Process tomography via sequential measurements on a single quantum system
CSIR Research Space (South Africa)
Bassa, H
2015-09-01
Full Text Available The authors utilize a discrete (sequential) measurement protocol to investigate quantum process tomography of a single two-level quantum system, with an unknown initial state, undergoing Rabi oscillations. The ignorance of the dynamical parameters...
Identification of single-input-single-output quantum linear systems
Levitt, Matthew; GuÅ£ǎ, Mǎdǎlin
2017-03-01
The purpose of this paper is to investigate system identification for single-input-single-output general (active or passive) quantum linear systems. For a given input we address the following questions: (1) Which parameters can be identified by measuring the output? (2) How can we construct a system realization from sufficient input-output data? We show that for time-dependent inputs, the systems which cannot be distinguished are related by symplectic transformations acting on the space of system modes. This complements a previous result of Guţă and Yamamoto [IEEE Trans. Autom. Control 61, 921 (2016), 10.1109/TAC.2015.2448491] for passive linear systems. In the regime of stationary quantum noise input, the output is completely determined by the power spectrum. We define the notion of global minimality for a given power spectrum, and characterize globally minimal systems as those with a fully mixed stationary state. We show that in the case of systems with a cascade realization, the power spectrum completely fixes the transfer function, so the system can be identified up to a symplectic transformation. We give a method for constructing a globally minimal subsystem direct from the power spectrum. Restricting to passive systems the analysis simplifies so that identifiability may be completely understood from the eigenvalues of a particular system matrix.
Delteil, Aymeric; Sun, Zhe; Fält, Stefan; Imamoğlu, Atac
2017-04-28
Photonic losses pose a major limitation for the implementation of a quantum state transfer between nodes of a quantum network. A measurement that heralds a successful transfer without revealing any information about the qubit may alleviate this limitation. Here, we demonstrate the heralded absorption of a single photonic qubit, generated by a single neutral quantum dot, by a single-electron charged quantum dot that is located 5 m away. The transfer of quantum information to the spin degree of freedom takes place upon the emission of a photon; for a properly chosen or prepared quantum dot, the detection of this photon yields no information about the qubit. We show that this process can be combined with local operations optically performed on the destination node by measuring classical correlations between the absorbed photon color and the final state of the electron spin. Our work suggests alternative avenues for the realization of quantum information protocols based on cascaded quantum systems.
Xu, Kebiao; Xie, Tianyu; Li, Zhaokai; Xu, Xiangkun; Wang, Mengqi; Ye, Xiangyu; Kong, Fei; Geng, Jianpei; Duan, Changkui; Shi, Fazhan; Du, Jiangfeng
2017-03-31
The adiabatic quantum computation is a universal and robust method of quantum computing. In this architecture, the problem can be solved by adiabatically evolving the quantum processor from the ground state of a simple initial Hamiltonian to that of a final one, which encodes the solution of the problem. Adiabatic quantum computation has been proved to be a compatible candidate for scalable quantum computation. In this Letter, we report on the experimental realization of an adiabatic quantum algorithm on a single solid spin system under ambient conditions. All elements of adiabatic quantum computation, including initial state preparation, adiabatic evolution (simulated by optimal control), and final state read-out, are realized experimentally. As an example, we found the ground state of the problem Hamiltonian S_{z}I_{z} on our adiabatic quantum processor, which can be mapped to the factorization of 35 into its prime factors 5 and 7.
Quantum optics with single quantum dot devices
International Nuclear Information System (INIS)
Zwiller, Valery; Aichele, Thomas; Benson, Oliver
2004-01-01
A single radiative transition in a single-quantum emitter results in the emission of a single photon. Single quantum dots are single-quantum emitters with all the requirements to generate single photons at visible and near-infrared wavelengths. It is also possible to generate more than single photons with single quantum dots. In this paper we show that single quantum dots can be used to generate non-classical states of light, from single photons to photon triplets. Advanced solid state structures can be fabricated with single quantum dots as their active region. We also show results obtained on devices based on single quantum dots
Post, E J
1999-01-01
This essay presents conclusive evidence of the impermissibility of Copenhagen's single system interpretation of the Schroedinger process. The latter needs to be viewed as a tool exclusively describing phase and orientation randomized ensembles and is not be used for isolated single systems. Asymptotic closeness of single system and ensemble behavior and the rare nature of true single system manifestations have prevented a definitive identification of this Copenhagen deficiency over the past three quarter century. Quantum uncertainty so becomes a basic trade mark of phase and orientation disordered ensembles. The ensuing void of usable single system tools opens a new inquiry for tools without statistical connotations. Three, in part already known, period integrals here identified as flux, charge and action counters emerge as diffeo-4 invariant tools fully compatible with the demands of the general theory of relativity. The discovery of the quantum Hall effect has been instrumental in forcing a distinction betw...
Simulation of a quantum NOT gate for a single qutrit system
Indian Academy of Sciences (India)
level system; qutrit; three-level transitions; one-qutrit quantum gate. ... Because of the fact that the three-level atom defines a total normalized state composed of superposition of three different single-level states, it is assumed that such a system ...
Tunable single-photon multi-channel quantum router based on an optomechanical system
Ma, Peng-Cheng; Yan, Lei-Lei; Zhang, Jian; Chen, Gui-Bin; Li, Xiao-Wei; Zhan, You-Bang
2018-01-01
Routing of photons plays a key role in optical communication networks and quantum networks. Although the quantum routing of signals has been investigated for various systems, both in theory and experiment, the general form of a quantum router with multi-output terminals still needs to be explored. Here, we propose an experimentally accessible tunable single-photon multi-channel routing scheme using an optomechanics cavity which is Coulomb coupled to a nanomechanical resonator. The router can extract single photons from the coherent input signal and directly modulate them into three different output channels. More importantly, the two output signal frequencies can be selected by adjusting the Coulomb coupling strength. For application purposes, we justify that there is insignificant influence from the vacuum and thermal noises on the performance of the router under cryogenic conditions. Our proposal may pave a new avenue towards multi-channel routers and quantum networks.
Probing correlated quantum many-body systems at the single-particle level
International Nuclear Information System (INIS)
Endres, Manuel
2013-01-01
The detection of correlation and response functions plays a crucial role in the experimental characterization of quantum many-body systems. In this thesis, we present novel techniques for the measurement of such functions at the single-particle level. Specifically, we show the single-atom- and single-site-resolved detection of an ultracold quantum gas in an optical lattice. The quantum gas is described by the Bose-Hubbard model, which features a zero temperature phase transition from a superfluid to a Mott-insulating state, a paradigm example of a quantum phase transition. We used the aforementioned detection techniques to study correlation and response properties across the superfluid-Mott-insulator transition. The single-atom sensitivity of our method is achieved by fluorescence detection of individual atoms with a high signal-to-noise ratio. A high-resolution objective collects the fluorescence light and yields in situ 'snapshots' of the quantum gas that allow for a single-site-resolved reconstruction of the atomic distribution. This allowed us to measure two-site and non-local correlation-functions across the superfluid-Mott-insulator transition. Non-local correlation functions are based on the information of an extended region of the system and play an important role for the characterization of low-dimensional quantum phases. While non-local correlation functions were so far only theoretical tools, our results show that they are actually experimentally accessible. Furthermore, we used a new thermometry scheme, based on the counting of individual thermal excitations, to measure the response of the system to lattice modulation. Using this method, we studied the excitation spectrum of the system across the two-dimensional superfluid-Mott-insulator transition. In particular, we detected a 'Higgs' amplitude mode in the strongly-interacting superfluid close to the transition point where the system is described by an effectively Lorentz-invariant low-energy theory
Probing correlated quantum many-body systems at the single-particle level
Energy Technology Data Exchange (ETDEWEB)
Endres, Manuel
2013-02-27
The detection of correlation and response functions plays a crucial role in the experimental characterization of quantum many-body systems. In this thesis, we present novel techniques for the measurement of such functions at the single-particle level. Specifically, we show the single-atom- and single-site-resolved detection of an ultracold quantum gas in an optical lattice. The quantum gas is described by the Bose-Hubbard model, which features a zero temperature phase transition from a superfluid to a Mott-insulating state, a paradigm example of a quantum phase transition. We used the aforementioned detection techniques to study correlation and response properties across the superfluid-Mott-insulator transition. The single-atom sensitivity of our method is achieved by fluorescence detection of individual atoms with a high signal-to-noise ratio. A high-resolution objective collects the fluorescence light and yields in situ 'snapshots' of the quantum gas that allow for a single-site-resolved reconstruction of the atomic distribution. This allowed us to measure two-site and non-local correlation-functions across the superfluid-Mott-insulator transition. Non-local correlation functions are based on the information of an extended region of the system and play an important role for the characterization of low-dimensional quantum phases. While non-local correlation functions were so far only theoretical tools, our results show that they are actually experimentally accessible. Furthermore, we used a new thermometry scheme, based on the counting of individual thermal excitations, to measure the response of the system to lattice modulation. Using this method, we studied the excitation spectrum of the system across the two-dimensional superfluid-Mott-insulator transition. In particular, we detected a 'Higgs' amplitude mode in the strongly-interacting superfluid close to the transition point where the system is described by an effectively Lorentz
Fusco, L.; Pigeon, S.; Apollaro, T. J. G.; Xuereb, A.; Mazzola, L.; Campisi, M.; Ferraro, A.; Paternostro, M.; De Chiara, G.
2014-07-01
We analyze the nature of the statistics of the work done on or by a quantum many-body system brought out of equilibrium. We show that, for the sudden quench and for an initial state that commutes with the initial Hamiltonian, it is possible to retrieve the whole nonequilibrium thermodynamics via single projective measurements of observables. We highlight, in a physically clear way, the qualitative implications for the statistics of work coming from considering processes described by operators that either commute or do not commute with the unperturbed Hamiltonian of a given system. We consider a quantum many-body system and derive an expression that allows us to give a physical interpretation, for a thermal initial state, to all of the cumulants of the work in the case of quenched operators commuting with the unperturbed Hamiltonian. In the commuting case, the observables that we need to measure have an intuitive physical meaning. Conversely, in the noncommuting case, we show that, although it is possible to operate fully within the single-measurement framework irrespectively of the size of the quench, some difficulties are faced in providing a clear-cut physical interpretation to the cumulants. This circumstance makes the study of the physics of the system nontrivial and highlights the nonintuitive phenomenology of the emergence of thermodynamics from the fully quantum microscopic description. We illustrate our ideas with the example of the Ising model in a transverse field showing the interesting behavior of the high-order statistical moments of the work distribution for a generic thermal state and linking them to the critical nature of the model itself.
Bright single photon source based on self-aligned quantum dot–cavity systems
DEFF Research Database (Denmark)
Maier, Sebastian; Gold, Peter; Forchel, Alfred
2014-01-01
We report on a quasi-planar quantum-dot-based single-photon source that shows an unprecedented high extraction efficiency of 42% without complex photonic resonator geometries or post-growth nanofabrication. This very high efficiency originates from the coupling of the photons emitted by a quantum...
The giant acoustic atom - a single quantum system with a deterministic time delay
Guo, Lingzhen; Grimsmo, Arne; Frisk Kockum, Anton; Pletyukhov, Mikhail; Johansson, Göran
2017-04-01
We investigate the quantum dynamics of a single transmon qubit coupled to surface acoustic waves (SAWs) via two distant connection points. Since the acoustic speed is five orders of magnitude slower than the speed of light, the travelling time between the two connection points needs to be taken into account. Therefore, we treat the transmon qubit as a giant atom with a deterministic time delay. We find that the spontaneous emission of the system, formed by the giant atom and the SAWs between its connection points, initially follows a polynomial decay law instead of an exponential one, as would be the case for a small atom. We obtain exact analytical results for the scattering properties of the giant atom up to two-phonon processes by using a diagrammatic approach. The time delay gives rise to novel features in the reflection, transmission, power spectra, and second-order correlation functions of the system. Furthermore, we find the short-time dynamics of the giant atom for arbitrary drive strength by a numerically exact method for open quantum systems with a finite-time-delay feedback loop. L. G. acknowledges financial support from Carl-Zeiss Stiftung (0563-2.8/508/2).
Specht, Holger P; Nölleke, Christian; Reiserer, Andreas; Uphoff, Manuel; Figueroa, Eden; Ritter, Stephan; Rempe, Gerhard
2011-05-12
The faithful storage of a quantum bit (qubit) of light is essential for long-distance quantum communication, quantum networking and distributed quantum computing. The required optical quantum memory must be able to receive and recreate the photonic qubit; additionally, it must store an unknown quantum state of light better than any classical device. So far, these two requirements have been met only by ensembles of material particles that store the information in collective excitations. Recent developments, however, have paved the way for an approach in which the information exchange occurs between single quanta of light and matter. This single-particle approach allows the material qubit to be addressed, which has fundamental advantages for realistic implementations. First, it enables a heralding mechanism that signals the successful storage of a photon by means of state detection; this can be used to combat inevitable losses and finite efficiencies. Second, it allows for individual qubit manipulations, opening up avenues for in situ processing of the stored quantum information. Here we demonstrate the most fundamental implementation of such a quantum memory, by mapping arbitrary polarization states of light into and out of a single atom trapped inside an optical cavity. The memory performance is tested with weak coherent pulses and analysed using full quantum process tomography. The average fidelity is measured to be 93%, and low decoherence rates result in qubit coherence times exceeding 180 microseconds. This makes our system a versatile quantum node with excellent prospects for applications in optical quantum gates and quantum repeaters.
Exact dimension estimation of interacting qubit systems assisted by a single quantum probe
Sone, Akira; Cappellaro, Paola
2017-12-01
Estimating the dimension of an Hilbert space is an important component of quantum system identification. In quantum technologies, the dimension of a quantum system (or its corresponding accessible Hilbert space) is an important resource, as larger dimensions determine, e.g., the performance of quantum computation protocols or the sensitivity of quantum sensors. Despite being a critical task in quantum system identification, estimating the Hilbert space dimension is experimentally challenging. While there have been proposals for various dimension witnesses capable of putting a lower bound on the dimension from measuring collective observables that encode correlations, in many practical scenarios, especially for multiqubit systems, the experimental control might not be able to engineer the required initialization, dynamics, and observables. Here we propose a more practical strategy that relies not on directly measuring an unknown multiqubit target system, but on the indirect interaction with a local quantum probe under the experimenter's control. Assuming only that the interaction model is given and the evolution correlates all the qubits with the probe, we combine a graph-theoretical approach and realization theory to demonstrate that the system dimension can be exactly estimated from the model order of the system. We further analyze the robustness in the presence of background noise of the proposed estimation method based on realization theory, finding that despite stringent constrains on the allowed noise level, exact dimension estimation can still be achieved.
International Nuclear Information System (INIS)
Sandulescu, A.; Stefanescu, E.
1987-07-01
On the basis of Lindblad theory of open quantum systems we obtain new optical equations for the system of two-level atom interacting with a single mode of the electromagnetic field. The conventional Block equations in a generalized form with field phases are obtained in the hypothesis that all the terms are slowly varying in the rotating frame.(authors)
Single-charge tunneling in ambipolar silicon quantum dots
Müller, Filipp
2015-01-01
Spin qubits in coupled quantum dots (QDs) are promising for future quantum information processing (QIP). A quantum bit (qubit) is the quantum mechanical analogon of a classical bit. In general, each quantum mechanical two-level system can represent a qubit. For the spin of a single charge carrier
International Nuclear Information System (INIS)
Gong, Longyan; Zhu, Hao; Zhao, Shengmei; Cheng, Weiwen; Sheng, Yubo
2012-01-01
We investigate numerically the quantum discord and the classical correlation in a one-dimensional slowly varying potential model and a one-dimensional Soukoulis–Economou ones, respectively. There are well-defined mobility edges in the slowly varying potential model, while there are discrepancies on mobility edges in the Soukoulis–Economou ones. In the slowly varying potential model, we find that extended and localized states can be distinguished by both the quantum discord and the classical correlation. There are sharp transitions in the quantum discord and the classical correlation at mobility edges. Based on these, we study “mobility edges” in the Soukoulis–Economou model using the quantum discord and the classical correlation, which gives another perspectives for these “mobility edges”. All these provide us good quantities, i.e., the quantum discord and the classical correlation, to reflect mobility edges in these one-dimensional aperiodic single-electron systems. Moreover, our studies propose a consistent interpretation of the discrepancies between previous numerical results about the Soukoulis–Economou model. -- Highlights: ► Quantum discord and classical correlation can signal mobility edges in two models. ► An interpretation for mobility edges in the Soukoulis–Economou model is proposed. ► Quantum discord and classical correlation can reflect well localization properties.
Simulation of a quantum NOT gate for a single qutrit system
Indian Academy of Sciences (India)
arises. In particular, a three-level system or qutrit has attracted the attention [9]. The qutrit has proved to be more efficient than qubit systems for executing some tasks. For instance, for quantum key distribution it provides better security than that obtained by employing two-level encoding protocols [10,11]. In fact, it has been ...
Cao, Cong; Duan, Yu-Wen; Chen, Xi; Zhang, Ru; Wang, Tie-Jun; Wang, Chuan
2017-07-24
Quantum router is a key element needed for the construction of future complex quantum networks. However, quantum routing with photons, and its inverse, quantum decoupling, are difficult to implement as photons do not interact, or interact very weakly in nonlinear media. In this paper, we investigate the possibility of implementing photonic quantum routing based on effects in cavity quantum electrodynamics, and present a scheme for single-photon quantum routing controlled by the other photon using a hybrid system consisting of a single nitrogen-vacancy (NV) center coupled with a whispering-gallery-mode resonator-waveguide structure. Different from the cases in which classical information is used to control the path of quantum signals, both the control and signal photons are quantum in our implementation. Compared with the probabilistic quantum routing protocols based on linear optics, our scheme is deterministic and also scalable to multiple photons. We also present a scheme for single-photon quantum decoupling from an initial state with polarization and spatial-mode encoding, which can implement an inverse operation to the quantum routing. We discuss the feasibility of our schemes by considering current or near-future techniques, and show that both the schemes can operate effectively in the bad-cavity regime. We believe that the schemes could be key building blocks for future complex quantum networks and large-scale quantum information processing.
Baishya, Bikash; Reddy, G N Manjunatha; Prabhu, Uday Ramesh; Row, T N Guru; Suryaprakash, N
2008-10-23
The proton NMR spectra of fluorine-substituted benzamides are very complex (Figure 1) due to severe overlap of (1)H resonances from the two aromatic rings, in addition to several short and long-range scalar couplings experienced by each proton. With no detectable scalar couplings between the inter-ring spins, the (1)H NMR spectra can be construed as an overlap of spectra from two independent phenyl rings. In the present study we demonstrate that it is possible to separate the individual spectrum for each aromatic ring by spin system filtering employing the multiple-quantum-single-quantum correlation methodology. Furthermore, the two spin states of fluorine are utilized to simplify the spectrum corresponding to each phenyl ring by the spin-state selection. The demonstrated technique reduces spectral complexity by a factor of 4, in addition to permitting the determination of long-range couplings of less than 0.2 Hz and the relative signs of heteronuclear couplings. The technique also aids the judicious choice of the spin-selective double-quantum-single-quantum J-resolved experiment to determine the long-range homonuclear couplings of smaller magnitudes.
Linear Quantum Systems: Non-Classical States and Robust Stability
2016-06-29
paper is to extend linear systems and signals theory to include single photon quantum signals . We provide detailed results describing how quantum...v) physical realizability results for finite level quantum systems. 15. SUBJECT TERMS Control Theory , Quantum Feedback, Quantum Algorithms 16...nominal linear models, and (v) physical realizability results for finite level quantum systems. Introduction: Classical linear systems theory
Near-field optical spectroscopy of single quantum wires
Harris, T. D.; Gershoni, D.; Grober, R. D.; Pfeiffer, L.; West, K.; Chand, N.
1996-02-01
Low temperature near-field scanning optical microscopy is used for spectroscopic studies of single, nanometer dimension, cleaved edge overgrown quantum wires. A direct experimental comparison between a two dimensional system and a single genuinely one dimensional quantum wire system, inaccessible to conventional far field optical spectroscopy, is enabled by the enhanced spatial resolution. We show that the photoluminescence of a single quantum wire is easily distinguished from that of the surrounding quantum well. Emission from localized centers is shown to dominate the photoluminescence from both wires and wells at low temperatures. A factor of 3 absorption enhancement for these wires compared to the wells is concluded from the photoluminescence excitation data.
Continuous quantum mechanics of single particles in closed and quasi-closed systems: Pt. 1 and 2
International Nuclear Information System (INIS)
Brieger, M.
2004-01-01
The established statistical interpretation of quantum mechanics never envisioned our today's ability to handle and investigate single particles in trap devices. After scrutinizing the development of quantum mechanics, we point out that Schroedinger's equation establishes an energy representation, which obtains the energy eigenvalues as extrema of the energy curve or on the energy hypersurface, respectively. We also strongly emphasize its never exhausted capability of accounting in classical terms and full detail for the dynamics of single particles in closed systems. This is demonstrated for several familiar examples. They show that the eigensolutions to Schroedinger's equation must not blindly be identified with physically stationary states. The gained insight into the true dynamics allows to describe, without involving QED, the time evolution of a complete spontaneous transition as being driven by unbalanced internal dynamics. This mechanism relies on the fact that perfect balances are only possible in the exact extrema of the total energy and that any deviation, which is characterized by nonstationary states, makes multipole moments oscillate and emit electromagnetic radiation. (orig.)
Continuous quantum mechanics of single particles in closed and quasi-closed systems: Pt. 1 and 2
Energy Technology Data Exchange (ETDEWEB)
Brieger, M. [DLR Deutsches Zentrum fuer Luft- und Raumfahrt e.V., Stuttgart (Germany). Inst. fuer Technische Physik
2004-07-01
The established statistical interpretation of quantum mechanics never envisioned our today's ability to handle and investigate single particles in trap devices. After scrutinizing the development of quantum mechanics, we point out that Schroedinger's equation establishes an energy representation, which obtains the energy eigenvalues as extrema of the energy curve or on the energy hypersurface, respectively. We also strongly emphasize its never exhausted capability of accounting in classical terms and full detail for the dynamics of single particles in closed systems. This is demonstrated for several familiar examples. They show that the eigensolutions to Schroedinger's equation must not blindly be identified with physically stationary states. The gained insight into the true dynamics allows to describe, without involving QED, the time evolution of a complete spontaneous transition as being driven by unbalanced internal dynamics. This mechanism relies on the fact that perfect balances are only possible in the exact extrema of the total energy and that any deviation, which is characterized by nonstationary states, makes multipole moments oscillate and emit electromagnetic radiation. (orig.)
Parallel quantum computing in a single ensemble quantum computer
International Nuclear Information System (INIS)
Long Guilu; Xiao, L.
2004-01-01
We propose a parallel quantum computing mode for ensemble quantum computer. In this mode, some qubits are in pure states while other qubits are in mixed states. It enables a single ensemble quantum computer to perform 'single-instruction-multidata' type of parallel computation. Parallel quantum computing can provide additional speedup in Grover's algorithm and Shor's algorithm. In addition, it also makes a fuller use of qubit resources in an ensemble quantum computer. As a result, some qubits discarded in the preparation of an effective pure state in the Schulman-Varizani and the Cleve-DiVincenzo algorithms can be reutilized
Photoluminescence studies of single InGaAs quantum dots
DEFF Research Database (Denmark)
Leosson, Kristjan; Jensen, Jacob Riis; Hvam, Jørn Märcher
1999-01-01
Semiconductor quantum dots are considered a promising material system for future optical devices and quantum computers. We have studied the low-temperature photoluminescence properties of single InGaAs quantum dots embedded in GaAs. The high spatial resolution required for resolving single dots...... to resolve luminescence lines from individual quantum dots, revealing an atomic-like spectrum of sharp transition lines. A parameter of fundamental importance is the intrinsic linewidth of these transitions. Using high-resolution spectroscopy we have determined the linewidth and investigated its dependence...... on temperature, which gives information about how the exciton confined to the quantum dot interacts with the surrounding lattice....
Operating Quantum States in Single Magnetic Molecules: Implementation of Grover's Quantum Algorithm
Godfrin, C.; Ferhat, A.; Ballou, R.; Klyatskaya, S.; Ruben, M.; Wernsdorfer, W.; Balestro, F.
2017-11-01
Quantum algorithms use the principles of quantum mechanics, such as, for example, quantum superposition, in order to solve particular problems outperforming standard computation. They are developed for cryptography, searching, optimization, simulation, and solving large systems of linear equations. Here, we implement Grover's quantum algorithm, proposed to find an element in an unsorted list, using a single nuclear 3 /2 spin carried by a Tb ion sitting in a single molecular magnet transistor. The coherent manipulation of this multilevel quantum system (qudit) is achieved by means of electric fields only. Grover's search algorithm is implemented by constructing a quantum database via a multilevel Hadamard gate. The Grover sequence then allows us to select each state. The presented method is of universal character and can be implemented in any multilevel quantum system with nonequal spaced energy levels, opening the way to novel quantum search algorithms.
Single-passage read-out of atomic quantum memory
DEFF Research Database (Denmark)
Fiurasek, J; Sherson, J; Opatrny, T
2005-01-01
Retrieving quantum information, collective atomic spin systems, quantum memory Udgivelsesdato: 17 Feb.......Retrieving quantum information, collective atomic spin systems, quantum memory Udgivelsesdato: 17 Feb....
Towards hybrid quantum systems: Trapping a single atom near a nanoscale solid-state structure
Directory of Open Access Journals (Sweden)
Tiecke T.G.
2013-08-01
Full Text Available We describe and demonstrate a method to deterministically trap single atoms near nanoscale solid-state objects. The trap is formed by the interference of an optical tweezer and its reflection from the nano object, creating a one-dimensional optical lattice where the first lattice site is at z0 ∼ λ/4 from the surface. Using a tapered optical fiber as the nanoscopic object, we characterize the loading into different lattice sites by means of the AC-Stark shift induced by a guided fiber mode. We demonstrate a loading efficiency of 94(6% into the first lattice site, and measure the cooperativity for the emission of the atom into the guided mode of the nanofiber. We show that by tailoring the dimensions of the nanofiber the distance of the trap to the surface can be adjusted. This method is applicable to a large variety of nanostructures and represents a promising starting point for interfacing single atoms with arbitrary nanoscale solid-state systems.
Quantum coherence and correlations in quantum system
Xi, Zhengjun; Li, Yongming; Fan, Heng
2015-01-01
Criteria of measure quantifying quantum coherence, a unique property of quantum system, are proposed recently. In this paper, we first give an uncertainty-like expression relating the coherence and the entropy of quantum system. This finding allows us to discuss the relations between the entanglement and the coherence. Further, we discuss in detail the relations among the coherence, the discord and the deficit in the bipartite quantum system. We show that, the one-way quantum deficit is equal to the sum between quantum discord and the relative entropy of coherence of measured subsystem. PMID:26094795
Field trial of a quantum secured 10 Gb/s DWDM transmission system over a single installed fiber.
Choi, Iris; Zhou, Yu Rong; Dynes, James F; Yuan, Zhiliang; Klar, Andreas; Sharpe, Andrew; Plews, Alan; Lucamarini, Marco; Radig, Christian; Neubert, Jörg; Griesser, Helmut; Eiselt, Michael; Chunnilall, Christopher; Lepert, Guillaume; Sinclair, Alastair; Elbers, Jörg-Peter; Lord, Andrew; Shields, Andrew
2014-09-22
We present results from the first field-trial of a quantum-secured DWDM transmission system, in which quantum key distribution (QKD) is combined with 4 × 10 Gb/s encrypted data and transmitted simultaneously over 26 km of field installed fiber. QKD is used to frequently refresh the key for AES-256 encryption of the 10 Gb/s data traffic. Scalability to over 40 DWDM channels is analyzed.
Non-Markovian spontaneous emission from a single quantum dot
DEFF Research Database (Denmark)
Madsen, Kristian Høeg; Ates, Serkan; Lund-Hansen, Toke
2011-01-01
We observe non-Markovian dynamics of a single quantum dot when tuned into resonance with a cavity mode. Excellent agreement between experiment and theory is observed providing the first quantitative description of such a system....
Chakraborty, Debdutta; Kar, Susmita; Chattaraj, Pratim Kumar
2015-12-21
The orbital free density functional theory and the single density equation approach are formally equivalent. An orbital free density based quantum dynamical strategy is used to study the quantum-classical correspondence in both weakly and strongly coupled van der Pol and Duffing oscillators in the presence of an external electric field in one dimension. The resulting quantum hydrodynamic equations of motion are solved through an implicit Euler type real space method involving a moving weighted least square technique. The Lagrangian framework used here allows the numerical grid points to follow the wave packet trajectory. The associated classical equations of motion are solved using a sixth order Runge-Kutta method and the Ehrenfest dynamics is followed through the solution of the time dependent Schrodinger equation using a time dependent Fourier Grid Hamiltonian technique. Various diagnostics reveal a close parallelism between classical regular as well as chaotic dynamics and that obtained from the Bohmian mechanics.
Quantum non demolition measurement of a single nuclear spin in a room temperature solid
Energy Technology Data Exchange (ETDEWEB)
Neumann, Phillip; Beck, Johannes; Steiner, Matthias; Rathgen, Helmut; Rempp, Florian; Zarrabi, Navid; Dolde, Florian; Jelezko, Fedor; Wrachtrup, Joerg [Universitaet Stuttgart (Germany); Hemmer, Philip [A and M University, Texas (United States)
2010-07-01
The measurement process and its interpretation are in the focus of quantum mechanics since its early days. Today's ability to isolate single quantum objects allows experimental demonstration of former ''gedankenexperiments'' like measurement induced quantum state collaps. Rapidly growing quantum technologies explore fundamental aspects of measurements in quantum computing, however for solid state systems such experiments require operation at very low temperatures. Here we show that projective quantum measurement can be performed on a single nuclear spin in diamond under ambient conditions. Using quantum non demolition (QND) readout we are able to detect quantum jumps and the quantum Zeno effect emphasising the addressability of fundamental questions of quantum mechanics in solids. Single shot measurements with fidelities exceeding 0.9 enable efficient state initialization, quantum error correction and entanglement pumping that is crucial for quantum information processing including measurement based schemes and distributed quantum networks.
Coherent optoelectronics with single quantum dots
Energy Technology Data Exchange (ETDEWEB)
Zrenner, A; Ester, P; Michaelis de Vasconcellos, S; Huebner, M C; Lackmann, L; Stufler, S [Universitaet Paderborn, Department Physik, Warburger Strasse 100, D-33098 Paderborn (Germany); Bichler, M [Walter Schottky Institut, Technische Universitaet Muenchen, Am Coulombwall, D-85748 Garching (Germany)], E-mail: zrenner@mail.upb.de
2008-11-12
The optical properties of semiconductor quantum dots are in many respects similar to those of atoms. Since quantum dots can be defined by state-of-the-art semiconductor technologies, they exhibit long-term stability and allow for well-controlled and efficient interactions with both optical and electrical fields. Resonant ps excitation of single quantum dot photodiodes leads to new classes of coherent optoelectronic functions and devices, which exhibit precise state preparation, phase-sensitive optical manipulations and the control of quantum states by electrical fields.
Simulation of a quantum NOT gate for a single qutrit system
Indian Academy of Sciences (India)
Estado de México, CP 56615, México. ∗. Corresponding author. E-mail: vlkmanuel@uaemex.mx. MS received 30 August 2014; revised 23 March 2015; accepted 30 March 2015. DOI: 10.1007/s12043-015-1116-3; ePublication: 4 November 2015. Abstract. A three-level system based an a three-level atom interacting with a ...
Quantum identity authentication with single photon
Hong, Chang ho; Heo, Jino; Jang, Jin Gak; Kwon, Daesung
2017-10-01
Quantum identity authentication with single photons is proposed in the paper. It can verify a user's identity without exposing to an authentication key information. The protocol guarantees high efficiency in that it can verify two bits of authentication information using just a single photon. The security of our authentication scheme is analyzed and confirmed in the case of a general attack. Moreover, the proposed protocol is practicable with current technology. Our quantum identity authentication protocol does not require quantum memory registration and any entangled photon sources.
Two-Way Communication with a Single Quantum Particle
Del Santo, Flavio; Dakić, Borivoje
2018-02-01
In this Letter we show that communication when restricted to a single information carrier (i.e., single particle) and finite speed of propagation is fundamentally limited for classical systems. On the other hand, quantum systems can surpass this limitation. We show that communication bounded to the exchange of a single quantum particle (in superposition of different spatial locations) can result in "two-way signaling," which is impossible in classical physics. We quantify the discrepancy between classical and quantum scenarios by the probability of winning a game played by distant players. We generalize our result to an arbitrary number of parties and we show that the probability of success is asymptotically decreasing to zero as the number of parties grows, for all classical strategies. In contrast, quantum strategy allows players to win the game with certainty.
Finite and profinite quantum systems
Vourdas, Apostolos
2017-01-01
This monograph provides an introduction to finite quantum systems, a field at the interface between quantum information and number theory, with applications in quantum computation and condensed matter physics. The first major part of this monograph studies the so-called `qubits' and `qudits', systems with periodic finite lattice as position space. It also discusses the so-called mutually unbiased bases, which have applications in quantum information and quantum cryptography. Quantum logic and its applications to quantum gates is also studied. The second part studies finite quantum systems, where the position takes values in a Galois field. This combines quantum mechanics with Galois theory. The third part extends the discussion to quantum systems with variables in profinite groups, considering the limit where the dimension of the system becomes very large. It uses the concepts of inverse and direct limit and studies quantum mechanics on p-adic numbers. Applications of the formalism include quantum optics and ...
Single Molecule Applications of Quantum Dots
DEFF Research Database (Denmark)
Rasmussen, Thomas Elmelund; Jauffred, Liselotte; Brewer, Jonathan R.
2013-01-01
Fluorescent nanocrystals composed of semiconductor materials were first introduced for biological applications in the late 1990s. The focus of this review is to give a brief survey of biological applications of quantum dots (QDs) at the single QD sensitivity level. These are described as follows:...... experiments held together with the prospects in localization microscopy and single molecule manipulation experiments gave QDs a promising future in single molecule research....
Designing single-qutrit quantum gates via tripod adiabatic passage
Directory of Open Access Journals (Sweden)
M. Amniat-Talab
2014-04-01
Full Text Available In this paper, we use stimulated Raman adiabatic passage technique to implement single-qutrit quantum gates in tripod systems. It is shown by using the Morris-Shore (MS transformation, the six-state problem with 5 pulsed fields can be reduced to a basis that decouples two states from the others. This imposes three pulses not connected to the initial condition with have the same shape. Using this method, the six-state penta-pod system is reduced to a tripod system. We can design single-qutrit quantum gates by ignoring the fragile dynamical phase, and by suitable design of Rabi frequencies of the effective Hamiltonian
Measurement of quantum noise in a single-electron transistor near the quantum limit
Xue, W. W.; Ji, Z.; Pan, Feng; Stettenheim, Joel; Blencowe, M. P.; Rimberg, A. J.
2009-09-01
Quantum measurement has challenged physicists for almost a century. Classically, there is no lower bound on the noise a measurement may add. Quantum mechanically, however, measuring a system necessarily perturbs it. When applied to electrical amplifiers, this means that improved sensitivity requires increased backaction that itself contributes noise. The result is a strict quantum limit on added amplifier noise. To approach this limit, a quantum-limited amplifier must possess an ideal balance between sensitivity and backaction; furthermore, its noise must dominate that of subsequent classical amplifiers. Here, we report the first complete and quantitative measurement of the quantum noise of a superconducting single-electron transistor (S-SET) near a double Cooper-pair resonance predicted to have the right combination of sensitivity and backaction. A simultaneous measurement of our S-SET's charge sensitivity indicates that it operates within a factor of 3.6 of the quantum limit, a fourfold improvement over the nearest comparable results.
International Nuclear Information System (INIS)
Haemmerling, Jens; Gutkin, Boris; Guhr, Thomas
2010-01-01
We study the emergence of collective dynamics in the integrable Hamiltonian system of two finite ensembles of coupled harmonic oscillators. After identification of a collective degree of freedom, the Hamiltonian is mapped onto a model of Caldeira-Leggett type, where the collective coordinate is coupled to an internal bath of phonons. In contrast to the usual Caldeira-Leggett model, the bath in the present case is part of the system. We derive an equation of motion for the collective coordinate which takes the form of a damped harmonic oscillator. We show that the distribution of quantum transition strengths induced by the collective mode is determined by its classical dynamics.
Quantum transport through single molecules
Osorio Oliveros, E.A.
2009-01-01
This thesis describes three-terminal transport measurements through single molecules. The interest in this field stems from the dream that single molecules will form the building blocks for future nanoscale electronic devices. The advantages are their small size -nanometers-, and their synthetic
Quantum Cybernetics and Complex Quantum Systems Science - A Quantum Connectionist Exploration
Gonçalves, Carlos Pedro
2014-01-01
Quantum cybernetics and its connections to complex quantum systems science is addressed from the perspective of complex quantum computing systems. In this way, the notion of an autonomous quantum computing system is introduced in regards to quantum artificial intelligence, and applied to quantum artificial neural networks, considered as autonomous quantum computing systems, which leads to a quantum connectionist framework within quantum cybernetics for complex quantum computing systems. Sever...
Distributed quantum computing with single photon sources
International Nuclear Information System (INIS)
Beige, A.; Kwek, L.C.
