum interference visibility of polarization correlations. The second issue addressed within the thesis is the simplification and practical implementation of quantum-assisted solutions to multiparty communication tasks. We show that entanglement is not the only non-classical resource endowing the quantum multiparty information processing its power. Instead, only the sequential communication and transformation of a single qubit can be sufficient to accomplish certain tasks. This we prove for two distinct communication tasks, secret sharing and communication complexity. Whereas the goal of the first is to split a cryptographic key among several parties in a way that its reconstruction requires their collaboration, the latter aims at reducing the amount of communication during distributed computational tasks. Importantly, our qubitassisted solutions to the problems are feasible with state-of-the-art technology. This we clearly demonstrate in the laboratory implementation for 6 and 5 parties
Efficient generation of photonic entanglement and multiparty quantum communication
International Nuclear Information System (INIS)
Trojek, Pavel
2007-09-01
This thesis deals largely with the problem of efficient generation of photonic entanglement with the principal aim of developing a bright source of polarization-entangled photon pairs, which meets the requirements for reliable and economic operation of quantum communication prototypes and demonstrators. Our approach uses a cor-related photon-pair emission in nonlinear process of spontaneous parametric downconversion pumped by light coming from a compact and cheap blue laser diode. Two alternative source configurations are examined within the thesis. The first makes use of a well established concept of degenerate non-collinear emission from a single type-II nonlinear crystal and the second relies on a novel method where the emissions from two adjacent type-I phase-matched nonlinear crystals operated in collinear non-degenerate regime are coherently overlapped. The latter approach showed to be more effective, yielding a total detected rate of almost 10 6 pairs/s at >98% quantum interference visibility of polarization correlations. The second issue addressed within the thesis is the simplification and practical implementation of quantum-assisted solutions to multiparty communication tasks. We show that entanglement is not the only non-classical resource endowing the quantum multiparty information processing its power. Instead, only the sequential communication and transformation of a single qubit can be sufficient to accomplish certain tasks. This we prove for two distinct communication tasks, secret sharing and communication complexity. Whereas the goal of the first is to split a cryptographic key among several parties in a way that its reconstruction requires their collaboration, the latter aims at reducing the amount of communication during distributed computational tasks. Importantly, our qubitassisted solutions to the problems are feasible with state-of-the-art technology. This we clearly demonstrate in the laboratory implementation for 6 and 5 parties
Efficient method for transport simulations in quantum cascade lasers
Directory of Open Access Journals (Sweden)
Maczka Mariusz
2017-01-01
Full Text Available An efficient method for simulating quantum transport in quantum cascade lasers is presented. The calculations are performed within a simple approximation inspired by Büttiker probes and based on a finite model for semiconductor superlattices. The formalism of non-equilibrium Green’s functions is applied to determine the selected transport parameters in a typical structure of a terahertz laser. Results were compared with those obtained for a infinite model as well as other methods described in literature.
The Efficiency of Quantum Identity Testing of Multiple States
Kada, Masaru; Nishimura, Harumichi; Yamakami, Tomoyuki
2008-01-01
We examine two quantum operations, the Permutation Test and the Circle Test, which test the identity of n quantum states. These operations naturally extend the well-studied Swap Test on two quantum states. We first show the optimality of the Permutation Test for any input size n as well as the optimality of the Circle Test for three input states. In particular, when n=3, we present a semi-classical protocol, incorporated with the Swap Test, which approximates the Circle Test efficiently. Furt...
Efficient decoding of random errors for quantum expander codes
Fawzi , Omar; Grospellier , Antoine; Leverrier , Anthony
2017-01-01
We show that quantum expander codes, a constant-rate family of quantum LDPC codes, with the quasi-linear time decoding algorithm of Leverrier, Tillich and Z\\'emor can correct a constant fraction of random errors with very high probability. This is the first construction of a constant-rate quantum LDPC code with an efficient decoding algorithm that can correct a linear number of random errors with a negligible failure probability. Finding codes with these properties is also motivated by Gottes...
Between general relativity and quantum theory
International Nuclear Information System (INIS)
Rayski, J.
1982-01-01
Some possibilities of reconciling general relativity with quantum theory are discussed. The procedure of quantization is certainly not unique, but depends upon the choice of the coordinate conditions. Most versions of quantization predict the existence of gravitons, but it is also possible to formulate a quantum theory with a classical gravity whereby the expectation values of Tsub(μν) constitute the sources of the classical metric field. (author)
Efficient tomography of a quantum many-body system
Lanyon, B. P.; Maier, C.; Holzäpfel, M.; Baumgratz, T.; Hempel, C.; Jurcevic, P.; Dhand, I.; Buyskikh, A. S.; Daley, A. J.; Cramer, M.; Plenio, M. B.; Blatt, R.; Roos, C. F.
2017-12-01
Quantum state tomography is the standard technique for estimating the quantum state of small systems. But its application to larger systems soon becomes impractical as the required resources scale exponentially with the size. Therefore, considerable effort is dedicated to the development of new characterization tools for quantum many-body states. Here we demonstrate matrix product state tomography, which is theoretically proven to allow for the efficient and accurate estimation of a broad class of quantum states. We use this technique to reconstruct the dynamical state of a trapped-ion quantum simulator comprising up to 14 entangled and individually controlled spins: a size far beyond the practical limits of quantum state tomography. Our results reveal the dynamical growth of entanglement and describe its complexity as correlations spread out during a quench: a necessary condition for future demonstrations of better-than-classical performance. Matrix product state tomography should therefore find widespread use in the study of large quantum many-body systems and the benchmarking and verification of quantum simulators and computers.
Analytical mechanics for relativity and quantum mechanics
Johns, Oliver Davis
2011-01-01
Analytical Mechanics for Relativity and Quantum Mechanics is an innovative and mathematically sound treatment of the foundations of analytical mechanics and the relation of classical mechanics to relativity and quantum theory. It is intended for use at the introductory graduate level. A distinguishing feature of the book is its integration of special relativity into teaching of classical mechanics. After a thorough review of the traditional theory, Part II of the book introduces extended Lagrangian and Hamiltonian methods that treat time as a transformable coordinate rather than the fixed parameter of Newtonian physics. Advanced topics such as covariant Langrangians and Hamiltonians, canonical transformations, and Hamilton-Jacobi methods are simplified by the use of this extended theory. And the definition of canonical transformation no longer excludes the Lorenz transformation of special relativity. This is also a book for those who study analytical mechanics to prepare for a critical exploration of quantum...
Positive Wigner functions render classical simulation of quantum computation efficient.
Mari, A; Eisert, J
2012-12-07
We show that quantum circuits where the initial state and all the following quantum operations can be represented by positive Wigner functions can be classically efficiently simulated. This is true both for continuous-variable as well as discrete variable systems in odd prime dimensions, two cases which will be treated on entirely the same footing. Noting the fact that Clifford and Gaussian operations preserve the positivity of the Wigner function, our result generalizes the Gottesman-Knill theorem. Our algorithm provides a way of sampling from the output distribution of a computation or a simulation, including the efficient sampling from an approximate output distribution in the case of sampling imperfections for initial states, gates, or measurements. In this sense, this work highlights the role of the positive Wigner function as separating classically efficiently simulable systems from those that are potentially universal for quantum computing and simulation, and it emphasizes the role of negativity of the Wigner function as a computational resource.
Quantum work relations and response theory in parity-time-symmetric quantum systems
Wei, Bo-Bo
2018-01-01
In this work, we show that a universal quantum work relation for a quantum system driven arbitrarily far from equilibrium extends to a parity-time- (PT -) symmetric quantum system with unbroken PT symmetry, which is a consequence of microscopic reversibility. The quantum Jarzynski equality, linear response theory, and Onsager reciprocal relations for the PT -symmetric quantum system are recovered as special cases of the universal quantum work relation in a PT -symmetric quantum system. In the regime of broken PT symmetry, the universal quantum work relation does not hold because the norm is not preserved during the dynamics.
Efficiently characterizing the total error in quantum circuits
Carignan-Dugas, Arnaud; Wallman, Joel J.; Emerson, Joseph
A promising technological advancement meant to enlarge our computational means is the quantum computer. Such a device would harvest the quantum complexity of the physical world in order to unfold concrete mathematical problems more efficiently. However, the errors emerging from the implementation of quantum operations are likewise quantum, and hence share a similar level of intricacy. Fortunately, randomized benchmarking protocols provide an efficient way to characterize the operational noise within quantum devices. The resulting figures of merit, like the fidelity and the unitarity, are typically attached to a set of circuit components. While important, this doesn't fulfill the main goal: determining if the error rate of the total circuit is small enough in order to trust its outcome. In this work, we fill the gap by providing an optimal bound on the total fidelity of a circuit in terms of component-wise figures of merit. Our bound smoothly interpolates between the classical regime, in which the error rate grows linearly in the circuit's length, and the quantum regime, which can naturally allow quadratic growth. Conversely, our analysis substantially improves the bounds on single circuit element fidelities obtained through techniques such as interleaved randomized benchmarking. This research was supported by the U.S. Army Research Office through Grant W911NF- 14-1-0103, CIFAR, the Government of Ontario, and the Government of Canada through NSERC and Industry Canada.
Relational quadrilateralland II: The Quantum Theory
Anderson, Edward; Kneller, Sophie
2014-04-01
We provide the quantum treatment of the relational quadrilateral. The underlying reduced configuration spaces are ℂℙ2 and the cone over this. We consider exact free and isotropic HO potential cases and perturbations about these. Moreover, our purely relational kinematical quantization is distinct from the usual one for ℂℙ2, which turns out to carry absolutist connotations instead. Thus, this paper is the first to note absolute-versus-relational motion distinctions at the kinematical rather than dynamical level. It is also an example of value to the discussion of kinematical quantization along the lines of Isham, 1984. The relational quadrilateral is the simplest RPM whose mathematics is not standard in atomic physics (the triangle and four particles on a line are both based on 𝕊2 and ℝ3 mathematics). It is far more typical of the general quantum relational N-a-gon than the previously studied case of the relational triangle. We consider useful integrals as regards perturbation theory and the peaking interpretation of quantum cosmology. We subsequently consider problem of time (PoT) applications of this: quantum Kuchař beables, the Machian version of the semiclassical approach and the timeless naïve Schrödinger interpretation. These go toward extending the combined Machian semiclassical-Histories-Timeless Approach of [Int. J. Mod. Phys. D23 (2014) 1450014] to the case of the quadrilateral, which will be treated in subsequent papers.
Machine learning with quantum relative entropy
Energy Technology Data Exchange (ETDEWEB)
Tsuda, Koji [Max Planck Institute for Biological Cybernetics, Spemannstr. 38, Tuebingen, 72076 (Germany)], E-mail: koji.tsuda@tuebingen.mpg.de
2009-12-01
Density matrices are a central tool in quantum physics, but it is also used in machine learning. A positive definite matrix called kernel matrix is used to represent the similarities between examples. Positive definiteness assures that the examples are embedded in an Euclidean space. When a positive definite matrix is learned from data, one has to design an update rule that maintains the positive definiteness. Our update rule, called matrix exponentiated gradient update, is motivated by the quantum relative entropy. Notably, the relative entropy is an instance of Bregman divergences, which are asymmetric distance measures specifying theoretical properties of machine learning algorithms. Using the calculus commonly used in quantum physics, we prove an upperbound of the generalization error of online learning.
Reasonable fermionic quantum information theories require relativity
International Nuclear Information System (INIS)
Friis, Nicolai
2016-01-01
We show that any quantum information theory based on anticommuting operators must be supplemented by a superselection rule deeply rooted in relativity to establish a reasonable notion of entanglement. While quantum information may be encoded in the fermionic Fock space, the unrestricted theory has a peculiar feature: the marginals of bipartite pure states need not have identical entropies, which leads to an ambiguous definition of entanglement. We solve this problem, by proving that it is removed by relativity, i.e., by the parity superselection rule that arises from Lorentz invariance via the spin-statistics connection. Our results hence unveil a fundamental conceptual inseparability of quantum information and the causal structure of relativistic field theory. (paper)
Machine learning with quantum relative entropy
International Nuclear Information System (INIS)
Tsuda, Koji
2009-01-01
Density matrices are a central tool in quantum physics, but it is also used in machine learning. A positive definite matrix called kernel matrix is used to represent the similarities between examples. Positive definiteness assures that the examples are embedded in an Euclidean space. When a positive definite matrix is learned from data, one has to design an update rule that maintains the positive definiteness. Our update rule, called matrix exponentiated gradient update, is motivated by the quantum relative entropy. Notably, the relative entropy is an instance of Bregman divergences, which are asymmetric distance measures specifying theoretical properties of machine learning algorithms. Using the calculus commonly used in quantum physics, we prove an upperbound of the generalization error of online learning.
Efficient eco-friendly inverted quantum dot sensitized solar cells
Park, Jinhyung; Sajjad, Muhammad T.; Jouneau, Pierre-Henri; Ruseckas, Arvydas; Faure-Vincent, Jérôme; Samuel, Ifor D. W.; Reiss, Peter; Aldakov, Dmitry
2016-01-01
Recent progress in quantum dot (QD) sensitized solar cells has demonstrated the possibility of low-cost and efficient photovoltaics. However, the standard device structure based on n-type materials often suffers from slow hole injection rate, which may lead to unbalanced charge transport. We have
Modeling the irradiance dependency of the quantum efficiency of potosynthesis
Silsbe, G.M.; Kromkamp, J.C.
2012-01-01
Measures of the quantum efficiency of photosynthesis (phi(PSII)) across an irradiance (E) gradient are an increasingly common physiological assay and alternative to traditional photosynthetic-irradiance (PE) assays. Routinely, the analysis and interpretation of these data are analogous to PE
Connecting and unmasking relativity and quantum theory
Koning, de W.L.; Willigenburg, van L.G.
2015-01-01
The answer lies right in front of us, but we refuse to see it. Both relativity and quantum theory, the two pillars of fundamental physics, are modified in this paper to make them also explain the physical phenomena they describe. With this explanation, all current inconsistencies between the two
Quantum gauge freedom in very special relativity
Energy Technology Data Exchange (ETDEWEB)
Upadhyay, Sudhaker, E-mail: sudhakerupadhyay@gmail.com [Centre for Theoretical Studies, Indian Institute of Technology Kharagpur, Kharagpur-721302, West Bengal (India); Panigrahi, Prasanta K., E-mail: pprasanta@iiserkol.ac.in [Indian Institute of Science Education and Research Kolkata, Mohanpur 741246, West Bengal (India)
2017-02-15
We demonstrate Yokoyama gaugeon formalism for the Abelian one-form gauge (Maxwell) as well as for Abelian two-form gauge theory in the very special relativity (VSR) framework. In VSR scenario, the extended action due to introduction of gaugeon fields also possesses form invariance under quantum gauge transformations. It is observed that the gaugeon field together with gauge field naturally acquire mass, which is different from the conventional Higgs mechanism. The quantum gauge transformation implements a shift in gauge parameter. Further, we analyze the BRST symmetric gaugeon formalism in VSR which embeds only one subsidiary condition rather than two.
Design of Efficient Mirror Adder in Quantum- Dot Cellular Automata
Mishra, Prashant Kumar; Chattopadhyay, Manju K.
2018-03-01
Lower power consumption is an essential demand for portable multimedia system using digital signal processing algorithms and architectures. Quantum dot cellular automata (QCA) is a rising nano technology for the development of high performance ultra-dense low power digital circuits. QCA based several efficient binary and decimal arithmetic circuits are implemented, however important improvements are still possible. This paper demonstrate Mirror Adder circuit design in QCA. We present comparative study of mirror adder cells designed using conventional CMOS technique and mirror adder cells designed using quantum-dot cellular automata. QCA based mirror adders are better in terms of area by order of three.
Efficient quantum algorithm for computing n-time correlation functions.
Pedernales, J S; Di Candia, R; Egusquiza, I L; Casanova, J; Solano, E
2014-07-11
We propose a method for computing n-time correlation functions of arbitrary spinorial, fermionic, and bosonic operators, consisting of an efficient quantum algorithm that encodes these correlations in an initially added ancillary qubit for probe and control tasks. For spinorial and fermionic systems, the reconstruction of arbitrary n-time correlation functions requires the measurement of two ancilla observables, while for bosonic variables time derivatives of the same observables are needed. Finally, we provide examples applicable to different quantum platforms in the frame of the linear response theory.
External quantum efficiency enhancement by photon recycling with backscatter evasion.
Nagano, Koji; Perreca, Antonio; Arai, Koji; Adhikari, Rana X
2018-05-01
The nonunity quantum efficiency (QE) in photodiodes (PD) causes deterioration of signal quality in quantum optical experiments due to photocurrent loss as well as the introduction of vacuum fluctuations into the measurement. In this paper, we report that the external QE enhancement of a PD was demonstrated by recycling the reflected photons. The external QE for an InGaAs PD was increased by 0.01-0.06 from 0.86-0.92 over a wide range of incident angles. Moreover, we confirmed that this technique does not increase backscattered light when the recycled beam is properly misaligned.
An Efficient Quantum Somewhat Homomorphic Symmetric Searchable Encryption
Sun, Xiaoqiang; Wang, Ting; Sun, Zhiwei; Wang, Ping; Yu, Jianping; Xie, Weixin
2017-04-01
In 2009, Gentry first introduced an ideal lattices fully homomorphic encryption (FHE) scheme. Later, based on the approximate greatest common divisor problem, learning with errors problem or learning with errors over rings problem, FHE has developed rapidly, along with the low efficiency and computational security. Combined with quantum mechanics, Liang proposed a symmetric quantum somewhat homomorphic encryption (QSHE) scheme based on quantum one-time pad, which is unconditional security. And it was converted to a quantum fully homomorphic encryption scheme, whose evaluation algorithm is based on the secret key. Compared with Liang's QSHE scheme, we propose a more efficient QSHE scheme for classical input states with perfect security, which is used to encrypt the classical message, and the secret key is not required in the evaluation algorithm. Furthermore, an efficient symmetric searchable encryption (SSE) scheme is constructed based on our QSHE scheme. SSE is important in the cloud storage, which allows users to offload search queries to the untrusted cloud. Then the cloud is responsible for returning encrypted files that match search queries (also encrypted), which protects users' privacy.
Relation between random walks and quantum walks
Boettcher, Stefan; Falkner, Stefan; Portugal, Renato
2015-05-01
Based on studies of four specific networks, we conjecture a general relation between the walk dimensions dw of discrete-time random walks and quantum walks with the (self-inverse) Grover coin. In each case, we find that dw of the quantum walk takes on exactly half the value found for the classical random walk on the same geometry. Since walks on homogeneous lattices satisfy this relation trivially, our results for heterogeneous networks suggest that such a relation holds irrespective of whether translational invariance is maintained or not. To develop our results, we extend the renormalization-group analysis (RG) of the stochastic master equation to one with a unitary propagator. As in the classical case, the solution ρ (x ,t ) in space and time of this quantum-walk equation exhibits a scaling collapse for a variable xdw/t in the weak limit, which defines dw and illuminates fundamental aspects of the walk dynamics, e.g., its mean-square displacement. We confirm the collapse for ρ (x ,t ) in each case with extensive numerical simulation. The exact values for dw themselves demonstrate that RG is a powerful complementary approach to study the asymptotics of quantum walks that weak-limit theorems have not been able to access, such as for systems lacking translational symmetries beyond simple trees.
International Nuclear Information System (INIS)
Plenio, Martin B; Semiao, Fernando L
2005-01-01
We demonstrate that a translation-invariant chain of interacting quantum systems can be used for high efficiency transfer of quantum entanglement and the generation of multiparticle entanglement over large distances and between arbitrary sites without the requirement of precise spatial or temporal control. The scheme is largely insensitive to disorder and random coupling strengths in the chain. We discuss harmonic oscillator systems both in the case of arbitrary Gaussian states and in situations when at most one excitation is in the system. The latter case, which we prove to be equivalent to an xy-spin chain, may be used to generate genuine multiparticle entanglement. Such a 'quantum data bus' may prove useful in future solid state architectures for quantum information processing
Study of silicon microstrips detector quantum efficiency using mathematical simulation
International Nuclear Information System (INIS)
Leyva Pernia, Diana; Cabal Rodriguez, Ana Ester; Pinnera Hernandez, Ibrahin; Fabelo, Antonio Leyva; Abreu Alfonso, Yamiel; Cruz Inclan, Carlos M.
2011-01-01
The paper shows the results from the application of mathematical simulation to study the quantum efficiency of a microstrips crystalline silicon detector, intended for medical imaging and the development of other applications such as authentication and dating of cultural heritage. The effects on the quantum efficiency of some parameters of the system, such as the detector-source geometry, X rays energy and detector dead zone thickness, were evaluated. The simulation results were compared with the theoretical prediction and experimental available data, resulting in a proper correspondence. It was concluded that the use of frontal configuration for incident energies lower than 17 keV is more efficient, however the use of the edge-on configuration for applications requiring the detection of energy above this value is recommended. It was also found that the reduction of the detector dead zone led to a considerable increase in quantum efficiency for any energy value in the interval from 5 to 100 keV.(author)
Finite Correlation Length Implies Efficient Preparation of Quantum Thermal States
Brandão, Fernando G. S. L.; Kastoryano, Michael J.
2018-05-01
Preparing quantum thermal states on a quantum computer is in general a difficult task. We provide a procedure to prepare a thermal state on a quantum computer with a logarithmic depth circuit of local quantum channels assuming that the thermal state correlations satisfy the following two properties: (i) the correlations between two regions are exponentially decaying in the distance between the regions, and (ii) the thermal state is an approximate Markov state for shielded regions. We require both properties to hold for the thermal state of the Hamiltonian on any induced subgraph of the original lattice. Assumption (ii) is satisfied for all commuting Gibbs states, while assumption (i) is satisfied for every model above a critical temperature. Both assumptions are satisfied in one spatial dimension. Moreover, both assumptions are expected to hold above the thermal phase transition for models without any topological order at finite temperature. As a building block, we show that exponential decay of correlation (for thermal states of Hamiltonians on all induced subgraphs) is sufficient to efficiently estimate the expectation value of a local observable. Our proof uses quantum belief propagation, a recent strengthening of strong sub-additivity, and naturally breaks down for states with topological order.
LHCb: Quantum Efficiency of Hybrid Photon Detectors for the LHCb RICH
Lambert, Robert W
2007-01-01
The production of 550 hybrid photon detectors to be used within the LHCb RICH detectors has recently finished. Photonis-DEP have succeeded in consistently improving the tube quantum efficiency, by a relative 27,% with respect to preseries and prototype tubes, when integrated over the energy spectrum.
Erbium-implanted silica colloids with 80% luminescence quantum efficiency
Slooff, L. H.; de Dood, M. J. A.; van Blaaderen, A.; Polman, A.
2000-06-01
Silica colloids with a diameter of 240-360 nm, grown by wet chemical synthesis using ethanol, ammonia, water, and tetraethoxysilane, were implanted with 350 keV Er ions, to peak concentrations of 0.2-1.1 at. % and put onto a silicon or glass substrate. After annealing at 700-900 °C the colloids show clear room-temperature photoluminescence at 1.53 μm, with lifetimes as high as 17 ms. By comparing data of different Er concentrations, the purely radiative lifetime is estimated to be 20-22 ms, indicating a high quantum efficiency of about 80%. This high quantum efficiency indicates that, after annealing, the silica colloids are almost free of OH impurities. Spinning a layer of polymethylmethacrylate over the silica spheres results in an optically transparent nanocomposite layer, that can be used as a planar optical waveguide amplifier at 1.5 μm that is fully compatible with polymer technology.
The relative entropy in the quantum mechanics
International Nuclear Information System (INIS)
Lecomte Montes, A.
1983-06-01
Relative Entropy is a generalization of entropy which substitutes the Liouville measure from classical mechanics or the trace from quantum mechanics by an arbitrary state. There are many different defintions of it in quantum mechanics because the algebra of observables is not commutative. In this work, three known defintions of the quantum relative entropy are studied and compared but specifically their common properties are presented. The best known defintion was proposed many years ago by Umegaki and later on by Lindblad. This defintion can be realized through a functional calculus for quadratic forms introduced by Pusz and Woronowicz, for two arbitrary states on a Csup(*)-algebra. The two other definitions investigated are the Naudt's entropy and the inference function of Marchand and Wyss. The first one can be expressed through the functional calculus too, it has then almost the same properties as the Umegaki-Lindblad defintion. The inference function can be considered only as some kind of 1/2-relative entropy. The function is nevertheless very important because it can be expressed as the logarithm of the transition probability between the basis state and the actual state. A general theory which includes the three defintions is not found yet, but it is shown that the functional calculus provides a great family of relative entropies. This is important for a unified theory of all defintions and their properties. (Author)
Relativity and quantum physics for beginners
Manly, Steven L
2009-01-01
As we humans have expanded our horizons to see things vastly smaller, faster, larger, and farther than ever before, we have been forced to confront preconceptions born of the human experience and create wholly new ways of looking at the world around us. The theories of relativity and quantum physics were developed out of this need and have provided us with phenomenal, mind-twisting insights into the strange and exciting reality show of our universe.Relativity and Quantum Physics For Beginners is an entertaining and accessible introduction to the bizarre concepts that fueled the scientific revolution of the 20th century and led to amazing advances in our understanding of the universe.
The quantum walk search algorithm: Factors affecting efficiency
Lovett, Neil B.; Everitt, Matthew; Heath, Robert M.; Kendon, Viv
2011-01-01
We numerically study the quantum walk search algorithm of Shenvi, Kempe and Whaley [PRA \\textbf{67} 052307] and the factors which affect its efficiency in finding an individual state from an unsorted set. Previous work has focused purely on the effects of the dimensionality of the dataset to be searched. Here, we consider the effects of interpolating between dimensions, connectivity of the dataset, and the possibility of disorder in the underlying substrate: all these factors affect the effic...
On uncertainty relations in quantum mechanics
International Nuclear Information System (INIS)
Ignatovich, V.K.
2004-01-01
Uncertainty relations (UR) are shown to have nothing specific for quantum mechanics (QM), being the general property valid for the arbitrary function. A wave function of a particle simultaneously having a precisely defined position and momentum in QM is demonstrated. Interference on two slits in a screen is shown to exist in classical mechanics. A nonlinear classical system of equations replacing the QM Schroedinger equation is suggested. This approach is shown to have nothing in common with the Bohm mechanics
Efficient calculation of dissipative quantum transport properties in semiconductor nanostructures
Energy Technology Data Exchange (ETDEWEB)
Greck, Peter
2012-11-26
We present a novel quantum transport method that follows the non-equilibrium Green's function (NEGF) framework but side steps any self-consistent calculation of lesser self-energies by replacing them by a quasi-equilibrium expression. We termed this method the multi-scattering Buettiker-Probe (MSB) method. It generalizes the so-called Buettiker-Probe model but takes into account all relevant individual scattering mechanisms. It is orders of magnitude more efficient than a fully selfconsistent non-equilibrium Green's function calculation for realistic devices, yet accurately reproduces the results of the latter method as well as experimental data. This method is fairly easy to implement and opens the path towards realistic three-dimensional quantum transport calculations. In this work, we review the fundamentals of the non-equilibrium Green's function formalism for quantum transport calculations. Then, we introduce our novel MSB method after briefly reviewing the original Buettiker-Probe model. Finally, we compare the results of the MSB method to NEGF calculations as well as to experimental data. In particular, we calculate quantum transport properties of quantum cascade lasers in the terahertz (THz) and the mid-infrared (MIR) spectral domain. With a device optimization algorithm based upon the MSB method, we propose a novel THz quantum cascade laser design. It uses a two-well period with alternating barrier heights and complete carrier thermalization for the majority of the carriers within each period. We predict THz laser operation for temperatures up to 250 K implying a new temperature record.
Majorization uncertainty relations for mixed quantum states
Puchała, Zbigniew; Rudnicki, Łukasz; Krawiec, Aleksandra; Życzkowski, Karol
2018-04-01
Majorization uncertainty relations are generalized for an arbitrary mixed quantum state ρ of a finite size N. In particular, a lower bound for the sum of two entropies characterizing the probability distributions corresponding to measurements with respect to two arbitrary orthogonal bases is derived in terms of the spectrum of ρ and the entries of a unitary matrix U relating both bases. The results obtained can also be formulated for two measurements performed on a single subsystem of a bipartite system described by a pure state, and consequently expressed as an uncertainty relation for the sum of conditional entropies.
High-Efficiency Quantum Interrogation Measurements via the Quantum Zeno Effect
International Nuclear Information System (INIS)
Kwiat, P. G.; White, A. G.; Mitchell, J. R.; Nairz, O.; Weihs, G.; Weinfurter, H.; Zeilinger, A.
1999-01-01
The phenomenon of quantum interrogation allows one to optically detect the presence of an absorbing object, without the measuring light interacting with it. In an application of the quantum Zeno effect, the object inhibits the otherwise coherent evolution of the light, such that the probability that an interrogating photon is absorbed can in principle be arbitrarily small. We have implemented this technique, achieving efficiencies of up to 73% , and consequently exceeding the 50% theoretical maximum of the original ''interaction-free'' measurement proposal. We have also predicted and experimentally verified a previously unsuspected dependence on loss. (c) 1999 The American Physical Society
Non-Markovian quantum processes: Complete framework and efficient characterization
Pollock, Felix A.; Rodríguez-Rosario, César; Frauenheim, Thomas; Paternostro, Mauro; Modi, Kavan
2018-01-01
Currently, there is no systematic way to describe a quantum process with memory solely in terms of experimentally accessible quantities. However, recent technological advances mean we have control over systems at scales where memory effects are non-negligible. The lack of such an operational description has hindered advances in understanding physical, chemical, and biological processes, where often unjustified theoretical assumptions are made to render a dynamical description tractable. This has led to theories plagued with unphysical results and no consensus on what a quantum Markov (memoryless) process is. Here, we develop a universal framework to characterize arbitrary non-Markovian quantum processes. We show how a multitime non-Markovian process can be reconstructed experimentally, and that it has a natural representation as a many-body quantum state, where temporal correlations are mapped to spatial ones. Moreover, this state is expected to have an efficient matrix-product-operator form in many cases. Our framework constitutes a systematic tool for the effective description of memory-bearing open-system evolutions.
Quantum theory and Einstein's general relativity
International Nuclear Information System (INIS)
Borzeszkowski, H. von; Treder, H.
1982-01-01
We dicusss the meaning and prove the accordance of general relativity, wave mechanics, and the quantization of Einstein's gravitation equations themselves. Firstly, we have the problem of the influence of gravitational fields on the de Broglie waves, which influence is in accordance with Einstein's weak principle of equivalence and the limitation of measurements given by Heisenberg's uncertainty relations. Secondly, the quantization of the gravitational fields is a ''quantization of geometry.'' However, classical and quantum gravitation have the same physical meaning according to limitations of measurements given by Einstein's strong principle of equivalence and the Heisenberg uncertainties for the mechanics of test bodies
Quantum entanglement and a metaphysics of relations
Esfeld, Michael
This paper argues for a metaphysics of relations based on a characterization of quantum entanglement in terms of non-separability, thereby regarding entanglement as a sort of holism. By contrast to a radical metaphysics of relations, the position set out in this paper recognizes things that stand in the relations, but claims that, as far as the relations are concerned, there is no need for these things to have qualitative intrinsic properties underlying the relations. This position thus opposes a metaphysics of individual things that are characterized by intrinsic properties. A principal problem of the latter position is that it seems that we cannot gain any knowledge of these properties insofar as they are intrinsic. Against this background, the rationale behind a metaphysics of relations is to avoid a gap between epistemology and metaphysics.
Origins of efficient green light emission in phase-separated InGaN quantum wells
International Nuclear Information System (INIS)
Lai, Y-L; Liu, C-P; Lin, Y-H; Hsueh, T-H; Lin, R-M; Lyu, D-Y; Peng, Z-X; Lin, T-Y
2006-01-01
Green-light-emitting InGaN/GaN multiple quantum wells (MQWs) with high luminescent efficiency were grown by metalorganic chemical vapour deposition (MOCVD). The microstructure of the sample was studied by high-resolution transmission electron microscopy (HRTEM) and high-resolution x-ray diffraction, while its optical behaviour was analysed in great detail by a variety of photoluminescence methods. Two InGaN-related peaks that were clearly found in the photoluminescence (PL) spectrum are assigned to quasi-quantum dots (516 nm) and the InGaN matrix (450 nm), respectively, due to a strong phase separation observed by HRTEM. Except for the strong indium aggregation regions (511 meV of Stokes shift), slight composition fluctuations were also observed in the InGaN matrix, which were speculated from an 'S-shaped' transition and a Stokes shift of 341 meV. Stronger carrier localization and an internal quantum efficiency of the dot-related emission (21.5%), higher than the InGaN-matrix related emission (7.5%), was demonstrated. Additionally, a shorter lifetime and 'two-component' PL decay were found for the low-indium-content regions (matrix). Thus, the carrier transport process within quantum wells is suggested to drift from the low-In-content matrix to the high-In-content dots, resulting in the enhanced luminescence efficiency of the green light emission
Orthogonality and quantum geometry: Towards a relational reconstruction of quantum theory
Zhong, S.
2015-01-01
This thesis is an in-depth mathematical study of the non-orthogonality relation between the (pure) states of quantum systems. In Chapter 2, I define quantum Kripke frames, the protagonists of this thesis. A quantum Kripke frame is a Kripke frame in which the binary relation possesses some simple
Optimal power and efficiency of quantum Stirling heat engines
Yin, Yong; Chen, Lingen; Wu, Feng
2017-01-01
A quantum Stirling heat engine model is established in this paper in which imperfect regeneration and heat leakage are considered. A single particle which contained in a one-dimensional infinite potential well is studied, and the system consists of countless replicas. Each particle is confined in its own potential well, whose occupation probabilities can be expressed by the thermal equilibrium Gibbs distributions. Based on the Schrödinger equation, the expressions of power output and efficiency for the engine are obtained. Effects of imperfect regeneration and heat leakage on the optimal performance are discussed. The optimal performance region and the optimal values of important parameters of the engine cycle are obtained. The results obtained can provide some guidelines for the design of a quantum Stirling heat engine.
Efficient steady-state solver for hierarchical quantum master equations
Zhang, Hou-Dao; Qiao, Qin; Xu, Rui-Xue; Zheng, Xiao; Yan, YiJing
2017-07-01
Steady states play pivotal roles in many equilibrium and non-equilibrium open system studies. Their accurate evaluations call for exact theories with rigorous treatment of system-bath interactions. Therein, the hierarchical equations-of-motion (HEOM) formalism is a nonperturbative and non-Markovian quantum dissipation theory, which can faithfully describe the dissipative dynamics and nonlinear response of open systems. Nevertheless, solving the steady states of open quantum systems via HEOM is often a challenging task, due to the vast number of dynamical quantities involved. In this work, we propose a self-consistent iteration approach that quickly solves the HEOM steady states. We demonstrate its high efficiency with accurate and fast evaluations of low-temperature thermal equilibrium of a model Fenna-Matthews-Olson pigment-protein complex. Numerically exact evaluation of thermal equilibrium Rényi entropies and stationary emission line shapes is presented with detailed discussion.
Reciprocal relativity of noninertial frames: quantum mechanics
Energy Technology Data Exchange (ETDEWEB)
Low, Stephen G [4301 Avenue D, Austin, Texas, 78751 (United States)
2007-04-06
Noninertial transformations on time-position-momentum-energy space {l_brace}t, q, p, e{r_brace} with invariant Born-Green metric ds{sup 2} = -dt{sup 2} + 1/c{sup 2} dq{sup 2} + 1/b{sup 2} (dp{sup 2} = 1/c{sup 2} de{sup 2}) and the symplectic metric -de and dt + dp and dq are studied. This U 1,3) group of transformations contains the Lorentz group as the inertial special case and, in the limit of small forces and velocities, reduces to the expected Hamilton transformations leaving invariant the symplectic metric and the nonrelativistic line element ds{sup 2} -dt{sup 2}. The U(1,3) transformations bound relative velocities by c and relative forces by b. Spacetime is no longer an invariant subspace but is relative to noninertial observer frames. In the limit of b {yields} {infinity}, spacetime is invariant. Born was lead to the metric by a concept of reciprocity between position and momentum degrees of freedom and for this reason we call this reciprocal relativity. For large b, such effects will almost certainly only manifest in a quantum regime. Wigner showed that special relativistic quantum mechanics follows from the projective representations of the inhomogeneous Lorentz group. Projective representations of a Lie group are equivalent to the unitary representations of its central extension. The same method of projective representations for the inhomogeneous U(1,3) group is used to define the quantum theory in the noninertial case. The central extension of the inhomogeneous U(1,3) group is the cover of the quaplectic group Q(1,3) U(1,3) x{sub s} H(4), H(4) is the Weyl-Heisenberg group. The H(4) group, and the associated Heisenberg commutation relations central to quantum mechanics, results directly from requiring projective representations. A set of second-order wave equations result from the representations of the Casimir operators.
Functional Basis for Efficient Physical Layer Classical Control in Quantum Processors
Ball, Harrison; Nguyen, Trung; Leong, Philip H. W.; Biercuk, Michael J.
2016-12-01
The rapid progress seen in the development of quantum-coherent devices for information processing has motivated serious consideration of quantum computer architecture and organization. One topic which remains open for investigation and optimization relates to the design of the classical-quantum interface, where control operations on individual qubits are applied according to higher-level algorithms; accommodating competing demands on performance and scalability remains a major outstanding challenge. In this work, we present a resource-efficient, scalable framework for the implementation of embedded physical layer classical controllers for quantum-information systems. Design drivers and key functionalities are introduced, leading to the selection of Walsh functions as an effective functional basis for both programing and controller hardware implementation. This approach leverages the simplicity of real-time Walsh-function generation in classical digital hardware, and the fact that a wide variety of physical layer controls, such as dynamic error suppression, are known to fall within the Walsh family. We experimentally implement a real-time field-programmable-gate-array-based Walsh controller producing Walsh timing signals and Walsh-synthesized analog waveforms appropriate for critical tasks in error-resistant quantum control and noise characterization. These demonstrations represent the first step towards a unified framework for the realization of physical layer controls compatible with large-scale quantum-information processing.
Fast and efficient wireless power transfer via transitionless quantum driving.
Paul, Koushik; Sarma, Amarendra K
2018-03-07
Shortcut to adiabaticity (STA) techniques have the potential to drive a system beyond the adiabatic limits. Here, we present a robust and efficient method for wireless power transfer (WPT) between two coils based on the so-called transitionless quantum driving (TQD) algorithm. We show that it is possible to transfer power between the coils significantly fast compared to its adiabatic counterpart. The scheme is fairly robust against the variations in the coupling strength and the coupling distance between the coils. Also, the scheme is found to be reasonably immune to intrinsic losses in the coils.
Exceeding Conventional Photovoltaic Efficiency Limits Using Colloidal Quantum Dots
Pach, Gregory F.
Colloidal quantum dots (QDs) are a widely investigated field of research due to their highly tunable nature in which the optical and electronic properties of the nanocrystal can be manipulated by merely changing the nanocrystal's size. Specifically, colloidal quantum dot solar cells (QDSCs) have become a promising candidate for future generation photovoltaic technology. Quantum dots exhibit multiple exciton generation (MEG) in which multiple electron-hole pairs are generated from a single high-energy photon. This process is not observed in bulk-like semiconductors and allows for QDSCs to achieve theoretical efficiency limits above the standard single-junction Shockley-Queisser limit. However, the fast expanding field of QDSC research has lacked standardization of synthetic techniques and device design. Therefore, we sought to detail methodology for synthesizing PbS and PbSe QDs as well as photovoltaic device fabrication techniques as a fast track toward constructing high-performance solar cells. We show that these protocols lead toward consistently achieving efficiencies above 8% for PbS QDSCs. Using the same methodology for building single-junction photovoltaic devices, we incorporated PbS QDs as a bottom cell into a monolithic tandem architecture along with solution-processed CdTe nanocrystals. Modeling shows that near-peak tandem device efficiencies can be achieved across a wide range of bottom cell band gaps, and therefore the highly tunable band gap of lead-chalcogenide QDs lends well towards a bottom cell in a tandem architecture. A fully functioning monolithic tandem device is realized through the development of a ZnTe/ZnO recombination layer that appropriately combines the two subcells in series. Multiple recent reports have shown nanocrystalline heterostructures to undergo the MEG process more efficiency than several other nanostrucutres, namely lead-chalcogenide QDs. The final section of my thesis expands upon a recent publication by Zhang et. al., which
Deterministic and efficient quantum cryptography based on Bell's theorem
International Nuclear Information System (INIS)
Chen Zengbing; Pan Jianwei; Zhang Qiang; Bao Xiaohui; Schmiedmayer, Joerg
2006-01-01
We propose a double-entanglement-based quantum cryptography protocol that is both efficient and deterministic. The proposal uses photon pairs with entanglement both in polarization and in time degrees of freedom; each measurement in which both of the two communicating parties register a photon can establish one and only one perfect correlation, and thus deterministically create a key bit. Eavesdropping can be detected by violation of local realism. A variation of the protocol shows a higher security, similar to the six-state protocol, under individual attacks. Our scheme allows a robust implementation under the current technology
Photocurrent extraction efficiency in colloidal quantum dot photovoltaics
Kemp, K. W.; Wong, C. T. O.; Hoogland, S. H.; Sargent, E. H.
2013-01-01
The efficiency of photocurrent extraction was studied directly inside operating Colloidal Quantum Dot (CQD) photovoltaic devices. A model was derived from first principles for a thin film p-n junction with a linearly spatially dependent electric field. Using this model, we were able to clarify the origins of recent improvement in CQD solar cell performance. From current-voltage diode characteristics under 1 sun conditions, we extracted transport lengths ranging from 39 nm to 86 nm for these materials. Characterization of the intensity dependence of photocurrent extraction revealed that the dominant loss mechanism limiting the transport length is trap-mediated recombination. © 2013 AIP Publishing LLC.
Deterministic and efficient quantum cryptography based on Bell's theorem
International Nuclear Information System (INIS)
Chen, Z.-B.; Zhang, Q.; Bao, X.-H.; Schmiedmayer, J.; Pan, J.-W.
2005-01-01
Full text: We propose a novel double-entanglement-based quantum cryptography protocol that is both efficient and deterministic. The proposal uses photon pairs with entanglement both in polarization and in time degrees of freedom; each measurement in which both of the two communicating parties register a photon can establish a key bit with the help of classical communications. Eavesdropping can be detected by checking the violation of local realism for the detected events. We also show that our protocol allows a robust implementation under current technology. (author)
Development of a System for Absolute Quantum Efficiency Determination of Hybrid Photo Diodes
Hammarstedt, P
2001-01-01
At CERN, the European Laboratory for Particle Physics, a new particle accelerator, the Large Hadron Collider (LHC), is under development. The detectors at LHC require development of highly sophisticated technologies, including Hybrid Photo Diodes (HPD) for high efficiency, high resolution single photon detection with a large area coverage. During the HPD development phase, one of the crucial parameters in the optimization of the photocathode creation process is the quantum efficiency. The aim of this Master Thesis has been to design and implement a system for high precision, high resolution quantum efficiency determination over a large, 200-700 nm photon wavelength range. Commercially available components have been obtained, an optomechanical system has been designed and built, and all the necessary data acquisition, control and analysis software has been implemented. The relative precision of the measurement system has been determined to 2%, with additional possible systematic errors less than 2%. Various qu...
Quantum integrable systems related to lie algebras
International Nuclear Information System (INIS)
Olshanetsky, M.A.; Perelomov, A.M.
1983-01-01
Some quantum integrable finite-dimensional systems related to Lie algebras are considered. This review continues the previous review of the same authors (1981) devoted to the classical aspects of these systems. The dynamics of some of these systems is closely related to free motion in symmetric spaces. Using this connection with the theory of symmetric spaces some results such as the forms of spectra, wave functions, S-matrices, quantum integrals of motion are derived. In specific cases the considered systems describe the one-dimensional n-body systems interacting pairwise via potentials g 2 v(q) of the following 5 types: vsub(I)(q)=q - 2 , vsub(II)(q)=sinh - 2 q, vsub(III)(q)=sin - 2 q, vsub(IV)(q)=P(q), vsub(V)(q)=q - 2 +#betta# 2 q 2 . Here P(q) is the Weierstrass function, so that the first three cases are merely subcases on the fourth. The system characterized by the Toda nearest-neighbour potential exp(qsub(j)-qsub(j+1)) is moreover considered. This review presents from a general and universal point of view results obtained mainly over the past fifteen years. Besides, it contains some new results both of physical and mathematical interest. (orig.)
Causality, relativity and quantum correlation experiments with ...
Indian Academy of Sciences (India)
gled photons are sent via an optical fiber network to two villages near Geneva, separated ... Quantum information processing; quantum communication. ... situation is presented as follows: The system that undergoes a measurement first, let us.
Jefferson Lab IR demo FEL photocathode quantum efficiency scanner
Gubeli, J; Grippo, A; Jordan, K; Shinn, M; Siggins, T
2001-01-01
Jefferson Laboratory's Free Electron Laser (FEL) incorporates a cesiated gallium arsenide (GaAs) DC photocathode gun as its electron source. By using a set of scanning mirrors, the surface of the GaAs wafer is illuminated with a 543.5nm helium-neon laser. Measuring the current flow across the biased photocathode generates a quantum efficiency (QE) map of the 1-in. diameter wafer surface. The resulting QE map provides a very detailed picture of the efficiency of the wafer surface. By generating a QE map in a matter of minutes, the photocathode scanner has proven to be an exceptional tool in quickly determining sensitivity and availability of the photocathode for operation.
DEFF Research Database (Denmark)
Leistikow, M.D.; Johansen, Jeppe; Kettelarij, A.J.
2009-01-01
We study experimentally time-resolved emission of colloidal CdSe quantum dots in an environment with a controlled local density of states LDOS. The decay rate is measured versus frequency and as a function of distance to a mirror. We observe a linear relation between the decay rate and the LDOS, ...... with the measured radiative rates. Our results are relevant for applications of CdSe quantum dots in spontaneous emission control and cavity quantum electrodynamics.......We study experimentally time-resolved emission of colloidal CdSe quantum dots in an environment with a controlled local density of states LDOS. The decay rate is measured versus frequency and as a function of distance to a mirror. We observe a linear relation between the decay rate and the LDOS......, allowing us to determine the size-dependent quantum efficiency and oscillator strength. We find that the quantum efficiency decreases with increasing emission energy mostly due to an increase in nonradiative decay. We manage to obtain the oscillator strength of the important class of CdSe quantum dots...
Improve photocurrent quantum efficiency of carbon nanotube by chemical treatment
International Nuclear Information System (INIS)
Wang Hongguang; Wei Jinquan; Jia Yi; Li Zhen; Zhu Hongwei; Wang Kunlin; Wu Dehai
2012-01-01
Highlights: ► The QE of photocurrent for the H 2 O 2 -treated CNTs reaches to 5.28% at U bias = 0.1 V. ► Moderate chemical treatment can enhance the QE of photocurrent of CNTs. ► Excessive chemical treatment decreases the photocurrent quantum efficiency of CNTs. - Abstract: High photocurrent quantum efficiency (QE) of carbon nanotubes (CNTs) is important to their photovoltaic applications. The ability of photocurrent generation of CNTs depends on their band structure and surface state. For given CNTs, it is possible to improve the QE of photocurrent by chemical modification. Here, we study the effects of simple chemical treatment on the QE of CNTs by measuring the photocurrent of macroscopic CNT bundles. The QE of the H 2 O 2 -treated CNT bundle reaches 5.28% at 0.1 V bias voltage at a laser (λ = 473 nm) illumination, which is 85% higher than that of the pristine sample. But the QE of the CNTs treated in concentrated HNO 3 is lower than that of the pristine sample. It shows that moderate chemical treatment can enhance the photocurrent QE and excessive chemical treatment will decrease the QE because of introducing lots of structural defects.
Efficiency enhancement of InGaN/GaN multiple quantum wells with graphene layer
International Nuclear Information System (INIS)
Deng, Zhen; Li, Zishen; Jiang, Yang; Ma, Ziguang; Fang, Yutao; Li, Yangfeng; Wang, Wenxin; Jia, Haiqiang; Chen, Hong
2015-01-01
In this work, a novel hybrid graphene/InGaN-based multiple quantum wells (MQWs) structure has been fabricated. Compared to the sample conventional structure (CS), the utilization of graphene transferred on top GaN layer significantly enhances the internal quantum efficiency and relatively photoluminescence intensity. Furthermore, the excitons in the MQWs of sample hybrid structure (HS) have a shorter decay lifetime of 3.4 ns than that of 6.7 ns for sample CS. These results are probably attributed to the free carriers in the graphene layer, which can screen the piezoelectric field in the active region and thus present a free quantum-confined Stark effect-like behavior. Our work demonstrates that the graphene on the top GaN layer can effectively increase the recombination rate in sample HS, which may further improve LEDs' performance. (orig.)
Extending quantum mechanics entails extending special relativity
International Nuclear Information System (INIS)
Aravinda, S; Srikanth, R
2016-01-01
The complementarity between signaling and randomness in any communicated resource that can simulate singlet statistics is generalized by relaxing the assumption of free will in the choice of measurement settings. We show how to construct an ontological extension for quantum mechanics (QMs) through the oblivious embedding of a sound simulation protocol in a Newtonian spacetime. Minkowski or other intermediate spacetimes are ruled out as the locus of the embedding by virtue of hidden influence inequalities. The complementarity transferred from a simulation to the extension unifies a number of results about quantum non-locality, and implies that special relativity has a different significance for the ontological model and for the operational theory it reproduces. Only the latter, being experimentally accessible, is required to be Lorentz covariant. There may be certain Lorentz non-covariant elements at the ontological level, but they will be inaccessible at the operational level in a valid extension. Certain arguments against the extendability of QM, due to Conway and Kochen (2009) and Colbeck and Renner (2012), are attributed to their assumption that the spacetime at the ontological level has Minkowski causal structure. (paper)
Role of the substrate reflectance and surface-bulk treatments in CsI quantum efficiency
Singh, B K; Nitti, M A; Valentini, A
2003-01-01
We have experimentally investigated the following aspects related to the quantum efficiency of CsI photocathodes: the type of substrate, the film thickness and the effect of a 'bulk treatment' during the film growth. We discovered that, using a high reflectivity aluminium substrate, the photoemission of very thin CsI film is enhanced. Our study also revealed that photocathodes become less sensitive to moisture when a negative bias voltage is applied to the substrate during the film deposition process.