2005-01-01
Full text: Distributed quantum computing requires the ability to perform nonlocal gate operations between the distant nodes (stationary qubits) of a large network. To achieve this, it has been proposed to interconvert stationary qubits with flying qubits. In contrast to this, we show that distributed quantum computing only requires the ability to encode stationary qubits into flying qubits but not the conversion of flying qubits into stationary qubits. We describe a scheme for the realization of an eventually deterministic controlled phase gate by performing measurements on pairs of flying qubits. Our scheme could be implemented with a linear optics quantum computing setup including sources for the generation of single photons on demand, linear optics elements and photon detectors. In the presence of photon loss and finite detector efficiencies, the scheme could be used to build large cluster states for one way quantum computing with a high fidelity. (author)
International Nuclear Information System (INIS)
Vourdas, A
2005-01-01
A finite quantum system in which the position and momentum take values in the Galois field GF(p l ) is constructed from a smaller quantum system in which the position and momentum take values in Z p , using field extension. The Galois trace is used in the definition of the Fourier transform. The Heisenberg-Weyl group of displacements and the Sp(2, GF(p l )) group of symplectic transformations are studied. A class of transformations inspired by the Frobenius maps in Galois fields is introduced. The relationship of this 'Galois quantum system' with its subsystems in which the position and momentum take values in subfields of GF(p l ) is discussed
Hybrid quantum systems: Outsourcing superconducting qubits
Cleland, Andrew
Superconducting qubits offer excellent prospects for manipulating quantum information, with good qubit lifetimes, high fidelity single- and two-qubit gates, and straightforward scalability (admittedly with multi-dimensional interconnect challenges). One interesting route for experimental development is the exploration of hybrid systems, i.e. coupling superconducting qubits to other systems. I will report on our group's efforts to develop approaches that will allow interfacing superconducting qubits in a quantum-coherent fashion to spin defects in solids, to optomechanical devices, and to resonant nanomechanical structures. The longer term goals of these efforts include transferring quantum states between different qubit systems; generating and receiving ``flying'' acoustic phonon-based as well as optical photon-based qubits; and ultimately developing systems that can be used for quantum memory, quantum computation and quantum communication, the last in both the microwave and fiber telecommunications bands. Work is supported by Grants from AFOSR, ARO, DOE and NSF.
Scheme of thinking quantum systems
International Nuclear Information System (INIS)
Yukalov, V I; Sornette, D
2009-01-01
A general approach describing quantum decision procedures is developed. The approach can be applied to quantum information processing, quantum computing, creation of artificial quantum intelligence, as well as to analyzing decision processes of human decision makers. Our basic point is to consider an active quantum system possessing its own strategic state. Processing information by such a system is analogous to the cognitive processes associated to decision making by humans. The algebra of probability operators, associated with the possible options available to the decision maker, plays the role of the algebra of observables in quantum theory of measurements. A scheme is advanced for a practical realization of decision procedures by thinking quantum systems. Such thinking quantum systems can be realized by using spin lattices, systems of magnetic molecules, cold atoms trapped in optical lattices, ensembles of quantum dots, or multilevel atomic systems interacting with electromagnetic field
Single Photon Experiments and Quantum Complementarity
Directory of Open Access Journals (Sweden)
Georgiev D. D.
2007-04-01
Full Text Available Single photon experiments have been used as one of the most striking illustrations of the apparently nonclassical nature of the quantum world. In this review we examine the mathematical basis of the principle of complementarity and explain why the Englert-Greenberger duality relation is not violated in the configurations of Unruh and of Afshar.
Mixed biexcitons in single quantum wells
DEFF Research Database (Denmark)
Wagner, Hans Peter; Langbein, Wolfgang Werner; Hvam, Jørn Märcher
1999-01-01
Biexcitonic complexes in a ZnSe single quantum well are investigated by spectrally resolved four-wave mixing (FWM). The formation of heavy-heavy-hole XXh and of mixed heavy-light-hole XXm biexcitons showing binding energies of Delta(h) = 4.8 meV and Delta(m)= 2.8 meV is identified by polarization...
Spin storage in quantum dot ensembles and single quantum dots
Energy Technology Data Exchange (ETDEWEB)
Heiss, Dominik
2009-10-15
This thesis deals with the investigation of spin relaxation of electrons and holes in small ensembles of self-assembled quantum dots using optical techniques. Furthermore, a method to detect the spin orientation in a single quantum dot was developed in the framework of this thesis. A spin storage device was used to optically generate oriented electron spins in small frequency selected quantum dot ensembles using circularly polarized optical excitation. The spin orientation can be determined by the polarization of the time delayed electroluminescence signal generated by the device after a continuously variable storage time. The degree of spin polarized initialization was found to be limited to 0.6 at high magnetic fields, where anisotropic effects are compensated. The spin relaxation was directly measured as a function of magnetic field, lattice temperature and s-shell transition energy of the quantum dot by varying the spin storage time up to 30 ms. Very long spin lifetimes are obtained with a lower limit of T{sub 1}=20 ms at B=4 T and T=1 K. A strong magnetic field dependence T{sub 1}{proportional_to}B{sup -5} has been observed for low temperatures of T=1 K which weakens as the temperature is increased. In addition, the temperature dependence has been determined with T{sub 1}{proportional_to}T{sup -1}. The characteristic dependencies on magnetic field and temperature lead to the identification of the spin relaxation mechanism, which is governed by spin-orbit coupling and mediated by single phonon scattering. This finding is qualitatively supported by the energy dependent measurements. The investigations were extended to a modified device design that enabled studying the spin relaxation dynamics of heavy holes in self-assembled quantum dots. The measurements show a polarization memory effect for holes with up to 0.1 degree of polarization. Furthermore, investigations of the time dynamics of the hole spin relaxation reveal surprisingly long lifetimes T{sub 1}{sup h
Spin storage in quantum dot ensembles and single quantum dots
International Nuclear Information System (INIS)
Heiss, Dominik
2009-01-01
This thesis deals with the investigation of spin relaxation of electrons and holes in small ensembles of self-assembled quantum dots using optical techniques. Furthermore, a method to detect the spin orientation in a single quantum dot was developed in the framework of this thesis. A spin storage device was used to optically generate oriented electron spins in small frequency selected quantum dot ensembles using circularly polarized optical excitation. The spin orientation can be determined by the polarization of the time delayed electroluminescence signal generated by the device after a continuously variable storage time. The degree of spin polarized initialization was found to be limited to 0.6 at high magnetic fields, where anisotropic effects are compensated. The spin relaxation was directly measured as a function of magnetic field, lattice temperature and s-shell transition energy of the quantum dot by varying the spin storage time up to 30 ms. Very long spin lifetimes are obtained with a lower limit of T 1 =20 ms at B=4 T and T=1 K. A strong magnetic field dependence T 1 ∝B -5 has been observed for low temperatures of T=1 K which weakens as the temperature is increased. In addition, the temperature dependence has been determined with T 1 ∝T -1 . The characteristic dependencies on magnetic field and temperature lead to the identification of the spin relaxation mechanism, which is governed by spin-orbit coupling and mediated by single phonon scattering. This finding is qualitatively supported by the energy dependent measurements. The investigations were extended to a modified device design that enabled studying the spin relaxation dynamics of heavy holes in self-assembled quantum dots. The measurements show a polarization memory effect for holes with up to 0.1 degree of polarization. Furthermore, investigations of the time dynamics of the hole spin relaxation reveal surprisingly long lifetimes T 1 h in the microsecond range, therefore, comparable with
Opto-electronics on Single Nanowire Quantum Dots
Van Kouwen, M.P.
2010-01-01
An important goal for nanoscale opto-electronics is the transfer of single electron spin states into single photon polarization states (and vice versa), thereby interfacing quantum transport and quantum optics. Such an interface enables new experiments in the field of quantum information processing. Single and entangled photon-pair generation can be used for quantum cryptography. Furthermore, photons can be used in the readout of a quantum computer based on electron spins. Semiconducting nano...
Quantum Transport in Mesoscopic Systems
Indian Academy of Sciences (India)
988. RESONANCE │ November 2010. GENERAL │ ARTICLE. Quantum Transport in Mesoscopic Systems. CoulombBlockadeandKondoEffect. Navinder Singh. Keywords. Quantum transport, mesoscopic systems, Coulomb blockade,. Kondo effect. Navinder Singh works in the Physical Research. Laboratory, Ahmedabad.
Manipulating Quantum Coherence in Solid State Systems
Flatté, Michael E; The NATO Advanced Study Institute "Manipulating Quantum Coherence in Solid State Systems"
2007-01-01
The NATO Advanced Study Institute "Manipulating Quantum Coherence in Solid State Systems", in Cluj-Napoca, Romania, August 29-September 9, 2005, presented a fundamental introduction to solid-state approaches to achieving quantum computation. This proceedings volume describes the properties of quantum coherence in semiconductor spin-based systems and the behavior of quantum coherence in superconducting systems. Semiconductor spin-based approaches to quantum computation have made tremendous advances in the past several years. Coherent populations of spins can be oriented, manipulated and detected experimentally. Rapid progress has been made towards performing the same tasks on individual spins (nuclear, ionic, or electronic) with all-electrical means. Superconducting approaches to quantum computation have demonstrated single qubits based on charge eigenstates as well as flux eigenstates. These topics have been presented in a pedagogical fashion by leading researchers in the fields of semiconductor-spin-based qu...
Single electron-spin memory with a semiconductor quantum dot
International Nuclear Information System (INIS)
Young, Robert J; Dewhurst, Samuel J; Stevenson, R Mark; Atkinson, Paola; Bennett, Anthony J; Ward, Martin B; Cooper, Ken; Ritchie, David A; Shields, Andrew J
2007-01-01
We show storage of the circular polarization of an optical field, transferring it to the spin-state of an individual electron confined in a single semiconductor quantum dot. The state is subsequently read out through the electronically-triggered emission of a single photon. The emitted photon shares the same polarization as the initial pulse but has a different energy, making the transfer of quantum information between different physical systems possible. With an applied magnetic field of 2 T, spin memory is preserved for at least 1000 times more than the exciton's radiative lifetime
Blok, M S; Kalb, N; Reiserer, A; Taminiau, T H; Hanson, R
2015-01-01
Single defect centers in diamond have emerged as a powerful platform for quantum optics experiments and quantum information processing tasks. Connecting spatially separated nodes via optical photons into a quantum network will enable distributed quantum computing and long-range quantum communication. Initial experiments on trapped atoms and ions as well as defects in diamond have demonstrated entanglement between two nodes over several meters. To realize multi-node networks, additional quantum bit systems that store quantum states while new entanglement links are established are highly desirable. Such memories allow for entanglement distillation, purification and quantum repeater protocols that extend the size, speed and distance of the network. However, to be effective, the memory must be robust against the entanglement generation protocol, which typically must be repeated many times. Here we evaluate the prospects of using carbon nuclear spins in diamond as quantum memories that are compatible with quantum networks based on single nitrogen vacancy (NV) defects in diamond. We present a theoretical framework to describe the dephasing of the nuclear spins under repeated generation of NV spin-photon entanglement and show that quantum states can be stored during hundreds of repetitions using typical experimental coupling parameters. This result demonstrates that nuclear spins with weak hyperfine couplings are promising quantum memories for quantum networks.
Quantum control of optomechanical systems
International Nuclear Information System (INIS)
Hofer, S.
2015-01-01
This thesis explores the prospects of entanglement-enhanced quantum control of optomechanical systems. We first discuss several pulsed schemes in which the radiation-pressure interaction is used to generate EPR entanglement between the mechanical mode of a cavity-optomechanical system and a travelling-wave light pulse. The entanglement created in this way can be used as a resource for mechanical state preparation. On the basis of this protocol, we introduce an optomechanical teleportation scheme to transfer an arbitrary light state onto the mechanical system. Furthermore, we describe how one can create a mechanical non-classical state (i.e., a state with a negative Wigner function) by single-photon detection, and, in a similar protocol, how optomechanical systems can be used to demonstrate the violation of a Bell inequality. The second part of the thesis is dedicated to time-continuous quantum control protocols. Making use of optimal-control techniques, we analyse measurement-based feedback cooling of a mechanical oscillator and demonstrate that ground-state cooling is achievable in the sideband-resolved, blue-detuned regime. We then extend this homodyne-detection based setup and introduce the notion of a time-continuous Bell measurement---a generalisation of the standard continuous variable Bell measurement to a continuous measurement setting. Combining this concept with continuous feedback we analyse the generation of a squeezed mechanical steady state via time-continuous teleportation, and the creation of bipartite mechanical entanglement by entanglement swapping. Finally we discuss an experiment demonstrating the evaluation of the conditional optomechanical quantum state by Kalman filtering, constituting a important step towards time-continuous quantum control of optomechanical systems and the possible realisation of the protocols presented in this thesis. (author) [de
Synchronization in Quantum Key Distribution Systems
Directory of Open Access Journals (Sweden)
Anton Pljonkin
2017-10-01
Full Text Available In the description of quantum key distribution systems, much attention is paid to the operation of quantum cryptography protocols. The main problem is the insufficient study of the synchronization process of quantum key distribution systems. This paper contains a general description of quantum cryptography principles. A two-line fiber-optic quantum key distribution system with phase coding of photon states in transceiver and coding station synchronization mode was examined. A quantum key distribution system was built on the basis of the scheme with automatic compensation of polarization mode distortions. Single-photon avalanche diodes were used as optical radiation detecting devices. It was estimated how the parameters used in quantum key distribution systems of optical detectors affect the detection of the time frame with attenuated optical pulse in synchronization mode with respect to its probabilistic and time-domain characteristics. A design method was given for the process that detects the time frame that includes an optical pulse during synchronization. This paper describes the main quantum communication channel attack methods by removing a portion of optical emission. This paper describes the developed synchronization algorithm that takes into account the time required to restore the photodetector’s operation state after the photon has been registered during synchronization. The computer simulation results of the developed synchronization algorithm were analyzed. The efficiency of the developed algorithm with respect to synchronization process protection from unauthorized gathering of optical emission is demonstrated herein.
Experimental quantum tossing of a single coin
International Nuclear Information System (INIS)
Nguyen, A T; Frison, J; Massar, S; Huy, K Phan
2008-01-01
The cryptographic protocol of coin tossing consists of two parties, Alice and Bob, who do not trust each other, but want to generate a random bit. If the parties use a classical communication channel and have unlimited computational resources, one of them can always cheat perfectly. If the parties use a quantum communication channel, there exist protocols such that neither party can cheat perfectly, although they may be able to significantly bias the coin. Here, we analyze in detail how the performance of a quantum coin tossing experiment should be compared to classical protocols, taking into account the inevitable experimental imperfections. We then report an all-optical fiber experiment in which a single coin is tossed whose randomness is higher than achievable by any classical protocol and present some easily realizable cheating strategies by Alice and Bob
Opto-electronics on Single Nanowire Quantum Dots
Van Kouwen, M.P.
2010-01-01
An important goal for nanoscale opto-electronics is the transfer of single electron spin states into single photon polarization states (and vice versa), thereby interfacing quantum transport and quantum optics. Such an interface enables new experiments in the field of quantum information processing.
On single-time reduction in quantum field theory
International Nuclear Information System (INIS)
Arkhipov, A.A.
1984-01-01
It is shown, how the causality and spectrality properties in qUantum field theory may help one to carry out a single-time reduction of the Bethe-Salpeter wave fUnction. The single-time reduction technique is not based on any concrete model of the quantum field theory. Axiomatic formulations underline the quantum field theory
Single quantum dots fundamentals, applications, and new concepts
2003-01-01
This book reviews recent advances in the exciting and rapid growing field of semiconductor quantum dots by contributions from some of the most prominent researchers in the field. Special focus is given to the optical and electronic properties of single quantum dots due to their potential applications in devices operating with single electrons and/or single photons. This includes quantum dots in electric and magnetic fields, cavity-quantum electrodynamics, nonclassical light generation, and coherent optical control of excitons. Single Quantum Dots also addresses various growth techniques as well as potential device applications such as quantum dot lasers, and new concepts like a single-photon source, and a single quantum dot laser.
Continuous quantum mechanics of single particles in closed and quasi-closed systems: Pt. III and IV
Energy Technology Data Exchange (ETDEWEB)
Brieger, M. [DLR Deutsches Zentrum fuer Luft- und Raumfahrt e.V., Stuttgart (Germany). Inst. fuer Technische Physik
2005-07-01
The rigorous solution to Schroedinger's nonrelativistic time-dependent equation of a single electron's spin-orbit or magnetic hyperfine interaction reveals the full dynamics of angular momentum coupling especially in the presence of an external, arbitrarily oriented magnetic field. Besides of making a description of major dynamical properties possible in simple classical terms, it also sheds new light on the seeming quantization of states: They turn out to be exceptional states of dynamical balance, which in the field-free case are only made possible by the respective pairs of Clebsch-Gordan coefficients. Moreover, the results not only show that integer and half-integer quantum numbers of the total angular momentum only apply to this special case but that in the general case they are also able to obtain the well-known splitting pattern of the stationary energy levels in the field as produced by separately identifiable, field-dependent contributions from the spin-orbit or the magnetic hyperfine interactions on the one hand, and the magnetic dipole interaction with external magnetic fields on the other in a way not accessible to the Breit-Rabi formula. The results further demonstrate that the total magnetic moment responds quite sensitively to even weak field strengths, i.e., with substantial changes although the linear Zeeman effect suggests their seeming constancy in low fields also for levels with vertical stroke M{sub J} vertical stroke < l+1/2. Although Schroedinger's equation is equivalent to an energy representation this detailed description of the behavior of the total magnetic moment is made possible by the fortunate fact that the coupling magnetic moments enter the Hamiltonian linearly. This circumstance can be exploited to describe in full detail how the total magnetic moment behaves in an arbitrarily oriented magnetic field. It is found that its motion in this environment consists of a basic Larmor precession about the field direction
Entanglement and quantum superposition induced by a single photon
Lü, Xin-You; Zhu, Gui-Lei; Zheng, Li-Li; Wu, Ying
2018-03-01
We predict the occurrence of single-photon-induced entanglement and quantum superposition in a hybrid quantum model, introducing an optomechanical coupling into the Rabi model. Originally, it comes from the photon-dependent quantum property of the ground state featured by the proposed hybrid model. It is associated with a single-photon-induced quantum phase transition, and is immune to the A2 term of the spin-field interaction. Moreover, the obtained quantum superposition state is actually a squeezed cat state, which can significantly enhance precision in quantum metrology. This work offers an approach to manipulate entanglement and quantum superposition with a single photon, which might have potential applications in the engineering of new single-photon quantum devices, and also fundamentally broaden the regime of cavity QED.
Decoherence in open quantum systems
International Nuclear Information System (INIS)
Isar, A.
2005-01-01
In the framework of the Lindblad theory for open quantum systems we determine the degree of quantum decoherence of a harmonic oscillator interacting with a thermal bath. In the present paper we have studied QD with the Markovian equation of Lindblad in order to understand the quantum to classical transition for a system consisting of an one-dimensional harmonic oscillator in interaction with a thermal bath in the framework of the theory of open quantum systems based on quantum dynamical semigroups. The role of QD became relevant in many interesting physical problems from field theory, atomic physics, quantum optics and quantum information processing, to which we can add material science, heavy ion collisions, quantum gravity and cosmology, condensed matter physics. Just to mention only a few of them: to understand the way in which QD enhances the quantum to classical transition of density fluctuations; to study systems of trapped and cold atoms (or ions) which may offer the possibility of engineering the environment, like trapped atoms inside cavities, relation between decoherence and other cavity QED effects (such as Casimir effect); on mesoscopic scale, decoherence in the context of Bose-Einstein condensation. In many cases physicists are interested in understanding the specific causes of QD just because they want to prevent decoherence from damaging quantum states and to protect the information stored in quantum states from the degrading effect of the interaction with the environment. Thus, decoherence is responsible for washing out the quantum interference effects which are desirable to be seen as signals in some experiments. QD has a negative influence on many areas relying upon quantum coherence effects, such as quantum computation and quantum control of atomic and molecular processes. The physics of information and computation is such a case, where decoherence is an obvious major obstacle in the implementation of information-processing hardware that takes
Quantum Effects in Biological Systems
2016-01-01
Since the last decade the study of quantum mechanical phenomena in biological systems has become a vibrant field of research. Initially sparked by evidence of quantum effects in energy transport that is instrumental for photosynthesis, quantum biology asks the question of how methods and models from quantum theory can help us to understand fundamental mechanisms in living organisms. This approach entails a paradigm change challenging the related disciplines: The successful framework of quantum theory is taken out of its low-temperature, microscopic regimes and applied to hot and dense macroscopic environments, thereby extending the toolbox of biology and biochemistry at the same time. The Quantum Effects in Biological Systems conference is a platform for researchers from biology, chemistry and physics to present and discuss the latest developments in the field of quantum biology. After meetings in Lisbon (2009), Harvard (2010), Ulm (2011), Berkeley (2012), Vienna (2013), Singapore (2014) and Florence (2015),...
Directory of Open Access Journals (Sweden)
Elezov M.S.
2017-01-01
Full Text Available Recently bright-light control of the SSPD has been demonstrated. This attack employed a “backdoor” in the detector biasing scheme. Under bright-light illumination, SSPD becomes resistive and remains “latched” in the resistive state even when the light is switched off. While the SSPD is latched, Eve can simulate SSPD single-photon response by sending strong light pulses, thus deceiving Bob. We developed the experimental setup for investigation of a dependence on latching threshold of SSPD on optical pulse length and peak power. By knowing latching threshold it is possible to understand essential requirements for development countermeasures against blinding attack on quantum key distribution system with SSPDs.
Single-shot work extraction in quantum thermodynamics revisited
Wang, Shang-Yung
2018-01-01
We revisit the problem of work extraction from a system in contact with a heat bath to a work storage system, and the reverse problem of state formation from a thermal system state in single-shot quantum thermodynamics. A physically intuitive and mathematically simple approach using only elementary majorization theory and matrix analysis is developed, and a graphical interpretation of the maximum extractable work, minimum work cost of formation, and corresponding single-shot free energies is presented. This approach provides a bridge between two previous methods based respectively on the concept of thermomajorization and a comparison of subspace dimensions. In addition, a conceptual inconsistency with regard to general work extraction involving transitions between multiple energy levels of the work storage system is clarified and resolved. It is shown that an additional contribution to the maximum extractable work in those general cases should be interpreted not as work extracted from the system, but as heat transferred from the heat bath. Indeed, the additional contribution is an artifact of a work storage system (essentially a suspended ‘weight’ that can be raised or lowered) that does not truly distinguish work from heat. The result calls into question the common concept that a work storage system in quantum thermodynamics is simply the quantum version of a suspended weight in classical thermodynamics.
Single-copy entanglement in critical quantum spin chains
International Nuclear Information System (INIS)
Eisert, J.; Cramer, M.
2005-01-01
We consider the single-copy entanglement as a quantity to assess quantum correlations in the ground state in quantum many-body systems. We show for a large class of models that already on the level of single specimens of spin chains, criticality is accompanied with the possibility of distilling a maximally entangled state of arbitrary dimension from a sufficiently large block deterministically, with local operations and classical communication. These analytical results--which refine previous results on the divergence of block entropy as the rate at which maximally entangled pairs can be distilled from many identically prepared chains--are made quantitative for general isotropic translationally invariant spin chains that can be mapped onto a quasifree fermionic system, and for the anisotropic XY model. For the XX model, we provide the asymptotic scaling of ∼(1/6)log 2 (L), and contrast it with the block entropy
Spectroscopy of Single Free Standing Quantum Wells
International Nuclear Information System (INIS)
Williams, M D; Hollars, C W; Huser, T; Jallow, N; Cochran, A; Bryant, R
2006-01-01
We investigated the interaction of quantum confined exciton states GaAs quantum wells with native surface states. Single molecule photoluminescence (PL) spectroscopy, developed by T. Huser at LLNL was used to probe the unique bare quantum wells in the free standing quantum well structure. The latter was developed by the M. D. Williams at Clark Atlanta University. The goals of the project during this budget cycle were to procure samples containing GaAs free standing QWs, identify suitable regions for PL analysis at Lawrence Livermore, analyze the structures at room temperature and at liquid nitrogen temperatures. The specific regions of interest on the sample structures were identified by scanning electron microscopy at Clark Atlanta prior to transport to LLNL. Previous attempts at other facilities using NSOM, cathodoluminescence, and conventional PL showed little luminescence activity at room temperature from the 200 (angstrom) thick wells. This suggested either excess recombination due to surface states in the quantum well region or insufficient absorption length for photoluminescence. The literature suggested that the effect of the defects could be eliminated by reducing the sample temperature below their associated activation energies. In our previous subcontract work with LLNL, a significant amount of effort was expended to modify the apparatus to allow low temperature measurements. The modifications were not successful and we concluded that in order to do the measurements at low temperature we would need to purchase a commercial optical cryostat to get reliable results. Ms. Rochelle Bryant worked during the summer as an intern at LLNL on the project under the supervision of C. Hollars and in collaboration with T. Huser and found that PL emission could be obtained at room temperature. This was a surprising result as the literature and our experience shows that there is no PL emission from GaAs at room temperature. We speculate that this is due to the small
Quantum private comparison employing single-photon interference
Liu, Bin; Xiao, Di; Huang, Wei; Jia, Heng-Yue; Song, Ting-Ting
2017-07-01
As a typical quantum cryptographic task between distrustful participants, quantum private comparison (QPC) has attracted a lot of attention in recent years. Here we propose two QPC protocols employing single-photon interference, a typical and interesting technology for quantum communications. Compared with the previous QPC protocols employing normal single states or entangled states, the proposed protocols achieve lower communication complexity utilizing the characteristics of single-photon interference. And we also proved the security of the proposed protocols in theory.
Decoherence in Quantum Spin Systems
De Raedt, H; Dobrovitski, VV; Landau, DP; Lewis, SP; Schuttler, HB
2003-01-01
Computer simulations of decoherence in quantum spin systems require the solution of the time-dependent Schrodinger equation for interacting quantum spin systems over extended periods of time. We use exact diagonalization, the Chebyshev polynomial technique, four Suzuki-formula algorithms, and the
Quantum Transport in Mesoscopic Systems
Indian Academy of Sciences (India)
A short introduction to the quantum transport in mesoscopic systems is given, and various regim- es of quantum transport such as diffusive, ballis- tic, and adiabatic are explained. The effect of interactions and inelastic scattering along with the characteristic coherent effects of mesoscopic systems give interesting new ...
Universal quantum gates for Single Cooper Pair Box based quantum computing
Echternach, P.; Williams, C. P.; Dultz, S. C.; Braunstein, S.; Dowling, J. P.
2000-01-01
We describe a method for achieving arbitrary 1-qubit gates and controlled-NOT gates within the context of the Single Cooper Pair Box (SCB) approach to quantum computing. Such gates are sufficient to support universal quantum computation.
Quantum technologies with hybrid systems
Kurizki, Gershon; Bertet, Patrice; Kubo, Yuimaru; Mølmer, Klaus; Petrosyan, David; Rabl, Peter; Schmiedmayer, Jörg
2015-01-01
An extensively pursued current direction of research in physics aims at the development of practical technologies that exploit the effects of quantum mechanics. As part of this ongoing effort, devices for quantum information processing, secure communication, and high-precision sensing are being implemented with diverse systems, ranging from photons, atoms, and spins to mesoscopic superconducting and nanomechanical structures. Their physical properties make some of these systems better suited than others for specific tasks; thus, photons are well suited for transmitting quantum information, weakly interacting spins can serve as long-lived quantum memories, and superconducting elements can rapidly process information encoded in their quantum states. A central goal of the envisaged quantum technologies is to develop devices that can simultaneously perform several of these tasks, namely, reliably store, process, and transmit quantum information. Hybrid quantum systems composed of different physical components with complementary functionalities may provide precisely such multitasking capabilities. This article reviews some of the driving theoretical ideas and first experimental realizations of hybrid quantum systems and the opportunities and challenges they present and offers a glance at the near- and long-term perspectives of this fascinating and rapidly expanding field. PMID:25737558
Open quantum systems recent developments
Joye, Alain; Pillet, Claude-Alain
2006-01-01
Understanding dissipative dynamics of open quantum systems remains a challenge in mathematical physics. This problem is relevant in various areas of fundamental and applied physics. From a mathematical point of view, it involves a large body of knowledge. Significant progress in the understanding of such systems has been made during the last decade. These books present in a self-contained way the mathematical theories involved in the modeling of such phenomena. They describe physically relevant models, develop their mathematical analysis and derive their physical implications. In Volume I the Hamiltonian description of quantum open systems is discussed. This includes an introduction to quantum statistical mechanics and its operator algebraic formulation, modular theory, spectral analysis and their applications to quantum dynamical systems. Volume II is dedicated to the Markovian formalism of classical and quantum open systems. A complete exposition of noise theory, Markov processes and stochastic differential...
Multi-group dynamic quantum secret sharing with single photons
Energy Technology Data Exchange (ETDEWEB)
Liu, Hongwei [School of Science and State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Ma, Haiqiang, E-mail: hqma@bupt.edu.cn [School of Science and State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Wei, Kejin [School of Science and State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Yang, Xiuqing [School of Science, Beijing Jiaotong University, Beijing 100044 (China); Qu, Wenxiu; Dou, Tianqi; Chen, Yitian; Li, Ruixue; Zhu, Wu [School of Science and State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876 (China)
2016-07-15
In this letter, we propose a novel scheme for the realization of single-photon dynamic quantum secret sharing between a boss and three dynamic agent groups. In our system, the boss can not only choose one of these three groups to share the secret with, but also can share two sets of independent keys with two groups without redistribution. Furthermore, the security of communication is enhanced by using a control mode. Compared with previous schemes, our scheme is more flexible and will contribute to a practical application. - Highlights: • A multi-group dynamic quantum secret sharing with single photons scheme is proposed. • Any one of the groups can be chosen to share secret through controlling the polarization of photons. • Two sets of keys can be shared simultaneously without redistribution.
Single-photon-level quantum memory at room temperature.
Reim, K F; Michelberger, P; Lee, K C; Nunn, J; Langford, N K; Walmsley, I A
2011-07-29
Room-temperature, easy-to-operate quantum memories are essential building blocks for future long distance quantum information networks operating on an intercontinental scale, because devices like quantum repeaters, based on quantum memories, will have to be deployed in potentially remote, inaccessible locations. Here we demonstrate controllable, broadband and efficient storage and retrieval of weak coherent light pulses at the single-photon level in warm atomic cesium vapor using the robust far off-resonant Raman memory scheme. We show that the unconditional noise floor of this technically simple quantum memory is low enough to operate in the quantum regime, even in a room-temperature environment.
Avoiding irreversible dynamics in quantum systems
Karasik, Raisa Iosifovna
2009-10-01
the interactions between the system and its environment in a special way to reduce decoherence. This property is used to discover new DFS that rely on rather counterintuitive phenomenon, which I call an "incoherent generation of coherences." I also provide examples of physical systems that support such states. These DFS can be used to suppress & coherence, but may not be sufficient for performing full quantum computation. I also explore the possibility of physically generating the DFS that are useful for quantum computation. For quantum computation we need to preserve at least two quantum states to encode the quantum analogue of classical bits. Here I aim to generate DFS in a system composed from a large collection of atoms or molecules and I need to determine how one should position atoms or molecules in 3D space so that the overall system possesses a DFS with at least two states (i.e., non-trivial DFS). I show that for many Markovian systems, non-trivial DFS can exist only when particles are located in exactly the same position in space. This, of course, is not possible in the real world. For these systems, I also show that states in DFS are states with infinite lifetime. However, for all practical applications we just need long-lived states. Thus in reality, we do just need to bring quantum particles close together to generate an imperfect DFS, i.e. a collection of long-lived states. This can be achieved, for example, for atoms within a single molecule.
Entanglement in open quantum systems
International Nuclear Information System (INIS)
Isar, A.
2007-01-01
In the framework of the theory of open systems based on quantum dynamical semigroups, we solve the master equation for two independent bosonic oscillators interacting with an environment in the asymptotic long-time regime. We give a description of the continuous-variable entanglement in terms of the covariance matrix of the quantum states of the considered system for an arbitrary Gaussian input state. Using the Peres-Simon necessary and sufficient condition for separability of two-mode Gaussian states, we show that the two non-interacting systems immersed in a common environment and evolving under a Markovian, completely positive dynamics become asymptotically entangled for certain environments, so that their non-local quantum correlations exist in the long-time regime. (author) Key words: quantum information theory, open systems, quantum entanglement, inseparable states
Directory of Open Access Journals (Sweden)
Alessandro Seri
2017-05-01
Full Text Available Quantum correlations between long-lived quantum memories and telecom photons that can propagate with low loss in optical fibers are an essential resource for the realization of large-scale quantum information networks. Significant progress has been realized in this direction with atomic and solid-state systems. Here, we demonstrate quantum correlations between a telecom photon and a multimode on-demand solid state quantum memory. This is achieved by mapping a correlated single photon onto a spin collective excitation in a Pr^{3+}:Y_{2}SiO_{5} crystal for a controllable time. The stored single photons are generated by cavity-enhanced spontaneous parametric down-conversion and heralded by their partner photons at telecom wavelength. These results represent the first demonstration of a multimode on-demand solid state quantum memory for external quantum states of light. They provide an important resource for quantum repeaters and pave the way for the implementation of quantum information networks with distant solid state quantum nodes.
Quantum transport of the single metallocene molecule
Yu, Jing-Xin; Chang, Jing; Wei, Rong-Kai; Liu, Xiu-Ying; Li, Xiao-Dong
2016-10-01
The Quantum transport of three single metallocene molecule is investigated by performing theoretical calculations using the non-equilibrium Green's function method combined with density functional theory. We find that the three metallocen molecules structure become stretched along the transport direction, the distance between two Cp rings longer than the other theory and experiment results. The lager conductance is found in nickelocene molecule, the main transmission channel is the electron coupling between molecule and the electrodes is through the Ni dxz and dyz orbitals and the s, dxz, dyz of gold. This is also confirmed by the highest occupied molecular orbital resonance at Fermi level. In addition, negative differential resistance effect is found in the ferrocene, cobaltocene molecules, this is also closely related with the evolution of the transmission spectrum under applied bias.
Noncommutative mathematics for quantum systems
Franz, Uwe
2016-01-01
Noncommutative mathematics is a significant new trend of mathematics. Initially motivated by the development of quantum physics, the idea of 'making theory noncommutative' has been extended to many areas of pure and applied mathematics. This book is divided into two parts. The first part provides an introduction to quantum probability, focusing on the notion of independence in quantum probability and on the theory of quantum stochastic processes with independent and stationary increments. The second part provides an introduction to quantum dynamical systems, discussing analogies with fundamental problems studied in classical dynamics. The desire to build an extension of the classical theory provides new, original ways to understand well-known 'commutative' results. On the other hand the richness of the quantum mathematical world presents completely novel phenomena, never encountered in the classical setting. This book will be useful to students and researchers in noncommutative probability, mathematical physi...
Single qudit realization of the Deutsch algorithm using superconducting many-level quantum circuits
Kiktenko, E. O.; Fedorov, A. K.; Strakhov, A. A.; Man'ko, V. I.
2015-07-01
Design of a large-scale quantum computer has paramount importance for science and technologies. We investigate a scheme for realization of quantum algorithms using noncomposite quantum systems, i.e., systems without subsystems. In this framework, n artificially allocated "subsystems" play a role of qubits in n-qubits quantum algorithms. With focus on two-qubit quantum algorithms, we demonstrate a realization of the universal set of gates using a d = 5 single qudit state. Manipulation with an ancillary level in the systems allows effective implementation of operators from U(4) group via operators from SU(5) group. Using a possible experimental realization of such systems through anharmonic superconducting many-level quantum circuits, we present a blueprint for a single qudit realization of the Deutsch algorithm, which generalizes previously studied realization based on the virtual spin representation (Kessel et al., 2002 [9]).
Simulation of n-qubit quantum systems. V. Quantum measurements
Radtke, T.; Fritzsche, S.
2010-02-01
The FEYNMAN program has been developed during the last years to support case studies on the dynamics and entanglement of n-qubit quantum registers. Apart from basic transformations and (gate) operations, it currently supports a good number of separability criteria and entanglement measures, quantum channels as well as the parametrizations of various frequently applied objects in quantum information theory, such as (pure and mixed) quantum states, hermitian and unitary matrices or classical probability distributions. With the present update of the FEYNMAN program, we provide a simple access to (the simulation of) quantum measurements. This includes not only the widely-applied projective measurements upon the eigenspaces of some given operator but also single-qubit measurements in various pre- and user-defined bases as well as the support for two-qubit Bell measurements. In addition, we help perform generalized and POVM measurements. Knowing the importance of measurements for many quantum information protocols, e.g., one-way computing, we hope that this update makes the FEYNMAN code an attractive and versatile tool for both, research and education. New version program summaryProgram title: FEYNMAN Catalogue identifier: ADWE_v5_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADWE_v5_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 27 210 No. of bytes in distributed program, including test data, etc.: 1 960 471 Distribution format: tar.gz Programming language: Maple 12 Computer: Any computer with Maple software installed Operating system: Any system that supports Maple; the program has been tested under Microsoft Windows XP and Linux Classification: 4.15 Catalogue identifier of previous version: ADWE_v4_0 Journal reference of previous version: Comput. Phys. Commun
International Nuclear Information System (INIS)
Chirikov, B.V.
1991-01-01
The overview of recent developments in the theory of quantum chaos is presented with the special emphasis on a number of unsolved problems and current apparent contradictions. The relation between dynamical quantum chaos and statistical random matrix theory is discussed. 97 refs
Local unitary invariants for multipartite quantum systems
Energy Technology Data Exchange (ETDEWEB)
Vrana, Peter, E-mail: vranap@math.bme.hu [Department of Theoretical Physics, Institute of Physics, Budapest University of Technology and Economics, H-1111 Budapest (Hungary)
2011-03-18
A method is presented to obtain local unitary invariants for multipartite quantum systems consisting of fermions or distinguishable particles. The invariants are organized into infinite families, in particular, the generalization to higher dimensional single-particle Hilbert spaces is straightforward. Many well-known invariants and their generalizations are also included.
Dynamical sensitivity control of a single-spin quantum sensor.
Lazariev, Andrii; Arroyo-Camejo, Silvia; Rahane, Ganesh; Kavatamane, Vinaya Kumar; Balasubramanian, Gopalakrishnan
2017-07-26
The Nitrogen-Vacancy (NV) defect in diamond is a unique quantum system that offers precision sensing of nanoscale physical quantities at room temperature beyond the current state-of-the-art. The benchmark parameters for nanoscale magnetometry applications are sensitivity, spectral resolution, and dynamic range. Under realistic conditions the NV sensors controlled by conventional sensing schemes suffer from limitations of these parameters. Here we experimentally show a new method called dynamical sensitivity control (DYSCO) that boost the benchmark parameters and thus extends the practical applicability of the NV spin for nanoscale sensing. In contrast to conventional dynamical decoupling schemes, where π pulse trains toggle the spin precession abruptly, the DYSCO method allows for a smooth, analog modulation of the quantum probe's sensitivity. Our method decouples frequency selectivity and spectral resolution unconstrained over the bandwidth (1.85 MHz-392 Hz in our experiments). Using DYSCO we demonstrate high-accuracy NV magnetometry without |2π| ambiguities, an enhancement of the dynamic range by a factor of 4 · 10 3 , and interrogation times exceeding 2 ms in off-the-shelf diamond. In a broader perspective the DYSCO method provides a handle on the inherent dynamics of quantum systems offering decisive advantages for NV centre based applications notably in quantum information and single molecule NMR/MRI.
Can a quantum state over time resemble a quantum state at a single time?
Horsman, Dominic; Heunen, Chris; Pusey, Matthew F; Barrett, Jonathan; Spekkens, Robert W
2017-09-01
The standard formalism of quantum theory treats space and time in fundamentally different ways. In particular, a composite system at a given time is represented by a joint state, but the formalism does not prescribe a joint state for a composite of systems at different times. If there were a way of defining such a joint state, this would potentially permit a more even-handed treatment of space and time, and would strengthen the existing analogy between quantum states and classical probability distributions. Under the assumption that the joint state over time is an operator on the tensor product of single-time Hilbert spaces, we analyse various proposals for such a joint state, including one due to Leifer and Spekkens, one due to Fitzsimons, Jones and Vedral, and another based on discrete Wigner functions. Finding various problems with each, we identify five criteria for a quantum joint state over time to satisfy if it is to play a role similar to the standard joint state for a composite system: that it is a Hermitian operator on the tensor product of the single-time Hilbert spaces; that it represents probabilistic mixing appropriately; that it has the appropriate classical limit; that it has the appropriate single-time marginals; that composing over multiple time steps is associative. We show that no construction satisfies all these requirements. If Hermiticity is dropped, then there is an essentially unique construction that satisfies the remaining four criteria.
Information in individual quantum systems
International Nuclear Information System (INIS)
Brukner, C.
1999-09-01
A new measure of information in quantum mechanics is proposed which takes into account that for quantum systems, the only feature known before an experiment is performed are the probabilities for various events to occur. The sum of the individual measures of information for mutually complementary observations is invariant under the choice of the particular set of complementary observations and conserved in time if there is no information exchange with an environment unitary transformation. This operational quantum information invariant results in k bits of information for a system consisting of $k$ qubits. For a composite system, maximal entanglement results if the total information carried by the system is exhausted in specifying joint properties, with no individual qubit carrying any information on its own. We interpret our results as implying that information is the most fundamental notion in quantum mechanics. Based on this observation we suggest ideas for a foundational principle for quantum theory. It is proposed here that the foundational principle for quantum theory may be identified through the assumption that the most elementary system carries one bit of information only. Therefore an elementary system can only give a definite answer in one specific measurement. The irreducible randomness of individual outcomes in other measurements and quantum complementarity are then necessary consequences. The most natural function between probabilities for outcomes to occur and the experimental parameters, consistent with the foundational principle proposed, is the well-known sinusoidal dependence. (author)
Scattering theory for open quantum systems
Energy Technology Data Exchange (ETDEWEB)
Behrndt, Jussi [Technische Univ. Berlin (Germany). Inst. fuer Mathematik; Malamud, Mark M. [Donetsk National University (Ukraine). Dept. of Mathematics; Neidhardt, Hagen [Weierstrass-Institut fuer Angewandte Analysis und Stochastik (WIAS) im Forschungsverbund Berlin e.V. (Germany)
2006-07-01
Quantum systems which interact with their environment are often modeled by maximal dissipative operators or so-called Pseudo-Hamiltonians. In this paper the scattering theory for such open systems is considered. First it is assumed that a single maximal dissipative operator A{sub D} in a Hilbert space H is used to describe an open quantum system. In this case the minimal self-adjoint dilation K of A{sub D} can be regarded as the Hamiltonian of a closed system which contains the open system {l_brace}A{sub D},h{r_brace}, but since K is necessarily not semibounded from below, this model is difficult to interpret from a physical point of view. In the second part of the paper an open quantum system is modeled with a family {l_brace}A({mu}){r_brace} of maximal dissipative operators depending on energy {mu}, and it is shown that the open system can be embedded into a closed system where the Hamiltonian is semibounded. Surprisingly it turns out that the corresponding scattering matrix can be completely recovered from scattering matrices of single Pseudo-Hamiltonians as in the first part of the paper. The general results are applied to a class of Sturm-Liouville operators arising in dissipative and quantum transmitting Schroedinger-Poisson systems. (orig.)
Stable Luminescence of Single Quantum Emitters: Applications in Quantum Optics
Directory of Open Access Journals (Sweden)
Naumov A.V.
2015-01-01
Full Text Available Abstract. In our work, we demonstrate the advantages and drawbacks of the methods for generating nonclassical light using single luminescent molecules in solid matrices at cryogenic temperatures when excitation of zero-phonon spectral lines is possible. It is shown that for certain impurity-matrix systems it is possible to guarantee the following: single-photon generation at a rate of up to tens-hundreds MHz, allocation of an extremely narrow generation band (a few MHz, wavelength tuning over a wide range (tens of nanometers, generation of biphoton radiation, high photostability and absence of a stochastic spectral dynamics.
Delteil, Aymeric; Gao, Wei-bo; Fallahi, Parisa; Miguel-Sanchez, Javier; Imamoǧlu, Atac
2014-03-01
Single-shot readout of individual qubits is typically the slowest process among the elementary single- and two-qubit operations required for quantum information processing. Here, we use resonance fluorescence from a single-electron charged quantum dot to read out the spin-qubit state in 800 nanoseconds with a fidelity exceeding 80%. Observation of the spin evolution on longer time scales reveals quantum jumps of the spin state: we use the experimentally determined waiting-time distribution to characterize the quantum jumps.
Single-flux-quantum circuit technology for superconducting radiation detectors
International Nuclear Information System (INIS)
Fujimaki, Akira; Onogi, Masashi; Matsumoto, Tomohiro; Tanaka, Masamitsu; Sekiya, Akito; Hayakawa, Hisao; Yorozu, Shinichi; Terai, Hirotaka; Yoshikawa, Nobuyuki
2003-01-01
We discuss the application of the single-flux-quantum (SFQ) logic circuits to multi superconducting radiation detectors system. The SFQ-based analog-to-digital converters (ADCs) have the advantage in current sensitivity, which can reach less than 10 nA in a well-tuned ADC. We have also developed the design technology of the SFQ circuits. We demonstrate high-speed operation of large-scale integrated circuits such as a 2x2 cross/bar switch, arithmetic logic unit, indicating that our present SFQ technology is applicable to the multi radiation detectors system. (author)
Guo, Y. N.; Tian, Q. L.; Mo, Y. F.; Zhang, G. L.; Zeng, K.
2018-04-01
In this paper, we have investigated the preservation of quantum Fisher information (QFI) of a single-qubit system coupled to a common zero temperature reservoir through the addition of noninteracting qubits. The results show that, the QFI is completely protected in both Markovian and non-Markovian regimes by increasing the number of additional qubits. Besides, the phenomena of QFI display monotonic decay or non-monotonic with revival oscillations depending on the number of additional qubits N - 1 in a common dissipative reservoir. If N < N c (a critical number depending on the reservoirs parameters), the behavior of QFI with monotonic decay occurs. However, if N ≥ N c , QFI exhibits non-monotonic behavior with revival oscillations. Moreover, we extend this model to investigate the effect of additional qubits and the initial conditions of the system on the geometric phase (GP). It is found that, the robustness of GP against the dissipative reservoir has been demonstrated by increasing gradually the number of additional qubits N - 1. Besides, the GP is sensitive to the initial parameter 𝜃, and possesses symmetric in a range regime [0,2 π].
Symmetry breaking by quantum coherence in single electron attachment
Krishnakumar, E.; Prabhudesai, Vaibhav S.; Mason, Nigel J.
2018-02-01
Quantum coherence-induced effects in atomic and molecular systems are the basis of several proposals for laser-based control of chemical reactions. So far, these rely on coherent photon beams inducing coherent reaction pathways that may interfere with one another, to achieve the desired outcome. This concept has been successfully exploited for removing the inversion symmetry in the dissociation of homonuclear diatomic molecules, but it remains to be seen if such quantum coherent effects can also be generated by the interaction of incoherent electrons with such molecules. Here we show that resonant electron attachment to H2 and the subsequent dissociation into H (n = 2) + H- is asymmetric about the inter-nuclear axis, whereas the asymmetry in D2 is far less pronounced. We explain this observation as due to attachment of a single electron resulting in a coherent superposition of two resonances of opposite parity. In addition to exemplifying a new quantum coherent process, our observation of coherent quantum dynamics involves the active participation of all three electrons and two nuclei, which could provide new tools for studying electron correlations as a means to control chemical processes, and demonstrates the role of coherent effects in electron-induced chemistry.
Universal blind quantum computation for hybrid system
Huang, He-Liang; Bao, Wan-Su; Li, Tan; Li, Feng-Guang; Fu, Xiang-Qun; Zhang, Shuo; Zhang, Hai-Long; Wang, Xiang
2017-08-01
As progress on the development of building quantum computer continues to advance, first-generation practical quantum computers will be available for ordinary users in the cloud style similar to IBM's Quantum Experience nowadays. Clients can remotely access the quantum servers using some simple devices. In such a situation, it is of prime importance to keep the security of the client's information. Blind quantum computation protocols enable a client with limited quantum technology to delegate her quantum computation to a quantum server without leaking any privacy. To date, blind quantum computation has been considered only for an individual quantum system. However, practical universal quantum computer is likely to be a hybrid system. Here, we take the first step to construct a framework of blind quantum computation for the hybrid system, which provides a more feasible way for scalable blind quantum computation.
Quantum Dot Systems : A versatile platform for quantum simulations
Barthelemy, P.J.C.; Vandersypen, L.M.K.
2013-01-01
Quantum mechanics often results in extremely complex phenomena, especially when the quantum system under consideration is composed of many interacting particles. The states of these many-body systems live in a space so large that classical numerical calculations cannot compute them. Quantum
Theory of single quantum dot lasers: Pauli-blocking-enhanced anti-bunching
International Nuclear Information System (INIS)
Su, Yumian; Bimberg, Dieter; Carmele, Alexander; Richter, Marten; Knorr, Andreas; Lüdge, Kathy; Schöll, Eckehard
2011-01-01
We present a theoretical model to describe the dynamics of a single semiconductor quantum dot interacting with a microcavity system. The confined quantum dot levels are pumped electrically via a carrier reservoir. The investigated dynamics includes semiconductor-specific, reservoir-induced Pauli-blocking terms in the equations of the photon probability functions. This enables a direct study of the photon statistics of the quantum light emission in dependence on the different pumping rates
Quantum Dot Systems: a versatile platform for quantum simulations
International Nuclear Information System (INIS)
Barthelemy, Pierre; Vandersypen, Lieven M.K.
2013-01-01
Quantum mechanics often results in extremely complex phenomena, especially when the quantum system under consideration is composed of many interacting particles. The states of these many-body systems live in a space so large that classical numerical calculations cannot compute them. Quantum simulations can be used to overcome this problem: complex quantum problems can be solved by studying experimentally an artificial quantum system operated to simulate the desired hamiltonian. Quantum dot systems have shown to be widely tunable quantum systems, that can be efficiently controlled electrically. This tunability and the versatility of their design makes them very promising quantum simulators. This paper reviews the progress towards digital quantum simulations with individually controlled quantum dots, as well as the analog quantum simulations that have been performed with these systems. The possibility to use large arrays of quantum dots to simulate the low-temperature Hubbard model is also discussed. The main issues along that path are presented and new ideas to overcome them are proposed. (copyright 2013 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Wu, Nan; Zhang, Cong; Jin, Xing Ri; Zhang, Ying Qiao; Lee, YoungPak
2018-02-19
Unidirectional reflectionless phenomena are investigated theoretically in a non-Hermitian quantum system composed of several quantum dots and a plasmonic waveguide. By adjusting the phase shifts between quantum dots, single- and dual-band unidirectional reflectionlessnesses are realized at exceptional points based on two and three quantum dots coupled to a plasmonic waveguide, respectively. In addition, single- and dual-band unidirectional perfect absorptions with high quality factors are obtained at the vicinity of exceptional points.
Contextual logic for quantum systems
International Nuclear Information System (INIS)
Domenech, Graciela; Freytes, Hector
2005-01-01
In this work we build a quantum logic that allows us to refer to physical magnitudes pertaining to different contexts from a fixed one without the contradictions with quantum mechanics expressed in no-go theorems. This logic arises from considering a sheaf over a topological space associated with the Boolean sublattices of the ortholattice of closed subspaces of the Hilbert space of the physical system. Different from standard quantum logics, the contextual logic maintains a distributive lattice structure and a good definition of implication as a residue of the conjunction
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
Optimised quantum hacking of superconducting nanowire single-photon detectors.
Tanner, Michael G; Makarov, Vadim; Hadfield, Robert H
2014-03-24
We explore bright-light control of superconducting nanowire single-photon detectors (SNSPDs) in the shunted configuration (a practical measure to avoid latching). In an experiment, we simulate an illumination pattern the SNSPD would receive in a typical quantum key distribution system under hacking attack. We show that it effectively blinds and controls the SNSPD. The transient blinding illumination lasts for a fraction of a microsecond and produces several deterministic fake clicks during this time. This attack does not lead to elevated timing jitter in the spoofed output pulse, and hence does not introduce significant errors. Five different SNSPD chip designs were tested. We consider possible countermeasures to this attack.
Optimised quantum hacking of superconducting nanowire single-photon detectors
Tanner, Michael G.; Makarov, Vadim; Hadfield, Robert H.
2014-03-01
We explore bright-light control of superconducting nanowire single-photon detectors (SNSPDs) in the shunted configuration (a practical measure to avoid latching). In an experiment, we simulate an illumination pattern the SNSPD would receive in a typical quantum key distribution system under hacking attack. We show that it effectively blinds and controls the SNSPD. The transient blinding illumination lasts for a fraction of a microsecond and produces several deterministic fake clicks during this time. This attack does not lead to elevated timing jitter in the spoofed output pulse, and hence does not introduce significant errors. Five different SNSPD chip designs were tested. We consider possible countermeasures to this attack.
Zoller, Peter; Cirac, Ignacio; Girvin, Steven; Massar, Serge
2013-03-01
This article reviews how interactions between atoms can be engineered by means of external fields, and how those interactions may be used to build quantum information processing devices and simulators. It also describes some of the obstacles one has to overcome in order to build such devices, as well as their potential impact in other branches of Physics.
Quantum dynamics in open quantum-classical systems.
Kapral, Raymond
2015-02-25
Often quantum systems are not isolated and interactions with their environments must be taken into account. In such open quantum systems these environmental interactions can lead to decoherence and dissipation, which have a marked influence on the properties of the quantum system. In many instances the environment is well-approximated by classical mechanics, so that one is led to consider the dynamics of open quantum-classical systems. Since a full quantum dynamical description of large many-body systems is not currently feasible, mixed quantum-classical methods can provide accurate and computationally tractable ways to follow the dynamics of both the system and its environment. This review focuses on quantum-classical Liouville dynamics, one of several quantum-classical descriptions, and discusses the problems that arise when one attempts to combine quantum and classical mechanics, coherence and decoherence in quantum-classical systems, nonadiabatic dynamics, surface-hopping and mean-field theories and their relation to quantum-classical Liouville dynamics, as well as methods for simulating the dynamics.
Simulation of quantum many-body systems and quantum computer
International Nuclear Information System (INIS)
Long Lugui
2010-01-01
Benioff and Feynman independently proposed quantum computer from the need of reversible computing and simulation of many-body systems. In this talk, I will briefly review the development of quantum computer, and report the study of many-body interactions in simple quantum computer and related development. (authors)
Quantum energy teleportation in a quantum Hall system
Energy Technology Data Exchange (ETDEWEB)
Yusa, Go; Izumida, Wataru; Hotta, Masahiro [Department of Physics, Tohoku University, Sendai 980-8578 (Japan)
2011-09-15
We propose an experimental method for a quantum protocol termed quantum energy teleportation (QET), which allows energy transportation to a remote location without physical carriers. Using a quantum Hall system as a realistic model, we discuss the physical significance of QET and estimate the order of energy gain using reasonable experimental parameters.
Single-atom gating and magnetic interactions in quantum corrals
Energy Technology Data Exchange (ETDEWEB)
Ngo, Anh T.; Kim, Eugene H.; Ulloa, Sergio E.
2017-04-01
Single-atom gating, achieved by manipulation of adatoms on a surface, has been shown in experiments to allow precise control over superposition of electronic states in quantum corrals. Using a Green's function approach, we demonstrate theoretically that such atom gating can also be used to control the coupling between magnetic degrees of freedom in these systems. Atomic gating enables control not only on the direct interaction between magnetic adatoms, but also over superpositions of many-body states which can then control long distance interactions. We illustrate this effect by considering the competition between direct exchange between magnetic impurities and the Kondo screening mediated by the host electrons, and how this is affected by gating. These results suggest that both magnetic and nonmagnetic single-atom gating may be used to investigate magnetic impurity systems with tailored interactions, and may allow the control of entanglement of different spin states.
Single-molecule tracking in living cells using single quantum dot applications.
Baba, Koichi; Nishida, Kohji
2012-01-01
Revealing the behavior of single molecules in living cells is very useful for understanding cellular events. Quantum dot probes are particularly promising tools for revealing how biological events occur at the single molecule level both in vitro and in vivo. In this review, we will introduce how single quantum dot applications are used for single molecule tracking. We will discuss how single quantum dot tracking has been used in several examples of complex biological processes, including membrane dynamics, neuronal function, selective transport mechanisms of the nuclear pore complex, and in vivo real-time observation. We also briefly discuss the prospects for single molecule tracking using advanced probes.
Photon Cascade from a Single Crystal Phase Nanowire Quantum Dot
DEFF Research Database (Denmark)
Bouwes Bavinck, Maaike; Jöns, Klaus D; Zieliński, Michal
2016-01-01
We report the first comprehensive experimental and theoretical study of the optical properties of single crystal phase quantum dots in InP nanowires. Crystal phase quantum dots are defined by a transition in the crystallographic lattice between zinc blende and wurtzite segments and therefore offe...
Single-photon superradiance from a quantum dot
DEFF Research Database (Denmark)
Tighineanu, Petru; Daveau, Raphaël Sura; Lehmann, Tau Bernstorff
2016-01-01
We report on the observation of single-photon superradiance from an exciton in a semiconductor quantum dot. The confinement by the quantum dot is strong enough for it to mimic a two-level atom, yet sufficiently weak to ensure superradiance. The electrostatic interaction between the electron and t...
High-resolution photoluminescence studies of single semiconductor quantum dots
DEFF Research Database (Denmark)
Leosson, Kristjan; Østergaard, John Erland; Jensen, Jacob Riis
2000-01-01
developed in the study of single quantum dots, characterized by sharp atomic-like transition lines revealing their zero-dimensional density of states. Substantial information about the fundamental properties of individual quantum dots, as well as their interactions with other dots and the host lattice, can...
Quantum cloning attacks against PUF-based quantum authentication systems
Yao, Yao; Gao, Ming; Li, Mo; Zhang, Jian
2016-08-01
With the advent of physical unclonable functions (PUFs), PUF-based quantum authentication systems have been proposed for security purposes, and recently, proof-of-principle experiment has been demonstrated. As a further step toward completing the security analysis, we investigate quantum cloning attacks against PUF-based quantum authentication systems and prove that quantum cloning attacks outperform the so-called challenge-estimation attacks. We present the analytical expression of the false-accept probability by use of the corresponding optimal quantum cloning machines and extend the previous results in the literature. In light of these findings, an explicit comparison is made between PUF-based quantum authentication systems and quantum key distribution protocols in the context of cloning attacks. Moreover, from an experimental perspective, a trade-off between the average photon number and the detection efficiency is discussed in detail.
Magnetic resonance spectroscopy of single centers in silicon quantum wells
Energy Technology Data Exchange (ETDEWEB)
Bagraev, Nikolay T., E-mail: impurity.dipole@mail.ioffe.r [Ioffe Physical-Technical Institute, 194021 St. Petersburg (Russian Federation); Klyachkin, Leonid E.; Kudryavtsev, Andrey A.; Malyarenko, Anna M. [Ioffe Physical-Technical Institute, 194021 St. Petersburg (Russian Federation)
2009-12-15
We present the new optically detected magnetic resonance (ODMR) technique which reveals single point defects in silicon quantum wells embedded in microcavities within frameworks of the excitonic normal-mode coupling (NMC) without the external cavity and the hf source.
Optical Studies of Single Quantum Dots
National Research Council Canada - National Science Library
Gammon, Daniel; Steel, Duncan G
2002-01-01
...: the atomlike entities known as quantum dots (QDs). Measuring 1-100 nm across, QDs are semiconductor structures in which the electron wavefunction is confined in all three dimensions by the potential energy barriers that form the QD's boundaries...
Quantum ion-acoustic oscillations in single-walled carbon nanotubes
Energy Technology Data Exchange (ETDEWEB)
Khan, S.A. [Kyoto Univ., Katsura (Japan). Graduate School of Engineering; Quaid-i-Azam Univ., Islamabad (Pakistan). National Centre for Physics; Iqbal, Z. [University of Management and Technology, Sialkot (Pakistan); Wazir, Z. [Riphah International Univ., Islamabad (Pakistan). Dept. of Basic Sciences; Rehman, Aman ur [Pakistan Institute of Engineering and Applied Sciences (PIEAS), Islamabad (Pakistan)
2016-08-01
Quantum ion-acoustic oscillations in single-walled carbon nanotubes are studied by employing a quantum hydrodynamics model. The dispersion equation is obtained by Fourier transformation, which exhibits the existence of quantum ion-acoustic wave affected by change of density balance due to presence of positive or negative heavy species as stationary ion clusters and wave potential at equilibrium. The numerical results are presented, and the role of quantum degeneracy, nanotube geometry, electron exchange-correlation effects, and concentration and polarity of heavy species on wave dispersion is pointed out for typical systems of interest.
Quantum Ion-Acoustic Oscillations in Single-Walled Carbon Nanotubes
Khan, S. A.; Iqbal, Z.; Wazir, Z.; Aman-ur-Rehman
2016-05-01
Quantum ion-acoustic oscillations in single-walled carbon nanotubes are studied by employing a quantum hydrodynamics model. The dispersion equation is obtained by Fourier transformation, which exhibits the existence of quantum ion-acoustic wave affected by change of density balance due to presence of positive or negative heavy species as stationary ion clusters and wave potential at equilibrium. The numerical results are presented, and the role of quantum degeneracy, nanotube geometry, electron exchange-correlation effects, and concentration and polarity of heavy species on wave dispersion is pointed out for typical systems of interest.
Isar, A.
2004-09-01
A master equation for the deformed quantum harmonic oscillator interacting with a dissipative environment, in particular with a thermal bath, is obtained in the microscopic model, using perturbation theory. The coefficients of the master equation depend on the deformation function. The steady state solution of the equation for the density matrix in the number representation is derived and the equilibrium energy of the deformed harmonic oscillator is calculated in the approximation of small deformation. Note from Publisher: This article contains the abstract and references only.
Operating single quantum emitters with a compact Stirling cryocooler.
Schlehahn, A; Krüger, L; Gschrey, M; Schulze, J-H; Rodt, S; Strittmatter, A; Heindel, T; Reitzenstein, S
2015-01-01
The development of an easy-to-operate light source emitting single photons has become a major driving force in the emerging field of quantum information technology. Here, we report on the application of a compact and user-friendly Stirling cryocooler in the field of nanophotonics. The Stirling cryocooler is used to operate a single quantum emitter constituted of a semiconductor quantum dot (QD) at a base temperature below 30 K. Proper vibration decoupling of the cryocooler and its surrounding enables free-space micro-photoluminescence spectroscopy to identify and analyze different charge-carrier states within a single quantum dot. As an exemplary application in quantum optics, we perform a Hanbury-Brown and Twiss experiment demonstrating a strong suppression of multi-photon emission events with g((2))(0) Stirling-cooled single quantum emitter under continuous wave excitation. Comparative experiments performed on the same quantum dot in a liquid helium (LHe)-flow cryostat show almost identical values of g((2))(0) for both configurations at a given temperature. The results of this proof of principle experiment demonstrate that low-vibration Stirling cryocoolers that have so far been considered exotic to the field of nanophotonics are an attractive alternative to expensive closed-cycle cryostats or LHe-flow cryostats, which could pave the way for the development of high-quality table-top non-classical light sources.
Speed limits for quantum gates in multiqubit systems
Ashhab, S.; De Groot, P.C.; Nori, F.
2012-01-01
We use analytical and numerical calculations to obtain speed limits for various unitary quantum operations in multiqubit systems under typical experimental conditions. The operations that we consider include single-, two-, and three-qubit gates, as well as quantum-state transfer in a chain of
Realization of quantum state privacy amplification in a nuclear magnetic resonance quantum system
International Nuclear Information System (INIS)
Hao, Liang; Wang, Chuan; Long, Gui Lu
2010-01-01
Quantum state privacy amplification (QSPA) is the quantum analogue of classical privacy amplification. If the state information of a series of single-particle states has some leakage, QSPA reduces this leakage by condensing the state information of two particles into the state of one particle. Recursive applications of the operations will eliminate the quantum state information leakage to a required minimum level. In this paper, we report the experimental implementation of a quantum state privacy amplification protocol in a nuclear magnetic resonance system. The density matrices of the states are constructed in the experiment, and the experimental results agree well with theory.
Storage of multiple single-photon pulses emitted from a quantum dot in a solid-state quantum memory.
Tang, Jian-Shun; Zhou, Zong-Quan; Wang, Yi-Tao; Li, Yu-Long; Liu, Xiao; Hua, Yi-Lin; Zou, Yang; Wang, Shuang; He, De-Yong; Chen, Geng; Sun, Yong-Nan; Yu, Ying; Li, Mi-Feng; Zha, Guo-Wei; Ni, Hai-Qiao; Niu, Zhi-Chuan; Li, Chuan-Feng; Guo, Guang-Can
2015-10-15
Quantum repeaters are critical components for distributing entanglement over long distances in presence of unavoidable optical losses during transmission. Stimulated by the Duan-Lukin-Cirac-Zoller protocol, many improved quantum repeater protocols based on quantum memories have been proposed, which commonly focus on the entanglement-distribution rate. Among these protocols, the elimination of multiple photons (or multiple photon-pairs) and the use of multimode quantum memory are demonstrated to have the ability to greatly improve the entanglement-distribution rate. Here, we demonstrate the storage of deterministic single photons emitted from a quantum dot in a polarization-maintaining solid-state quantum memory; in addition, multi-temporal-mode memory with 1, 20 and 100 narrow single-photon pulses is also demonstrated. Multi-photons are eliminated, and only one photon at most is contained in each pulse. Moreover, the solid-state properties of both sub-systems make this configuration more stable and easier to be scalable. Our work will be helpful in the construction of efficient quantum repeaters based on all-solid-state devices.
Storage of multiple single-photon pulses emitted from a quantum dot in a solid-state quantum memory
Tang, Jian-Shun; Zhou, Zong-Quan; Wang, Yi-Tao; Li, Yu-Long; Liu, Xiao; Hua, Yi-Lin; Zou, Yang; Wang, Shuang; He, De-Yong; Chen, Geng; Sun, Yong-Nan; Yu, Ying; Li, Mi-Feng; Zha, Guo-Wei; Ni, Hai-Qiao; Niu, Zhi-Chuan; Li, Chuan-Feng; Guo, Guang-Can
2015-01-01
Quantum repeaters are critical components for distributing entanglement over long distances in presence of unavoidable optical losses during transmission. Stimulated by the Duan–Lukin–Cirac–Zoller protocol, many improved quantum repeater protocols based on quantum memories have been proposed, which commonly focus on the entanglement-distribution rate. Among these protocols, the elimination of multiple photons (or multiple photon-pairs) and the use of multimode quantum memory are demonstrated to have the ability to greatly improve the entanglement-distribution rate. Here, we demonstrate the storage of deterministic single photons emitted from a quantum dot in a polarization-maintaining solid-state quantum memory; in addition, multi-temporal-mode memory with 1, 20 and 100 narrow single-photon pulses is also demonstrated. Multi-photons are eliminated, and only one photon at most is contained in each pulse. Moreover, the solid-state properties of both sub-systems make this configuration more stable and easier to be scalable. Our work will be helpful in the construction of efficient quantum repeaters based on all-solid-state devices. PMID:26468996
Dynamics of complex quantum systems
Akulin, Vladimir M
2014-01-01
This book gathers together a range of similar problems that can be encountered in different fields of modern quantum physics and that have common features with regard to multilevel quantum systems. The main motivation was to examine from a uniform standpoint various models and approaches that have been developed in atomic, molecular, condensed matter, chemical, laser and nuclear physics in various contexts. The book should help senior-level undergraduate, graduate students and researchers putting particular problems in these fields into a broader scientific context and thereby taking advantage of well-established techniques used in adjacent fields. This second edition has been expanded to include substantial new material (e.g. new sections on Dynamic Localization and on Euclidean Random Matrices and new chapters on Entanglement, Open Quantum Systems, and Coherence Protection). It is based on the author’s lectures at the Moscow Institute of Physics and Technology, at the CNRS Aimé Cotton Laboratory, and on ...
Linear optical quantum computing in a single spatial mode.
Humphreys, Peter C; Metcalf, Benjamin J; Spring, Justin B; Moore, Merritt; Jin, Xian-Min; Barbieri, Marco; Kolthammer, W Steven; Walmsley, Ian A
2013-10-11
We present a scheme for linear optical quantum computing using time-bin-encoded qubits in a single spatial mode. We show methods for single-qubit operations and heralded controlled-phase (cphase) gates, providing a sufficient set of operations for universal quantum computing with the Knill-Laflamme-Milburn [Nature (London) 409, 46 (2001)] scheme. Our protocol is suited to currently available photonic devices and ideally allows arbitrary numbers of qubits to be encoded in the same spatial mode, demonstrating the potential for time-frequency modes to dramatically increase the quantum information capacity of fixed spatial resources. As a test of our scheme, we demonstrate the first entirely single spatial mode implementation of a two-qubit quantum gate and show its operation with an average fidelity of 0.84±0.07.
Quantum Privacy Amplification for a Sequence of Single Qubits
International Nuclear Information System (INIS)
Deng Fuguo; Long Guilu
2006-01-01
We present a scheme for quantum privacy amplification (QPA) for a sequence of single qubits. The QPA procedure uses a unitary operation with two controlled-not gates and a Hadamard gate. Every two qubits are performed with the unitary gate operation, and a measurement is made on one photon and the other one is retained. The retained qubit carries the state information of the discarded one. In this way, the information leakage is reduced. The procedure can be performed repeatedly so that the information leakage is reduced to any arbitrarily low level. With this QPA scheme, the quantum secure direct communication with single qubits can be implemented with arbitrarily high security. We also exploit this scheme to do privacy amplification on the single qubits in quantum information sharing for long-distance communication with quantum repeaters.
On quantum mechanics for macroscopic systems
International Nuclear Information System (INIS)
Primas, H.
1992-01-01
The parable of Schroedinger's cat may lead to several up-to date questions: how to treat open systems in quantum theory, how to treat thermodynamically irreversible processes in the quantum mechanics framework, how to explain, following the quantum theory, the existence, phenomenologically evident, of classical observables, what implies the predicted existence by the quantum theory of non localized macroscopic material object ?
Exceptional points in open quantum systems
International Nuclear Information System (INIS)
Mueller, Markus; Rotter, Ingrid
2008-01-01
Open quantum systems are embedded in the continuum of scattering wavefunctions and are naturally described by non-Hermitian Hamilton operators. In the complex energy plane, exceptional points appear at which two (or more) eigenvalues of the Hamilton operator coalesce. Although they are a countable set of single points in the complex energy plane and therefore of measure zero, they determine decisively the dynamics of open quantum systems. A powerful method for the description of open quantum systems is the Feshbach projection operator formalism. It is used in the present paper as a basic tool for the study of exceptional points and of the role they play for the dynamics of open quantum systems. Among others, the topological structure of the exceptional points, the rigidity of the phases of the eigenfunctions in their vicinity, the enhancement of observable values due to the reduced phase rigidity and the appearance of phase transitions are considered. The results are compared with existing experimental data on microwave cavities. In the last section, some questions being still unsolved, are considered
Tuning Single Quantum Dot Emission with a Micromirror.
Yuan, Gangcheng; Gómez, Daniel; Kirkwood, Nicholas; Mulvaney, Paul
2018-02-14
The photoluminescence of single quantum dots fluctuates between bright (on) and dark (off) states, also termed fluorescence intermittency or blinking. This blinking limits the performance of quantum dot-based devices such as light-emitting diodes and solar cells. However, the origins of the blinking remain unresolved. Here, we use a movable gold micromirror to determine both the quantum yield of the bright state and the orientation of the excited state dipole of single quantum dots. We observe that the quantum yield of the bright state is close to unity for these single QDs. Furthermore, we also study the effect of a micromirror on blinking, and then evaluate excitation efficiency, biexciton quantum yield, and detection efficiency. The mirror does not modify the off-time statistics, but it does change the density of optical states available to the quantum dot and hence the on times. The duration of the on times can be lengthened due to an increase in the radiative recombination rate.
Quantum communications system with integrated photonic devices
Energy Technology Data Exchange (ETDEWEB)
Nordholt, Jane E.; Peterson, Charles Glen; Newell, Raymond Thorson; Hughes, Richard John
2017-11-14
Security is increased in quantum communication (QC) systems lacking a true single-photon laser source by encoding a transmitted optical signal with two or more decoy-states. A variable attenuator or amplitude modulator randomly imposes average photon values onto the optical signal based on data input and the predetermined decoy-states. By measuring and comparing photon distributions for a received QC signal, a single-photon transmittance is estimated. Fiber birefringence is compensated by applying polarization modulation. A transmitter can be configured to transmit in conjugate polarization bases whose states of polarization (SOPs) can be represented as equidistant points on a great circle on the Poincare sphere so that the received SOPs are mapped to equidistant points on a great circle and routed to corresponding detectors. Transmitters are implemented in quantum communication cards and can be assembled from micro-optical components, or transmitter components can be fabricated as part of a monolithic or hybrid chip-scale circuit.
Negele, John W
1988-01-01
This book explains the fundamental concepts and theoretical techniques used to understand the properties of quantum systems having large numbers of degrees of freedom. A number of complimentary approaches are developed, including perturbation theory; nonperturbative approximations based on functional integrals; general arguments based on order parameters, symmetry, and Fermi liquid theory; and stochastic methods.
Quantum Transport in Mesoscopic Systems
Indian Academy of Sciences (India)
Home; Journals; Resonance – Journal of Science Education; Volume 15; Issue 11. Quantum Transport in Mesoscopic Systems - Coulomb Blockade and Kondo Effect ... Author Affiliations. Navinder Singh1. Room No 457 Theoretical Physics Division Physical Research Laboratory Navrangpura Ahmedabad 380 009 ...
Quantum Indeterminacy of Cosmic Systems
Energy Technology Data Exchange (ETDEWEB)
Hogan, Craig J. [Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
2013-12-30
It is shown that quantum uncertainty of motion in systems controlled mainly by gravity generally grows with orbital timescale $H^{-1}$, and dominates classical motion for trajectories separated by distances less than $\\approx H^{-3/5}$ in Planck units. For example, the cosmological metric today becomes indeterminate at macroscopic separations, $H_0^{-3/5}\\approx 60$ meters. Estimates suggest that entangled non-localized quantum states of geometry and matter may significantly affect fluctuations during inflation, and connect the scale of dark energy to that of strong interactions.
Unstable Systems and Quantum Zeno Phenomena in Quantum Field Theory
Facchi, P.; Pascazio, S.
2003-02-01
We analyze the Zeno phenomenon in quantum field theory. The decay of an unstable system can be modified by changing the time interval between successive measurements (or by varying the coupling to an external system that plays the role of measuring apparatus). We speak of quantum Zeno effect if the decay is slowed and of inverse quantum Zeno (or Heraclitus) effect if it is accelerated. The analysis of the transition between these two regimes requires close scrutiny of the features of the interaction Hamiltonian. We look in detail at quantum field theoretical models of the Lee type.
Quantum interference of electrically generated single photons from a quantum dot
International Nuclear Information System (INIS)
Patel, Raj B; Bennett, Anthony J; Shields, Andrew J; Cooper, Ken; Atkinson, Paola; Nicoll, Christine A; Ritchie, David A
2010-01-01
Quantum interference lies at the foundation of many protocols for scalable quantum computing and communication with linear optics. To observe these effects the light source must emit photons that are indistinguishable. From a technological standpoint, it would be beneficial to have electrical control over the emission. Here we report of an electrically driven single-photon source emitting indistinguishable photons. The device consists of a layer of InAs quantum dots embedded in the intrinsic region of a p-i-n diode. Indistinguishability of consecutive photons is tested in a two-photon interference experiment under two modes of operation, continuous and pulsed current injection. We also present a complete theory based on the interference of photons with a Lorentzian spectrum which we compare to both our continuous wave and pulsed experiments. In the former case, a visibility was measured limited only by the timing resolution of our detection system. In the case of pulsed injection, we employ a two-pulse voltage sequence which suppresses multi-photon emission and allows us to carry out temporal filtering of photons which have undergone dephasing. The characteristic Hong-Ou-Mandel 'dip' is measured, resulting in a visibility of 64 ± 4%.
Tahan, Charles; Friesen, Mark; Joynt, Robert; Eriksson, M. A.
2003-03-01
Although electron spin qubits in semiconductors are attractive from the viewpoint of low environmental coupling and long coherence times, spin readout remains a challenge for quantum dot quantum computing. Unfortunately, promising schemes based on spin-charge transduction introduce external couplings in the form of reference qubits or Coulomb blockade leads. Here, we propose a twist on the spin-charge transduction scheme, converting spin information to orbital information within a single quantum dot (QD). The same QD can be used for initialization, gating, and readout, without unnecessary external couplings. We present detailed investigations into such a scheme in both SiGe and GaAs systems: simulations, including capacitive coupling to a RF-SET, calculations of coherent oscillation times which determine the read-out speed, and calculations of electron spin relaxation times which determine the initialization speed. We find that both initialization and readout can be performed within the same architecture. Work supported by NSF-QuBIC and MRSEC programs, ARDA, and NSA.