The problem of time quantum mechanics versus general relativity
Anderson, Edward
2017-01-01
This book is a treatise on time and on background independence in physics. It first considers how time is conceived of in each accepted paradigm of physics: Newtonian, special relativity, quantum mechanics (QM) and general relativity (GR). Substantial differences are moreover uncovered between what is meant by time in QM and in GR. These differences jointly source the Problem of Time: Nine interlinked facets which arise upon attempting concurrent treatment of the QM and GR paradigms, as is required in particular for a background independent theory of quantum gravity. A sizeable proportion of current quantum gravity programs - e.g. geometrodynamical and loop quantum gravity approaches to quantum GR, quantum cosmology, supergravity and M-theory - are background independent in this sense. This book's foundational topic is thus furthermore of practical relevance in the ongoing development of quantum gravity programs. This book shows moreover that eight of the nine facets of the Problem of Time already occur upon ...
Improved quantum efficiency models of CZTSe: GE nanolayer solar cells with a linear electric field.
Lee, Sanghyun; Price, Kent J; Saucedo, Edgardo; Giraldo, Sergio
2018-02-08
We fabricated and characterized CZTSe:Ge nanolayer (quantum efficiency for Ge doped CZTSe devices. The linear electric field model is developed with the incomplete gamma function of the quantum efficiency as compared to the empirical data at forward bias conditions. This model is characterized with a consistent set of parameters from a series of measurements and the literature. Using the analytical modelling method, the carrier collection profile in the absorber is calculated and closely fitted by the developed mathematical expressions to identify the carrier dynamics during the quantum efficiency measurement of the device. The analytical calculation is compared with the measured quantum efficiency data at various bias conditions.
International Nuclear Information System (INIS)
Jun, Niu; Zhi, Yang; Ben-Kang, Chang
2009-01-01
The mathematical expression of the electron diffusion and drift length L DE of exponential doping photocathode is deduced. In the quantum efficiency equation of the reffection-mode uniform doping cathode, substituting L DE for L D , the equivalent quantum efficiency equation of the reffection-mode exponential doping cathode is obtained. By using the equivalent equation, theoretical simulation and experimental analysis shows that the equivalent index formula and formula-doped cathode quantum efficiency results in line. The equivalent equation avoids complicated calculation, thereby simplifies the process of solving the quantum efficiency of exponential doping photocathode
Limits to solar power conversion efficiency with applications to quantum and thermal systems
Byvik, C. E.; Buoncristiani, A. M.; Smith, B. T.
1983-01-01
An analytical framework is presented that permits examination of the limit to the efficiency of various solar power conversion devices. Thermodynamic limits to solar power efficiency are determined for both quantum and thermal systems, and the results are applied to a variety of devices currently considered for use in space systems. The power conversion efficiency for single-threshold energy quantum systems receiving unconcentrated air mass zero solar radiation is limited to 31 percent. This limit applies to photovoltaic cells directly converting solar radiation, or indirectly, as in the case of a thermophotovoltaic system. Photoelectrochemical cells rely on an additional chemical reaction at the semiconductor-electrolyte interface, which introduces additional second-law demands and a reduction of the solar conversion efficiency. Photochemical systems exhibit even lower possible efficiencies because of their relatively narrow absorption bands. Solar-powered thermal engines in contact with an ambient reservoir at 300 K and operating at maximum power have a peak conversion efficiency of 64 percent, and this occurs for a thermal reservoir at a temperature of 2900 K. The power conversion efficiency of a solar-powered liquid metal magnetohydrodydnamic generator, a solar-powered steam turbine electric generator, and an alkali metal thermoelectric converter is discussed.
Quantum efficiency harmonic analysis of exciton annihilation in organic light emitting diodes
Energy Technology Data Exchange (ETDEWEB)
Price, J. S.; Giebink, N. C., E-mail: ncg2@psu.edu [Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States)
2015-06-29
Various exciton annihilation processes are known to impact the efficiency roll-off of organic light emitting diodes (OLEDs); however, isolating and quantifying their contribution in the presence of other factors such as changing charge balance continue to be a challenge for routine device characterization. Here, we analyze OLED electroluminescence resulting from a sinusoidal dither superimposed on the device bias and show that nonlinearity between recombination current and light output arising from annihilation mixes the quantum efficiency measured at different dither harmonics in a manner that depends uniquely on the type and magnitude of the annihilation process. We derive a series of analytical relations involving the DC and first harmonic external quantum efficiency that enable annihilation rates to be quantified through linear regression independent of changing charge balance and evaluate them for prototypical fluorescent and phosphorescent OLEDs based on the emitters 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran and platinum octaethylporphyrin, respectively. We go on to show that, in most cases, it is sufficient to calculate the needed quantum efficiency harmonics directly from derivatives of the DC light versus current curve, thus enabling this analysis to be conducted solely from standard light-current-voltage measurement data.
High-Efficiency Iron Photosensitizer Explained with Quantum Wavepacket Dynamics
DEFF Research Database (Denmark)
Pápai, Mátyás Imre; Vankó, György; Rozgonyi, Tamas
2016-01-01
designed to destabilize the MC states. Using first-principles quantum nuclear wavepacket simulations we achieve a detailed understanding of the photoexcited decay mechanism, demonstrating that it is dominated by an ultrafast intersystem crossing from 1MLCT–3MLCT proceeded by slower kinetics associated...... with the conversion into the 3MC states. The slowest component of the 3MLCT decay, important in the context of photosensitizers, is much longer than related Fe(II) complexes because the population transfer to the 3MC states occurs in a region of the potential where the energy gap between the 3MLCT and 3MC states...
A highly efficient single-photon source based on a quantum dot in a photonic nanowire
DEFF Research Database (Denmark)
Claudon, Julien; Bleuse, Joel; Malik, Nitin Singh
2010-01-01
–4 or a semiconductor quantum dot5–7. Achieving a high extraction efficiency has long been recognized as a major issue, and both classical solutions8 and cavity quantum electrodynamics effects have been applied1,9–12. We adopt a different approach, based on an InAs quantum dot embedded in a GaAs photonic nanowire......The development of efficient solid-state sources of single photons is a major challenge in the context of quantum communication,optical quantum information processing and metrology1. Such a source must enable the implementation of a stable, single-photon emitter, like a colour centre in diamond2...
Universal quantum uncertainty relations between nonergodicity and loss of information
Awasthi, Natasha; Bhattacharya, Samyadeb; SenDe, Aditi; Sen, Ujjwal
2018-03-01
We establish uncertainty relations between information loss in general open quantum systems and the amount of nonergodicity of the corresponding dynamics. The relations hold for arbitrary quantum systems interacting with an arbitrary quantum environment. The elements of the uncertainty relations are quantified via distance measures on the space of quantum density matrices. The relations hold for arbitrary distance measures satisfying a set of intuitively satisfactory axioms. The relations show that as the nonergodicity of the dynamics increases, the lower bound on information loss decreases, which validates the belief that nonergodicity plays an important role in preserving information of quantum states undergoing lossy evolution. We also consider a model of a central qubit interacting with a fermionic thermal bath and derive its reduced dynamics to subsequently investigate the information loss and nonergodicity in such dynamics. We comment on the "minimal" situations that saturate the uncertainty relations.
Investigations into quantum theory and relativity theory
International Nuclear Information System (INIS)
Cox, I.D.
1982-03-01
This thesis falls into two parts. The first is concerned with damping theory as a particular approach to the description of the dynamical evolution of non-closed systems. Appealing ultimately to the Liouville/Von-Neuman equation in the weak coupling regime, the current-voltage characteristics of both the normal and Josephson tunnelling junctions, treated as open systems are obtained. It is then shown that the same results may be obtained via the combined scattering and density matrix formalism (which does not appeal to the Liouville/Von-Neuman equation), and that this method has certain advantages over the conventional formalism. In the second part an extended (non-quantum) theory of relativity in a five dimensional space is developed and a number of interesting consequences thereof obtained. In particular a generalised set of Maxwell equations for electro-dynamics is derived, and some of the implications of the new set of equations are described. Furthermore a treatment of the five-dimensional analogue of the Schwarzschild problem in general relativity is given, together with the resulting implications for planetary motion. (author)
Relativity, symmetry and the structure of quantum theory
Klink, William H; Schweiger, Wolfgang
Quantum theory is one of the most successful of all physical theories. Our everyday world is dominated by devices that function because of knowledge of the quantum world. Yet many, physicists and non-physicists alike, find the theory which explains the behavior of the quantum world baffling and strange. This book is the first in a series of three that argues that relativity and symmetry determine the structure of quantum theory. That is to say, the structure of quantum theory is what it is because of relativity and symmetry. There are different types of relativity, each leading to a particular type of quantum theory. This book deals specifically with what we call Newton relativity, the form of relativity built into Newtonian mechanics, and the quantum theory to which it gives rise, which we call Galilean (often misleadingly called non-relativistic) quantum theory. Key Features: • Meaning and significance of the term of relativity; discussion of the principle of relativity. • Relation of symmetry to relati...
International Nuclear Information System (INIS)
Bodendorfer, N; Zipfel, A
2016-01-01
Building on a recent proposal for a quantum reduction to spherical symmetry from full loop quantum gravity, we investigate the relation between a quantisation of spherically symmetric general relativity and a reduction at the quantum level. To this end, we generalise the previously proposed quantum reduction by dropping the gauge fixing condition on the radial diffeomorphisms, thus allowing us to make direct contact with previous work on reduced quantisation. A dictionary between spherically symmetric variables and observables with respect to the reduction constraints in the full theory is discussed, as well as an embedding of reduced quantum states to a subsector of the quantum symmetry reduced full theory states. On this full theory subsector, the quantum algebra of the mentioned observables is computed and shown to qualitatively reproduce the quantum algebra of the reduced variables in the large quantum number limit for a specific choice of regularisation. Insufficiencies in recovering the reduced algebra quantitatively from the full theory are attributed to the oversimplified full theory quantum states we use. (paper)
Energy Technology Data Exchange (ETDEWEB)
Ollis, D.F. [North Carolina State Univ., Raleigh, NC (United States)
1996-09-01
In the remediation industries, a useful treatment technology must be {open_quotes}general, robust, and cheap{close_quotes}. Among oxidation processes, heterogeneous photocatalysis is now broadly demonstrated to destroy common water and air contaminants. The potential process uses of highly stable titania, long lived lamps (one year), and room temperature operation, indicating a simple and robust process. We are left to address the third criterion: Can photocatalysis be {open_quotes}cheap{close_quotes}? In both liquid phase and gas phase treatment and purification by photocatalysis, it is established that the primary barrier to commercialization is often cost. Cost in return is dominated by the efficiency with which solar or lamp photons are harvested for productive light, and subsequent dark, reactions. This paper therefore defines fundamental needs in photocatalysis for pollution control in terms of activities which could lead to quantum efficiency enhancement. We first recall three related definitions. The quantum yield (QY) is the ratio of molecules of reactant converted per photon absorbed, a fundamental quantity. A less fundamental, but more easily measured variable is the quantum efficiency (QE), the ratio of molecules converted per photon entering the reactor. A third variable is the energy required per order of magnitude pollutant reduction, or EEO, a definition which provides for easy energy cost comparisons among different technologies. Each measure cited here reflects the photon, and thus the electrical, cost of this photochemistry.
Efficient learning algorithm for quantum perceptron unitary weights
Seow, Kok-Leong; Behrman, Elizabeth; Steck, James
2015-01-01
For the past two decades, researchers have attempted to create a Quantum Neural Network (QNN) by combining the merits of quantum computing and neural computing. In order to exploit the advantages of the two prolific fields, the QNN must meet the non-trivial task of integrating the unitary dynamics of quantum computing and the dissipative dynamics of neural computing. At the core of quantum computing and neural computing lies the qubit and perceptron, respectively. We see that past implementat...
Origin of low quantum efficiency of photoluminescence of InP/ZnS nanocrystals
DEFF Research Database (Denmark)
Shirazi, Roza; Kovacs, Andras; Corell, Dennis Dan
2013-01-01
In this paper, we study the origin of a strong wavelength dependence of the quantum efficiency of InP/ZnS nanocrystals. We find that while the average size of the nanocrystals increased by 50%, resulting in longer emission wavelength, the quantum efficiency drops more than one order of magnitude...
Detective quantum efficiency gains compared with speed gains for hypersensitized astronomical plates
International Nuclear Information System (INIS)
Kaye, A.L.
1977-01-01
It is reasonable to assume that gains in detective quantum efficiency (DQE) are far better criteria for assessing the performance of hypersensitizing techniques than gains in speed. It is shown here that gains in speed can be misleading, for some methods of hypersensitization give plates of increased speed but reduced detective quantum efficiency. (author)
High-efficiency Gaussian key reconciliation in continuous variable quantum key distribution
Bai, ZengLiang; Wang, XuYang; Yang, ShenShen; Li, YongMin
2016-01-01
Efficient reconciliation is a crucial step in continuous variable quantum key distribution. The progressive-edge-growth (PEG) algorithm is an efficient method to construct relatively short block length low-density parity-check (LDPC) codes. The qua-sicyclic construction method can extend short block length codes and further eliminate the shortest cycle. In this paper, by combining the PEG algorithm and qua-si-cyclic construction method, we design long block length irregular LDPC codes with high error-correcting capacity. Based on these LDPC codes, we achieve high-efficiency Gaussian key reconciliation with slice recon-ciliation based on multilevel coding/multistage decoding with an efficiency of 93.7%.
The relation between classical and quantum mechanics
International Nuclear Information System (INIS)
Taylor, Peter.
1984-01-01
The thesis examines the relationship between classical and quantum mechanics from philosophical, mathematical and physical standpoints. Arguments are presented in favour of 'conjectural realism' in scientific theories, distinguished by explicit contextual structure and empirical testability. The formulations of classical and quantum mechanics, based on a general theory of mechanics is investigated, as well as the mathematical treatments of these subjects. Finally the thesis questions the validity of 'classical limits' and 'quantisations' in intertheoretic reduction. (UK)
Klink, William H.; Schweiger, Wolfgang
2018-03-01
This book covers relativistic quantum theory from the point of view of a particle theory, based on the irreducible representations of the Poincaré group, the group that expresses the symmetry of Einstein relativity. There are several ways of formulating such a theory; this book develops what is called relativistic point form quantum mechanics, which, unlike quantum field theory, deals with a fixed number of particles in a relativistically invariant way. A chapter is devoted to applications of point form quantum mechanics to nuclear physics.
International Nuclear Information System (INIS)
Gambini, Rodolfo; Porto, Rafael A; Pullin, Jorge
2004-01-01
The use of a relational time in quantum mechanics is a framework in which one promotes to quantum operators all variables in a system, and later chooses one of the variables to operate like a 'clock'. Conditional probabilities are computed for variables of the system to take certain values when the 'clock' specifies a certain time. This framework is attractive in contexts where the assumption of usual quantum mechanics of the existence of an external, perfectly classical clock, appears unnatural, as in quantum cosmology. Until recently, there were problems with such constructions in ordinary quantum mechanics with additional difficulties in the context of constrained theories like general relativity. A scheme we recently introduced to consistently discretize general relativity removed such obstacles. Since the clock is now an object subject to quantum fluctuations, the resulting evolution in time is not exactly unitary and pure states decohere into mixed states. Here we work out in detail the type of decoherence generated, and we find it to be of Lindblad type. This is attractive since it implies that one can have loss of coherence without violating the conservation of energy. We apply the framework to a simple cosmological model to illustrate how a quantitative estimate of the effect could be computed. For most quantum systems it appears to be too small to be observed, although certain macroscopic quantum systems could in the future provide a testing ground for experimental observation
Toward efficient fiber-based quantum interface (Conference Presentation)
Soshenko, Vladimir; Vorobyov, Vadim V.; Bolshedvorsky, Stepan; Lebedev, Nikolay; Akimov, Alexey V.; Sorokin, Vadim; Smolyaninov, Andrey
2016-04-01
NV center in diamond is attracting a lot of attention in quantum information processing community [1]. Been spin system in clean and well-controlled environment of diamond it shows outstanding performance as quantum memory even at room temperature, spin control with single shot optical readout and possibility to build up quantum registers even on single NV center. Moreover, NV centers could be used as high-resolution sensitive elements of detectors of magnetic or electric field, temperature, tension, force or rotation. For all of these applications collection of the light emitted by NV center is crucial point. There were number of approaches suggested to address this issue, proposing use of surface plasmoms [2], manufacturing structures in diamond [3] etc. One of the key feature of any practically important interface is compatibility with the fiber technology. Several groups attacking this problem using various approaches. One of them is placing of nanodiamonds in the holes of photonic crystal fiber [4], another is utilization of AFM to pick and place nanodiamond on the tapered fiber[5]. We have developed a novel technique of placing a nanodiamond with single NV center on the tapered fiber by controlled transfer of a nanodiamond from one "donor" tapered fiber to the "target" clean tapered fiber. We verify our ability to transfer only single color centers by means of measurement of second order correlation function. With this technique, we were able to double collection efficiency of confocal microscope. The majority of the factors limiting the collection of photons via optical fiber are technical and may be removed allowing order of magnitude improved in collection. We also discuss number of extensions of this technique to all fiber excitation and integration with nanostructures. References: [1] Marcus W. Doherty, Neil B. Manson, Paul Delaney, Fedor Jelezko, Jörg Wrachtrup, Lloyd C.L. Hollenberg , " The nitrogen-vacancy colour centre in diamond," Physics Reports
Combining relativity and quantum mechanics: Schroedinger's interpretation of ψ
International Nuclear Information System (INIS)
Barut, A.O.
1987-07-01
The incongruence between quantum theory and relativity theory is traced to the probability interpretation of the former. The classical continium interpretation of ψ removes the difficulty. How quantum properties of matter and light, and in particular the radiative problems, like spontaneous emission and Lamb shift, may be accounted in a first quantized Maxwell-Dirac system is discussed. (author). 17 refs
Can quantum theory and special relativity peacefully coexist?
Seevinck, M.P.
This white paper aims to identify an open problem in ‘Quantum Physics and the Nature of Reality’—namely whether quantum theory and special relativity are formally compatible—, to indicate what the underlying issues are, and put forward ideas about how the problem might be addressed.
Can quantum theory and special relativity peacefully coexist?
Seevinck, M.P.; Briggs, A.
2010-01-01
This white paper aims to identify an open problem in ‘Quantum Physics and the Nature of Reality’—namely whether quantum theory and special relativity are formally compatible—, to indicate what the underlying issues are, and put forward ideas about how the problem might be addressed.
Optimal and efficient decoding of concatenated quantum block codes
International Nuclear Information System (INIS)
Poulin, David
2006-01-01
We consider the problem of optimally decoding a quantum error correction code--that is, to find the optimal recovery procedure given the outcomes of partial ''check'' measurements on the system. In general, this problem is NP hard. However, we demonstrate that for concatenated block codes, the optimal decoding can be efficiently computed using a message-passing algorithm. We compare the performance of the message-passing algorithm to that of the widespread blockwise hard decoding technique. Our Monte Carlo results using the five-qubit and Steane's code on a depolarizing channel demonstrate significant advantages of the message-passing algorithms in two respects: (i) Optimal decoding increases by as much as 94% the error threshold below which the error correction procedure can be used to reliably send information over a noisy channel; and (ii) for noise levels below these thresholds, the probability of error after optimal decoding is suppressed at a significantly higher rate, leading to a substantial reduction of the error correction overhead
Effects of image processing on the detective quantum efficiency
Energy Technology Data Exchange (ETDEWEB)
Park, Hye-Suk; Kim, Hee-Joung; Cho, Hyo-Min; Lee, Chang-Lae; Lee, Seung-Wan; Choi, Yu-Na [Yonsei University, Wonju (Korea, Republic of)
2010-02-15
The evaluation of image quality is an important part of digital radiography. The modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE) are widely accepted measurements of the digital radiographic system performance. However, as the methodologies for such characterization have not been standardized, it is difficult to compare directly reported the MTF, NPS, and DQE results. In this study, we evaluated the effect of an image processing algorithm for estimating the MTF, NPS, and DQE. The image performance parameters were evaluated using the international electro-technical commission (IEC 62220-1)-defined RQA5 radiographic techniques. Computed radiography (CR) posterior-anterior (PA) images of a hand for measuring the signal to noise ratio (SNR), the slit images for measuring the MTF, and the white images for measuring the NPS were obtained, and various multi-Scale image contrast amplification (MUSICA) factors were applied to each of the acquired images. All of the modifications of the images obtained by using image processing had a considerable influence on the evaluated image quality. In conclusion, the control parameters of image processing can be accounted for evaluating characterization of image quality in same way. The results of this study should serve as a baseline for based on evaluating imaging systems and their imaging characteristics by MTF, NPS, and DQE measurements.
Effects of image processing on the detective quantum efficiency
International Nuclear Information System (INIS)
Park, Hye-Suk; Kim, Hee-Joung; Cho, Hyo-Min; Lee, Chang-Lae; Lee, Seung-Wan; Choi, Yu-Na
2010-01-01
The evaluation of image quality is an important part of digital radiography. The modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE) are widely accepted measurements of the digital radiographic system performance. However, as the methodologies for such characterization have not been standardized, it is difficult to compare directly reported the MTF, NPS, and DQE results. In this study, we evaluated the effect of an image processing algorithm for estimating the MTF, NPS, and DQE. The image performance parameters were evaluated using the international electro-technical commission (IEC 62220-1)-defined RQA5 radiographic techniques. Computed radiography (CR) posterior-anterior (PA) images of a hand for measuring the signal to noise ratio (SNR), the slit images for measuring the MTF, and the white images for measuring the NPS were obtained, and various multi-Scale image contrast amplification (MUSICA) factors were applied to each of the acquired images. All of the modifications of the images obtained by using image processing had a considerable influence on the evaluated image quality. In conclusion, the control parameters of image processing can be accounted for evaluating characterization of image quality in same way. The results of this study should serve as a baseline for based on evaluating imaging systems and their imaging characteristics by MTF, NPS, and DQE measurements.
Effects of image processing on the detective quantum efficiency
Park, Hye-Suk; Kim, Hee-Joung; Cho, Hyo-Min; Lee, Chang-Lae; Lee, Seung-Wan; Choi, Yu-Na
2010-04-01
Digital radiography has gained popularity in many areas of clinical practice. This transition brings interest in advancing the methodologies for image quality characterization. However, as the methodologies for such characterizations have not been standardized, the results of these studies cannot be directly compared. The primary objective of this study was to standardize methodologies for image quality characterization. The secondary objective was to evaluate affected factors to Modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) according to image processing algorithm. Image performance parameters such as MTF, NPS, and DQE were evaluated using the international electro-technical commission (IEC 62220-1)-defined RQA5 radiographic techniques. Computed radiography (CR) images of hand posterior-anterior (PA) for measuring signal to noise ratio (SNR), slit image for measuring MTF, white image for measuring NPS were obtained and various Multi-Scale Image Contrast Amplification (MUSICA) parameters were applied to each of acquired images. In results, all of modified images were considerably influence on evaluating SNR, MTF, NPS, and DQE. Modified images by the post-processing had higher DQE than the MUSICA=0 image. This suggests that MUSICA values, as a post-processing, have an affect on the image when it is evaluating for image quality. In conclusion, the control parameters of image processing could be accounted for evaluating characterization of image quality in same way. The results of this study could be guided as a baseline to evaluate imaging systems and their imaging characteristics by measuring MTF, NPS, and DQE.
Efficiency droop in nonpolar InGaN quantum wells
Energy Technology Data Exchange (ETDEWEB)
Schade, Lukas; Schwarz, Ulrich [Fraunhofer Institut fuer Angewandte Festkoerperphysik (IAF), Freiburg im Breisgau (Germany); Institut fuer Mikrosystemtechnik (IMTEK), Universitaet Freiburg, Freiburg im Breisgau (Germany); Wernicke, Tim; Rass, Jens; Ploch, Simon [Institut fuer Festkoerperphysik, Technische Universitaet Berlin (Germany); Weyers, Markus [Ferdinand-Braun-Institut (FBH), Berlin (Germany); Kneissl, Michael [Institut fuer Festkoerperphysik, Technische Universitaet Berlin (Germany); Ferdinand-Braun-Institut (FBH), Berlin (Germany)
2012-07-01
InGaN quantum wells (QWs) exhibit a decline of the internal efficiency at high charge carrier excitation. This has been observed for polar as well as for semipolar and nonpolar oriented QWs. Polar stands for the (0001) growth direction with strong piezoelectric fields. Due to the vanishing fields, the orthogonal growth directions (a or m) are called nonpolar, while all directions between are merged as semipolar orientations. In contrast to the polar and many semipolar QWs, nonpolar InGaN QWs provide a special property: optical polarization of the radiative transitions, which is a result of the anisotropic strain within pseudomorphic grown nonpolar QWs. Using this property, the broadened effective emission can be resolved into two fundamental transitions. They are spectrally separated by a defined energy which corresponds to the energy distance of the valence subbands. We studied nonpolar InGaN/InGaN Multi-QWs grown on low defect density GaN substrates with a setup for confocal microscopy. To reach high excitation densities of charge carriers, we use either a combination of an UV laser and highly focusing objectives or an electric pulse generator. The emission is spectrally analysed and compared to established models.
Highly efficient photonic nanowire single-photon sources for quantum information applications
DEFF Research Database (Denmark)
Gregersen, Niels; Claudon, J.; Munsch, M.
2013-01-01
to a collection efficiency of only 1-2 %, and efficient light extraction thus poses a major challenge in SPS engineering. Initial efforts to improve the efficiency have exploited cavity quantum electrodynamics (cQED) to efficiently couple the emitted photons to the optical cavity mode. An alternative approach......Within the emerging field of optical quantum information processing, the current challenge is to construct the basic building blocks for the quantum computing and communication systems. A key component is the singlephoton source (SPS) capable of emitting single photons on demand. Ideally, the SPS...... must feature near-unity efficiency, where the efficiency is defined as the number of detected photons per trigger, the probability g(2)(τ=0) of multi-photon emission events should be 0 and the emitted photons are required to be indistinguishable. An optically or electrically triggered quantum light...
Colaux, Henri; Dawson, Daniel M; Ashbrook, Sharon E
2014-08-07
The conversion between multiple- and single-quantum coherences is integral to many nuclear magnetic resonance (NMR) experiments of quadrupolar nuclei. This conversion is relatively inefficient when effected by a single pulse, and many composite pulse schemes have been developed to improve this efficiency. To provide the maximum improvement, such schemes typically require time-consuming experimental optimization. Here, we demonstrate an approach for generating amplitude-modulated pulses to enhance the efficiency of the triple- to single-quantum conversion. The optimization is performed using the SIMPSON and MATLAB packages and results in efficient pulses that can be used without experimental reoptimisation. Most significant signal enhancements are obtained when good estimates of the inherent radio-frequency nutation rate and the magnitude of the quadrupolar coupling are used as input to the optimization, but the pulses appear robust to reasonable variations in either parameter, producing significant enhancements compared to a single-pulse conversion, and also comparable or improved efficiency over other commonly used approaches. In all cases, the ease of implementation of our method is advantageous, particularly for cases with low sensitivity, where the improvement is most needed (e.g., low gyromagnetic ratio or high quadrupolar coupling). Our approach offers the potential to routinely improve the sensitivity of high-resolution NMR spectra of nuclei and systems that would, perhaps, otherwise be deemed "too challenging".
Quantum uncertainty relation based on the mean deviation
Sharma, Gautam; Mukhopadhyay, Chiranjib; Sazim, Sk; Pati, Arun Kumar
2018-01-01
Traditional forms of quantum uncertainty relations are invariably based on the standard deviation. This can be understood in the historical context of simultaneous development of quantum theory and mathematical statistics. Here, we present alternative forms of uncertainty relations, in both state dependent and state independent forms, based on the mean deviation. We illustrate the robustness of this formulation in situations where the standard deviation based uncertainty relation is inapplica...
High-Efficiency Colloidal Quantum Dot Photovoltaics via Robust Self-Assembled Monolayers
Kim, Gi-Hwan
2015-11-11
© 2015 American Chemical Society. The optoelectronic tunability offered by colloidal quantum dots (CQDs) is attractive for photovoltaic applications but demands proper band alignment at electrodes for efficient charge extraction at minimal cost to voltage. With this goal in mind, self-assembled monolayers (SAMs) can be used to modify interface energy levels locally. However, to be effective SAMs must be made robust to treatment using the various solvents and ligands required for to fabricate high quality CQD solids. We report robust self-assembled monolayers (R-SAMs) that enable us to increase the efficiency of CQD photovoltaics. Only by developing a process for secure anchoring of aromatic SAMs, aided by deposition of the SAMs in a water-free deposition environment, were we able to provide an interface modification that was robust against the ensuing chemical treatments needed in the fabrication of CQD solids. The energy alignment at the rectifying interface was tailored by tuning the R-SAM for optimal alignment relative to the CQD quantum-confined electron energy levels. This resulted in a CQD PV record power conversion efficiency (PCE) of 10.7% with enhanced reproducibility relative to controls.
Quantum reversibility is relative, or does a quantum measurement reset initial conditions?
Zurek, Wojciech H
2018-07-13
I compare the role of the information in classical and quantum dynamics by examining the relation between information flows in measurements and the ability of observers to reverse evolutions. I show that in the Newtonian dynamics reversibility is unaffected by the observer's retention of the information about the measurement outcome. By contrast-even though quantum dynamics is unitary, hence, reversible-reversing quantum evolution that led to a measurement becomes, in principle, impossible for an observer who keeps the record of its outcome. Thus, quantum irreversibility can result from the information gain rather than just its loss-rather than just an increase of the (von Neumann) entropy. Recording of the outcome of the measurement resets, in effect, initial conditions within the observer's (branch of) the Universe. Nevertheless, I also show that the observer's friend-an agent who knows what measurement was successfully carried out and can confirm that the observer knows the outcome but resists his curiosity and does not find out the result-can, in principle, undo the measurement. This relativity of quantum reversibility sheds new light on the origin of the arrow of time and elucidates the role of information in classical and quantum physics. Quantum discord appears as a natural measure of the extent to which dissemination of information about the outcome affects the ability to reverse the measurement.This article is part of a discussion meeting issue 'Foundations of quantum mechanics and their impact on contemporary society'. © 2018 The Author(s).
Resource-efficient linear-optical quantum router
Czech Academy of Sciences Publication Activity Database
Lemr, K.; Bartkiewicz, K.; Černoch, A.; Soubusta, Jan
2013-01-01
Roč. 87, č. 6 (2013), "062333-1"-"062333-7" ISSN 1050-2947 Institutional research plan: CEZ:AV0Z10100522 Keywords : quantum router * signal qubit * quantum communications Subject RIV: BH - Optics, Masers, Lasers Impact factor: 2.991, year: 2013
Efficient amplification of photonic qubits by optimal quantum cloning
Czech Academy of Sciences Publication Activity Database
Bartkiewicz, K.; Černoch, A.; Lemr, K.; Soubusta, Jan; Stobińska, M.
2014-01-01
Roč. 89, č. 6 (2014), "062322-1"-"062322-10" ISSN 1050-2947 Institutional support: RVO:68378271 Keywords : optimal quantum cloning * cryptography * qubit * phase-independent quantum amplifier Subject RIV: BH - Optics, Masers, Lasers Impact factor: 2.808, year: 2014
Fliller, Raymond P; Hartung, Walter
2005-01-01
A system was developed at INFN Milano for preparing cesium telluride photo-cathodes and transferring them into an RF gun under ultra-high vacuum. This system has been in use at the Fermilab NICADD Photo-Injector Laboratory (FNPL) since 1997. A similar load-lock system is used at the TeSLA Test Facility at DESY-Hamburg. Two 1.625-cell high duty cycle RF guns have been fabricated for the project. Studies of the photo-emission and field emission ("dark current") behavior of both RF guns have been carried out. Unexpected phenomena were observed in one of the RF guns. In situ changes in the cathode's quantum efficiency and dark current with time were seen during operation of the photo-injector. These changes were correlated with the magnetostatic field at the cathode.* In addition, multipacting is observed in the RF guns under certain conditions. Recent measurements indicate a correlation between multipacting, anomalous photo-emission behavior, and anomalous field emission behavior. Results will be presented.
Quantum rings and recursion relations in 2D quantum gravity
International Nuclear Information System (INIS)
Kachru, S.
1992-01-01
This paper discusses tachyon condensate perturbations to the action of the two-dimensional string theory corresponding to the c + 1 matrix model. These are shown to deform the action of the ground ring on the tachyon modules, confirming a conjecture of Witten. The ground ring structure is used to derive recursion relations which relate (N + 1) and N tachyon bulk scattering amplitudes. These recursion relations allow one to compute all bulk amplitudes
A Comparison of the recombination efficiency in green-emitting InGaN quantum dots and quantum wells
International Nuclear Information System (INIS)
Park, Il-Kyu; Kwon, Min-Ki; Park, Seong-Ju
2012-01-01
A comparative investigation of the recombination efficiency of green-emitting InGaN quantum dots (QDs) and quantum wells (QWs) is reported in this paper. Optical investigations using temperature dependent photoluminescence (PL) results showed that the internal quantum efficiency of InGaN QDs at room temperature was 8.7 times larger than that found for InGaN QWs because they provided dislocation-free recombination sites for the electrical charge carriers. The excitation power-dependent PL and electroluminescence results showed that the effect of the polarization induced electric field on the recombination process of electrical charge carriers in the QDs was negligibly small whereas it was dominant in the QWs. These results indicate that InGaN QDs are more beneficial than QWs in improving the luminescence efficiency of LEDs in the green spectral range.
Highly Efficient Perovskite-Quantum-Dot Light-Emitting Diodes by Surface Engineering
Pan, Jun; Quan, Li Na; Zhao, Yongbiao; Peng, Wei; Banavoth, Murali; Sarmah, Smritakshi P.; Yuan, Mingjian; Sinatra, Lutfan; AlYami, Noktan; Liu, Jiakai; Yassitepe, Emre; Yang, Zhenyu; Voznyy, Oleksandr; Comin, Riccardo; Hedhili, Mohamed N.; Mohammed, Omar F.; Lu, Zheng Hong; Kim, Dong Ha; Sargent, Edward H.; Bakr, Osman
2016-01-01
A two-step ligand-exchange strategy is developed, in which the long-carbon-chain ligands on all-inorganic perovskite (CsPbX3, X = Br, Cl) quantum dots (QDs) are replaced with halide-ion-pair ligands. Green and blue light-emitting diodes made from the halide-ion-paircapped quantum dots exhibit high external quantum efficiencies compared with the untreated QDs.
Highly Efficient Perovskite-Quantum-Dot Light-Emitting Diodes by Surface Engineering
Pan, Jun
2016-08-16
A two-step ligand-exchange strategy is developed, in which the long-carbon-chain ligands on all-inorganic perovskite (CsPbX3, X = Br, Cl) quantum dots (QDs) are replaced with halide-ion-pair ligands. Green and blue light-emitting diodes made from the halide-ion-paircapped quantum dots exhibit high external quantum efficiencies compared with the untreated QDs.
Generalization of uncertainty relation for quantum and stochastic systems
Koide, T.; Kodama, T.
2018-06-01
The generalized uncertainty relation applicable to quantum and stochastic systems is derived within the stochastic variational method. This relation not only reproduces the well-known inequality in quantum mechanics but also is applicable to the Gross-Pitaevskii equation and the Navier-Stokes-Fourier equation, showing that the finite minimum uncertainty between the position and the momentum is not an inherent property of quantum mechanics but a common feature of stochastic systems. We further discuss the possible implication of the present study in discussing the application of the hydrodynamic picture to microscopic systems, like relativistic heavy-ion collisions.
Tightness Entropic Uncertainty Relation in Quantum Markovian-Davies Environment
Zhang, Jun; Liu, Liang; Han, Yan
2018-05-01
In this paper, we investigate the tightness of entropic uncertainty relation in the absence (presence) of the quantum memory which the memory particle being weakly coupled to a decohering Davies-type Markovian environment. The results show that the tightness of the quantum uncertainty relation can be controlled by the energy relaxation time F, the dephasing time G and the rescaled temperature p, the perfect tightness can be arrived by dephasing and energy relaxation satisfying F = 2G and p = 1/2. In addition, the tightness of the memory-assisted entropic uncertainty relation and the entropic uncertainty relation can be influenced mainly by the purity. While in memory-assisted model, the purity and quantum correlation can also influence the tightness actively while the quantum entanglement can influence the tightness slightly.
From special relativity to quantum mechanics through interval
International Nuclear Information System (INIS)
Malcor, R.
1985-01-01
Quantum mechanics is an optics with one more spatial dimension, the angle of phase. Wave-particle duality is nothing else than geometric tangent-point duality. The 'interval' of special relativity is proportional to the phase
Some relations of parameters in quantum field theory
International Nuclear Information System (INIS)
Ishikawa, K.
1986-01-01
Two schemes of parameter relations, linear relation and non-linear relation are discussed. The linear relation of coupling constants is derived directly from an underlying symmetry of the classical theory and is preserved usually in the quantum theory. The non-linear relation is not derived by a same manner but is derived by more involved way which is intrinsically connected with quantum theory. An underlying symmetry which leads the linear relation is shown to be essential in the non-linear relation too. Some extension is also discussed
Modeling of detective quantum efficiency considering scatter-reduction devices
Energy Technology Data Exchange (ETDEWEB)
Park, Ji Woong; Kim, Dong Woon; Kim, Ho Kyung [Pusan National University, Busan (Korea, Republic of)
2016-05-15
The reduction of signal-to-noise ratio (SNR) cannot be restored and thus has become a severe issue in digital mammography.1 Therefore, antiscatter grids are typically used in mammography. Scatter-cleanup performance of various scatter-reduction devices, such as air gaps,2 linear (1D) or cellular (2D) grids,3, 4 and slot-scanning devices,5 has been extensively investigated by many research groups. In the present time, a digital mammography system with the slotscanning geometry is also commercially available.6 In this study, we theoretically investigate the effect of scattered photons on the detective quantum efficiency (DQE) performance of digital mammography detectors by using the cascaded-systems analysis (CSA) approach. We show a simple DQE formalism describing digital mammography detector systems equipped with scatter reduction devices by regarding the scattered photons as additive noise sources. The LFD increased with increasing PMMA thickness, and the amounts of LFD indicated the corresponding SF. The estimated SFs were 0.13, 0.21, and 0.29 for PMMA thicknesses of 10, 20, and 30 mm, respectively. While the solid line describing the measured MTF for PMMA with 0 mm was the result of least-squares of regression fit using Eq. (14), the other lines were simply resulted from the multiplication of the fit result (for PMMA with 0 mm) with the (1-SF) estimated from the LFDs in the measured MTFs. Spectral noise-power densities over the entire frequency range were not much changed with increasing scatter. On the other hand, the calculation results showed that the spectral noise-power densities increased with increasing scatter. This discrepancy may be explained by that the model developed in this study does not account for the changes in x-ray interaction parameters for varying spectral shapes due to beam hardening with increasing PMMA thicknesses.
Efficient Computation of Transition State Resonances and Reaction Rates from a Quantum Normal Form
Schubert, Roman; Waalkens, Holger; Wiggins, Stephen
2006-01-01
A quantum version of a recent formulation of transition state theory in phase space is presented. The theory developed provides an algorithm to compute quantum reaction rates and the associated Gamov-Siegert resonances with very high accuracy. The algorithm is especially efficient for
Enhancement of Radiative Efficiency with Staggered InGaN Quantum Well Light Emitting Diodes
Energy Technology Data Exchange (ETDEWEB)
Tansu, Nelson; Dierolf, Volkmar; Huang, Gensheng; Penn, Samson; Zhao, Hongping; Liu, Guangyu; Li, Xiaohang; Poplawsky, Jonathan
2011-07-14
The technology on the large overlap InGaN QWs developed in this program is currently implemented in commercial technology in enhancing the internal quantum efficiency in major LED industry in US and Asia. The scientific finding from this work supported by the DOE enabled the implementation of this step-like staggered quantum well in the commercial LEDs.
International Nuclear Information System (INIS)
D'Ariano, Giacomo Mauro
2010-01-01
I will argue that the proposal of establishing operational foundations of Quantum Theory should have top-priority, and that the Lucien Hardy's program on Quantum Gravity should be paralleled by an analogous program on Quantum Field Theory (QFT), which needs to be reformulated, notwithstanding its experimental success. In this paper, after reviewing recently suggested operational 'principles of the quantumness', I address the problem on whether Quantum Theory and Special Relativity are unrelated theories, or instead, if the one implies the other. I show how Special Relativity can be indeed derived from causality of Quantum Theory, within the computational paradigm 'the universe is a huge quantum computer', reformulating QFT as a Quantum-Computational Field Theory (QCFT). In QCFT Special Relativity emerges from the fabric of the computational network, which also naturally embeds gauge invariance. In this scheme even the quantization rule and the Planck constant can in principle be derived as emergent from the underlying causal tapestry of space-time. In this way Quantum Theory remains the only theory operating the huge computer of the universe.Is the computational paradigm only a speculative tautology (theory as simulation of reality), or does it have a scientific value? The answer will come from Occam's razor, depending on the mathematical simplicity of QCFT. Here I will just start scratching the surface of QCFT, analyzing simple field theories, including Dirac's. The number of problems and unmotivated recipes that plague QFT strongly motivates us to undertake the QCFT project, since QCFT makes all such problems manifest, and forces a re-foundation of QFT.
High Efficiency Quantum Well Waveguide Solar Cells, Phase I
National Aeronautics and Space Administration — The long-term objective of this program is to develop flexible, lightweight, single-junction solar cells using quantum structured designs that can achieve ultra-high...
High efficiency detection technology on quantum action using radiation excitation
International Nuclear Information System (INIS)
Okubo, Masataka; Ukibe, Masahiro; Sakamoto, Isao; Hayashi, Nobuyuki; Shoji, Akira; Kobayashi, Naoto
2000-01-01
In 1998 fiscal year, as a local quasi particle loss process, it was elucidated that there was a quasi particle loss induced with magnetic flux quantum trapped by a detector on its cooling. Hitherto, it was reported that action of a tunnel junction detector was different by its magnetic history. That is, the detector had unstability such as variation of its action on its cooling. Therefore, the quasi particle loss induced by magnetic flux quantum forming cause of the unstability was quantitatively evaluated. As a result, it was elucidated that output of the detector was reduced half only by trapping the magnetic flux quantum with numbers corresponding to weak magnetic field like geomagnetism. And, this phenomenon was also described by using a model concept with quasi particle trapping due to the magnetic flux quantum. (G.K.)
Efficient Quantum Information Transfer Through a Uniform Channel
Directory of Open Access Journals (Sweden)
Paola Verrucchi
2011-06-01
Full Text Available Effective quantum-state and entanglement transfer can be obtained by inducing a coherent dynamics in quantum wires with homogeneous intrawire interactions. This goal is accomplished by optimally tuning the coupling between the wire endpoints and the two qubits there attached. A general procedure to determine such value is devised, and scaling laws between the optimal coupling and the length of the wire are found. The procedure is implemented in the case of a wire consisting of a spin-1/2 XY chain: results for the time dependence of the quantities which characterize quantum-state and entanglement transfer are found of extremely good quality also for very long wires. The present approach does not require engineered intrawire interactions nor a specific initial pulse shaping, and can be applied to a vast class of quantum channels.
Entangling efficiency of linear-optical quantum gates
Czech Academy of Sciences Publication Activity Database
Lemr, Karel; Černoch, Antonín; Soubusta, Jan; Dušek, M.
2012-01-01
Roč. 86, č. 3 (2012), "032321-1"-"032321-5" ISSN 1050-2947 R&D Projects: GA ČR GAP205/12/0382 Institutional research plan: CEZ:AV0Z10100522 Keywords : linear-optical quantum gates * quantum physics Subject RIV: BH - Optics, Masers, Lasers Impact factor: 3.042, year: 2012 http://pra.aps.org/pdf/PRA/v86/i3/e032321
High Quantum Efficiency 1024x1024 Longwave Infrared SLS FPA and Camera, Phase II
National Aeronautics and Space Administration — We propose a high quantum efficiency (QE) 1024x1024 longwave infrared focal plane array (LWIR FPA) and CAMERA with ~ 12 micron cutoff wavelength made from...
High Efficiency Quantum Dot III-V Multijunction Solar Cell for Space Power, Phase II
National Aeronautics and Space Administration — We are proposing to utilize quantum dots to develop a super high-efficiency multijunction III-V solar cell for space. In metamorphic triple junction space solar...
Efficient construction of two-dimensional cluster states with probabilistic quantum gates
International Nuclear Information System (INIS)
Chen Qing; Cheng Jianhua; Wang Kelin; Du Jiangfeng
2006-01-01
We propose an efficient scheme for constructing arbitrary two-dimensional (2D) cluster states using probabilistic entangling quantum gates. In our scheme, the 2D cluster state is constructed with starlike basic units generated from 1D cluster chains. By applying parallel operations, the process of generating 2D (or higher-dimensional) cluster states is significantly accelerated, which provides an efficient way to implement realistic one-way quantum computers
Determination of turbine relative efficiency in SHPP
Directory of Open Access Journals (Sweden)
Džepčeski Dane
2017-01-01
Full Text Available To assess the fulfillment of contract conditions for the equipment delivery, determining the properties and capabilities of a generating unit or some part of it, the measurements carried out under real operating conditions were necessary. In this paper, the results of the test that was carried out in a small hydropower plant (SHPP, aimed at determining the relative efficiency of the hydraulic turbine and its comparison with the guaranteed values, are presented. The dependence of the turbine efficiency on the turbine discharge was determined based on the test results, using the index method. The test was performed at one net head.
Efficient quantum computation in a network with probabilistic gates and logical encoding
DEFF Research Database (Denmark)
Borregaard, J.; Sørensen, A. S.; Cirac, J. I.
2017-01-01
An approach to efficient quantum computation with probabilistic gates is proposed and analyzed in both a local and nonlocal setting. It combines heralded gates previously studied for atom or atomlike qubits with logical encoding from linear optical quantum computation in order to perform high......-fidelity quantum gates across a quantum network. The error-detecting properties of the heralded operations ensure high fidelity while the encoding makes it possible to correct for failed attempts such that deterministic and high-quality gates can be achieved. Importantly, this is robust to photon loss, which...... is typically the main obstacle to photonic-based quantum information processing. Overall this approach opens a path toward quantum networks with atomic nodes and photonic links....
International Nuclear Information System (INIS)
Yu Watanabe; Masahito Ueda
2012-01-01
Full text: When we try to obtain information about a quantum system, we need to perform measurement on the system. The measurement process causes unavoidable state change. Heisenberg discussed a thought experiment of the position measurement of a particle by using a gamma-ray microscope, and found a trade-off relation between the error of the measured position and the disturbance in the momentum caused by the measurement process. The trade-off relation epitomizes the complementarity in quantum measurements: we cannot perform a measurement of an observable without causing disturbance in its canonically conjugate observable. However, at the time Heisenberg found the complementarity, quantum measurement theory was not established yet, and Kennard and Robertson's inequality erroneously interpreted as a mathematical formulation of the complementarity. Kennard and Robertson's inequality actually implies the indeterminacy of the quantum state: non-commuting observables cannot have definite values simultaneously. However, Kennard and Robertson's inequality reflects the inherent nature of a quantum state alone, and does not concern any trade-off relation between the error and disturbance in the measurement process. In this talk, we report a resolution to the complementarity in quantum measurements. First, we find that it is necessary to involve the estimation process from the outcome of the measurement for quantifying the error and disturbance in the quantum measurement. We clarify the implicitly involved estimation process in Heisenberg's gamma-ray microscope and other measurement schemes, and formulate the error and disturbance for an arbitrary quantum measurement by using quantum estimation theory. The error and disturbance are defined in terms of the Fisher information, which gives the upper bound of the accuracy of the estimation. Second, we obtain uncertainty relations between the measurement errors of two observables [1], and between the error and disturbance in the
International Nuclear Information System (INIS)
Wen-Jie, Liu; Han-Wu, Chen; Zhi-Qiang, Li; Zhi-Hao, Liu; Wen-Bo, Hu; Ting-Huai, Ma
2009-01-01
A novel efficient deterministic secure quantum communication scheme based on four-qubit cluster states and single-photon identity authentication is proposed. In this scheme, the two authenticated users can transmit two bits of classical information per cluster state, and its efficiency of the quantum communication is 1/3, which is approximately 1.67 times that of the previous protocol presented by Wang et al [Chin. Phys. Lett. 23 (2006) 2658]. Security analysis shows the present scheme is secure against intercept-resend attack and the impersonator's attack. Furthermore, it is more economic with present-day techniques and easily processed by a one-way quantum computer. (general)
Quantum geometry of resurgent perturbative/nonperturbative relations
Energy Technology Data Exchange (ETDEWEB)
Basar, Gökçe [Maryland Center for Fundamental Physics, University of Maryland, College Park, MD 20742 (United States); Dunne, Gerald V. [Department of Physics, University of Connecticut, Storrs, CT 06269-3046 (United States); Ünsal, Mithat [Department of Physics, North Carolina State University, Raleigh, NC 27695-8202 (United States)
2017-05-16
For a wide variety of quantum potentials, including the textbook ‘instanton’ examples of the periodic cosine and symmetric double-well potentials, the perturbative data coming from fluctuations about the vacuum saddle encodes all non-perturbative data in all higher non-perturbative sectors. Here we unify these examples in geometric terms, arguing that the all-orders quantum action determines the all-orders quantum dual action for quantum spectral problems associated with a classical genus one elliptic curve. Furthermore, for a special class of genus one potentials this relation is particularly simple: this class includes the cubic oscillator, symmetric double-well, symmetric degenerate triple-well, and periodic cosine potential. These are related to the Chebyshev potentials, which are in turn related to certain N=2 supersymmetric quantum field theories, to mirror maps for hypersurfaces in projective spaces, and also to topological c=3 Landau-Ginzburg models and ‘special geometry’. These systems inherit a natural modular structure corresponding to Ramanujan’s theory of elliptic functions in alternative bases, which is especially important for the quantization. Insights from supersymmetric quantum field theory suggest similar structures for more complicated potentials, corresponding to higher genus. Our approach is very elementary, using basic classical geometry combined with all-orders WKB.
Some relations between quantum Turing machines and Turing machines
Sicard, Andrés; Vélez, Mario
1999-01-01
For quantum Turing machines we present three elements: Its components, its time evolution operator and its local transition function. The components are related with the components of deterministic Turing machines, the time evolution operator is related with the evolution of reversible Turing machines and the local transition function is related with the transition function of probabilistic and reversible Turing machines.