QUANTUM AND CLASSICAL CORRELATIONS IN GAUSSIAN OPEN QUANTUM SYSTEMS
Directory of Open Access Journals (Sweden)
Aurelian ISAR
2015-01-01
Full Text Available In the framework of the theory of open systems based on completely positive quantum dynamical semigroups, we give a description of the continuous-variable quantum correlations (quantum entanglement and quantum discord for a system consisting of two noninteracting bosonic modes embedded in a thermal environment. We solve the Kossakowski-Lindblad master equation for the time evolution of the considered system and describe the entanglement and discord in terms of the covariance matrix for Gaussian input states. For all values of the temperature of the thermal reservoir, an initial separable Gaussian state remains separable for all times. We study the time evolution of logarithmic negativity, which characterizes the degree of entanglement, and show that in the case of an entangled initial squeezed thermal state, entanglement suppression takes place for all temperatures of the environment, including zero temperature. We analyze the time evolution of the Gaussian quantum discord, which is a measure of all quantum correlations in the bipartite state, including entanglement, and show that it decays asymptotically in time under the effect of the thermal bath. This is in contrast with the sudden death of entanglement. Before the suppression of the entanglement, the qualitative evolution of quantum discord is very similar to that of the entanglement. We describe also the time evolution of the degree of classical correlations and of quantum mutual information, which measures the total correlations of the quantum system.
Room temperature excitation spectroscopy of single quantum dots
Directory of Open Access Journals (Sweden)
Christian Blum
2011-08-01
Full Text Available We report a single molecule detection scheme to investigate excitation spectra of single emitters at room temperature. We demonstrate the potential of single emitter photoluminescence excitation spectroscopy by recording excitation spectra of single CdSe nanocrystals over a wide spectral range of 100 nm. The spectra exhibit emission intermittency, characteristic of single emitters. We observe large variations in the spectra close to the band edge, which represent the individual heterogeneity of the observed quantum dots. We also find specific excitation wavelengths for which the single quantum dots analyzed show an increased propensity for a transition to a long-lived dark state. We expect that the additional capability of recording excitation spectra at room temperature from single emitters will enable insights into the photophysics of emitters that so far have remained inaccessible.
Gong, Li-Hua; He, Xiang-Tao; Tan, Ru-Chao; Zhou, Zhi-Hong
2018-01-01
In order to obtain high-quality color images, it is important to keep the hue component unchanged while emphasize the intensity or saturation component. As a public color model, Hue-Saturation Intensity (HSI) model is commonly used in image processing. A new single channel quantum color image encryption algorithm based on HSI model and quantum Fourier transform (QFT) is investigated, where the color components of the original color image are converted to HSI and the logistic map is employed to diffuse the relationship of pixels in color components. Subsequently, quantum Fourier transform is exploited to fulfill the encryption. The cipher-text is a combination of a gray image and a phase matrix. Simulations and theoretical analyses demonstrate that the proposed single channel quantum color image encryption scheme based on the HSI model and quantum Fourier transform is secure and effective.
Near-field strong coupling of single quantum dots.
Groß, Heiko; Hamm, Joachim M; Tufarelli, Tommaso; Hess, Ortwin; Hecht, Bert
2018-03-01
Strong coupling and the resultant mixing of light and matter states is an important asset for future quantum technologies. We demonstrate deterministic room temperature strong coupling of a mesoscopic colloidal quantum dot to a plasmonic nanoresonator at the apex of a scanning probe. Enormous Rabi splittings of up to 110 meV are accomplished by nanometer-precise positioning of the quantum dot with respect to the nanoresonator probe. We find that, in addition to a small mode volume of the nanoresonator, collective coherent coupling of quantum dot band-edge states and near-field proximity interaction are vital ingredients for the realization of near-field strong coupling of mesoscopic quantum dots. The broadband nature of the interaction paves the road toward ultrafast coherent manipulation of the coupled quantum dot-plasmon system under ambient conditions.
Semi-quantum Dialogue Based on Single Photons
Ye, Tian-Yu; Ye, Chong-Qiang
2018-02-01
In this paper, we propose two semi-quantum dialogue (SQD) protocols by using single photons as the quantum carriers, where one requires the classical party to possess the measurement capability and the other does not have this requirement. The security toward active attacks from an outside Eve in the first SQD protocol is guaranteed by the complete robustness of present semi-quantum key distribution (SQKD) protocols, the classical one-time pad encryption, the classical party's randomization operation and the decoy photon technology. The information leakage problem of the first SQD protocol is overcome by the classical party' classical basis measurements on the single photons carrying messages which makes him share their initial states with the quantum party. The security toward active attacks from Eve in the second SQD protocol is guaranteed by the classical party's randomization operation, the complete robustness of present SQKD protocol and the classical one-time pad encryption. The information leakage problem of the second SQD protocol is overcome by the quantum party' classical basis measurements on each two adjacent single photons carrying messages which makes her share their initial states with the classical party. Compared with the traditional information leakage resistant QD protocols, the advantage of the proposed SQD protocols lies in that they only require one party to have quantum capabilities. Compared with the existing SQD protocol, the advantage of the proposed SQD protocols lies in that they only employ single photons rather than two-photon entangled states as the quantum carriers. The proposed SQD protocols can be implemented with present quantum technologies.
High-Dimensional Single-Photon Quantum Gates: Concepts and Experiments
Babazadeh, Amin; Erhard, Manuel; Wang, Feiran; Malik, Mehul; Nouroozi, Rahman; Krenn, Mario; Zeilinger, Anton
2017-11-01
Transformations on quantum states form a basic building block of every quantum information system. From photonic polarization to two-level atoms, complete sets of quantum gates for a variety of qubit systems are well known. For multilevel quantum systems beyond qubits, the situation is more challenging. The orbital angular momentum modes of photons comprise one such high-dimensional system for which generation and measurement techniques are well studied. However, arbitrary transformations for such quantum states are not known. Here we experimentally demonstrate a four-dimensional generalization of the Pauli X gate and all of its integer powers on single photons carrying orbital angular momentum. Together with the well-known Z gate, this forms the first complete set of high-dimensional quantum gates implemented experimentally. The concept of the X gate is based on independent access to quantum states with different parities and can thus be generalized to other photonic degrees of freedom and potentially also to other quantum systems.
High-Dimensional Single-Photon Quantum Gates: Concepts and Experiments.
Babazadeh, Amin; Erhard, Manuel; Wang, Feiran; Malik, Mehul; Nouroozi, Rahman; Krenn, Mario; Zeilinger, Anton
2017-11-03
Transformations on quantum states form a basic building block of every quantum information system. From photonic polarization to two-level atoms, complete sets of quantum gates for a variety of qubit systems are well known. For multilevel quantum systems beyond qubits, the situation is more challenging. The orbital angular momentum modes of photons comprise one such high-dimensional system for which generation and measurement techniques are well studied. However, arbitrary transformations for such quantum states are not known. Here we experimentally demonstrate a four-dimensional generalization of the Pauli X gate and all of its integer powers on single photons carrying orbital angular momentum. Together with the well-known Z gate, this forms the first complete set of high-dimensional quantum gates implemented experimentally. The concept of the X gate is based on independent access to quantum states with different parities and can thus be generalized to other photonic degrees of freedom and potentially also to other quantum systems.
Quantum Computing in Solid State Systems
Ruggiero, B; Granata, C
2006-01-01
The aim of Quantum Computation in Solid State Systems is to report on recent theoretical and experimental results on the macroscopic quantum coherence of mesoscopic systems, as well as on solid state realization of qubits and quantum gates. Particular attention has been given to coherence effects in Josephson devices. Other solid state systems, including quantum dots, optical, ion, and spin devices which exhibit macroscopic quantum coherence are also discussed. Quantum Computation in Solid State Systems discusses experimental implementation of quantum computing and information processing devices, and in particular observations of quantum behavior in several solid state systems. On the theoretical side, the complementary expertise of the contributors provides models of the various structures in connection with the problem of minimizing decoherence.
No-go theorem for passive single-rail linear optical quantum computing.
Wu, Lian-Ao; Walther, Philip; Lidar, Daniel A
2013-01-01
Photonic quantum systems are among the most promising architectures for quantum computers. It is well known that for dual-rail photons effective non-linearities and near-deterministic non-trivial two-qubit gates can be achieved via the measurement process and by introducing ancillary photons. While in principle this opens a legitimate path to scalable linear optical quantum computing, the technical requirements are still very challenging and thus other optical encodings are being actively investigated. One of the alternatives is to use single-rail encoded photons, where entangled states can be deterministically generated. Here we prove that even for such systems universal optical quantum computing using only passive optical elements such as beam splitters and phase shifters is not possible. This no-go theorem proves that photon bunching cannot be passively suppressed even when extra ancilla modes and arbitrary number of photons are used. Our result provides useful guidance for the design of optical quantum computers.
Quantum systems, channels, information. A mathematical introduction
Energy Technology Data Exchange (ETDEWEB)
Holevo, Alexander S.
2012-07-01
The subject of this book is theory of quantum system presented from information science perspective. The central role is played by the concept of quantum channel and its entropic and information characteristics. Quantum information theory gives a key to understanding elusive phenomena of quantum world and provides a background for development of experimental techniques that enable measuring and manipulation of individual quantum systems. This is important for the new efficient applications such as quantum computing, communication and cryptography. Research in the field of quantum informatics, including quantum information theory, is in progress in leading scientific centers throughout the world. This book gives an accessible, albeit mathematically rigorous and self-contained introduction to quantum information theory, starting from primary structures and leading to fundamental results and to exiting open problems.
Perturbative approach to Markovian open quantum systems.
Li, Andy C Y; Petruccione, F; Koch, Jens
2014-05-08
The exact treatment of Markovian open quantum systems, when based on numerical diagonalization of the Liouville super-operator or averaging over quantum trajectories, is severely limited by Hilbert space size. Perturbation theory, standard in the investigation of closed quantum systems, has remained much less developed for open quantum systems where a direct application to the Lindblad master equation is desirable. We present such a perturbative treatment which will be useful for an analytical understanding of open quantum systems and for numerical calculation of system observables which would otherwise be impractical.
Relativistic Quantum Transport in Graphene Systems
2015-07-09
Enhancement of quantum entanglement by nonlinear dynamics in optomechanical systems...Nonlinear dynamics and quantum entanglement in optomechanical systems,” Physical Review Letters 112, 110406, 1-6 (2014). 12. L. Ying, Y.-C. Lai, and...interact with the potential barrier, however, can lead to relatively strong tunneling. In a small energy interval the quantum tunneling rate can thus
Logical entropy of quantum dynamical systems
Directory of Open Access Journals (Sweden)
Ebrahimzadeh Abolfazl
2016-01-01
Full Text Available This paper introduces the concepts of logical entropy and conditional logical entropy of hnite partitions on a quantum logic. Some of their ergodic properties are presented. Also logical entropy of a quantum dynamical system is dehned and ergodic properties of dynamical systems on a quantum logic are investigated. Finally, the version of Kolmogorov-Sinai theorem is proved.
Cui, Ping
-electrode coupling is further proposed to recover all existing nonlinear current-voltage behaviors including the nonequilibrium Kondo effect. Transport theory based on the exact QDT formalism will be developed in future. In Chapter 8, we study the quantum measurement of a qubit with a quantum-point-contact detector. On the basis of a unified quantum master equation (a form of QDT), we study the measurement-induced relaxation and dephasing of the qubit. Our treatment pays particular attention on the detailed-balance relation, which is a consequence of properly accounting for the energy exchange between the qubit and detector during the measurement process. We also derive a conditional quantum master equation for quantum measurement in general, and study the readout characteristics of the qubit measurement. Our theory is applicable to the quantum measurement at arbitrary voltage and temperature. A number of remarkable new features are found and highlighted in concern with their possible relevance to future experiments. In Chapter 9, we discuss the further development of QDT, aiming at an efficient evaluation of many-electron systems. This will be carried out by reducing the many-particle (Fermion or Boson) QDT to a single-particle one by exploring, e.g. the Wick's contraction theorem. It also results in a time-dependent density functional theory (TDDFT) for transport through complex large-scale (e.g. molecules) systems. Primary results of the TDDFT-QDT are reported. In Chapter 10, we summary the thesis, and comment and remark on the future work on both the theoretical and application aspects of QDT.
Eigenfunctions in chaotic quantum systems
International Nuclear Information System (INIS)
Baecker, Arnd
2007-01-01
The structure of wavefunctions of quantum systems strongly depends on the underlying classical dynamics. In this text a selection of articles on eigenfunctions in systems with fully chaotic dynamics and systems with a mixed phase space is summarized. Of particular interest are statistical properties like amplitude distribution and spatial autocorrelation function and the implication of eigenfunction structures on transport properties. For systems with a mixed phase space the separation into regular and chaotic states does not always hold away from the semiclassical limit, such that chaotic states may completely penetrate into the region of the regular island. The consequences of this flooding are discussed and universal aspects highlighted. (orig.)
Eigenfunctions in chaotic quantum systems
Energy Technology Data Exchange (ETDEWEB)
Baecker, Arnd
2007-07-01
The structure of wavefunctions of quantum systems strongly depends on the underlying classical dynamics. In this text a selection of articles on eigenfunctions in systems with fully chaotic dynamics and systems with a mixed phase space is summarized. Of particular interest are statistical properties like amplitude distribution and spatial autocorrelation function and the implication of eigenfunction structures on transport properties. For systems with a mixed phase space the separation into regular and chaotic states does not always hold away from the semiclassical limit, such that chaotic states may completely penetrate into the region of the regular island. The consequences of this flooding are discussed and universal aspects highlighted. (orig.)
Past Quantum States of a Monitored System
DEFF Research Database (Denmark)
Gammelmark, Søren; Julsgaard, Brian; Mølmer, Klaus
2013-01-01
. On the one hand, our formalism shows how smoothing procedures for estimation of past classical signals by a quantum probe [M. Tsang, Phys. Rev. Lett. 102 250403 (2009)] apply also to describe the past state of the quantum system itself. On the other hand, it generalizes theories of pre- and postselected...... quantum states [Y. Aharonov and L. Vaidman, J. Phys. A 24 2315 (1991)] to systems subject to any quantum measurement scenario, any coherent evolution, and any Markovian dissipation processes....
Including Memory Friction in Single- and Two-State Quantum Dynamics Simulations.
Brown, Paul A; Messina, Michael
2016-03-03
We present a simple computational algorithm that allows for the inclusion of memory friction in a quantum dynamics simulation of a small, quantum, primary system coupled to many atoms in the surroundings. We show how including a memory friction operator, F̂, in the primary quantum system's Hamiltonian operator builds memory friction into the dynamics of the primary quantum system. We show that, in the harmonic, semi-classical limit, this friction operator causes the classical phase-space centers of a wavepacket to evolve exactly as if it were a classical particle experiencing memory friction. We also show that this friction operator can be used to include memory friction in the quantum dynamics of an anharmonic primary system. We then generalize the algorithm so that it can be used to treat a primary quantum system that is evolving, non-adiabatically on two coupled potential energy surfaces, i.e., a model that can be used to model H atom transfer, for example. We demonstrate this approach's computational ease and flexibility by showing numerical results for both harmonic and anharmonic primary quantum systems in the single surface case. Finally, we present numerical results for a model of non-adiabatic H atom transfer between a reactant and product state that includes memory friction on one or both of the non-adiabatic potential energy surfaces and uncover some interesting dynamical effects of non-memory friction on the H atom transfer process.
Quantum measurements between a single spin and a torsional nanomechanical resonator
D'Urso, B.; Gurudev Dutt, M. V.; Dhingra, S.; Nusran, N. M.
2011-04-01
While the motions of macroscopic objects must ultimately be governed by quantum mechanics, the distinctive features of quantum mechanics can be hidden or washed out by thermal excitations and coupling to the environment. We propose a system consisting of a graphene nanomechanical oscillator (NMO) coupled with a single spin through a uniform external magnetic field, which could become the building block for a wide range of quantum nanomechanical devices. The choice of graphene as the NMO material is critical for minimizing the moment of inertia of the oscillator. The spin originates from a nitrogen-vacancy (NV) center in a diamond nanocrystal that is positioned on the NMO. This coupling results in quantum non-demolition (QND) measurements of the oscillator and spin states, enabling a bridge between the quantum and classical worlds for a simple readout of the NV center spin and observation of the discrete states of the NMO.
Strong coupling of a single photon to a superconducting qubit using circuit quantum electrodynamics.
Wallraff, A; Schuster, D I; Blais, A; Frunzio, L; Huang, R- S; Majer, J; Kumar, S; Girvin, S M; Schoelkopf, R J
2004-09-09
The interaction of matter and light is one of the fundamental processes occurring in nature, and its most elementary form is realized when a single atom interacts with a single photon. Reaching this regime has been a major focus of research in atomic physics and quantum optics for several decades and has generated the field of cavity quantum electrodynamics. Here we perform an experiment in which a superconducting two-level system, playing the role of an artificial atom, is coupled to an on-chip cavity consisting of a superconducting transmission line resonator. We show that the strong coupling regime can be attained in a solid-state system, and we experimentally observe the coherent interaction of a superconducting two-level system with a single microwave photon. The concept of circuit quantum electrodynamics opens many new possibilities for studying the strong interaction of light and matter. This system can also be exploited for quantum information processing and quantum communication and may lead to new approaches for single photon generation and detection.
Single-ion quantum lock-in amplifier.
Kotler, Shlomi; Akerman, Nitzan; Glickman, Yinnon; Keselman, Anna; Ozeri, Roee
2011-05-05
Quantum metrology uses tools from quantum information science to improve measurement signal-to-noise ratios. The challenge is to increase sensitivity while reducing susceptibility to noise, tasks that are often in conflict. Lock-in measurement is a detection scheme designed to overcome this difficulty by spectrally separating signal from noise. Here we report on the implementation of a quantum analogue to the classical lock-in amplifier. All the lock-in operations--modulation, detection and mixing--are performed through the application of non-commuting quantum operators to the electronic spin state of a single, trapped Sr(+) ion. We significantly increase its sensitivity to external fields while extending phase coherence by three orders of magnitude, to more than one second. Using this technique, we measure frequency shifts with a sensitivity of 0.42 Hz Hz(-1/2) (corresponding to a magnetic field measurement sensitivity of 15 pT Hz(-1/2)), obtaining an uncertainty of less than 10 mHz (350 fT) after 3,720 seconds of averaging. These sensitivities are limited by quantum projection noise and improve on other single-spin probe technologies by two orders of magnitude. Our reported sensitivity is sufficient for the measurement of parity non-conservation, as well as the detection of the magnetic field of a single electronic spin one micrometre from an ion detector with nanometre resolution. As a first application, we perform light shift spectroscopy of a narrow optical quadrupole transition. Finally, we emphasize that the quantum lock-in technique is generic and can potentially enhance the sensitivity of any quantum sensor. ©2011 Macmillan Publishers Limited. All rights reserved
Resonance fluorescence and quantum interference of a single NV center
Ma, Yong-Hong; Zhang, Xue-Feng; Wu, E.
2017-11-01
The detection of a single nitrogen-vacancy center in diamond has attracted much interest, since it is expected to lead to innovative applications in various domains of quantum information, including quantum metrology, information processing and communications, as well as in various nanotechnologies, such as biological and subdiffraction limit imaging, and tests of entanglement in quantum mechanics. We propose a novel scheme of a single NV center coupled with a multi-mode superconducting microwave cavity driven by coherent fields in squeezed vacuum. We numerically investigate the spectra in-phase quadrature and out-of-phase quadrature for different driving regimes with or without detunings. It shows that the maximum squeezing can be obtained for optimal Rabi fields. Moreover, with the same parameters, the maximum squeezing is greatly increased when the detunings are nonzero compared to the resonance case.
Quantum delayed-choice experiment with a single neutral atom.
Li, Gang; Zhang, Pengfei; Zhang, Tiancai
2017-10-01
We present a proposal to implement a quantum delayed-choice (QDC) experiment with a single neutral atom, such as a rubidium or cesium atom. In our proposal, a Ramsey interferometer is adopted to observe the wave-like or particle-like behaviors of a single atom depending on the existence or absence of the second π/2-rotation. A quantum-controlled π/2-rotation on target atom is realized through a Rydberg-Rydberg interaction by another ancilla atom. It shows that a heavy neutral atom can also have a morphing behavior between the particle and the wave. The realization of the QDC experiment with such heavy neutral atoms not only is significant to understand the Bohr's complementarity principle in matter-wave and matter-particle domains but also has great potential on the quantum information process with neutral atoms.
Spin quantum tunneling via entangled states in a dimer of exchange coupled single-molecule magnets
Tiron, R.; Wernsdorfer, W.; Aliaga-Alcalde, N.; Foguet-Albiol, D.; Christou, G.
2004-03-01
A new family of supramolecular, antiferromagnetically exchange-coupled dimers of single-molecule magnets (SMMs) has recently been reported [W. Wernsdorfer, N. Aliaga-Alcalde, D.N. Hendrickson, and G. Christou, Nature 416, 406 (2002)]. Each SMM acts as a bias on its neighbor, shifting the quantum tunneling resonances of the individual SMMs. Hysteresis loop measurements on a single crystal of SMM-dimers have now established quantum tunneling of the magnetization via entangled states of the dimer. This shows that the dimer really does behave as a quantum-mechanically coupled dimer. The transitions are well separated, suggesting long coherence times compared to the time scale of the energy splitting. This result is of great importance if such systems are to be used for quantum computing. It also allows the measurement of the longitudinal and transverse superexchange coupling constants [Phys. Rev. Lett. 91, 227203 (2003)].
Highly efficient photonic nanowire single-photon sources for quantum information applications
DEFF Research Database (Denmark)
Gregersen, Niels; Claudon, J.; Munsch, M.
2013-01-01
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......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...... emitter, e.g. a nitrogen-vacancy center or a semiconductor quantum dot (QD), embedded in a solid-state semiconductor host material appears as an attractive platform for generating such single photons. However, for a QD in bulk material, the large index contrast at the semiconductor-air interface leads...
Simultaneous SU(2) rotations on multiple quantum dot exciton qubits using a single shaped pulse
Mathew, Reuble; Yang, Hong Yi Shi; Hall, Kimberley C.
2015-10-01
Recent experimental demonstration of a parallel (π ,2 π ) single qubit rotation on excitons in two distant quantum dots [Nano Lett. 13, 4666 (2013), 10.1021/nl4018176] is extended in numerical simulations to the design of pulses for more general quantum state control, demonstrating the feasibility of full SU(2) rotations of each exciton qubit. Our results show that simultaneous high-fidelity quantum control is achievable within the experimentally accessible parameter space for commercial Fourier-domain pulse shaping systems. The identification of a threshold of distinguishability for the two quantum dots (QDs) for achieving high-fidelity parallel rotations, corresponding to a difference in transition energies of ˜0.25 meV , points to the possibility of controlling more than 10 QDs with a single shaped optical pulse.
Multi-Color Single Particle Tracking with Quantum Dots
DEFF Research Database (Denmark)
Christensen, Eva Arnspang; Brewer, J. R.; Lagerholm, B. C.
2012-01-01
Quantum dots (QDs) have long promised to revolutionize fluorescence detection to include even applications requiring simultaneous multi-species detection at single molecule sensitivity. Despite the early promise, the unique optical properties of QDs have not yet been fully exploited in e. g...
Rapid single flux quantum logic in high temperature superconductor technology
Shunmugavel, K.
2006-01-01
A Josephson junction is the basic element of rapid single flux quantum logic (RSFQ) circuits. A high operating speed and low power consumption are the main advantages of RSFQ logic over semiconductor electronic circuits. To realize complex RSFQ circuits in HTS technology one needs a reproducible
Observation of quantum state collapse and revival due to the single-photon Kerr effect.
Kirchmair, Gerhard; Vlastakis, Brian; Leghtas, Zaki; Nigg, Simon E; Paik, Hanhee; Ginossar, Eran; Mirrahimi, Mazyar; Frunzio, Luigi; Girvin, S M; Schoelkopf, R J
2013-03-14
To create and manipulate non-classical states of light for quantum information protocols, a strong, nonlinear interaction at the single-photon level is required. One approach to the generation of suitable interactions is to couple photons to atoms, as in the strong coupling regime of cavity quantum electrodynamic systems. In these systems, however, the quantum state of the light is only indirectly controlled by manipulating the atoms. A direct photon-photon interaction occurs in so-called Kerr media, which typically induce only weak nonlinearity at the cost of significant loss. So far, it has not been possible to reach the single-photon Kerr regime, in which the interaction strength between individual photons exceeds the loss rate. Here, using a three-dimensional circuit quantum electrodynamic architecture, we engineer an artificial Kerr medium that enters this regime and allows the observation of new quantum effects. We realize a gedanken experiment in which the collapse and revival of a coherent state can be observed. This time evolution is a consequence of the quantization of the light field in the cavity and the nonlinear interaction between individual photons. During the evolution, non-classical superpositions of coherent states (that is, multi-component 'Schrödinger cat' states) are formed. We visualize this evolution by measuring the Husimi Q function and confirm the non-classical properties of these transient states by cavity state tomography. The ability to create and manipulate superpositions of coherent states in such a high-quality-factor photon mode opens perspectives for combining the physics of continuous variables with superconducting circuits. The single-photon Kerr effect could be used in quantum non-demolition measurement of photons, single-photon generation, autonomous quantum feedback schemes and quantum logic operations.
Quantum sensors based on single diamond defects
International Nuclear Information System (INIS)
Jelezko Fedor
2014-01-01
NV centers in diamond are promising sensors able to detect electric and magnetic fields at nanoscale. Here we report on the detection of biomolecules using magnetic noise induced by their electron and nuclear spins. Presented results show first steps towards establishing novel sensing technology for visualizing single proteins and study of their dynamics. (author)
A Single Molecule Investigation of the Photostability of Quantum Dots
DEFF Research Database (Denmark)
Christensen, Eva Arnspang; Kulatunga, Pasad; Lagerholm, B. Christoffer
2012-01-01
Quantum dots (QDs) are very attractive probes for multi-color fluorescence applications. We report here however that single QDs that are subject to continuous blue excitation from a 100W mercury arc lamp will undergo a continuous blue-switching of the emission wavelength eventually reaching a per...... is especially detrimental for multi-color single molecule applications, as we regularly observe spectral blue-shifts of 50 nm, or more even after only ten seconds of illumination....
Energy Technology Data Exchange (ETDEWEB)
Castillo-Ojeda, R. [Universidad Politecnica de Pachuca, Km. 20, Rancho Luna, Ex-Hacienda de Santa Barbara, Municipio de Zempoala, Hidalgo 43830 (Mexico); Diaz-Reyes, J., E-mail: jdiazr2001@yahoo.co [Instituto Politecnico Nacional, Centro de Investigacion en Biotecnologia Aplicada, CIBA-IPN, Ex Hacienda de San Juan Molino, Km. 1.5. Tepetitla, Tlaxcala 90700 (Mexico); Galvan-Arellano, M.; Pena-Sierra, R. [CINVESTAV-IPN, Depto. de Ing. Electrica, SEES. Apdo. 14-740, Mexico, D.F. 07000 (Mexico)
2011-06-15
This work presents the results of the growth and characterization of Al{sub x}Ga{sub 1-x}As/GaAs multilayer structures obtained in a metallic-arsenic-based-MOCVD system. The main goal is to explore the ability of the growth system to grow high quality multilayer structures like quantum wells. The use of metallic arsenic could introduce important differences in the growth process due to the absence of the hydride group V precursor (AsH{sub 3}), which manifests in the electrical and optical characteristics of both GaAs and Al{sub x}Ga{sub 1-x}As layers. The characterization of these epilayers and structures was performed using low-temperature photoluminescence, Hall effect measurements, X-ray diffraction, Raman spectroscopy, secondary ion mass spectroscopy (SIMS) and Atomic Force Microscopy (AFM). - Research highlights: {yields} This work is reported the growth of AlxGa1-xAs/GaAs/AlxGa1-xAs heterostructures by a solid arsenic based MOCVD system. {yields} The results obtained with this system are comparable with those obtained with the traditional arsine based growth system. {yields} The main limitation of the alternative MOCVD system is related to the lack of monoatomic hydrogen on the growth surface that acts modifying the surface kinetics and enhancing the carbon incorporation. {yields} The experimental results indicate that it can be grown AlxGa1-xAs using elemental arsenic by MOCVD, which can be used to optoelectronic devices.
Readout of a single electron spin in a double quantum dot using a quantum point contact
International Nuclear Information System (INIS)
Zhang Jianping; Ouyang Shihua; You, J Q; Lam, C.-H.
2008-01-01
We study the dynamics of a single electron spin in a double quantum dot (DQD) and its readout via a quantum point contact (QPC). We model the system microscopically and derive rate equations for the reduced electron density matrix of the DQD. Two cases with one and two electrons in the DQD are studied. In the one-electron case, with different Zeeman splittings in the two dots, the electron spin states are distinctly characterized by a constant and an oscillatory current through the QPC. In the two-electron case, the readout of the spin state of the electron in one of the dots called the qubit dot is essentially similar after considering hyperfine interactions between the electrons and the nuclear spins of the host materials and a uniform magnetic field applied to the DQD. Moreover, to ensure that an electron is properly injected into the qubit dot, we propose to determine the success of the electron injection from the variations of the QPC current after applying an oscillating magnetic field to the qubit dot
Exciton dephasing in single InGaAs quantum dots
DEFF Research Database (Denmark)
Leosson, Kristjan; Østergaard, John Erland; Jensen, Jacob Riis
2000-01-01
The homogeneous linewidth of excitonic transitions is a parameter of fundamental physical importance. In self-assembled quantum dot systems, a strong inhomogeneous broadening due to dot size fluctuations masks the homogeneous linewidth associated with transitions between individual states....... The homogeneous and inhomogeneous broadening of InGaAs quantum dot luminescence is of central importance for the potential application of this material system in optoelectronic devices. Recent measurements of MOCVD-grown InAs/InGaAs quantum dots indicate a large homogeneous broadening at room temperature due...... to fast dephasing. We present an investigation of the low-temperature homogeneous linewidth of individual PL lines from MBE-grown In0.5Ga0.5As/GaAs quantum dots....
Vision for single flux quantum very large scale integrated technology
Silver, Arnold; Bunyk, Paul; Kleinsasser, Alan; Spargo, John
2006-05-01
Single flux quantum (SFQ) electronics is extremely fast and has very low on-chip power dissipation. SFQ VLSI is an excellent candidate for high-performance computing and other applications requiring extremely high-speed signal processing. Despite this, SFQ technology has generally not been accepted for system implementation. We argue that this is due, at least in part, to the use of outdated tools to produce SFQ circuits and chips. Assuming the use of tools equivalent to those employed in the semiconductor industry, we estimate the density of Josephson junctions, circuit speed, and power dissipation that could be achieved with SFQ technology. Today, CMOS lithography is at 90-65 nm with about 20 layers. Assuming equivalent technology, aggressively increasing the current density above 100 kA cm-2 to achieve junction speeds approximately 1000 GHz, and reducing device footprints by converting device profiles from planar to vertical, one could expect to integrate about 250 M Josephson junctions cm-2 into SFQ digital circuits. This should enable circuit operation with clock frequencies above 200 GHz and place approximately 20 K gates within a radius of one clock period. As a result, complete microprocessors, including integrated memory registers, could be fabricated on a single chip. This technology was exported from the United States in accordance with the US Department of Commerce Export Administration Regulations (EAR) for ultimate destination in the United Kingdom. Diversion contrary to US law prohibited.
Vision for single flux quantum very large scale integrated technology
International Nuclear Information System (INIS)
Silver, Arnold; Bunyk, Paul; Kleinsasser, Alan; Spargo, John
2006-01-01
Single flux quantum (SFQ) electronics is extremely fast and has very low on-chip power dissipation. SFQ VLSI is an excellent candidate for high-performance computing and other applications requiring extremely high-speed signal processing. Despite this, SFQ technology has generally not been accepted for system implementation. We argue that this is due, at least in part, to the use of outdated tools to produce SFQ circuits and chips. Assuming the use of tools equivalent to those employed in the semiconductor industry, we estimate the density of Josephson junctions, circuit speed, and power dissipation that could be achieved with SFQ technology. Today, CMOS lithography is at 90-65 nm with about 20 layers. Assuming equivalent technology, aggressively increasing the current density above 100 kA cm -2 to achieve junction speeds approximately 1000 GHz, and reducing device footprints by converting device profiles from planar to vertical, one could expect to integrate about 250 M Josephson junctions cm -2 into SFQ digital circuits. This should enable circuit operation with clock frequencies above 200 GHz and place approximately 20 K gates within a radius of one clock period. As a result, complete microprocessors, including integrated memory registers, could be fabricated on a single chip
Pilot-wave quantum theory with a single Bohm's trajectory
Avanzini, Francesco; Fresch, Barbara; Moro, Giorgio J.
2015-01-01
The representation of a quantum system as the spatial configuration of its constituents evolving in time as a trajectory under the action of the wave-function, is the main objective of the Bohm theory. However, its standard formulation is referred to the statistical ensemble of its possible trajectories. The statistical ensemble is introduced in order to establish the exact correspondence (the Born's rule) between the probability density on the spatial configurations and the quantum distribut...
Single Purpose Satellite Systems
Watkins, Warren
1989-01-01
This paper examines the need for tactically responsive space systems capable of supporting battlefield and fleet commanders. Terminology used to describe this category of satellite system varies according to organization or agency. The Defense Advanced Research Projects Agency's Lightsat, the Naval Space Command's SPINSAT, and the Air Force Space Command s TACSAT, are reviewed. The United State Space Command's space support mission IS addressed and the role single-purpose satellites can play ...
Quantum phase transitions in Bose-Fermi systems
International Nuclear Information System (INIS)
Petrellis, D.; Leviatan, A.; Iachello, F.
2011-01-01
Research highlights: → We study quantum phase transitions in a system of N bosons and a single-j fermion. → Classical order parameters and correlation diagrams of quantum levels are determined. → The odd fermion strongly influences the location and nature of the phase transition. → Experimental evidence for the U(5)-SU(3) transition in odd-even nuclei is presented. - Abstract: Quantum phase transitions in a system of N bosons with angular momentum L = 0, 2 (s, d) and a single fermion with angular momentum j are investigated both classically and quantum mechanically. It is shown that the presence of the odd fermion strongly influences the location and nature of the phase transition, especially the critical value of the control parameter at which the phase transition occurs. Experimental evidence for the U(5)-SU(3) (spherical to axially-deformed) transition in odd-even nuclei is presented.
Quantum fluctuations and the single-junction Coulomb blockade
Energy Technology Data Exchange (ETDEWEB)
Girvin, S.M. (Department of Physics, Indiana University, Bloomington, IN (USA)); Glazman, L.I. (Institute of Microelectronics Technology and High Purity Materials, U.S.S.R. Academy of Science, Moscow District (U.S.S.R.)); Jonson, M. (Solid State Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN (USA)); Penn, D.R.; Stiles, M.D. (National Institute of Standards and Technology, Gaithersburg, MD (USA))
1990-06-25
We investigate the effect of quantum fluctuations on the Coulomb blockade in a single tunnel junction coupled to its environment by a transmission line of arbitrary impedance {ital Z}({omega}). The quantized oscillation modes of the transmission line are suddenly displaced when an electron tunnels through the junction. For small {ital Z} (relative to the quantum of resitance), a weak power-law zero-bias anomaly occurs associated with the infrared-divergent shakeup of low-frequency transmission-line modes. For large {ital Z}, the full blockade is recovered. Comparison with recent experiments is made.
Single-cell atomic quantum memory for light
International Nuclear Information System (INIS)
Opatrny, Tomas
2006-01-01
Recent experiments demonstrating atomic quantum memory for light [B. Julsgaard et al., Nature 432, 482 (2004)] involve two macroscopic samples of atoms, each with opposite spin polarization. It is shown here that a single atomic cell is enough for the memory function if the atoms are optically pumped with suitable linearly polarized light, and quadratic Zeeman shift and/or ac Stark shift are used to manipulate rotations of the quadratures. This should enhance the performance of our quantum memory devices since less resources are needed and losses of light in crossing different media boundaries are avoided
Nowak, Krzysztof M; Ohta, Takeshi; Suganuma, Takashi; Yokotsuka, Toshio; Fujimoto, Junichi; Mizoguchi, Hakaru
2012-12-01
Quantum cascade laser (QCL) is a very attractive seed source for a multikilowatt pulsed CO2 lasers applied for driving extreme ultraviolet emitting plasmas. In this Letter, we investigate output beam properties of a QCL designed to address P18 and P20 lines of 10.6 micron band of CO2 molecule. In particular, output beam quality and stability are investigated for the first time. A well-defined linear polarization and a single-mode operation enabled a use of phase retrieval method for full description of QCL output beam. A direct, multi-image numerical phase retrieval technique was developed and successfully applied to the measured intensity patterns of a QCL beam. Very good agreement between the measured and reconstructed beam profiles was observed at distances ranging from QCL aperture to infinity, proving a good understanding of the beam propagation. The results also confirm a high spatial coherence and high stability of the beam parameters, the features expected from an excellent seed source.
Quantum entanglement and quantum information in biological systems (DNA)
Hubač, Ivan; Švec, Miloslav; Wilson, Stephen
2017-12-01
Recent studies of DNA show that the hydrogen bonds between given base pairs can be treated as diabatic systems with spin-orbit coupling. For solid state systems strong diabaticity and spin-orbit coupling the possibility of forming Majorana fermions has been discussed. We analyze the hydrogen bonds in the base pairs in DNA from this perspective. Our analysis is based on a quasiparticle supersymmetric transformation which couples electronic and vibrational motion and includes normal coordinates and the corresponding momenta. We define qubits formed by Majorana fermions in the hydrogen bonds and also discuss the entangled states in base pairs. Quantum information and quantum entropy are introduced. In addition to the well-known classical information connected with the DNA base pairs, we also consider quantum information and show that the classical and quantum information are closely connected.