Some applications of uncertainty relations in quantum information
Majumdar, A. S.; Pramanik, T.
2016-08-01
We discuss some applications of various versions of uncertainty relations for both discrete and continuous variables in the context of quantum information theory. The Heisenberg uncertainty relation enables demonstration of the Einstein, Podolsky and Rosen (EPR) paradox. Entropic uncertainty relations (EURs) are used to reveal quantum steering for non-Gaussian continuous variable states. EURs for discrete variables are studied in the context of quantum memory where fine-graining yields the optimum lower bound of uncertainty. The fine-grained uncertainty relation is used to obtain connections between uncertainty and the nonlocality of retrieval games for bipartite and tripartite systems. The Robertson-Schrödinger (RS) uncertainty relation is applied for distinguishing pure and mixed states of discrete variables.
Quantum Computing and the Limits of the Efficiently Computable
CERN. Geneva
2015-01-01
I'll discuss how computational complexity---the study of what can and can't be feasibly computed---has been interacting with physics in interesting and unexpected ways. I'll first give a crash course about computer science's P vs. NP problem, as well as about the capabilities and limits of quantum computers. I'll then touch on speculative models of computation that would go even beyond quantum computers, using (for example) hypothetical nonlinearities in the Schrodinger equation. Finally, I'll discuss BosonSampling ---a proposal for a simple form of quantum computing, which nevertheless seems intractable to simulate using a classical computer---as well as the role of computational complexity in the black hole information puzzle.
Terahertz Quantum Cascade Laser With Efficient Coupling and Beam Profile
Chattopadhyay, Goutam; Kawamura, Jonathan H.; Lin, Robert H.; Williams, Benjamin
2012-01-01
Quantum cascade lasers (QCLs) are unipolar semiconductor lasers, where the wavelength of emitted radiation is determined by the engineering of quantum states within the conduction band in coupled multiple-quantum-well heterostructures to have the desired energy separation. The recent development of terahertz QCLs has provided a new generation of solid-state sources for radiation in the terahertz frequency range. Terahertz QCLs have been demonstrated from 0.84 to 5.0 THz both in pulsed mode and continuous wave mode (CW mode). The approach employs a resonant-phonon depopulation concept. The metal-metal (MM) waveguide fabrication is performed using Cu-Cu thermo-compression bonding to bond the GaAs/AlGaAs epitaxial layer to a GaAs receptor wafer.
Combining neural networks and signed particles to simulate quantum systems more efficiently
Sellier, Jean Michel
2018-04-01
Recently a new formulation of quantum mechanics has been suggested which describes systems by means of ensembles of classical particles provided with a sign. This novel approach mainly consists of two steps: the computation of the Wigner kernel, a multi-dimensional function describing the effects of the potential over the system, and the field-less evolution of the particles which eventually create new signed particles in the process. Although this method has proved to be extremely advantageous in terms of computational resources - as a matter of fact it is able to simulate in a time-dependent fashion many-body systems on relatively small machines - the Wigner kernel can represent the bottleneck of simulations of certain systems. Moreover, storing the kernel can be another issue as the amount of memory needed is cursed by the dimensionality of the system. In this work, we introduce a new technique which drastically reduces the computation time and memory requirement to simulate time-dependent quantum systems which is based on the use of an appropriately tailored neural network combined with the signed particle formalism. In particular, the suggested neural network is able to compute efficiently and reliably the Wigner kernel without any training as its entire set of weights and biases is specified by analytical formulas. As a consequence, the amount of memory for quantum simulations radically drops since the kernel does not need to be stored anymore as it is now computed by the neural network itself, only on the cells of the (discretized) phase-space which are occupied by particles. As its is clearly shown in the final part of this paper, not only this novel approach drastically reduces the computational time, it also remains accurate. The author believes this work opens the way towards effective design of quantum devices, with incredible practical implications.
International Nuclear Information System (INIS)
Sewell, G.L.
1986-01-01
The author shows how the basic axioms of quantum field theory, general relativity and statistical thermodynamics lead, in a model-independent way, to a generalized Hawking-Unruh effect, whereby the gravitational fields carried by a class of space-time manifolds with event horizons thermalize ambient quantum fields. The author is concerned with a quantum field on a space-time x containing a submanifold X' bounded by event horizons. The objective is to show that, for a wide class of space-times, the global vacuum state of the field reduces, in X', to a thermal state, whose temperature depends on the geometry. The statistical thermodynaical, geometrical, and quantum field theoretical essential ingredients for the reduction of the vacuum state are discussed
Quantum mechanics, gravity and modified quantization relations.
Calmet, Xavier
2015-08-06
In this paper, we investigate a possible energy scale dependence of the quantization rules and, in particular, from a phenomenological point of view, an energy scale dependence of an effective [Formula: see text] (reduced Planck's constant). We set a bound on the deviation of the value of [Formula: see text] at the muon scale from its usual value using measurements of the anomalous magnetic moment of the muon. Assuming that inflation has taken place, we can conclude that nature is described by a quantum theory at least up to an energy scale of about 10(16) GeV. © 2015 The Author(s) Published by the Royal Society. All rights reserved.
Quantum vacuum energy in general relativity
Energy Technology Data Exchange (ETDEWEB)
Henke, Christian [University of Technology at Clausthal, Department of Mathematics, Clausthal-Zellerfeld (Germany)
2018-02-15
The paper deals with the scale discrepancy between the observed vacuum energy in cosmology and the theoretical quantum vacuum energy (cosmological constant problem). Here, we demonstrate that Einstein's equation and an analogy to particle physics leads to the first physical justification of the so-called fine-tuning problem. This fine-tuning could be automatically satisfied with the variable cosmological term Λ(a) = Λ{sub 0} + Λ{sub 1}a{sup -(4-ε)}, 0 < ε << 1, where a is the scale factor. As a side effect of our solution of the cosmological constant problem, the dynamical part of the cosmological term generates an attractive force and solves the missing mass problem of dark matter. (orig.)
Quantum Thermodynamics at Strong Coupling: Operator Thermodynamic Functions and Relations
Directory of Open Access Journals (Sweden)
Jen-Tsung Hsiang
2018-05-01
Full Text Available Identifying or constructing a fine-grained microscopic theory that will emerge under specific conditions to a known macroscopic theory is always a formidable challenge. Thermodynamics is perhaps one of the most powerful theories and best understood examples of emergence in physical sciences, which can be used for understanding the characteristics and mechanisms of emergent processes, both in terms of emergent structures and the emergent laws governing the effective or collective variables. Viewing quantum mechanics as an emergent theory requires a better understanding of all this. In this work we aim at a very modest goal, not quantum mechanics as thermodynamics, not yet, but the thermodynamics of quantum systems, or quantum thermodynamics. We will show why even with this minimal demand, there are many new issues which need be addressed and new rules formulated. The thermodynamics of small quantum many-body systems strongly coupled to a heat bath at low temperatures with non-Markovian behavior contains elements, such as quantum coherence, correlations, entanglement and fluctuations, that are not well recognized in traditional thermodynamics, built on large systems vanishingly weakly coupled to a non-dynamical reservoir. For quantum thermodynamics at strong coupling, one needs to reexamine the meaning of the thermodynamic functions, the viability of the thermodynamic relations and the validity of the thermodynamic laws anew. After a brief motivation, this paper starts with a short overview of the quantum formulation based on Gelin & Thoss and Seifert. We then provide a quantum formulation of Jarzynski’s two representations. We show how to construct the operator thermodynamic potentials, the expectation values of which provide the familiar thermodynamic variables. Constructing the operator thermodynamic functions and verifying or modifying their relations is a necessary first step in the establishment of a viable thermodynamics theory for
Influence of dislocation density on internal quantum efficiency of GaN-based semiconductors
Directory of Open Access Journals (Sweden)
Jiadong Yu
2017-03-01
Full Text Available By considering the effects of stress fields coming from lattice distortion as well as charge fields coming from line charges at edge dislocation cores on radiative recombination of exciton, a model of carriers’ radiative and non-radiative recombination has been established in GaN-based semiconductors with certain dislocation density. Using vector average of the stress fields and the charge fields, the relationship between dislocation density and the internal quantum efficiency (IQE is deduced. Combined with related experimental results, this relationship is fitted well to the trend of IQEs of bulk GaN changing with screw and edge dislocation density, meanwhile its simplified form is fitted well to the IQEs of AlGaN multiple quantum well LEDs with varied threading dislocation densities but the same light emission wavelength. It is believed that this model, suitable for different epitaxy platforms such as MOCVD and MBE, can be used to predict to what extent the luminous efficiency of GaN-based semiconductors can still maintain when the dislocation density increases, so as to provide a reasonable rule of thumb for optimizing the epitaxial growth of GaN-based devices.
Non-linear effects and thermoelectric efficiency of quantum dot-based single-electron transistors.
Talbo, Vincent; Saint-Martin, Jérôme; Retailleau, Sylvie; Dollfus, Philippe
2017-11-01
By means of advanced numerical simulation, the thermoelectric properties of a Si-quantum dot-based single-electron transistor operating in sequential tunneling regime are investigated in terms of figure of merit, efficiency and power. By taking into account the phonon-induced collisional broadening of energy levels in the quantum dot, both heat and electrical currents are computed in a voltage range beyond the linear response. Using our homemade code consisting in a 3D Poisson-Schrödinger solver and the resolution of the Master equation, the Seebeck coefficient at low bias voltage appears to be material independent and nearly independent on the level broadening, which makes this device promising for metrology applications as a nanoscale standard of Seebeck coefficient. Besides, at higher voltage bias, the non-linear characteristics of the heat current are shown to be related to the multi-level effects. Finally, when considering only the electronic contribution to the thermal conductance, the single-electron transistor operating in generator regime is shown to exhibit very good efficiency at maximum power.
Luminescence quantum efficiency determination in LiYF4:Nd3+ using photoacoustic spectroscopy
International Nuclear Information System (INIS)
Franca, E.J.
1989-01-01
Optical properties of LiYF 4 :Nd 3+ were studied using absorption, emission, excitation and photo acoustic spectroscopies. The Nd 3+ transitions were identified and the Stark sublevels were determined for the 4 I 9/2 , 4 I 11/2 and 4 F 3/2 levels. It is also presented and analysed three methods for the luminescence quantum efficiency determination, based on parameters from the spectra mentioned above. These methods were applied to four groups centered on 517, 577, 743 and 792nm. The first method provided values too high due to its assumption that the material has only one luminescent channel. The values obtained from the second one are still somewhat high but closer to the expected ones. The superestimation can be atributed to the imprecision in the existing branching ratios values, needed in this method. The third one, developed from the other two, provided values closer to the expected ones, but also affected by experimental conditions limitations, mainly related to the spectral resolution of the photoacustic spectra. The obtained results show that this method, once improved and associated to better experimental conditions, will lead to more accurate luminescence quantum efficiency values. (author) [pt
Decoherence effect on quantum-memory-assisted entropic uncertainty relations
Ming, Fei; Wang, Dong; Huang, Ai-Jun; Sun, Wen-Yang; Ye, Liu
2018-01-01
Uncertainty principle significantly provides a bound to predict precision of measurement with regard to any two incompatible observables, and thereby plays a nontrivial role in quantum precision measurement. In this work, we observe the dynamical features of the quantum-memory-assisted entropic uncertainty relations (EUR) for a pair of incompatible measurements in an open system characterized by local generalized amplitude damping (GAD) noises. Herein, we derive the dynamical evolution of the entropic uncertainty with respect to the measurement affecting by the canonical GAD noises when particle A is initially entangled with quantum memory B. Specifically, we examine the dynamics of EUR in the frame of three realistic scenarios: one case is that particle A is affected by environmental noise (GAD) while particle B as quantum memory is free from any noises, another case is that particle B is affected by the external noise while particle A is not, and the last case is that both of the particles suffer from the noises. By analytical methods, it turns out that the uncertainty is not full dependent of quantum correlation evolution of the composite system consisting of A and B, but the minimal conditional entropy of the measured subsystem. Furthermore, we present a possible physical interpretation for the behavior of the uncertainty evolution by means of the mixedness of the observed system; we argue that the uncertainty might be dramatically correlated with the systematic mixedness. Furthermore, we put forward a simple and effective strategy to reduce the measuring uncertainty of interest upon quantum partially collapsed measurement. Therefore, our explorations might offer an insight into the dynamics of the entropic uncertainty relation in a realistic system, and be of importance to quantum precision measurement during quantum information processing.
Categories of relations as models of quantum theory
Directory of Open Access Journals (Sweden)
Chris Heunen
2015-11-01
Full Text Available Categories of relations over a regular category form a family of models of quantum theory. Using regular logic, many properties of relations over sets lift to these models, including the correspondence between Frobenius structures and internal groupoids. Over compact Hausdorff spaces, this lifting gives continuous symmetric encryption. Over a regular Mal'cev category, this correspondence gives a characterization of categories of completely positive maps, enabling the formulation of quantum features. These models are closer to Hilbert spaces than relations over sets in several respects: Heisenberg uncertainty, impossibility of broadcasting, and behavedness of rank one morphisms.
Efficient quantum state transfer in an engineered chain of quantum bits
Sandberg, Martin; Knill, Emanuel; Kapit, Eliot; Vissers, Michael R.; Pappas, David P.
2016-03-01
We present a method of performing quantum state transfer in a chain of superconducting quantum bits. Our protocol is based on engineering the energy levels of the qubits in the chain and tuning them all simultaneously with an external flux bias. The system is designed to allow sequential adiabatic state transfers, resulting in on-demand quantum state transfer from one end of the chain to the other. Numerical simulations of the master equation using realistic parameters for capacitive nearest-neighbor coupling, energy relaxation, and dephasing show that fast, high-fidelity state transfer should be feasible using this method.
Indefinite-metric quantum field theory of general relativity, 6
International Nuclear Information System (INIS)
Nakanishi, Noboru
1979-01-01
The canonical commutation relations are analyzed in detail in the indefinite-metric quantum field theory of gravity based on the vierbein formalism. It is explicitly verified that the BRS charge, the local-Lorentz-BRS charge and the Poincare generators satisfy the expected commutation relations. (author)
Indefinite-metric quantum field theory of general relativity, 2
International Nuclear Information System (INIS)
Nakanishi, Noboru
1978-01-01
The canonical commutation relations are analyzed in detail in the manifestly covariant quantum field theory of general relativity proposed previously. It is explicitly proved that the BRS charge is indeed the generator of the BRS transformation both in the Landau gauge and in the non-Landau one. The equivalence between the field equations and the Heisenberg equations is confirmed. (author)
Functional methods underlying classical mechanics, relativity and quantum theory
International Nuclear Information System (INIS)
Kryukov, A
2013-01-01
The paper investigates the physical content of a recently proposed mathematical framework that unifies the standard formalisms of classical mechanics, relativity and quantum theory. In the framework states of a classical particle are identified with Dirac delta functions. The classical space is ''made'' of these functions and becomes a submanifold in a Hilbert space of states of the particle. The resulting embedding of the classical space into the space of states is highly non-trivial and accounts for numerous deep relations between classical and quantum physics and relativity. One of the most striking results is the proof that the normal probability distribution of position of a macroscopic particle (equivalently, position of the corresponding delta state within the classical space submanifold) yields the Born rule for transitions between arbitrary quantum states.
Origin of low quantum efficiency of photoluminescence of InP/ZnS nanocrystals
Energy Technology Data Exchange (ETDEWEB)
Shirazi, Roza, E-mail: rozas@fotonik.dtu.dk [Department of Photonics Engineering, Technical University of Denmark, Oersted Plads 343, 2800 Kgs Lyngby (Denmark); Kovacs, Andras [Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Peter Grunberg Institute, Forschungszentrum Julich, 52425 Julich (Germany); Dan Corell, Dennis [Department of Photonics Engineering, Technical University of Denmark, Riso, Frederiksborgvej 399, 4000 Roskilde (Denmark); Gritti, Claudia [Department of Photonics Engineering, Technical University of Denmark, Oersted Plads 343, 2800 Kgs Lyngby (Denmark); Thorseth, Anders; Dam-Hansen, Carsten; Michael Petersen, Paul [Department of Photonics Engineering, Technical University of Denmark, Riso, Frederiksborgvej 399, 4000 Roskilde (Denmark); Kardynal, Beata [Department of Photonics Engineering, Technical University of Denmark, Oersted Plads 343, 2800 Kgs Lyngby (Denmark); PGI-9, Forschungszentrum Julich, JARA FIT, 52425 Julich (Germany)
2014-01-15
In this paper, we study the origin of a strong wavelength dependence of the quantum efficiency of InP/ZnS nanocrystals. We find that while the average size of the nanocrystals increased by 50%, resulting in longer emission wavelength, the quantum efficiency drops more than one order of magnitude compared to the quantum efficiency of the small nanocrystals. By correlating this result with the time-resolved photoluminescence we find that the reduced photoluminescence efficiency is caused by a fast growing fraction of non-emissive nanocrystals while the quality of the nanocrystals that emit light is similar for all samples. Transmission electron microscopy reveals the polycrystalline nature of many of the large nanocrystals, pointing to the grain boundaries as one possible site for the photoluminescence quenching defects. -- Highlights: • We investigate drop of quantum efficiency of InP/ZnS nanocrystals emitting at longer wavelengths. • We correlate quantum efficiency measurements with time-resolved carrier dynamics. • We find that only a small fraction of larger nanocrystals is optically active.
Origin of low quantum efficiency of photoluminescence of InP/ZnS nanocrystals
International Nuclear Information System (INIS)
Shirazi, Roza; Kovacs, Andras; Dan Corell, Dennis; Gritti, Claudia; Thorseth, Anders; Dam-Hansen, Carsten; Michael Petersen, Paul; Kardynal, Beata
2014-01-01
In this paper, we study the origin of a strong wavelength dependence of the quantum efficiency of InP/ZnS nanocrystals. We find that while the average size of the nanocrystals increased by 50%, resulting in longer emission wavelength, the quantum efficiency drops more than one order of magnitude compared to the quantum efficiency of the small nanocrystals. By correlating this result with the time-resolved photoluminescence we find that the reduced photoluminescence efficiency is caused by a fast growing fraction of non-emissive nanocrystals while the quality of the nanocrystals that emit light is similar for all samples. Transmission electron microscopy reveals the polycrystalline nature of many of the large nanocrystals, pointing to the grain boundaries as one possible site for the photoluminescence quenching defects. -- Highlights: • We investigate drop of quantum efficiency of InP/ZnS nanocrystals emitting at longer wavelengths. • We correlate quantum efficiency measurements with time-resolved carrier dynamics. • We find that only a small fraction of larger nanocrystals is optically active
Geometry, commutation relations and the quantum fictitious force
DEFF Research Database (Denmark)
Botero, J.; Cirone, M.A.; Dahl, Jens Peder
2003-01-01
We express the commutation relation between the operators of the momentum and the radial unit vectors in D dimensions in differential and integral form. We connect this commutator with the quantum fictitious potential emerging in the radial Schrodinger equation of an s-wave.......We express the commutation relation between the operators of the momentum and the radial unit vectors in D dimensions in differential and integral form. We connect this commutator with the quantum fictitious potential emerging in the radial Schrodinger equation of an s-wave....
Preparation of reflective CsI photocathodes with reproducible high quantum efficiency
Maier-Komor, P.; Bauer, B. B.; Friese, J.; Gernhäuser, R.; Kienle, P.; Körner, H. J.; Montermann, G.; Zeitelhack, K.
1995-02-01
CsI as a solid UV-photocathode material has many promising applications in fast gaseous photon detectors. They are proposed in large area Ring Imaging CHerenkov (RICH) devices in forthcoming experiments at various high-energy particle accelerators. A high photon-to-electron conversion efficiency is a basic requirement for the successful operation of these devices. High reproducible quantum efficiencies could be achieved with CsI layers prepared by electron beam evaporation from a water-cooled copper crucible. CsI films were deposited in the thickness range of 30 to 500 μg/cm 2. Absorption coefficients and quantum efficiencies were measured in the wavelength region of 150 nm to 250 nm. The influence of various evaporation parameters on the quantum efficiency were investigated.
Preparation of reflective CsI photocathodes with reproducible high quantum efficiency
Energy Technology Data Exchange (ETDEWEB)
Maier-Komor, P. [Technische Univ. Muenchen, Garching (Germany). Physik-Department; Bauer, B.B. [Technische Univ. Muenchen, Garching (Germany). Physik-Department; Friese, J. [Technische Univ. Muenchen, Garching (Germany). Physik-Department; Gernhaeuser, R. [Technische Univ. Muenchen, Garching (Germany). Physik-Department; Kienle, P. [Technische Univ. Muenchen, Garching (Germany). Physik-Department; Koerner, H.J. [Technische Univ. Muenchen, Garching (Germany). Physik-Department; Montermann, G. [Technische Univ. Muenchen, Garching (Germany). Physik-Department; Zeitelhack, K. [Technische Univ. Muenchen, Garching (Germany). Physik-Department
1995-08-01
CsI as a solid UV-photocathode material has many promising applications in fast gaseous photon detectors. They are proposed in large area Ring Imaging CHerenkov (RICH) devices in forthcoming experiments at various high-energy particle accelerators. A high photon-to-electron conversion efficiency is a basic requirement for the successful operation of these devices. High reproducible quantum efficiencies could be achieved with CsI layers prepared by electron beam evaporation from a water-cooled copper crucible. CsI films were deposited in the thickness range of 30 to 500 {mu}g/cm{sup 2}. Absorption coefficients and quantum efficiencies were measured in the wavelength region of 150 nm to 250 nm. The influence of various evaporation parameters on the quantum efficiency were investigated. (orig.).
Efficient spray-coated colloidal quantum dot solar cells
Kramer, Illan J.; Minor, James C.; Moreno-Bautista, Gabriel; Rollny, Lisa R.; Kanjanaboos, Pongsakorn; Kopilovic, Damir; Thon, Susanna; Carey, Graham H.; Chou, Kang Wei; Zhitomirsky, David; Amassian, Aram; Sargent, E. H.
2014-01-01
(Figure Presented). A colloidal quantum dot solar cell is fabricated by spray-coating under ambient conditions. By developing a room-temperature spray-coating technique and implementing a fully automated process with near monolayer control - an approach termed as sprayLD - an electronic defect is eliminated resulting in solar cell performance and statistical distribution superior to prior batch-processed methods along with a hero performance of 8.1%.
Efficient spray-coated colloidal quantum dot solar cells
Kramer, Illan J.
2014-11-10
(Figure Presented). A colloidal quantum dot solar cell is fabricated by spray-coating under ambient conditions. By developing a room-temperature spray-coating technique and implementing a fully automated process with near monolayer control - an approach termed as sprayLD - an electronic defect is eliminated resulting in solar cell performance and statistical distribution superior to prior batch-processed methods along with a hero performance of 8.1%.
Entanglement witness via quantum-memory-assisted entropic uncertainty relation
Shi, Jiadong; Ding, Zhiyong; Wu, Tao; He, Juan; Yu, Lizhi; Sun, Wenyang; Wang, Dong; Ye, Liu
2017-12-01
By virtue of the quantum-memory-assisted entropic uncertainty relation (EUR), we analyze entanglement witness via the efficiencies of the estimates proposed by Berta (2010 Nat. Phys. 6 659) and Pati (2012 Phys. Rev. A 86 042105). The results show that, without a structured reservoir, the entanglement regions witnessed by these EUR estimates are only determined by the chosen estimated setup, and have no correlation with the explicit form of the initial state. On the other hand, with the structured reservoirs, the time regions during which the entanglement can be witnessed, and the corresponding entanglement regions closely depend on the choice of the estimated setup, the initial state and the state purity p . Concretely, for a pure state with p=1 , the entanglement can be witnessed by both estimates, while for mixed states with p=0.78 , it can only be witnessed using the Pati estimate. What is more, we find that the time regions incorporating the Pati estimate become discontinuous for the initial state with ≤ft| {{φ }\\prime } \\right> ={≤ft(≤ft| 01 \\right> +≤ft| 10 \\right> \\right)}/{\\sqrt{2}} , and the corresponding entanglement regions remain the same; however the entanglement can only be witnessed once by utilizing the Berta estimate.
Efficiency dip observed with InGaN-based multiple quantum well solar cells
Lai, Kunyu; Lin, G. J.; Wu, Yuhrenn; Tsai, Menglun; He, Jr-Hau
2014-01-01
The dip of external quantum efficiency (EQE) is observed on In0.15Ga0.85N/GaN multiple quantum well (MQW) solar cells upon the increase of incident optical power density. With indium composition increased to 25%, the EQE dip becomes much less noticeable. The composition dependence of EQE dip is ascribed to the competition between radiative recombination and photocurrent generation in the active region, which are dictated by quantum-confined Stark effect (QCSE) and composition fluctuation in the MQWs.
Efficient Raman generation in a waveguide: A route to ultrafast quantum random number generation
Energy Technology Data Exchange (ETDEWEB)
England, D. G.; Bustard, P. J.; Moffatt, D. J.; Nunn, J.; Lausten, R.; Sussman, B. J., E-mail: ben.sussman@nrc.ca [National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6 (Canada)
2014-02-03
The inherent uncertainty in quantum mechanics offers a source of true randomness which can be used to produce unbreakable cryptographic keys. We discuss the development of a high-speed random number generator based on the quantum phase fluctuations in spontaneously initiated stimulated Raman scattering (SISRS). We utilize the tight confinement and long interaction length available in a Potassium Titanyl Phosphate waveguide to generate highly efficient SISRS using nanojoule pulse energies, reducing the high pump power requirements of the previous approaches. We measure the random phase of the Stokes output using a simple interferometric setup to yield quantum random numbers at 145 Mbps.
Kaganskiy, Arsenty; Fischbach, Sarah; Strittmatter, André; Rodt, Sven; Heindel, Tobias; Reitzenstein, Stephan
2018-04-01
We report on the realization of scalable single-photon sources (SPSs) based on single site-controlled quantum dots (SCQDs) and deterministically fabricated microlenses. The fabrication process comprises the buried-stressor growth technique complemented with low-temperature in-situ electron-beam lithography for the integration of SCQDs into microlens structures with high yield and high alignment accuracy. The microlens-approach leads to a broadband enhancement of the photon-extraction efficiency of up to (21 ± 2)% and a high suppression of multi-photon events with g (2)(τ = 0) SPSs which, can be applied in photonic quantum circuits and advanced quantum computation schemes.
Fluorescent porous silicon biological probes with high quantum efficiency and stability.
Tu, Chang-Ching; Chou, Ying-Nien; Hung, Hsiang-Chieh; Wu, Jingda; Jiang, Shaoyi; Lin, Lih Y
2014-12-01
We demonstrate porous silicon biological probes as a stable and non-toxic alternative to organic dyes or cadmium-containing quantum dots for imaging and sensing applications. The fluorescent silicon quantum dots which are embedded on the porous silicon surface are passivated with carboxyl-terminated ligands through stable Si-C covalent bonds. The porous silicon bio-probes have shown photoluminescence quantum yield around 50% under near-UV excitation, with high photochemical and thermal stability. The bio-probes can be efficiently conjugated with antibodies, which is confirmed by a standard enzyme-linked immunosorbent assay (ELISA) method.
PsiQuaSP-A library for efficient computation of symmetric open quantum systems.
Gegg, Michael; Richter, Marten
2017-11-24
In a recent publication we showed that permutation symmetry reduces the numerical complexity of Lindblad quantum master equations for identical multi-level systems from exponential to polynomial scaling. This is important for open system dynamics including realistic system bath interactions and dephasing in, for instance, the Dicke model, multi-Λ system setups etc. Here we present an object-oriented C++ library that allows to setup and solve arbitrary quantum optical Lindblad master equations, especially those that are permutationally symmetric in the multi-level systems. PsiQuaSP (Permutation symmetry for identical Quantum Systems Package) uses the PETSc package for sparse linear algebra methods and differential equations as basis. The aim of PsiQuaSP is to provide flexible, storage efficient and scalable code while being as user friendly as possible. It is easily applied to many quantum optical or quantum information systems with more than one multi-level system. We first review the basics of the permutation symmetry for multi-level systems in quantum master equations. The application of PsiQuaSP to quantum dynamical problems is illustrated with several typical, simple examples of open quantum optical systems.
Ascertaining the uncertainty relations via quantum correlations
International Nuclear Information System (INIS)
Li, Jun-Li; Du, Kun; Qiao, Cong-Feng
2014-01-01
We propose a new scheme to express the uncertainty principle in the form of inequality of the bipartite correlation functions for a given multipartite state, which provides an experimentally feasible and model-independent way to verify various uncertainty and measurement disturbance relations. By virtue of this scheme, the implementation of experimental measurement on the measurement disturbance relation to a variety of physical systems becomes practical. The inequality in turn, also imposes a constraint on the strength of correlation, i.e. it determines the maximum value of the correlation function for two-body system and a monogamy relation of the bipartite correlation functions for multipartite system. (paper)
Continuity relations and quantum wave equations
International Nuclear Information System (INIS)
Goedecke, G.H.; Davis, B.T.
2010-01-01
We investigate the mathematical synthesis of the Schroedinger, Klein-Gordon, Pauli-Schroedinger, and Dirac equations starting from probability continuity relations. We utilize methods similar to those employed by R. E. Collins (Lett. Nuovo Cimento, 18 (1977) 581) in his construction of the Schroedinger equation from the position probability continuity relation for a single particle. Our new results include the mathematical construction of the Pauli-Schroedinger and Dirac equations from the position probability continuity relations for a particle that can transition between two states or among four states, respectively.
Photoluminescence efficiency in AlGaN quantum wells
Energy Technology Data Exchange (ETDEWEB)
Tamulaitis, G.; Mickevičius, J. [Institute of Applied Research and Semiconductor Physics Department, Vilnius University, Sauletekio av. 9-III, Vilnius LT-10222 (Lithuania); Jurkevičius, J., E-mail: jonas.jurkevicius@ff.vu.lt [Institute of Applied Research and Semiconductor Physics Department, Vilnius University, Sauletekio av. 9-III, Vilnius LT-10222 (Lithuania); Shur, M.S. [Department of ECE and CIE, Rensselaer Polytechnic Institute (United States); Shatalov, M.; Yang, J.; Gaska, R. [Sensor Electronic Technology, Inc. (United States)
2014-11-15
Photoluminescence spectroscopy of AlGaN/AlGaN multiple quantum wells under quasi-steady-state conditions in the temperature range from 8 to 300 K revealed a strong dependence of droop onset threshold on temperature that was explained by the influence of carrier delocalization. The delocalization at room temperature results predominantly in enhancement of bimolecular radiative recombination, while being favorable for enhancement of nonradiative recombination at low temperatures. Studies of stimulated emission confirmed the strong influence of carrier localization on droop.
An efficient quantum scheme for Private Set Intersection
Shi, Run-hua; Mu, Yi; Zhong, Hong; Cui, Jie; Zhang, Shun
2016-01-01
Private Set Intersection allows a client to privately compute set intersection with the collaboration of the server, which is one of the most fundamental and key problems within the multiparty collaborative computation of protecting the privacy of the parties. In this paper, we first present a cheat-sensitive quantum scheme for Private Set Intersection. Compared with classical schemes, our scheme has lower communication complexity, which is independent of the size of the server's set. Therefore, it is very suitable for big data services in Cloud or large-scale client-server networks.
Special Relativity, Causality and Quantum Mechanics - 1
Indian Academy of Sciences (India)
postulate of the special theory of relativity (STR) stipulating the ... STR may be a more general principle to orga- nize our ... keep the laws of mechanics invariant in all inertial frames. .... cording to a different set of transformation equations.
Quantum Rényi relative entropies affirm universality of thermodynamics.
Misra, Avijit; Singh, Uttam; Bera, Manabendra Nath; Rajagopal, A K
2015-10-01
We formulate a complete theory of quantum thermodynamics in the Rényi entropic formalism exploiting the Rényi relative entropies, starting from the maximum entropy principle. In establishing the first and second laws of quantum thermodynamics, we have correctly identified accessible work and heat exchange in both equilibrium and nonequilibrium cases. The free energy (internal energy minus temperature times entropy) remains unaltered, when all the entities entering this relation are suitably defined. Exploiting Rényi relative entropies we have shown that this "form invariance" holds even beyond equilibrium and has profound operational significance in isothermal process. These results reduce to the Gibbs-von Neumann results when the Rényi entropic parameter α approaches 1. Moreover, it is shown that the universality of the Carnot statement of the second law is the consequence of the form invariance of the free energy, which is in turn the consequence of maximum entropy principle. Further, the Clausius inequality, which is the precursor to the Carnot statement, is also shown to hold based on the data processing inequalities for the traditional and sandwiched Rényi relative entropies. Thus, we find that the thermodynamics of nonequilibrium state and its deviation from equilibrium together determine the thermodynamic laws. This is another important manifestation of the concepts of information theory in thermodynamics when they are extended to the quantum realm. Our work is a substantial step towards formulating a complete theory of quantum thermodynamics and corresponding resource theory.
Leibniz's relationalism and the crisis of Anschauung in quantum mechanics
International Nuclear Information System (INIS)
Herbig, Ralf
2009-01-01
Heisenberg's pioneering work ''Ueber quantentheoretische Umdeutung kinematischer und mechanischer Beziehungen'' (1925) illustrates corner points of Leibniz's theory of knowledge. It succeeds to distill kinematics of circles with velocity from an analysis of the Larmor model for the Zeeman effect. Aim of this novel kinematics is Heisenberg's time-free quantum algebra. The circle kinematica are strictly relational, and they can serve as fundament of a prototheory of quantum physics just to be developed. The kinematics of the circles implicates finally a staged term of illustrativeness. [de
On quantum efficiency of photoluminescence in ZnO layers and nanostructures
Energy Technology Data Exchange (ETDEWEB)
Reshchikov, M.A., E-mail: mreshchi@vcu.ed [Physics Department, Virginia Commonwealth University, 701 W. Grace St., Richmond, VA 23284 (United States); El-Shaer, A.; Behrends, A.; Bakin, A.; Waag, A. [Institute of Semiconductor Technology, Technical University of Braunschweig, Braunschweig D-38106 (Germany)
2009-12-15
In this work we studied PL in ZnO layers and nanostructures, including ZnO homoepitaxial layers on ZnO substrate and ZnO-Zn{sub 1-x}Mg{sub x}O single quantum well (SQW) structures grown on sapphire substrates by MBE, and ZnO nanowires grown on sapphire by MOCVD. The external quantum efficiency (QE) of PL in O-face ZnO layers exceeded that in Zn-face ZnO layers by two orders of magnitude at low temperatures. In a sample with SQW the combined external QE from the 4.6-nm-wide SQW and 50-nm-thick Zn{sub 1-x}Mg{sub x}O barriers achieved 28% at 15 K. The highest external QE was observed in one of the samples with ZnO nanowires-52% at 15 K and 2% at 300 K. Contribution of defect-related PL bands in ZnO nanowires samples was extremely low.
Directory of Open Access Journals (Sweden)
Xiao Guo
2017-10-01
Full Text Available Electrostatic properties of asymmetrically contacted carbon nanotube barrier-free bipolar diode photodetector are studied by solving the Poisson equation self-consistently with equilibrium carrier statistics. For electric field parallel to tube’s axis, the maximum electric field occurs near contact but decays rapidly in a few nanometers, followed by a slowly increasing trend when it extends to the center of channel. By considering the field ionization and the diffusion effect of exciton, a model of estimation on quantum efficiency for the device is made. We find that the quantum efficiency increases with increasing exciton lifetime, decreasing diffusion constant and channel length. For devices with a channel length shorter than 50 nm, the contribution of field ionization to the quantum efficiency can reach 60%.
Experimental bit commitment based on quantum communication and special relativity.
Lunghi, T; Kaniewski, J; Bussières, F; Houlmann, R; Tomamichel, M; Kent, A; Gisin, N; Wehner, S; Zbinden, H
2013-11-01
Bit commitment is a fundamental cryptographic primitive in which Bob wishes to commit a secret bit to Alice. Perfectly secure bit commitment between two mistrustful parties is impossible through asynchronous exchange of quantum information. Perfect security is however possible when Alice and Bob split into several agents exchanging classical and quantum information at times and locations suitably chosen to satisfy specific relativistic constraints. Here we report on an implementation of a bit commitment protocol using quantum communication and special relativity. Our protocol is based on [A. Kent, Phys. Rev. Lett. 109, 130501 (2012)] and has the advantage that it is practically feasible with arbitrary large separations between the agents in order to maximize the commitment time. By positioning agents in Geneva and Singapore, we obtain a commitment time of 15 ms. A security analysis considering experimental imperfections and finite statistics is presented.
Uncertainty relation and simultaneous measurements in quantum theory
International Nuclear Information System (INIS)
Busch, P.
1982-01-01
In this thesis the question for the interpretation of the uncertainty relation is picked up, and a program for the justification of its individualistic interpretation is formulated. By means of quantum mechanical models for the position and momentum measurement a justification of the interpretaton has been tried by reconstruction of the origin of the uncertainties from the conditions of the measuring devices and the determination of the relation of the measured results to the object. By means of a model of the common measurement it could be shown how the uncertainty relation results from the not eliminable mutual disturbance of the devices and the uncertainty relation for the measuring system. So finally the commutation relation is conclusive. For the illustration the split experiment is discussed, first according to Heisenberg with fixed split, then for the quantum mechanical, movable split (Bohr-Einstein). (orig./HSI) [de
An efficient quantum mechanical method for radical pair recombination reactions.
Lewis, Alan M; Fay, Thomas P; Manolopoulos, David E
2016-12-28
The standard quantum mechanical expressions for the singlet and triplet survival probabilities and product yields of a radical pair recombination reaction involve a trace over the states in a combined electronic and nuclear spin Hilbert space. If this trace is evaluated deterministically, by performing a separate time-dependent wavepacket calculation for each initial state in the Hilbert space, the computational effort scales as O(Z 2 logZ), where Z is the total number of nuclear spin states. Here we show that the trace can also be evaluated stochastically, by exploiting the properties of spin coherent states. This results in a computational effort of O(MZlogZ), where M is the number of Monte Carlo samples needed for convergence. Example calculations on a strongly coupled radical pair with Z>10 6 show that the singlet yield can be converged to graphical accuracy using just M=200 samples, resulting in a speed up by a factor of >5000 over a standard deterministic calculation. We expect that this factor will greatly facilitate future quantum mechanical simulations of a wide variety of radical pairs of interest in chemistry and biology.
Scales of Time Where the Quantum Discord Allows an Efficient Execution of the DQC1 Algorithm
Directory of Open Access Journals (Sweden)
M. Ávila
2014-01-01
Full Text Available The power of one qubit deterministic quantum processor (DQC1 (Knill and Laflamme (1998 generates a nonclassical correlation known as quantum discord. The DQC1 algorithm executes in an efficient way with a characteristic time given by τ=Tr[Un]/2n, where Un is an n qubit unitary gate. For pure states, quantum discord means entanglement while for mixed states such a quantity is more than entanglement. Quantum discord can be thought of as the mutual information between two systems. Within the quantum discord approach the role of time in an efficient evaluation of τ is discussed. It is found that the smaller the value of t/T is, where t is the time of execution of the DQC1 algorithm and T is the scale of time where the nonclassical correlations prevail, the more efficient the calculation of τ is. A Mösbauer nucleus might be a good processor of the DQC1 algorithm while a nuclear spin chain would not be efficient for the calculation of τ.
DEA best practice assesses relative efficiency, profitability
International Nuclear Information System (INIS)
Taylor, D.T.; Thompson, R.G.
1995-01-01
The US Federal Energy Regulatory Commission (FERC), in its Order 636 of Apr. 8, 1992, stated, ''All natural gas suppliers, including pipelines, will compete for gas purchases on an equal footing.'' This FERC order changed the economic environment in the natural gas pipeline industry. Now, gas pipeline companies must know their market position, since rate of return regulation is no longer relevant. They must be managed more than before as companies have been in less-regulated parts of the oil and gas business. How they adapt to the new environment, therefore, can be instructive to companies throughout the energy industry. In this article, DEA best-practice methods measure relative efficiency and profitability potential. This measurement reflects fundamental economic relationships. The operational efficiency model analyzed is as follows: Y 1 = f(x 1 , x 2 ), where Y 1 is gross profits, x 1 is total assets (capital employed), and x 2 is total employees (labor employed). Y 1 is a comprehensive indicator of a pipeline's output, whereas x 1 represents the pipeline's total capital employed, and x 2 represents the pipeline's total labor employed. This model reflects principles long studied in economics
Hermiticity of quantum observables versus commutation relations
International Nuclear Information System (INIS)
Shirokov, M.I.
2002-01-01
In order to obtain sum rules and spectral representations the Hermiticity property = of observables is used. It is shown that for certain Ψ and Φ the property turn out to be inconsistent with the commutation relations that contain Α. The known Schwinger paradox is explained by this inconsistency
Jiang, Chunyan; Jing, Liang; Huang, Xin; Liu, Mengmeng; Du, Chunhua; Liu, Ting; Pu, Xiong; Hu, Weiguo; Wang, Zhong Lin
2017-09-26
The piezo-phototronic effect is the tuning of piezoelectric polarization charges at the interface to largely enhance the efficiency of optoelectronic processes related to carrier separation or recombination. Here, we demonstrated the enhanced short-circuit current density and the conversion efficiency of InGaN/GaN multiple quantum well solar cells with an external stress applied on the device. The external-stress-induced piezoelectric charges generated at the interfaces of InGaN and GaN compensate the piezoelectric charges induced by lattice mismatch stress in the InGaN wells. The energy band realignment is calculated with a self-consistent numerical model to clarify the enhancement mechanism of optical-generated carriers. This research not only theoretically and experimentally proves the piezo-phototronic effect modulated the quantum photovoltaic device but also provides a great promise to maximize the use of solar energy in the current energy revolution.
Quantum efficiency measurement system for large area CsI photodetectors
Cusanno, F; Colilli, S; Crateri, R; Fratoni, R; Frullani, S; Garibaldi, F; Giuliani, F; Gricia, M; Lucentini, M; Mostarda, A; Santavenere, F; Veneroni, P; Breuer, H; Iodice, M; Urciuoli, G M; De Cataldo, G; De Leo, R; Lagamba, L; Braem, André
2003-01-01
A proximity focusing freon/CsI RICH detector has been built for kaon physics at Thomas Jefferson National Accelerator Facility (TJNAF or Jefferson Lab), Hall A. The Cherenkov photons are detected by a UV photosensitive CsI film which has been obtained by vacuum evaporation. A dedicated evaporation facility for large area photocathodes has been built for this task. A measuring system has been built to allow the evaluation of the absolute quantum efficiency (QE) just after the evaporation. The evaporation facility is described here, as well as the quantum efficiency measurement device. Results of the QE on-line measurements, for the first time on large area photocathodes, are reported.
Absolute determination of photoluminescence quantum efficiency using an integrating sphere setup
International Nuclear Information System (INIS)
Leyre, S.; Coutino-Gonzalez, E.; Hofkens, J.; Joos, J. J.; Poelman, D.; Smet, P. F.; Ryckaert, J.; Meuret, Y.; Durinck, G.; Hanselaer, P.; Deconinck, G.
2014-01-01
An integrating sphere-based setup to obtain a quick and reliable determination of the internal quantum efficiency of strongly scattering luminescent materials is presented. In literature, two distinct but similar measurement procedures are frequently mentioned: a “two measurement” and a “three measurement” approach. Both methods are evaluated by applying the rigorous integrating sphere theory. It was found that both measurement procedures are valid. Additionally, the two methods are compared with respect to the uncertainty budget of the obtained values of the quantum efficiency. An inter-laboratory validation using the two distinct procedures was performed. The conclusions from the theoretical study were confirmed by the experimental data
Measurement of the quantum efficiency of TMAE and TEA from threshold to 120 nm
International Nuclear Information System (INIS)
Holroyd, R.A.; Preses, J.M.; Woody, C.L.; Johnson, R.A.
1986-01-01
Several existing and planned high energy physics experiments incorporate detectors which use either TMAE (tetrakis-dimethylaminoethylene) or TEA (triethylamine) as their photosensitive agent. Understanding the operation of these devices requires knowledge of the absolute photoionization quantum efficiencies and absorption lengths of TMAE and TEA. In an experiment performed at the National Synchrotron Light source at Brookhaven National Laboratory, we have measured these parameters from 120 nm to 280 nm. The quantum efficiencies were normalized to the known photoionization yields of benzene and cis-2-butene. The results of these measurements and details of the experiment are presented in this paper
Baran, Derya; Gasparini, Nicola; Wadsworth, Andrew; Tan, Ching Hong; Wehbe, Nimer; Song, Xin; Hamid, Zeinab; Zhang, Weimin; Neophytou, Marios; Kirchartz, Thomas; Brabec, Christoph J; Durrant, James R; McCulloch, Iain
2018-05-25
Nonfullerene solar cells have increased their efficiencies up to 13%, yet quantum efficiencies are still limited to 80%. Here we report efficient nonfullerene solar cells with quantum efficiencies approaching unity. This is achieved with overlapping absorption bands of donor and acceptor that increases the photon absorption strength in the range from about 570 to 700 nm, thus, almost all incident photons are absorbed in the active layer. The charges generated are found to dissociate with negligible geminate recombination losses resulting in a short-circuit current density of 20 mA cm -2 along with open-circuit voltages >1 V, which is remarkable for a 1.6 eV bandgap system. Most importantly, the unique nano-morphology of the donor:acceptor blend results in a substantially improved stability under illumination. Understanding the efficient charge separation in nonfullerene acceptors can pave the way to robust and recombination-free organic solar cells.
Baran, Derya; Gasparini, Nicola; Wadsworth, Andrew; Tan, Ching Hong; Wehbe, Nimer; Song, Xin; Hamid, Zeinab; Zhang, Weimin; Neophytou, Marios; Kirchartz, Thomas; Brabec, Christoph J.; Durrant, James R.; McCulloch, Iain
2018-01-01
Nonfullerene solar cells have increased their efficiencies up to 13%, yet quantum efficiencies are still limited to 80%. Here we report efficient nonfullerene solar cells with quantum efficiencies approaching unity. This is achieved with overlapping absorption bands of donor and acceptor that increases the photon absorption strength in the range from about 570 to 700 nm, thus, almost all incident photons are absorbed in the active layer. The charges generated are found to dissociate with negligible geminate recombination losses resulting in a short-circuit current density of 20 mA cm-2 along with open-circuit voltages >1 V, which is remarkable for a 1.6 eV bandgap system. Most importantly, the unique nano-morphology of the donor:acceptor blend results in a substantially improved stability under illumination. Understanding the efficient charge separation in nonfullerene acceptors can pave the way to robust and recombination-free organic solar cells.
Baran, Derya
2018-05-21
Nonfullerene solar cells have increased their efficiencies up to 13%, yet quantum efficiencies are still limited to 80%. Here we report efficient nonfullerene solar cells with quantum efficiencies approaching unity. This is achieved with overlapping absorption bands of donor and acceptor that increases the photon absorption strength in the range from about 570 to 700 nm, thus, almost all incident photons are absorbed in the active layer. The charges generated are found to dissociate with negligible geminate recombination losses resulting in a short-circuit current density of 20 mA cm-2 along with open-circuit voltages >1 V, which is remarkable for a 1.6 eV bandgap system. Most importantly, the unique nano-morphology of the donor:acceptor blend results in a substantially improved stability under illumination. Understanding the efficient charge separation in nonfullerene acceptors can pave the way to robust and recombination-free organic solar cells.
Risko, Chad
2011-03-15
The recent and rapid enhancement in power conversion efficiencies of organic-based, bulk heterojunction solar cells has been a consequence of both improved materials design and better understanding of the underlying physical processes involved in photocurrent generation. In this Perspective, we first present an overview of the application of quantum-chemical techniques to study the intrinsic material properties and molecular- and nano-scale processes involved in device operation. In the second part, these quantum-chemical tools are applied to an oligomer-based study on a collection of donor-acceptor copolymers that have been used in the highest-efficiency solar cell devices reported to date. The quantum-chemical results are found to be in good agreement with the empirical data related to the electronic and optical properties. In particular, they provide insight into the natures of the electronic excitations responsible for the near-infrared/visible absorption profiles, as well as into the energetics of the low-lying singlet and triplet states. These results lead to a better understanding of the inherent differences among the materials, and highlight the usefulness of quantum chemistry as an instrument for material design. Importantly, the results also point to the need to continue the development of integrated, multi scale modeling approaches to provide a thorough understanding of the materials properties. © The Royal Society of Chemistry 2011.
Scaling-Up Quantum Heat Engines Efficiently via Shortcuts to Adiabaticity
Directory of Open Access Journals (Sweden)
Mathieu Beau
2016-04-01
Full Text Available The finite-time operation of a quantum heat engine that uses a single particle as a working medium generally increases the output power at the expense of inducing friction that lowers the cycle efficiency. We propose to scale up a quantum heat engine utilizing a many-particle working medium in combination with the use of shortcuts to adiabaticity to boost the nonadiabatic performance by eliminating quantum friction and reducing the cycle time. To this end, we first analyze the finite-time thermodynamics of a quantum Otto cycle implemented with a quantum fluid confined in a time-dependent harmonic trap. We show that nonadiabatic effects can be controlled and tailored to match the adiabatic performance using a variety of shortcuts to adiabaticity. As a result, the nonadiabatic dynamics of the scaled-up many-particle quantum heat engine exhibits no friction, and the cycle can be run at maximum efficiency with a tunable output power. We demonstrate our results with a working medium consisting of particles with inverse-square pairwise interactions that includes non-interacting and hard-core bosons as limiting cases.
Angularly Deformed Special Relativity and its Results for Quantum Mechanics
Glinka, Lukasz Andrzej
2015-01-01
In this paper, the deformed Special Relativity, which leads to an essentially new theoretical context of quantum mechanics, is presented. The formulation of the theory arises from a straightforward analogy with the Special Relativity, but its foundations are laid through the hypothesis on breakdown of the velocity-momentum parallelism which affects onto the Einstein equivalence principle between mass and energy of a relativistic particle. Furthermore, the derivation is based on the technique ...