Fundamental limits to single-photon detection determined by quantum coherence and backaction
Young, Steve M.; Sarovar, Mohan; Léonard, François
2018-03-01
Single-photon detectors have achieved impressive performance and have led to a number of new scientific discoveries and technological applications. Existing models of photodetectors are semiclassical in that the field-matter interaction is treated perturbatively and time-separated from physical processes in the absorbing matter. An open question is whether a fully quantum detector, whereby the optical field, the optical absorption, and the amplification are considered as one quantum system, could have improved performance. Here we develop a theoretical model of such photodetectors and employ simulations to reveal the critical role played by quantum coherence and amplification backaction in dictating the performance. We show that coherence and backaction lead to trade-offs between detector metrics and also determine optimal system designs through control of the quantum-classical interface. Importantly, we establish the design parameters that result in a ideal photodetector with 100% efficiency, no dark counts, and minimal jitter, thus paving the route for next-generation detectors.
Quantum mechanics in complex systems
Hoehn, Ross Douglas
This document should be considered in its separation; there are three distinct topics contained within and three distinct chapters within the body of works. In a similar fashion, this abstract should be considered in three parts. Firstly, we explored the existence of multiply-charged atomic ions by having developed a new set of dimensional scaling equations as well as a series of relativistic augmentations to the standard dimensional scaling procedure and to the self-consistent field calculations. Secondly, we propose a novel method of predicting drug efficacy in hopes to facilitate the discovery of new small molecule therapeutics by modeling the agonist-protein system as being similar to the process of Inelastic Electron Tunneling Spectroscopy. Finally, we facilitate the instruction in basic quantum mechanical topics through the use of quantum games; this method of approach allows for the generation of exercises with the intent of conveying the fundamental concepts within a first year quantum mechanics classroom. Furthermore, no to be mentioned within the body of the text, yet presented in appendix form, certain works modeling the proliferation of cells types within the confines of man-made lattices for the purpose of facilitating artificial vascular transplants. In Chapter 2, we present a theoretical framework which describes multiply-charged atomic ions, their stability within super-intense laser fields, also lay corrections to the systems due to relativistic effects. Dimensional scaling calculations with relativistic corrections for systems: H, H-, H 2-, He, He-, He2-, He3- within super-intense laser fields were completed. Also completed were three-dimensional self consistent field calculations to verify the dimensionally scaled quantities. With the aforementioned methods the system's ability to stably bind 'additional' electrons through the development of multiple isolated regions of high potential energy leading to nodes of high electron density is shown
Dissipation and decoherence in quantum systems
International Nuclear Information System (INIS)
Menskii, Mikhail B
2003-01-01
The theory of dissipative quantum systems and its relation to the quantum theory of continuous measurements are reviewed. Constructing a correct theory of a dissipative quantum system requires that the system's interaction with its environment (reservoir) be taken into account. Since information about the system is 'recorded' in the state of the reservoir, the quantum theory of continuous measurements can be used to account for the influence of the reservoir. If based on the use of restricted path integrals, this theory does not require an explicit reservoir model and is therefore much simpler technically. (reviews of topical problems)
Vacuum Rabi spectra of a single quantum emitter.
Ota, Yasutomo; Ohta, Ryuichi; Kumagai, Naoto; Iwamoto, Satoshi; Arakawa, Yasuhiko
2015-04-10
We report the observation of the vacuum Rabi splitting of a single quantum emitter by measuring its direct spontaneous emission into free space. We use a semiconductor quantum dot inside a photonic crystal nanocavity, in conjunction with an appropriate cavity design and filtering with a polarizer and an aperture, enabling the extraction of the inherently weak emitter's signal. The emitter's vacuum Rabi spectra exhibit clear differences from those measured by detecting the cavity photon leakage. Moreover, we observe an asymmetric vacuum Rabi spectrum induced by interference between the emitter and cavity detection channels. Our observations lay the groundwork for accessing various cavity quantum electrodynamics phenomena that manifest themselves only in the emitter's direct spontaneous emission.
Quantum Control of Open Systems and Dense Atomic Ensembles
DiLoreto, Christopher
Controlling the dynamics of open quantum systems; i.e. quantum systems that decohere because of interactions with the environment, is an active area of research with many applications in quantum optics and quantum computation. My thesis expands the scope of this inquiry by seeking to control open systems in proximity to an additional system. The latter could be a classical system such as metal nanoparticles, or a quantum system such as a cluster of similar atoms. By modelling the interactions between the systems, we are able to expand the accessible state space of the quantum system in question. For a single, three-level quantum system, I examine isolated systems that have only normal spontaneous emission. I then show that intensity-intensity correlation spectra, which depend directly on the density matrix of the system, can be used detect whether transitions share a common energy level. This detection is possible due to the presence of quantum interference effects between two transitions if they are connected. This effect allows one to asses energy level structure diagrams in complex atoms/molecules. By placing an open quantum system near a nanoparticle dimer, I show that the spontaneous emission rate of the system can be changed "on demand" by changing the polarization of an incident, driving field. In a three-level, Lambda system, this allows a qubit to both retain high qubit fidelity when it is operating, and to be rapidly initialized to a pure state once it is rendered unusable by decoherence. This type of behaviour is not possible in a single open quantum system; therefore adding a classical system nearby extends the overall control space of the quantum system. An open quantum system near identical neighbours in a dense ensemble is another example of how the accessible state space can be expanded. I show that a dense ensemble of atoms rapidly becomes disordered with states that are not directly excited by an incident field becoming significantly populated
Perturbation theory of large quantum systems
Hugenholtz, N.M.
1957-01-01
The time-independent perturbation theory of quantum mechanics is studied for the case of very large systems, i.e. systems with large spatial dimensions (large volume Ω), and a large number of degrees of freedom. Examples of such systems are met with in the quantum theory of fields, solid state
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
The Relation between Structure and Quantum Interference in Single Molecule Junctions
DEFF Research Database (Denmark)
Markussen, Troels; Stadler, Robert; Thygesen, Kristian Sommer
2010-01-01
Quantum interference (QI) of electron pathways has recently attracted increased interest as an enabling tool for single-molecule electronic devices. Although various molecular systems have been shown to exhibit QI effects and a number of methods have been proposed for its analysis, simple...
Quantum key distribution and 1 Gbps data encryption over a single fibre
Energy Technology Data Exchange (ETDEWEB)
Eraerds, P; Walenta, N; Gisin, N; Zbinden, H [Group of Applied Physics-Optique, University of Geneva, Rue de l' Ecole-de-Medecine 20, 1205 Geneva (Switzerland); Legre, M, E-mail: patrick.eraerds@unige.c, E-mail: nino.walenta@unige.c [idQuantique SA, Chemin de la Marbrerie 3, 1227, Geneva (Switzerland)
2010-06-15
We perform quantum key distribution (QKD) over a single fibre in the presence of four classical channels in a C-band dense wavelength division multiplexing (DWDM) configuration using a commercial QKD system. The classical channels are used for key distillation and 1 Gbps encrypted communication, rendering the entire system independent of any other communication channel than a single dedicated fibre. We successfully distil secret keys over fibre spans of up to 50 km. The separation between the quantum channel at 1551.72 nm and the nearest classical channel is only 200 GHz, while the classical channels are all separated by 100 GHz. In addition to that, we discuss possible improvements and alternative configurations, e.g. whether it is advantageous to choose the quantum channel at 1310 nm or to opt for a pure C-band (1530-1565 nm) configuration.
Macroscopic quantum systems and gravitational phenomena
International Nuclear Information System (INIS)
Pikovski, I.
2014-01-01
Low-energy quantum systems are studied theoretically in light of possible experiments to test the interplay between quantum theory and general relativity. The research focus in this thesis is on quantum systems which can be controlled with very high precision and which allow for tests of quantum theory at novel scales in terms of mass and size. The pulsed regime of opto-mechanics is explored and it is shown how short optical pulses can be used to prepare and characterize quantum states of a massive mechanical resonator, and how some phenomenological models of quantum gravity can be probed. In addition, quantum interferometry with photons and matter-waves in the presence of gravitational time dilation is considered. It is shown that time dilation causes entanglement between internal states and the center-of-mass position and that it leads to decoherence of all composite quantum systems. The results of the thesis show that the interplay between quantum theory and general relativity affects even low-energy quantum systems and that it offers novel phenomena which can be probed in experiments. (author) [de
Controllable Subspaces of Open Quantum Dynamical Systems
International Nuclear Information System (INIS)
Zhang Ming; Gong Erling; Xie Hongwei; Hu Dewen; Dai Hongyi
2008-01-01
This paper discusses the concept of controllable subspace for open quantum dynamical systems. It is constructively demonstrated that combining structural features of decoherence-free subspaces with the ability to perform open-loop coherent control on open quantum systems will allow decoherence-free subspaces to be controllable. This is in contrast to the observation that open quantum dynamical systems are not open-loop controllable. To a certain extent, this paper gives an alternative control theoretical interpretation on why decoherence-free subspaces can be useful for quantum computation.
Capacity on wireless quantum cellular communication system
Zhou, Xiang-Zhen; Yu, Xu-Tao; Zhang, Zai-Chen
2018-03-01
Quantum technology is making excellent prospects in future communication networks. Entanglement generation and purification are two major components in quantum networks. Combining these two techniques with classical cellular mobile communication, we proposed a novel wireless quantum cellular(WQC) communication system which is possible to realize commercial mobile quantum communication. In this paper, the architecture and network topology of WQC communication system are discussed, the mathematical model of WQC system is extracted and the serving capacity, indicating the ability to serve customers, is defined and calculated under certain circumstances.
Quasi-Periodically Driven Quantum Systems
Verdeny, Albert; Puig, Joaquim; Mintert, Florian
2016-10-01
Floquet theory provides rigorous foundations for the theory of periodically driven quantum systems. In the case of non-periodic driving, however, the situation is not so well understood. Here, we provide a critical review of the theoretical framework developed for quasi-periodically driven quantum systems. Although the theoretical footing is still under development, we argue that quasi-periodically driven quantum systems can be treated with generalisations of Floquet theory in suitable parameter regimes. Moreover, we provide a generalisation of the Floquet-Magnus expansion and argue that quasi-periodic driving offers a promising route for quantum simulations.
Heo, Jino; Kang, Min-Sung; Hong, Chang-Ho; Choi, Seong-Gon; Hong, Jong-Phil
2017-08-01
We propose quantum information processing schemes to generate and swap entangled states based on the interactions between flying photons and quantum dots (QDs) confined within optical cavities for quantum communication. To produce and distribute entangled states (Bell and Greenberger-Horne-Zeilinger [GHZ] states) between the photonic qubits of flying photons of consumers (Alice and Bob) and electron-spin qubits of a provider (trust center, or TC), the TC employs the interactions of the QD-cavity system, which is composed of a charged QD (negatively charged exciton) inside a single-sided cavity. Subsequently, the TC constructs an entanglement channel (Bell state and 4-qubit GHZ state) to link one consumer with another through entanglement swapping, which can be realized to exploit a probe photon with interactions of the QD-cavity systems and single-qubit measurements without Bell state measurement, for quantum communication between consumers. Consequently, the TC, which has quantum nodes (QD-cavity systems), can accomplish constructing the entanglement channel (authenticated channel) between two separated consumers from the distributions of entangled states and entanglement swapping. Furthermore, our schemes using QD-cavity systems, which are feasible with a certain probability of success and high fidelity, can be experimentally implemented with technology currently in use.
Single-cell magnetic imaging using a quantum diamond microscope.
Glenn, D R; Lee, K; Park, H; Weissleder, R; Yacoby, A; Lukin, M D; Lee, H; Walsworth, R L; Connolly, C B
2015-08-01
We apply a quantum diamond microscope for detection and imaging of immunomagnetically labeled cells. This instrument uses nitrogen-vacancy (NV) centers in diamond for correlated magnetic and fluorescence imaging. Our device provides single-cell resolution and a field of view (∼1 mm(2)) two orders of magnitude larger than that of previous NV imaging technologies, enabling practical applications. To illustrate, we quantified cancer biomarkers expressed by rare tumor cells in a large population of healthy cells.
Single cell magnetic imaging using a quantum diamond microscope
Park, H.; Weissleder, R.; Yacoby, A.; Lukin, M. D.; Lee, H.; Walsworth, R. L.; Connolly, C. B.
2015-01-01
We apply a quantum diamond microscope to detection and imaging of immunomagnetically labeled cells. This instrument uses nitrogen-vacancy (NV) centers in diamond for correlated magnetic and fluorescence imaging. Our device provides single-cell resolution and two orders of magnitude larger field of view (~1 mm2) than previous NV imaging technologies, enabling practical applications. To illustrate, we quantify cancer biomarkers expressed by rare tumor cells in a large population of healthy cells. PMID:26098019
Rapid single flux quantum logic in high temperature superconductor technology
Shunmugavel, K.
2006-01-01
A Josephson junction is the basic element of rapid single flux quantum logic (RSFQ) circuits. A high operating speed and low power consumption are the main advantages of RSFQ logic over semiconductor electronic circuits. To realize complex RSFQ circuits in HTS technology one needs a reproducible fabrication of Josephson junctions with low parameter spread. High quality HTS junctions require a fully epitaxial multilayer structure with clean interfaces and a smooth surface morphology. Neodymium...
Novel single photon sources for new generation of quantum communications
2017-06-13
state single photon sources that was published in Nature Photonics in October 2016. 15. SUBJECT TERMS diamond color center, diamond, AOARD 16. SECURITY...platform for quantum emitters. We developed means to increase their density, developed basic methods to engineer them, and demonstrate coupling to...manipulation of a silicon vacancy color cent er in a nanodiamond. We demonstrate ultra fast coherent control of a photon, that make s this defect
Magnetic Quantum Tunneling and Symmetry in Single Molecule Magnets
Kent, Andrew D.
2003-03-01
We have studied the symmetry of magnetic quantum tunneling (MQT) in single molecule magnets (SMMs) using a micro-Hall effect magnetometer and high field vector superconducting magnet system. In the most widely studied SMM, Mn12-acetate, an average crystal 4-fold symmetry in the magnetic response is shown to be due to local molecular environments of 2-fold symmetry that are rotated by 90 degrees with respect to one another. We attribute this to ligand disorder that leads to local rhombic distortions, a model first proposed by Cornia et al. based on x-ray diffraction data [1]. We have magnetically distilled a Mn12-acetate crystal to study a subset of these lower (2-fold) site symmetry molecules and present evidence for a spin-parity effect consistent with a local 2-fold symmetry [2]. These results highlight the importance of subtle changes in molecule environment in modulating magnetic anisotropy and MQT. [1] Cornia et al. Phys. Rev. Lett. 89, 257201 (2002) [2] E. del Barco, A. D. Kent, E. Rumberger, D. H. Hendrickson, G. Christou, submitted for publication (2002) and Europhys. Lett. 60, 768 (2002)
Quantum algorithm for simulating the dynamics of an open quantum system
International Nuclear Information System (INIS)
Wang Hefeng; Ashhab, S.; Nori, Franco
2011-01-01
In the study of open quantum systems, one typically obtains the decoherence dynamics by solving a master equation. The master equation is derived using knowledge of some basic properties of the system, the environment, and their interaction: One basically needs to know the operators through which the system couples to the environment and the spectral density of the environment. For a large system, it could become prohibitively difficult to even write down the appropriate master equation, let alone solve it on a classical computer. In this paper, we present a quantum algorithm for simulating the dynamics of an open quantum system. On a quantum computer, the environment can be simulated using ancilla qubits with properly chosen single-qubit frequencies and with properly designed coupling to the system qubits. The parameters used in the simulation are easily derived from the parameters of the system + environment Hamiltonian. The algorithm is designed to simulate Markovian dynamics, but it can also be used to simulate non-Markovian dynamics provided that this dynamics can be obtained by embedding the system of interest into a larger system that obeys Markovian dynamics. We estimate the resource requirements for the algorithm. In particular, we show that for sufficiently slow decoherence a single ancilla qubit could be sufficient to represent the entire environment, in principle.
Quantum-classical interface based on single flux quantum digital logic
McDermott, R.; Vavilov, M. G.; Plourde, B. L. T.; Wilhelm, F. K.; Liebermann, P. J.; Mukhanov, O. A.; Ohki, T. A.
2018-04-01
We describe an approach to the integrated control and measurement of a large-scale superconducting multiqubit array comprising up to 108 physical qubits using a proximal coprocessor based on the Single Flux Quantum (SFQ) digital logic family. Coherent control is realized by irradiating the qubits directly with classical bitstreams derived from optimal control theory. Qubit measurement is performed by a Josephson photon counter, which provides access to the classical result of projective quantum measurement at the millikelvin stage. We analyze the power budget and physical footprint of the SFQ coprocessor and discuss challenges and opportunities associated with this approach.
Quantum optics with single nanodiamonds flying over gold films: Towards a Robust quantum plasmonics
Energy Technology Data Exchange (ETDEWEB)
Mollet, O.; Drezet, A.; Huant, S. [Institut Néel, CNRS and Université Joseph Fourier, BP 166, F-38042 Grenoble (France)
2013-12-04
A nanodiamond (ND) hosting nitrogen-vacancy (NV) color centers is attached on the apex of an optical tip for near-field microscopy. Its fluorescence is used to launch surface plasmon-polaritons (SPPs) in a thin polycrystalline gold film. It is shown that the quantum nature of the initial source of light is preserved after conversion to SPPs. This opens the way to a deterministic quantum plasmonics, where single SPPs can be injected at well-defined positions in a plasmonic device produced by top-down approaches.
Dynamical entropy for infinite quantum systems
International Nuclear Information System (INIS)
Hudetz, T.
1990-01-01
We review the recent physical application of the so-called Connes-Narnhofer-Thirring entropy, which is the successful quantum mechanical generalization of the classical Kolmogorov-Sinai entropy and, by its very conception, is a dynamical entropy for infinite quantum systems. We thus comparingly review also the physical applications of the classical dynamical entropy for infinite classical systems. 41 refs. (Author)
Linear response theory for quantum open systems
Wei, J. H.; Yan, YiJing
2011-01-01
Basing on the theory of Feynman's influence functional and its hierarchical equations of motion, we develop a linear response theory for quantum open systems. Our theory provides an effective way to calculate dynamical observables of a quantum open system at its steady-state, which can be applied to various fields of non-equilibrium condensed matter physics.
Controlling the Shannon Entropy of Quantum Systems
Xing, Yifan; Wu, Jun
2013-01-01
This paper proposes a new quantum control method which controls the Shannon entropy of quantum systems. For both discrete and continuous entropies, controller design methods are proposed based on probability density function control, which can drive the quantum state to any target state. To drive the entropy to any target at any prespecified time, another discretization method is proposed for the discrete entropy case, and the conditions under which the entropy can be increased or decreased are discussed. Simulations are done on both two- and three-dimensional quantum systems, where division and prediction are used to achieve more accurate tracking. PMID:23818819
Photonic reagent control of dynamically homologous quantum systems
International Nuclear Information System (INIS)
Beltrani, Vincent; Dominy, Jason; Ho, Tak-San; Rabitz, Herschel
2007-01-01
The general objective of quantum control is the manipulation of atomic scale physical and chemical phenomena through the application of external control fields. These tailored fields, or photonic reagents, exhibit systematic properties analogous to those of ordinary laboratory reagents. This analogous behavior is explored further here by considering the controlled response of a family of homologous quantum systems to a single common photonic reagent. A level set of dynamically homologous quantum systems is defined as the family that produces the same value(s) for a target physical observable(s) when controlled by a common photonic reagent. This paper investigates the scope of homologous quantum system control using the level set exploration technique (L-SET). L-SET enables the identification of continuous families of dynamically homologous quantum systems. Each quantum system is specified by a point in a hypercube whose edges are labeled by Hamiltonian matrix elements. Numerical examples are presented with simple finite level systems to illustrate the L-SET concepts. Both connected and disconnected families of dynamically homologous systems are shown to exist
Double-slit experiment with single wave-driven particles and its relation to quantum mechanics.
Andersen, Anders; Madsen, Jacob; Reichelt, Christian; Rosenlund Ahl, Sonja; Lautrup, Benny; Ellegaard, Clive; Levinsen, Mogens T; Bohr, Tomas
2015-07-01
In a thought-provoking paper, Couder and Fort [Phys. Rev. Lett. 97, 154101 (2006)] describe a version of the famous double-slit experiment performed with droplets bouncing on a vertically vibrated fluid surface. In the experiment, an interference pattern in the single-particle statistics is found even though it is possible to determine unambiguously which slit the walking droplet passes. Here we argue, however, that the single-particle statistics in such an experiment will be fundamentally different from the single-particle statistics of quantum mechanics. Quantum mechanical interference takes place between different classical paths with precise amplitude and phase relations. In the double-slit experiment with walking droplets, these relations are lost since one of the paths is singled out by the droplet. To support our conclusions, we have carried out our own double-slit experiment, and our results, in particular the long and variable slit passage times of the droplets, cast strong doubt on the feasibility of the interference claimed by Couder and Fort. To understand theoretically the limitations of wave-driven particle systems as analogs to quantum mechanics, we introduce a Schrödinger equation with a source term originating from a localized particle that generates a wave while being simultaneously guided by it. We show that the ensuing particle-wave dynamics can capture some characteristics of quantum mechanics such as orbital quantization. However, the particle-wave dynamics can not reproduce quantum mechanics in general, and we show that the single-particle statistics for our model in a double-slit experiment with an additional splitter plate differs qualitatively from that of quantum mechanics.
Double-slit experiment with single wave-driven particles and its relation to quantum mechanics
Andersen, Anders; Madsen, Jacob; Reichelt, Christian; Rosenlund Ahl, Sonja; Lautrup, Benny; Ellegaard, Clive; Levinsen, Mogens T.; Bohr, Tomas
2015-07-01
In a thought-provoking paper, Couder and Fort [Phys. Rev. Lett. 97, 154101 (2006), 10.1103/PhysRevLett.97.154101] describe a version of the famous double-slit experiment performed with droplets bouncing on a vertically vibrated fluid surface. In the experiment, an interference pattern in the single-particle statistics is found even though it is possible to determine unambiguously which slit the walking droplet passes. Here we argue, however, that the single-particle statistics in such an experiment will be fundamentally different from the single-particle statistics of quantum mechanics. Quantum mechanical interference takes place between different classical paths with precise amplitude and phase relations. In the double-slit experiment with walking droplets, these relations are lost since one of the paths is singled out by the droplet. To support our conclusions, we have carried out our own double-slit experiment, and our results, in particular the long and variable slit passage times of the droplets, cast strong doubt on the feasibility of the interference claimed by Couder and Fort. To understand theoretically the limitations of wave-driven particle systems as analogs to quantum mechanics, we introduce a Schrödinger equation with a source term originating from a localized particle that generates a wave while being simultaneously guided by it. We show that the ensuing particle-wave dynamics can capture some characteristics of quantum mechanics such as orbital quantization. However, the particle-wave dynamics can not reproduce quantum mechanics in general, and we show that the single-particle statistics for our model in a double-slit experiment with an additional splitter plate differs qualitatively from that of quantum mechanics.
On-Chip Single-Plasmon Nanocircuit Driven by a Self-Assembled Quantum Dot.
Wu, Xiaofei; Jiang, Ping; Razinskas, Gary; Huo, Yongheng; Zhang, Hongyi; Kamp, Martin; Rastelli, Armando; Schmidt, Oliver G; Hecht, Bert; Lindfors, Klas; Lippitz, Markus
2017-07-12
Quantum photonics holds great promise for future technologies such as secure communication, quantum computation, quantum simulation, and quantum metrology. An outstanding challenge for quantum photonics is to develop scalable miniature circuits that integrate single-photon sources, linear optical components, and detectors on a chip. Plasmonic nanocircuits will play essential roles in such developments. However, for quantum plasmonic circuits, integration of stable, bright, and narrow-band single photon sources in the structure has so far not been reported. Here we present a plasmonic nanocircuit driven by a self-assembled GaAs quantum dot. Through a planar dielectric-plasmonic hybrid waveguide, the quantum dot efficiently excites narrow-band single plasmons that are guided in a two-wire transmission line until they are converted into single photons by an optical antenna. Our work demonstrates the feasibility of fully on-chip plasmonic nanocircuits for quantum optical applications.
Quantum equilibria for macroscopic systems
International Nuclear Information System (INIS)
Grib, A; Khrennikov, A; Parfionov, G; Starkov, K
2006-01-01
Nash equilibria are found for some quantum games with particles with spin-1/2 for which two spin projections on different directions in space are measured. Examples of macroscopic games with the same equilibria are given. Mixed strategies for participants of these games are calculated using probability amplitudes according to the rules of quantum mechanics in spite of the macroscopic nature of the game and absence of Planck's constant. A possible role of quantum logical lattices for the existence of macroscopic quantum equilibria is discussed. Some examples for spin-1 cases are also considered
Non-perturbative description of quantum systems
Feranchuk, Ilya; Le, Van-Hoang; Ulyanenkov, Alexander
2015-01-01
This book introduces systematically the operator method for the solution of the Schrödinger equation. This method permits to describe the states of quantum systems in the entire range of parameters of Hamiltonian with a predefined accuracy. The operator method is unique compared with other non-perturbative methods due to its ability to deliver in zeroth approximation the uniformly suitable estimate for both ground and excited states of quantum system. The method has been generalized for the application to quantum statistics and quantum field theory. In this book, the numerous applications of operator method for various physical systems are demonstrated. Simple models are used to illustrate the basic principles of the method which are further used for the solution of complex problems of quantum theory for many-particle systems. The results obtained are supplemented by numerical calculations, presented as tables and figures.
Open quantum spin systems in semiconductor quantum dots and atoms in optical lattices
International Nuclear Information System (INIS)
Schwager, Heike
2012-01-01
In this Thesis, we study open quantum spin systems from different perspectives. The first part is motivated by technological challenges of quantum computation. An important building block for quantum computation and quantum communication networks is an interface between material qubits for storage and data processing and travelling photonic qubits for communication. We propose the realisation of a quantum interface between a travelling-wave light field and the nuclear spins in a quantum dot strongly coupled to a cavity. Our scheme is robust against cavity decay as it uses the decay of the cavity to achieve the coupling between nuclear spins and the travelling-wave light fields. A prerequiste for such a quantum interface is a highly polarized ensemble of nuclear spins. High polarization of the nuclear spin ensemble is moreover highly desirable as it protects the potential electron spin qubit from decoherence. Here we present the theoretical description of an experiment in which highly asymmetric dynamic nuclear spin pumping is observed in a single self-assembled InGaAs quantum dot. The second part of this Thesis is devoted to fundamental studies of dissipative spin systems. We study general one-dimensional spin chains under dissipation and propose a scheme to realize a quantum spin system using ultracold atoms in an optical lattice in which both coherent interaction and dissipation can be engineered and controlled. This system enables the study of non-equilibrium and steady state physics of open and driven spin systems. We find, that the steady state expectation values of different spin models exhibit discontinuous behaviour at degeneracy points of the Hamiltonian in the limit of weak dissipation. This effect can be used to dissipatively probe the spectrum of the Hamiltonian. We moreover study spin models under the aspect of state preparation and show that dissipation drives certain spin models into highly entangled state. Finally, we study a spin chain with
Open quantum spin systems in semiconductor quantum dots and atoms in optical lattices
Energy Technology Data Exchange (ETDEWEB)
Schwager, Heike
2012-07-04
In this Thesis, we study open quantum spin systems from different perspectives. The first part is motivated by technological challenges of quantum computation. An important building block for quantum computation and quantum communication networks is an interface between material qubits for storage and data processing and travelling photonic qubits for communication. We propose the realisation of a quantum interface between a travelling-wave light field and the nuclear spins in a quantum dot strongly coupled to a cavity. Our scheme is robust against cavity decay as it uses the decay of the cavity to achieve the coupling between nuclear spins and the travelling-wave light fields. A prerequiste for such a quantum interface is a highly polarized ensemble of nuclear spins. High polarization of the nuclear spin ensemble is moreover highly desirable as it protects the potential electron spin qubit from decoherence. Here we present the theoretical description of an experiment in which highly asymmetric dynamic nuclear spin pumping is observed in a single self-assembled InGaAs quantum dot. The second part of this Thesis is devoted to fundamental studies of dissipative spin systems. We study general one-dimensional spin chains under dissipation and propose a scheme to realize a quantum spin system using ultracold atoms in an optical lattice in which both coherent interaction and dissipation can be engineered and controlled. This system enables the study of non-equilibrium and steady state physics of open and driven spin systems. We find, that the steady state expectation values of different spin models exhibit discontinuous behaviour at degeneracy points of the Hamiltonian in the limit of weak dissipation. This effect can be used to dissipatively probe the spectrum of the Hamiltonian. We moreover study spin models under the aspect of state preparation and show that dissipation drives certain spin models into highly entangled state. Finally, we study a spin chain with
Mixing and entropy increase in quantum systems
International Nuclear Information System (INIS)
Narnhofer, H.; Pflug, A.; Thirring, W.
1989-01-01
This paper attempts to explain the key feature of deterministic chaotic classical systems and how they can be translated to quantum systems. To do so we develop the appropriate algebraic language for the non-specialist. 22 refs. (Author)
Probing quantum coherence in single-atom electron spin resonance
Willke, Philip; Paul, William; Natterer, Fabian D.; Yang, Kai; Bae, Yujeong; Choi, Taeyoung; Fernández-Rossier, Joaquin; Heinrich, Andreas J.; Lutz, Christoper P.
2018-01-01
Spin resonance of individual spin centers allows applications ranging from quantum information technology to atomic-scale magnetometry. To protect the quantum properties of a spin, control over its local environment, including energy relaxation and decoherence processes, is crucial. However, in most existing architectures, the environment remains fixed by the crystal structure and electrical contacts. Recently, spin-polarized scanning tunneling microscopy (STM), in combination with electron spin resonance (ESR), allowed the study of single adatoms and inter-atomic coupling with an unprecedented combination of spatial and energy resolution. We elucidate and control the interplay of an Fe single spin with its atomic-scale environment by precisely tuning the phase coherence time T2 using the STM tip as a variable electrode. We find that the decoherence rate is the sum of two main contributions. The first scales linearly with tunnel current and shows that, on average, every tunneling electron causes one dephasing event. The second, effective even without current, arises from thermally activated spin-flip processes of tip spins. Understanding these interactions allows us to maximize T2 and improve the energy resolution. It also allows us to maximize the amplitude of the ESR signal, which supports measurements even at elevated temperatures as high as 4 K. Thus, ESR-STM allows control of quantum coherence in individual, electrically accessible spins. PMID:29464211
Probing quantum coherence in single-atom electron spin resonance.
Willke, Philip; Paul, William; Natterer, Fabian D; Yang, Kai; Bae, Yujeong; Choi, Taeyoung; Fernández-Rossier, Joaquin; Heinrich, Andreas J; Lutz, Christoper P
2018-02-01
Spin resonance of individual spin centers allows applications ranging from quantum information technology to atomic-scale magnetometry. To protect the quantum properties of a spin, control over its local environment, including energy relaxation and decoherence processes, is crucial. However, in most existing architectures, the environment remains fixed by the crystal structure and electrical contacts. Recently, spin-polarized scanning tunneling microscopy (STM), in combination with electron spin resonance (ESR), allowed the study of single adatoms and inter-atomic coupling with an unprecedented combination of spatial and energy resolution. We elucidate and control the interplay of an Fe single spin with its atomic-scale environment by precisely tuning the phase coherence time T 2 using the STM tip as a variable electrode. We find that the decoherence rate is the sum of two main contributions. The first scales linearly with tunnel current and shows that, on average, every tunneling electron causes one dephasing event. The second, effective even without current, arises from thermally activated spin-flip processes of tip spins. Understanding these interactions allows us to maximize T 2 and improve the energy resolution. It also allows us to maximize the amplitude of the ESR signal, which supports measurements even at elevated temperatures as high as 4 K. Thus, ESR-STM allows control of quantum coherence in individual, electrically accessible spins.
Electromagnetically induced transparency in quantum dot systems
International Nuclear Information System (INIS)
Jiang Yiwen; Zhu Kadi; Wu Zhuojie; Yuan Xiaozhong; Yao Ming
2006-01-01
Electromagnetically induced transparency (EIT) in quantum dot exciton systems in which the exciton behaves as a two-level system is investigated theoretically. It is shown that due to strong exciton-phonon coupling EIT can occur in such a quantum dot system and ultraslow light can propagate. The nonlinear optical absorption and Kerr coefficient based on EIT are also calculated. The numerical results show that giant nonlinear optical effects can be obtained while the frequency of the signal field differs only by an amount of LO phonon frequency from the exciton frequency in quantum dot systems
Quantum turnstile operation of single-molecule magnets
International Nuclear Information System (INIS)
Moldoveanu, V; Dinu, I V; Tanatar, B; Moca, C P
2015-01-01
The time-dependent transport through single-molecule magnets coupled to magnetic or non-magnetic electrodes is studied in the framework of the generalized master equation method. We investigate the transient regime induced by the periodic switching of the source and drain contacts. If the electrodes have opposite magnetizations the quantum turnstile operation allows the stepwise writing of intermediate excited states. In turn, the transient currents provide a way to read these states. Within our approach we take into account both the uniaxial and transverse anisotropy. The latter may induce additional quantum tunneling processes which affect the efficiency of the proposed read-and-write scheme. An equally weighted mixture of molecular spin states can be prepared if one of the electrodes is ferromagnetic. (paper)
Threshold quantum secret sharing based on single qubit
Lu, Changbin; Miao, Fuyou; Meng, Keju; Yu, Yue
2018-03-01
Based on unitary phase shift operation on single qubit in association with Shamir's ( t, n) secret sharing, a ( t, n) threshold quantum secret sharing scheme (or ( t, n)-QSS) is proposed to share both classical information and quantum states. The scheme uses decoy photons to prevent eavesdropping and employs the secret in Shamir's scheme as the private value to guarantee the correctness of secret reconstruction. Analyses show it is resistant to typical intercept-and-resend attack, entangle-and-measure attack and participant attacks such as entanglement swapping attack. Moreover, it is easier to realize in physic and more practical in applications when compared with related ones. By the method in our scheme, new ( t, n)-QSS schemes can be easily constructed using other classical ( t, n) secret sharing.
A triple quantum dot in a single-wall carbon nanotube
DEFF Research Database (Denmark)
Grove-Rasmussen, Kasper; Jørgensen, Henrik Ingerslev; Hayashi, T.
2008-01-01
A top-gated single-wall carbon nanotube is used to define three coupled quantum dots in series between two electrodes. The additional electron number on each quantum dot is controlled by top-gate voltages allowing for current measurements of single, double, and triple quantum dot stability diagrams...
Dynamic control of plasmon generation by an individual quantum system.
Große, Christoph; Kabakchiev, Alexander; Lutz, Theresa; Froidevaux, Romain; Schramm, Frank; Ruben, Mario; Etzkorn, Markus; Schlickum, Uta; Kuhnke, Klaus; Kern, Klaus
2014-10-08
Controlling light on the nanoscale in a similar way as electric currents has the potential to revolutionize the exchange and processing of information. Although light can be guided on this scale by coupling it to plasmons, that is, collective electron oscillations in metals, their local electronic control remains a challenge. Here, we demonstrate that an individual quantum system is able to dynamically gate the electrical plasmon generation. Using a single molecule in a double tunnel barrier between two electrodes we show that this gating can be exploited to monitor fast changes of the quantum system itself and to realize a single-molecule plasmon-generating field-effect transistor operable in the gigahertz range. This opens new avenues toward atomic scale quantum interfaces bridging nanoelectronics and nanophotonics.
Numerical approaches to complex quantum, semiclassical and classical systems
International Nuclear Information System (INIS)
Schubert, Gerald
2008-01-01
In this work we analyse the capabilities of several numerical techniques for the description of different physical systems. Thereby, the considered systems range from quantum over semiclassical to classical and from few- to many-particle systems. In chapter 1 we investigate the behaviour of a single quantum particle in the presence of an external disordered background (static potentials). Starting from the quantum percolation problem, we address the fundamental question of a disorder induced (Anderson-) transition from extended to localised single-particle eigenstates. Distinguishing isolating from conducting states by applying a local distribution approach for the local density of states (LDOS), we detect the quantum percolation threshold in two- and three-dimensions. Extending the quantum percolation model to a quantum random resistor model, we comment on the possible relevance of our results to the influence of disorder on the conductivity in graphene sheets. For the calculation of the LDOS as well as for the Chebyshev expansion of the time evolution operator, the kernel polynomial method (KPM) is the key numerical technique. In chapter 2 we examine how a single quantum particle is influenced by retarded bosonic fields that are inherent to the system. Within the Holstein model, these bosonic degrees of freedom (phonons) give rise to an infinite dimensional Hilbert space, posing a true many-particle problem. Constituting a minimal model for polaron formation, the Holstein model allows us to study the optical absorption and activated transport in polaronic systems. Using a two-dimensional variant of the KPM, we calculate for the first time quasi-exactly the optical absorption and dc-conductivity as a function of temperature. In chapter 3 we come back to the time evolution of a quantum particle in an external, static potential and investigate the capability of semiclassical approximations to it. We address basic quantum effects as tunneling, interference and
Numerical approaches to complex quantum, semiclassical and classical systems
Energy Technology Data Exchange (ETDEWEB)
Schubert, Gerald
2008-11-03
In this work we analyse the capabilities of several numerical techniques for the description of different physical systems. Thereby, the considered systems range from quantum over semiclassical to classical and from few- to many-particle systems. In chapter 1 we investigate the behaviour of a single quantum particle in the presence of an external disordered background (static potentials). Starting from the quantum percolation problem, we address the fundamental question of a disorder induced (Anderson-) transition from extended to localised single-particle eigenstates. Distinguishing isolating from conducting states by applying a local distribution approach for the local density of states (LDOS), we detect the quantum percolation threshold in two- and three-dimensions. Extending the quantum percolation model to a quantum random resistor model, we comment on the possible relevance of our results to the influence of disorder on the conductivity in graphene sheets. For the calculation of the LDOS as well as for the Chebyshev expansion of the time evolution operator, the kernel polynomial method (KPM) is the key numerical technique. In chapter 2 we examine how a single quantum particle is influenced by retarded bosonic fields that are inherent to the system. Within the Holstein model, these bosonic degrees of freedom (phonons) give rise to an infinite dimensional Hilbert space, posing a true many-particle problem. Constituting a minimal model for polaron formation, the Holstein model allows us to study the optical absorption and activated transport in polaronic systems. Using a two-dimensional variant of the KPM, we calculate for the first time quasi-exactly the optical absorption and dc-conductivity as a function of temperature. In chapter 3 we come back to the time evolution of a quantum particle in an external, static potential and investigate the capability of semiclassical approximations to it. We address basic quantum effects as tunneling, interference and
Radio frequency single electron transistors: readout for a solid state quantum computer
International Nuclear Information System (INIS)
Buehler, T.M.; Reilly, D.J.; Starrett, R.P.; Brenner, R.; Hamilton, A.R.; Clark, R.G.; Court, N.A.; Dzurak, A.S.