Noncommutative unification of general relativity and quantum mechanics
International Nuclear Information System (INIS)
Heller, Michael; Pysiak, Leszek; Sasin, Wieslaw
2005-01-01
We present a model unifying general relativity and quantum mechanics based on a noncommutative geometry. This geometry is developed in terms of a noncommutative algebra A which is defined on a transformation groupoid Γ given by the action of a noncompact group G on the total space E of a principal fiber bundle over space-time M. The case is important since to obtain physical effects predicted by the model we should assume that G is a Lorentz group or some of its representations. We show that the generalized Einstein equation of the model has the form of the eigenvalue equation for the generalized Ricci operator, and all relevant operators in the quantum sector of the model are random operators; we study their dynamics. We also show that the model correctly reproduces general relativity and the usual quantum mechanics. It is interesting that the latter is recovered by performing the measurement of any observable. In the act of such a measurement the model 'collapses' to the usual quantum mechanics
Brown, Craig; Ambrosi, Richard M.; Abbey, Tony; Godet, Olivier; O'Brien, R.; Turner, M. J. L.; Holland, Andrew; Pool, Peter J.; Burt, David; Vernon, David
2008-07-01
Future generations of X-ray astronomy instruments will require position sensitive detectors in the form of charge-coupled devices (CCDs) for X-ray spectroscopy and imaging with the ability to probe the X-ray universe with greater efficiency. This will require the development of CCDs with structures that will improve their quantum efficiency over the current state of the art. The quantum efficiency improvements would have to span a broad energy range (0.2 keV to >15 keV). These devices will also have to be designed to withstand the harsh radiation environments associated with orbits that extend beyond the Earth's magnetosphere. This study outlines the most recent work carried out at the University of Leicester focused on improving the quantum efficiency of an X-ray sensitive CCD through direct manipulation of the device depletion region. It is also shown that increased spectral resolution is achieved using this method due to a decrease in the number of multi-pixel events. A Monte Carlo and analytical models of the CCD have been developed and used to determine the depletion depths achieved through variation of the device substrate voltage, Vss. The models are also used to investigate multi-pixel event distributions and quantum efficiency as a function of depletion depth.
Efficient interfacing of light and surface plasmon polaritons for quantum optics applications
DEFF Research Database (Denmark)
Eran, Kot
interaction are the window to the underlying quantum world. It is no surprise then that there has always been push to find more, and gain better control over systems in which this interaction can be studied. In the past two decades, this end was further motivated as applications were envisioned to coherent...... control of matter. These include applications such as efficient photon collection, single-photon switching and transistors, and long-range optical coupling of quantum bits for quantum communications. However, generating and controlling strong coherent interaction between otherwise very weakly interacting...... light and quantum emitters proves a difficult task. Current days solutions range from cavities, atomic ensembles, photonic band gaps structures, ion traps and optical latices are all being improved and studied but none has yet to emerge as superior. Recently, another proposal for such a strong coupling...
Efficient spin filter using multi-terminal quantum dot with spin-orbit interaction
Directory of Open Access Journals (Sweden)
Yokoyama Tomohiro
2011-01-01
Full Text Available Abstract We propose a multi-terminal spin filter using a quantum dot with spin-orbit interaction. First, we formulate the spin Hall effect (SHE in a quantum dot connected to three leads. We show that the SHE is significantly enhanced by the resonant tunneling if the level spacing in the quantum dot is smaller than the level broadening. We stress that the SHE is tunable by changing the tunnel coupling to the third lead. Next, we perform a numerical simulation for a multi-terminal spin filter using a quantum dot fabricated on semiconductor heterostructures. The spin filter shows an efficiency of more than 50% when the conditions for the enhanced SHE are satisfied. PACS numbers: 72.25.Dc,71.70.Ej,73.63.Kv,85.75.-d
Energy Technology Data Exchange (ETDEWEB)
Li, Tian, E-mail: tianlee@umd.edu, E-mail: dage@ece.umd.edu; Dagenais, Mario, E-mail: tianlee@umd.edu, E-mail: dage@ece.umd.edu [Department of Electrical Engineering, University of Maryland, College Park, Maryland 20742 (United States); Lu, Haofeng; Fu, Lan; Tan, Hark Hoe; Jagadish, Chennupati [Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra ACT 0200 (Australia)
2015-02-02
Reduced quantum dot (QD) absorption due to state filling effects and enhanced electron transport in doped QDs are demonstrated to play a key role in solar energy conversion. Reduced QD state absorption with increased n-doping is observed in the self-assembled In{sub 0.5}Ga{sub 0.5}As/GaAs QDs from high resolution below-bandgap external quantum efficiency (EQE) measurement, which is a direct consequence of the Pauli exclusion principle. We also show that besides partial filling of the quantum states, electron-doping produces negatively charged QDs that exert a repulsive Coulomb force on the mobile electrons, thus altering the electron trajectory and reducing the probability of electron capture, leading to an improved collection efficiency of photo-generated carriers, as indicated by an absolute above-bandgap EQE measurement. The resulting redistribution of the mobile electron in the planar direction is further validated by the observed photoluminescence intensity dependence on doping.
Directory of Open Access Journals (Sweden)
Somsak Panyakeow
2010-10-01
Full Text Available Laterally close-packed quantum dots (QDs called quantum dot molecules (QDMs are grown by modified molecular beam epitaxy (MBE. Quantum dots could be aligned and cross hatched. Quantum rings (QRs created from quantum dot transformation during thin or partial capping are used as templates for the formations of bi-quantum dot molecules (Bi-QDMs and quantum dot rings (QDRs. Preferable quantum dot nanostructure for quantum computation based on quantum dot cellular automata (QCA is laterally close-packed quantum dot molecules having four quantum dots at the corners of square configuration. These four quantum dot sets are called quadra-quantum dots (QQDs. Aligned quadra-quantum dots with two electron confinements work like a wire for digital information transmission by Coulomb repulsion force, which is fast and consumes little power. Combination of quadra-quantum dots in line and their cross-over works as logic gates and memory bits. Molecular Beam Epitaxial growth technique called 'Droplet Epitaxy' has been developed for several quantum nanostructures such as quantum rings and quantum dot rings. Quantum rings are prepared by using 20 ML In-Ga (15:85 droplets deposited on a GaAs substrate at 390'C with a droplet growth rate of 1ML/s. Arsenic flux (7'8'10-6Torr is then exposed for InGaAs crystallization at 200'C for 5 min. During droplet epitaxy at a high droplet thickness and high temperature, out-diffusion from the centre of droplets occurs under anisotropic strain. This leads to quantum ring structures having non-uniform ring stripes and deep square-shaped nanoholes. Using these peculiar quantum rings as templates, four quantum dots situated at the corners of a square shape are regrown. Two of these four quantum dots are aligned either or, which are preferable crystallographic directions of quantum dot alignment in general.
Increasing the quantum efficiency of GaAs solar cells by embedding InAs quantum dots
Salii, R. A.; Mintairov, S. A.; Nadtochiy, A. M.; Payusov, A. S.; Brunkov, P. N.; Shvarts, M. Z.; Kalyuzhnyy, N. A.
2016-11-01
Development of Metalorganic Vapor Phase Epitaxy (MOVPE) technology of InAs quantum dots (QDs) in GaAs for photovoltaic applications is presented. The growth peculiarities in InAs-GaAs lattice-mismatched system were considered. The photoluminescence (PL) intensity dependences on different growth parameters were obtained. The multimodal distribution of QDs by sizes was found using AFM and PL methods. GaAs solar cell nanoheterostructures with imbedded QD arrays were designed and obtained. Ones have been demonstrated a significant increase of quantum efficiency and photogenerated current of QD solar cells due to photo effect in InAs QD array (0.59 mA/cm2 for AM1.5D and 82 mA/cm2 for AM0).
Simple and efficient absorption filter for single photons from a cold atom quantum memory.
Stack, Daniel T; Lee, Patricia J; Quraishi, Qudsia
2015-03-09
The ability to filter unwanted light signals is critical to the operation of quantum memories based on neutral atom ensembles. Here we demonstrate an efficient frequency filter which uses a vapor cell filled with (85)Rb and a buffer gas to attenuate both residual laser light and noise photons by nearly two orders of magnitude with little loss to the single photons associated with our cold (87)Rb quantum memory. This simple, passive filter provides an additional 18 dB attenuation of our pump laser and erroneous spontaneous emissions for every 1 dB loss of the single photon signal. We show that the addition of a frequency filter increases the non-classical correlations and the retrieval efficiency of our quantum memory by ≈ 35%.
On the relation of the theoretical foundations of quantum theory and general relativity theory
International Nuclear Information System (INIS)
Kober, Martin
2010-01-01
The specific content of the present thesis is presented in the following way. First the most important contents of quantum theory and general relativity theory are presented. In connection with the general relativity theory the mathematical property of the diffeomorphism invariance plays the deciding role, while concerning the quantum theory starting from the Copenhagen interpretation first the measurement problem is treated, before basing on the analysis of concrete phenomena and the mathematical apparatus of quantum theory the nonlocality is brought into focus as an important property. This means that both theories suggest a relationalistic view of the nature of the space. This analysis of the theoretical foundations of quantum theory and general relativity theory in relation to the nature of the space obtains only under inclusion of Kant's philosophy and his analysis of the terms space and time as fundamental forms of perception its full persuasive power. Then von Weizsaeckers quantum theory of the ur-alternatives is presented. Finally attempts are made to apply the obtained knowledge to the question of the quantum-theoretical formulation of general relativity theory.
Simple formalism for efficient derivatives and multi-determinant expansions in quantum Monte Carlo
Filippi, Claudia; Assaraf, R.; Moroni, S.
2016-01-01
We present a simple and general formalism to compute efficiently the derivatives of a multi-determinant Jastrow-Slater wave function, the local energy, the interatomic forces, and similar quantities needed in quantum Monte Carlo. Through a straightforward manipulation of matrices evaluated on the
The effect of nonadiabaticity on the efficiency of quantum memory based on an optical cavity
Veselkova, N. G.; Sokolov, I. V.
2017-07-01
Quantum efficiency is an important characteristic of quantum memory devices that are aimed at recording the quantum state of light signals and its storing and reading. In the case of memory based on an ensemble of cold atoms placed in an optical cavity, the efficiency is restricted, in particular, by relaxation processes in the system of active atomic levels. We show how the effect of the relaxation on the quantum efficiency can be determined in a regime of the memory usage in which the evolution of signals in time is not arbitrarily slow on the scale of the field lifetime in the cavity and when the frequently used approximation of the adiabatic elimination of the quantized cavity mode field cannot be applied. Taking into account the effect of the nonadiabaticity on the memory quality is of interest in view of the fact that, in order to increase the field-medium coupling parameter, a higher cavity quality factor is required, whereas storing and processing of sequences of many signals in the memory implies that their duration is reduced. We consider the applicability of the well-known efficiency estimates via the system cooperativity parameter and estimate a more general form. In connection with the theoretical description of the memory of the given type, we also discuss qualitative differences in the behavior of a random source introduced into the Heisenberg-Langevin equations for atomic variables in the cases of a large and a small number of atoms.
Energy Technology Data Exchange (ETDEWEB)
Schmidt, Tobias D., E-mail: Tobias.Schmidt@physik.uni-augsburg.de; Reichardt, Lukas J.; Wehrmeister, Sebastian; Scholz, Bert J.; Mayr, Christian; Brütting, Wolfgang, E-mail: Wolfgang.Bruetting@physik.uni-augsburg.de [Institute of Physics, University of Augsburg, 86135 Augsburg (Germany); Rausch, Andreas F.; Wehlus, Thomas; Reusch, Thilo C. G. [OSRAM OLED GmbH, Wernerwerkstrasse 2, 93049 Regensburg (Germany); Ciarnáin, Rossá Mac; Danz, Norbert [Fraunhofer Institute for Applied Optics and Precision Engineering, 07745 Jena (Germany)
2014-07-28
Emitter orientation will play a major role in future applications of organic light-emitting diodes due to its strong impact on the efficiency of the devices. Up to now, determining the orientation of transition dipole moments required elaborate angular-dependent measurements of the light emission pattern. In this paper, we present a simplified and straightforward method to extract the emitter orientation from external quantum efficiency measurements. We demonstrate the validity of the method on three different dye-doped emitting systems.
Scale relativity: from quantum mechanics to chaotic dynamics.
Nottale, L.
Scale relativity is a new approach to the problem of the origin of fundamental scales and of scaling laws in physics, which consists in generalizing Einstein's principle of relativity to the case of scale transformations of resolutions. We recall here how it leads one to the concept of fractal space-time, and to introduce a new complex time derivative operator which allows to recover the Schrödinger equation, then to generalize it. In high energy quantum physics, it leads to the introduction of a Lorentzian renormalization group, in which the Planck length is reinterpreted as a lowest, unpassable scale, invariant under dilatations. These methods are successively applied to two problems: in quantum mechanics, that of the mass spectrum of elementary particles; in chaotic dynamics, that of the distribution of planets in the Solar System.
The Coulomb potential in quantum mechanics and related topics
International Nuclear Information System (INIS)
Haeringen, H. van.
1978-01-01
This dissertation consists of an analytic study of the Coulomb interaction in nonrelativistic quantum mechanics and some related topics. The author investigates in a number of self-contained articles various interesting and important properties of the Coulomb potential. Some of these properties are shared by other potentials which also play a role in quantum mechanics. For such related interactions a comparative study is made. The principal difficulties in the description of proton-deuteron scattering and break-up reactions, due to the Coulomb interaction, are studied by working out a simple model. The bound states are studied for the Coulomb plus Yamaguchi potential, for the symmetric shifted Coulomb potential, and for local potentials with an inverse-distance-squared asymptotic behaviour. (Auth.)
Indefinite-metric quantum field theory of general relativity, 15
International Nuclear Information System (INIS)
Nakanishi, Noboru
1982-01-01
In the manifestly covariant canonical formalism of quantum gravity, it is known that the equal-time commutator between a tensor field and the B field b sub(rho) is consistent with the rules of tensor analysis. Another tensorlike commutation relation is shown to exist for the equal-time commutator between a tensor and b sub(rho), but at the same time its limitation is clarified. The quantum-gravity extension of the invariant D function is defined and provied to be affine-invariant. The four-dimensional commutation relation between a tensor and b sub(rho) is investigated, and it is shown that the commutator consists of a completely tensorlike, manifestly affine-covariant part and a remainder, which is clearly distinguishable from the former. (author)
Quadra-quantum Dots and Related Patterns of Quantum Dot Molecules:
Directory of Open Access Journals (Sweden)
Somsak Panyakeow
2010-10-01
Full Text Available Abstract Laterally close-packed quantum dots (QDs called quantum dot molecules (QDMs are grown by modified molecular beam epitaxy (MBE. Quantum dots could be aligned and cross hatched. Quantum rings (QRs created from quantum dot transformation during thin or partial capping are used as templates for the formations of bi-quantum dot molecules (Bi-QDMs and quantum dot rings (QDRs. Preferable quantum dot nanostructure for quantum computation based on quantum dot cellular automata (QCA is laterally close-packed quantum dot molecules having four quantum dots at the corners of square configuration. These four quantum dot sets are called quadra-quantum dots (QQDs. Aligned quadra-quantum dots with two electron confinements work like a wire for digital information transmission by Coulomb repulsion force, which is fast and consumes little power. Combination of quadra-quantum dots in line and their cross-over works as logic gates and memory bits. Molecular Beam Epitaxial growth technique called ‘‘Droplet Epitaxy” has been developed for several quantum nanostructures such as quantum rings and quantum dot rings. Quantum rings are prepared by using 20 ML In-Ga (15:85 droplets deposited on a GaAs substrate at 390°C with a droplet growth rate of 1ML/s. Arsenic flux (7–8×10-6Torr is then exposed for InGaAs crystallization at 200°C for 5 min. During droplet epitaxy at a high droplet thickness and high temperature, out-diffusion from the centre of droplets occurs under anisotropic strain. This leads to quantum ring structures having non-uniform ring stripes and deep square-shaped nanoholes. Using these peculiar quantum rings as templates, four quantum dots situated at the corners of a square shape are regrown. Two of these four quantum dots are aligned either or , which are preferable crystallographic directions of quantum dot alignment in general.
Quantum physics, relativity and complex spacetime towards a new synthesis
Kaiser, Gerald
1990-01-01
A new synthesis of the principles of quantum mechanics and Relativity is proposed in the context of complex differential geometry. The positivity of the energy implies that wave functions and fields can be extended to complex spacetime, and it is shown that this complexification has a solid physical interpretation as an extended phase space. The extended fields can be said to be realistic wavelet transforms of the original fields. A new, algebraic theory of wavelets is developed.
An Efficient and Secure Arbitrary N-Party Quantum Key Agreement Protocol Using Bell States
Liu, Wen-Jie; Xu, Yong; Yang, Ching-Nung; Gao, Pei-Pei; Yu, Wen-Bin
2018-01-01
Two quantum key agreement protocols using Bell states and Bell measurement were recently proposed by Shukla et al. (Quantum Inf. Process. 13(11), 2391-2405, 2014). However, Zhu et al. pointed out that there are some security flaws and proposed an improved version (Quantum Inf. Process. 14(11), 4245-4254, 2015). In this study, we will show Zhu et al.'s improvement still exists some security problems, and its efficiency is not high enough. For solving these problems, we utilize four Pauli operations { I, Z, X, Y} to encode two bits instead of the original two operations { I, X} to encode one bit, and then propose an efficient and secure arbitrary N-party quantum key agreement protocol. In the protocol, the channel checking with decoy single photons is introduced to avoid the eavesdropper's flip attack, and a post-measurement mechanism is used to prevent against the collusion attack. The security analysis shows the present protocol can guarantee the correctness, security, privacy and fairness of quantum key agreement.
Role of information theoretic uncertainty relations in quantum theory
Energy Technology Data Exchange (ETDEWEB)
Jizba, Petr, E-mail: p.jizba@fjfi.cvut.cz [FNSPE, Czech Technical University in Prague, Břehová 7, 115 19 Praha 1 (Czech Republic); ITP, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin (Germany); Dunningham, Jacob A., E-mail: J.Dunningham@sussex.ac.uk [Department of Physics and Astronomy, University of Sussex, Falmer, Brighton, BN1 9QH (United Kingdom); Joo, Jaewoo, E-mail: j.joo@surrey.ac.uk [Advanced Technology Institute and Department of Physics, University of Surrey, Guildford, GU2 7XH (United Kingdom)
2015-04-15
Uncertainty relations based on information theory for both discrete and continuous distribution functions are briefly reviewed. We extend these results to account for (differential) Rényi entropy and its related entropy power. This allows us to find a new class of information-theoretic uncertainty relations (ITURs). The potency of such uncertainty relations in quantum mechanics is illustrated with a simple two-energy-level model where they outperform both the usual Robertson–Schrödinger uncertainty relation and Shannon entropy based uncertainty relation. In the continuous case the ensuing entropy power uncertainty relations are discussed in the context of heavy tailed wave functions and Schrödinger cat states. Again, improvement over both the Robertson–Schrödinger uncertainty principle and Shannon ITUR is demonstrated in these cases. Further salient issues such as the proof of a generalized entropy power inequality and a geometric picture of information-theoretic uncertainty relations are also discussed.
Role of information theoretic uncertainty relations in quantum theory
International Nuclear Information System (INIS)
Jizba, Petr; Dunningham, Jacob A.; Joo, Jaewoo
2015-01-01
Uncertainty relations based on information theory for both discrete and continuous distribution functions are briefly reviewed. We extend these results to account for (differential) Rényi entropy and its related entropy power. This allows us to find a new class of information-theoretic uncertainty relations (ITURs). The potency of such uncertainty relations in quantum mechanics is illustrated with a simple two-energy-level model where they outperform both the usual Robertson–Schrödinger uncertainty relation and Shannon entropy based uncertainty relation. In the continuous case the ensuing entropy power uncertainty relations are discussed in the context of heavy tailed wave functions and Schrödinger cat states. Again, improvement over both the Robertson–Schrödinger uncertainty principle and Shannon ITUR is demonstrated in these cases. Further salient issues such as the proof of a generalized entropy power inequality and a geometric picture of information-theoretic uncertainty relations are also discussed
Heterostructures for Increased Quantum Efficiency in Nitride LEDs
Energy Technology Data Exchange (ETDEWEB)
Davis, Robert F. [Carnegie Mellon Univ., Pittsburgh, PA (United States)
2010-09-30
Task 1. Development of an advanced LED simulator useful for the design of efficient nitride-based devices. Simulator will contain graphical interface software that can be used to specify the device structure, the material parameters, the operating conditions and the desired output results. Task 2. Theoretical and experimental investigations regarding the influence on the microstructure, defect concentration, mechanical stress and strain and IQE of controlled changes in the chemistry and process route of deposition of the buffer layer underlying the active region of nitride-based blue- and greenemitting LEDs. Task 3. Theoretical and experimental investigations regarding the influence on the physical properties including polarization and IQE of controlled changes in the geometry, chemistry, defect density, and microstructure of components in the active region of nitride-based blue- and green-emitting LEDs. Task 4. Theoretical and experimental investigations regarding the influence on IQE of novel heterostructure designs to funnel carriers into the active region for enhanced recombination efficiency and elimination of diffusion beyond this region. Task 5. Theoretical and experimental investigations regarding the influence of enhanced p-type doping on the chemical, electrical, and microstructural characteristics of the acceptor-doped layers, the hole injection levels at Ohmic contacts, the specific contact resistivity and the IQE of nitride-based blue- and green-emitting LEDs. Development and optical and electrical characterization of reflective Ohmic contacts to n- and p-type GaN films.
Relational motivation for conformal operator ordering in quantum cosmology
International Nuclear Information System (INIS)
Anderson, Edward
2010-01-01
Operator ordering in quantum cosmology is a major as-yet unsettled ambiguity with not only formal but also physical consequences. We determine the Lagrangian origin of the conformal invariance that underlies the conformal operator-ordering choice in quantum cosmology. This arises particularly naturally and simply from relationalist product-type actions (such as the Jacobi action for mechanics or Baierlein-Sharp-Wheeler-type actions for general relativity), for which all that is required is for the kinetic and potential factors to rescale in compensation to each other. These actions themselves mathematically sharply implement philosophical principles relevant to whole-universe modelling, so that the motivation for conformal operator ordering in quantum cosmology is thereby substantially strengthened. Relationalist product-type actions also give emergent times which amount to recovering Newtonian, proper and cosmic time in various contexts. The conformal scaling of these actions directly tells us how emergent time scales; if one follows suit with the Newtonian time or the lapse in the more commonly used difference-type Euler-Lagrange or Arnowitt-Deser-Misner-type actions, one sees how these too obey a more complicated conformal invariance. Moreover, our discovery of the conformal scaling of the emergent time permits relating how this simplifies equations of motion with how affine parametrization simplifies geodesics.
Quantum effects from a purely geometrical relativity theory
International Nuclear Information System (INIS)
Ellis, Homer G
2005-01-01
A purely geometrical relativity theory results from a construction that produces from three-dimensional space a happy unification of Kaluza's five-dimensional theory and Weyl's conformal theory. The theory can provide geometrical explanations for the following observed phenomena, among others: (a) visibility lifetimes of elementary particles of lengths inversely proportional to their rest masses; (b) the equality of charge magnitude among all charged particles interacting at an event; (c) the propensity of electrons in atoms to be seen in discretely spaced orbits; and (d) 'quantum jumps' between those orbits. This suggests the possibility that the theory can provide a deterministic underpinning of quantum mechanics like that provided to thermodynamics by the molecular theory of gases
Elliott, Thomas J.; Gu, Mile
2018-03-01
Continuous-time stochastic processes pervade everyday experience, and the simulation of models of these processes is of great utility. Classical models of systems operating in continuous-time must typically track an unbounded amount of information about past behaviour, even for relatively simple models, enforcing limits on precision due to the finite memory of the machine. However, quantum machines can require less information about the past than even their optimal classical counterparts to simulate the future of discrete-time processes, and we demonstrate that this advantage extends to the continuous-time regime. Moreover, we show that this reduction in the memory requirement can be unboundedly large, allowing for arbitrary precision even with a finite quantum memory. We provide a systematic method for finding superior quantum constructions, and a protocol for analogue simulation of continuous-time renewal processes with a quantum machine.
OP09O-OP404-9 Wide Field Camera 3 CCD Quantum Efficiency Hysteresis
Collins, Nick
2009-01-01
The HST/Wide Field Camera (WFC) 3 UV/visible channel CCD detectors have exhibited an unanticipated quantum efficiency hysteresis (QEH) behavior. At the nominal operating temperature of -83C, the QEH feature contrast was typically 0.1-0.2% or less. The behavior was replicated using flight spare detectors. A visible light flat-field (540nm) with a several times full-well signal level can pin the detectors at both optical (600nm) and near-UV (230nm) wavelengths, suppressing the QEH behavior. We are characterizing the timescale for the detectors to become unpinned and developing a protocol for flashing the WFC3 CCDs with the instrument's internal calibration system in flight. The HST/Wide Field Camera 3 UV/visible channel CCD detectors have exhibited an unanticipated quantum efficiency hysteresis (QEH) behavior. The first observed manifestation of QEH was the presence in a small percentage of flat-field images of a bowtie-shaped contrast that spanned the width of each chip. At the nominal operating temperature of -83C, the contrast observed for this feature was typically 0.1-0.2% or less, though at warmer temperatures contrasts up to 5% (at -50C) have been observed. The bowtie morphology was replicated using flight spare detectors in tests at the GSFC Detector Characterization Laboratory by power cycling the detector while cold. Continued investigation revealed that a clearly-related global QE suppression at the approximately 5% level can be produced by cooling the detector in the dark; subsequent flat-field exposures at a constant illumination show asymptotically increasing response. This QE "pinning" can be achieved with a single high signal flat-field or a series of lower signal flats; a visible light (500-580nm) flat-field with a signal level of several hundred thousand electrons per pixel is sufficient for QE pinning at both optical (600nm) and near-UV (230nm) wavelengths. We are characterizing the timescale for the detectors to become unpinned and developing a
Efficient quantum entanglement distribution over an arbitrary collective-noise channel
Sheng, Yu-Bo; Deng, Fu-Guo
2010-04-01
We present an efficient quantum entanglement distribution over an arbitrary collective-noise channel. The basic idea in the present scheme is that two parties in quantum communication first transmit the entangled states in the frequency degree of freedom which suffers little from the noise in an optical fiber. After the two parties share the photon pairs, they add some operations and equipments to transfer the frequency entanglement of pairs into the polarization entanglement with the success probability of 100%. Finally, they can get maximally entangled polarization states with polarization independent wavelength division multiplexers and quantum frequency up-conversion which can erase distinguishability for frequency. Compared with conventional entanglement purification protocols, the present scheme works in a deterministic way in principle. Surprisingly, the collective noise leads to an additional advantage.
Schuster, Jonathan; Bellotti, Enrico
2013-06-01
We have investigated the quantum effiency in HgCdTe photovoltaic pixel arrays employing a photon-trapping structure realized with a periodic array of pillars intended to provide broadband operation. We have found that the quantum efficiency depends heavily on the passivation of the pillar surface. Pillars passivated with anodicoxide have a large fixed positive charge on the pillar surface. We use our three-dimensional numerical simulation model to study the effect of surface charge and surface recombination velocity on the exterior of the pillars. We then evaluate the quantum efficiency of this structure subject to different surface conditions. We have found that by themselves, the surface charge and surface recombination are detrimental to the quantum efficiency but the quantum efficiency is recovered when both phenomena are present. We will discuss the effects of these phenomena and the trade offs that exist between the two.
Reconsideration of the Uncertainty Relations and Quantum Measurements
Directory of Open Access Journals (Sweden)
Dumitru S.
2008-04-01
Full Text Available Discussions on uncertainty relations (UR and quantum measurements (QMS persisted until nowadays in publications about quantum mechanics (QM. They originate mainly from the conventional interpretation of UR (CIUR. In the most of the QM literarure, it is underestimated the fact that, over the years, a lot of deficiencies regarding CIUR were signaled. As a rule the alluded deficiencies were remarked disparately and discussed as punctual and non-essential questions. Here we approach an investigation of the mentioned deficiencies collected in a conclusive ensemble. Subsequently we expose a reconsideration of the major problems referring to UR and QMS. We reveal that all the basic presumption of CIUR are troubled by insurmountable deficiencies which require the indubitable failure of CIUR and its necessary abandonment. Therefore the UR must be deprived of their statute of crucialpieces for physics. So, the aboriginal versions of UR appear as being in postures of either (i thought-experimental fictions or (ii simple QM formulae and, any other versions of them, have no connection with the QMS. Then the QMS must be viewed as an additional subject comparatively with the usual questions of QM. For a theoretical description of QMS we propose an information-transmission model, in which the quantum observables are considered as random variables. Our approach directs to natural solutions and simplifications for many problems regarding UR and QMS.
Reconsideration of the Uncertainty Relations and Quantum Measurements
Directory of Open Access Journals (Sweden)
Dumitru S.
2008-04-01
Full Text Available Discussions on uncertainty relations (UR and quantum measurements (QMS persisted until nowadays in publications about quantum mechanics (QM. They originate mainly from the conventional interpretation of UR (CIUR. In the most of the QM literarure, it is underestimated the fact that, over the years, a lot of deficiencies regarding CIUR were signaled. As a rule the alluded deficiencies were remarked disparately and dis- cussed as punctual and non-essential questions. Here we approach an investigation of the mentioned deficiencies collected in a conclusive ensemble. Subsequently we expose a reconsideration of the major problems referring to UR and QMS. We reveal that all the basic presumption of CIUR are troubled by insurmountable deficiencies which require the indubitable failure of CIUR and its necessary abandonment. Therefore the UR must be deprived of their statute of crucial pieces for physics. So, the aboriginal versions of UR appear as being in postures of either (i thought-experimental fictions or (ii sim- ple QM formulae and, any other versions of them, have no connection with the QMS. Then the QMS must be viewed as an additional subject comparatively with the usual questions of QM. For a theoretical description of QMS we propose an information- transmission model, in which the quantum observables are considered as random vari- ables. Our approach directs to natural solutions and simplifications for many problems regarding UR and QMS.
Quantum systems related to root systems and radial parts of Laplace operators
Olshanetsky, M. A.; Perelomov, A. M.
2002-01-01
The relation between quantum systems associated to root systems and radial parts of Laplace operators on symmetric spaces is established. From this it follows the complete integrability of some quantum systems.
Efficiency versus speed in quantum heat engines: Rigorous constraint from Lieb-Robinson bound
Shiraishi, Naoto; Tajima, Hiroyasu
2017-08-01
A long-standing open problem whether a heat engine with finite power achieves the Carnot efficiency is investgated. We rigorously prove a general trade-off inequality on thermodynamic efficiency and time interval of a cyclic process with quantum heat engines. In a first step, employing the Lieb-Robinson bound we establish an inequality on the change in a local observable caused by an operation far from support of the local observable. This inequality provides a rigorous characterization of the following intuitive picture that most of the energy emitted from the engine to the cold bath remains near the engine when the cyclic process is finished. Using this description, we prove an upper bound on efficiency with the aid of quantum information geometry. Our result generally excludes the possibility of a process with finite speed at the Carnot efficiency in quantum heat engines. In particular, the obtained constraint covers engines evolving with non-Markovian dynamics, which almost all previous studies on this topic fail to address.
Quantum efficiency of silica-coated rare-earth doped yttrium silicate
International Nuclear Information System (INIS)
Cervantes-Vásquez, D.; Contreras, O.E.; Hirata, G.A.
2013-01-01
The photoluminescent properties of rare earth-activated white-emitting Y 2 SiO 5 :Ce,Tb nanocrystalline phosphor prepared by two different methods, pressure-assisted combustion synthesis and sol–gel, were studied. The synthesized phosphor samples were post-annealed at 1373 K and 1623 K in order to obtain the X1-Y 2 SiO 5 and X2-Y 2 SiO 5 phases, respectively, which were confirmed by X-ray diffraction measurements. Photoluminescence analysis showed the contribution of two blue-emission bands within the 380–450 nm region originating from 5d–4f transitions in Ce 3+ ions and a well-defined green emission of Tb 3+ ions located at 545 nm corresponding to 5 D 4 → 7 F 5 electronic transitions. Thereafter, Y 2 SiO 5 :Ce,Tb powders were coated with colloidal silica in order to investigate the effect of silica coatings on their luminescent properties. Absolute fluorescence quantum efficiency measurements were carefully performed, which revealed an increase of 12% of efficiency in coated compared with bare-Y 2 SiO 5 :Ce,Tb phosphor. -- Highlights: • Y 2 SiO 5 :Ce,Tb phosphor powders were successfully coated with colloidal silica. • Post-annealing treatments improved the quantum efficiency of silica-coated Y 2 SiO 5 :Ce,Tb phosphors. • Absolute fluorescence quantum efficiency measurements showed an increase of 12%
Kim, Young-Hoon; Wolf, Christoph; Kim, Young-Tae; Cho, Himchan; Kwon, Woosung; Do, Sungan; Sadhanala, Aditya; Park, Chan Gyung; Rhee, Shi-Woo; Im, Sang Hyuk; Friend, Richard H; Lee, Tae-Woo
2017-07-25
Colloidal metal-halide perovskite quantum dots (QDs) with a dimension less than the exciton Bohr diameter D B (quantum size regime) emerged as promising light emitters due to their spectrally narrow light, facile color tuning, and high photoluminescence quantum efficiency (PLQE). However, their size-sensitive emission wavelength and color purity and low electroluminescence efficiency are still challenging aspects. Here, we demonstrate highly efficient light-emitting diodes (LEDs) based on the colloidal perovskite nanocrystals (NCs) in a dimension > D B (regime beyond quantum size) by using a multifunctional buffer hole injection layer (Buf-HIL). The perovskite NCs with a dimension greater than D B show a size-irrespective high color purity and PLQE by managing the recombination of excitons occurring at surface traps and inside the NCs. The Buf-HIL composed of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) and perfluorinated ionomer induces uniform perovskite particle films with complete film coverage and prevents exciton quenching at the PEDOT:PSS/perovskite particle film interface. With these strategies, we achieved a very high PLQE (∼60.5%) in compact perovskite particle films without any complex post-treatments and multilayers and a high current efficiency of 15.5 cd/A in the LEDs of colloidal perovskite NCs, even in a simplified structure, which is the highest efficiency to date in green LEDs that use colloidal organic-inorganic metal-halide perovskite nanoparticles including perovskite QDs and NCs. These results can help to guide development of various light-emitting optoelectronic applications based on perovskite NCs.
Efficient experimental design of high-fidelity three-qubit quantum gates via genetic programming
Devra, Amit; Prabhu, Prithviraj; Singh, Harpreet; Arvind; Dorai, Kavita
2018-03-01
We have designed efficient quantum circuits for the three-qubit Toffoli (controlled-controlled-NOT) and the Fredkin (controlled-SWAP) gate, optimized via genetic programming methods. The gates thus obtained were experimentally implemented on a three-qubit NMR quantum information processor, with a high fidelity. Toffoli and Fredkin gates in conjunction with the single-qubit Hadamard gates form a universal gate set for quantum computing and are an essential component of several quantum algorithms. Genetic algorithms are stochastic search algorithms based on the logic of natural selection and biological genetics and have been widely used for quantum information processing applications. We devised a new selection mechanism within the genetic algorithm framework to select individuals from a population. We call this mechanism the "Luck-Choose" mechanism and were able to achieve faster convergence to a solution using this mechanism, as compared to existing selection mechanisms. The optimization was performed under the constraint that the experimentally implemented pulses are of short duration and can be implemented with high fidelity. We demonstrate the advantage of our pulse sequences by comparing our results with existing experimental schemes and other numerical optimization methods.
Efficiency studies on semipolar GaInN-GaN quantum well structures
Energy Technology Data Exchange (ETDEWEB)
Scholz, Ferdinand; Meisch, Tobias; Elkhouly, Karim [Institute of Optoelectronics, Ulm University (Germany)
2016-12-15
In order to clarify the reasons for the fairly poor electroluminescence (EL) performance of semipolar LED structures grown on patterned sapphire wafers, we have analyzed both, pure photoluminescence (PL) test structures without doping only containing 5 GaInN quantum wells and full EL test structures, all emitting at a wavelength of about 510 nm. Evaluating the PL intensity over a wide range of temperatures and excitation powers, we conclude that such quantum wells possess a fairly large internal quantum efficiency of about 20%. However, on EL test structures containing nominally the same quantum wells, we obtained an optical output power of only about 150μW at an applied current of 20 mA. This may be due partly to some thermal destruction of the quantum wells by the overgrowth with p-GaN. Even more important seems to be the not yet finally optimized p-doping of these structures. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Directory of Open Access Journals (Sweden)
E TEYAR
2007-12-01
Full Text Available The use of semi-conducting materials in the photoelectrochemical detoxification of water became a very important research field. For this purpose, TiO2 nanostructures thin films with size of 18 nm to 45nm have been synthesized at low temperature. It is found by means of cyclic voltametry and coulometry measurements that the best photoelectrochemical quantum efficiency under UV monochromatic light with a wavelength of 365 nm and a solution of NaOH 0.1N is obtained in the case of thermal oxidation deposition method which can reach 28% compared to ultrasonic spray and dip coating methods of which the quantum is less than 20%. The crystal structure has an influence on the photo-degradation of methanol. The crystal structure which is recommended for this task is the anatase one, especially in the dipping case when the quantum increases after addition of methanol more than twice compared to the solution of NaOH without methanol. The photoelectrochemical quantum efficiency of these films is related to the number of dips and annealing under air at 550°C during one hour. The annealing has no effect on the quantum efficiency of the films, but decreases there photocatalytic activity as showed by the measure of the photocurrent related to methanol photodegradation. The annealing has no effect on the crystal structure of the material. The impedance spectroscopy of six dips deposited films with and without methanol shows that the annealing increases the doping and weakly decreases the film quantum efficiency. This implies, the importance of surface morphology which the rough is decreasing as showed by scanning electron microscopy. The effect of the precursor concentration in ethanol have been investigated by using films, synthesized at T=550°C. The quantum efficiency increases weakly according the precursor concentration. It tends towards a saturation at great concentrations of precursor. In Na OH with methanol added, it passes by a maximum at
An efficient numerical progressive diagonalization scheme for the quantum Rabi model revisited
International Nuclear Information System (INIS)
Pan, Feng; Bao, Lina; Dai, Lianrong; Draayer, Jerry P
2017-01-01
An efficient numerical progressive diagonalization scheme for the quantum Rabi model is revisited. The advantage of the scheme lies in the fact that the quantum Rabi model can be solved almost exactly by using the scheme that only involves a finite set of one variable polynomial equations. The scheme is especially efficient for a specified eigenstate of the model, for example, the ground state. Some low-lying level energies of the model for several sets of parameters are calculated, of which one set of the results is compared to that obtained from the Braak’s exact solution proposed recently. It is shown that the derivative of the entanglement measure defined in terms of the reduced von Neumann entropy with respect to the coupling parameter does reach the maximum near the critical point deduced from the classical limit of the Dicke model, which may provide a probe of the critical point of the crossover in finite quantum many-body systems, such as that in the quantum Rabi model. (paper)
Energy Technology Data Exchange (ETDEWEB)
Prudaev, I. A., E-mail: funcelab@gmail.com; Kopyev, V. V.; Romanov, I. S.; Oleynik, V. L. [National Research Tomsk State University (Russian Federation)
2017-02-15
The dependences of the quantum efficiency of InGaN/GaN multiple quantum well light-emitting diodes on the temperature and excitation level are studied. The experiment is performed for two luminescence excitation modes. A comparison of the results obtained during photo- and electroluminescence shows an additional (to the loss associated with Auger recombination) low-temperature loss in the high-density current region. This causes inversion of the temperature dependence of the quantum efficiency at temperatures lower than 220–300 K. Analysis shows that the loss is associated with electron leakage from the light-emitting-diode active region. The experimental data are explained using the ballistic-overflow model. The simulation results are in qualitative agreement with the experimental dependences of the quantum efficiency on temperature and current density.
Reshchikov, M. A.; Foussekis, M.; McNamara, J. D.; Behrends, A.; Bakin, A.; Waag, A.
2012-04-01
The optical properties of high-quality GaN co-doped with silicon and zinc are investigated by using temperature-dependent continuous-wave and time-resolved photoluminescence measurements. The blue luminescence band is related to the ZnGa acceptor in GaN:Si,Zn, which exhibits an exceptionally high absolute internal quantum efficiency (IQE). An IQE above 90% was calculated for several samples having different concentrations of Zn. Accurate and reliable values of the IQE were obtained by using several approaches based on rate equations. The concentrations of the ZnGa acceptors and free electrons were also estimated from the photoluminescence measurements.
"High Quantum Efficiency of Band-Edge Emission from ZnO Nanowires"
Energy Technology Data Exchange (ETDEWEB)
GARGAS, DANIEL; GAO, HANWEI; WANG, HUNGTA; PEIDONG, YANG
2010-12-01
External quantum efficiency (EQE) of photoluminescence as high as 20 percent from isolated ZnO nanowires were measured at room temperature. The EQE was found to be highly dependent on photoexcitation density, which underscores the importance of uniform optical excitation during the EQE measurement. An integrating sphere coupled to a microscopic imaging system was used in this work, which enabled the EQE measurement on isolated ZnO nanowires. The EQE values obtained here are significantly higher than those reported for ZnO materials in forms of bulk, thin films or powders. Additional insight on the radiative extraction factor of one-dimensional nanostructures was gained by measuring the internal quantum efficiency of individual nanowires. Such quantitative EQE measurements provide a sensitive, noninvasive method to characterize the optical properties of low-dimensional nanostructures and allow tuning of synthesis parameters for optimization of nanoscale materials.
Quantum efficiencies of near-infrared emission from Ni2+-doped glass-ceramics
International Nuclear Information System (INIS)
Suzuki, Takenobu; Arai, Yusuke; Ohishi, Yasutake
2008-01-01
A systematic method to evaluate potentials of Ni 2+ -doped transparent glass-ceramics as a new broadband optical gain media is presented. At first, near-infrared emission of various ceramics were investigated to explore the suitable crystalline phase to be grown in the glass-ceramics. The quantum efficiency of Ni 2+ near-infrared emission estimated by the Struck-Fonger analysis was higher than 95% for spinel-type structure gallate crystals MgGa 2 O 4 and LiGa 5 O 8 at room temperature. Transparent glass-ceramics containing Ni 2+ :LiGa 5 O 8 could be prepared and the quantum efficiency for the glass-ceramics was measured to be about 10%. This value shows a potential of Ni-doped transparent glass-ceramics as a broadband gain media
Enhanced quantum efficiency for CsI grown on a graphite-based substrate coating
Friese, J; Homolka, J; Kastenmüller, A; Maier-Komor, P; Peter, M; Zeitelhack, K; Kienle, P; Körner, H J
1999-01-01
Quantum efficiencies (QE) in the vacuum ultraviolet (VUV) wavelength region have been measured for solid CsI layers on various substrates. The CsI films were deposited applying electron beam evaporation. The QE measurements were performed utilizing synchrotron radiation as well as light from a deuterium lamp. A GaAsP diode with a sensitivity calibration traceable to a primary radiation standard was used for normalization. For CsI layers grown on resin-stabilized graphite films a significant enhancement of QE was observed. Substrates suitable for gas detector applications and aging properties were investigated. The procedures to prepare and reproduce high quantum efficient CsI layers are described.
Kaya, Mine; Hajimirza, Shima
2018-05-25
This paper uses surrogate modeling for very fast design of thin film solar cells with improved solar-to-electricity conversion efficiency. We demonstrate that the wavelength-specific optical absorptivity of a thin film multi-layered amorphous-silicon-based solar cell can be modeled accurately with Neural Networks and can be efficiently approximated as a function of cell geometry and wavelength. Consequently, the external quantum efficiency can be computed by averaging surrogate absorption and carrier recombination contributions over the entire irradiance spectrum in an efficient way. Using this framework, we optimize a multi-layer structure consisting of ITO front coating, metallic back-reflector and oxide layers for achieving maximum efficiency. Our required computation time for an entire model fitting and optimization is 5 to 20 times less than the best previous optimization results based on direct Finite Difference Time Domain (FDTD) simulations, therefore proving the value of surrogate modeling. The resulting optimization solution suggests at least 50% improvement in the external quantum efficiency compared to bare silicon, and 25% improvement compared to a random design.
Extent of the Immirzi ambiguity in quantum general relativity
International Nuclear Information System (INIS)
Marugan, Guillermo A Mena
2002-01-01
The Ashtekar-Barbero formulation of general relativity admits a one-parameter family of canonical transformations that preserves the expressions of the Gauss and diffeomorphism constraints. The loop quantization of the connection formalism based on each of these canonical sets leads to different predictions. This phenomenon is called the Immirzi ambiguity. It has been recently argued that this ambiguity could be generalized to the extent of a spatially dependent function instead of a parameter. This would ruin the predictability of loop quantum gravity. We prove that such expectations are not realized, so that the Immirzi ambiguity introduces exclusively a freedom in the choice of a real number. (letter to the editor)
Indefinite-metric quantum field theory of general relativity, 5
International Nuclear Information System (INIS)
Nakanishi, Noboru
1979-01-01
The indefinite-metric quantum field theory of general relativity is extended to the coupled system of the gravitational field and a Dirac field on the basis of the vierbein formalism. The six extra degrees of freedom involved in vierbein are made unobservable by introducing an extra subsidiary condition Q sub(s) + phys> = 0, where Q sub(s) denotes a new BRS charge corresponding to the local Lorentz invariance. It is shown that a manifestly covariant, unitary, canonical theory can be constructed consistently on the basis of the vierbein formalism. (author)
Free-electron laser and related quantum beams
International Nuclear Information System (INIS)
Minehara, Eisuke J.
2003-01-01
Past, present and future development programs of the JAERI super-conducting rf linac-based FELs and light sources with and without energy recovery have been discussed and introduced briefly. The JAERI FEL group has successfully discovered, and realized the brand-new FEL lasing mode of 255 fs ultra fast pulse, 6-9% high-efficiency, one GW high peak power, a few kW average power, and wide tunability of medium and far infrared wavelength regions at the same time. Using the new lasing, we could realize a powerful and efficient free-electron laser (FEL) for industrial uses near future. In order to realize such a tunable, ultra-short-pulse, high averaged-power FEL, we have needed the efficient and powerful CW FEL driver of the JAERI compact, stand-alone and zero-boil-off super-conducting rf linac with an energy-recovery geometry. The JAERI energy-recovery and/or super-conducting rf linac driver has been developed to use as an industrial electron irradiator, and millimeter-wave, far-infrared, mid-infrared, near-infrared and shorter wavelength quantum beam sources. (author)
Free-electron laser and related quantum beams
Energy Technology Data Exchange (ETDEWEB)
Minehara, Eisuke J [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment
2003-07-01
Past, present and future development programs of the JAERI super-conducting rf linac-based FELs and light sources with and without energy recovery have been discussed and introduced briefly. The JAERI FEL group has successfully discovered, and realized the brand-new FEL lasing mode of 255 fs ultra fast pulse, 6-9% high-efficiency, one GW high peak power, a few kW average power, and wide tunability of medium and far infrared wavelength regions at the same time. Using the new lasing, we could realize a powerful and efficient free-electron laser (FEL) for industrial uses near future. In order to realize such a tunable, ultra-short-pulse, high averaged-power FEL, we have needed the efficient and powerful CW FEL driver of the JAERI compact, stand-alone and zero-boil-off super-conducting rf linac with an energy-recovery geometry. The JAERI energy-recovery and/or super-conducting rf linac driver has been developed to use as an industrial electron irradiator, and millimeter-wave, far-infrared, mid-infrared, near-infrared and shorter wavelength quantum beam sources. (author)
Energy Technology Data Exchange (ETDEWEB)
Bernstein, J.D.; Olson, J.M.
1981-01-01
Photohydrogen production, 200-700 ..mu..mol H/sub 2/ h/sup -1/ (mg bacteriochlorophyll a)/sup -1/ has been obtained in a system containing unit membrane vesicles (Complex I) from the green photosynthetic bacterium Chlorobium limicola f. thiosulfatophilum, ascorbate, N,N,N',N'-tetramethyl-p-phenylenediamine, dithioerythritol, an oxygen scavenging mixture, either methyl viologen (MV) or clostridial ferredoxin (CPS Fd) as electron carrier, and either CPS hydrogenase or platinum asbestos as catalyst. All components are necessary for maximum activity, and spinach Fd cannot be substituted for CPS Fd. Higher rates of photohydrogen production are obtained using MV or CPS Fd with hydrogenase than with MV and Pt asbestos. The highest quantum efficiencies (7-10% at 0.2-0.9 mW absorbed light and over 20% at lower light) were obtained with CPS Fd, hydrogenase and non-saturating 812 nm light. With saturating white light, however, rates of photohydrogen production varied relatively little among the various combinations of electron carrier and catalyst tested. The reaction rate is unaffected by 0.03% Triton X-100, and is insensitive to treatment with antimycin a or m-chloro-carbonyl cyanide phenylhydrazone.This indicates that neither electron flow through an endogenous cyclic chain, nor maintenance of a proton gradient are involved in this process.
Kearns, F L; Hudson, P S; Boresch, S; Woodcock, H L
2016-01-01
Enzyme activity is inherently linked to free energies of transition states, ligand binding, protonation/deprotonation, etc.; these free energies, and thus enzyme function, can be affected by residue mutations, allosterically induced conformational changes, and much more. Therefore, being able to predict free energies associated with enzymatic processes is critical to understanding and predicting their function. Free energy simulation (FES) has historically been a computational challenge as it requires both the accurate description of inter- and intramolecular interactions and adequate sampling of all relevant conformational degrees of freedom. The hybrid quantum mechanical molecular mechanical (QM/MM) framework is the current tool of choice when accurate computations of macromolecular systems are essential. Unfortunately, robust and efficient approaches that employ the high levels of computational theory needed to accurately describe many reactive processes (ie, ab initio, DFT), while also including explicit solvation effects and accounting for extensive conformational sampling are essentially nonexistent. In this chapter, we will give a brief overview of two recently developed methods that mitigate several major challenges associated with QM/MM FES: the QM non-Boltzmann Bennett's acceptance ratio method and the QM nonequilibrium work method. We will also describe usage of these methods to calculate free energies associated with (1) relative properties and (2) along reaction paths, using simple test cases with relevance to enzymes examples. © 2016 Elsevier Inc. All rights reserved.
Entanglement growth and simulation efficiency in one-dimensional quantum lattice systems
Perales, Alvaro; Vidal, Guifre
2007-01-01
We study the evolution of one-dimensional quantum lattice systems when the ground state is perturbed by altering one site in the middle of the chain. For a large class of models, we observe a similar pattern of entanglement growth during the evolution, characterized by a moderate increase of significant Schmidt coefficients in all relevant bipartite decompositions of the state. As a result, the evolution can be accurately described by a matrix product state and efficiently simulated using the...
Wu, Feng; Sun, Haiding; Ajia, Idris A.; Roqan, Iman S.; Zhang, Daliang; Dai, Jiangnan; Chen, Changqing; Feng, Zhe Chuan; Li, Xiaohang
2017-01-01
Significant internal quantum efficiency (IQE) enhancement of GaN/AlGaN multiple quantum wells (MQWs) emitting at similar to 350 nm was achieved via a step quantum well (QW) structure design. The MQW structures were grown on AlGaN/AlN/sapphire templates by metal-organic chemical vapor deposition (MOCVD). High resolution x-ray diffraction (HR-XRD) and scanning transmission electron microscopy (STEM) were performed, showing sharp interface of the MQWs. Weak beam dark field imaging was conducted, indicating a similar dislocation density of the investigated MQWs samples. The IQE of GaN/AlGaN MQWs was estimated by temperature dependent photoluminescence (TDPL). An IQE enhancement of about two times was observed for the GaN/AlGaN step QW structure, compared with conventional QW structure. Based on the theoretical calculation, this IQE enhancement was attributed to the suppressed polarization-induced field, and thus the improved electron-hole wave-function overlap in the step QW.
Wu, Feng
2017-05-03
Significant internal quantum efficiency (IQE) enhancement of GaN/AlGaN multiple quantum wells (MQWs) emitting at similar to 350 nm was achieved via a step quantum well (QW) structure design. The MQW structures were grown on AlGaN/AlN/sapphire templates by metal-organic chemical vapor deposition (MOCVD). High resolution x-ray diffraction (HR-XRD) and scanning transmission electron microscopy (STEM) were performed, showing sharp interface of the MQWs. Weak beam dark field imaging was conducted, indicating a similar dislocation density of the investigated MQWs samples. The IQE of GaN/AlGaN MQWs was estimated by temperature dependent photoluminescence (TDPL). An IQE enhancement of about two times was observed for the GaN/AlGaN step QW structure, compared with conventional QW structure. Based on the theoretical calculation, this IQE enhancement was attributed to the suppressed polarization-induced field, and thus the improved electron-hole wave-function overlap in the step QW.
Brennan, Thomas P.; Trejo, Orlando; Roelofs, Katherine E.; Xu, John; Prinz, Fritz B.; Bent, Stacey F.
2013-01-01
Atomic layer deposition (ALD) was used to grow both PbS quantum dots and Al2O3 barrier layers in a solid-state quantum dot-sensitized solar cell (QDSSC). Barrier layers grown prior to quantum dots resulted in a near-doubling of device efficiency (0.30% to 0.57%) whereas barrier layers grown after quantum dots did not improve efficiency, indicating the importance of quantum dots in recombination processes. © 2013 The Royal Society of Chemistry.
An energy and cost efficient majority-based RAM cell in quantum-dot cellular automata
Directory of Open Access Journals (Sweden)
Milad Bagherian Khosroshahy
Full Text Available Nanotechnologies, notably quantum-dot cellular automata, have achieved major attentions for their prominent features as compared to the conventional CMOS circuitry. Quantum-dot cellular automata, particularly owning to its considerable reduction in size, high switching speed and ultra-low energy consumption, is considered as a potential alternative for the CMOS technology. As the memory unit is one of the most essential components in a digital system, designing a well-optimized QCA random access memory (RAM cell is an important area of research. In this paper, a new five-input majority gate is presented which is suitable for implementing efficient single-layer QCA circuits. In addition, a new RAM cell with set and reset capabilities is designed based on the proposed majority gate, which has an efficient and low-energy structure. The functionality, performance and energy consumption of the proposed designs are evaluated based on the QCADesigner and QCAPro tools. According to the simulation results, the proposed RAM design leads to on average 38% lower total energy dissipation, 25% smaller area, 20% lower cell count, 28% lower delay and 60% lower QCA cost as compared to its previous counterparts. Keywords: Quantum-dot cellular automata (QCA, Majority gate, Random access memory (RAM, Energy efficiency
Quantum efficiency and excited-state relaxation dynamics in neodymium-doped phosphate laser glasses
International Nuclear Information System (INIS)
Caird, J.A.; Ramponi, A.J.; Staver, P.R.
1991-01-01
Radiometrically calibrated spectroscopic techniques employing an integrating-sphere detection system have been used to determine the fluorescence quantum efficiencies for two commercially available Nd 3+ -doped phosphate laser glasses, LG-750 and LG-760. Quantum efficiencies and fluorescence lifetimes were measured for samples with various neodymium concentrations. It is shown that the effects of concentration quenching are accurately described when both resonant nonradiative excitation hopping (the Burshtein model) and annihilation by cross relaxation are accounted for by Foerster--Dexter dipole--dipole energy-transfer theory. The Foerster--Dexter critical range for nonradiative excitation hopping was found to be R DD =11 A, while the critical range for cross relaxation was close to R DA =4 A in these glasses. The quantum efficiency at low Nd 3+ concentrations was (92±5)%, implying a nonradiative relaxation rate of 210±150 s -1 for isolated ions. Improved values for the radiative lifetimes and the stimulated emission cross sections for these glasses were also deduced from the measurements
Fluctuation relation for heat exchange in Markovian open quantum systems
Ramezani, M.; Golshani, M.; Rezakhani, A. T.
2018-04-01
A fluctuation relation for the heat exchange of an open quantum system under a thermalizing Markovian dynamics is derived. We show that the probability that the system absorbs an amount of heat from its bath, at a given time interval, divided by the probability of the reverse process (releasing the same amount of heat to the bath) is given by an exponential factor which depends on the amount of heat and the difference between the temperatures of the system and the bath. Interestingly, this relation is akin to the standard form of the fluctuation relation (for forward-backward dynamics). We also argue that the probability of the violation of the second law of thermodynamics in the form of the Clausius statement (i.e., net heat transfer from a cold system to its hot bath) drops exponentially with both the amount of heat and the temperature differences of the baths.
Efficiency of free-energy calculations of spin lattices by spectral quantum algorithms
International Nuclear Information System (INIS)
Master, Cyrus P.; Yamaguchi, Fumiko; Yamamoto, Yoshihisa
2003-01-01
Ensemble quantum algorithms are well suited to calculate estimates of the energy spectra for spin-lattice systems. Based on the phase estimation algorithm, these algorithms efficiently estimate discrete Fourier coefficients of the density of states. Their efficiency in calculating the free energy per spin of general spin lattices to bounded error is examined. We find that the number of Fourier components required to bound the error in the free energy due to the broadening of the density of states scales polynomially with the number of spins in the lattice. However, the precision with which the Fourier components must be calculated is found to be an exponential function of the system size
A novel high-efficiency single-mode quantum dot single photon source
DEFF Research Database (Denmark)
Gerard, J.M.; Gregersen, Niels; Nielsen, Torben Roland
2008-01-01
We present a novel single-mode single photon source exploiting the emission of a semiconductor quantum dot (QD) located inside a photonic wire. Besides an excellent coupling (>95%) of QD spontaneous emission to the fundamental guided mode [1], we show that a single photon collection efficiency...... above 80% within a 0.5 numerical aperture can be achieved using a bottom Bragg mirror and a tapering of the nanowire tip. Because this photon collection strategy does not exploit the Purcell effect, it could also be efficiently applied to broadband single photon emitters such as F-centers in diamond....
Minimum detection efficiency for the loophole-free confirmation of quantum contextuality
International Nuclear Information System (INIS)
Xiang Yang; Hong Fang-Yu
2013-01-01
Klyachko—Can—Binicioğlu—Shumovsky (KCBS) inequality is a Bell-like inequality, the violation of which can be used to confirm the existence of quantum contextuality. However, the imperfection of detection efficiency may cause the so-called loophole in actual KCBS's experiments. We derive an alternative KCBS inequality to deal with the loophole in actual KCBS's experiments. We prove that if the experimental data violate this KCBS inequality, the loophole-free violation of the original KCBS inequality will occur. We show that the minimum detection efficiency needed for a loophole-free violation of the KCBS inequality is about 0.9738
International Nuclear Information System (INIS)
Wei, L.F.; Nori, Franco
2003-01-01
Based on the exact conditional quantum dynamics for a two-ion system, we propose an efficient single-step scheme for coherently manipulating quantum information of two trapped cold ions by using a pair of synchronous laser pulses. Neither the auxiliary atomic level nor the Lamb-Dicke approximation are needed
Dispersion relations in quantum electrodynamics on the noncommutative Minkowski space
Energy Technology Data Exchange (ETDEWEB)
Zahn, J.W.
2006-12-15
We study field theories on the noncommutative Minkowski space with noncommuting time. The focus lies on dispersion relations in quantized interacting models in the Yang-Feldman formalism. In particular, we compute the two-point correlation function of the field strength in noncommutative quantum electrodynamics to second order. At this, we take into account the covariant coordinates that allow the construction of local gauge invariant quantities (observables). It turns out that this does not remove the well-known severe infrared problem, as one might have hoped. Instead, things become worse, since nonlocal divergences appear. We also show that these cancel in a supersymmetric version of the theory if the covariant coordinates are adjusted accordingly. Furthermore, we study the {phi}{sup 3} and the Wess-Zumino model and show that the distortion of the dispersion relations is moderate for parameters typical for the Higgs field. We also discuss the formulation of gauge theories on noncommutative spaces and study classical electrodynamics on the noncommutative Minkowski space using covariant coordinates. In particular, we compute the change of the speed of light due to nonlinear effects in the presence of a background field. Finally, we examine the so-called twist approach to quantum field theory on the noncommutative Minkowski space and point out some conceptual problems of this approach. (orig.)
Dispersion relations in quantum electrodynamics on the noncommutative Minkowski space
International Nuclear Information System (INIS)
Zahn, J.W.
2006-12-01
We study field theories on the noncommutative Minkowski space with noncommuting time. The focus lies on dispersion relations in quantized interacting models in the Yang-Feldman formalism. In particular, we compute the two-point correlation function of the field strength in noncommutative quantum electrodynamics to second order. At this, we take into account the covariant coordinates that allow the construction of local gauge invariant quantities (observables). It turns out that this does not remove the well-known severe infrared problem, as one might have hoped. Instead, things become worse, since nonlocal divergences appear. We also show that these cancel in a supersymmetric version of the theory if the covariant coordinates are adjusted accordingly. Furthermore, we study the Φ 3 and the Wess-Zumino model and show that the distortion of the dispersion relations is moderate for parameters typical for the Higgs field. We also discuss the formulation of gauge theories on noncommutative spaces and study classical electrodynamics on the noncommutative Minkowski space using covariant coordinates. In particular, we compute the change of the speed of light due to nonlinear effects in the presence of a background field. Finally, we examine the so-called twist approach to quantum field theory on the noncommutative Minkowski space and point out some conceptual problems of this approach. (orig.)
Furno, Mauro; Rosenow, Thomas C.; Gather, Malte C.; Lüssem, Björn; Leo, Karl
2012-10-01
We report on a theoretical framework for the efficiency analysis of complex, multi-emitter organic light emitting diodes (OLEDs). The calculation approach makes use of electromagnetic modeling to quantify the overall OLED photon outcoupling efficiency and a phenomenological description for electrical and excitonic processes. From the comparison of optical modeling results and measurements of the total external quantum efficiency, we obtain reliable estimates of internal quantum yield. As application of the model, we analyze high-efficiency stacked white OLEDs and comment on the various efficiency loss channels present in the devices.
Byun, Ho-June; Lee, Ju Chul; Yang, Heesun
2011-03-01
InP quantum dots (QDs) were solvothermally synthesized by using a greener phosphorus source of P(N(CH(3))(2))(3) instead of highly toxic P(TMS)(3) widely used, and subsequently subjected to a size-sorting processing. While as-grown QDs showed an undetectably low emission intensity, post-synthetic treatments such as photo-etching, photo-radiation, and photo-assisted ZnS shell coating gave rise to a substantial increase in emission efficiency due to the effective removal and passivation of surface states. The emission efficiency of the photo-etched QDs was further enhanced by a consecutive UV photo-radiation, attributable to the photo-oxidation at QD surface. Furthermore, a relatively thick ZnS shell on the surface of InP QDs that were surface-modified with hydrophilic ligands beforehand was photochemically generated in an aqueous solution at room temperature. The resulting InP/ZnS core/shell QDs, emitting from blue to red wavelengths, were more efficient than the above photo-treated InP QDs, and their luminescent properties (emission bandwidth and quantum yield) were comparable to those of InP QDs synthesized with P(TMS)(3). Structural, size, and compositional analyses on InP/ZnS QDs were also conducted to elucidate their core/shell structure. Copyright © 2010 Elsevier Inc. All rights reserved.
InP/ZnSe/ZnS core-multishell quantum dots for improved luminescence efficiency
Greco, Tonino; Ippen, Christian; Wedel, Armin
2012-04-01
Semiconductor quantum dots (QDs) exhibit unique optical properties like size-tunable emission color, narrow emission peak, and high luminescence efficiency. QDs are therefore investigated towards their application in light-emitting devices (QLEDs), solar cells, and for bio-imaging purposes. In most cases QDs made from cadmium compounds like CdS, CdSe or CdTe are studied because of their facile and reliable synthesis. However, due to the toxicity of Cd compounds and the corresponding regulation (e.g. RoHS directive in Europe) these materials are not feasible for customer applications. Indium phosphide is considered to be the most promising alternative because of the similar band gap (InP 1.35 eV, CdSe 1.73 eV). InP QDs do not yet reach the quality of CdSe QDs, especially in terms of photoluminescence quantum yield and peak width. Typically, QDs are coated with another semiconductor material of wider band gap, often ZnS, to passivate surface defects and thus improve luminescence efficiency. Concerning CdSe QDs, multishell coatings like CdSe/CdS/ZnS or CdSe/ZnSe/ZnS have been shown to be advantageous due to the improved compatibility of lattice constants. Here we present a method to improve the luminescence efficiency of InP QDs by coating a ZnSe/ZnS multishell instead of a ZnS single shell. ZnSe exhibits an intermediate lattice constant of 5.67 Å between those of InP (5.87 Å) and ZnS (5.41 Å) and thus acts as a wetting layer. As a result, InP/ZnSe/ZnS is introduced as a new core-shell quantum dot material which shows improved photoluminescence quantum yield (up to 75 %) compared to the conventional InP/ZnS system.
Evidence on the relation between public capital and Government efficiency
Francisca Guedes de Oliveira
2010-01-01
This paper intends to contribute to the literature by providing empirical evidence on the relation between public capital stock and government efficiency. We present some objective indicators fo government efficiency and explore the mentioned relation. we find a positive and significant relation between both variables that survives the introduction of controls and robustness checking.
Zhang, Zhanjun
2004-01-01
Comment: The wrong mutual information, quantum bit error rate and secure transmission efficiency in Wojcik's eavesdropping scheme [PRL90(03)157901]on ping-pong protocol have been pointed out and corrected
Indefinite-metric quantum field theory of general relativity
International Nuclear Information System (INIS)
Nakanishi, Noboru
1978-01-01
Quantum field theory of Einstein's general relativity is formulated in the indefinitemetric Hilbert space in such a way that asymptotic fields are manifestly Lorentz covariant and the physical S-matrix is unitary. The general coordinate transformation is transcribed into a q-number transformation, called the BRS transformation. Its abstract definition is presented on the basis of the BRS transformation for the Yang-Mills theory. The BRS transformation for general relativity is then explicitly constructed. The gauge-fixing Lagrangian density and the Faddeev-Popov one are introduced in such a way that their sum behaves like a scalar density under the BRS transformation. One can then proceed in the same way as in the Kugo-Ojima formalism of the Yang-Mills theory to establish the unitarity of the physical S-matrix. (author)
Quantum efficiency of silica-coated rare-earth doped yttrium silicate
Energy Technology Data Exchange (ETDEWEB)
Cervantes-Vásquez, D., E-mail: dcervant@cnyn.unam.mx [Centro de Investigación Científica y de Educación Superior de Ensenada, Carretera Ensenada-Tijuana No. 3918, Zona Playitas, C.P. 22860 Ensenada, B.C., México (Mexico); Contreras, O.E.; Hirata, G.A. [Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México, Km. 107 Carretera Tijuana-Ensenada, C.P. 22800 Ensenada, B.C., México (Mexico)
2013-11-15
The photoluminescent properties of rare earth-activated white-emitting Y{sub 2}SiO{sub 5}:Ce,Tb nanocrystalline phosphor prepared by two different methods, pressure-assisted combustion synthesis and sol–gel, were studied. The synthesized phosphor samples were post-annealed at 1373 K and 1623 K in order to obtain the X1-Y{sub 2}SiO{sub 5} and X2-Y{sub 2}SiO{sub 5} phases, respectively, which were confirmed by X-ray diffraction measurements. Photoluminescence analysis showed the contribution of two blue-emission bands within the 380–450 nm region originating from 5d–4f transitions in Ce{sup 3+} ions and a well-defined green emission of Tb{sup 3+} ions located at 545 nm corresponding to {sup 5}D{sub 4}→{sup 7}F{sub 5} electronic transitions. Thereafter, Y{sub 2}SiO{sub 5}:Ce,Tb powders were coated with colloidal silica in order to investigate the effect of silica coatings on their luminescent properties. Absolute fluorescence quantum efficiency measurements were carefully performed, which revealed an increase of 12% of efficiency in coated compared with bare-Y{sub 2}SiO{sub 5}:Ce,Tb phosphor. -- Highlights: • Y{sub 2}SiO{sub 5}:Ce,Tb phosphor powders were successfully coated with colloidal silica. • Post-annealing treatments improved the quantum efficiency of silica-coated Y{sub 2}SiO{sub 5}:Ce,Tb phosphors. • Absolute fluorescence quantum efficiency measurements showed an increase of 12%.
International Nuclear Information System (INIS)
Park, Jong Hyeok; Lim, Yong Taik; Park, O Ok; Yu, Jae-Woong; Kim, Jai Kyeong; Kim, Young Chul
2004-01-01
Light-emitting devices based on environmentally stable, blue-emitting polymer/dielectric nanolayer nanocomposites were fabricated by blending poly(di-octylfluorene) (PDOF) with organo-clay. By reducing the excimer formation that leads to long wavelength tails, the photoluminescence (PL) and electroluminescence (EL) color purity of the device was enhanced. When a conjugated polymer/dielectric nanolayer nanocomposite is applied to an EL device, we expect an electronic structure similar to the well-known quantum well in small nanodomains. The ratio of PDOF/organo-clay was regulated from 2:1 to 0.5:1 (w/w). The light-emitting device of 0.5:1 (w/w) blend demonstrated the highest quantum efficiency (QE), 0.72% (ph/el), which is ∼500 times higher value compared with that of the pure PDOF layer device. However, the driving voltage of the nanocomposite devices tended to increase with increasing organo-clay content
Smolin, John A; Gambetta, Jay M; Smith, Graeme
2012-02-17
We provide an efficient method for computing the maximum-likelihood mixed quantum state (with density matrix ρ) given a set of measurement outcomes in a complete orthonormal operator basis subject to Gaussian noise. Our method works by first changing basis yielding a candidate density matrix μ which may have nonphysical (negative) eigenvalues, and then finding the nearest physical state under the 2-norm. Our algorithm takes at worst O(d(4)) for the basis change plus O(d(3)) for finding ρ where d is the dimension of the quantum state. In the special case where the measurement basis is strings of Pauli operators, the basis change takes only O(d(3)) as well. The workhorse of the algorithm is a new linear-time method for finding the closest probability distribution (in Euclidean distance) to a set of real numbers summing to one.
Quantum Coherent Three-Terminal Thermoelectrics: Maximum Efficiency at Given Power Output
Directory of Open Access Journals (Sweden)
Robert S. Whitney
2016-05-01
Full Text Available This work considers the nonlinear scattering theory for three-terminal thermoelectric devices used for power generation or refrigeration. Such systems are quantum phase-coherent versions of a thermocouple, and the theory applies to systems in which interactions can be treated at a mean-field level. It considers an arbitrary three-terminal system in any external magnetic field, including systems with broken time-reversal symmetry, such as chiral thermoelectrics, as well as systems in which the magnetic field plays no role. It is shown that the upper bound on efficiency at given power output is of quantum origin and is stricter than Carnot’s bound. The bound is exactly the same as previously found for two-terminal devices and can be achieved by three-terminal systems with or without broken time-reversal symmetry, i.e., chiral and non-chiral thermoelectrics.
Improvement of quantum efficiency in green light-emitting diodes with pre-TMIn flow treatment
International Nuclear Information System (INIS)
Lee, Ya-Ju; Chen, Yi-Ching; Lu, Tien-Chang
2011-01-01
The effects of pre-trimethlyindium (TMIn) flow on the improved electrical characteristics and highly stable temperature properties of InGaN green light-emitting diodes (LEDs) are discussed. For the LED sample with a pre-TMIn flow treatment, the tunnelling of injected carriers associated with threading defects is significantly reduced, which promotes the diffusion-recombination of injected carriers, as well as the overall emission efficiency of the LED. In addition, the pre-TMIn flow treatment evidently reduces the dependence of external quantum efficiency on temperature and efficiency droop of green LEDs. As a result, we conclude that the pre-TMIn flow treatment is a promising scheme for the improvement of output performance of InGaN-based green LEDs.
Tsai, Meng-Lin; Tu, Wei-Chen; Tang, Libin; Wei, Tzu-Chiao; Wei, Wan-Rou; Lau, Shu Ping; Chen, Lih-Juann; He, Jr-Hau
2015-01-01
By employing graphene quantum dots (GQDs), we have achieved a high efficiency of 16.55% in n-type Si heterojunction solar cells. The efficiency enhancement is based on the photon downconversion phenomenon of GQDs to make more photons absorbed in the depletion region for effective carrier separation, leading to the enhanced photovoltaic effect. The short circuit current and the fill factor are increased from 35.31 to 37.47 mA/cm2 and 70.29% to 72.51%, respectively. The work demonstrated here holds the promise for incorporating graphene-based materials in commercially available solar devices for developing ultra-high efficiency photovoltaic cells in the future.
Tsai, Meng-Lin
2015-12-16
By employing graphene quantum dots (GQDs), we have achieved a high efficiency of 16.55% in n-type Si heterojunction solar cells. The efficiency enhancement is based on the photon downconversion phenomenon of GQDs to make more photons absorbed in the depletion region for effective carrier separation, leading to the enhanced photovoltaic effect. The short circuit current and the fill factor are increased from 35.31 to 37.47 mA/cm2 and 70.29% to 72.51%, respectively. The work demonstrated here holds the promise for incorporating graphene-based materials in commercially available solar devices for developing ultra-high efficiency photovoltaic cells in the future.
Quantum quenches in the Luttinger model and its close relatives
Cazalilla, M. A.; Chung, Ming-Chiang
2016-06-01
A number of results on quantum quenches in the Luttinger and related models are surveyed with emphasis on post-quench correlations. For the Luttinger model and initial gaussian states, we discuss both sudden and smooth quenches of the interaction and the emergence of a steady state described by a generalized Gibbs ensemble. Comparisons between analytics and numerics, and the question of universality or lack thereof are also discussed. The relevance of the theoretical results to current and future experiments in the fields of ultracold atomic gases and mesoscopic systems of electrons is also briefly touched upon. Wherever possible, our approach is pedagogical and self-contained. This work is dedicated to the memory of our colleague Alejandro Muramatsu.
Relating zeta functions of discrete and quantum graphs
Harrison, Jonathan; Weyand, Tracy
2018-02-01
We write the spectral zeta function of the Laplace operator on an equilateral metric graph in terms of the spectral zeta function of the normalized Laplace operator on the corresponding discrete graph. To do this, we apply a relation between the spectrum of the Laplacian on a discrete graph and that of the Laplacian on an equilateral metric graph. As a by-product, we determine how the multiplicity of eigenvalues of the quantum graph, that are also in the spectrum of the graph with Dirichlet conditions at the vertices, depends on the graph geometry. Finally we apply the result to calculate the vacuum energy and spectral determinant of a complete bipartite graph and compare our results with those for a star graph, a graph in which all vertices are connected to a central vertex by a single edge.
Surrealism, art, and modern science relativity, quantum mechanics, epistemology
Parkinson, Gavin
2008-01-01
During the same period that Surrealism originated and flourished between the wars, great advances were being made in the field of physics. This book offers the first full history, analysis and interpretation of Surrealism's engagement with the theory of relativity and quantum mechanics, and its reception of the philosophical consequences of those two major turning points in our understanding of the physical world. After surveying the revolution in physics in the early twentieth century and the discoveries of Planck, Bohr, Einstein, Schrodinger, and others, Gavin Parkinson explores the diverse uses of physics by individuals in and around the Surrealist group in Paris. In so doing, he offers exciting new readings of the art and writings of such key figures of the Surrealist milieu as André Breton, Georges Bataille, Salvador Dalí, Roger Caillois, Max Ernst, and Tristan Tzara.
Relative fault and efficient negligence: Comparative negligence explained
Dari-Mattiacci, G.; Hendriks, E.S.
2013-01-01
This paper shows that the rule of comparative negligence with relative fault - a sharing of the loss proportional to the parties’ relative departures from due care - induces the parties to an accident to be efficiently negligent. Comparative negligence is more efficient than simple or contributory
Achieving the classical Carnot efficiency in a strongly coupled quantum heat engine
Xu, Y. Y.; Chen, B.; Liu, J.
2018-02-01
Generally, the efficiency of a heat engine strongly coupled with a heat bath is less than the classical Carnot efficiency. Through a model-independent method, we show that the classical Carnot efficiency is achieved in a strongly coupled quantum heat engine. First, we present the first law of quantum thermodynamics in strong coupling. Then, we show how to achieve the Carnot cycle and the classical Carnot efficiency at strong coupling. We find that this classical Carnot efficiency stems from the fact that the heat released in a nonequilibrium process is balanced by the absorbed heat. We also analyze the restrictions in the achievement of the Carnot cycle. The first restriction is that there must be two corresponding intervals of the controllable parameter in which the corresponding entropies of the work substance at the hot and cold temperatures are equal, and the second is that the entropy of the initial and final states in a nonequilibrium process must be equal. Through these restrictions, we obtain the positive work conditions, including the usual one in which the hot temperature should be higher than the cold, and a new one in which there must be an entropy interval at the hot temperature overlapping that at the cold. We demonstrate our result through a paradigmatic model—a two-level system in which a work substance strongly interacts with a heat bath. In this model, we find that the efficiency may abruptly decrease to zero due to the first restriction, and that the second restriction results in the control scheme becoming complex.
Samant, Sanjiv S.; Gopal, Arun; DiBianca, Frank A.
2003-06-01
Megavoltage x-ray imaging suffers from relatively poor contrast and spatial resolution compared to diagnostic kilovoltage x-ray imaging due to the dominant Compton scattering in the former. Recently available amorphous silicon/selenium based flat-panel imagers overcome many of the limitations of poor contrast and spatial resolution that affect conventional video based electronic portal imaging devices (EPIDs). An alternative technology is presented here: kinestatic charge detection (KCD). The KCD uses a slot photon beam, high-pressure gas (xenon, 100 atm) and a multi-ion rectangular chamber in scanning mode. An electric field is used to regulate the cation drift velocity. By matching the scanning speed with that of the cation drift, the cations remain static in the object frame of reference, allowing temporal integration of the signal. KCD imaging is characterized by reduced scatter and a high signal-to-noise ratio. Measurements and Monte Carlo simulations of modulation transfer function (MTF), noise power spectrum (NPS) and the detective quantum efficiency (DQE) of a prototype small field of view KCD detector (384 channels, 0.5 mm spacing) were carried out. Measurements yield DQE[0]=0.19 and DQE[0.5cy/mm]=0.01. KCD imaging is compared to film and commercial EPID systems using phantoms, with the KCD requiring an extremely low dose (0.1 cGy) per image. A proposed cylindrical chamber design with a higher ion-collection depth is expected to further improve image quality (DQE[0]>0.25).
Perez, Luis
Dye-sensitized solar cells (DSSC) have the potential to replace traditional and cost-inefficient crystalline silicon or ruthenium solar cells. This can only be accomplished by optimizing DSSC's energy efficiency. One of the major components in a dye-sensitized solar cell is the porous layer of titanium dioxide. This layer is coated with a molecular dye that absorbs sunlight. The research conducted for this paper focuses on the different methods used to dye the porous TiO2 layer with ferritin-encapsulated quantum dots. Multiple anodes were dyed using a method known as SILAR which involves deposition through alternate immersion in two different solutions. The efficiencies of DSSCs with ferritin-encapsulated lead sulfide dye deposited using SILAR were subsequently compared against the efficiencies produced by cells using the traditional immersion method. It was concluded that both methods resulted in similar efficiencies (? .074%) however, the SILAR method dyed the TiO2 coating significantly faster than the immersion method. On a related note, our experiments concluded that conducting 2 SILAR cycles yields the highest possible efficiency for this particular binding method. National Science Foundation.
Development of III-Sb Quantum Dot Systems for High Efficiency Intermediate Band Solar Cells
Energy Technology Data Exchange (ETDEWEB)
Huffaker, Diana [Univ. of California, Los Angeles, CA (United States); Hubbard, Seth [Rochester Inst. of Technology, NY (United States); Norman, Andrew [National Renewable Energy Lab. (NREL), Golden, CO (United States)
2015-07-31
This project aimed to develop solar cells that can help reduce cost per watt. This work focused on developing solar cells that utilize quantum dot (QD) nanomaterials to provide multijunction solar cell efficiency at the cost of single junction solar cell. We focused on a novel concept known as intermediate band solar cells (IBSC) where an additional energy band is inserted in a single solar cell to accommodate sub-bandgap photons absorption which otherwise are lost through transmission. The additional energy band can be achieved by growing QDs within a solar cell p-n junction. Though numerous studies have been conducted to develop such QD systems, very small improvements in solar energy conversion efficiency have been reported. This is mainly due to non-optimal material parameters such as band gap, band offset etc. In this work, we identified and developed a novel QD material system that meets the requirements of IBSC more closely than the current state-of-the-art technology. To achieve these goals, we focused on three important areas of solar cell design: band structure calculations of new materials, efficient device design for high efficiency, and development of new semiconductor materials. In this project, we focused on III-Sb materials as they possess a wide range of energy bandgaps from 0.2 eV to 2eV. Despite the difficulty involved in realizing these materials, we were successfully developed these materials through a systematic approach. Materials studied in this work are AlAsSb (Aluminum Arsenide Antimonide), InAlAs (Indium Aluminum Arsenide) and InAs (Indium Arsenide). InAs was used to develop QD layers within AlAsSb and InAlAs p-n junctions. As the QDs have very small volume, up to 30 QD layers been inserted into the p-n junction to enhance light absorption. These QD multi-stack devices helped in understanding the challenges associated with the development of quantum dot solar cells. The results from this work show that the quantum dot solar cells indeed
High-efficiency red electroluminescent device based on multishelled InP quantum dots.
Jo, Jung-Ho; Kim, Jong-Hoon; Lee, Ki-Heon; Han, Chang-Yeol; Jang, Eun-Pyo; Do, Young Rag; Yang, Heesun
2016-09-01
We report on the synthesis of highly fluorescent red-emitting InP quantum dots (QDs) and their application to the fabrication of a high-efficiency QD-light-emitting diode (QLED). The core/shell heterostructure of the QDs is elaborately tailored toward a multishelled structure with a composition-gradient ZnSeS intermediate shell and an outer ZnS shell. Using the resulting InP/ZnSeS/ZnS QDs as an emitting layer, all-solution-processible red InP QLEDs are fabricated with a hybrid multilayered device structure having an organic hole transport layer (HTL) and an inorganic ZnO nanoparticle electron transport layer. Two HTLs of poly(9-vinlycarbazole) or poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenyl-amine), whose hole mobilities are different by at least three orders of magnitude, are individually applied for QLED fabrication and such HTL-dependent device performances are compared. Our best red device displays exceptional figures of merit such as a maximum luminance of 2849 cd/m2, a current efficiency of 4.2 cd/A, and an external quantum efficiency of 2.5%.
Private quantum computation: an introduction to blind quantum computing and related protocols
Fitzsimons, Joseph F.
2017-06-01
Quantum technologies hold the promise of not only faster algorithmic processing of data, via quantum computation, but also of more secure communications, in the form of quantum cryptography. In recent years, a number of protocols have emerged which seek to marry these concepts for the purpose of securing computation rather than communication. These protocols address the task of securely delegating quantum computation to an untrusted device while maintaining the privacy, and in some instances the integrity, of the computation. We present a review of the progress to date in this emerging area.
Hardware-efficient bosonic quantum error-correcting codes based on symmetry operators
Niu, Murphy Yuezhen; Chuang, Isaac L.; Shapiro, Jeffrey H.
2018-03-01
We establish a symmetry-operator framework for designing quantum error-correcting (QEC) codes based on fundamental properties of the underlying system dynamics. Based on this framework, we propose three hardware-efficient bosonic QEC codes that are suitable for χ(2 )-interaction based quantum computation in multimode Fock bases: the χ(2 ) parity-check code, the χ(2 ) embedded error-correcting code, and the χ(2 ) binomial code. All of these QEC codes detect photon-loss or photon-gain errors by means of photon-number parity measurements, and then correct them via χ(2 ) Hamiltonian evolutions and linear-optics transformations. Our symmetry-operator framework provides a systematic procedure for finding QEC codes that are not stabilizer codes, and it enables convenient extension of a given encoding to higher-dimensional qudit bases. The χ(2 ) binomial code is of special interest because, with m ≤N identified from channel monitoring, it can correct m -photon-loss errors, or m -photon-gain errors, or (m -1 )th -order dephasing errors using logical qudits that are encoded in O (N ) photons. In comparison, other bosonic QEC codes require O (N2) photons to correct the same degree of bosonic errors. Such improved photon efficiency underscores the additional error-correction power that can be provided by channel monitoring. We develop quantum Hamming bounds for photon-loss errors in the code subspaces associated with the χ(2 ) parity-check code and the χ(2 ) embedded error-correcting code, and we prove that these codes saturate their respective bounds. Our χ(2 ) QEC codes exhibit hardware efficiency in that they address the principal error mechanisms and exploit the available physical interactions of the underlying hardware, thus reducing the physical resources required for implementing their encoding, decoding, and error-correction operations, and their universal encoded-basis gate sets.
International Nuclear Information System (INIS)
Zhang Jun; Li Qian; Di Xiaowei; Liu Zhiliang; Xu Gang
2008-01-01
Multicolored semiconductor quantum dots have shown great promise for construction of miniaturized light-emitting diodes with compact size, low weight and cost, and high luminescent efficiency. The unique size-dependent luminescent property of quantum dots offers the feasibility of constructing single-color or full-color output light-emitting diodes with one type of material. In this paper, we have demonstrated the facile fabrication of blue-, green-, red- and full-color-emitting semiconductor quantum dot optical films via a layer-by-layer assembly technique. The optical films were constructed by alternative deposition of different colored quantum dots with a series of oppositely charged species, in particular, the new use of cationic starch on glass substrates. Semiconductor ZnSe quantum dots exhibiting blue emission were deposited for fabrication of blue-emitting optical films, while semiconductor CdTe quantum dots with green and red emission were utilized for construction of green- and red-emitting optical films. The assembly of integrated blue, green and red semiconductor quantum dots resulted in full-color-emitting optical films. The luminescent optical films showed very bright emitting colors under UV irradiation, and displayed dense, smooth and efficient luminous features, showing brighter luminescence in comparison with their corresponding quantum dot aqueous colloid solutions. The assembled optical films provide the prospect of miniaturized light-emitting-diode applications.
Efficient quantum secret sharing scheme with two-particle entangled states
International Nuclear Information System (INIS)
Zhu Zhen-Chao; Fu An-Min; Zhang Yu-Qing
2011-01-01
This paper proposes a protocol for multi-party quantum secret sharing utilizing four non-orthogonal two-particle entangled states following some ideas in the schemes proposed by Liu et al. (2006 Chin. Phys. Lett. 23 3148) and Zhang et al. (2009 Chin. Phys. B 18 2149) respectively. The theoretical efficiency for qubits of the new protocol is improved from 50% to approaching 100%. All the entangled states can be used for generating the private key except those used for the eavesdropping check. The validity of a probable attack called opaque cheat attack to this kind of protocols is considered in the paper for the first time. (general)
Quantum Dots in Two-Dimensional Perovskite Matrices for Efficient Near-Infrared Light Emission
Yang, Zhenyu
2017-03-13
Quantum-dot-in-perovskite solids are excellent candidates for infrared light-emitting applications. The first generation of dot-in-perovskite light-emitting diodes (LEDs) has shown bright infrared electroluminescence with tunable emission wavelength; however, their performance has been limited by degradation of the active layer at practical operating voltages. This arises from the instability of the three-dimensional (3D) organolead halide perovskite matrix. Herein we report the first dot-in-perovskite solids that employ two-dimensional (2D) perovskites as the matrix. 2D perovskite passivation is achieved via an in situ alkylammonium/alkylamine substitution carried out during the quantum dot (QD) ligand exchange process. This single-step film preparation process enables deposition of the QD/perovskite active layers with thicknesses of 40 nm, over seven times thinner than the first-generation dot-in-perovskite thin films that relied on a multistep synthesis. The dot-in-perovskite film roughness improved from 31 nm for the first-generation films to 3 nm for films as a result of this new approach. The best devices exhibit external quantum efficiency peaks exceeding 2% and radiances of ∼1 W sr–1 m–2, with an improved breakdown voltage up to 7.5 V. Compared to first-generation dot-in-perovskites, this new process reduces materials consumptions 10-fold and represents a promising step toward manufacturable devices.
Quantum Dots in Two-Dimensional Perovskite Matrices for Efficient Near-Infrared Light Emission
Yang, Zhenyu; Voznyy, Oleksandr; Walters, Grant; Fan, James Z.; Liu, Min; Kinge, Sachin; Hoogland, Sjoerd; Sargent, Edward H.
2017-01-01
Quantum-dot-in-perovskite solids are excellent candidates for infrared light-emitting applications. The first generation of dot-in-perovskite light-emitting diodes (LEDs) has shown bright infrared electroluminescence with tunable emission wavelength; however, their performance has been limited by degradation of the active layer at practical operating voltages. This arises from the instability of the three-dimensional (3D) organolead halide perovskite matrix. Herein we report the first dot-in-perovskite solids that employ two-dimensional (2D) perovskites as the matrix. 2D perovskite passivation is achieved via an in situ alkylammonium/alkylamine substitution carried out during the quantum dot (QD) ligand exchange process. This single-step film preparation process enables deposition of the QD/perovskite active layers with thicknesses of 40 nm, over seven times thinner than the first-generation dot-in-perovskite thin films that relied on a multistep synthesis. The dot-in-perovskite film roughness improved from 31 nm for the first-generation films to 3 nm for films as a result of this new approach. The best devices exhibit external quantum efficiency peaks exceeding 2% and radiances of ∼1 W sr–1 m–2, with an improved breakdown voltage up to 7.5 V. Compared to first-generation dot-in-perovskites, this new process reduces materials consumptions 10-fold and represents a promising step toward manufacturable devices.
Practical expressions describing detective quantum efficiency in flat-panel detectors
Kim, H. K.
2011-11-01
In radiology, image quality excellence is a balance between system performance and patient dose, hence x-ray systems must be designed to ensure the maximum image quality is obtained for the lowest consistent dose. The concept of detective quantum efficiency (DQE) is widely used to quantify, understand, measure, and predict the performance of x-ray detectors and imaging systems. Cascaded linear-systems theory can be used to estimate DQE based on the system design parameters and this theoretical DQE can be utilized for determining the impact of various physical processes, such as secondary quantum sinks, noise aliasing, reabsorption noise, and others. However, the prediction of DQE usually requires tremendous efforts to determine each parameter consisting of the cascaded linear-systems model. In this paper, practical DQE formalisms assessing both the photoconductor- and scintillator-based flat-panel detectors under quantum-noise-limited operation are described. The developed formalisms are experimentally validated and discussed for their limits. The formalisms described in this paper would be helpful for the rapid prediction of the DQE performances of developing systems as well as the optimal design of systems.
Meinardi, Francesco; Ehrenberg, Samantha; Dhamo, Lorena; Carulli, Francesco; Mauri, Michele; Bruni, Francesco; Simonutti, Roberto; Kortshagen, Uwe; Brovelli, Sergio
2017-02-01
Building-integrated photovoltaics is gaining consensus as a renewable energy technology for producing electricity at the point of use. Luminescent solar concentrators (LSCs) could extend architectural integration to the urban environment by realizing electrode-less photovoltaic windows. Crucial for large-area LSCs is the suppression of reabsorption losses, which requires emitters with negligible overlap between their absorption and emission spectra. Here, we demonstrate the use of indirect-bandgap semiconductor nanostructures such as highly emissive silicon quantum dots. Silicon is non-toxic, low-cost and ultra-earth-abundant, which avoids the limitations to the industrial scaling of quantum dots composed of low-abundance elements. Suppressed reabsorption and scattering losses lead to nearly ideal LSCs with an optical efficiency of η = 2.85%, matching state-of-the-art semi-transparent LSCs. Monte Carlo simulations indicate that optimized silicon quantum dot LSCs have a clear path to η > 5% for 1 m2 devices. We are finally able to realize flexible LSCs with performances comparable to those of flat concentrators, which opens the way to a new design freedom for building-integrated photovoltaics elements.
Is relativistic quantum mechanics compatible with special relativity?
International Nuclear Information System (INIS)
Lavenda, B.H.
2001-01-01
The transformation from a time-dependent random walk to quantum mechanics converts a modified Bessel function into an ordinary one together with a phase factor e iπ/2 for each time the electron flips both direction and handedness. Causality requires the argument to be greater than the order of the Bessel function. Assuming equal probabilities for jumps ±1, the normalized modified Bessel function of an imaginary argument is the solution of the finite difference differential Schroedinger equation whereas the same function of a real argument satisfies the diffusion equation. In the nonrelativistic limit, the stability condition of the difference scheme contains the mass whereas in the ultrarelativistic limit only the velocity of light appears. Particle waves in the nonrelativistic limit become elastic waves in the ultrarelativistic limit with a phase shift in the frequency and wave number of π/2. The ordinary Bessel function satisfies a second order recurrence relation which is a finite difference differential wave equation, using non-nearest neighbors, whose solutions are the chirality components of a free-particle in the zero fermion mass limit. Reintroducing the mass by a phase transformation transforms the wave equation into the Klein-Gordon equation but does not admit a solution in terms of ordinary Bessel functions. However, a sign change of the mass term permits a solution in terms of a modified Bessel function whose recurrence formulas produce all the results of special relativity. The Lorentz transformation maximizes the integral of the modified Bessel function and determines the paths of steepest descent in the classical limit. If the definitions of frequency and wave number in terms of the phase were used in special relativity, the condition that the frame be inertial would equate the superluminal phase velocity with the particle velocity in violation of causality. In order to get surfaces of constant phase to move at the group velocity, an integrating
The relation between Euclidean and Lorentzian 2D quantum gravity
Ambjørn, J.; Correia, J.; Kristjansen, C.; Loll, R.
1999-01-01
Starting from 2D Euclidean quantum gravity, we show that one recovers 2D Lorentzian quantum gravity by removing all baby universes. Using a peeling procedure to decompose the discrete, triangulated geometries along a one-dimensional path, we explicitly associate with each Euclidean space-time a
Monogamy relations of quantum entanglement for partially coherently superposed states
Shi, Xian
2017-12-01
Not Available Project partially supported by the National Key Research and Development Program of China (Grant No. 2016YFB1000902), the National Natural Science Foundation of China (Grant Nos. 61232015, 61472412, and 61621003), the Beijing Science and Technology Project (2016), Tsinghua-Tencent-AMSS-Joint Project (2016), and the Key Laboratory of Mathematics Mechanization Project: Quantum Computing and Quantum Information Processing.
Relating loop quantum cosmology to loop quantum gravity: symmetric sectors and embeddings
International Nuclear Information System (INIS)
Engle, J
2007-01-01
In this paper we address the meaning of states in loop quantum cosmology (LQC), in the context of loop quantum gravity. First, we introduce a rigorous formulation of an embedding proposed by Bojowald and Kastrup, of LQC states into loop quantum gravity. Then, using certain holomorphic representations, a new class of embeddings, called b-embeddings, are constructed, following the ideas of Engle (2006 Quantum field theory and its symmetry reduction Class. Quantum Gravity 23 2861-94). We exhibit a class of operators preserving each of these embeddings, and show their consistency with the LQC quantization. In the b-embedding case, the classical analogues of these operators separate points in phase space. Embedding at the gauge and diffeomorphism invariant level is discussed briefly in the conclusions
Quantum tunneling of magnetization and related phenomena in molecular materials.
Gatteschi, Dante; Sessoli, Roberta
2003-01-20
Molecules comprising a large number of coupled paramagnetic centers are attracting much interest because they may show properties which are intermediate between those of simple paramagnets and classical bulk magnets and provide unambiguous evidence of quantum size effects in magnets. To date, two cluster families, usually referred to as Mn12 and Fe8, have been used to test theories. However, it is reasonable to predict that other classes of molecules will be discovered which have similar or superior properties. To do this it is necessary that synthetic chemists have a good understanding of the correlation between the structure and properties of the molecules, for this it is necessary that concepts such as quantum tunneling, quantum coherence, quantum oscillations are understood. The goal of this article is to review the fundamental concepts needed to understand quantum size effects in molecular magnets and to critically report what has been done in the field to date.
Courtney, Joseph M; Rienstra, Chad M
2016-08-01
We present a systematic study of dipolar double quantum (DQ) filtering in (13)C-labeled organic solids over a range of magic-angle spinning rates, using the SPC-n recoupling sequence element with a range of n symmetry values from 3 to 11. We find that efficient recoupling can be achieved for values n⩾7, provided that the (13)C nutation frequency is on the order of 100kHz or greater. The decoupling-field dependence was investigated and explicit heteronuclear decoupling interference conditions identified. The major determinant of DQ filtering efficiency is the decoupling interference between (13)C and (1)H fields. For (13)C nutation frequencies greater than 75kHz, optimal performance is observed without an applied (1)H field. At spinning rates exceeding 20kHz, symmetry conditions as low as n=3 were found to perform adequately. Copyright © 2016 Elsevier Inc. All rights reserved.
Simple formalism for efficient derivatives and multi-determinant expansions in quantum Monte Carlo
Energy Technology Data Exchange (ETDEWEB)
Filippi, Claudia, E-mail: c.filippi@utwente.nl [MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede (Netherlands); Assaraf, Roland, E-mail: assaraf@lct.jussieu.fr [Sorbonne Universités, UPMC Univ Paris 06, CNRS, Laboratoire de Chimie Théorique CC 137-4, place Jussieu F-75252 Paris Cedex 05 (France); Moroni, Saverio, E-mail: moroni@democritos.it [CNR-IOM DEMOCRITOS, Istituto Officina dei Materiali, and SISSA Scuola Internazionale Superiore di Studi Avanzati, Via Bonomea 265, I-34136 Trieste (Italy)
2016-05-21
We present a simple and general formalism to compute efficiently the derivatives of a multi-determinant Jastrow-Slater wave function, the local energy, the interatomic forces, and similar quantities needed in quantum Monte Carlo. Through a straightforward manipulation of matrices evaluated on the occupied and virtual orbitals, we obtain an efficiency equivalent to algorithmic differentiation in the computation of the interatomic forces and the optimization of the orbital parameters. Furthermore, for a large multi-determinant expansion, the significant computational gain afforded by a recently introduced table method is here extended to the local value of any one-body operator and to its derivatives, in both all-electron and pseudopotential calculations.
Recombination dynamics and internal quantum efficiency in InGaN
International Nuclear Information System (INIS)
Murotani, Hideaki; Andoh, Hiroya; Tsukamoto, Takehiko; Sugiura, Toko; Yamada, Yoichi; Tabata, Takuya; Honda, Yoshio; Yamaguchi, Masahito; Amano, Hiroshi
2014-01-01
Recombination dynamics and internal quantum efficiency (IQE) of green luminescent InGaN nanowires with different crystalline qualities have been studied by means photoluminescence (PL) and time-resolved PL spectroscopy. Temperature- and excitation-power-density-dependent PL spectroscopy enabled to evaluate the IQE as a function of excitation power density. The shape of the efficiency curves at low temperature strongly depended on the magnitude of nonradiative recombination processes. This leads to the misestimation of the IQE in the lower quality nanowire. In addition, the PL decay curves were well described by a double exponential function both at 6 and 300 K. The PL decay time of the faster component was affected by nonradiative recombination processes even at low temperature. This indicated that the radiative recombination lifetime cannot be estimated from the PL decay time in the lower quality nanowire. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Ivanov, Mikhail V; Babikov, Dmitri
2012-05-14
Efficient method is proposed for computing thermal rate constant of recombination reaction that proceeds according to the energy transfer mechanism, when an energized molecule is formed from reactants first, and is stabilized later by collision with quencher. The mixed quantum-classical theory for the collisional energy transfer and the ro-vibrational energy flow [M. Ivanov and D. Babikov, J. Chem. Phys. 134, 144107 (2011)] is employed to treat the dynamics of molecule + quencher collision. Efficiency is achieved by sampling simultaneously (i) the thermal collision energy, (ii) the impact parameter, and (iii) the incident direction of quencher, as well as (iv) the rotational state of energized molecule. This approach is applied to calculate third-order rate constant of the recombination reaction that forms the (16)O(18)O(16)O isotopomer of ozone. Comparison of the predicted rate vs. experimental result is presented.
Characterizing quantum correlations. Entanglement, uncertainty relations and exponential families
Energy Technology Data Exchange (ETDEWEB)
Niekamp, Soenke
2012-04-20
This thesis is concerned with different characterizations of multi-particle quantum correlations and with entropic uncertainty relations. The effect of statistical errors on the detection of entanglement is investigated. First, general results on the statistical significance of entanglement witnesses are obtained. Then, using an error model for experiments with polarization-entangled photons, it is demonstrated that Bell inequalities with lower violation can have higher significance. The question for the best observables to discriminate between a state and the equivalence class of another state is addressed. Two measures for the discrimination strength of an observable are defined, and optimal families of observables are constructed for several examples. A property of stabilizer bases is shown which is a natural generalization of mutual unbiasedness. For sets of several dichotomic, pairwise anticommuting observables, uncertainty relations using different entropies are constructed in a systematic way. Exponential families provide a classification of states according to their correlations. In this classification scheme, a state is considered as k-correlated if it can be written as thermal state of a k-body Hamiltonian. Witness operators for the detection of higher-order interactions are constructed, and an algorithm for the computation of the nearest k-correlated state is developed.