2002-01-01
Full text: Quantum computers promise unprecedented computational power if they can be scaled to a large number of qubits. Essential to the operation of such a machine is readout: the determination of the final quantum state of the system. In the case of the silicon based solid state architecture proposed by Kane, readout is achieved by determining the direction of a single electron spin via the detection of a spin dependent tunneling event. This requires a highly sensitive electrometer that can detect the motion of a single electron in a timescale less than the spin relaxation time. The Radio Frequency Single Electron Transistor (RF-SET) is a device that possesses both the charge sensitivity (oq ∼ 10 -6 / √Hz), approaching the quantum limit) and fast response required to perform readout in such a system. Here we describe the fabrication and operation of transmission mode RF-SETs and discuss the application of these novel electrometers in the readout of a solid state quantum computer
Quantum-Sequencing: Fast electronic single DNA molecule sequencing
Casamada Ribot, Josep; Chatterjee, Anushree; Nagpal, Prashant
2014-03-01
A major goal of third-generation sequencing technologies is to develop a fast, reliable, enzyme-free, high-throughput and cost-effective, single-molecule sequencing method. Here, we present the first demonstration of unique ``electronic fingerprint'' of all nucleotides (A, G, T, C), with single-molecule DNA sequencing, using Quantum-tunneling Sequencing (Q-Seq) at room temperature. We show that the electronic state of the nucleobases shift depending on the pH, with most distinct states identified at acidic pH. We also demonstrate identification of single nucleotide modifications (methylation here). Using these unique electronic fingerprints (or tunneling data), we report a partial sequence of beta lactamase (bla) gene, which encodes resistance to beta-lactam antibiotics, with over 95% success rate. These results highlight the potential of Q-Seq as a robust technique for next-generation sequencing.
Simple Atomic Quantum Memory Suitable for Semiconductor Quantum Dot Single Photons.
Wolters, Janik; Buser, Gianni; Horsley, Andrew; Béguin, Lucas; Jöckel, Andreas; Jahn, Jan-Philipp; Warburton, Richard J; Treutlein, Philipp
2017-08-11
Quantum memories matched to single photon sources will form an important cornerstone of future quantum network technology. We demonstrate such a memory in warm Rb vapor with on-demand storage and retrieval, based on electromagnetically induced transparency. With an acceptance bandwidth of δf=0.66 GHz, the memory is suitable for single photons emitted by semiconductor quantum dots. In this regime, vapor cell memories offer an excellent compromise between storage efficiency, storage time, noise level, and experimental complexity, and atomic collisions have negligible influence on the optical coherences. Operation of the memory is demonstrated using attenuated laser pulses on the single photon level. For a 50 ns storage time, we measure η_{e2e}^{50 ns}=3.4(3)% end-to-end efficiency of the fiber-coupled memory, with a total intrinsic efficiency η_{int}=17(3)%. Straightforward technological improvements can boost the end-to-end-efficiency to η_{e2e}≈35%; beyond that, increasing the optical depth and exploiting the Zeeman substructure of the atoms will allow such a memory to approach near unity efficiency. In the present memory, the unconditional read-out noise level of 9×10^{-3} photons is dominated by atomic fluorescence, and for input pulses containing on average μ_{1}=0.27(4) photons, the signal to noise level would be unity.
Simple Atomic Quantum Memory Suitable for Semiconductor Quantum Dot Single Photons
Wolters, Janik; Buser, Gianni; Horsley, Andrew; Béguin, Lucas; Jöckel, Andreas; Jahn, Jan-Philipp; Warburton, Richard J.; Treutlein, Philipp
2017-08-01
Quantum memories matched to single photon sources will form an important cornerstone of future quantum network technology. We demonstrate such a memory in warm Rb vapor with on-demand storage and retrieval, based on electromagnetically induced transparency. With an acceptance bandwidth of δ f =0.66 GHz , the memory is suitable for single photons emitted by semiconductor quantum dots. In this regime, vapor cell memories offer an excellent compromise between storage efficiency, storage time, noise level, and experimental complexity, and atomic collisions have negligible influence on the optical coherences. Operation of the memory is demonstrated using attenuated laser pulses on the single photon level. For a 50 ns storage time, we measure ηe2 e 50 ns=3.4 (3 )% end-to-end efficiency of the fiber-coupled memory, with a total intrinsic efficiency ηint=17 (3 )%. Straightforward technological improvements can boost the end-to-end-efficiency to ηe 2 e≈35 %; beyond that, increasing the optical depth and exploiting the Zeeman substructure of the atoms will allow such a memory to approach near unity efficiency. In the present memory, the unconditional read-out noise level of 9 ×10-3 photons is dominated by atomic fluorescence, and for input pulses containing on average μ1=0.27 (4 ) photons, the signal to noise level would be unity.
Quantum non-demolition detection of single microwave photons in a circuit
Johnson, B. R.; Reed, M. D.; Houck, A. A.; Schuster, D. I.; Bishop, Lev S.; Ginossar, E.; Gambetta, J. M.; Dicarlo, L.; Frunzio, L.; Girvin, S. M.; Schoelkopf, R. J.
2010-09-01
Thorough control of quantum measurement is key to the development of quantum information technologies. Many measurements are destructive, removing more information from the system than they obtain. Quantum non-demolition (QND) measurements allow repeated measurements that give the same eigenvalue. They could be used for several quantum information processing tasks such as error correction, preparation by measurement and one-way quantum computing. Achieving QND measurements of photons is especially challenging because the detector must be completely transparent to the photons while still acquiring information about them. Recent progress in manipulating microwave photons in superconducting circuits has increased demand for a QND detector that operates in the gigahertz frequency range. Here we demonstrate a QND detection scheme that measures the number of photons inside a high-quality-factor microwave cavity on a chip. This scheme maps a photon number, n, onto a qubit state in a single-shot by means of qubit-photon logic gates. We verify the operation of the device for n=0 and 1 by analysing the average correlations of repeated measurements, and show that it is 90% QND. It differs from previously reported detectors because its sensitivity is strongly selective to chosen photon number states. This scheme could be used to monitor the state of a photon-based memory in a quantum computer.
Quantum walks, quantum gates, and quantum computers
International Nuclear Information System (INIS)
Hines, Andrew P.; Stamp, P. C. E.
2007-01-01
The physics of quantum walks on graphs is formulated in Hamiltonian language, both for simple quantum walks and for composite walks, where extra discrete degrees of freedom live at each node of the graph. It is shown how to map between quantum walk Hamiltonians and Hamiltonians for qubit systems and quantum circuits; this is done for both single-excitation and multiexcitation encodings. Specific examples of spin chains, as well as static and dynamic systems of qubits, are mapped to quantum walks, and walks on hyperlattices and hypercubes are mapped to various gate systems. We also show how to map a quantum circuit performing the quantum Fourier transform, the key element of Shor's algorithm, to a quantum walk system doing the same. The results herein are an essential preliminary to a Hamiltonian formulation of quantum walks in which coupling to a dynamic quantum environment is included
Quantum-field theories as representations of a single $^\\ast$-algebra
Raab, Andreas
2013-01-01
We show that many well-known quantum field theories emerge as representations of a single $^\\ast$-algebra. These include free quantum field theories in flat and curved space-times, lattice quantum field theories, Wightman quantum field theories, and string theories. We prove that such theories can be approximated on lattices, and we give a rigorous definition of the continuum limit of lattice quantum field theories.
Quantum Flexoelectricity in Low Dimensional Systems
Kalinin, Sergei V.; Meunien, Vincent
2007-01-01
Symmetry breaking at surfaces and interfaces and the capability to support large strain gradients in nanoscale systems enable new forms of electromechanical coupling. Here we introduce the concept of quantum flexoelectricity, a phenomenon that is manifested when the mechanical deformation of non-polar quantum systems results in the emergence of net dipole moments and hence linear electromechanical coupling proportional to local curvature. The concept is illustrated in carbon systems, includin...
Limit cycles in quantum systems
Energy Technology Data Exchange (ETDEWEB)
Niemann, Patrick
2015-04-27
In this thesis we investigate Limit Cycles in Quantum Systems. Limit cycles are a renormalization group (RG) topology. When degrees of freedom are integrated out, the coupling constants flow periodically in a closed curve. The presence of limit cycles is restricted by the necessary condition of discrete scale invariance. A signature of discrete scale invariance and limit cycles is log-periodic behavior. The first part of this thesis is concerned with the study of limit cycles with the similarity renormalization group (SRG). Limit cycles are mainly investigated within conventional renormalization group frameworks, where degrees of freedom, which are larger than a given cutoff, are integrated out. In contrast, in the SRG potentials are unitarily transformed and thereby obtain a band-diagonal structure. The width of the band structure can be regarded as an effective cutoff. We investigate the appearance of limit cycles in the SRG evolution. Our aim is to extract signatures as well as the scaling factor of the limit cycle. We consider the 1/R{sup 2}-potential in a two-body system and a three-body system with large scattering lengths. Both systems display a limit cycle. Besides the frequently used kinetic energy generator we apply the exponential and the inverse generator. In the second part of this thesis, Limit Cycles at Finite Density, we examine the pole structure of the scattering amplitude for distinguishable fermions at zero temperature in the medium. Unequal masses and a filled Fermi sphere for each fermion species are considered. We focus on negative scattering lengths and the unitary limit. The properties of the three-body spectrum in the medium and implications for the phase structure of ultracold Fermi gases are discussed.
Lateral photocurrent spreading in single quantum well infrared photodetectors
Ershov, Maxim
1998-01-01
Lateral physical effects in single quantum well infrared photodetectors (SQWIPs) under non-uniform illumination over detector area are considered. These effects are due mainly to the in-plane transport of the photoinduced charge in the QW. The length of the lateral photocurrent spreading is determined by the in-plane conductivity of the carriers in the QW and characteristic time of the QW recharging, and can be as large as 10-10000 mkm. Closed-form analytical expressions for SQWIP responsivit...
Song, Xuerui; Wang, Liujun; Feng, Fupan; Lou, Liren; Diao, Wenting; Duan, Chongdi
2018-03-01
Developing gyroscopes based on quantum systems are important for inertial sensing applications, and its underlying physics is of fundamental interest. In this paper, we proposed a new type of gyroscope based on the Berry phase generated during rotation of the quantum system by using a single 13C nuclear spin coupled with a nearby nitrogen-vacancy center in diamond. Due to the atom-scale size of the quantum system, rotation information can be obtained with high spatial resolution. The gyroscope can be manipulated at room temperature and without the need for a strong magnetic field, which is also beneficial to its further applications.
Computer-automated tuning of semiconductor double quantum dots into the single-electron regime
Energy Technology Data Exchange (ETDEWEB)
Baart, T. A.; Vandersypen, L. M. K. [QuTech, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Eendebak, P. T. [QuTech, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Netherlands Organisation for Applied Scientific Research (TNO), P.O. Box 155, 2600 AD Delft (Netherlands); Reichl, C.; Wegscheider, W. [Solid State Physics Laboratory, ETH Zürich, 8093 Zürich (Switzerland)
2016-05-23
We report the computer-automated tuning of gate-defined semiconductor double quantum dots in GaAs heterostructures. We benchmark the algorithm by creating three double quantum dots inside a linear array of four quantum dots. The algorithm sets the correct gate voltages for all the gates to tune the double quantum dots into the single-electron regime. The algorithm only requires (1) prior knowledge of the gate design and (2) the pinch-off value of the single gate T that is shared by all the quantum dots. This work significantly alleviates the user effort required to tune multiple quantum dot devices.
International Nuclear Information System (INIS)
Zhu, Ka-Di; Li, Wai-Sang
2003-01-01
The quantum coherent oscillations in a coherently driven quantum dot-cavity system with the presence of strong exciton-phonon interactions are investigated theoretically in a fully quantum treatment. It is shown that even at zero temperature, the strong exciton-phonon interactions still affect the quantum coherent oscillations significantly
Stabilization of classic and quantum systems
International Nuclear Information System (INIS)
Buts, V.A.
2012-01-01
It is shown that the mechanism of quantum whirligig can be successfully used for stabilization of classical systems. In particular, the conditions for stabilization of charged particles and radiation fluxes in plasma are found.
Higher-order spin and charge dynamics in a quantum dot-lead hybrid system.
Otsuka, Tomohiro; Nakajima, Takashi; Delbecq, Matthieu R; Amaha, Shinichi; Yoneda, Jun; Takeda, Kenta; Allison, Giles; Stano, Peter; Noiri, Akito; Ito, Takumi; Loss, Daniel; Ludwig, Arne; Wieck, Andreas D; Tarucha, Seigo
2017-09-22
Understanding the dynamics of open quantum systems is important and challenging in basic physics and applications for quantum devices and quantum computing. Semiconductor quantum dots offer a good platform to explore the physics of open quantum systems because we can tune parameters including the coupling to the environment or leads. Here, we apply the fast single-shot measurement techniques from spin qubit experiments to explore the spin and charge dynamics due to tunnel coupling to a lead in a quantum dot-lead hybrid system. We experimentally observe both spin and charge time evolution via first- and second-order tunneling processes, and reveal the dynamics of the spin-flip through the intermediate state. These results enable and stimulate the exploration of spin dynamics in dot-lead hybrid systems, and may offer useful resources for spin manipulation and simulation of open quantum systems.
Thermalization and its mechanism for generic isolated quantum systems.
Rigol, Marcos; Dunjko, Vanja; Olshanii, Maxim
2008-04-17
An understanding of the temporal evolution of isolated many-body quantum systems has long been elusive. Recently, meaningful experimental studies of the problem have become possible, stimulating theoretical interest. In generic isolated systems, non-equilibrium dynamics is expected to result in thermalization: a relaxation to states in which the values of macroscopic quantities are stationary, universal with respect to widely differing initial conditions, and predictable using statistical mechanics. However, it is not obvious what feature of many-body quantum mechanics makes quantum thermalization possible in a sense analogous to that in which dynamical chaos makes classical thermalization possible. For example, dynamical chaos itself cannot occur in an isolated quantum system, in which the time evolution is linear and the spectrum is discrete. Some recent studies even suggest that statistical mechanics may give incorrect predictions for the outcomes of relaxation in such systems. Here we demonstrate that a generic isolated quantum many-body system does relax to a state well described by the standard statistical-mechanical prescription. Moreover, we show that time evolution itself plays a merely auxiliary role in relaxation, and that thermalization instead happens at the level of individual eigenstates, as first proposed by Deutsch and Srednicki. A striking consequence of this eigenstate-thermalization scenario, confirmed for our system, is that knowledge of a single many-body eigenstate is sufficient to compute thermal averages-any eigenstate in the microcanonical energy window will do, because they all give the same result.
Realization of electrically tunable single quantum dot nanocavities
Energy Technology Data Exchange (ETDEWEB)
Hofbauer, Felix Florian Georg
2009-03-15
We investigated the design, fabrication and optical investigation of electrically tunable single quantum dot-photonic crystal defect nanocavities operating in both the weak and strong coupling regimes of the light matter interaction. We demonstrate that the quantum confined Stark effect can be employed to quickly and reversibly switch the dot-cavity coupling, simply by varying a gate voltage. Our results show that exciton transitions from individual dots can be tuned by up to {proportional_to}4 meV relative to the nanocavity mode, before the emission quenches due to carrier tunneling escape from the dots. We directly probe spontaneous emission, irreversible polariton decay and the statistics of the emitted photons from a single-dot nanocavity in the weak and strong coupling regimes. New information is obtained on the nature of the dot-cavity coupling in the weak coupling regime and electrical control of zero dimensional polaritons is demonstrated for the first time. The structures investigated are p-i-n photodiodes consisting of an 180nm thick free-standing GaAs membrane into which a two dimensional photonic crystal is formed by etching a triangular lattice of air holes. Low mode volume nanocavities (V{sub mode}<1.6 ({lambda}/n){sup 3}) are realized by omitting 3 holes in a line to form L3 cavities and a single layer of InGaAs self-assembled quantum dots is embedded into the midpoint of the membrane. The nanocavities are electrically contacted via 35 nm thick p- and n-doped contact layers in the GaAs membrane. In the weak coupling regime, time resolved spectroscopy reveals a {proportional_to}7 x shortening of the spontaneous emission lifetime as the dot is tuned through the nanocavity mode, due to the Purcell effect. Upon strongly detuning the same quantum dot transition from the nanocavity mode we observe an additional {proportional_to}8 x lengthening of the spontaneous emission lifetime. These observations unequivocally highlight two regimes of dot
Exotic Quantum Order in Low-Dimensional Systems
Girvin, Steven M.
1997-01-01
Strongly correlated quantum systems in low dimensions often exhibit novel quantum ordering. This ordering is sometimes hidden and can be revealed only by examining new `dual' types of correlations. Such ordering leads to novel collective modes and fractional quantum numbers. Examples will be presented from quantum spin chains and the quantum Hall effect.
CIME School on Quantum Many Body Systems
Rivasseau, Vincent; Solovej, Jan Philip; Spencer, Thomas
2012-01-01
The book is based on the lectures given at the CIME school "Quantum many body systems" held in the summer of 2010. It provides a tutorial introduction to recent advances in the mathematics of interacting systems, written by four leading experts in the field: V. Rivasseau illustrates the applications of constructive Quantum Field Theory to 2D interacting electrons and their relation to quantum gravity; R. Seiringer describes a proof of Bose-Einstein condensation in the Gross-Pitaevski limit and explains the effects of rotating traps and the emergence of lattices of quantized vortices; J.-P. Solovej gives an introduction to the theory of quantum Coulomb systems and to the functional analytic methods used to prove their thermodynamic stability; finally, T. Spencer explains the supersymmetric approach to Anderson localization and its relation to the theory of random matrices. All the lectures are characterized by their mathematical rigor combined with physical insights.
Chen, Dong-Xu; Liu, Rui-Feng; Zhang, Pei; Li, Hong-Rong; Gao, Hong; Li, Fu-Li
2013-11-01
We report an experimental proposal of quantum key distribution without sharing reference frame by using single photon rotational-invariant subspace. The rotational-invariant subspace is achieved by taking advantage of photon's spin-orbital composite states. Our scheme is simple and can be developed as a compact QKD system under current technology. Earth-to-satellite QKD is an emerging scenario that will benefit from our protocol.
Extracting random numbers from quantum tunnelling through a single diode.
Bernardo-Gavito, Ramón; Bagci, Ibrahim Ethem; Roberts, Jonathan; Sexton, James; Astbury, Benjamin; Shokeir, Hamzah; McGrath, Thomas; Noori, Yasir J; Woodhead, Christopher S; Missous, Mohamed; Roedig, Utz; Young, Robert J
2017-12-19
Random number generation is crucial in many aspects of everyday life, as online security and privacy depend ultimately on the quality of random numbers. Many current implementations are based on pseudo-random number generators, but information security requires true random numbers for sensitive applications like key generation in banking, defence or even social media. True random number generators are systems whose outputs cannot be determined, even if their internal structure and response history are known. Sources of quantum noise are thus ideal for this application due to their intrinsic uncertainty. In this work, we propose using resonant tunnelling diodes as practical true random number generators based on a quantum mechanical effect. The output of the proposed devices can be directly used as a random stream of bits or can be further distilled using randomness extraction algorithms, depending on the application.
Storing single photons emitted by a quantum memory on a highly excited Rydberg state.
Distante, Emanuele; Farrera, Pau; Padrón-Brito, Auxiliadora; Paredes-Barato, David; Heinze, Georg; de Riedmatten, Hugues
2017-01-19
Strong interaction between two single photons is a long standing and important goal in quantum photonics. This would enable a new regime of nonlinear optics and unlock several applications in quantum information science, including photonic quantum gates and deterministic Bell-state measurements. In the context of quantum networks, it would be important to achieve interactions between single photons from independent photon pairs storable in quantum memories. So far, most experiments showing nonlinearities at the single-photon level have used weak classical input light. Here we demonstrate the storage and retrieval of a paired single photon emitted by an ensemble quantum memory in a strongly nonlinear medium based on highly excited Rydberg atoms. We show that nonclassical correlations between the two photons persist after retrieval from the Rydberg ensemble. Our result is an important step towards deterministic photon-photon interactions, and may enable deterministic Bell-state measurements with multimode quantum memories.
Marshman, Emily; Singh, Chandralekha
2017-06-01
Single photon experiments involving a Mach-Zehnder interferometer can illustrate the fundamental principles of quantum mechanics, e.g., the wave-particle duality of a single photon, single photon interference, and the probabilistic nature of quantum measurement involving single photons. These experiments explicitly make the connection between the abstract quantum theory and concrete laboratory settings and have the potential to help students develop a solid grasp of the foundational issues in quantum mechanics. Here we describe students' conceptual difficulties with these topics in the context of Mach-Zehnder interferometer experiments with single photons and how the difficulties found in written surveys and individual interviews were used as a guide in the development of a Quantum Interactive Learning Tutorial (QuILT). The QuILT uses an inquiry-based approach to learning and takes into account the conceptual difficulties found via research to help upper-level undergraduate and graduate students learn about foundational quantum mechanics concepts using the concrete quantum optics context. It strives to help students learn the basics of quantum mechanics in the context of single photon experiment, develop the ability to apply fundamental quantum principles to experimental situations in quantum optics, and explore the differences between classical and quantum ideas in a concrete context. We discuss the findings from in-class evaluations suggesting that the QuILT was effective in helping students learn these abstract concepts.
Noise management to achieve superiority in quantum information systems
Nemoto, Kae; Devitt, Simon; Munro, William J.
2017-06-01
Quantum information systems are expected to exhibit superiority compared with their classical counterparts. This superiority arises from the quantum coherences present in these quantum systems, which are obviously absent in classical ones. To exploit such quantum coherences, it is essential to control the phase information in the quantum state. The phase is analogue in nature, rather than binary. This makes quantum information technology fundamentally different from our classical digital information technology. In this paper, we analyse error sources and illustrate how these errors must be managed for the system to achieve the required fidelity and a quantum superiority. This article is part of the themed issue 'Quantum technology for the 21st century'.
Quantum system lifetimes and measurement perturbations
International Nuclear Information System (INIS)
Najakov, E.
1977-05-01
The recently proposed description of quantum system decay in terms of repeated measurement perturbations is modified. The possibility of retarded reductions to a unique quantum state, due to ineffective localization of the decay products at initial time measurements, is simply taken into account. The exponential decay law is verified again. A modified equation giving the observed lifetime in terms of unperturbed quantum decay law, measurement frequency and reduction law is derived. It predicts deviations of the observed lifetime from the umperturbed one, together with a dependence on experimental procedures. The influence of different model unperturbed decay laws and reduction laws on this effect is studied
Single ion impact detection and scanning probe aligned ion implantation for quantum bit formation
International Nuclear Information System (INIS)
Weis, Christoph D.
2011-01-01
Quantum computing and quantum information processing is a promising path to replace classical information processing via conventional computers which are approaching fundamental physical limits. Instead of classical bits, quantum bits (qubits) are utilized for computing operations. Due to quantum mechanical phenomena such as superposition and entanglement, a completely different way of information processing is achieved, enabling enhanced performance for certain problem sets. Various proposals exist on how to realize a quantum bit. Among them are electron or nuclear spins of defect centers in solid state systems. Two such candidates with spin degree of freedom are single donor atoms in silicon and nitrogen vacancy (NV) defect centers in diamond. Both qubit candidates possess extraordinary qualities which makes them promising building blocks. Besides certain advantages, the qubits share the necessity to be placed precisely in their host materials and device structures. A commonly used method is to introduce the donor atoms into the substrate materials via ion implantation. For this, focused ion beam systems can be used, or collimation techniques as in this work. A broad ion beam hits the back of a scanning probe microscope (SPM) cantilever with incorporated apertures. The high resolution imaging capabilities of the SPM allows the non destructive location of device areas and the alignment of the cantilever and thus collimated ion beam spot to the desired implant locations. In this work, this technique is explored, applied and pushed forward to meet necessary precision requirements. The alignment of the ion beam to surface features, which are sensitive to ion impacts and thus act as detectors, is demonstrated. The technique is also used to create NV center arrays in diamond substrates. Further, single ion impacts into silicon device structures are detected which enables deliberate single ion doping.
Single ion impact detection and scanning probe aligned ion implantation for quantum bit formation
Energy Technology Data Exchange (ETDEWEB)
Weis, Christoph D.
2011-10-04
Quantum computing and quantum information processing is a promising path to replace classical information processing via conventional computers which are approaching fundamental physical limits. Instead of classical bits, quantum bits (qubits) are utilized for computing operations. Due to quantum mechanical phenomena such as superposition and entanglement, a completely different way of information processing is achieved, enabling enhanced performance for certain problem sets. Various proposals exist on how to realize a quantum bit. Among them are electron or nuclear spins of defect centers in solid state systems. Two such candidates with spin degree of freedom are single donor atoms in silicon and nitrogen vacancy (NV) defect centers in diamond. Both qubit candidates possess extraordinary qualities which makes them promising building blocks. Besides certain advantages, the qubits share the necessity to be placed precisely in their host materials and device structures. A commonly used method is to introduce the donor atoms into the substrate materials via ion implantation. For this, focused ion beam systems can be used, or collimation techniques as in this work. A broad ion beam hits the back of a scanning probe microscope (SPM) cantilever with incorporated apertures. The high resolution imaging capabilities of the SPM allows the non destructive location of device areas and the alignment of the cantilever and thus collimated ion beam spot to the desired implant locations. In this work, this technique is explored, applied and pushed forward to meet necessary precision requirements. The alignment of the ion beam to surface features, which are sensitive to ion impacts and thus act as detectors, is demonstrated. The technique is also used to create NV center arrays in diamond substrates. Further, single ion impacts into silicon device structures are detected which enables deliberate single ion doping.
Energy Technology Data Exchange (ETDEWEB)
Song, Guo-Zhu; Zhang, Mei; Ai, Qing; Yang, Guo-Jian [Department of Physics, Applied Optics Beijing Area Major Laboratory, Beijing Normal University, Beijing 100875 (China); Alsaedi, Ahmed; Hobiny, Aatef [NAAM-Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589 (Saudi Arabia); Deng, Fu-Guo, E-mail: fgdeng@bnu.edu.cn [Department of Physics, Applied Optics Beijing Area Major Laboratory, Beijing Normal University, Beijing 100875 (China); NAAM-Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589 (Saudi Arabia)
2017-03-15
We propose a heralded quantum repeater based on the scattering of photons off single emitters in one-dimensional waveguides. We show the details by implementing nonlocal entanglement generation, entanglement swapping, and entanglement purification modules with atoms in waveguides, and discuss the feasibility of the repeater with currently achievable technology. In our scheme, the faulty events can be discarded by detecting the polarization of the photons. That is, our protocols are accomplished with a fidelity of 100% in principle, which is advantageous for implementing realistic long-distance quantum communication. Moreover, additional atomic qubits are not required, but only a single-photon medium. Our scheme is scalable and attractive since it can be realized in solid-state quantum systems. With the great progress on controlling atom-waveguide systems, the repeater may be very useful in quantum information processing in the future.
Note on quantum groups and integrable systems
Popolitov, A.
2016-01-01
The free-field formalism for quantum groups [preprint ITEP-M3/94, CRM-2202 hep-th/9409093] provides a special choice of coordinates on a quantum group. In these coordinates the construction of associated integrable system [arXiv:1207.1869] is especially simple. This choice also fits into general framework of cluster varieties [math.AG/0311245]—natural changes in coordinates are cluster mutations.
Single photon emission and quantum ring-cavity coupling in InAs/GaAs quantum rings
Energy Technology Data Exchange (ETDEWEB)
Gallardo, E; Nowak, A K; Sanvitto, D; Meulen, H P van der; Calleja, J M [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); MartInez, L J; Prieto, I; Alija, A R; Granados, D; Taboada, A G; GarcIa, J M; Postigo, P A [Instituto de Microelectronica de Madrid, Centro Nacional de MicrotecnologIa, CSIC, Isaac Newton 8, PTM Tres Cantos, E-28760 Madrid (Spain); Sarkar, D, E-mail: eva.gallardo@uam.e [Department of Physics and Astronomy, University of Sheffield, S3 7RH (United Kingdom)
2010-02-01
Different InAs/GaAs quantum rings embedded in a photonic crystal microcavity are studied by quantum correlation measurements. Single photon emission, with g{sup (2)}(0) values around 0.3, is demonstrated for a quantum ring not coupled to the microcavity. Characteristic rise-times are found to be longer for excitons than for biexcitons, resulting in the time asymmetry of the exciton-biexciton cross-correlation. No antibunching is observed in another quantum ring weakly coupled to the microcavity.
Quantum State Restoration and Single-Copy Tomography for Ground States of Hamiltonians
Farhi, Edward; Gosset, David; Hassidim, Avinatan; Lutomirski, Andrew; Nagaj, Daniel; Shor, Peter
2010-11-01
Given a single copy of an unknown quantum state, the no-cloning theorem limits the amount of information that can be extracted from it. Given a gapped Hamiltonian, in most situations it is impractical to compute properties of its ground state, even though in principle all the information about the ground state is encoded in the Hamiltonian. We show in this Letter that if you know the Hamiltonian of a system and have a single copy of its ground state, you can use a quantum computer to efficiently compute its local properties. Specifically, in this scenario, we give efficient algorithms that copy small subsystems of the state and estimate the full statistics of any local measurement.
Controlling speedup in open quantum systems through manipulation of system-reservoir bound states
Behzadi, N.; Ahansaz, B.; Ektesabi, A.; Faizi, E.
2017-05-01
In this paper, we give a mechanism for controlling speedup of a single-qubit open quantum system by exclusively manipulating the system-reservoir bound states using additional noninteracting qubits. It is demonstrated that providing stronger bound states in the system-reservoir spectrum makes the single qubit evolve with higher speed. We examine the performance of the mechanism for different spectral densities such as Lorentzian and ohmic and find out the decisive role of bound states' manipulation in the speeding up of quantum evolution.
Poly-silicon quantum-dot single-electron transistors
International Nuclear Information System (INIS)
Kang, Kwon-Chil; Lee, Joung-Eob; Lee, Jung-Han; Lee, Jong-Ho; Shin, Hyung-Cheol; Park, Byung-Gook
2012-01-01
For operation of a single-electron transistors (SETs) at room temperature, we proposed a fabrication method for a SET with a self-aligned quantum dot by using polycrystalline silicon (poly-Si). The self-aligned quantum dot is formed by the selective etching of a silicon nanowire on a planarized surface and the subsequent deposition and etch-back of poly-silicon or chemical mechanical polishing (CMP). The two tunneling barriers of the SET are fabricated by thermal oxidation. Also, to decrease the leakage current and control the gate capacitance, we deposit a hard oxide mask layer. The control gate is formed by using an electron beam and photolithography on chemical vapor deposition (CVD). Owing to the small capacitance of the narrow control gate due to the tetraethyl orthosilicate (TEOS) hard mask, we observe clear Coulomb oscillation peaks and differential trans-conductance curves at room temperature. The clear oscillation period of the fabricated SET is 2.0 V.
Multi-state discrimination below the quantum noise limit at the single-photon level
Ferdinand, A. R.; DiMario, M. T.; Becerra, F. E.
2017-10-01
Measurements approaching the ultimate quantum limits of sensitivity are central in quantum information processing, quantum metrology, and communication. Quantum measurements to discriminate multiple states at the single-photon level are essential for optimizing information transfer in low-power optical communications and quantum communications, and can enhance the capabilities of many quantum information protocols. Here, we theoretically investigate and experimentally demonstrate the discrimination of multiple coherent states of light with sensitivities surpassing the quantum noise limit (QNL) at the single-photon level under realistic conditions of loss and noise based on strategies implementing globally-optimized adaptive measurements with single photon counting and displacement operations. These discrimination strategies can provide realistic advantages to enhance information transfer at low powers, and are compatible with photon number resolving detection, which provides robustness at high powers, thus allowing for surpassing the QNL at arbitrary input power levels under realistic conditions.
Efficient fiber-coupled single-photon sources based on quantum dots
DEFF Research Database (Denmark)
Daveau, Raphaël Sura
This thesis presents the study of solid-state quantum emitters in two dierent forms. The rst part of the thesis deals with quantum dot based single-photon sources with an emphasis on ecient photon extraction into an optical ber. The second part of the thesis covers a theoretical study of optical...... 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...... the characterization of single quantum dots. The second method, evanescent coupling from a tapered waveguide to a microber, demonstrates a chip-to-ber coupling eciency exceeding 80 % in passive re- ection measurements. The characterization of quantum dots from this device establishes a ber-coupled source eciency of 15...
Quantum Tunneling of Magnetization in Trigonal Single-Molecule Magnets
Liu, Junjie; Del Barco, Enrique; Hill, Stephen
2012-02-01
We perform a numerical analysis of the quantum tunneling of magnetization (QTM) that occurs in a spin S = 6 single-molecule magnet (SMM) with idealized C3 symmetry. The deconstructive points in the QTM are located by following the Berry-phase interference (BPI) oscillations. We find that the O4^3 (=12[Sz,S+^3 +S-^3 ]) operator unfreezes odd-k QTM resonances and generates three-fold patterns of BPI minima in all resonances, including k = 0! This behavior cannot be reproduced with operators that possess even rotational symmetry about the quantization axis. We find also that the k = 0 BPI minima shift away from zero longitudinal field. The wider implications of these results will be discussed in terms of the QTM behavior observed in other SMMs.
Full counting statistics of a single-molecule quantum dot
Dong, Bing; Ding, G. H.; Lei, X. L.
2013-08-01
We investigate the full counting statistics of a single quantum dot strongly coupled to a local phonon and weakly tunnel connected to two metallic electrodes. By employing the generalized nonequilibrium Green-function method and the Lang-Firsov transformation, we derive an explicit analytical formula for the cumulant generating function, which makes one able to identify distinctly the elastic and inelastic contributions to the current and zero-frequency shot noise. We find that at zero temperature, the inelastic effect causes upward steps in the current and downward jumps in the noise at the bias voltages corresponding to the opening of the inelastic channels, which are ascribed to the vibration-induced complex dependencies of electronic self-energies on the energy and bias voltage. More interestingly, the Fano factor exhibits oscillatory behavior with increasing bias voltage and its minimum value is observed to be smaller than one-half.
On the Velocity of Moving Relativistic Unstable Quantum Systems
Directory of Open Access Journals (Sweden)
K. Urbanowski
2015-01-01
Full Text Available We study properties of moving relativistic quantum unstable systems. We show that in contrast to the properties of classical particles and quantum stable objects the velocity of freely moving relativistic quantum unstable systems cannot be constant in time. We show that this new quantum effect results from the fundamental principles of the quantum theory and physics: it is a consequence of the principle of conservation of energy and of the fact that the mass of the quantum unstable system is not defined. This effect can affect the form of the decay law of moving relativistic quantum unstable systems.
Incoherent control of locally controllable quantum systems
International Nuclear Information System (INIS)
Dong Daoyi; Zhang Chenbin; Rabitz, Herschel; Pechen, Alexander; Tarn, T.-J.
2008-01-01
An incoherent control scheme for state control of locally controllable quantum systems is proposed. This scheme includes three steps: (1) amplitude amplification of the initial state by a suitable unitary transformation, (2) projective measurement of the amplified state, and (3) final optimization by a unitary controlled transformation. The first step increases the amplitudes of some desired eigenstates and the corresponding probability of observing these eigenstates, the second step projects, with high probability, the amplified state into a desired eigenstate, and the last step steers this eigenstate into the target state. Within this scheme, two control algorithms are presented for two classes of quantum systems. As an example, the incoherent control scheme is applied to the control of a hydrogen atom by an external field. The results support the suggestion that projective measurements can serve as an effective control and local controllability information can be used to design control laws for quantum systems. Thus, this scheme establishes a subtle connection between control design and controllability analysis of quantum systems and provides an effective engineering approach in controlling quantum systems with partial controllability information.
The Geometric Phase in Quantum Systems
International Nuclear Information System (INIS)
Pascazio, S
2003-01-01
The discovery of the geometric phase is one of the most interesting and intriguing findings of the last few decades. It led to a deeper understanding of the concept of phase in quantum mechanics and motivated a surge of interest in fundamental quantum mechanical issues, disclosing unexpected applications in very diverse fields of physics. Although the key ideas underlying the existence of a purely geometrical phase had already been proposed in 1956 by Pancharatnam, it was Michael Berry who revived this issue 30 years later. The clarity of Berry's seminal paper, in 1984, was extraordinary. Research on the topic flourished at such a pace that it became difficult for non-experts to follow the many different theoretical ideas and experimental proposals which ensued. Diverse concepts in independent areas of mathematics, physics and chemistry were being applied, for what was (and can still be considered) a nascent arena for theory, experiments and technology. Although collections of papers by different authors appeared in the literature, sometimes with ample introductions, surprisingly, to the best of my knowledge, no specific and exhaustive book has ever been written on this subject. The Geometric Phase in Quantum Systems is the first thorough book on geometric phases and fills an important gap in the physical literature. Other books on the subject will undoubtedly follow. But it will take a fairly long time before other authors can cover that same variety of concepts in such a comprehensive manner. The book is enjoyable. The choice of topics presented is well balanced and appropriate. The appendices are well written, understandable and exhaustive - three rare qualities. I also find it praiseworthy that the authors decided to explicitly carry out most of the calculations, avoiding, as much as possible, the use of the joke 'after a straightforward calculation, one finds...' This was one of the sentences I used to dislike most during my undergraduate studies. A student is
Quantum Flexoelectricity in Low Dimensional Systems
Energy Technology Data Exchange (ETDEWEB)
Kalinin, Sergei V [ORNL; Meunier, Vincent [ORNL
2008-01-01
Symmetry breaking at surfaces and interfaces and the capability to support large strain gradients in nanoscale systems enable new forms of electromechanical coupling. Here we introduce the concept of quantum flexoelectricity, a phenomenon that is manifested when the mechanical deformation of non-polar quantum systems results in the emergence of net dipole moments and hence linear electromechanical coupling proportional to local curvature. The concept is illustrated in carbon systems, including polyacetylene and nano graphitic ribbons. Using density functional theory calculations for systems made of up to 400 atoms, we determine the flexoelectric coefficients to be of the order of ~ 0.1 e, in agreement with the prediction of linear theory. The implications of quantum flexoelectricity on electromechanical device applications, and physics of carbon based materials are discussed.