Characterizing quantum correlations. Entanglement, uncertainty relations and exponential families
International Nuclear Information System (INIS)
Niekamp, Soenke
2012-01-01
This thesis is concerned with different characterizations of multi-particle quantum correlations and with entropic uncertainty relations. The effect of statistical errors on the detection of entanglement is investigated. First, general results on the statistical significance of entanglement witnesses are obtained. Then, using an error model for experiments with polarization-entangled photons, it is demonstrated that Bell inequalities with lower violation can have higher significance. The question for the best observables to discriminate between a state and the equivalence class of another state is addressed. Two measures for the discrimination strength of an observable are defined, and optimal families of observables are constructed for several examples. A property of stabilizer bases is shown which is a natural generalization of mutual unbiasedness. For sets of several dichotomic, pairwise anticommuting observables, uncertainty relations using different entropies are constructed in a systematic way. Exponential families provide a classification of states according to their correlations. In this classification scheme, a state is considered as k-correlated if it can be written as thermal state of a k-body Hamiltonian. Witness operators for the detection of higher-order interactions are constructed, and an algorithm for the computation of the nearest k-correlated state is developed.
Directory of Open Access Journals (Sweden)
A. Malasi
2016-10-01
Full Text Available Plasmonic nanoparticles are amongst the most effective ways to resonantly couple optical energy into and out of nanometer sized volumes. However, controlling and/or tuning the transfer of this incident energy to the surrounding near and far field is one of the most interesting challenges in this area. Due to the dielectric properties of metallic silver (Ag, its nanoparticles have amongst the highest radiative quantum efficiencies (η, i.e., the ability to radiatively transfer the incident energy to the surrounding. Here we report the discovery that bimetallic nanoparticles of Ag made with immiscible and plasmonically weak Co metal can show comparable and/or even higher η values. The enhancement is a result of the narrowing of the plasmon bandwidth from these bimetal systems. The phenomenological explanation of this effect based on the dipolar approximation points to the reduction in radiative losses within the Ag nanoparticles when in contact with cobalt. This is also supported by a model of coupling between poor and good conductors based on the surface to volume ratio. This study presents a new type of bandwidth engineering, one based on using bimetal nanostructures, to tune and/or enhance the quality factor and quantum efficiency for near and far-field plasmonic applications.
An energy and cost efficient majority-based RAM cell in quantum-dot cellular automata
Khosroshahy, Milad Bagherian; Moaiyeri, Mohammad Hossein; Navi, Keivan; Bagherzadeh, Nader
Nanotechnologies, notably quantum-dot cellular automata, have achieved major attentions for their prominent features as compared to the conventional CMOS circuitry. Quantum-dot cellular automata, particularly owning to its considerable reduction in size, high switching speed and ultra-low energy consumption, is considered as a potential alternative for the CMOS technology. As the memory unit is one of the most essential components in a digital system, designing a well-optimized QCA random access memory (RAM) cell is an important area of research. In this paper, a new five-input majority gate is presented which is suitable for implementing efficient single-layer QCA circuits. In addition, a new RAM cell with set and reset capabilities is designed based on the proposed majority gate, which has an efficient and low-energy structure. The functionality, performance and energy consumption of the proposed designs are evaluated based on the QCADesigner and QCAPro tools. According to the simulation results, the proposed RAM design leads to on average 38% lower total energy dissipation, 25% smaller area, 20% lower cell count, 28% lower delay and 60% lower QCA cost as compared to its previous counterparts.
High Efficiency Quantum Well Waveguide Solar Cells and Methods for Constructing the Same
Welser, Roger E. (Inventor); Sood, Ashok K. (Inventor)
2014-01-01
Photon absorption, and thus current generation, is hindered in conventional thin-film solar cell designs, including quantum well structures, by the limited path length of incident light passing vertically through the device. Optical scattering into lateral waveguide structures provides a physical mechanism to increase photocurrent generation through in-plane light trapping. However, the insertion of wells of high refractive index material with lower energy gap into the device structure often results in lower voltage operation, and hence lower photovoltaic power conversion efficiency. The voltage output of an InGaAs quantum well waveguide photovoltaic device can be increased by employing a III-V material structure with an extended wide band gap emitter heterojunction. Analysis of the light IV characteristics reveals that non-radiative recombination components of the underlying dark diode current have been reduced, exposing the limiting radiative recombination component and providing a pathway for realizing solar-electric conversion efficiency of 30% or more in single junction cells.
Entanglement-fidelity relations for inaccurate ancilla-driven quantum computation
International Nuclear Information System (INIS)
Morimae, Tomoyuki; Kahn, Jonas
2010-01-01
It was shown by T. Morimae [Phys. Rev. A 81, 060307(R) (2010)] that the gate fidelity of an inaccurate one-way quantum computation is upper bounded by a decreasing function of the amount of entanglement in the register. This means that a strong entanglement causes the low gate fidelity in the one-way quantum computation with inaccurate measurements. In this paper, we derive similar entanglement-fidelity relations for the inaccurate ancilla-driven quantum computation. These relations again imply that a strong entanglement in the register causes the low gate fidelity in the ancilla-driven quantum computation if the measurements on the ancilla are inaccurate.
Equivalence relations between deterministic and quantum mechanical systems
International Nuclear Information System (INIS)
Hooft, G.
1988-01-01
Several quantum mechanical models are shown to be equivalent to certain deterministic systems because a basis can be found in terms of which the wave function does not spread. This suggests that apparently indeterministic behavior typical for a quantum mechanical world can be the result of locally deterministic laws of physics. We show how certain deterministic systems allow the construction of a Hilbert space and a Hamiltonian so that at long distance scales they may appear to behave as quantum field theories, including interactions but as yet no mass term. These observations are suggested to be useful for building theories at the Planck scale
General tradeoff relations of quantum nonlocality in the Clauser–Horne–Shimony–Holt scenario
Energy Technology Data Exchange (ETDEWEB)
Su, Hong-Yi, E-mail: hongyisu@chonnam.ac.kr [Department of Physics Education, Chonnam National University, Gwangju 500-757 (Korea, Republic of); Chen, Jing-Ling [Theoretical Physics Division, Chern Institute of Mathematics, Nankai University, Tianjin 300071 (China); Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore 117543 (Singapore); Hwang, Won-Young, E-mail: wyhwang@jnu.ac.kr [Department of Physics Education, Chonnam National University, Gwangju 500-757 (Korea, Republic of)
2017-02-15
General tradeoff relations present in nonlocal correlations of bipartite systems are studied, regardless of any specific quantum states and measuring directions. Extensions to multipartite scenarios are possible and very promising. Tsirelson’s bound can be derived out in particular. The close connection with uncertainty relations is also presented and discussed. - Highlights: • Quantum violation of CHSH inequalities is found to satisfy tradeoff relations. • Tsirelson’s bound for quantum mechanics can be directly implied from these tradeoffs. • Tradeoff relations shed new light on uncertainty relations in summation forms.
One interpretation for both Quantum Mechanics and General Relativity
Energy Technology Data Exchange (ETDEWEB)
Halewijn, Ewoud
2014-07-01
In reconciling General Relativity with Quantum Mechanics, it is challenging to resolve the combined mathematical equations and to find an interpretation that makes sense ontologically. Such an interpretation has been developed by quantizing descriptive components in both the theories and other views. The resulting micro-components have been re-integrated within the scope of known gaps between science and 'the real world'. The odd peculiarities in these theories have been made look 'normal' by fully untraditionally answering fundamental questions. The interpretation is suggesting that we define time as a discrete operator and its eigenvalues as constraints on space-time manifolds, in order to reconcile the mathematical equations. Outside the mathematical arena we suggest reconsidering the concepts of Black Holes, the Big Bang, the epistemological problem of perception in philosophy and the supposed clash between scientific and the spiritual worldviews. It is concluded that developing one consistent ontological interpretation for both theorie is possible. It is a weird story, but it is making powerful suggestions for reviewing some of our fundamental convictions.
International Nuclear Information System (INIS)
Scemama, Anthony; Caffarel, Michel; Oseret, Emmanuel; Jalby, William
2013-01-01
Various strategies to implement efficiently quantum Monte Carlo (QMC) simulations for large chemical systems are presented. These include: (i) the introduction of an efficient algorithm to calculate the computationally expensive Slater matrices. This novel scheme is based on the use of the highly localized character of atomic Gaussian basis functions (not the molecular orbitals as usually done), (ii) the possibility of keeping the memory footprint minimal, (iii) the important enhancement of single-core performance when efficient optimization tools are used, and (iv) the definition of a universal, dynamic, fault-tolerant, and load-balanced framework adapted to all kinds of computational platforms (massively parallel machines, clusters, or distributed grids). These strategies have been implemented in the QMC-Chem code developed at Toulouse and illustrated with numerical applications on small peptides of increasing sizes (158, 434, 1056, and 1731 electrons). Using 10-80 k computing cores of the Curie machine (GENCI-TGCC-CEA, France), QMC-Chem has been shown to be capable of running at the peta scale level, thus demonstrating that for this machine a large part of the peak performance can be achieved. Implementation of large-scale QMC simulations for future exa scale platforms with a comparable level of efficiency is expected to be feasible. (authors)
Al-Khalili, Jim
2003-01-01
In this lively look at quantum science, a physicist takes you on an entertaining and enlightening journey through the basics of subatomic physics. Along the way, he examines the paradox of quantum mechanics--beautifully mathematical in theory but confoundingly unpredictable in the real world. Marvel at the Dual Slit experiment as a tiny atom passes through two separate openings at the same time. Ponder the peculiar communication of quantum particles, which can remain in touch no matter how far apart. Join the genius jewel thief as he carries out a quantum measurement on a diamond without ever touching the object in question. Baffle yourself with the bizzareness of quantum tunneling, the equivalent of traveling partway up a hill, only to disappear then reappear traveling down the opposite side. With its clean, colorful layout and conversational tone, this text will hook you into the conundrum that is quantum mechanics.
International Nuclear Information System (INIS)
Aurola, A.; Marochkin, V.; Tuuva, T.
2016-01-01
The benefits of pixelated planar direct conversion semiconductor radiation detectors comprising a thick fully depleted substrate are that they offer low crosstalk, small output capacitance, and that the planar configuration simplifies manufacturing. In order to provide high quantum efficiency for high energy X-rays and Gamma-rays such a radiation detector should be as thick as possible. The maximum thickness and thus the maximum quantum efficiency has been limited by the substrate doping concentration: the lower the substrate doping the thicker the detector can be before reaching the semiconductor material's electric breakdown field. Thick direct conversion semiconductor detectors comprising vertical three-dimensional electrodes protruding through the substrate have been previously proposed by Sherwood Parker in order to promote rapid detection of radiation. An additional advantage of these detectors is that their thickness is not limited by the substrate doping, i.e., the size of the maximum electric field value in the detector does not depend on detector thickness. However, the thicker the substrate of such three dimensional detectors is the larger the output capacitance is and thus the larger the output noise is. In the novel direct conversion pixelated radiation detector utilizing a novel three dimensional semiconductor architecture, which is proposed in this work, the detector thickness is not limited by the substrate doping and the output capacitance is small and does not depend on the detector thickness. In addition, by incorporating an additional node to the novel three-dimensional semiconductor architecture it can be utilized as a high voltage transistor that can deliver current across high voltages. Furthermore, it is possible to connect a voltage difference of any size to the proposed novel three dimensional semiconductor architecture provided that it is thick enough—this is a novel feature that has not been previously possible for semiconductor
Yassitepe, Emre; Yang, Zhenyu; Voznyy, Oleksandr; Kim, Younghoon; Walters, Grant; Castañ eda, Juan Andres; Kanjanaboos, Pongsakorn; Yuan, Mingjian; Gong, Xiwen; Fan, Fengjia; Pan, Jun; Hoogland, Sjoerd; Comin, Riccardo; Bakr, Osman; Padilha, Lazaro A.; Nogueira, Ana F.; Sargent, Edward H.
2016-01-01
Cesium lead halide perovskite quantum dots (PQDs) have attracted significant interest for optoelectronic applications in view of their high brightness and narrow emission linewidth at visible wavelengths. A remaining challenge is the degradation of PQDs during purification from the synthesis solution. This is attributed to proton transfer between oleic acid and oleylamine surface capping agents that leads to facile ligand loss. Here, a new synthetic method is reported that enhances the colloidal stability of PQDs by capping them solely using oleic acid (OA). Quaternary alkylammonium halides are used as precursors, eliminating the need for oleylamine. This strategy enhances the colloidal stability of OA capped PQDs during purification, allowing us to remove excess organic content in thin films. Inverted red, green, and blue PQD light-emitting diodes (LED) are fabricated for the first time with solution-processed polymer-based hole transport layers due to higher robustness of OA capped PQDs to solution processing. The blue and green LEDs exhibit threefold and tenfold improved external quantum efficiency (EQE), respectively, compared to prior related reports for amine/ammonium capped cross-linked PQDs. The brightest blue LED based on all inorganic CsPb(Br1- xClx)3 PQDs is also reported. Â© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Yassitepe, Emre
2016-10-31
Cesium lead halide perovskite quantum dots (PQDs) have attracted significant interest for optoelectronic applications in view of their high brightness and narrow emission linewidth at visible wavelengths. A remaining challenge is the degradation of PQDs during purification from the synthesis solution. This is attributed to proton transfer between oleic acid and oleylamine surface capping agents that leads to facile ligand loss. Here, a new synthetic method is reported that enhances the colloidal stability of PQDs by capping them solely using oleic acid (OA). Quaternary alkylammonium halides are used as precursors, eliminating the need for oleylamine. This strategy enhances the colloidal stability of OA capped PQDs during purification, allowing us to remove excess organic content in thin films. Inverted red, green, and blue PQD light-emitting diodes (LED) are fabricated for the first time with solution-processed polymer-based hole transport layers due to higher robustness of OA capped PQDs to solution processing. The blue and green LEDs exhibit threefold and tenfold improved external quantum efficiency (EQE), respectively, compared to prior related reports for amine/ammonium capped cross-linked PQDs. The brightest blue LED based on all inorganic CsPb(Br1- xClx)3 PQDs is also reported. Â© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Internal quantum efficiency in yellow-amber light emitting AlGaN-InGaN-GaN heterostructures
Energy Technology Data Exchange (ETDEWEB)
Ngo, Thi Huong; Gil, Bernard; Valvin, Pierre [Laboratoire Charles Coulomb – UMR 5221, CNRS and University Montpellier, Case courier 074, 34095 Montpellier Cedex 5 (France); Damilano, Benjamin; Lekhal, Kaddour; De Mierry, Philippe [CRHEA-CNRS Centre de Recherche sur l' Hétéro-Epitaxie et ses Applications, Centre National de la Recherche Scientifique, rue Bernard Gregory, 06560 Valbonne (France)
2015-09-21
We determine the internal quantum efficiency of strain-balanced AlGaN-InGaN-GaN hetero-structures designed for yellow-amber light emission, by using a recent model based on the kinetics of the photoluminescence decay initiated by Iwata et al. [J. Appl. Phys. 117, 075701 (2015)]. Our results indicate that low temperature internal quantum efficiencies sit in the 50% range and we measure that adding an AlGaN layer increases the internal quantum efficiency from 50% up to 57% with respect to the GaN-InGaN case. More dramatic, it almost doubles from 2.5% up to 4.3% at room temperature.
Comparative studies of efficiency droop in polar and non-polar InGaN quantum wells
Energy Technology Data Exchange (ETDEWEB)
Davies, M. J.; Dawson, P.; Hammersley, S. [School of Physics and Astronomy, Photon Science Institute, University of Manchester, M13 9PL Manchester (United Kingdom); Zhu, T.; Kappers, M. J.; Humphreys, C. J.; Oliver, R. A. [Department of Material Science and Metallurgy, 27 Charles Babbage Road, University of Cambridge, Cambridge CB3 0FS (United Kingdom)
2016-06-20
We report on a comparative study of efficiency droop in polar and non-polar InGaN quantum well structures at T = 10 K. To ensure that the experiments were carried out with identical carrier densities for any particular excitation power density, we used laser pulses of duration ∼100 fs at a repetition rate of 400 kHz. For both types of structures, efficiency droop was observed to occur for carrier densities of above 7 × 10{sup 11 }cm{sup −2 }pulse{sup −1} per quantum well; also both structures exhibited similar spectral broadening in the droop regime. These results show that efficiency droop is intrinsic in InGaN quantum wells, whether polar or non-polar, and is a function, specifically, of carrier density.
Comparative studies of efficiency droop in polar and non-polar InGaN quantum wells
International Nuclear Information System (INIS)
Davies, M. J.; Dawson, P.; Hammersley, S.; Zhu, T.; Kappers, M. J.; Humphreys, C. J.; Oliver, R. A.
2016-01-01
We report on a comparative study of efficiency droop in polar and non-polar InGaN quantum well structures at T = 10 K. To ensure that the experiments were carried out with identical carrier densities for any particular excitation power density, we used laser pulses of duration ∼100 fs at a repetition rate of 400 kHz. For both types of structures, efficiency droop was observed to occur for carrier densities of above 7 × 10 11 cm −2 pulse −1 per quantum well; also both structures exhibited similar spectral broadening in the droop regime. These results show that efficiency droop is intrinsic in InGaN quantum wells, whether polar or non-polar, and is a function, specifically, of carrier density.
Energy Technology Data Exchange (ETDEWEB)
Li, Jiahua [School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); Key Laboratory of Fundamental Physical Quantities Measurement of Ministry of Education, Wuhan 430074 (China); Yu, Rong, E-mail: yurong321@126.com [School of Science, Hubei Province Key Laboratory of Intelligent Robot, Wuhan Institute of Technology, Wuhan 430073 (China); Ma, Jinyong; Wu, Ying, E-mail: yingwu2@163.com [School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China)
2014-10-28
The ability to engineer and convert photons between different modes in a solid-state approach has extensive technological implications not only for classical communication systems but also for future quantum networks. In this paper, we put forward a scheme for coherent mode conversion of optical photons by utilizing the intermediate coupling between a single quantum dot and a bimodal photonic crystal microcavity via a waveguide. Here, one mode of the photonic crystal microcavity is coherently driven by an external single-frequency continuous-wave laser field and the two cavity modes are not coupled to each other due to their orthogonal polarizations. The undriven cavity mode is thus not directly coupled to the input driving laser and the only way it can get light is via the quantum dot. The influences of the system parameters on the photon-conversion efficiency are analyzed in detail in the limit of weak probe field and it is found that high photon-conversion efficiency can be achieved under appropriate conditions. It is shown that the cavity dark mode, which is a superposition of the two optical modes and is decoupled from the quantum dot, can appear in such a hybrid optical system. We discuss the properties of the dark mode and indicate that the formation of the dark mode enables the efficient transfer of optical fields between the two cavity modes.
Wang, Jin; Mora-Seró, Iván; Pan, Zhenxiao; Zhao, Ke; Zhang, Hua; Feng, Yaoyu; Yang, Guang; Zhong, Xinhua; Bisquert, Juan
2013-10-23
Searching suitable panchromatic QD sensitizers for expanding the light-harvesting range, accelerating charge separation, and retarding charge recombination is an effective way to improve power conversion efficiency (PCE) of quantum-dot-sensitized solar cells (QDSCs). One possible way to obtain a wide absorption range is to use the exciplex state of a type-II core/shell-structured QDs. In addition, this system could also provide a fast charge separation and low charge-recombination rate. Herein, we report on using a CdTe/CdSe type-II core/shell QD sensitizer with an absorption range extending into the infrared region because of its exciplex state, which is covalently linked to TiO2 mesoporous electrodes by dropping a bifunctional linker molecule mercaptopropionic acid (MPA)-capped QD aqueous solution onto the film electrode. High loading and a uniform distribution of QD sensitizer throughout the film electrode thickness have been confirmed by energy dispersive X-ray (EDX) elemental mapping. The accelerated electron injection and retarded charge-recombination pathway in the built CdTe/CdSe QD cells in comparison with reference CdSe QD-based cells have been confirmed by impedance spectroscopy, fluorescence decay, and intensity-modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS) analysis. With the combination of the high QD loading and intrinsically superior optoelectronic properties of type-II core/shell QD (wide absorption range, fast charge separation, and slow charge recombination), the resulting CdTe/CdSe QD-based regenerative sandwich solar cells exhibit a record PCE of 6.76% (J(sc) = 19.59 mA cm(-2), V(oc) = 0.606 V, and FF = 0.569) with a mask around the active film under a full 1 sun illumination (simulated AM 1.5), which is the highest reported to date for liquid-junction QDSCs.
Gujarati, Tanvi P.; Wu, Yukai; Duan, Luming
2018-03-01
Duan-Lukin-Cirac-Zoller quantum repeater protocol, which was proposed to realize long distance quantum communication, requires usage of quantum memories. Atomic ensembles interacting with optical beams based on off-resonant Raman scattering serve as convenient on-demand quantum memories. Here, a complete free space, three-dimensional theory of the associated read and write process for this quantum memory is worked out with the aim of understanding intrinsic retrieval efficiency. We develop a formalism to calculate the transverse mode structure for the signal and the idler photons and use the formalism to study the intrinsic retrieval efficiency under various configurations. The effects of atomic density fluctuations and atomic motion are incorporated by numerically simulating this system for a range of realistic experimental parameters. We obtain results that describe the variation in the intrinsic retrieval efficiency as a function of the memory storage time for skewed beam configuration at a finite temperature, which provides valuable information for optimization of the retrieval efficiency in experiments.
Quantum mechanics versus relativity: an experimental test of the structure of spacetime
International Nuclear Information System (INIS)
Emelyanov, S A
2012-01-01
We have performed an experimental test under the conditions in which quantum mechanics predicts spatially discontinuous single-particle transport. The transport is beyond the relativistic paradigm of movement in Cartesian space and therefore may well be nonlocal. Our test has demonstrated that such transport does exist. This fact opens the door for a realistic interpretation of quantum mechanics in so far as the requirement of Lorentz invariance appears inapplicable to any version of quantum theory. Moreover, as quantum mechanics proposes a particle dynamics beyond relativity, it automatically requires an adequate ‘quantum’ concept of spacetime, for which the relativistic concept is only a limiting case. The quantum concept allows absolute simultaneity and hence revives the notion of absolute time. It also goes beyond the relativistic curvilinear Cartesian order of space to account for quantum phenomena such as discontinuity and nonlocality in the spirit of Bohm's concept of the implicate order.
Internal quantum efficiency and tunable colour temperature in monolithic white InGaN/GaN LED
Titkov, Ilya E.; Yadav, Amit; Zerova, Vera L.; Zulonas, Modestas; Tsatsulnikov, Andrey F.; Lundin, Wsevolod V.; Sakharov, Alexey V.; Rafailov, Edik U.
2014-03-01
Internal Quantum Efficiency (IQE) of two-colour monolithic white light emitting diode (LED) was measured by temperature dependant electro-luminescence (TDEL) and analysed with modified rate equation based on ABC model. External, internal and injection efficiencies of blue and green quantum wells were analysed separately. Monolithic white LED contained one green InGaN QW and two blue QWs being separated by GaN barrier. This paper reports also the tunable behaviour of correlated colour temperature (CCT) in pulsed operation mode and effect of self-heating on device performance.
Optimizing the internal quantum efficiency of GaInN SQW structures for green light emitters
International Nuclear Information System (INIS)
Fuhrmann, D.; Rossow, U.; Netzel, C.; Bremers, H.; Hangleiter, A.; Ade, G.; Hinze, P.
2006-01-01
Ga x In 1-x N/GaN single quantum well (QW) structures emitting in the range of 450 nm to 620 nm have been grown by MOVPE. Temperature and excitation power dependent photoluminescence (PL) was used to determine the internal quantum efficiency (IQE) for these structures. For the blue emitting QWs high IQE values on the order of 60% were achieved. Due to a reduced growth temperature, reduced growth rate and increased V/III ratio we obtained QWs with good morphology and high In content above 25%. Thinner QWs with high In content showed a clear improvement of IQE compared to QW-structures with larger thickness but smaller In-content emitting at the same wavelength. Between λ peak =460 nm and 530 nm we observed a slight reduction in IQE with values of 58% at 490 nm and 40% at 525 nm. But towards λ peak =620 nm IQE decreased due to the electric field induced separation of the electron and hole wavefunction down to 1%. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
International Nuclear Information System (INIS)
Au, Giang H T; Shih, Wan Y; Shih, Wei-Heng
2015-01-01
Quantum dots (QDs) are semiconducting nanoparticles with photoluminescence properties that do not photobleach. Due to these advantages, using QDs for non-viral gene delivery has the additional benefit of being able to track the delivery of the genes in real time as it happens. We investigate the efficacy of mercaptopropionic acid (MPA)-capped CdSe aqueous quantum dots (AQDs) electrostatically complexed with branched polyethyleneimine (PEI) both as a non-viral gene delivery vector and as a fluorescent probe for tracking the delivery of genes into nuclei. The MPA-capped CdSe AQDs that were completely synthesized in water were the model AQDs. A nominal MPA:Cd:Se = 4:3:1 was chosen for optimal photoluminescence and zeta potential. The gene delivery study was carried out in vitro using a human colon cancer cell line, HT29 (ATCC). The model gene was a plasmid DNA (pDNA) that can express red fluorescent protein (RFP). Positively charged branched PEI was employed to provide a proton buffer to the AQDs to allow for endosomal escape. It is shown that by using a PEI-AQD complex with a PEI/AQD molar ratio of 300 and a nominal pDNA/PEI-AQD ratio of 6, we can achieve 75 ± 2.6% RFP expression efficiency with cell vitality remaining at 78 ± 4% of the control. (paper)
Mahpeykar, Seyed Milad; Wang, Xihua
2017-02-01
Colloidal quantum dot (CQD) solar cells have been under the spotlight in recent years mainly due to their potential for low-cost solution-processed fabrication and efficient light harvesting through multiple exciton generation (MEG) and tunable absorption spectrum via the quantum size effect. Despite the impressive advances achieved in charge carrier mobility of quantum dot solids and the cells' light trapping capabilities, the recent progress in CQD solar cell efficiencies has been slow, leaving them behind other competing solar cell technologies. In this work, using comprehensive optoelectronic modeling and simulation, we demonstrate the presence of a strong efficiency loss mechanism, here called the "efficiency black hole", that can significantly hold back the improvements achieved by any efficiency enhancement strategy. We prove that this efficiency black hole is the result of sole focus on enhancement of either light absorption or charge extraction capabilities of CQD solar cells. This means that for a given thickness of CQD layer, improvements accomplished exclusively in optic or electronic aspect of CQD solar cells do not necessarily translate into tangible enhancement in their efficiency. The results suggest that in order for CQD solar cells to come out of the mentioned black hole, incorporation of an effective light trapping strategy and a high quality CQD film at the same time is an essential necessity. Using the developed optoelectronic model, the requirements for this incorporation approach and the expected efficiencies after its implementation are predicted as a roadmap for CQD solar cell research community.
Efficient Implementation of Many-body Quantum Chemical Methods on the Intel Xeon Phi Coprocessor
Energy Technology Data Exchange (ETDEWEB)
Apra, Edoardo; Klemm, Michael; Kowalski, Karol
2014-12-01
This paper presents the implementation and performance of the highly accurate CCSD(T) quantum chemistry method on the Intel Xeon Phi coprocessor within the context of the NWChem computational chemistry package. The widespread use of highly correlated methods in electronic structure calculations is contingent upon the interplay between advances in theory and the possibility of utilizing the ever-growing computer power of emerging heterogeneous architectures. We discuss the design decisions of our implementation as well as the optimizations applied to the compute kernels and data transfers between host and coprocessor. We show the feasibility of adopting the Intel Many Integrated Core Architecture and the Intel Xeon Phi coprocessor for developing efficient computational chemistry modeling tools. Remarkable scalability is demonstrated by benchmarks. Our solution scales up to a total of 62560 cores with the concurrent utilization of Intel Xeon processors and Intel Xeon Phi coprocessors.
Design of Efficient Full Adder in Quantum-Dot Cellular Automata
Directory of Open Access Journals (Sweden)
Bibhash Sen
2013-01-01
Full Text Available Further downscaling of CMOS technology becomes challenging as it faces limitation of feature size reduction. Quantum-dot cellular automata (QCA, a potential alternative to CMOS, promises efficient digital design at nanoscale. Investigations on the reduction of QCA primitives (majority gates and inverters for various adders are limited, and very few designs exist for reference. As a result, design of adders under QCA framework is gaining its importance in recent research. This work targets developing multi-layered full adder architecture in QCA framework based on five-input majority gate proposed here. A minimum clock zone (2 clock with high compaction (0.01 μm2 for a full adder around QCA is achieved. Further, the usefulness of such design is established with the synthesis of high-level logic. Experimental results illustrate the significant improvements in design level in terms of circuit area, cell count, and clock compared to that of conventional design approaches.
Influence of wet chemical cleaning on quantum efficiency of GaN photocathode
International Nuclear Information System (INIS)
Wang Xiao-Hui; Gao Pin; Wang Hong-Gang; Li Biao; Chang Ben-Kang
2013-01-01
GaN samples 1–3 are cleaned by a 2:2:1 solution of sulfuric acid (98%) to hydrogen peroxide (30%) to de-ionized water; hydrochloric acid (37%); or a 4:1 solution of sulfuric acid (98%) to hydrogen peroxide (30%). The samples are activated by Cs/O after the same annealing process. X-ray photoelectron spectroscopy after the different ways of wet chemical cleaning shows: sample 1 has the largest proportion of Ga, N, and O among the three samples, while its C content is the lowest. After activation the quantum efficiency curves show sample 1 has the best photocathode performance. We think the wet chemical cleaning method is a process which will mainly remove C contamination. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Highly efficient quantum dot-based photoconductive THz materials and devices
Rafailov, E. U.; Leyman, R.; Carnegie, D.; Bazieva, N.
2013-09-01
We demonstrate Terahertz (THz) signal sources based on photoconductive (PC) antenna devices comprising active layers of InAs semiconductor quantum dots (QDs) on GaAs. Antenna structures comprised of multiple active layers of InAs:GaAs PC materials are optically pumped using ultrashort pulses generated by a Ti:Sapphire laser and CW dualwavelength laser diodes. We also characterised THz output signals using a two-antenna coherent detection system. We discuss preliminary performance data from such InAs:GaAs THz devices which exhibit efficient emission of both pulsed and continuous wave (CW) THz signals and significant optical-to-THz conversion at both absorption wavelength ranges, <=850 nm and <=1300 nm.
Effects of Frequency Dependence of the External Quantum Efficiency of Perovskite Solar Cells.
Ravishankar, Sandheep; Aranda, Clara; Boix, Pablo P; Anta, Juan A; Bisquert, Juan; Garcia-Belmonte, Germà
2018-06-07
Perovskite solar cells are known to show very long response time scales, on the order of milliseconds to seconds. This generates considerable doubt over the validity of the measured external quantum efficiency (EQE) and consequently the estimation of the short-circuit current density. We observe a variation as high as 10% in the values of the EQE of perovskite solar cells for different optical chopper frequencies between 10 and 500 Hz, indicating a need to establish well-defined protocols of EQE measurement. We also corroborate these values and obtain new insights regarding the working mechanisms of perovskite solar cells from intensity-modulated photocurrent spectroscopy measurements, identifying the evolution of the EQE over a range of frequencies, displaying a singular reduction at very low frequencies. This reduction in EQE is ascribed to additional resistive contributions hindering charge extraction in the perovskite solar cell at short-circuit conditions, which are delayed because of the concomitant large low-frequency capacitance.
In Situ Passivation for Efficient PbS Quantum Dot Solar Cells by Precursor Engineering.
Wang, Yongjie; Lu, Kunyuan; Han, Lu; Liu, Zeke; Shi, Guozheng; Fang, Honghua; Chen, Si; Wu, Tian; Yang, Fan; Gu, Mengfan; Zhou, Sijie; Ling, Xufeng; Tang, Xun; Zheng, Jiawei; Loi, Maria Antonietta; Ma, Wanli
2018-04-01
Current efforts on lead sulfide quantum dot (PbS QD) solar cells are mostly paid to the device architecture engineering and postsynthetic surface modification, while very rare work regarding the optimization of PbS synthesis is reported. Here, PbS QDs are successfully synthesized using PbO and PbAc 2 · 3H 2 O as the lead sources. QD solar cells based on PbAc-PbS have demonstrated a high power conversion efficiency (PCE) of 10.82% (and independently certificated values of 10.62%), which is significantly higher than the PCE of 9.39% for PbO-PbS QD based ones. For the first time, systematic investigations are carried out on the effect of lead precursor engineering on the device performance. It is revealed that acetate can act as an efficient capping ligands together with oleic acid, providing better surface coverage and replace some of the harmful hydroxyl (OH) ligands during the synthesis. Then the acetate on the surface can be exchanged by iodide and lead to desired passivation. This work demonstrates that the precursor engineering has great potential in performance improvement. It is also pointed out that the initial synthesis is an often neglected but critical stage and has abundant room for optimization to further improve the quality of the resultant QDs, leading to breakthrough efficiency. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Delayed Slater determinant update algorithms for high efficiency quantum Monte Carlo
McDaniel, T.; D'Azevedo, E. F.; Li, Y. W.; Wong, K.; Kent, P. R. C.
2017-11-01
Within ab initio Quantum Monte Carlo simulations, the leading numerical cost for large systems is the computation of the values of the Slater determinants in the trial wavefunction. Each Monte Carlo step requires finding the determinant of a dense matrix. This is most commonly iteratively evaluated using a rank-1 Sherman-Morrison updating scheme to avoid repeated explicit calculation of the inverse. The overall computational cost is, therefore, formally cubic in the number of electrons or matrix size. To improve the numerical efficiency of this procedure, we propose a novel multiple rank delayed update scheme. This strategy enables probability evaluation with an application of accepted moves to the matrices delayed until after a predetermined number of moves, K. The accepted events are then applied to the matrices en bloc with enhanced arithmetic intensity and computational efficiency via matrix-matrix operations instead of matrix-vector operations. This procedure does not change the underlying Monte Carlo sampling or its statistical efficiency. For calculations on large systems and algorithms such as diffusion Monte Carlo, where the acceptance ratio is high, order of magnitude improvements in the update time can be obtained on both multi-core central processing units and graphical processing units.
International Nuclear Information System (INIS)
Chen, I-C; Hwang Tzonelih; Li C-M
2008-01-01
On the basis of the modified four-coherent-state post-selection quantum key distribution protocol (Namiki and Hirano 2006 Preprint quant-ph/0608144v1), two 1-out-of-2 quantum oblivious transfer (QOT 2 1 ) protocols are proposed. The first proposed protocol (called the receiver-based QOT 2 1 protocol) requires the coherent states to be prepared by the receiver, whereas the second protocol (called the sender-based QOT 2 1 protocol) allows the coherent states to be generated by the sender. The main advantages of the proposed protocols are that (i) no quantum bit commitment schemes and the assumption of quantum memory are needed; (ii) less communication cost between participants is required, i.e. the receiver-based QOT 2 1 protocol requires only one quantum communication and one classical communication and the sender-based QOT 2 1 protocol requires only one quantum communication between participants during protocol execution; and (iii) the utilization of quantum states is very efficient, wherein the receiver-based and the sender-based QOT 2 1 protocols use only two coherent pulses and one coherent pulse respectively for sending the sender's two messages
Go Pink! The Effect of Secondary Quanta on Detective Quantum Efficiency
Energy Technology Data Exchange (ETDEWEB)
Watson, Scott [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2017-09-05
Photons are never directly observable. Consequently, we often use photoelectric detectors (eg CCDs) to record associated photoelectrons statistically. Nonetheless, it is an implicit goal of radiographic detector designers to achieve the maximum possible detector efficiency1. In part the desire for ever higher efficiency has been due to the fact that detectors are far less expensive than associated accelerator facilities (e.g. DARHT and PHERMEX2). In addition, higher efficiency detectors often have better spatial resolution. Consequently, the optimization of the detector, not the accelerator, is the system component with the highest leverage per dollar. In recent years, imaging scientists have adopted the so-called Detective Quantum Efficiency, or DQE as a summary measure of detector performance. Unfortunately, owing to the complex nature of the trade-space associated with detector components, and the natural desire for simplicity and low(er) cost, there has been a recent trend in Los Alamos to focus only on the zerofrequency efficiency, or DQE(0), when designing such systems. This narrow focus leads to system designs that neglect or even ignore the importance of high-spatial-frequency image components. In this paper we demonstrate the significant negative impact of these design choices on the Noise Power Spectrum1 (NPS) and recommend a more holistic approach to detector design. Here we present a statistical argument which indicates that a very large number (>20) of secondary quanta (typically visible light and/or recorded photo-electrons) are needed to take maximum advantage of the primary quanta (typically x-rays or protons) which are available to form an image. Since secondary particles come in bursts, they are not independent. In short, we want to maximize the pink nature of detector noise at DARHT.
Relation of a unified quantum field theory of spinors to the structure of general relativity
International Nuclear Information System (INIS)
Kober, Martin
2009-01-01
Based on a unified quantum field theory of spinors assumed to describe all matter fields and their interactions we construct the space-time structure of general relativity according to a general connection within the corresponding spinor space. The tetrad field and the corresponding metric field are composed from a space-time dependent basis of spinors within the internal space of the fundamental matter field. Similar to twistor theory the Minkowski signature of the space-time metric is related to this spinor nature of elementary matter, if we assume the spinor space to be endowed with a symplectic structure. The equivalence principle and the property of background independence arise from the fact that all elementary fields are composed from the fundamental spinor field. This means that the structure of space-time according to general relativity seems to be a consequence of a fundamental theory of matter fields and not a presupposition as in the usual setting of relativistic quantum field theories.
The complex and quaternionic quantum bit from relativity of simultaneity on an interferometer.
Garner, Andrew J P; Müller, Markus P; Dahlsten, Oscar C O
2017-12-01
The patterns of fringes produced by an interferometer have long been important testbeds for our best contemporary theories of physics. Historically, interference has been used to contrast quantum mechanics with classical physics, but recently experiments have been performed that test quantum theory against even more exotic alternatives. A physically motivated family of theories are those where the state space of a two-level system is given by a sphere of arbitrary dimension. This includes classical bits, and real, complex and quaternionic quantum theory. In this paper, we consider relativity of simultaneity (i.e. that observers may disagree about the order of events at different locations) as applied to a two-armed interferometer, and show that this forbids most interference phenomena more complicated than those of complex quantum theory. If interference must depend on some relational property of the setting (such as path difference), then relativity of simultaneity will limit state spaces to standard complex quantum theory, or a subspace thereof. If this relational assumption is relaxed, we find one additional theory compatible with relativity of simultaneity: quaternionic quantum theory. Our results have consequences for current laboratory interference experiments: they have to be designed carefully to avoid rendering beyond-quantum effects invisible by relativity of simultaneity.
Efficient charge carrier injection into sub-250 nm AlGaN multiple quantum well light emitting diodes
Energy Technology Data Exchange (ETDEWEB)
Mehnke, Frank, E-mail: mehnke@physik.tu-berlin.de; Kuhn, Christian; Guttmann, Martin; Reich, Christoph; Kolbe, Tim; Rass, Jens; Wernicke, Tim [Technische Universität Berlin, Institut für Festkörperphysik, Hardenbergstr. 36, EW 6-1, 10623 Berlin (Germany); Kueller, Viola; Knauer, Arne; Lapeyrade, Mickael; Einfeldt, Sven; Weyers, Markus [Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin (Germany); Kneissl, Michael [Technische Universität Berlin, Institut für Festkörperphysik, Hardenbergstr. 36, EW 6-1, 10623 Berlin (Germany); Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin (Germany)
2014-08-04
The design and Mg-doping profile of AlN/Al{sub 0.7}Ga{sub 0.3}N electron blocking heterostructures (EBH) for AlGaN multiple quantum well (MQW) light emitting diodes (LEDs) emitting below 250 nm was investigated. By inserting an AlN electron blocking layer (EBL) into the EBH, we were able to increase the quantum well emission power and significantly reduce long wavelength parasitic luminescence. Furthermore, electron leakage was suppressed by optimizing the thickness of the AlN EBL while still maintaining sufficient hole injection. Ultraviolet (UV)-C LEDs with very low parasitic luminescence (7% of total emission power) and external quantum efficiencies of 0.19% at 246 nm have been realized. This concept was applied to AlGaN MQW LEDs emitting between 235 nm and 263 nm with external quantum efficiencies ranging from 0.002% to 0.93%. After processing, we were able to demonstrate an UV-C LED emitting at 234 nm with 14.5 μW integrated optical output power and an external quantum efficiency of 0.012% at 18.2 A/cm{sup 2}.
Efficient charge carrier injection into sub-250 nm AlGaN multiple quantum well light emitting diodes
International Nuclear Information System (INIS)
Mehnke, Frank; Kuhn, Christian; Guttmann, Martin; Reich, Christoph; Kolbe, Tim; Rass, Jens; Wernicke, Tim; Kueller, Viola; Knauer, Arne; Lapeyrade, Mickael; Einfeldt, Sven; Weyers, Markus; Kneissl, Michael
2014-01-01
The design and Mg-doping profile of AlN/Al 0.7 Ga 0.3 N electron blocking heterostructures (EBH) for AlGaN multiple quantum well (MQW) light emitting diodes (LEDs) emitting below 250 nm was investigated. By inserting an AlN electron blocking layer (EBL) into the EBH, we were able to increase the quantum well emission power and significantly reduce long wavelength parasitic luminescence. Furthermore, electron leakage was suppressed by optimizing the thickness of the AlN EBL while still maintaining sufficient hole injection. Ultraviolet (UV)-C LEDs with very low parasitic luminescence (7% of total emission power) and external quantum efficiencies of 0.19% at 246 nm have been realized. This concept was applied to AlGaN MQW LEDs emitting between 235 nm and 263 nm with external quantum efficiencies ranging from 0.002% to 0.93%. After processing, we were able to demonstrate an UV-C LED emitting at 234 nm with 14.5 μW integrated optical output power and an external quantum efficiency of 0.012% at 18.2 A/cm 2
Unification of General Relativity with Quantum Field Theory
International Nuclear Information System (INIS)
Ni Jun
2011-01-01
In the frame of quantum field theory, instead of using the action principle, we deduce the Einstein equation from purely the general covariant principle and the homogeneity of spacetime. The Einstein equation is shown to be the gauge equation to guarantee the local symmetry of spacetime translation. Gravity is an apparent force due to the curvature of spacetime resulted from the conservation of energy-momentum. In the action of quantum field theory, only electroweak-strong interactions should be considered with the curved spacetime metric determined by the Einstein equation. (general)
Loop space representation of quantum general relativity and the group of loops
International Nuclear Information System (INIS)
Gambini, R.
1991-01-01
The action of the constraints of quantum general relativity on a general state in the loop representation is coded in terms of loop derivatives. These differential operators are related to the infinitesimal generators of the group of loops and generalize the area derivative first considered by Mandelstam. A new sector of solutions of the physical states space of nonperturbative quantum general relativity is found. (orig.)
Quantum communication in noisy environments
International Nuclear Information System (INIS)
Aschauer, H.
2004-01-01
In this thesis, we investigate how protocols in quantum communication theory are influenced by noise. Specifically, we take into account noise during the transmission of quantum information and noise during the processing of quantum information. We describe three novel quantum communication protocols which can be accomplished efficiently in a noisy environment: (1) Factorization of Eve: We show that it is possible to disentangle transmitted qubits a posteriori from the quantum channel's degrees of freedom. (2) Cluster state purification: We give multi-partite entanglement purification protocols for a large class of entangled quantum states. (3) Entanglement purification protocols from quantum codes: We describe a constructive method to create bipartite entanglement purification protocols form quantum error correcting codes, and investigate the properties of these protocols, which can be operated in two different modes, which are related to quantum communication and quantum computation protocols, respectively
High Efficiency Multijunction Solar Cells with Finely-Tuned Quantum Wells
Varonides, Argyrios C.
The field of high efficiency (inorganic) photovoltaics (PV) is rapidly maturing in both efficiency goals and cover all cost reduction of fabrication. On one hand, know-how from space industry in new solar cell design configurations and on the other, fabrication cost reduction challenges for terrestrial uses of solar energy, have paved the way to a new generation of PV devices, capable of capturing most of the solar spectrum. For quite a while now, the goal of inorganic solar cell design has been the total (if possible) capture-absorption of the solar spectrum from a single solar cell, designed in such a way that a multiple of incident wavelengths could be simultaneously absorbed. Multi-absorption in device physics indicates parallel existence of different materials that absorb solar photons of different energies. Bulk solid state devices absorb at specific energy thresholds, depending on their respective energy gap (EG). More than one energy gaps would on principle offer new ways of photon absorption: if such a structure could be fabricated, two or more groups of photons could be absorbed simultaneously. The point became then what lattice-matched semiconductor materials could offer such multiple levels of absorption without much recombination losses. It was soon realized that such layer multiplicity combined with quantum size effects could lead to higher efficiency collection of photo-excited carriers. At the moment, the main reason that slows down quantum effect solar cell production is high fabrication cost, since it involves primarily expensive methods of multilayer growth. Existing multi-layer cells are fabricated in the bulk, with three (mostly) layers of lattice-matched and non-lattice-matched (pseudo-morphic) semiconductor materials (GaInP/InGaN etc), where photo-carrier collection occurs in the bulk of the base (coming from the emitter which lies right under the window layer). These carriers are given excess to conduction via tunnel junction (grown between
Quantum cosmological relational model of shape and scale in 1D
International Nuclear Information System (INIS)
Anderson, Edward
2011-01-01
Relational particle models are useful toy models for quantum cosmology and the problem of time in quantum general relativity. This paper shows how to extend existing work on concrete examples of relational particle models in 1D to include a notion of scale. This is useful as regards forming a tight analogy with quantum cosmology and the emergent semiclassical time and hidden time approaches to the problem of time. This paper shows furthermore that the correspondence between relational particle models and classical and quantum cosmology can be strengthened using judicious choices of the mechanical potential. This gives relational particle mechanics models with analogues of spatial curvature, cosmological constant, dust and radiation terms. A number of these models are then tractable at the quantum level. These models can be used to study important issues (1) in canonical quantum gravity: the problem of time, the semiclassical approach to it and timeless approaches to it (such as the naive Schroedinger interpretation and records theory) and (2) in quantum cosmology, such as in the investigation of uniform states, robustness and the qualitative understanding of the origin of structure formation.
Verifying detailed fluctuation relations for discrete feedback-controlled quantum dynamics
Camati, Patrice A.; Serra, Roberto M.
2018-04-01
Discrete quantum feedback control consists of a managed dynamics according to the information acquired by a previous measurement. Energy fluctuations along such dynamics satisfy generalized fluctuation relations, which are useful tools to study the thermodynamics of systems far away from equilibrium. Due to the practical challenge to assess energy fluctuations in the quantum scenario, the experimental verification of detailed fluctuation relations in the presence of feedback control remains elusive. We present a feasible method to experimentally verify detailed fluctuation relations for discrete feedback control quantum dynamics. Two detailed fluctuation relations are developed and employed. The method is based on a quantum interferometric strategy that allows the verification of fluctuation relations in the presence of feedback control. An analytical example to illustrate the applicability of the method is discussed. The comprehensive technique introduced here can be experimentally implemented at a microscale with the current technology in a variety of experimental platforms.
Dealing with quantum weirdness: Holism and related issues
International Nuclear Information System (INIS)
Elby, A.R.
1995-12-01
Various issues are discussed in interpretation of quantum mechanics. All these explorations point toward the same conclusion, that some systems are holistically connected, i.e., some composite systems have properties that cannot, even in principle, be reduced to the properties of its subsystems. This is argued to be the central metaphysical lesson of quantum theory; this will remain pertinent even if quantum mechanics gets replaced by a superior theory. Chap. 2 discusses nonlocality and rules out hidden-variable theories that approximately reproduce the perfect correlations of quantum mechanics, as well as theories that obey locality conditions weaker than those needed to derive Bell's inequality. Chap. 3 shows that SQUID experiments can rule out non-invasive measurability if not macrorealism. Chap. 4 looks at interpretational issues surrounding decoherence, the dissipative interaction between a system and its environment. Decoherence klcan help ''modal'' interpretations pick out the desired ''preferred'' basis. Chap. 5 explores what varieties of causation can and cannot ''explain'' EPR correlations. Instead of relying on ''watered down'' causal explanations, we should instead develop new, holistic explanatory frameworks
Quantum information and information loss in general relativity
Hooft, G. 't
1996-01-01
When it comes to performing thought experiments with black holes, Einstein-Bohr like discussions have to be re-opened. For instance one can ask what happens to the quantum state of a black hole when the wave function of a single ingoing particle is replaced by an other one that is orthogonal to the
Relational description of the measurement process in quantum field theory
International Nuclear Information System (INIS)
Gambini, Rodolfo; Porto, Rafael A.
2002-01-01
We have recently introduced a realistic, covariant, interpretation for the reduction process in relativistic quantum mechanics. The basic problem for a covariant description is the dependence of the states on the frame within which collapse takes place. A suitable use of the causal structure of the devices involved in the measurement process allowed us to introduce a covariant notion for the collapse of quantum states. However, a fully consistent description in the relativistic domain requires the extension of the interpretation to quantum fields. The extension is far from straightforward. Besides the obvious difficulty of dealing with the infinite degrees of freedom of the field theory, one has to analyse the restrictions imposed by causality concerning the allowed operations in a measurement process. In this paper we address these issues. We shall show that, in the case of partial causally connected measurements, our description allows us to include a wider class of causal operations than the one resulting from the standard way of computing conditional probabilities. This alternative description could be experimentally tested. A verification of this proposal would give stronger support to the realistic interpretations of the states in quantum mechanics. (author)
Resonances from perturbations of quantum graphs with rationally related edges
Czech Academy of Sciences Publication Activity Database
Exner, Pavel; Lipovský, Jiří
2010-01-01
Roč. 43, č. 10 (2010), 105301/1-105301/21 ISSN 1751-8113 R&D Projects: GA MŠk LC06002 Institutional research plan: CEZ:AV0Z10480505 Keywords : quantum graphs * resonances * analyze Subject RIV: BE - Theoretical Physics Impact factor: 1.641, year: 2010
Limpens, R.; Gregorkiewicz, T.
2013-01-01
The percentage of dark silicon nanocrystals, i.e., the nanocrystals that are not able to radiatively recombine after absorption of a photon, is investigated by combining measurements of external and internal quantum efficiencies. The study is conducted on samples prepared by co-sputtering and
Extending quantum efficiency roll-over threshold with compositionally graded InGaN/GaN LED
Mishra, Pawan; Ng, Tien Khee; Janjua, Bilal; Shen, Chao; Eid, Jessica; Alyamani, Ahmed Y.; El-Desouki, Munir M.; Ooi, Boon S.
2014-01-01
We report a significant improvement in the electrical characteristic of compositionally graded InGaN/GaN multiple-quantum-well (MQWs) micro-LED. The efficiency droop in this device occurred at ∼20 times higher injection levels (∼275 A/cm2) compared to a conventional step-MQWs microLED (∼14 A/cm2).
Bocian, Kacper; Rudziński, Wojciech; Weymann, Ireneusz
2018-05-01
We theoretically study the spin-resolved subgap transport properties of a Cooper pair splitter based on a triple quantum dot attached to superconducting and ferromagnetic leads. Using the Keldysh Green's function formalism, we analyze the dependence of the Andreev conductance, Cooper pair splitting efficiency, and tunnel magnetoresistance on the gate and bias voltages applied to the system. We show that the system's transport properties are strongly affected by spin dependence of tunneling processes and quantum interference between different local and nonlocal Andreev reflections. We also study the effects of finite hopping between the side quantum dots on the Andreev current. This allows for identifying the optimal conditions for enhancing the Cooper pair splitting efficiency of the device. We find that the splitting efficiency exhibits a nonmonotonic dependence on the degree of spin polarization of the leads and the magnitude and type of hopping between the dots. An almost perfect splitting efficiency is predicted in the nonlinear response regime when the energies of the side quantum dots are tuned to the energies of the corresponding Andreev bound states. In addition, we analyzed features of the tunnel magnetoresistance (TMR) for a wide range of the gate and bias voltages, as well as for different model parameters, finding the corresponding sign changes of the TMR in certain transport regimes. The mechanisms leading to these effects are thoroughly discussed.
Czech Academy of Sciences Publication Activity Database
Horáček, Miroslav
2005-01-01
Roč. 76, č. 9 (2005), 093704:1-6 ISSN 0034-6748 R&D Projects: GA ČR(CZ) GA202/03/1575 Keywords : electron bombarded CCD * modulation transfer function * detective quantum efficiency Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering Impact factor: 1.235, year: 2005
Energy Technology Data Exchange (ETDEWEB)
2011-08-01
Fact sheet on the FlashQE system, a 2011 R&D 100 Award winner. A solid-state optical system by NREL and Tau Science measures solar cell quantum efficiency in less than a second, enabling a suite of new capabilities for solar cell manufacturers.
Extending quantum efficiency roll-over threshold with compositionally graded InGaN/GaN LED
Mishra, Pawan
2014-12-01
We report a significant improvement in the electrical characteristic of compositionally graded InGaN/GaN multiple-quantum-well (MQWs) micro-LED. The efficiency droop in this device occurred at ∼20 times higher injection levels (∼275 A/cm2) compared to a conventional step-MQWs microLED (∼14 A/cm2).
Efficient controlled-phase gate for single-spin qubits in quantum dots
Meunier, T.; Calado, V.E.; Vandersypen, L.M.K.
2011-01-01
Two-qubit interactions are at the heart of quantum information processing. For single-spin qubits in semiconductor quantum dots, the exchange gate has always been considered the natural two-qubit gate. The recent integration of a magnetic field or g-factor gradients in coupled quantum dot systems
High-efficiency wavefunction updates for large scale Quantum Monte Carlo
Kent, Paul; McDaniel, Tyler; Li, Ying Wai; D'Azevedo, Ed
Within ab intio Quantum Monte Carlo (QMC) simulations, the leading numerical cost for large systems is the computation of the values of the Slater determinants in the trial wavefunctions. The evaluation of each Monte Carlo move requires finding the determinant of a dense matrix, which is traditionally iteratively evaluated using a rank-1 Sherman-Morrison updating scheme to avoid repeated explicit calculation of the inverse. For calculations with thousands of electrons, this operation dominates the execution profile. We propose a novel rank- k delayed update scheme. This strategy enables probability evaluation for multiple successive Monte Carlo moves, with application of accepted moves to the matrices delayed until after a predetermined number of moves, k. Accepted events grouped in this manner are then applied to the matrices en bloc with enhanced arithmetic intensity and computational efficiency. This procedure does not change the underlying Monte Carlo sampling or the sampling efficiency. For large systems and algorithms such as diffusion Monte Carlo where the acceptance ratio is high, order of magnitude speedups can be obtained on both multi-core CPU and on GPUs, making this algorithm highly advantageous for current petascale and future exascale computations.
High-efficiency optical pumping of nuclear polarization in a GaAs quantum well
Mocek, R. W.; Korenev, V. L.; Bayer, M.; Kotur, M.; Dzhioev, R. I.; Tolmachev, D. O.; Cascio, G.; Kavokin, K. V.; Suter, D.
2017-11-01
The dynamic polarization of nuclear spins by photoexcited electrons is studied in a high quality GaAs/AlGaAs quantum well. We find a surprisingly high efficiency of the spin transfer from the electrons to the nuclei as reflected by a maximum nuclear field of 0.9 T in a tilted external magnetic field of 1 T strength only. This high efficiency is due to a low leakage of spin out of the polarized nuclear system, because mechanisms of spin relaxation other than the hyperfine interaction are strongly suppressed, leading to a long nuclear relaxation time of up to 1000 s. A key ingredient to that end is the low impurity concentration inside the heterostructure, while the electrostatic potential from charged impurities in the surrounding barriers becomes screened through illumination by which the spin relaxation time is increased compared to keeping the system in the dark. This finding indicates a strategy for obtaining high nuclear spin polarization as required for long-lasting carrier spin coherence.
ZnSe Light Emitting Diode Quantum Efficiency and Emission Characterization
Directory of Open Access Journals (Sweden)
Sahbudin U.K.
2016-01-01
Full Text Available ZnSe has demonstrated as a potential candidate in realizing advance LED in some appications for current and future works that utilize a cheaper preparation technique. Blue and white LEDs have been shown to spread across compound semiconductors. This II-VI compound semiconductor with a direct and wide band gap is used in the study which focused on a preparation and its characterization. The device is developed using a circular chip of ZnSe but only part of the active region is designed to allow shorter computation time. Analyses of the proposed LED are performed in an environment that allows optical transition and nonradiative recombination mechanisms. Voltage variation from 0 V to 1.5 V is maintained throughout the observation. The curent-voltage plot shows the p-n junction or diode behavior with central emissive layer. The two dimensions surface emission rate obtained indicates that voltage increment causes the emission concentration to become higher near the central pcontact. The LED efficiency is assessed in terms of internal quantum efficiency and emitting rate.
Duality and the Knizhnik-Polyakov-Zamolodchikov relation in Liouville quantum gravity.
Duplantier, Bertrand; Sheffield, Scott
2009-04-17
We present a (mathematically rigorous) probabilistic and geometrical proof of the Knizhnik-Polyakov-Zamolodchikov relation between scaling exponents in a Euclidean planar domain D and in Liouville quantum gravity. It uses the properly regularized quantum area measure dmicro_{gamma}=epsilon;{gamma;{2}/2}e;{gammah_{epsilon}(z)}dz, where dz is the Lebesgue measure on D, gamma is a real parameter, 02 is shown to be related to the quantum measure dmu_{gamma;{'}}, gamma;{'}<2, by the fundamental duality gammagamma;{'}=4.
Comparing EU hospital efficiency using diagnosis-related groups
Rhodes, G.; Wiley, M.; Tomas, R.; Casas, M.; Leidl, R.
1997-01-01
This article considers the feasibility of comparing the differences in efficiency and price in the provision of hospital products defined on the basis of diagnosis-related groups (DRGs). Two measures of resource use are compared, the length of stay and the administrative price, both independently
The Relative Efficiency of Charter Schools: A Cost Frontier Approach
Gronberg, Timothy J.; Jansen, Dennis W.; Taylor, Lori L.
2012-01-01
Charters represent an expansion of public school choice, offering free, publicly funded educational alternatives to traditional public schools. One relatively unexplored research question concerning charter schools asks whether charter schools are more efficient suppliers of educational services than are traditional public schools. The potential…
Correcting quantum errors with entanglement.
Brun, Todd; Devetak, Igor; Hsieh, Min-Hsiu
2006-10-20
We show how entanglement shared between encoder and decoder can simplify the theory of quantum error correction. The entanglement-assisted quantum codes we describe do not require the dual-containing constraint necessary for standard quantum error-correcting codes, thus allowing us to "quantize" all of classical linear coding theory. In particular, efficient modern classical codes that attain the Shannon capacity can be made into entanglement-assisted quantum codes attaining the hashing bound (closely related to the quantum capacity). For systems without large amounts of shared entanglement, these codes can also be used as catalytic codes, in which a small amount of initial entanglement enables quantum communication.
Zhou, Ru; Niu, Haihong; Ji, Fengwei; Wan, Lei; Mao, Xiaoli; Guo, Huier; Xu, Jinzhang; Cao, Guozhong
2016-11-01
PbS is a promising light harvester for near-infrared (NIR) responsive quantum dot (QD) photovoltaics due to its narrow bulk band gap (0.41 eV) and large exciton Bohr radius (18 nm). However, the relatively low conduction band (CB) and high-density surface defects of PbS as two major drawbacks for its use in solar cells severely hamper the photovoltaic performance enhancement. In this work, a modified solution-based successive ionic layer adsorption and reaction (SILAR) utilizing mixed cationic precursors of Pb2+ and Cd2+ is explored, and such a scheme offers two benefits, band-structure tailoring and surface passivation. In-situ deposited CdS suppresses the excessive growth of PbS in the mesopores, thereby facilitating the favorable electron injection from PbS to TiO2 in view of the up-shifted CB level of QDs; the intimate interpenetration of two sulfides with each other leads to superior passivation of trap state defects on PbS, which suppresses the interfacial charge recombination. With the construction of photovoltaics based on such a hybrid (Pb,Cd)S/CdS configuration, impressive power conversion efficiency up to 4.08% has been reached, outperforming that of the conventional PbS/CdS pattern (2.95%). This work highlights the great importance of band-structure tailoring and surface passivation for constructing highly efficient PbS QD photovoltaics.
Su, Zhaofeng; Guan, Ji; Li, Lvzhou
2018-01-01
Quantum entanglement is an indispensable resource for many significant quantum information processing tasks. However, in practice, it is difficult to distribute quantum entanglement over a long distance, due to the absorption and noise in quantum channels. A solution to this challenge is a quantum repeater, which can extend the distance of entanglement distribution. In this scheme, the time consumption of classical communication and local operations takes an important place with respect to time efficiency. Motivated by this observation, we consider a basic quantum repeater scheme that focuses on not only the optimal rate of entanglement concentration but also the complexity of local operations and classical communication. First, we consider the case where two different two-qubit pure states are initially distributed in the scenario. We construct a protocol with the optimal entanglement-concentration rate and less consumption of local operations and classical communication. We also find a criterion for the projective measurements to achieve the optimal probability of creating a maximally entangled state between the two ends. Second, we consider the case in which two general pure states are prepared and general measurements are allowed. We get an upper bound on the probability for a successful measurement operation to produce a maximally entangled state without any further local operations.
Predictable quantum efficient detector based on n-type silicon photodiodes
Dönsberg, Timo; Manoocheri, Farshid; Sildoja, Meelis; Juntunen, Mikko; Savin, Hele; Tuovinen, Esa; Ronkainen, Hannu; Prunnila, Mika; Merimaa, Mikko; Tang, Chi Kwong; Gran, Jarle; Müller, Ingmar; Werner, Lutz; Rougié, Bernard; Pons, Alicia; Smîd, Marek; Gál, Péter; Lolli, Lapo; Brida, Giorgio; Rastello, Maria Luisa; Ikonen, Erkki
2017-12-01
The predictable quantum efficient detector (PQED) consists of two custom-made induced junction photodiodes that are mounted in a wedged trap configuration for the reduction of reflectance losses. Until now, all manufactured PQED photodiodes have been based on a structure where a SiO2 layer is thermally grown on top of p-type silicon substrate. In this paper, we present the design, manufacturing, modelling and characterization of a new type of PQED, where the photodiodes have an Al2O3 layer on top of n-type silicon substrate. Atomic layer deposition is used to deposit the layer to the desired thickness. Two sets of photodiodes with varying oxide thicknesses and substrate doping concentrations were fabricated. In order to predict recombination losses of charge carriers, a 3D model of the photodiode was built into Cogenda Genius semiconductor simulation software. It is important to note that a novel experimental method was developed to obtain values for the 3D model parameters. This makes the prediction of the PQED responsivity a completely autonomous process. Detectors were characterized for temperature dependence of dark current, spatial uniformity of responsivity, reflectance, linearity and absolute responsivity at the wavelengths of 488 nm and 532 nm. For both sets of photodiodes, the modelled and measured responsivities were generally in agreement within the measurement and modelling uncertainties of around 100 parts per million (ppm). There is, however, an indication that the modelled internal quantum deficiency may be underestimated by a similar amount. Moreover, the responsivities of the detectors were spatially uniform within 30 ppm peak-to-peak variation. The results obtained in this research indicate that the n-type induced junction photodiode is a very promising alternative to the existing p-type detectors, and thus give additional credibility to the concept of modelled quantum detector serving as a primary standard. Furthermore, the manufacturing of
Quantum spaces, central extensions of Lie groups and related quantum field theories
Poulain, Timothé; Wallet, Jean-Christophe
2018-02-01
Quantum spaces with su(2) noncommutativity can be modelled by using a family of SO(3)-equivariant differential *-representations. The quantization maps are determined from the combination of the Wigner theorem for SU(2) with the polar decomposition of the quantized plane waves. A tracial star-product, equivalent to the Kontsevich product for the Poisson manifold dual to su(2) is obtained from a subfamily of differential *-representations. Noncommutative (scalar) field theories free from UV/IR mixing and whose commutative limit coincides with the usual ϕ 4 theory on ℛ3 are presented. A generalization of the construction to semi-simple possibly non simply connected Lie groups based on their central extensions by suitable abelian Lie groups is discussed. Based on a talk presented by Poulain T at the XXVth International Conference on Integrable Systems and Quantum symmetries (ISQS-25), Prague, June 6-10 2017.
Quantum mechanics in general relativity and its special - relativistic limit
International Nuclear Information System (INIS)
Tagirov, Eh.A.
1998-01-01
Quantum mechanics of a neutral point-like particle in the general Riemannian space-time is constructed starting with the general Fock representation of the quantum scalar field. The known ambiguity of the representation is removed by the requirement that the quasi-one-particle wave functions in configurational space should admit the Born probabilistic interpretation after a transformation, generally nonlocal, and therefore may be considered as the one-particle wave functions. Operators of momentum and spatial position of a particle acting in the space of these transformed wave functions are deduced consecutively from basic naturally defined operators of the observables in the Fock space. They coincide with the canonical ones only in the case of the infinite velocity of light. In particular, even in the Minkowski space-time and inertial frames of reference , the operators of curvilinear coordinates do not commute
DEFF Research Database (Denmark)
Hansen, Per Lunnemann; Rabouw, Freddy T.; van Dijk-Moes, Relinde J. A.
2013-01-01
We demonstrate that a simple silver coated ball lens can be used to accurately measure the entire distribution of radiative transition rates of quantum dot nanocrystals. This simple and cost-effective implementation of Drexhage’s method that uses nanometer-controlled optical mode density variatio...
Miao, Yanqin; Tao, Peng; Wang, Kexiang; Li, Hongxin; Zhao, Bo; Gao, Long; Wang, Hua; Xu, Bingshe; Zhao, Qiang
2017-11-01
Two highly efficient red neutral iridium(III) complexes, Ir1 and Ir2, were rationally designed and synthesized by selecting two pyridylimidazole derivatives as the ancillary ligands. Both Ir1 and Ir2 show nearly the same photoluminescence emission with the maximum peak at 595 nm (shoulder band at about 638 nm) and achieve high solution quantum yields of up to 0.47 for Ir1 and 0.57 for Ir2. Employing Ir1 and Ir2 as emitters, the fabricated red organic light-emitting diodes (OLEDs) show outstanding performance with the maximum external quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) of 20.98%, 33.04 cd/A, and 33.08 lm/W for the Ir1-based device and 22.15%, 36.89 cd/A, and 35.85 lm/W for the Ir2-based device, respectively. Furthermore, using Ir2 as red emitter, a trichromatic hybrid white OLED, showing good warm white emission with low correlated color temperature of white device also realizes excellent device efficiencies with the maximum EQE, CE, and PE reaching 22.74%, 44.77 cd/A, and 46.89 lm/W, respectively. Such high electroluminescence performance for red and white OLEDs indicates that Ir1 and Ir2 as efficient red phosphors have great potential for future OLED displays and lightings applications.
Directory of Open Access Journals (Sweden)
Hyeoung Woo Park
2012-01-01
Full Text Available We have investigated the effect of water (H2O cooling and heat treatment on the luminescence efficiency of core CdSe quantum dots (QDs. The photoluminescence (PL quantum yield of the CdSe QDs was enhanced up to ~85%, and some periodic bright points were observed in wide color ranges during the heat treatment of QDs mixed with H2O. The PL enhancement of QDs could be attributed to the recovery of QDs surface traps by unreacted ligands confined within the hydrophilic H2O molecule containers.
DEFF Research Database (Denmark)
Gregersen, Niels; Munsch, Mathieu; Malik, Nitin S.
2013-01-01
Efficient coupling between a localized quantum emitter and a well defined optical channel represents a powerful route to realize single-photon sources and spin-photon interfaces. The tailored fiber-like photonic nanowire embedding a single quantum dot has recently demonstrated an appealing...... potential. However, the device requires a delicate, sharp needle-like taper with performance sensitive to minute geometrical details. To overcome this limitation we demonstrate the photonic trumpet, exploiting an opposite tapering strategy. The trumpet features a strongly Gaussian far-field emission...
ZnSe passivation layer for the efficiency enhancement of CuInS2 quantum dots sensitized solar cells
International Nuclear Information System (INIS)
Peng, Zhuoyin; Liu, Yueli; Zhao, Yinghan; Chen, Keqiang; Cheng, Yuqing; Kovalev, Valery; Chen, Wen
2014-01-01
Highlights: • ZnSe is employed as passivation layer in CuInS 2 quantum dots sensitized solar cells. • Slight red-shift has been occurred in UV–vis absorption spectra with ZnSe coating. • CuInS 2 based solar cells coated by ZnSe have better efficiency than that of ZnS. • Higher rate of charge transport can be produced after coating with ZnSe. -- Abstract: The effect of ZnSe passivation layer is investigated in the CuInS 2 quantum dot sensitized solar cells, which is used to improve the photovoltaic performance. The CuInS 2 quantum dot sensitized TiO 2 photo-anodes are prepared by assembly linking technique, and then deposited by the ZnSe passivation layer using the successive ionic layer absorption and reaction technique. The optical absorption edge and photoluminescence peak have slightly red-shifted after the passivation layer coating. Under solar light illumination, the ZnSe passivation layer based CuInS 2 quantum dot sensitized solar cells have the higher photovoltaic efficiency of 0.95% and incident photon conversion efficiency response than that of pure CuInS 2 based solar cells and ZnS passivation layer based solar cells, as the electron injection rate becomes faster after coating with ZnSe passivation layer
A comparison of digital radiography systems in terms of effective detective quantum efficiency
Energy Technology Data Exchange (ETDEWEB)
Bertolini, Marco; Nitrosi, Andrea; Rivetti, Stefano; Lanconelli, Nico; Pattacini, Pierpaolo; Ginocchi, Vladimiro; Iori, Mauro [Department of Advanced Technology, Medical Physics Unit, Azienda Ospedaliera ASMN, Istituto di Ricovero e Cura a Carattere Scientifico, Reggio Emilia 42123 (Italy); Fisica Medica, Ospedale di Sassuolo S.p.A., Modena 41049 (Italy); Alma Mater Studiorum, Physics Department, University of Bologna, Bologna 40127 (Italy); Department of Diagnostic Imaging, Radiology Unit, Azienda Ospedaliera ASMN, Istituto di Ricovero e Cura a Carattere Scientifico, Reggio Emilia 42123 (Italy); Department of Diagnostic Imaging, Radiology Unit, Azienda USL, Reggio Emilia 42122 (Italy); Department of Advanced Technology, Medical Physics Unit, Azienda Ospedaliera ASMN, Istituto di Ricovero e Cura a Carattere Scientifico, Reggio Emilia 42123 (Italy)
2012-05-15
Purpose: The purpose of this study is to compare digital radiography systems using the metric effective detective quantum efficiency (eDQE), which better reflects digital radiography imaging system performance under clinical operating conditions, in comparison with conventional metrics such as modulation transfer function (MTF), normalized noise power spectra (NNPS), and detective quantum efficiency (DQE). Methods: The eDQE was computed by the calculation of the MTF, the NNPS, the phantom attenuation and scatter, and estimation of x-ray flux. The physical characterization of the systems was obtained with the standard beam conditions RQA5 and RQA9, using the PA Chest phantom proposed by AAPM Report no. 31 simulating the attenuation and scatter characteristics of the adult human thorax. The MTF (eMTF) was measured by using an edge test placed at the frontal surface of the phantom, the NNPS (eNNPS) was calculated from images of the phantom acquired at three different exposure levels covering the operating range of the system (E{sub 0}, which is the exposure at which a system is normally operated, 1/3 E{sub 0}, and 3 E0), and scatter measurements were assessed by using a beam-stop technique. The integral of DQE (IDQE) and eDQE (IeDQE) was calculated over the whole spatial frequency range. Results: The eMTF results demonstrate degradation due to magnification and the presence of scattered radiation. The eNNPS was influenced by the grid presence, and in some systems, it contained structured noise. At typical clinical exposure levels, the magnitude of eDQE(0) with respect to DQE(0) at RQA9 beam conditions was 13%, 17%, 16%, 36%, and 24%, respectively, for Carestream DRX-1, Carestream DRX-1C, Carestream Direct View CR975, Philips Digital Diagnost VM, and GE Revolution XR/d. These results were confirmed by the ratio of IeDQE and IDQE in the same conditions. Conclusions: The authors confirm the robustness and reproducibility of the eDQE method. As expected, the DR systems
A comparison of digital radiography systems in terms of effective detective quantum efficiency
International Nuclear Information System (INIS)
Bertolini, Marco; Nitrosi, Andrea; Rivetti, Stefano; Lanconelli, Nico; Pattacini, Pierpaolo; Ginocchi, Vladimiro; Iori, Mauro
2012-01-01
Purpose: The purpose of this study is to compare digital radiography systems using the metric effective detective quantum efficiency (eDQE), which better reflects digital radiography imaging system performance under clinical operating conditions, in comparison with conventional metrics such as modulation transfer function (MTF), normalized noise power spectra (NNPS), and detective quantum efficiency (DQE). Methods: The eDQE was computed by the calculation of the MTF, the NNPS, the phantom attenuation and scatter, and estimation of x-ray flux. The physical characterization of the systems was obtained with the standard beam conditions RQA5 and RQA9, using the PA Chest phantom proposed by AAPM Report no. 31 simulating the attenuation and scatter characteristics of the adult human thorax. The MTF (eMTF) was measured by using an edge test placed at the frontal surface of the phantom, the NNPS (eNNPS) was calculated from images of the phantom acquired at three different exposure levels covering the operating range of the system (E 0 , which is the exposure at which a system is normally operated, 1/3 E 0 , and 3 E0), and scatter measurements were assessed by using a beam-stop technique. The integral of DQE (IDQE) and eDQE (IeDQE) was calculated over the whole spatial frequency range. Results: The eMTF results demonstrate degradation due to magnification and the presence of scattered radiation. The eNNPS was influenced by the grid presence, and in some systems, it contained structured noise. At typical clinical exposure levels, the magnitude of eDQE(0) with respect to DQE(0) at RQA9 beam conditions was 13%, 17%, 16%, 36%, and 24%, respectively, for Carestream DRX-1, Carestream DRX-1C, Carestream Direct View CR975, Philips Digital Diagnost VM, and GE Revolution XR/d. These results were confirmed by the ratio of IeDQE and IDQE in the same conditions. Conclusions: The authors confirm the robustness and reproducibility of the eDQE method. As expected, the DR systems performed
International Nuclear Information System (INIS)
Liu Yang; Yang Yongchun
2016-01-01
The effects of Mg doping in the quantum barriers (QBs) on the efficiency droop of GaN based light emitting diodes (LEDs) were investigated through a duel wavelength method. Barrier Mg doping would lead to the enhanced hole transportation and reduced polarization field in the quantum wells (QWs), both may reduce the efficiency droop. However, heavy Mg doping in the QBs would strongly deteriorate the crystal quality of the QWs grown after the doped QB. When increasing the injection current, the carriers would escape from the QWs between n-GaN and the doped QB and recombine non-radiatively in the QWs grown after the doped QB, leading to a serious efficiency droop. (paper)
Highly Efficient Moisture-Triggered Nanogenerator Based on Graphene Quantum Dots.
Huang, Yaxin; Cheng, Huhu; Shi, Gaoquan; Qu, Liangti
2017-11-08
A high-performance moisture triggered nanogenerator is fabricated by using graphene quantum dots (GQDs) as the active material. GQDs are prepared by direct oxidation and etching of natural graphite powder, which have small sizes of 2-5 nm and abundant oxygen-containing functional groups. After the treatment by electrochemical polarization, the GQDs-based moisture triggered nanogenerator can deliver a high voltage up to 0.27 V under 70% relative humidity variation, and a power density of 1.86 mW cm -2 with an optimized load resistor. The latter value is much higher than the moisture-electric power generators reported previously. The GQD moisture triggered nanogenerator is promising for self-power electronics and miniature sensors.
Quantum group and Manin plane related to a coloured braid group representation
International Nuclear Information System (INIS)
Basu Mallick, B.
1993-07-01
By considering 'coloured' braid group representation we have obtained a quantum group, which reduces to the standards GL q (2) and GL pq (2) cases at some particular limits of the 'colour' parameters. In spite of quite complicated nature, all of these new quantum group relations can be expressed neatly in the Heisenberg-Weyl form, for a nontrivial choice of the basis elements. Furthermore, it is possible to associate invariant Manin planes, parametrized by the 'colour' variables, with such quantum group structure. (author). 26 refs
International Nuclear Information System (INIS)
Christian, George M.; Hammersley, Simon; Davies, Matthew J.; Dawson, Philip; Kappers, Menno J.; Massabuau, Fabien C.P.; Oliver, Rachel A.; Humphreys, Colin J.
2016-01-01
We report on the effects of varying the number of quantum wells (QWs) in an InGaN/GaN multiple QW (MQW) structure containing a 23 nm thick In0.05Ga0.95N prelayer doped with Si. The calculated conduction and valence bands for the structures show an increasing total electric field across the QWs with increasing number of QWs. This is due to the reduced strength of the surface polarisation field, which opposes the built-in field across the QWs, as its range is increased over thicker samples. Low temperature photoluminescence (PL) measurements show a red shifted QW emission peak energy, which is attributed to the enhanced quantum confined Stark effect with increasing total field strength across the QWs. Low temperature PL time decay measurements and room temperature internal quantum efficiency (IQE) measurements show decreasing radiative recombination rates and decreasing IQE, respectively, with increasing number of QWs. These are attributed to the increased spatial separation of the electron and hole wavefunctions, consistent with the calculated band profiles. It is also shown that, for samples with fewer QWs, the reduction of the total field across the QWs makes the radiative recombination rate sufficiently fast that it is competitive with the efficiency losses associated with the thermal escape of carriers. (copyright 2016 The Authors. Phys. Status Solidi C published by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Relative efficiency calculation of a HPGe detector using MCNPX code
International Nuclear Information System (INIS)
Medeiros, Marcos P.C.; Rebello, Wilson F.; Lopes, Jose M.; Silva, Ademir X.
2015-01-01
High-purity germanium detectors (HPGe) are mandatory tools for spectrometry because of their excellent energy resolution. The efficiency of such detectors, quoted in the list of specifications by the manufacturer, frequently refers to the relative full-energy peak efficiency, related to the absolute full-energy peak efficiency of a 7.6 cm x 7.6 cm (diameter x height) NaI(Tl) crystal, based on the 1.33 MeV peak of a 60 Co source positioned 25 cm from the detector. In this study, we used MCNPX code to simulate a HPGe detector (Canberra GC3020), from Real-Time Neutrongraphy Laboratory of UFRJ, to survey the spectrum of a 60 Co source located 25 cm from the detector in order to calculate and confirm the efficiency declared by the manufacturer. Agreement between experimental and simulated data was achieved. The model under development will be used for calculating and comparison purposes with the detector calibration curve from software Genie2000™, also serving as a reference for future studies. (author)
Energy Technology Data Exchange (ETDEWEB)
Erol, V. [Department of Computer Engineering, Institute of Science, Okan University, Istanbul (Turkey); Netas Telecommunication Inc., Istanbul (Turkey)
2016-04-21
Entanglement has been studied extensively for understanding the mysteries of non-classical correlations between quantum systems. In the bipartite case, there are well known monotones for quantifying entanglement such as concurrence, relative entropy of entanglement (REE) and negativity, which cannot be increased via local operations. The study on these monotones has been a hot topic in quantum information [1-7] in order to understand the role of entanglement in this discipline. It can be observed that from any arbitrary quantum pure state a mixed state can obtained. A natural generalization of this observation would be to consider local operations classical communication (LOCC) transformations between general pure states of two parties. Although this question is a little more difficult, a complete solution has been developed using the mathematical framework of the majorization theory [8]. In this work, we analyze the relation between entanglement monotones concurrence and negativity with respect to majorization for general two-level quantum systems of two particles.
Directory of Open Access Journals (Sweden)
Gibran eManasseh
2013-11-01
Full Text Available The retina is one of the best known quantum detectors with rods able to reliably respond to single photons. However, estimates on the number of photons eliciting conscious perception, based on signal detection theory, are systematically above these values after discounting by retinal losses. One possibility is that there is a trade-off between the limited motor resources available to living systems and the excellent reliability of the visual photoreceptors. On this view, the limits to sensory thresholds are not set by the individual reliability of the receptors within each sensory modality (as often assumed but rather by the limited central processing and motor resources available to process the constant inflow of sensory information. To investigate this issue, we reproduced the classical experiment from Hetch aimed to determine the sensory threshold in human vision. We combined a careful physical control of the stimulus parameters with high temporal/spatial resolution recordings of EEG signals and behavioral variables over a relatively large sample of subjects (12. Contrarily to the idea that the limits to visual sensitivity are fully set by the statistical fluctuations in photon absorption on retinal photoreceptors we observed that the state of ongoing neural oscillations before any photon impinges the retina helps to determine if the responses of photoreceptors have access to central conscious processing. Our results suggest that motivational and attentional off-retinal mechanisms play a major role in reducing the QE efficiency of the human visual system when compared to the efficiency of isolated retinal photoreceptors. Yet, this mechanism might subserve adaptive behavior by enhancing the overall multisensory efficiency of the whole system composed by diverse reliable sensory modalities.
Comment on 'Immirzi parameter in quantum general relativity'
International Nuclear Information System (INIS)
Samuel, Joseph
2001-01-01
The Immirzi parameter is a free parameter which appears in the physical predictions of loop quantum gravity and is sometimes viewed as a quantization ambiguity. Interpretations have been offered for the Immirzi ambiguity, but there does not appear to be a clear understanding or even a consensus about its origin and significance. We show that a previously discussed example containing a 'finite dimensional analogue' of the Immirzi ambiguity is fallacious, in the sense that the ambiguity in this example is not intrinsic to the system, but introduced artificially by compactifying the configuration space
The Hyloquantum: the uncertainty (-relation) between myth and quantum mechanics
International Nuclear Information System (INIS)
Weissitsch, R.
2010-01-01
It was the challenge, to draw a bow from antiquity to the present day and to characterize the 'Intermediate' as concisely as possible and to examine out possible commonalities in 2600 years of development and evolution of the (natural) science. Despite all the apparent incompatibility between Thales' observations of nature and the modern (particle) physics, i.e. between views, which were about to break away from mythical ideas, and beliefs that are now turning back to a certain myth, such a community could be found. The Unifying of thought from ancient times to today is at its core, the fusion of a conception of the world, which appears to be the opposite of the quantization and refers to continuous processes. This dialectical pair that opened the thought of 'either - or' new doors, gives additional, yet to be discovered possibilities, which can be described as the principle of Hyloquantums. The term 'Hyloquant' / 'Hyloquantum' is a neologism of the author. The term Hyloquantum subsumes multiple levels of description to a metaphysics of physics.The term 'Hyle' describes the 'substance, matter' of which a body is built. The idea of an eternal and 'universal matter', was an idea of the Presocratics, but is common in modern notions of ever smaller particles (quarks and Quantum foam) again.In contrast to the 100 years of existing conception of a discontinuous structure of the quantum world, is the Newtonian notion that nature is a continuum, and thus laws are deducible. The (quantum) 'jumps', which apparently occur in the microcosm, are diametrically to the beliefs and statements of the 'flowing' (natural) events in the macrocosm.The Hyloquantum is the essential substance of all being, and it corresponds to the inner world of the outside world as much as the outside of the inner world. It is not conceptually elusive combination of physically separate ideas (continuum vs. Quantum.), from which ultimately everything is composed. The extension of the old idea that one is
Quantum walks, deformed relativity and Hopf algebra symmetries.
Bisio, Alessandro; D'Ariano, Giacomo Mauro; Perinotti, Paolo
2016-05-28
We show how the Weyl quantum walk derived from principles in D'Ariano & Perinotti (D'Ariano & Perinotti 2014Phys. Rev. A90, 062106. (doi:10.1103/PhysRevA.90.062106)), enjoying a nonlinear Lorentz symmetry of dynamics, allows one to introduce Hopf algebras for position and momentum of the emerging particle. We focus on two special models of Hopf algebras-the usual Poincaré and theκ-Poincaré algebras. © 2016 The Author(s).
Type II GaSb/GaAs quantum dot/ring stacks with extended photoresponse for efficient solar cells
Energy Technology Data Exchange (ETDEWEB)
Carrington, Peter James, E-mail: p.carrington@lancaster.ac.uk [Physics Department, Lancaster University, Lancaster LA1 4YB (United Kingdom); Mahajumi, Abu Syed [Physics Department, Lancaster University, Lancaster LA1 4YB (United Kingdom); Wagener, Magnus C.; Botha, Johannes Reinhardt [Department of Physics, Nelson Mandela Metropolitan University, Port Elizabeth (South Africa); Zhuang Qian; Krier, Anthony [Physics Department, Lancaster University, Lancaster LA1 4YB (United Kingdom)
2012-05-15
We report on the fabrication of GaAs based p-i-n solar cells containing 5 and 10 layers of type II GaSb quantum rings grown by molecular beam epitaxy. Solar cells containing quantum rings show improved efficiency at longer wavelengths into the near-IR extending up to 1500 nm and show enhanced short-circuit current under 1 sun illumination compared to a GaAs control cell. A reduction in the open-circuit voltage is observed due to the build-up of internal strain. The MBE growth, formation and photoluminescence of single and stacked layers of GaSb/GaAs quantum rings are also presented.
Type II GaSb/GaAs quantum dot/ring stacks with extended photoresponse for efficient solar cells
International Nuclear Information System (INIS)
Carrington, Peter James; Mahajumi, Abu Syed; Wagener, Magnus C.; Botha, Johannes Reinhardt; Zhuang Qian; Krier, Anthony
2012-01-01
We report on the fabrication of GaAs based p–i–n solar cells containing 5 and 10 layers of type II GaSb quantum rings grown by molecular beam epitaxy. Solar cells containing quantum rings show improved efficiency at longer wavelengths into the near-IR extending up to 1500 nm and show enhanced short-circuit current under 1 sun illumination compared to a GaAs control cell. A reduction in the open-circuit voltage is observed due to the build-up of internal strain. The MBE growth, formation and photoluminescence of single and stacked layers of GaSb/GaAs quantum rings are also presented.
DEFF Research Database (Denmark)
Lund-Hansen, Toke; Stobbe, Søren; Julsgaard, Brian
2008-01-01
We present time-resolved spontaneous emission measurements of single quantum dots embedded in photonic crystal waveguides. Quantum dots that couple to a photonic crystal waveguide are found to decay up to 27 times faster than uncoupled quantum dots. From these measurements -factors of up to 0.89 ...... taking into account that the light-matter coupling is strongly enhanced due to the significant slow-down of light in the photonic crystal waveguides....
Directory of Open Access Journals (Sweden)
Ja-Ryong Koo
2012-03-01
Full Text Available We demonstrate red phosphorescent organic light-emitting diodes (OLEDs with multiple quantum well structures which confine triplet exciton inside an emitting layer (EML region. Five types of OLEDs, from a single to five quantum wells, are fabricated with charge control layers to produce high efficiencies, and the performance of the devices is investigated. The improved quantum efficiency and lifetime of the OLED with four quantum wells, and its suppressed quantum efficiency roll-off of 17.6%, can be described by the increased electron–hole charge balance owing to the bipolar property as well as the efficient triplet exciton confinement within each EML, and by prevention of serious triplet–triplet and/or triplet–polaron annihilation as well as the Förster self-quenching due to charge control layers.
Energy Technology Data Exchange (ETDEWEB)
Xia, Mengling; Liu, Chao, E-mail: hite@whut.edu.cn; Han, Jianjun; Zhao, Xiujian
2017-06-15
CdS/Cd{sub 1−x}Zn{sub x}S sandwich-structured quantum dots (QDs) were precipitated in silicate glasses with high quantum efficiency up to 53%. The QDs were composed by a CdS core with a Cd{sub 1−x}Zn{sub x}S shell of about 1–3 nm in thickness through heat-treatment at 550 °C for 10 h. With the increased heat-treatment temperature, the intensity ratio between the intrinsic emission and the defects emission increased and the Stokes shift decreased from 84 to 4 meV, which was caused by both the increased size and passivated surface defects of the QDs.
Energy Technology Data Exchange (ETDEWEB)
Zhang, Shukui [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Poelker, Matthew [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Stutzman, Marcy L. [Thomas Jefferson National Accelerator Facility, Newport News, VA (United States); Chen, Yiqiao [SVT Associates, Inc., Eden Prairie, MN (United States); Moy, Aaron [SVT Associates, Inc., Eden Prairie, MN (United States)
2015-09-01
Polarized photocathodes with higher Quantum efficiency (QE) would help to reduce the technological challenge associated with producing polarized beams at milliampere levels, because less laser light would be required, which simplifies photocathode cooling requirements. And for a given amount of available laser power, higher QE would extend the photogun operating lifetime. The distributed Bragg reflector (DBR) concept was proposed to enhance the QE of strained-superlattice photocathodes by increasing the absorption of the incident photons using a Fabry-Perot cavity formed between the front surface of the photocathode and the substrate that includes a DBR, without compromising electron polarization. Here we present recent results showing QE enhancement of a GaAs/GaAsP strained-superlattice photocathode made with a DBR structure. Typically, a GaAs/GaAsP strained-superlattice photocathode without DBR provides a QE of 1%, at a laser wavelength corresponding to peak polarization. In comparison, the GaAs/GaAsP strained-superlattice photocathodes with DBR exhibited an enhancement of over 2 when the incident laser wavelength was tuned to meet the resonant condition for the Fabry-Perot resonator.
Work function and quantum efficiency study of metal oxide thin films on Ag(100)
Chang, V.; Noakes, T. C. Q.; Harrison, N. M.
2018-04-01
Increasing the quantum efficiency (QE) of metal photocathodes is in the design and development of photocathodes for free-electron laser applications. The growth of metal oxide thin films on certain metal surfaces has previously been shown to reduce the work function (WF). Using a photoemission model B. Camino et al. [Comput. Mater. Sci. 122, 331 (2016), 10.1016/j.commatsci.2016.05.025] based on the three-step model combined with density functional theory calculations we predict that the growth of a finite number of MgO(100) or BaO(100) layers on the Ag(100) surface increases significantly the QE compared with the clean Ag(100) surface for a photon energy of 4.7 eV. Different mechanisms for affecting the QE are identified for the different metal oxide thin films. The addition of MgO(100) increases the QE due to the reduction of the WF and the direct excitation of electrons from the Ag surface to the MgO conduction band. For BaO(100) thin films, an additional mechanism is in operation as the oxide film also photoemits at this energy. We also note that a significant increase in the QE for photons with an energy of a few eV above the WF is achieved due to an increase in the inelastic mean-free path of the electrons.
International Nuclear Information System (INIS)
Duun, Sune; Haahr, Rasmus G; Hansen, Ole; Birkelund, Karen; Thomsen, Erik V
2010-01-01
The development of annular photodiodes for use in a reflectance pulse oximetry sensor is presented. Wearable and wireless body sensor systems for long-term monitoring require sensors that minimize power consumption. We have fabricated large area 2D ring-shaped silicon photodiodes optimized for minimizing the optical power needed in reflectance pulse oximetry. To simplify packaging, backside photodiodes are made which are compatible with assembly using surface mounting technology without pre-packaging. Quantum efficiencies up to 95% and area-specific noise equivalent powers down to 30 fW Hz -1/2 cm -1 are achieved. The photodiodes are incorporated into a wireless pulse oximetry sensor system embedded in an adhesive patch presented elsewhere as 'The Electronic Patch'. The annular photodiodes are fabricated using two masked diffusions of first boron and subsequently phosphor. The surface is passivated with a layer of silicon nitride also serving as an optical filter. As the final process, after metallization, a hole in the center of the photodiode is etched using deep reactive ion etch.
Lee, Y.; Bescond, M.; Logoteta, D.; Cavassilas, N.; Lannoo, M.; Luisier, M.
2018-05-01
We propose an efficient method to quantum mechanically treat anharmonic interactions in the atomistic nonequilibrium Green's function simulation of phonon transport. We demonstrate that the so-called lowest-order approximation, implemented through a rescaling technique and analytically continued by means of the Padé approximants, can be used to accurately model third-order anharmonic effects. Although the paper focuses on a specific self-energy, the method is applicable to a very wide class of physical interactions. We apply this approach to the simulation of anharmonic phonon transport in realistic Si and Ge nanowires with uniform or discontinuous cross sections. The effect of increasing the temperature above 300 K is also investigated. In all the considered cases, we are able to obtain a good agreement with the routinely adopted self-consistent Born approximation, at a remarkably lower computational cost. In the more complicated case of high temperatures (≫300 K), we find that the first-order Richardson extrapolation applied to the sequence of the Padé approximants N -1 /N results in a significant acceleration of the convergence.
Escartin, Terenz R.; Nano, Tomi F.; Cunningham, Ian A.
2016-03-01
The detective quantum efficiency (DQE), expressed as a function of spatial frequency, describes the ability of an x-ray detector to produce high signal-to-noise ratio (SNR) images. While regulatory and scientific communities have used the DQE as a primary metric for optimizing detector design, the DQE is rarely used by end users to ensure high system performance is maintained. Of concern is that image quality varies across different systems for the same exposures with no current measures available to describe system performance. Therefore, here we conducted an initial DQE measurement survey of clinical x-ray systems using a DQE-testing instrument to identify their range of performance. Following laboratory validation, experiments revealed that the DQE of five different systems under the same exposure level (8.0 μGy) ranged from 0.36 to 0.75 at low spatial frequencies, and 0.02 to 0.4 at high spatial frequencies (3.5 cycles/mm). Furthermore, the DQE dropped substantially with decreasing detector exposure by a factor of up to 1.5x in the lowest spatial frequency, and a factor of 10x at 3.5 cycles/mm due to the effect of detector readout noise. It is concluded that DQE specifications in purchasing decisions, combined with periodic DQE testing, are important factors to ensure patients receive the health benefits of high-quality images for low x-ray exposures.
Bok, Jan; Schauer, Petr
2014-01-01
In the paper, the SEM detector is evaluated by the modulation transfer function (MTF) which expresses the detector's influence on the SEM image contrast. This is a novel approach, since the MTF was used previously to describe only the area imaging detectors, or whole imaging systems. The measurement technique and calculation of the MTF for the SEM detector are presented. In addition, the measurement and calculation of the detective quantum efficiency (DQE) as a function of the spatial frequency for the SEM detector are described. In this technique, the time modulated e-beam is used in order to create well-defined input signal for the detector. The MTF and DQE measurements are demonstrated on the Everhart-Thornley scintillation detector. This detector was alternated using the YAG:Ce, YAP:Ce, and CRY18 single-crystal scintillators. The presented MTF and DQE characteristics show good imaging properties of the detectors with the YAP:Ce or CRY18 scintillator, especially for a specific type of the e-beam scan. The results demonstrate the great benefit of the description of SEM detectors using the MTF and DQE. In addition, point-by-point and continual-sweep e-beam scans in SEM were discussed and their influence on the image quality was revealed using the MTF. © 2013 Wiley Periodicals, Inc.
Luminescent ZnO quantum dots as an efficient sensor for free chlorine detection in water.
Singh, Kulvinder; Mehta, S K
2016-04-21
Highly luminescent ZnO quantum dots (QDs) synthesized via a simple and facile route are used for the preparation of an optical sensor for the detection of free chlorine. The concentration of free chlorine greatly affects the PL emission of the ZnO QDs at 525 nm. Since hypochlorite gains electrons with high efficiency, it takes electrons from the oxygen vacancies of ZnO QDs, which gives rise to defect emission in ZnO QDs. UV-vis data analysis shows that free chlorine does not affect the optical absorption spectra of ZnO QDs. The optical sensing of free chlorine using ZnO QDs has several advantages, like quick response time, good selectivity and of course high sensitivity. The pH has very little effect on the PL emission of ZnO QDs. It does not interfere in the sensing mechanism for free chlorine. After 60 s, the response of the ZnO QDs remains stable. The present sensor shows high selectivity with respect to various common cations, as well as anions.
Quantum efficiency investigations of type-II InAs/GaSb midwave infrared superlattice photodetectors
Energy Technology Data Exchange (ETDEWEB)
Giard, E., E-mail: edouard.giard@onera.fr; Ribet-Mohamed, I.; Jaeck, J.; Viale, T.; Haïdar, R. [ONERA, DOTA, Chemin de la Hunière, 91761 Palaiseau Cedex (France); Taalat, R.; Delmas, M.; Rodriguez, J.-B.; Christol, P. [Institut d' Electronique du Sud, UMR-CNRS 5214, Université Montpellier 2, Place Eugène Bataillon, 34095 Montpellier Cedex 5 (France); Steveler, E.; Bardou, N. [Laboratoire de Photonique et de Nanostructures (LPN-CNRS), Route de Nozay, 91460 Marcoussis (France); Boulard, F. [CEA, LETI, MINATEC Campus, 17 Avenue des martyrs, 38054 Grenoble (France)
2014-07-28
We present in this paper a comparison between different type-II InAs/GaSb superlattice (T2SL) photodiodes and focal plane array (FPA) in the mid-wavelength infrared domain to understand which phenomenon drives the performances of the T2SL structure in terms of quantum efficiency (QE). Our measurements on test photodiodes suggest low minority carrier diffusion length in the “InAs-rich” design, which penalizes carriers' collection in this structure for low bias voltage and front side illumination. This analysis is completed by a comparison of the experimental data with a fully analytic model, which allows to infer a hole diffusion length shorter than 100 nm. In addition, measurements on a FPA with backside illumination are finally presented. Results show an average QE in the 3–4.7 μm window equal to 42% for U{sub bias} = −0.1 V, 77 K operating temperature and no anti-reflection coating. These measurements, completed by modulation transfer function and noise measurements, reveal that the InAs-rich design, despite a low hole diffusion length, is promising for high performance infrared imaging applications.
Surface modification effects on defect-related photoluminescence in colloidal CdS quantum dots.
Lee, TaeGi; Shimura, Kunio; Kim, DaeGwi
2018-05-03
We investigated the effects of surface modification on the defect-related photoluminescence (PL) band in colloidal CdS quantum dots (QDs). A size-selective photoetching process and a surface modification technique with a Cd(OH)2 layer enabled the preparation of size-controlled CdS QDs with high PL efficiency. The Stokes shift of the defect-related PL band before and after the surface modification was ∼1.0 eV and ∼0.63 eV, respectively. This difference in the Stokes shifts suggests that the origin of the defect-related PL band was changed by the surface modification. Analysis by X-ray photoelectron spectroscopy revealed that the surface of the CdS QDs before and after the surface modification was S rich and Cd rich, respectively. These results suggest that Cd-vacancy acceptors and S-vacancy donors affect PL processes in CdS QDs before and after the surface modification, respectively.
Cheng, Qifa; Xu, Jing; Wang, Tao; Fan, Ling; Ma, Ruifang; Yu, Xinzhi; Zhu, Jian; Xu, Zhi; Lu, Bingan
2017-11-01
Photoelectrocatalysis (PEC) has been demonstrated as a promising technique for hydrogen production. However, the high over-potential and high recombination rate of photo-induced electron-hole pairs lead to poor hydrogen production efficiency. In order to overcome these problems, TiO2 and Au dual quantum dots (QDs) on three-dimensional graphene flowers (Au@TiO2@3DGFs) was synthesized by an electro-deposition strategy. The combination of Au and TiO2 modulates the band gap of TiO2, shifts the absorption to visible lights and improves the utilization efficiency of solar light. Simultaneously, the size-quantization TiO2 on 3DGFs not only achieves a larger specific surface area over conventional nanomaterials, but also promotes the separation of the photo-induced electron-hole pairs. Besides, the 3DGFs as a scaffold for QDs can provide more active sites and stable structure. Thus, the newly-developed Au@TiO2@3DGFs composite exhibited an impressive PEC activity and excellent durability. Under -240 mV potential (vs. RHE), the photoelectric current density involved visible light illumination (100 mW cm-2) reached 90 mA cm-2, which was about 3.6 times of the natural current density (without light, only 25 mA cm-2). It worth noting that the photoelectric current density did not degrade and even increased to 95 mA cm-2 over 90 h irradiation, indicating an amazing chemical stability.
Efficient colorimetric pH sensor based on responsive polymer-quantum dot integrated graphene oxide.