Nanoscale thermal imaging of dissipation in quantum systems.
Halbertal, D; Cuppens, J; Shalom, M Ben; Embon, L; Shadmi, N; Anahory, Y; Naren, H R; Sarkar, J; Uri, A; Ronen, Y; Myasoedov, Y; Levitov, L S; Joselevich, E; Geim, A K; Zeldov, E
2016-11-17
Energy dissipation is a fundamental process governing the dynamics of physical, chemical and biological systems. It is also one of the main characteristics that distinguish quantum from classical phenomena. In particular, in condensed matter physics, scattering mechanisms, loss of quantum information or breakdown of topological protection are deeply rooted in the intricate details of how and where the dissipation occurs. Yet the microscopic behaviour of a system is usually not formulated in terms of dissipation because energy dissipation is not a readily measurable quantity on the micrometre scale. Although nanoscale thermometry has gained much recent interest, existing thermal imaging methods are not sensitive enough for the study of quantum systems and are also unsuitable for the low-temperature operation that is required. Here we report a nano-thermometer based on a superconducting quantum interference device with a diameter of less than 50 nanometres that resides at the apex of a sharp pipette: it provides scanning cryogenic thermal sensing that is four orders of magnitude more sensitive than previous devices-below 1 μK Hz -1/2 . This non-contact, non-invasive thermometry allows thermal imaging of very low intensity, nanoscale energy dissipation down to the fundamental Landauer limit of 40 femtowatts for continuous readout of a single qubit at one gigahertz at 4.2 kelvin. These advances enable the observation of changes in dissipation due to single-electron charging of individual quantum dots in carbon nanotubes. They also reveal a dissipation mechanism attributable to resonant localized states in graphene encapsulated within hexagonal boron nitride, opening the door to direct thermal imaging of nanoscale dissipation processes in quantum matter.
Single-flux-quantum logic circuits exploiting collision-based fusion gates
International Nuclear Information System (INIS)
Asai, T.; Yamada, K.; Amemiya, Y.
2008-01-01
We propose a single-flux-quantum (SFQ) logic circuit based on the fusion computing systems--collision-based and reaction-diffusion fusion computers. A fusion computing system consists of regularly arrayed unit cells (fusion gates), where each unit has two input arms and two output arms and is connected to its neighboring cells with the arms. We designed functional SFQ circuits that implemented the fusion computation. The unit cell was able to be made with ten Josephson junctions. Circuit simulation with standard Nb/Al-AlOx/Nb 2.5-kA/cm 2 process parameters showed that the SFQ fusion computing systems could operate at 10 GHz clock
Quantum scaling in many-body systems
Continentino, Mucio A
2001-01-01
This book on quantum phase transitions has been written by one of the pioneers in the application of scaling ideas to many-body systems - a new and exciting subject that has relevance to many areas of condensed matter and theoretical physics. One of the few books on the subject, it emphasizes strongly correlated electronic systems. Although dealing with complex problems in statistical mechanics, it does not lose sight of the experiments and the actual physical systems which motivate the theoretical work. The book starts by presenting the scaling theory of quantum critical phenomena. Critical e
Compact quantum dots for single-molecule imaging.
Smith, Andrew M; Nie, Shuming
2012-10-09
Single-molecule imaging is an important tool for understanding the mechanisms of biomolecular function and for visualizing the spatial and temporal heterogeneity of molecular behaviors that underlie cellular biology (1-4). To image an individual molecule of interest, it is typically conjugated to a fluorescent tag (dye, protein, bead, or quantum dot) and observed with epifluorescence or total internal reflection fluorescence (TIRF) microscopy. While dyes and fluorescent proteins have been the mainstay of fluorescence imaging for decades, their fluorescence is unstable under high photon fluxes necessary to observe individual molecules, yielding only a few seconds of observation before complete loss of signal. Latex beads and dye-labeled beads provide improved signal stability but at the expense of drastically larger hydrodynamic size, which can deleteriously alter the diffusion and behavior of the molecule under study. Quantum dots (QDs) offer a balance between these two problematic regimes. These nanoparticles are composed of semiconductor materials and can be engineered with a hydrodynamically compact size with exceptional resistance to photodegradation (5). Thus in recent years QDs have been instrumental in enabling long-term observation of complex macromolecular behavior on the single molecule level. However these particles have still been found to exhibit impaired diffusion in crowded molecular environments such as the cellular cytoplasm and the neuronal synaptic cleft, where their sizes are still too large (4,6,7). Recently we have engineered the cores and surface coatings of QDs for minimized hydrodynamic size, while balancing offsets to colloidal stability, photostability, brightness, and nonspecific binding that have hindered the utility of compact QDs in the past (8,9). The goal of this article is to demonstrate the synthesis, modification, and characterization of these optimized nanocrystals, composed of an alloyed HgxCd1-xSe core coated with an
Quantum fluctuations and coherence in high-precision single-electron capture.
Kashcheyevs, Vyacheslavs; Timoshenko, Janis
2012-11-21
The phase of a single quantum state is undefined unless the history of its creation provides a reference point. Thus, quantum interference may seem hardly relevant for the design of deterministic single-electron sources which strive to isolate individual charge carriers quickly and completely. We provide a counterexample by analyzing the nonadiabatic separation of a localized quantum state from a Fermi sea due to a closing tunnel barrier. We identify the relevant energy scales and suggest ways to separate the contributions of quantum nonadiabatic excitation and back tunneling to the rare noncapture events. In the optimal regime of balanced decay and nonadiabaticity, our simple electron trap turns into a single-lead Landau-Zener back tunneling interferometer, revealing the dynamical phase accumulated between the particle capture and leakage. The predicted "quantum beats in back tunneling" may turn the error of a single-electron source into a valuable signal revealing essentially nonadiabatic energy scales of a dynamic quantum dot.
Tomograms for open quantum systems: In(finite) dimensional optical and spin systems
International Nuclear Information System (INIS)
Thapliyal, Kishore; Banerjee, Subhashish; Pathak, Anirban
2016-01-01
Tomograms are obtained as probability distributions and are used to reconstruct a quantum state from experimentally measured values. We study the evolution of tomograms for different quantum systems, both finite and infinite dimensional. In realistic experimental conditions, quantum states are exposed to the ambient environment and hence subject to effects like decoherence and dissipation, which are dealt with here, consistently, using the formalism of open quantum systems. This is extremely relevant from the perspective of experimental implementation and issues related to state reconstruction in quantum computation and communication. These considerations are also expected to affect the quasiprobability distribution obtained from experimentally generated tomograms and nonclassicality observed from them. -- Highlights: •Tomograms are constructed for open quantum systems. •Finite and infinite dimensional quantum systems are studied. •Finite dimensional systems (phase states, single & two qubit spin states) are studied. •A dissipative harmonic oscillator is considered as an infinite dimensional system. •Both pure dephasing as well as dissipation effects are studied.
Studies of quantum levels in GaInNAs single quantum wells
International Nuclear Information System (INIS)
Shirakata, Sho; Kondow, Masahiko; Kitatani, Takeshi
2006-01-01
Spectroscopic studies have been carried out on the quantum levels in GaInNAs/GaAs single quantum wells (SQWs). Photoluminescence (PL), PL excitation (PLE), photoreflectance (PR), and high-density-excited PL (HDE-PL) were measured on high quality GaInNAs SQWs, Ga 0.65 In 0.35 N 0.01 As 0.99 /GaAs (well thickness: l z =10 nm) and Ga 0.65 In 0.35 N 0.005 As 0.995 /GaAs (l z =3∝10 nm), grown by molecular-beam epitaxy. For Ga 0.65 In 0.35 N 0.01 As 0.99 /GaAs (l z =10 nm), PL at 8 K exhibited a peak at 1.07 eV due to the exciton-related transition between quantum levels of ground states (e1-hh1). Both PR and PLE exhibited three transitions (1.17, 1.20 and 1.32 eV), and the former two transitions were assigned to as either of e1-lh1 and e2-hh2 transitions, while the transition at 1.32 eV was assigned to as the e2-lh2 transition. For HDE-PL, a new PL peak was observed at about 1.2 eV, and it was assigned to the unresolved e1-lh1 and e2-hh2 transitions. Similar optical measurements have been done on the Ga 0.65 In 0.35 N 0.005 As 0.995 /GaAs with various l z (3∝10 nm). Dependence of optical spectra and energies of quantum levels on l z have been studied. It has been found that HDE-PL in combination with PLE is a good tool for the study of the quantum level of GaInNAs SQW. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (Abstract Copyright [2006], Wiley Periodicals, Inc.)
Adiabatic Theorem for Quantum Spin Systems
Bachmann, S.; De Roeck, W.; Fraas, M.
2017-08-01
The first proof of the quantum adiabatic theorem was given as early as 1928. Today, this theorem is increasingly applied in a many-body context, e.g., in quantum annealing and in studies of topological properties of matter. In this setup, the rate of variation ɛ of local terms is indeed small compared to the gap, but the rate of variation of the total, extensive Hamiltonian, is not. Therefore, applications to many-body systems are not covered by the proofs and arguments in the literature. In this Letter, we prove a version of the adiabatic theorem for gapped ground states of interacting quantum spin systems, under assumptions that remain valid in the thermodynamic limit. As an application, we give a mathematical proof of Kubo's linear response formula for a broad class of gapped interacting systems. We predict that the density of nonadiabatic excitations is exponentially small in the driving rate and the scaling of the exponent depends on the dimension.
Criticality and entanglement in random quantum systems
International Nuclear Information System (INIS)
Refael, G; Moore, J E
2009-01-01
We review studies of entanglement entropy in systems with quenched randomness, concentrating on universal behavior at strongly random quantum critical points. The disorder-averaged entanglement entropy provides insight into the quantum criticality of these systems and an understanding of their relationship to non-random ('pure') quantum criticality. The entanglement near many such critical points in one dimension shows a logarithmic divergence in subsystem size, similar to that in the pure case but with a different universal coefficient. Such universal coefficients are examples of universal critical amplitudes in a random system. Possible measurements are reviewed along with the one-particle entanglement scaling at certain Anderson localization transitions. We also comment briefly on higher dimensions and challenges for the future.
Epidemic Dynamics in Open Quantum Spin Systems
Pérez-Espigares, Carlos; Marcuzzi, Matteo; Gutiérrez, Ricardo; Lesanovsky, Igor
2017-10-01
We explore the nonequilibrium evolution and stationary states of an open many-body system that displays epidemic spreading dynamics in a classical and a quantum regime. Our study is motivated by recent experiments conducted in strongly interacting gases of highly excited Rydberg atoms where the facilitated excitation of Rydberg states competes with radiative decay. These systems approximately implement open quantum versions of models for population dynamics or disease spreading where species can be in a healthy, infected or immune state. We show that in a two-dimensional lattice, depending on the dominance of either classical or quantum effects, the system may display a different kind of nonequilibrium phase transition. We moreover discuss the observability of our findings in laser driven Rydberg gases with particular focus on the role of long-range interactions.
Time dilation in quantum systems and decoherence
Pikovski, Igor; Zych, Magdalena; Costa, Fabio; Brukner, Časlav
2017-02-01
Both quantum mechanics and general relativity are based on principles that defy our daily intuitions, such as time dilation, quantum interference and entanglement. Because the regimes where the two theories are typically tested are widely separated, their foundational principles are rarely jointly studied. Recent works have found that novel phenomena appear for quantum particles with an internal structure in the presence of time dilation, which can take place at low energies and in weak gravitational fields. Here we briefly review the effects of time dilation on quantum interference and generalize the results to a variety of systems. In addition, we provide an extended study of the basic principles of quantum theory and relativity that are of relevance for the effects and also address several questions that have been raised, such as the description in different reference frames, the role of the equivalence principle and the effective irreversibility of the decoherence. The manuscript clarifies some of the counterintuitive aspects arising when quantum phenomena and general relativistic effects are jointly considered.
Time dilation in quantum systems and decoherence
International Nuclear Information System (INIS)
Pikovski, Igor; Zych, Magdalena; Costa, Fabio; Brukner, Časlav
2017-01-01
Both quantum mechanics and general relativity are based on principles that defy our daily intuitions, such as time dilation, quantum interference and entanglement. Because the regimes where the two theories are typically tested are widely separated, their foundational principles are rarely jointly studied. Recent works have found that novel phenomena appear for quantum particles with an internal structure in the presence of time dilation, which can take place at low energies and in weak gravitational fields. Here we briefly review the effects of time dilation on quantum interference and generalize the results to a variety of systems. In addition, we provide an extended study of the basic principles of quantum theory and relativity that are of relevance for the effects and also address several questions that have been raised, such as the description in different reference frames, the role of the equivalence principle and the effective irreversibility of the decoherence. The manuscript clarifies some of the counterintuitive aspects arising when quantum phenomena and general relativistic effects are jointly considered. (paper)
Effective operator formalism for open quantum systems
DEFF Research Database (Denmark)
Reiter, Florentin; Sørensen, Anders Søndberg
2012-01-01
We present an effective operator formalism for open quantum systems. Employing perturbation theory and adiabatic elimination of excited states for a weakly driven system, we derive an effective master equation which reduces the evolution to the ground-state dynamics. The effective evolution...
Recent advances in quantum integrable systems
Energy Technology Data Exchange (ETDEWEB)
Amico, L.; Belavin, A.; Buffenoir, E.; Castro Alvaredo, A.; Caudrelier, V.; Chakrabarti, A.; Corrig, E.; Crampe, N.; Deguchi, T.; Dobrev, V.K.; Doikou, A.; Doyon, B.; Feher, L.; Fioravanti, D.; Gohmann, F.; Hallnas, M.; Jimbo, M.; Konno, N.C.H.; Korchemsky, G.; Kulish, P.; Lassalle, M.; Maillet, J.M.; McCoy, B.; Mintchev, M.; Pakuliak, S.; Quano, F.Y.Z.; Ragnisco, R.; Ravanini, F.; Rittenberg, V.; Rivasseau, V.; Rossi, M.; Satta, G.; Sedrakyan, T.; Shiraishi, J.; Suzuki, N.C.J.; Yamada, Y.; Zamolodchikov, A.; Ishimoto, Y.; Nagy, Z.; Posta, S.; Sedra, M.B.; Zuevskiy, A.; Gohmann, F
2005-07-01
This meeting was dedicated to different aspects of the theory of quantum integrable systems. The organizers have intended to concentrate on topics related to the study of correlation functions, to systems with boundaries and to models at roots of unity. This document gathers the abstracts of 32 contributions, most of the contributions are accompanied by the set of transparencies.
Recent advances in quantum integrable systems
International Nuclear Information System (INIS)
Amico, L.; Belavin, A.; Buffenoir, E.; Castro Alvaredo, A.; Caudrelier, V.; Chakrabarti, A.; Corrig, E.; Crampe, N.; Deguchi, T.; Dobrev, V.K.; Doikou, A.; Doyon, B.; Feher, L.; Fioravanti, D.; Gohmann, F.; Hallnas, M.; Jimbo, M.; Konno, N.C.H.; Korchemsky, G.; Kulish, P.; Lassalle, M.; Maillet, J.M.; McCoy, B.; Mintchev, M.; Pakuliak, S.; Quano, F.Y.Z.; Ragnisco, R.; Ravanini, F.; Rittenberg, V.; Rivasseau, V.; Rossi, M.; Satta, G.; Sedrakyan, T.; Shiraishi, J.; Suzuki, N.C.J.; Yamada, Y.; Zamolodchikov, A.; Ishimoto, Y.; Nagy, Z.; Posta, S.; Sedra, M.B.; Zuevskiy, A.; Gohmann, F.
2005-01-01
This meeting was dedicated to different aspects of the theory of quantum integrable systems. The organizers have intended to concentrate on topics related to the study of correlation functions, to systems with boundaries and to models at roots of unity. This document gathers the abstracts of 32 contributions, most of the contributions are accompanied by the set of transparencies
Kepler-16 Circumbinary System Validates Quantum Celestial Mechanics
Directory of Open Access Journals (Sweden)
Potter F.
2012-01-01
Full Text Available We report the application of quantum celestial mechanics (QCM to the Kepler-16 cir- cumbinary system which has a single planet orbiting binary stars with the important system parameters known to within one percent. Other gravitationally bound systems such as the Solar System of planets and the Jovian satellite systems have large uncertain- ties in their total angular momentum. Therefore, Kepler-16 allows us for the first time to determine whether the QCM predicted angular momentum per mass quantization is valid.
Time resolved heat exchange in driven quantum systems
Florencia Ludovico, María; Lim, Jong Soo; Moskalets, Michael; Arrachea, Liliana; Sánchez, David
2014-12-01
We study time-dependent heat transport in systems composed of a resonant level periodically forced with an external power source and coupled to a fermionic continuum. This simple model contains the basic ingredients to understand time resolved energy exchange in quantum capacitors that behave as single particle emitters. We analyse the behaviour of the dynamic heat current for driving frequencies within the non-adiabatic regime, showing that it does not obey a Joule dissipation law.
International Nuclear Information System (INIS)
Lukishova, S.G.; Knox, R.P.; Freivald, P.; McNamara, A.; Boyd, R.W.; Stroud, Jr. C.R.; Schmid, A.W.; Marshall, K.L.
2006-01-01
This paper describes a new application for liquid crystals: quantum information technology. A deterministically polarized single-photon source that efficiently produces photons exhibiting antibunching is a pivotal hardware element in absolutely secure quantum communication. Planar-aligned nematic liquid crystal hosts deterministically align the single dye molecules which produce deterministically polarized single (antibunched) photons. In addition, 1-D photonic bandgap cholesteric liquid crystals will increase single-photon source efficiency. The experiments and challenges in the observation of deterministically polarized fluorescence from single dye molecules in planar-aligned glassy nematic-liquid-crystal oligomer as well as photon antibunching in glassy cholesteric oligomer are described for the first time
Teleportation in an indivisible quantum system
Directory of Open Access Journals (Sweden)
Kiktenko E.O.
2016-01-01
Full Text Available Teleportation protocol is conventionally treated as a method for quantum state transfer between two spatially separated physical carriers. Recent experimental progress in manipulation with high-dimensional quantum systems opens a new framework for implementation of teleportation protocols. We show that the one-qubit teleportation can be considered as a state transfer between subspaces of the whole Hilbert space of an indivisible eight-dimensional system. We explicitly show all corresponding operations and discuss an alternative way of implementation of similar tasks.
International Nuclear Information System (INIS)
Nakamura, Tatsuya; Abe, Yuji; Kasai, Seiya; Hasegawa, Hideki; Hashizume, Tamotsu
2006-01-01
A new single electron (SE) binary-decision diagram (BDD) node device having a single quantum dot connected to three nanowire branches through tunnel barriers was fabricated using etched AlGaAs/GaAs nanowires and nanometer-sized Schottky wrap gates (WPGs), and their operation was characterized experimentally, for the hexagonal BDD quantum circuit. Fabricated devices showed clear and steep single electron pass switching by applying only an input voltage signal, which was completely different from switching properties in the previous SE BDD node devices composed of two single electron switches. As the possible switching mechanism, the correlation between the probabilities of tunnelling thorough a single quantum dot in exit branches was discussed
Genuine quantum correlations in quantum many-body systems: a review of recent progress.
De Chiara, Gabriele; Sanpera, Anna
2018-04-19
Quantum information theory has considerably helped in the understanding of quantum many-body systems. The role of quantum correlations and in particular, bipartite entanglement, has become crucial to characterise, classify and simulate quantum many body systems. Furthermore, the scaling of entanglement has inspired modifications to numerical techniques for the simulation of many-body systems leading to the, now established, area of tensor networks. However, the notions and methods brought by quantum information do not end with bipartite entanglement. There are other forms of correlations embedded in the ground, excited and thermal states of quantum many-body systems that also need to be explored and might be utilised as potential resources for quantum technologies. The aim of this work is to review the most recent developments regarding correlations in quantum many-body systems focussing on multipartite entanglement, quantum nonlocality, quantum discord, mutual information but also other non classical measures of correlations based on quantum coherence. Moreover, we also discuss applications of quantum metrology in quantum many-body systems. © 2018 IOP Publishing Ltd.
EDITORIAL: CAMOP: Quantum Non-Stationary Systems CAMOP: Quantum Non-Stationary Systems
Dodonov, Victor V.; Man'ko, Margarita A.
2010-09-01
Although time-dependent quantum systems have been studied since the very beginning of quantum mechanics, they continue to attract the attention of many researchers, and almost every decade new important discoveries or new fields of application are made. Among the impressive results or by-products of these studies, one should note the discovery of the path integral method in the 1940s, coherent and squeezed states in the 1960-70s, quantum tunneling in Josephson contacts and SQUIDs in the 1960s, the theory of time-dependent quantum invariants in the 1960-70s, different forms of quantum master equations in the 1960-70s, the Zeno effect in the 1970s, the concept of geometric phase in the 1980s, decoherence of macroscopic superpositions in the 1980s, quantum non-demolition measurements in the 1980s, dynamics of particles in quantum traps and cavity QED in the 1980-90s, and time-dependent processes in mesoscopic quantum devices in the 1990s. All these topics continue to be the subject of many publications. Now we are witnessing a new wave of interest in quantum non-stationary systems in different areas, from cosmology (the very first moments of the Universe) and quantum field theory (particle pair creation in ultra-strong fields) to elementary particle physics (neutrino oscillations). A rapid increase in the number of theoretical and experimental works on time-dependent phenomena is also observed in quantum optics, quantum information theory and condensed matter physics. Time-dependent tunneling and time-dependent transport in nano-structures are examples of such phenomena. Another emerging direction of study, stimulated by impressive progress in experimental techniques, is related to attempts to observe the quantum behavior of macroscopic objects, such as mirrors interacting with quantum fields in nano-resonators. Quantum effects manifest themselves in the dynamics of nano-electromechanical systems; they are dominant in the quite new and very promising field of circuit
Wavevector multiplexed atomic quantum memory via spatially-resolved single-photon detection.
Parniak, Michał; Dąbrowski, Michał; Mazelanik, Mateusz; Leszczyński, Adam; Lipka, Michał; Wasilewski, Wojciech
2017-12-15
Parallelized quantum information processing requires tailored quantum memories to simultaneously handle multiple photons. The spatial degree of freedom is a promising candidate to facilitate such photonic multiplexing. Using a single-photon resolving camera, we demonstrate a wavevector multiplexed quantum memory based on a cold atomic ensemble. Observation of nonclassical correlations between Raman scattered photons is confirmed by an average value of the second-order correlation function [Formula: see text] in 665 separated modes simultaneously. The proposed protocol utilizing the multimode memory along with the camera will facilitate generation of multi-photon states, which are a necessity in quantum-enhanced sensing technologies and as an input to photonic quantum circuits.
Operation of a quantum dot in the finite-state machine mode: Single-electron dynamic memory
Energy Technology Data Exchange (ETDEWEB)
Klymenko, M. V. [Department of Chemistry, University of Liège, B4000 Liège (Belgium); Klein, M. [The Fritz Haber Center for Molecular Dynamics and the Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904 (Israel); Levine, R. D. [The Fritz Haber Center for Molecular Dynamics and the Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904 (Israel); Crump Institute for Molecular Imaging and Department of Molecular and Medical Pharmacology, David Geffen School of Medicine and Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095 (United States); Remacle, F., E-mail: fremacle@ulg.ac.be [Department of Chemistry, University of Liège, B4000 Liège (Belgium); The Fritz Haber Center for Molecular Dynamics and the Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904 (Israel)
2016-07-14
A single electron dynamic memory is designed based on the non-equilibrium dynamics of charge states in electrostatically defined metallic quantum dots. Using the orthodox theory for computing the transfer rates and a master equation, we model the dynamical response of devices consisting of a charge sensor coupled to either a single and or a double quantum dot subjected to a pulsed gate voltage. We show that transition rates between charge states in metallic quantum dots are characterized by an asymmetry that can be controlled by the gate voltage. This effect is more pronounced when the switching between charge states corresponds to a Markovian process involving electron transport through a chain of several quantum dots. By simulating the dynamics of electron transport we demonstrate that the quantum box operates as a finite-state machine that can be addressed by choosing suitable shapes and switching rates of the gate pulses. We further show that writing times in the ns range and retention memory times six orders of magnitude longer, in the ms range, can be achieved on the double quantum dot system using experimentally feasible parameters, thereby demonstrating that the device can operate as a dynamic single electron memory.
Operation of a quantum dot in the finite-state machine mode: Single-electron dynamic memory
International Nuclear Information System (INIS)
Klymenko, M. V.; Klein, M.; Levine, R. D.; Remacle, F.
2016-01-01
A single electron dynamic memory is designed based on the non-equilibrium dynamics of charge states in electrostatically defined metallic quantum dots. Using the orthodox theory for computing the transfer rates and a master equation, we model the dynamical response of devices consisting of a charge sensor coupled to either a single and or a double quantum dot subjected to a pulsed gate voltage. We show that transition rates between charge states in metallic quantum dots are characterized by an asymmetry that can be controlled by the gate voltage. This effect is more pronounced when the switching between charge states corresponds to a Markovian process involving electron transport through a chain of several quantum dots. By simulating the dynamics of electron transport we demonstrate that the quantum box operates as a finite-state machine that can be addressed by choosing suitable shapes and switching rates of the gate pulses. We further show that writing times in the ns range and retention memory times six orders of magnitude longer, in the ms range, can be achieved on the double quantum dot system using experimentally feasible parameters, thereby demonstrating that the device can operate as a dynamic single electron memory.
Generation of Quantum Correlations in Bipartite Gaussian Open Quantum Systems
Isar, Aurelian
2018-02-01
We describe the generation of quantum correlations (entanglement, discord and steering) in a system composed of two coupled non-resonant bosonic modes immersed in a common thermal reservoir, in the framework of the theory of open systems. We show that for separable initial squeezed thermal states entanglement generation may take place, for definite values of squeezing parameter, average photon numbers, temperature of the thermal bath, dissipation constant and strength of interaction between the two bosonic modes. We also show that for initial uni-modal squeezed states Gaussian discord can be generated for all non-zero values of the strength of interaction between the modes. Likewise, for an initial separable state, a generation of Gaussian steering may take place temporarily, for definite values of the parameters characterizing the initial state and the thermal environment, and the strength of coupling between the two modes.
An exactly solvable system from quantum optics
Energy Technology Data Exchange (ETDEWEB)
Maciejewski, Andrzej J., E-mail: maciejka@astro.ia.uz.zgora.pl [J. Kepler Institute of Astronomy, University of Zielona Góra, Licealna 9, PL-65-417 Zielona Góra (Poland); Przybylska, Maria, E-mail: M.Przybylska@if.uz.zgora.pl [Institute of Physics, University of Zielona Góra, Licealna 9, 65-417 Zielona Góra (Poland); Stachowiak, Tomasz, E-mail: stachowiak@cft.edu.pl [Center for Theoretical Physics PAS, Al. Lotników 32/46, 02-668 Warsaw (Poland)
2015-07-31
We investigate a generalisation of the Rabi system in the Bargmann–Fock representation. In this representation the eigenproblem of the considered quantum model is described by a system of two linear differential equations with one independent variable. The system has only one irregular singular point at infinity. We show how the quantisation of the model is related to asymptotic behaviour of solutions in a vicinity of this point. The explicit formulae for the spectrum and eigenfunctions of the model follow from an analysis of the Stokes phenomenon. An interpretation of the obtained results in terms of differential Galois group of the system is also given. - Highlights: • New exactly solvable system from quantum optics is found. • Normalisation condition for system in Bargmann representation is used. • Formulae for spectrum and eigenfunctions from analysis of Stokes phenomenon are given.
Hu, C Y
2017-03-28
The future Internet is very likely the mixture of all-optical Internet with low power consumption and quantum Internet with absolute security guaranteed by the laws of quantum mechanics. Photons would be used for processing, routing and com-munication of data, and photonic transistor using a weak light to control a strong light is the core component as an optical analogue to the electronic transistor that forms the basis of modern electronics. In sharp contrast to previous all-optical tran-sistors which are all based on optical nonlinearities, here I introduce a novel design for a high-gain and high-speed (up to terahertz) photonic transistor and its counterpart in the quantum limit, i.e., single-photon transistor based on a linear optical effect: giant Faraday rotation induced by a single electronic spin in a single-sided optical microcavity. A single-photon or classical optical pulse as the gate sets the spin state via projective measurement and controls the polarization of a strong light to open/block the photonic channel. Due to the duality as quantum gate for quantum information processing and transistor for optical information processing, this versatile spin-cavity quantum transistor provides a solid-state platform ideal for all-optical networks and quantum networks.
Rau, Markus; Heindel, Tobias; Unsleber, Sebastian; Braun, Tristan; Fischer, Julian; Frick, Stefan; Nauerth, Sebastian; Schneider, Christian; Vest, Gwenaelle; Reitzenstein, Stephan; Kamp, Martin; Forchel, Alfred; Höfling, Sven; Weinfurter, Harald
2014-04-01
Highly efficient single-photon sources (SPS) can increase the secure key rate of quantum key distribution (QKD) systems compared to conventional attenuated laser systems. Here we report on a free space QKD test using an electrically driven quantum dot single-photon source (QD SPS) that does not require a separate laser setup for optical pumping and thus allows for a simple and compact SPS QKD system. We describe its implementation in our 500 m free space QKD system in downtown Munich. Emulating a BB84 protocol operating at a repetition rate of 125 MHz, we could achieve sifted key rates of 5-17 kHz with error ratios of 6-9% and {{\\text{g}}^{(2)}}(0)-values of 0.39-0.76.
Single photon emission from charged excitons in CdTe/ZnTe quantum dots
Belyaev, K. G.; Rakhlin, M. V.; Sorokin, S. V.; Klimko, G. V.; Gronin, S. V.; Sedova, I. V.; Mukhin, I. S.; Ivanov, S. V.; Toropov, A. A.
2017-11-01
We report on micro-photoluminescence studies of individual self-organized CdTe/ZnTe quantum dots intended for single-photon-source applications in a visible spectral range. The quantum dots surface density below 1010 per cm2 was achieved by using a thermally activated regime of molecular beam epitaxy that allowed fabrication of etched mesa-structures containing only a few emitting quantum dots. The single photon emission with the autocorrelation function g(2)(0)<0.2 was detected and identified as recombination of charged excitons in the individual quantum dot.
Quantum dissipation of a simple conservative system
International Nuclear Information System (INIS)
Ibeh, G. J.; Mshelia, E. D.
2014-01-01
A model of quantum dissipative system is presented. Here dissipation of energy is demonstrated as based on the coupling of a free translational motion of a centre of mass to a harmonic oscillator. The two-dimensional arrangement of two coupled particles of different masses is considered.
System and method for making quantum dots
Bakr, Osman M.
2015-05-28
Embodiments of the present disclosure provide for methods of making quantum dots (QDs) (passivated or unpassivated) using a continuous flow process, systems for making QDs using a continuous flow process, and the like. In one or more embodiments, the QDs produced using embodiments of the present disclosure can be used in solar photovoltaic cells, bio-imaging, IR emitters, or LEDs.
Parallel decoherence in composite quantum systems
Indian Academy of Sciences (India)
For the standard quantum Brownian motion (QBM) model, we point out the occurrence of simultaneous (parallel), mutually irreducible and autonomous decoherence processes. Besides the standard Brownian particle, we show that there is at least another system undergoing the dynamics described by the QBM model.
Effective Hamiltonian approach to periodically perturbed quantum optical systems
International Nuclear Information System (INIS)
Sainz, I.; Klimov, A.B.; Saavedra, C.
2006-01-01
We apply the method of Lie-type transformations to Floquet Hamiltonians for periodically perturbed quantum systems. Some typical examples of driven quantum systems are considered in the framework of this approach and corresponding effective time dependent Hamiltonians are found
Zhou, Hua; Su, Yang; Wang, Rong; Zhu, Yong; Shen, Huiping; Pu, Tao; Wu, Chuanxin; Zhao, Jiyong; Zhang, Baofu; Xu, Zhiyong
2017-10-01
Online reconstruction of a time-variant quantum state from the encoding/decoding results of quantum communication is addressed by developing a method of evolution reconstruction from a single measurement record with random time intervals. A time-variant two-dimensional state is reconstructed on the basis of recovering its expectation value functions of three nonorthogonal projectors from a random single measurement record, which is composed from the discarded qubits of the six-state protocol. The simulated results prove that our method is robust to typical metro quantum channels. Our work extends the Fourier-based method of evolution reconstruction from the version for a regular single measurement record with equal time intervals to a unified one, which can be applied to arbitrary single measurement records. The proposed protocol of evolution reconstruction runs concurrently with the one of quantum communication, which can facilitate the online quantum tomography.
Single-photon-level quantum image memory based on cold atomic ensembles.
Ding, Dong-Sheng; Zhou, Zhi-Yuan; Shi, Bao-Sen; Guo, Guang-Can
2013-01-01
A quantum memory is a key component for quantum networks, which will enable the distribution of quantum information. Its successful development requires storage of single-photon light. Encoding photons with spatial shape through higher-dimensional states significantly increases their information-carrying capability and network capacity. However, constructing such quantum memories is challenging. Here we report the first experimental realization of a true single-photon-carrying orbital angular momentum stored via electromagnetically induced transparency in a cold atomic ensemble. Our experiments show that the non-classical pair correlation between trigger photon and retrieved photon is retained, and the spatial structure of input and retrieved photons exhibits strong similarity. More importantly, we demonstrate that single-photon coherence is preserved during storage. The ability to store spatial structure at the single-photon level opens the possibility for high-dimensional quantum memories.
The brachistochrone problem in open quantum systems
International Nuclear Information System (INIS)
Rotter, Ingrid
2007-01-01
Recently, the quantum brachistochrone problem has been discussed in the literature by using non-Hermitian Hamilton operators of different types. Here, it is demonstrated that the passage time is tunable in realistic open quantum systems due to the biorthogonality of the eigenfunctions of the non-Hermitian Hamilton operator. As an example, the numerical results obtained by Bulgakov et al for the transmission through microwave cavities of different shapes are analyzed from the point of view of the brachistochrone problem. The passage time is shortened in the crossover from the weak-coupling to the strong-coupling regime where the resonance states overlap and many branch points (exceptional points) in the complex plane exist. The effect can not be described in the framework of the standard quantum mechanics with the Hermitian Hamilton operator and consideration of S matrix poles
The brachistochrone problem in open quantum systems
Energy Technology Data Exchange (ETDEWEB)
Rotter, Ingrid [Max-Planck-Institut fuer Physik komplexer Systeme, D-01187 Dresden (Germany)
2007-11-30
Recently, the quantum brachistochrone problem has been discussed in the literature by using non-Hermitian Hamilton operators of different types. Here, it is demonstrated that the passage time is tunable in realistic open quantum systems due to the biorthogonality of the eigenfunctions of the non-Hermitian Hamilton operator. As an example, the numerical results obtained by Bulgakov et al for the transmission through microwave cavities of different shapes are analyzed from the point of view of the brachistochrone problem. The passage time is shortened in the crossover from the weak-coupling to the strong-coupling regime where the resonance states overlap and many branch points (exceptional points) in the complex plane exist. The effect can not be described in the framework of the standard quantum mechanics with the Hermitian Hamilton operator and consideration of S matrix poles.
The brachistochrone problem in open quantum systems
Rotter, Ingrid
2007-11-01
Recently, the quantum brachistochrone problem has been discussed in the literature by using non-Hermitian Hamilton operators of different types. Here, it is demonstrated that the passage time is tunable in realistic open quantum systems due to the biorthogonality of the eigenfunctions of the non-Hermitian Hamilton operator. As an example, the numerical results obtained by Bulgakov et al for the transmission through microwave cavities of different shapes are analyzed from the point of view of the brachistochrone problem. The passage time is shortened in the crossover from the weak-coupling to the strong-coupling regime where the resonance states overlap and many branch points (exceptional points) in the complex plane exist. The effect can not be described in the framework of the standard quantum mechanics with the Hermitian Hamilton operator and consideration of S matrix poles.
Classical and quantum discrete dynamical systems
Kornyak, V. V.
2013-01-01
We study deterministic and quantum dynamics from a constructive "finite" point of view, since the introduction of the continuum or other actual infinities in physics poses severe conceptual and technical difficulties, and while all of these concepts are not really needed in physics, which is in fact an empirical science. Particular attention is paid to the symmetry properties of discrete systems. For a consistent description of the symmetries of dynamical systems at different time instants and the symmetries of various parts of such systems, we introduce discrete analogs of gauge connections. These gauge structures are particularly important to describe the quantum behavior. The symmetries govern the fundamental properties of the behavior of dynamical systems. In particular, we can show that the moving soliton-like structures are inevitable in a deterministic (classical) dynamical system, whose symmetry group breaks the set of states into a finite number of orbits of the group. We demonstrate that the quantum behavior is a natural consequence of symmetries of dynamical systems. This behavior is a result of the fundamental inability to trace the identity of indistinguish-able objects during their evolution. Information is only available on invariant statements and values related with such objects. Using general mathematical arguments, any quantum dynamics can be shown to reduce to a sequence of permutations. The quantum interferences occur in the invariant subspaces of permutation representations of the symmetry groups of dynamical systems. The observables can be expressed in terms of permutation invariants. We also show that in order to describe quantum phenomena it is sufficient to use cyclotomic fields—the minimal extensions of natural numbers suitable for quantum mechanics, instead of a non-constructive number system—the field of complex numbers. The finite groups of symmetries play the central role in this review. In physics there is an additional reason
Multi-scale analysis for random quantum systems with interaction
Chulaevsky, Victor
2014-01-01
The study of quantum disorder has generated considerable research activity in mathematics and physics over past 40 years. While single-particle models have been extensively studied at a rigorous mathematical level, little was known about systems of several interacting particles, let alone systems with positive spatial particle density. Creating a consistent theory of disorder in multi-particle quantum systems is an important and challenging problem that largely remains open. Multi-scale Analysis for Random Quantum Systems with Interaction presents the progress that had been recently achieved in this area. The main focus of the book is on a rigorous derivation of the multi-particle localization in a strong random external potential field. To make the presentation accessible to a wider audience, the authors restrict attention to a relatively simple tight-binding Anderson model on a cubic lattice Zd. This book includes the following cutting-edge features: * an introduction to the state-of-the-art single-...