Paek, Kwanyeol; Yang, Hyunseung; Lee, Junhyuk; Park, Junwoo; Kim, Bumjoon J
2014-03-25
In this paper, we report the development of a versatile platform for a highly efficient and stable graphene oxide (GO)-based optical sensor that exhibits distinctive ratiometric color responses. To demonstrate the applicability of the platform, we fabricated a colorimetric, GO-based pH sensor that responds to a wide range of pH changes. Our sensing system is based on responsive polymer and quantum dot (QD) hybrids integrated on a single GO sheet (MQD-GO), with the GO providing an excellent signal-to-noise ratio and high dispersion stability in water. The photoluminescence emissions of the blue and orange color-emitting QDs (BQDs and OQDs) in MQD-GO can be controlled independently by different pH-responsive linkers of poly(acrylic acid) (PAA) (pKa=4.5) and poly(2-vinylpyridine) (P2VP) (pKa=3.0) that can tune the efficiencies of Förster resonance energy transfer from the BQDs to the GO and from the OQDs to the GO, respectively. As a result, the color of MQD-GO changes from orange to near-white to blue over a wide range of pH values. The detailed mechanism of the pH-dependent response of the MQD-GO sensor was elucidated by measurements of time-resolved fluorescence and dynamic light scattering. Furthermore, the MQD-GO sensor showed excellent reversibility and high dispersion stability in pure water, indicating that our system is an ideal platform for biological and environmental applications. Our colorimetric GO-based optical sensor can be expanded easily to various other multifunctional, GO-based sensors by using alternate stimuli-responsive polymers.
Myasthenia Gravis Impairment Index: Responsiveness, meaningful change, and relative efficiency.
Barnett, Carolina; Bril, Vera; Kapral, Moira; Kulkarni, Abhaya V; Davis, Aileen M
2017-12-05
To study responsiveness and meaningful change of the Myasthenia Gravis Impairment Index (MGII) and its relative efficiency compared to other measures. We enrolled 95 patients receiving prednisone, IV immunoglobulin (IVIg), or plasma exchange (PLEX) and 54 controls. Patients were assessed with the MGII and other measures-including the Quantitative Myasthenia Gravis Score, Myasthenia Gravis Composite, and Myasthenia Gravis Activities of Daily Living-at baseline and 3-4 weeks after treatment. Statistical markers of responsiveness included between-groups and within-group differences, and we estimated the relative efficiency of the MGII compared to other measures. Patient-meaningful change was assessed with an anchor-based method, using the patient's impression of change. We determined the minimal detectable change (MDC) and the minimal important difference (MID) at the group and individual level. Treated patients had a higher change in MGII scores than controls (analysis of covariance p 1 favoring the MGII. The MGII demonstrated responsiveness to prednisone, IVIg, and PLEX in patients with myasthenia. There is a differential response in ocular and generalized symptoms to type of therapy. The MGII has higher relative efficiency than comparison measures and is viable for use in clinical trials. Copyright © 2017 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Neurology.
Anti-hydrogen: The cusp between quantum mechanics and general relativity
International Nuclear Information System (INIS)
Noyes, H.P.
1992-09-01
We argue that the crossing (CPT) symmetry of relativistic quantum mechanics requires that both the coulombic and the Newtonian force between pairs of particles will reverse when one is replaced by its anti-particle. For consistency, this requires a theory in which both the equivalence principles and gauge invariance are abandoned. thus whether anti-hydrogen ''falls'' up or down will provide an experiment crusis separating general relativity and gauge invariance from this version of quantum mechanics
Position-momentum uncertainty relations in the presence of quantum memory
DEFF Research Database (Denmark)
Furrer, Fabian; Berta, Mario; Tomamichel, Marco
2014-01-01
A prominent formulation of the uncertainty principle identifies the fundamental quantum feature that no particle may be prepared with certain outcomes for both position and momentum measurements. Often the statistical uncertainties are thereby measured in terms of entropies providing a clear oper....... As an illustration, we evaluate the uncertainty relations for position and momentum measurements, which is operationally significant in that it implies security of a quantum key distribution scheme based on homodyne detection of squeezed Gaussian states....
Sahin, Mehmet
2018-05-23
In this study, the effects of the shell material and confinement type on the conversion efficiency of core/shell quantum dot nanocrystal (QDNC) solar cells have been investigated in detail. For this purpose, the conventional, i.e. original, detailed balance model, developed by Shockley and Queisser to calculate an upper limit for the conversion efficiency of silicon p-n junction solar cells, is modified in a simple and effective way to calculate the conversion efficiency of core/shell QDNC solar cells. Since the existing model relies on the gap energy ([Formula: see text]) of the solar cell, it does not make an estimation about the effect of QDNC materials on the efficiency of the solar cells, and gives the same efficiency values for several QDNC solar cells with the same [Formula: see text]. The proposed modification, however, estimates a conversion efficiency in relation to the material properties and also the confinement type of the QDNCs. The results of the modified model show that, in contrast to the original one, the conversion efficiencies of different QDNC solar cells, even if they have the same [Formula: see text], become different depending upon the confinement type and shell material of the core/shell QDNCs, and this is crucial in the design and fabrication of the new generation solar cells to predict the confinement type and also appropriate QDNC materials for better efficiency.
Sahin, Mehmet
2018-05-01
In this study, the effects of the shell material and confinement type on the conversion efficiency of core/shell quantum dot nanocrystal (QDNC) solar cells have been investigated in detail. For this purpose, the conventional, i.e. original, detailed balance model, developed by Shockley and Queisser to calculate an upper limit for the conversion efficiency of silicon p–n junction solar cells, is modified in a simple and effective way to calculate the conversion efficiency of core/shell QDNC solar cells. Since the existing model relies on the gap energy () of the solar cell, it does not make an estimation about the effect of QDNC materials on the efficiency of the solar cells, and gives the same efficiency values for several QDNC solar cells with the same . The proposed modification, however, estimates a conversion efficiency in relation to the material properties and also the confinement type of the QDNCs. The results of the modified model show that, in contrast to the original one, the conversion efficiencies of different QDNC solar cells, even if they have the same , become different depending upon the confinement type and shell material of the core/shell QDNCs, and this is crucial in the design and fabrication of the new generation solar cells to predict the confinement type and also appropriate QDNC materials for better efficiency.
Meyer, Toni; Körner, Christian; Vandewal, Koen; Leo, Karl
2018-04-01
In two terminal tandem solar cells, the current density - voltage (jV) characteristic of the individual subcells is typically not directly measurable, but often required for a rigorous device characterization. In this work, we reconstruct the jV-characteristic of organic solar cells from measurements of the external quantum efficiency under applied bias voltages and illumination. We show that it is necessary to perform a bias irradiance variation at each voltage and subsequently conduct a mathematical correction of the differential to the absolute external quantum efficiency to obtain an accurate jV-characteristic. Furthermore, we show that measuring the external quantum efficiency as a function of voltage for a single bias irradiance of 0.36 AM1.5g equivalent sun provides a good approximation of the photocurrent density over voltage curve. The method is tested on a selection of efficient, common single-junctions. The obtained conclusions can easily be transferred to multi-junction devices with serially connected subcells.
Formal scattering theory approach to S-matrix relations in supersymmetric quantum mechanics
International Nuclear Information System (INIS)
Amado, R.D.; Cannata, F.; Dedonder, J.P.
1988-01-01
Combining the methods of scattering theory and supersymmetric quantum mechanics we obtain relations between the S matrix and its supersymmetric partner. These relations involve only asymptotic quantities and do not require knowledge of the dynamical details. For example, for coupled channels with no threshold differences the relations involve the asymptotic normalization constant of the bound state removed by supersymmetry
An Efficient Inductive Genetic Learning Algorithm for Fuzzy Relational Rules
Directory of Open Access Journals (Sweden)
Antonio
2012-04-01
Full Text Available Fuzzy modelling research has traditionally focused on certain types of fuzzy rules. However, the use of alternative rule models could improve the ability of fuzzy systems to represent a specific problem. In this proposal, an extended fuzzy rule model, that can include relations between variables in the antecedent of rules is presented. Furthermore, a learning algorithm based on the iterative genetic approach which is able to represent the knowledge using this model is proposed as well. On the other hand, potential relations among initial variables imply an exponential growth in the feasible rule search space. Consequently, two filters for detecting relevant potential relations are added to the learning algorithm. These filters allows to decrease the search space complexity and increase the algorithm efficiency. Finally, we also present an experimental study to demonstrate the benefits of using fuzzy relational rules.
Energy Technology Data Exchange (ETDEWEB)
Le, Quyet Van [School; Kim, Jong Beom [Department; Kim, Soo Young [School; Lee, Byeongdu [X-ray; Lee, Dong Ryeol [Department
2017-08-15
We have investigated the effect of reaction temperature of hot-injection method on the structural properties of CsPbX3 (X: Br, I, Cl) perovskite nanocrystals (NCs) using the small- and wide-angle X-ray scattering. It is confirmed that the size of the NCs decreased as the reaction temperature decreased, resulting stronger quantum confinement. The cubic-phase perovskite NCs were formed despite the reaction temperatures increased from 140 to 180 °C. However, monodispersive NC cubes which are required for densely packing self-assembly film were only formed at lower temperatures. From the X-ray scattering measurements, the spin-coated film from more monodispersive perovskite nanocubes synthesized at lower temperatures resulted in more preferred orientation. This dense-packing perovskite film with preferred orientation yielded efficient light-emitting diode (LED) performance. Thus, the dense-packing structure of NC assemblies formed after spin-coating should be considered for high-efficient LEDs based on perovskite quantum dots in addition to quantum confinement effect of the quantum dots.
Effect of AlSb quantum dots on efficiency of GaAs solar cell (Conference Presentation)
Mansoori, Ahmad; Addamane, Sadhvikas J.; Renteria, Emma J.; Shima, Darryl M.; Hains, Christopher P.; Balakrishnan, Ganesh
2016-09-01
Quantum Dots (QDs) have a broad applications in science and specifically in solar cell. Many research groups show that by adding QDs with lower bandgap respect to host material, the overall absorption of sun spectrum coverage will increase. Here, we propose using QDs with higher band gap respect to host material to improve efficiency of solar cell by improving quantum efficiency. GaAs solar cells have the highest efficiency in single junction solar cells. However, the absorption of GaAs is not good enough in wavelength lower than 550nm. AlSb can absorb shorter wavelength with higher absorption coefficient and also recombination rate should be lower because of higher bandgap of AlSb respect to GaAs. We embed AlSb QDs in GaAs solar cells and results show slight improvement in quantum efficiency and also in overall efficiency. Coverage of AlSb QDs has a direct impact on quality of AlSb QDs and efficiency of cell. In the higher coverage, intermixing between GaAs and AlSb causes to shift bandgap to lower value (having AlGaSb QDs instead of pure AlSb QDs). This intermixing decrease the Voc and overall efficiency of cell. In lower coverage, AlSb can survive from intermixing and overall performance of cell improves. Optimizing growth condition of AlSb QDs is a key point for this work. By using AlSb QDs, we can decrease the thickness of active layer of GaAs solar cells and have a thinner solar cell.
Rollny, Lisa
Understanding colloidal stabilization can influence the design of optoelectronic devices and enable improvements to their performance and stability. For photovoltaics, important characteristics of the active layer material are high conductivity along with a minimum of recombination centers. In order to capitalize on the benefits of solution-processed materials, it is important to minimize the number of processing steps: ideally, to achieve a low-cost solution, materials would be deposited using a single process step compatible with roll-to-roll manufacturing. Prior to this work, the highest-performing colloidal quantum dots (CQD) solar cells have relied on several deposition steps that are repeated in a layer-by-layer (LBL) fashion. The purpose of these process steps has been to remove the long insulating ligands used in synthesis and replace them with short ligands that allow electrical conduction. The large number of steps combined, typically implemented via spin coating, leads to inefficient materials utilization and fails to show a path to a manufacturable solution. In this work, the first CQD solar cells were designed, built, and characterized combining state-of-art performance with scalable manufacture. Firstly, I report the first automated CQD synthesis to result in CQDs that form high-performance CQD solar cells. I analyze the CQD synthesis and by separating it into two phases---nucleation and growth phase---my insights are used to create higher-quality CQDs exhibiting enhanced monodispersity. I then proceed to develop a CQD ink: a CQD solution ready for direct deposition to form a semiconducting film exhibiting low trap state density. In early trials the CQD ink showed only limited power conversion efficiencies of 2%. I designed a new ink strategy, which I term cleavable hemiketal ligands. This novel two-component ligand strategy enables the combination of colloidal stabilization (via this longer two-component ligand) and cleavability (enabling excellent
Rotating Wigner molecules and spin-related behaviors in quantum rings
International Nuclear Information System (INIS)
Yang Ning; Zhu Jialin; Dai Zhensheng
2008-01-01
The trial wavefunctions for few-electron quantum rings are presented to describe the spin-dependent rotating Wigner molecule states. The wavefunctions are constructed from the single-particle orbits which contain two variational parameters to describe the shape and size dependence of electron localization in the ring-like confinement. They can explicitly show the size dependence of single-particle orbital occupation to give an understanding of the spin rules of ground states without magnetic fields. They can also correctly describe the spin and angular momentum transitions in magnetic fields. By examining the von Neumann entropy, it is demonstrated that the wavefunctions can illustrate the entanglement between electrons in quantum rings, including the AB oscillations as well as the spin and size dependence of the entropy. Such trial wavefunctions will be useful in investigating spin-related quantum behaviors of a few electrons in quantum rings
International Congress on Energy Efficiency and Energy Related Materials
Bahsi, Zehra; Ozer, Mehmet; ENEFM2013
2014-01-01
The International Congress on Energy Efficiency and Energy Related Materials (ENEFM2013) was held on 9-12 October, 2013. This three-day congress focused on the latest developments of sustainable energy technologies, materials for sustainable energy applications and environmental & economic perspectives of energy. These proceedings include 63 peer reviewed technical papers, submitted from leading academic and research institutions from over 23 countries, representing some of the most cutting edge research available. The papers included were presented at the congress in the following sessions: General Issues Wind Energy Solar Energy Nuclear Energy Biofuels and Bioenergy Energy Storage Energy Conservation and Efficiency Energy in Buildings Economical and Environmental Issues Environment Energy Requirements Economic Development Materials for Sustainable Energy Hydrogen Production and Storage Photovoltaic Cells Thermionic Converters Batteries and Superconductors Phase Change Materials Fuel Cells Supercon...
Directory of Open Access Journals (Sweden)
Yufeng Li
2017-11-01
Full Text Available Ag coated microgroove with extreme large aspect-ratio of 500:1 was fabricated on p-GaN capping layer to investigate the coupling behavior between quantum wells and surface plasmon in highly spatial resolution. Significant photoluminescence enhancement was observed when the distance between Ag film and QWs was reduced from 220 nm to about 20 nm. A maximum enhancement ratio of 18-fold was achieved at the groove bottom where the surface plasmonic coupling was considered the strongest. Such enhancement ratio was found highly affected by the excitation power density. It also shows high correlation to the internal quantum efficiency as a function of coupling effect and a maximum Purcell Factor of 1.75 was estimated at maximum coupling effect, which matches number calculated independently from the time-resolved photoluminescence measurement. With such Purcell Factor, the efficiency was greatly enhanced and the droop was significantly suppressed.
International Nuclear Information System (INIS)
Vishnubhatla, K C; Kumar, R Sai Santosh; Rao, D Narayana; Rao, S Venugopal; Osellame, R; Ramponi, R; Bhaktha, S N B; Mattarelli, M; Montagna, M; Turrell, S; Chiappini, A; Chiasera, A; Ferrari, M; Righini, G C
2009-01-01
The femtosecond laser direct writing technique was employed to inscribe gratings and waveguides in high quantum efficiency erbium-doped Baccarat glass. Using the butt coupling technique, a systematic study of waveguide loss with respect to input pulse energy and writing speed was performed to achieve the best waveguide with low propagation loss (PL). By pumping at 980 nm, we observed signal enhancement in these active waveguides in the telecom spectral region. The refractive index change was smooth and we estimated it to be ∼10 -3 . The high quantum efficiency (∼80%) and a best PL of ∼0.9 dB cm -1 combined with signal enhancement makes Baccarat glass a potential candidate for application in photonics.
International Nuclear Information System (INIS)
Pani, R.; Cinti, M.N.; Scafe, R.; Pellegrini, R.; Vittorini, F.; Bennati, P.; Ridolfi, S.; Lo Meo, S.; Mattioli, M.; Baldazzi, G.; Pisacane, F.; Navarria, F.; Moschini, G.; Boccaccio, P.; Orsolini Cencelli, V.; Sacco, D.
2009-01-01
The performance of the new prototype of high quantum efficiency PMT (43% at 380 nm), Hamamatsu R7600U-200, was studied coupled to a LaBr 3 :Ce crystal with the size of o12.5 mmx12.5 mm. The energy resolution results were compared with ones from two PMTs, Hamamatsu R7600U and R6231MOD, with 22% and 30% quantum efficiency (QE), respectively. Moreover, the photodetectors were equipped with tapered and un-tapered voltage dividers to study the non-linearity effects on pulse height distribution, due to very high peak currents induced in the PMT by the fast and intense light pulse of LaBr 3 :Ce. The results show an energy resolution improvement with UBA PMT of about 20%, in the energy range of 80-662 keV, with respect to the BA one.
International Nuclear Information System (INIS)
Ji, Se-Wan; Nha, Hyunchul; Kim, M S
2015-01-01
It is a topic of fundamental and practical importance how a quantum correlated state can be reliably distributed through a noisy channel for quantum information processing. The concept of quantum steering recently defined in a rigorous manner is relevant to study it under certain circumstances and here we address quantum steerability of Gaussian states to this aim. In particular, we attempt to reformulate the criterion for Gaussian steering in terms of local and global purities and show that it is sufficient and necessary for the case of steering a 1-mode system by an N-mode system. It subsequently enables us to reinforce a strong monogamy relation under which only one party can steer a local system of 1-mode. Moreover, we show that only a negative partial-transpose state can manifest quantum steerability by Gaussian measurements in relation to the Peres conjecture. We also discuss our formulation for the case of distributing a two-mode squeezed state via one-way quantum channels making dissipation and amplification effects, respectively. Finally, we extend our approach to include non-Gaussian measurements, more precisely, all orders of higher-order squeezing measurements, and find that this broad set of non-Gaussian measurements is not useful to demonstrate steering for Gaussian states beyond Gaussian measurements. (paper)
Extremely high absolute internal quantum efficiency of photoluminescence in co-doped GaN:Zn,Si
Reshchikov, M. A.; Willyard, A. G.; Behrends, A.; Bakin, A.; Waag, A.
2011-10-01
We report on the fabrication of GaN co-doped with silicon and zinc by metalorganic vapor phase epitaxy and a detailed study of photoluminescence in this material. We observe an exceptionally high absolute internal quantum efficiency of blue photoluminescence in GaN:Zn,Si. The value of 0.93±0.04 has been obtained from several approaches based on rate equations.
Energy Technology Data Exchange (ETDEWEB)
Ledentsov, Nikolay Jr.; Reich, Christoph; Mehnke, Frank; Kuhn, Christian; Wernicke, Tim; Kolbe, Tim; Lobo Ploch, Neysha; Rass, Jens [Institute of Solid State Physics, Technische Universitaet Berlin (Germany); Kueller, Viola [Ferdinand-Braun-Institut, Berlin (Germany); Kneissl, Michael [Institute of Solid State Physics, Technische Universitaet Berlin (Germany); Ferdinand-Braun-Institut, Berlin (Germany)
2013-07-01
We studied (In)AlGaN multiple quantum wells (MQWs) emitting in the UV-B spectral region with photoluminescence and electroluminescence spectroscopy. The internal quantum efficiency (IQE) was determined by temperature dependent measurements (5 K-300 K). The quantum confined Stark effect (QCSE) was investigated by studying the shift of the emission energy with increasing excitation power density. In the first series, Al{sub 0.27}Ga{sub 0.73}N MQWs with different Al{sub x}Ga{sub 1-x}N barriers (0.32
High Quantum Efficiency Back-Illuminated AlGaN-Based Solar-Blind Ultraviolet p—i—n Photodetectors
International Nuclear Information System (INIS)
Wang Guo-Sheng; Lu Hai; Xie Feng; Chen Dun-Jun; Ren Fang-Fang; Zhang Rong; Zheng You-Dou
2012-01-01
AlGaN-based back-illuminated solar-blind ultraviolet (UV) p—i—n photodetectors (PDs) with high quantum efficiency are fabricated on sapphire substrates. To improve the overall performance of the PD, a series of structural design considerations and growth procedures are implemented in the epitaxy process. A distinct wavelength-selective photo-response peak of the PD is obtained in the solar-blind region. When operating in photovoltaic mode, the PD exhibits a solar-blind/UV rejection ratio of up to 4 orders of magnitude and a peak responsivity of ∼113.5 mA/W at 270 nm, which corresponds to an external quantum efficiency of ∼52%. Under a reverse bias of −5 V, the PD shows a low dark current of ∼1.8 pA and an enhanced peak quantum efficiency of ∼64%. The thermal noise limited detectivity is estimated to be ∼ 3.3 × 10 13 cm·Hz 1/2 W −1
Energy Technology Data Exchange (ETDEWEB)
Cinti, Maria Nerina, E-mail: marianerina.cinti@uniroma1.it [Department of Molecular Medicine, Sapienza University of Rome, Rome 00161 (Italy); INFN Rome 1 Section, Rome (Italy); Pani, Roberto; Pellegrini, Rosanna [Department of Molecular Medicine, Sapienza University of Rome, Rome 00161 (Italy); INFN Rome 1 Section, Rome (Italy); Bennati, Paolo [Department of Molecular Medicine, Sapienza University of Rome, Rome 00161 (Italy); Orlandi, Chiara [Medical Physics Post Graduate School, Sapienza University of Rome, Rome 00161 (Italy); Fabbri, Andrea [Department of Physics, Roma Tre University, Rome (Italy); INFN Rome 3 Section, Rome (Italy); Ridolfi, Stefano; Scafè, Raffaele [Department of Molecular Medicine, Sapienza University of Rome, Rome 00161 (Italy)
2013-10-01
High quantum efficiency semiconductor photodetectors have recently drawn the attention of the scientific community for their potential in the realization of a new class of scintillation imagers with very high energy and spatial resolution performance. However, this goal does not seem within easy reach, due to various technological issues such as, for example, the difficulty to scale the characteristics of a single detector to an imager with suitable dimensions. Lately a definite technical improvement in increasing quantum efficiency up to 42% for position sensitive photomultipliers was achieved. The aim of this work is thus to test this new technological progress and to study the possible implications in imaging applications. Four Hamamatsu PMTs were tested: two multi anode photomultipliers, one with a bialkali (27% quantum efficiency) and the other one with a super-bialkali photocathode (38% quantum efficiency), and two 1×1 in. PMTs, both equipped with an ultra bialkali photocathode (42% quantum efficiency). In particular one of the ultra bialkali PMT has also an increased efficiency of first dynode charge collection. The results were compared with the ones obtained with a reference PMT (Hamamatsu R6231), mainly used in spectroscopy. The PMTs were coupled to LaBr3(Ce), NaI(Tl) and LSO(Ce) continuous scintillation crystals. The tests were done using two independent electronic chains: one dedicated for spectroscopic application and a second one, using a multi wire 64 channel readout, for imaging applications. The super-bialkali MA-PMTs have shown high energy resolution, both with spectroscopic and imaging setup, highlighting the appropriateness of these devices for the development of imaging devices with high spectroscopic performance. -- Highlights: • A study of energy resolution results coming from position sensitive photomultipliers are proposed. • The study is also extended on mono- anode photomultiplier. • The selected scintillation crystal is LeBr3(Ce
International Nuclear Information System (INIS)
Balondo Iyela, Daddy; Govaerts, Jan; Hounkonnou, M. Norbert
2013-01-01
Within the context of supersymmetric quantum mechanics and its related hierarchies of integrable quantum Hamiltonians and potentials, a general programme is outlined and applied to its first two simplest illustrations. Going beyond the usual restriction of shape invariance for intertwined potentials, it is suggested to require a similar relation for Hamiltonians in the hierarchy separated by an arbitrary number of levels, N. By requiring further that these two Hamiltonians be in fact identical up to an overall shift in energy, a periodic structure is installed in the hierarchy which should allow for its resolution. Specific classes of orthogonal polynomials characteristic of such periodic hierarchies are thereby generated, while the methods of supersymmetric quantum mechanics then lead to generalised Rodrigues formulae and recursion relations for such polynomials. The approach also offers the practical prospect of quantum modelling through the engineering of quantum potentials from experimental energy spectra. In this paper, these ideas are presented and solved explicitly for the cases N= 1 and N= 2. The latter case is related to the generalised Laguerre polynomials, for which indeed new results are thereby obtained. In the context of dressing chains and deformed polynomial Heisenberg algebras, some partial results for N⩾ 3 also exist in the literature, which should be relevant to a complete study of the N⩾ 3 general periodic hierarchies
Energy Technology Data Exchange (ETDEWEB)
Balondo Iyela, Daddy [International Chair in Mathematical Physics and Applications (ICMPA–UNESCO Chair), University of Abomey–Calavi, 072 B. P. 50 Cotonou, Republic of Benin (Benin); Centre for Cosmology, Particle Physics and Phenomenology (CP3), Institut de Recherche en Mathématique et Physique (IRMP), Université catholique de Louvain U.C.L., 2, Chemin du Cyclotron, B-1348 Louvain-la-Neuve (Belgium); Département de Physique, Université de Kinshasa (UNIKIN), B.P. 190 Kinshasa XI, Democratic Republic of Congo (Congo, The Democratic Republic of the); Govaerts, Jan [International Chair in Mathematical Physics and Applications (ICMPA–UNESCO Chair), University of Abomey–Calavi, 072 B. P. 50 Cotonou, Republic of Benin (Benin); Centre for Cosmology, Particle Physics and Phenomenology (CP3), Institut de Recherche en Mathématique et Physique (IRMP), Université catholique de Louvain U.C.L., 2, Chemin du Cyclotron, B-1348 Louvain-la-Neuve (Belgium); Hounkonnou, M. Norbert [International Chair in Mathematical Physics and Applications (ICMPA–UNESCO Chair), University of Abomey–Calavi, 072 B. P. 50 Cotonou, Republic of Benin (Benin)
2013-09-15
Within the context of supersymmetric quantum mechanics and its related hierarchies of integrable quantum Hamiltonians and potentials, a general programme is outlined and applied to its first two simplest illustrations. Going beyond the usual restriction of shape invariance for intertwined potentials, it is suggested to require a similar relation for Hamiltonians in the hierarchy separated by an arbitrary number of levels, N. By requiring further that these two Hamiltonians be in fact identical up to an overall shift in energy, a periodic structure is installed in the hierarchy which should allow for its resolution. Specific classes of orthogonal polynomials characteristic of such periodic hierarchies are thereby generated, while the methods of supersymmetric quantum mechanics then lead to generalised Rodrigues formulae and recursion relations for such polynomials. The approach also offers the practical prospect of quantum modelling through the engineering of quantum potentials from experimental energy spectra. In this paper, these ideas are presented and solved explicitly for the cases N= 1 and N= 2. The latter case is related to the generalised Laguerre polynomials, for which indeed new results are thereby obtained. In the context of dressing chains and deformed polynomial Heisenberg algebras, some partial results for N⩾ 3 also exist in the literature, which should be relevant to a complete study of the N⩾ 3 general periodic hierarchies.
Modeling the frequency-dependent detective quantum efficiency of photon-counting x-ray detectors.
Stierstorfer, Karl
2018-01-01
To find a simple model for the frequency-dependent detective quantum efficiency (DQE) of photon-counting detectors in the low flux limit. Formula for the spatial cross-talk, the noise power spectrum and the DQE of a photon-counting detector working at a given threshold are derived. Parameters are probabilities for types of events like single counts in the central pixel, double counts in the central pixel and a neighboring pixel or single count in a neighboring pixel only. These probabilities can be derived in a simple model by extensive use of Monte Carlo techniques: The Monte Carlo x-ray propagation program MOCASSIM is used to simulate the energy deposition from the x-rays in the detector material. A simple charge cloud model using Gaussian clouds of fixed width is used for the propagation of the electric charge generated by the primary interactions. Both stages are combined in a Monte Carlo simulation randomizing the location of impact which finally produces the required probabilities. The parameters of the charge cloud model are fitted to the spectral response to a polychromatic spectrum measured with our prototype detector. Based on the Monte Carlo model, the DQE of photon-counting detectors as a function of spatial frequency is calculated for various pixel sizes, photon energies, and thresholds. The frequency-dependent DQE of a photon-counting detector in the low flux limit can be described with an equation containing only a small set of probabilities as input. Estimates for the probabilities can be derived from a simple model of the detector physics. © 2017 American Association of Physicists in Medicine.
The research on noise equivalent quanta and detective quantum efficiency of screen-film system
International Nuclear Information System (INIS)
Xie Jingdong; Wang Changyuan; Yuan Yude; Zhang Menglong; Wang Jian; Zheng Hao; Sun Yong
2002-01-01
Objective: To examine the noise equivalent quanta (NEQ) and detective quantum efficiency (DQE) of screen-film system. Methods: Green 400 screen-Kodak film and CaWO 4 screen-Fuji film were used in the study. The characteristic curves were obtained by distance method. The square wave technique was employed to determine the modulation transfer function (MTF). The Wiener spectrum (WS) was determined by Fourier analysis on uniformly exposed films. The NEQ and DQE were calculated from the characteristic curve slope, MTF, and WS measurements. Results: (1) The NEQ value of Green 400 screen-Kodak film system was 1.48 x 10 6 mm -2 when the spatial frequency was 0.6 cycles/mm, and it was 0.65 times larger than that of CaWO 4 screen-Fuji film system; The NEQ value of Green 400 screen-Kodak film system was 0.329 x 10 4 mm -2 when the spatial frequency was 4.0 cycles/mm, and it was 1.55 times larger than that of CaWO 4 screen-Fuji film system. (2) The DQE value of Green 400 screen-Kodak film system was 0.224 when the spatial frequency was 0.6 cycles/mm, and it was 1.6 times larger than that of CaWO 4 screen-Fuji film system; The DQE value of Green 400 screen-Kodak film system was 0.052 when the spatial frequency was 4.0 cycles/mm, and it was 3.7 times larger than that of CaWO 4 screen-Fuji film system. Conclusion: The Green 400 Screen-Kodak film system has superior NEQ when the spatial frequency was more than 3.0 cycles/mm and has superior DQE among the total spatial frequency in comparison with CaWO 4 screen-Fuji film system
A Relation Between Topological Quantum Field Theory and the Kodama State
Oda, Ichiro
2003-01-01
We study a relation between topological quantum field theory and the Kodama (Chern-Simons) state. It is shown that the Kodama (Chern-Simons) state describes a topological state with unbroken diffeomorphism invariance in Yang-Mills theory and Einstein's general relativity in four dimensions. We give a clear explanation of "why" such a topological state exists.
Special relativity and quantum theory: a collection of papers on the Poincari Group
International Nuclear Information System (INIS)
Noz, M.E.; Kim, Y.S.
1988-01-01
When the present form of quantum mechanics was formulated in 1927, the most pressing problem was how to make it consistent with special relativity. This still remains a most important and urgent theoretical problem in physics. The underlying language for both disciplines is group theory, and E.P. Wigner's 1939 paper on the Poincari group laid the foundation for unifying the concepts and algorithms of quantum mechanics and special relativity. This volume comprises forty-five papers, including those by P.A.M. Dirac, R.P. Feynman, S. Weinberg, E.P. Wigner and H. Yukawa, covering representations of the Poincari group, time-energy uncertainty relation, covariant pictures of quantum bound states, Lorentz-Dirac deformation in high-enery physics, gauge degrees of freedom for massless particles, group contractions applied to the large-momentum/zero-mass limit, localization problems, and physical applications of the Lorentz group
Energy Technology Data Exchange (ETDEWEB)
Kilic, Bayram, E-mail: bkilic@yalova.edu.tr [Yalova University, Department of Energy Systems Engineering, Faculty of Engineering, 77100 Yalova (Turkey); Günes, Taylan; Besirli, Ilknur; Sezginer, Merve [Yalova University, Department of Energy Systems Engineering, Faculty of Engineering, 77100 Yalova (Turkey); Tuzemen, Sebahattin [Department of Physics, Faculty of Science, Atatürk University, Erzurum 25240 (Turkey)
2014-11-01
Graphical abstract: - Highlights: • The structural and optical characterizations of ZnO nanoflowers were carried out on ITO by hydrothermal method. • Dye sensitized solar cell based ZnO nanoflowers were constructed on substrate. • The surface morphology effect on quantum efficiency and solar conversion efficiency were investigated. - Abstract: 3-dimensional ZnO nanoflower were obtained on FTO (F:SnO{sub 2}) substrate by hydrothermal method in order to produce high efficiency dye sensitized solar cells (DSSCs). We showed that nanoflowers structures have nanoscale branches that stretch to fill gaps on the substrate and these branches of nano-leaves provide both a larger surface area and a direct pathway for electron transport along the channels. It was found that the solar conversion efficiency and quantum efficiency (QE) or incident photon to current conversion efficiencies (IPCE) is highly dependent on nanoflower surface due to high electron injection process. The highest solar conversion efficiency of 5.119 and QE of 60% was obtained using ZnO nanoflowers/N719 dye/I{sup −}/I{sup −}{sub 3} electrolyte. In this study, three dimensional (3D)-nanoflower and one dimensional (1D)-nanowires ZnO nanostructures were also compared against each other in respect to solar conversion efficiency and QE measurements. In the case of the 1D-ZnO nanowire conversion efficiency (η) of 2.222% and IPCE 47% were obtained under an illumination of 100 mW/cm{sup 2}. It was confirmed that the performance of the 3D-nanoflowers was better than about 50% that of the 1D-nanowire dye-sensitized solar cells.
Expressing complementarity and the x-p commutation relation through further quantum inequalities
International Nuclear Information System (INIS)
Alvarez-Estrada, Ramon F
2010-01-01
Complementarity and the commutation relation of position (x) and momentum (p) imply much more than the fundamental x-p uncertainty inequality. Here, we display some further consequences of the former that could have certain pedagogical interest and, so, contribute to the teaching of quantum mechanics. Inspired by an elementary derivation of the x-p uncertainty inequality, based upon a positive quadratic polynomial, we explore one possible extension, via quartic polynomials and simple algebra and integrations. Our analysis, aimed at providing some further pedagogic expression of genuine quantum behaviours, yields other quantum inequalities for expectation values, expressed through suitable discriminants associated with quartic algebraic equations, which differ from (and are not a strict consequence of) the x-p uncertainty inequality. Those quantum inequalities are confirmed, and genuine non-classical behaviours are exhibited, for simple cases: a harmonic oscillator, a hydrogenic atom and free Gaussian wave packets. The physical interest of the expectation values involved in the quantum inequalities and of the latter is discussed, in the framework of quantum optics and squeezing phenomena.
Perturbative Quantum Gravity and its Relation to Gauge Theory
Directory of Open Access Journals (Sweden)
Bern Zvi
2002-01-01
Full Text Available In this review we describe a non-trivial relationship between perturbative gauge theory and gravity scattering amplitudes. At the semi-classical or tree-level, the scattering amplitudes of gravity theories in flat space can be expressed as a sum of products of well defined pieces of gauge theory amplitudes. These relationships were first discovered by Kawai, Lewellen, and Tye in the context of string theory, but hold more generally. In particular, they hold for standard Einstein gravity. A method based on $D$-dimensional unitarity can then be used to systematically construct all quantum loop corrections order-by-order in perturbation theory using as input thegravity tree amplitudes expressed in terms of gauge theory ones. More generally, the unitarity method provides a means for perturbatively quantizing massless gravity theories without the usual formal apparatus associated with the quantization of constrained systems. As one application, this method was used to demonstrate that maximally supersymmetric gravity is less divergent in the ultraviolet than previously thought.
The relation between quantum W algebras and Lie algebras
International Nuclear Information System (INIS)
Boer, J. de; Tjin, T.
1994-01-01
By quantizing the generalized Drinfeld-Sokolov reduction scheme for arbitrary sl 2 embeddings we show that a large set W of quantum W algebras can be viewed as (BRST) cohomologies of affine Lie algebras. The set W contains many known W algebras such as W N and W 3 (2) . Our formalism yields a completely algorithmic method for calculating the W algebra generators and their operator product expansions, replacing the cumbersome construction of W algebras as commutants of screening operators. By generalizing and quantizing the Miura transformation we show that any W algebra in W can be embedded into the universal enveloping algebra of a semisimple affine Lie algebra which is, up to shifts in level, isomorphic to a subalgebra of the original affine algebra. Therefore any realization of this semisimple affine Lie algebra leads to a realization of the W algebra. In particular, one obtains in this way a general and explicit method for constructing the free field realizations and Fock resolutions for all algebras in W. Some examples are explicitly worked out. (orig.)
Photovoltaic efficiency of intermediate band solar cells based on CdTe/CdMnTe coupled quantum dots
Prado, Silvio J.; Marques, Gilmar E.; Alcalde, Augusto M.
2017-11-01
In this work we show the calculation of optimized efficiencies of intermediate band solar cells (IBSCs) based on Mn-doped II-VI CdTe/CdMnTe coupled quantum dot (QD) structures. We focus our attention on the combined effects of geometrical and Mn-doping parameters on optical properties and solar cell efficiency. In the framework of {k \\cdot p} theory, we accomplish detailed calculations of electronic structure, transition energies, optical selection rules and their corresponding intra- and interband oscillator strengths. With these results and by following the intermediate band model, we have developed a strategy which allows us to find optimal photovoltaic efficiency values. We also show that the effects of band admixture which can lead to degradation of optical transitions and reduction of efficiency can be partly minimized by a careful selection of the structural parameters and Mn-concentration. Thus, the improvement of band engineering is mandatory for any practical implementation of QD systems as IBSC hardware. Finally, our calculations show that it is possible to reach significant efficiency, up to ∼26%, by selecting a restricted space of parameters such as quantum dot size and shape and Mn-concentration effects, to improve the modulation of optical absorption in the structures.
Photovoltaic efficiency of intermediate band solar cells based on CdTe/CdMnTe coupled quantum dots.
Prado, Silvio J; Marques, Gilmar E; Alcalde, Augusto M
2017-11-08
In this work we show the calculation of optimized efficiencies of intermediate band solar cells (IBSCs) based on Mn-doped II-VI CdTe/CdMnTe coupled quantum dot (QD) structures. We focus our attention on the combined effects of geometrical and Mn-doping parameters on optical properties and solar cell efficiency. In the framework of [Formula: see text] theory, we accomplish detailed calculations of electronic structure, transition energies, optical selection rules and their corresponding intra- and interband oscillator strengths. With these results and by following the intermediate band model, we have developed a strategy which allows us to find optimal photovoltaic efficiency values. We also show that the effects of band admixture which can lead to degradation of optical transitions and reduction of efficiency can be partly minimized by a careful selection of the structural parameters and Mn-concentration. Thus, the improvement of band engineering is mandatory for any practical implementation of QD systems as IBSC hardware. Finally, our calculations show that it is possible to reach significant efficiency, up to ∼26%, by selecting a restricted space of parameters such as quantum dot size and shape and Mn-concentration effects, to improve the modulation of optical absorption in the structures.
Coping efficiently with now-relative medical data.
Stantic, Bela; Terenziani, Paolo; Sattar, Abdul
2008-11-06
In Medical Informatics, there is an increasing awareness that temporal information plays a crucial role, so that suitable database approaches are needed to store and support it. Specifically, most clinical data are intrinsically temporal, and a relevant part of them are now-relative (i.e., they are valid at the current time). Even if previous studies indicate that the treatment of now-relative data has a crucial impact on efficiency, current approaches have several limitations. In this paper we propose a novel approach, which is based on a new representation of now, and on query transformations. We also experimentally demonstrate that our approach outperforms its best competitors in the literature to the extent of a factor of more than ten, both in number of disk accesses and of CPU usage.
Energy Technology Data Exchange (ETDEWEB)
Hammersley, S.; Dawson, P. [School of Physics and Astronomy, Photon Science Institute, University of Manchester, Manchester M13 9PL (United Kingdom); Kappers, M. J.; Massabuau, F. C.-P.; Sahonta, S.-L.; Oliver, R. A.; Humphreys, C. J. [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom)
2015-09-28
InGaN-based light emitting diodes and multiple quantum wells designed to emit in the green spectral region exhibit, in general, lower internal quantum efficiencies than their blue-emitting counter parts, a phenomenon referred to as the “green gap.” One of the main differences between green-emitting and blue-emitting samples is that the quantum well growth temperature is lower for structures designed to emit at longer wavelengths, in order to reduce the effects of In desorption. In this paper, we report on the impact of the quantum well growth temperature on the optical properties of InGaN/GaN multiple quantum wells designed to emit at 460 nm and 530 nm. It was found that for both sets of samples increasing the temperature at which the InGaN quantum well was grown, while maintaining the same indium composition, led to an increase in the internal quantum efficiency measured at 300 K. These increases in internal quantum efficiency are shown to be due reductions in the non-radiative recombination rate which we attribute to reductions in point defect incorporation.
International Nuclear Information System (INIS)
Hammersley, S.; Dawson, P.; Kappers, M. J.; Massabuau, F. C.-P.; Sahonta, S.-L.; Oliver, R. A.; Humphreys, C. J.
2015-01-01
InGaN-based light emitting diodes and multiple quantum wells designed to emit in the green spectral region exhibit, in general, lower internal quantum efficiencies than their blue-emitting counter parts, a phenomenon referred to as the “green gap.” One of the main differences between green-emitting and blue-emitting samples is that the quantum well growth temperature is lower for structures designed to emit at longer wavelengths, in order to reduce the effects of In desorption. In this paper, we report on the impact of the quantum well growth temperature on the optical properties of InGaN/GaN multiple quantum wells designed to emit at 460 nm and 530 nm. It was found that for both sets of samples increasing the temperature at which the InGaN quantum well was grown, while maintaining the same indium composition, led to an increase in the internal quantum efficiency measured at 300 K. These increases in internal quantum efficiency are shown to be due reductions in the non-radiative recombination rate which we attribute to reductions in point defect incorporation
Guo, L. Jay
2015-10-01
adopted by other material systems as well. Based on these understandings, we have also developed colored perovskite PV by integrating an optical cavity with the perovskite semiconductors [4]. The principle and experimental results will be presented. 1. J. Y. Lee, K. T. Lee, S.Y. Seo, L. J. Guo, "Decorative power generating panels creating angle insensitive transmissive colors," Sci. Rep. 4, 4192, 2014. 2. K. T. Lee, J.Y. Lee, S.-Y. Seo, and L. J. Guo, "Colored ultra-thin hybrid photovoltaics with high quantum efficiency," Light: Science and Applications, 3, e215, 2014. 3. K. T. Lee, S.-Y. Seo, J.Y. Lee, and L. J. Guo, "Ultrathin metal-semiconductor-metal resonator for angle invariant visible band transmission filters," Appl. Phys. Lett. 104, 231112, (2014); and "Strong resonance effect in a lossy medium-based optical cavity for angle robust spectrum filters," Adv. Mater, 26, 6324-6328, 2014. 4. K. T. Lee, M. Fukuda, L. J. Guo, "Colored, see-through perovskite solar cells employing an optical cavity," Submitted, 2015
Efficient fiber-coupled single-photon sources based on quantum dots
DEFF Research Database (Denmark)
Daveau, Raphaël Sura
refrigeration with coupled quantum wells. Many photonic quantum information processing applications would benet from a highbrightness, ber-coupled source of triggered single photons. This thesis presents a study of such sources based on quantum dots coupled to unidirectional photonic-crystal waveguide devices.......6 %. This latter method opens a promising future for increasing the eciency and reliability of planar chip-based single-photon sources. Refrigeration of a solid-state system with light has potential applications for cooling small-scale electronic and photonic circuits. We show theoretically that two coupled...... semiconductor quantum wells are ecient cooling media because they support long-lived indirect electron-hole pairs. These pairs can be thermally excited to distinct higher-energy states with faster radiative recombination, thereby creating an ecient escape channel to remove thermal energy from the system. From...
High Efficiency Quantum Dot III-V Multijunction Solar Cell for Space Power, Phase I
National Aeronautics and Space Administration — Quantum dots are nanoscale materials that have already improved the performance of optical sensors, lasers, and light emitting diodes. The unique properties of these...
High Efficiency Quantum Dot III-V Thermophotovoltaic Cell for Space Power, Phase I
National Aeronautics and Space Administration — Quantum dots are nanoscale materials that have already improved the performance of optical sensors, lasers, light emitting diodes and solar cells. The unique...
Labelle, A. J.; Bonifazi, Marcella; Tian, Y.; Wong, C.; Hoogland, S.; Favraud, Gael; Walters, G.; Sutherland, B.; Liu, M.; Li, Jun; Zhang, Xixiang; Kelley, Shana O.; Sargent, E. H.; Fratalocchi, Andrea
2017-01-01
The engineering of broadband absorbers to harvest white light in thin-film semiconductors is a major challenge in developing renewable materials for energy harvesting. Many solution-processed materials with high manufacturability and low cost, such as semiconductor quantum dots, require the use of film structures with thicknesses on the order of 1 μm to absorb incoming photons completely. The electron transport lengths in these media, however, are 1 order of magnitude smaller than this length, hampering further progress with this platform. Herein, we show that, by engineering suitably disordered nanoplasmonic structures, we have created a new class of dispersionless epsilon-near-zero composite materials that efficiently harness white light. Our nanostructures localize light in the dielectric region outside the epsilon-near-zero material with characteristic lengths of 10-100 nm, resulting in an efficient system for harvesting broadband light when a thin absorptive film is deposited on top of the structure. By using a combination of theory and experiments, we demonstrate that ultrathin layers down to 50 nm of colloidal quantum dots deposited atop the epsilon-near-zero material show an increase in broadband absorption ranging from 200% to 500% compared to a planar structure of the same colloidal quantum-dot-absorber average thickness. When the epsilon-near-zero nanostructures were used in an energy-harvesting module, we observed a spectrally averaged 170% broadband increase in the external quantum efficiency of the device, measured at wavelengths between 400 and 1200 nm. Atomic force microscopy and photoluminescence excitation measurements demonstrate that the properties of these epsilon-near-zero structures apply to general metals and could be used to enhance the near-field absorption of semiconductor structures more widely. We have developed an inexpensive electrochemical deposition process that enables scaled-up production of this nanomaterial for large
Labelle, A. J.
2017-02-03
The engineering of broadband absorbers to harvest white light in thin-film semiconductors is a major challenge in developing renewable materials for energy harvesting. Many solution-processed materials with high manufacturability and low cost, such as semiconductor quantum dots, require the use of film structures with thicknesses on the order of 1 μm to absorb incoming photons completely. The electron transport lengths in these media, however, are 1 order of magnitude smaller than this length, hampering further progress with this platform. Herein, we show that, by engineering suitably disordered nanoplasmonic structures, we have created a new class of dispersionless epsilon-near-zero composite materials that efficiently harness white light. Our nanostructures localize light in the dielectric region outside the epsilon-near-zero material with characteristic lengths of 10-100 nm, resulting in an efficient system for harvesting broadband light when a thin absorptive film is deposited on top of the structure. By using a combination of theory and experiments, we demonstrate that ultrathin layers down to 50 nm of colloidal quantum dots deposited atop the epsilon-near-zero material show an increase in broadband absorption ranging from 200% to 500% compared to a planar structure of the same colloidal quantum-dot-absorber average thickness. When the epsilon-near-zero nanostructures were used in an energy-harvesting module, we observed a spectrally averaged 170% broadband increase in the external quantum efficiency of the device, measured at wavelengths between 400 and 1200 nm. Atomic force microscopy and photoluminescence excitation measurements demonstrate that the properties of these epsilon-near-zero structures apply to general metals and could be used to enhance the near-field absorption of semiconductor structures more widely. We have developed an inexpensive electrochemical deposition process that enables scaled-up production of this nanomaterial for large
International Nuclear Information System (INIS)
Ren, Peng; Zhang, Ning; Xue, Bin; Liu, Zhe; Wang, Junxi; Li, Jinmin
2016-01-01
The challenge for improving the internal quantum efficiency (IQE) of InGaN-based light emitting diodes (LED) in the green light range is referred to as the ‘green gap’. However the IQE of InGaN-based LEDs often drops when the emission peak wavelength is adjusted through reducing the growth temperature. Although hydrogen (H 2 ) can improve surface morphology, it reduces the indium incorporation significantly. Here, a novel usage of H 2 treatment on the GaN barrier before the InGaN quantum well is demonstrated to enhance indium incorporation efficiency and improve the IQE simultaneously for the first time. The mechanism behind it is systematically investigated and explained in detail. The possible reason for this phenomenon is the strain relieving function by the undulant GaN barrier surface after H 2 treatment. Test measurements show that applying 0.2 min H 2 treatment on the barrier would reduce defects and enhance indium incorporation, which would improve the localization effect and finally lead to a higher IQE. Although further increasing the treatment time to 0.4 min incorporates more indium atoms, the IQE decreases at the expense of more defects and a larger polarization field than the 0.2 min sample. (paper)
International Nuclear Information System (INIS)
Namiot, V.A.; Chernavskii, D.S.
2003-01-01
It is well known, that in the classical mechanics the dynamic chaos is possible. When it takes place, the exact prediction of events in the future appears impossible. But in the quantum theory the dynamic chaos (connected with perturbations of the initial conditions) formally is absent. Nevertheless, as it is shown in this Letter, in case of the quantum theory there are other reasons related directly to so-called paradoxes of formal logic which do not allow one to predict the future precisely
Cytotoxicity of InP/ZnS quantum dots related to reactive oxygen species generation
Chibli, Hicham; Carlini, Lina; Park, Soonhyang; Dimitrijevic, Nada M.; Nadeau, Jay L.
2011-06-01
Indium phosphide (InP) quantum dots (QDs) have emerged as a presumably less hazardous alternative to cadmium-based particles, but their cytotoxicity has not been well examined. Although their constituent elements are of very low toxicity to cells in culture, they nonetheless exhibit phototoxicity related to generation of reactive oxygen species by excited electrons and/or holes interacting with water and molecular oxygen. Using spin-trap electron paramagnetic resonance (EPR) spectroscopy and reporter assays, we find a considerable amount of superoxide and a small amount of hydroxyl radical formed under visible illumination of biocompatible InP QDs with a single ZnS shell, comparable to what is seen with CdTe. A double thickness shell reduces the reactive oxygen species concentration approximately two-fold. Survival assays in five cell lines correspondingly indicate a distinct reduction in toxicity with the double-shell InP QDs. Toxicity varies significantly across cell lines according to the efficiency of uptake, being overall significantly less than what is seen with CdTe or CdSe/ZnS. This indicates that InP QDs are a useful alternative to cadmium-containing QDs, while remaining capable of electron-transfer processes that may be undesirable or which may be exploited for photosensitization applications.