Method for preparation and readout of polyatomic molecules in single quantum states
Patterson, David
2018-03-01
Polyatomic molecular ions contain many desirable attributes of a useful quantum system, including rich internal degrees of freedom and highly controllable coupling to the environment. To date, the vast majority of state-specific experimental work on molecular ions has concentrated on diatomic species. The ability to prepare and read out polyatomic molecules in single quantum states would enable diverse experimental avenues not available with diatomics, including new applications in precision measurement, sensitive chemical and chiral analysis at the single-molecule level, and precise studies of Hz-level molecular tunneling dynamics. While cooling the motional state of a polyatomic ion via sympathetic cooling with a laser-cooled atomic ion is straightforward, coupling this motional state to the internal state of the molecule has proven challenging. Here we propose a method for readout and projective measurement of the internal state of a trapped polyatomic ion. The method exploits the rich manifold of technically accessible rotational states in the molecule to realize robust state preparation and readout with far less stringent engineering than quantum logic methods recently demonstrated on diatomic molecules. The method can be applied to any reasonably small (≲10 atoms) polyatomic ion with an anisotropic polarizability.
Gruneisen, Mark T.; Flanagan, Michael B.; Sickmiller, Brett A.
2017-12-01
The efficient coupling of photons from a free-space quantum channel into a single-mode optical fiber (SMF) has important implications for quantum network concepts involving SMF interfaces to quantum detectors, atomic systems, integrated photonics, and direct coupling to a fiber network. Propagation through atmospheric turbulence, however, leads to wavefront errors that degrade mode matching with SMFs. In a free-space quantum channel, this leads to photon losses in proportion to the severity of the aberration. This is particularly problematic for satellite-Earth quantum channels, where atmospheric turbulence can lead to significant wavefront errors. This report considers propagation from low-Earth orbit to a terrestrial ground station and evaluates the efficiency with which photons couple either through a circular field stop or into an SMF situated in the focal plane of the optical receiver. The effects of atmospheric turbulence on the quantum channel are calculated numerically and quantified through the quantum bit error rate and secure key generation rates in a decoy-state BB84 protocol. Numerical simulations include the statistical nature of Kolmogorov turbulence, sky radiance, and an adaptive-optics system under closed-loop control.
Exciton-polariton dynamics in quantum dot-cavity system
Energy Technology Data Exchange (ETDEWEB)
Neto, Antonio F.; Lima, William J.; Villas-Boas, Jose M. [Universidade Federal de Uberlandia (UFU), MG (Brazil). Inst. de Fisica
2012-07-01
Full text: One of the basic requirement for quantum information processing systems is the ability to completely control the state of a single qubit. This imply in know all sources of decoherence and elaborate ways to avoid them. In recent work, A. Laucht et al. [1] presented detailed theoretical and experimental investigations of electrically tunable single quantum dot (QD) - photonic crystal (PhC) nanocavity systems operating in the strong coupling regime of the light matter interaction. Unlike previous studies, where the exciton-cavity spectral detuning was varied by changing the lattice temperature, or by the adsorption of inert gases at low temperatures, they employ the quantum confined Stark-effect to electro-optically control the exciton-cavity detuning. The new built device enabled them to systematically probe the emission spectrum of the strongly coupled system as a function of external control parameters, as for example the incoherent excitation power density or the lattice temperature. Those studies reveal for the first time insights in dephasing mechanisms of 0D exciton polaritons [1]. In another study [2], using a similar device, they investigate the coupling between two different QDs with a single cavity mode. In both works, incoherent pumping was used, but for quantum information, coherent and controlled excitations are necessary. Here, we theoretically investigate the dynamics a single quantum dot inside a cavity under coherent pulse excitation and explore a wide range of parameters, as for example, the exciton-cavity detunings, the excitation power, the spontaneous decay, and pure dephasing. We use density matrix formalism in the Lindblad form, and we solve it numerically. Our results show that coherent excitation can be used to probe strong coupling between exciton and cavity mode by monitoring the exciton Rabi oscillation as function of the cavity detuning. This can give new insights for future experimental measurement focusing on quantum
DEFF Research Database (Denmark)
Nielsen, Per Kær; Lodahl, Peter; Jauho, Antti-Pekka
2013-01-01
We study the fundamental limit on single-photon indistinguishability imposed by decoherence due to phonon interactions in semiconductor quantum dot-cavity quantum electrodynamics systems. Employing an exact diagonalization approach we find large differences compared to standard methods. An import...
Oriented conjugation of single-domain antibodies and quantum dots.
Brazhnik, Kristina; Nabiev, Igor; Sukhanova, Alyona
2014-01-01
Nanoparticle-based biodetection routinely employs monoclonal antibodies (mAbs) for targeting. However, the large size of mAbs limits the number of ligands per nanoparticle and severely restricts the bioavailability and distribution of these probes in a sample. Furthermore, conventional conjugation techniques provide nanoprobes with irregular orientation of mAbs on the nanoparticle surface and often provoke mAb unfolding. Here, we describe a protocol for engineering a new generation of ultrasmall diagnostic nanoprobes through oriented conjugation of semiconductor quantum dots (QDs) with 13 kDa single-domain antibodies (sdAbs) derived from llama immunoglobulin G (IgG). The sdAbs are conjugated with QDs in a highly oriented manner via an additional cysteine residue specifically integrated into the sdAb C-terminus. The resultant nanoprobes are <12 nm in diameter, ten times smaller in volume compared to the known alternatives. They have been proved highly efficient in flow cytometry and immunuhistochemical diagnostics. This approach can be easily extended to other semiconductor and plasmonic nanoparticles.
Quantum Linear System Algorithm for Dense Matrices
Wossnig, Leonard; Zhao, Zhikuan; Prakash, Anupam
2018-02-01
Solving linear systems of equations is a frequently encountered problem in machine learning and optimization. Given a matrix A and a vector b the task is to find the vector x such that A x =b . We describe a quantum algorithm that achieves a sparsity-independent runtime scaling of O (κ2√{n }polylog(n )/ɛ ) for an n ×n dimensional A with bounded spectral norm, where κ denotes the condition number of A , and ɛ is the desired precision parameter. This amounts to a polynomial improvement over known quantum linear system algorithms when applied to dense matrices, and poses a new state of the art for solving dense linear systems on a quantum computer. Furthermore, an exponential improvement is achievable if the rank of A is polylogarithmic in the matrix dimension. Our algorithm is built upon a singular value estimation subroutine, which makes use of a memory architecture that allows for efficient preparation of quantum states that correspond to the rows of A and the vector of Euclidean norms of the rows of A .
Dissipation Assisted Quantum Memory with Coupled Spin Systems
Jiang, Liang; Verstraete, Frank; Cirac, Ignacio; Lukin, Mikhail
2009-05-01
Dissipative dynamics often destroys quantum coherences. However, one can use dissipation to suppress decoherence. A well-known example is the so-called quantum Zeno effect, in which one can freeze the evolution using dissipative processes (e.g., frequently projecting the system to its initial state). Similarly, the undesired decoherence of quantum bits can also be suppressed using controlled dissipation. We propose and analyze the use of this generalization of quantum Zeno effect for protecting the quantum information encoded in the coupled spin systems. This new approach may potentially enhance the performance of quantum memories, in systems such as nitrogen-vacancy color-centers in diamond.
Security of practical quantum key distribution systems
Energy Technology Data Exchange (ETDEWEB)
Jain, Nitin
2015-02-24
This thesis deals with practical security aspects of quantum key distribution (QKD) systems. At the heart of the theoretical model of any QKD system lies a quantum-mechanical security proof that guarantees perfect secrecy of messages - based on certain assumptions. However, in practice, deviations between the theoretical model and the physical implementation could be exploited by an attacker to break the security of the system. These deviations may arise from technical limitations and operational imperfections in the physical implementation and/or unrealistic assumptions and insufficient constraints in the theoretical model. In this thesis, we experimentally investigate in depth several such deviations. We demonstrate the resultant vulnerabilities via proof-of-principle attacks on a commercial QKD system from ID Quantique. We also propose countermeasures against the investigated loopholes to secure both existing and future QKD implementations.
Quantum mechanical simulation methods for studying biological systems
International Nuclear Information System (INIS)
Bicout, D.; Field, M.
1996-01-01
Most known biological mechanisms can be explained using fundamental laws of physics and chemistry and a full understanding of biological processes requires a multidisciplinary approach in which all the tools of biology, chemistry and physics are employed. An area of research becoming increasingly important is the theoretical study of biological macromolecules where numerical experimentation plays a double role of establishing a link between theoretical models and predictions and allowing a quantitative comparison between experiments and models. This workshop brought researchers working on different aspects of the development and application of quantum mechanical simulation together, assessed the state-of-the-art in the field and highlighted directions for future research. Fourteen lectures (theoretical courses and specialized seminars) deal with following themes: 1) quantum mechanical calculations of large systems, 2) ab initio molecular dynamics where the calculation of the wavefunction and hence the energy and forces on the atoms for a system at a single nuclear configuration are combined with classical molecular dynamics algorithms in order to perform simulations which use a quantum mechanical potential energy surface, 3) quantum dynamical simulations, electron and proton transfer processes in proteins and in solutions and finally, 4) free seminars that helped to enlarge the scope of the workshop. (N.T.)
Single-quadrature continuous-variable quantum key distribution
DEFF Research Database (Denmark)
Gehring, Tobias; Jacobsen, Christian Scheffmann; Andersen, Ulrik Lund
2016-01-01
Most continuous-variable quantum key distribution schemes are based on the Gaussian modulation of coherent states followed by continuous quadrature detection using homodyne detectors. In all previous schemes, the Gaussian modulation has been carried out in conjugate quadratures thus requiring two...... commercialization of continuous-variable quantum key distribution, provided that the low noise requirement can be achieved....
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....
An E-payment system based on quantum group signature
Xiaojun, Wen
2010-12-01
Security and anonymity are essential to E-payment systems. However, existing E-payment systems will easily be broken into soon with the emergence of quantum computers. In this paper, we propose an E-payment system based on quantum group signature. In contrast to classical E-payment systems, our quantum E-payment system can protect not only the users' anonymity but also the inner structure of customer groups. Because of adopting the two techniques of quantum key distribution, a one-time pad and quantum group signature, unconditional security of our E-payment system is guaranteed.
Single-electron switching effect in graphene parallel-coupled double quantum dots
Arai, M.; Masubuchi, S.; Machida, T.
2011-12-01
We have fabricated parallel-coupled quantum dots on single-layer graphene. The tunnel coupling between the quantum dots can be tuned by a graphene in-plane gate. Owing to the tunnel coupling, the Coulomb blockade oscillation peaks exhibit periodic shifts as the number of electron in the non-conducting side-coupled QD is changed. The result suggests the observation of the single electron switching effect, which is a prerequisite for a single photon detection scheme using parallel-coupled quantum dots.
DEFF Research Database (Denmark)
Li, H.W.; Kardynal, Beata; Ellis, D.J.P.
2008-01-01
Quantum dot resonant tunneling diode single photon detector with independently defined absorption and sensing areas is demonstrated. The device, in which the tunneling is constricted to an aperture in an insulating layer in the emitter, shows electrical characteristics typical of high quality...... resonant tunneling diodes. A single photon detection efficiency of 2.1%+/- 0.1% at 685 nm was measured corresponding to an internal quantum efficiency of 14%. The devices are simple to fabricate, robust, and show promise for large absorption area single photon detectors based on quantum dot structures....
Quantum dynamics of dynamically unstable, integrable few-mode systems
Mathew, Ranchu; Tiesinga, Eite
2017-04-01
Recently, quenches in isolated ultra-cold atomic quantum systems have become a subject of intense study. We consider quantum few-mode systems that are integrable in their classical mean-field limit and become dynamically unstable after a quench of a system parameter. Specifically, we study the cases of a Bose-Einstein condensate (BEC) in a double-well potential and of an antiferromagnetic F = 1 spinor BEC constrained to a single spatial mode. First, we study the time dynamics of a coherent state after the quench within the truncated Wigner approximation and find that due to phase-space mixing the systems relax to a steady state. Using action-angle formalism and guided by insights from the related pendulum system, we obtain analytical expressions for the time evolution of expectation values of observables and their long-time values. We also study the full quantum dynamics of the systems. Comparing their results with the TWA results, we find agreement in the long-time expectation value of the observables. The relaxation time scales, however, are different.
Aspelmeyer, Markus; Schwab, Keith
2008-09-01
The last five years have witnessed an amazing development in the field of nano- and micromechanics. What was widely considered fantasy ten years ago is about to become an experimental reality: the quantum regime of mechanical systems is within reach of current experiments. Two factors (among many) have contributed significantly to this situation. As part of the widespread effort into nanoscience and nanofabrication, it is now possible to produce high-quality nanomechanical and micromechanical resonators, spanning length scales of millimetres to nanometres, and frequencies from kilohertz to gigahertz. Researchers coupled these mechanical elements to high-sensitivity actuation and readout systems such as single-electron transistors, quantum dots, atomic point contacts, SQUID loops, high-finesse optical or microwave-cavities etc. Some of these ultra-sensitive readout schemes are in principle capable of detection at the quantum limit and a large part of the experimental effort is at present devoted to achieving this. On the other hand, the fact that the groups working in the field come from various different physics backgrounds—the authors of this editorial are a representative sample—has been a constant source of inspiration for helpful theoretical and experimental tools that have been adapted from other fields to the mechanical realm. To name just one example: ideas from quantum optics have led to the recent demonstration (both in theory and experiment) that coupling a mechanical resonator to a high-finesse optical cavity can be fully analogous to the well-known sideband-resolved laser cooling of ions and hence is capable in principle of cooling a mechanical mode into its quantum ground state. There is no doubt that such interdisciplinarity has been a crucial element for the development of the field. It is interesting to note that a very similar sociological phenomenon occurred earlier in the quantum information community, an area which is deeply enriched by the
Exemplifying Quantum Systems in a Finite Element Basis
International Nuclear Information System (INIS)
Young, Toby D.
2009-01-01
This paper presents a description of the abstractions required for the expression and solution of the linear single-particle Schroedinger equation in a finite element basis. This paper consists of two disparate themes: First, to layout and establish the foundations of finite element analysis as an approximate numerical solution to extendable quantum mechanical systems; and second, to promote a high-performance open-source computational model for the approximate numerical solution to quantum mechanical systems. The structural foundation of the one-and two-dimensional time-independent Schroedinger equation describing an infinite potential well is explored and a brief overview of the hierarchal design of the computational library written in C++ is given.
Double-slit experiment with single wave-driven particles and its relation to quantum mechanics
DEFF Research Database (Denmark)
Andersen, Anders Peter; Madsen, Jacob; Reichelt, Christian Günther
2015-01-01
even though it is possible to determine unambiguously which slit the walking droplet passes. Here we argue, however, that the single-particle statistics in such an experiment will be fundamentally different from the single-particle statistics of quantum mechanics. Quantum mechanical interference takes......¨dinger equation with a source term originating from a localized particle that generates a wave while being simultaneously guided by it. We show that the ensuing particle-wave dynamics can capture some characteristics of quantum mechanics such as orbital quantization. However, the particle-wave dynamics can...... not reproduce quantum mechanics in general, and we show that the single-particle statistics for our model in a double-slit experiment with an additional splitter plate differs qualitatively from that of quantum mechanics....
Rapid single-flux quantum control of the energy potential in a double SQUID qubit circuit
International Nuclear Information System (INIS)
Castellano, Maria Gabriella; Chiarello, Fabio; Leoni, Roberto; Torrioli, Guido; Carelli, Pasquale; Cosmelli, Carlo; Khabipov, Marat; Zorin, Alexander B; Balashov, Dmitri
2007-01-01
We report on the development and test of an integrated system composed of a flux qubit and a rapid single-flux quantum (RSFQ) circuit that allows qubit manipulation. The goal is to demonstrate the feasibility of control electronics integrated on the same chip as the qubit, in view of the application in quantum computation with superconducting devices. RSFQ logic relies on the storage and transmission of magnetic flux quanta and can be profitably used with superconducting qubits because of the speed, scalability, compatibility with the qubit fabrication process and low temperature environment. While standard RSFQ circuitry is well assessed, the application to quantum computing requires a complete rescaling of parameter values, in order to preserve the qubit coherence and reduce the power dissipation. In the system presented in this paper, the qubit role is played by a superconducting loop interrupted by a small dc SQUID, usually called a double SQUID, which behaves as a tunable rf-SQUID. Its energy potential has the shape of a double well, with the barrier between the wells controlled by magnetic flux applied to the inner dc SQUID. Here for the first time we report measurements at a base temperature of 370 mK in which flux control pulses with desired characteristics were supplied by a RSFQ circuit fabricated using non-standard parameters in the same chip as the qubit
Quantum Monte Carlo approaches for correlated systems
Becca, Federico
2017-01-01
Over the past several decades, computational approaches to studying strongly-interacting systems have become increasingly varied and sophisticated. This book provides a comprehensive introduction to state-of-the-art quantum Monte Carlo techniques relevant for applications in correlated systems. Providing a clear overview of variational wave functions, and featuring a detailed presentation of stochastic samplings including Markov chains and Langevin dynamics, which are developed into a discussion of Monte Carlo methods. The variational technique is described, from foundations to a detailed description of its algorithms. Further topics discussed include optimisation techniques, real-time dynamics and projection methods, including Green's function, reptation and auxiliary-field Monte Carlo, from basic definitions to advanced algorithms for efficient codes, and the book concludes with recent developments on the continuum space. Quantum Monte Carlo Approaches for Correlated Systems provides an extensive reference ...
Observing the evolution of a quantum system that does not evolve
International Nuclear Information System (INIS)
De Liberato, Simone
2007-01-01
This article deals with the problem of gathering information on the time evolution of a single metastable quantum system whose evolution is impeded by the quantum Zeno effect. It has been found it is in principle possible to obtain some information on the time evolution and, depending on the specific system, even to measure its average decay rate, even if the system does not undergo any evolution at all
The Heteronuclear Single-Quantum Correlation (HSQC) Experiment: Vectors versus Product Operators
de la Vega-Herna´ndez, Karen; Antuch, Manuel
2015-01-01
A vectorial representation of the full sequence of events occurring during the 2D-NMR heteronuclear single-quantum correlation (HSQC) experiment is presented. The proposed vectorial representation conveys an understanding of the magnetization evolution during the HSQC pulse sequence for those who have little or no quantum mechanical background.…
Classical synchronization indicates persistent entanglement in isolated quantum systems
Witthaut, Dirk; Wimberger, Sandro; Burioni, Raffaella; Timme, Marc
2017-04-01
Synchronization and entanglement constitute fundamental collective phenomena in multi-unit classical and quantum systems, respectively, both equally implying coordinated system states. Here, we present a direct link for a class of isolated quantum many-body systems, demonstrating that synchronization emerges as an intrinsic system feature. Intriguingly, quantum coherence and entanglement arise persistently through the same transition as synchronization. This direct link between classical and quantum cooperative phenomena may further our understanding of strongly correlated quantum systems and can be readily observed in state-of-the-art experiments, for example, with ultracold atoms.
Single-Photon Technologies Based on Quantum-Dots in Photonic Crystals
DEFF Research Database (Denmark)
Lehmann, Tau Bernstorff
In this thesis, the application of semiconductor quantum-dots in photonic crystals is explored as aresource for single-photon technology.Two platforms based on photonic crystals, a cavity and a waveguide, are examined as platformssingle-photon sources. Both platforms demonstrate strong single-photon...... purity under quasi-resonantexcitation. Furthermore the waveguide based platform demonstrates indistinguishable single-photonsat timescales up to 13 ns.A setup for active demultiplexing of single-photons to a three-fold single-photon state is proposed.Using a fast electro-optical modulator, single-photons...... from a quantum-dot are routed on timescalesof the exciton lifetime. Using active demultiplexing a three-fold single-photon state is generated at anextracted rate of 2:03 ±0:49 Hz.An on-chip power divider integrated with a quantum-dot is investigated. Correlation measurementof the photon statistic...
On Mathematical Modeling Of Quantum Systems
Achuthan, P.; Narayanankutty, Karuppath
2009-07-01
The world of physical systems at the most fundamental levels is replete with efficient, interesting models possessing sufficient ability to represent the reality to a considerable extent. So far, quantum mechanics (QM) forming the basis of almost all natural phenomena, has found beyond doubt its intrinsic ingenuity, capacity and robustness to stand the rigorous tests of validity from and through appropriate calculations and experiments. No serious failures of quantum mechanical predictions have been reported, yet. However, Albert Einstein, the greatest theoretical physicist of the twentieth century and some other eminent men of science have stated firmly and categorically that QM, though successful by and large, is incomplete. There are classical and quantum reality models including those based on consciousness. Relativistic quantum theoretical approaches to clearly understand the ultimate nature of matter as well as radiation have still much to accomplish in order to qualify for a final theory of everything (TOE). Mathematical models of better, suitable character as also strength are needed to achieve satisfactory explanation of natural processes and phenomena. We, in this paper, discuss some of these matters with certain apt illustrations as well.
Secure alignment of coordinate systems using quantum correlation
Rezazadeh, F.; Mani, A.; Karimipour, V.
2017-08-01
We show that two parties far apart can use shared entangled states and classical communication to align their coordinate systems with a very high fidelity. Moreover, compared with previous methods proposed for such a task, i.e., sending parallel or antiparallel pairs or groups of spin states, our method has the extra advantages of using single-qubit measurements and also being secure, so that third parties do not extract any information about the aligned coordinate system established between the two parties. The latter property is important in many other quantum information protocols in which measurements inevitably play a significant role.
Quantum scaling in many-body systems an approach to quantum phase transitions
Continentino, Mucio
2017-01-01
Quantum phase transitions are strongly relevant in a number of fields, ranging from condensed matter to cold atom physics and quantum field theory. This book, now in its second edition, approaches the problem of quantum phase transitions from a new and unifying perspective. Topics addressed include the concepts of scale and time invariance and their significance for quantum criticality, as well as brand new chapters on superfluid and superconductor quantum critical points, and quantum first order transitions. The renormalisation group in real and momentum space is also established as the proper language to describe the behaviour of systems close to a quantum phase transition. These phenomena introduce a number of theoretical challenges which are of major importance for driving new experiments. Being strongly motivated and oriented towards understanding experimental results, this is an excellent text for graduates, as well as theorists, experimentalists and those with an interest in quantum criticality.
Quantum Information Biology: From Theory of Open Quantum Systems to Adaptive Dynamics
Asano, Masanari; Basieva, Irina; Khrennikov, Andrei; Ohya, Masanori; Tanaka, Yoshiharu; Yamato, Ichiro
This chapter reviews quantum(-like) information biology (QIB). Here biology is treated widely as even covering cognition and its derivatives: psychology and decision making, sociology, and behavioral economics and finances. QIB provides an integrative description of information processing by bio-systems at all scales of life: from proteins and cells to cognition, ecological and social systems. Mathematically QIB is based on the theory of adaptive quantum systems (which covers also open quantum systems). Ideologically QIB is based on the quantum-like (QL) paradigm: complex bio-systems process information in accordance with the laws of quantum information and probability. This paradigm is supported by plenty of statistical bio-data collected at all bio-scales. QIB re ects the two fundamental principles: a) adaptivity; and, b) openness (bio-systems are fundamentally open). In addition, quantum adaptive dynamics provides the most generally possible mathematical representation of these principles.
Single-shot secure quantum network coding on butterfly network with free public communication
Owari, Masaki; Kato, Go; Hayashi, Masahito
2018-01-01
Quantum network coding on the butterfly network has been studied as a typical example of quantum multiple cast network. We propose a secure quantum network code for the butterfly network with free public classical communication in the multiple unicast setting under restricted eavesdropper’s power. This protocol certainly transmits quantum states when there is no attack. We also show the secrecy with shared randomness as additional resource when the eavesdropper wiretaps one of the channels in the butterfly network and also derives the information sending through public classical communication. Our protocol does not require verification process, which ensures single-shot security.
Injection of a single electron from static to moving quantum dots.
Bertrand, Benoit; Hermelin, Sylvain; Mortemousque, Pierre-André; Takada, Shintaro; Yamamoto, Michihisa; Tarucha, Seigo; Ludwig, Arne; Wieck, Andreas D; Bäuerle, Christopher; Meunier, Tristan
2016-05-27
We study the injection mechanism of a single electron from a static quantum dot into a moving quantum dot. The moving quantum dots are created with surface acoustic waves (SAWs) in a long depleted channel. We demonstrate that the injection process is characterized by an activation law with a threshold that depends on the SAW amplitude and on the dot-channel potential gradient. By sufficiently increasing the SAW modulation amplitude, we can reach a regime where the transfer has unity probability and is potentially adiabatic. This study points to the relevant regime to use moving dots in quantum information protocols.
Quantum cascade laser infrared spectroscopy of single cancer cells
Patel, Imran
2017-03-27
Quantum cascade laser infrared spectroscopy is a next generation novel imaging technique allowing high resolution spectral imaging of cells. We show after spectral pre-processing, identification of different cancer cell populations within minutes.
Coherent Dynamics of a Hybrid Quantum Spin-Mechanical Oscillator System
Lee, Kenneth William, III
A fully functional quantum computer must contain at least two important components: a quantum memory for storing and manipulating quantum information and a quantum data bus to securely transfer information between quantum memories. Typically, a quantum memory is composed of a matter system, such as an atom or an electron spin, due to their prolonged quantum coherence. Alternatively, a quantum data bus is typically composed of some propagating degree of freedom, such as a photon, which can retain quantum information over long distances. Therefore, a quantum computer will likely be a hybrid quantum device, consisting of two or more disparate quantum systems. However, there must be a reliable and controllable quantum interface between the memory and bus in order to faithfully interconvert quantum information. The current engineering challenge for quantum computers is scaling the device to large numbers of controllable quantum systems, which will ultimately depend on the choice of the quantum elements and interfaces utilized in the device. In this thesis, we present and characterize a hybrid quantum device comprised of single nitrogen-vacancy (NV) centers embedded in a high quality factor diamond mechanical oscillator. The electron spin of the NV center is a leading candidate for the realization of a quantum memory due to its exceptional quantum coherence times. On the other hand, mechanical oscillators are highly sensitive to a wide variety of external forces, and have the potential to serve as a long-range quantum bus between quantum systems of disparate energy scales. These two elements are interfaced through crystal strain generated by vibrations of the mechanical oscillator. Importantly, a strain interface allows for a scalable architecture, and furthermore, opens the door to integration into a larger quantum network through coupling to an optical interface. There are a few important engineering challenges associated with this device. First, there have been no
Probing quantum Hall states with single-electron transistors at high magnetic fields
Gustafsson, Martin; Yankowitz, Matthew; Forsythe, Carlos; Zhu, Xiaoyang; Dean, Cory
The sequence of fractional quantum Hall states in graphene is not yet fully understood, largely due to disorder-induced limitations of conventional transport studies. Measurements of magnetotransport in other 2D crystals are further complicated by the difficulties in making ohmic contact to the materials. On the other hand, bulk electronic compressibility can provide clear signatures of the integer and fractional quantum Hall effects, does not require ohmic contact, and can be localized to regions of low disorder. The single-electron transistor (SET) is a suitable tool for such experiments due to its small size and high charge sensitivity, which allow electric fields penetrating the 2D electron system to be detected locally and with high fidelity. Here we report studies of exfoliated 2D van der Waals materials fully encapsulated in flakes of hexagonal boron nitride. SETs are fabricated lithographically on top of the encapsulation, yielding a structure which lends itself to experiments at high electric and magnetic fields. We demonstrate the method on monolayer graphene, where we observe fractional quantum Hall states at all filling factors ν = n / 3 up to n = 17 and extract their associated energy gaps for magnetic fields up to 31 tesla.
Frequency and bandwidth conversion of single photons in a room-temperature diamond quantum memory.
Fisher, Kent A G; England, Duncan G; MacLean, Jean-Philippe W; Bustard, Philip J; Resch, Kevin J; Sussman, Benjamin J
2016-04-05
The spectral manipulation of photons is essential for linking components in a quantum network. Large frequency shifts are needed for conversion between optical and telecommunication frequencies, while smaller shifts are useful for frequency-multiplexing quantum systems, in the same way that wavelength division multiplexing is used in classical communications. Here we demonstrate frequency and bandwidth conversion of single photons in a room-temperature diamond quantum memory. Heralded 723.5 nm photons, with 4.1 nm bandwidth, are stored as optical phonons in the diamond via a Raman transition. Upon retrieval from the diamond memory, the spectral shape of the photons is determined by a tunable read pulse through the reverse Raman transition. We report central frequency tunability over 4.2 times the input bandwidth, and bandwidth modulation between 0.5 and 1.9 times the input bandwidth. Our results demonstrate the potential for diamond, and Raman memories in general, as an integrated platform for photon storage and spectral conversion.
Noise management to achieve superiority in quantum information systems.
Nemoto, Kae; Devitt, Simon; Munro, William J
2017-08-06
Quantum information systems are expected to exhibit superiority compared with their classical counterparts. This superiority arises from the quantum coherences present in these quantum systems, which are obviously absent in classical ones. To exploit such quantum coherences, it is essential to control the phase information in the quantum state. The phase is analogue in nature, rather than binary. This makes quantum information technology fundamentally different from our classical digital information technology. In this paper, we analyse error sources and illustrate how these errors must be managed for the system to achieve the required fidelity and a quantum superiority.This article is part of the themed issue 'Quantum technology for the 21st century'. © 2017 The Author(s).
Sapienza, Luca; Liu, Jin; Song, Jin Dong; Fält, Stefan; Wegscheider, Werner; Badolato, Antonio; Srinivasan, Kartik
2017-07-24
We report on a combined photoluminescence imaging and atomic force microscopy study of single, isolated self-assembled InAs quantum dots. The motivation of this work is to determine an approach that allows to assess single quantum dots as candidates for quantum nanophotonic devices. By combining optical and scanning probe characterization techniques, we find that single quantum dots often appear in the vicinity of comparatively large topographic features. Despite this, the quantum dots generally do not exhibit significant differences in their non-resonantly pumped emission spectra in comparison to quantum dots appearing in defect-free regions, and this behavior is observed across multiple wafers produced in different growth chambers. Such large surface features are nevertheless a detriment to applications in which single quantum dots are embedded within nanofabricated photonic devices: they are likely to cause large spectral shifts in the wavelength of cavity modes designed to resonantly enhance the quantum dot emission, thereby resulting in a nominally perfectly-fabricated single quantum dot device failing to behave in accordance with design. We anticipate that the approach of screening quantum dots not only based on their optical properties, but also their surrounding surface topographies, will be necessary to improve the yield of single quantum dot nanophotonic devices.
Ultra-Low Power Optical Transistor Using a Single Quantum Dot Embedded in a Photonic Wire
DEFF Research Database (Denmark)
Nguyen, H.A.; Grange, T.; Malik, N.S.
2017-01-01
Using a single InAs quantum dot embedded in a GaAs photonic wire, we realize a giant non-linearity between two optical modes to experimentally demonstrate an all-optical transistor triggered by 10 photons.......Using a single InAs quantum dot embedded in a GaAs photonic wire, we realize a giant non-linearity between two optical modes to experimentally demonstrate an all-optical transistor triggered by 10 photons....
Water drops kinematic analysis: the classic-quantum and single-multiparticle viewpoints
Wrachien, Daniele; Lorenzini, Giulio
2013-03-01
One of the most challenging modelling problems in science is that of a particle crossing a gaseous mean. In sprinkler irrigation this applies to a water droplet travelling from the nozzle to the ground. The challenge mainly refers to the intense difficulty in writing and solving the system of governing equations for such complicate process, where many non-linearities occur when describing the relations and dependences among one influential parameter and another. The problem becomes even more complicate when not just a single droplet alone is assessed but a multi-droplet system is accounted for as, in addition to the inter-parameter dependencies, it is also observed an inter-droplet reciprocal affection, mainly due to electrical interactions between the hydrogen and the oxygen atoms of the different water molecules. An alternative to traditional classic approaches to analyse water droplet dynamics in sprinkler irrigation have been recently proposed in the form of a quantum approach, but the whole classic-quantum and single-droplet versus multi-droplet alternatives need to be discussed and pinpointed and these are among the main aims of the present paper which focuses on the theoretical part of the issue, thus highlighting the new perspectives of a deeper comprehension in the spray flow related phenomena.
On-chip single photon filtering and multiplexing in hybrid quantum photonic circuits.
Elshaari, Ali W; Zadeh, Iman Esmaeil; Fognini, Andreas; Reimer, Michael E; Dalacu, Dan; Poole, Philip J; Zwiller, Val; Jöns, Klaus D
2017-08-30
Quantum light plays a pivotal role in modern science and future photonic applications. Since the advent of integrated quantum nanophotonics different material platforms based on III-V nanostructures-, colour centers-, and nonlinear waveguides as on-chip light sources have been investigated. Each platform has unique advantages and limitations; however, all implementations face major challenges with filtering of individual quantum states, scalable integration, deterministic multiplexing of selected quantum emitters, and on-chip excitation suppression. Here we overcome all of these challenges with a hybrid and scalable approach, where single III-V quantum emitters are positioned and deterministically integrated in a complementary metal-oxide-semiconductor-compatible photonic circuit. We demonstrate reconfigurable on-chip single-photon filtering and wavelength division multiplexing with a foot print one million times smaller than similar table-top approaches, while offering excitation suppression of more than 95 dB and efficient routing of single photons over a bandwidth of 40 nm. Our work marks an important step to harvest quantum optical technologies' full potential.Combining different integration platforms on the same chip is currently one of the main challenges for quantum technologies. Here, Elshaari et al. show III-V Quantum Dots embedded in nanowires operating in a CMOS compatible circuit, with controlled on-chip filtering and tunable routing.
Quantum discord dynamics of two qubits in single-mode cavities
International Nuclear Information System (INIS)
Wang Chen; Chen Qing-Hu
2013-01-01
The dynamics of quantum discord for two identical qubits in two independent single-mode cavities and a common single-mode cavity are discussed. For the initial Bell state with correlated spins, while the entanglement sudden death can occur, the quantum discord vanishes only at discrete moments in the independent cavities and never vanishes in the common cavity. Interestingly, quantum discord and entanglement show opposite behavior in the common cavity, unlike in the independent cavities. For the initial Bell state with anti-correlated spins, quantum discord and entanglement behave in the same way for both independent cavities and a common cavity. It is found that the detunings always stabilize the quantum discord. (general)
HIGH-SPEED SINGLE QUANTUM DOT IMAGING OF IN LIVE CELLS REVEAL HOP DIFFUSION
DEFF Research Database (Denmark)
Lagerholm, B. Christoffer; Clausen, Mathias P.
2011-01-01
Ultra high-speed single particle tracking (image frame rates 40-50 kHz) experiments with 40 nm gold particles has indicated that lipids and proteins in the plasma membrane undergo hop-diffusion between nanometer sized compartments (Fujiwara et al. (2002) J Cell Biol. 157:1071-81). These findings...... have yet to be independently confirmed. In this work, we show that high-speed single particle tracking with quantum dots (QDs) and using a standard wide-field fluorescence microscope and an EMCCD is possible at image acquisition rates of up to ~2000 Hz. The spatial precision in these experiments is ~40...... nm (as determined from the standard deviation of repeated position measurements of an immobile QD on a cell). Using this system, we show that membrane proteins and lipids, which have been exogenously labeled with functionalized QDs, show examples of three types of motion in the plasma membrane...
Quantum properties of a parametric four-wave mixing in a Raman type atomic system
Directory of Open Access Journals (Sweden)
Sharypov A.V.
2017-01-01
Full Text Available We present a study of the quantum properties of two light fields used to parametric four-wave mixing in a Raman type atomic system. The system realizes an effective Hamiltonian of beamsplitter type coupling between the light fields, which allows to control squeezing and amplitude distribution of the light fields, as well as realizing their entanglement. The scheme can be feasibly applied to engineer the quantum properties of two single-mode light fields in properly chosen input states.
Murashita, Yûto; Gong, Zongping; Ashida, Yuto; Ueda, Masahito
2017-10-01
The thermodynamics of quantum coherence has attracted growing attention recently, where the thermodynamic advantage of quantum superposition is characterized in terms of quantum thermodynamics. We investigate the thermodynamic effects of quantum coherent driving in the context of the fluctuation theorem. We adopt a quantum-trajectory approach to investigate open quantum systems under feedback control. In these systems, the measurement backaction in the forward process plays a key role, and therefore the corresponding time-reversed quantum measurement and postselection must be considered in the backward process, in sharp contrast to the classical case. The state reduction associated with quantum measurement, in general, creates a zero-probability region in the space of quantum trajectories of the forward process, which causes singularly strong irreversibility with divergent entropy production (i.e., absolute irreversibility) and hence makes the ordinary fluctuation theorem break down. In the classical case, the error-free measurement ordinarily leads to absolute irreversibility, because the measurement restricts classical paths to the region compatible with the measurement outcome. In contrast, in open quantum systems, absolute irreversibility is suppressed even in the presence of the projective measurement due to those quantum rare events that go through the classically forbidden region with the aid of quantum coherent driving. This suppression of absolute irreversibility exemplifies the thermodynamic advantage of quantum coherent driving. Absolute irreversibility is shown to emerge in the absence of coherent driving after the measurement, especially in systems under time-delayed feedback control. We show that absolute irreversibility is mitigated by increasing the duration of quantum coherent driving or decreasing the delay time of feedback control.
Engineering quantum hyperentangled states in atomic systems
International Nuclear Information System (INIS)
Nawaz, Mehwish; Islam, Rameez ul; Ikram, Manzoor; Abbas, Tasawar
2017-01-01
Hyperentangled states have boosted many quantum informatics tasks tremendously due to their high information content per quantum entity. Until now, however, the engineering and manipulation of such states were limited to photonic systems only. In present article, we propose generating atomic hyperentanglement involving atomic internal states as well as atomic external momenta states. Hypersuperposition, hyperentangled cluster, Bell and Greenberger–Horne–Zeilinger states are engineered deterministically through resonant and off-resonant Bragg diffraction of neutral two-level atoms. Based on the characteristic parameters of the atomic Bragg diffraction, such as comparatively large interaction times and spatially well-separated outputs, such decoherence resistant states are expected to exhibit good overall fidelities and offer the evident benefits of full controllability, along with extremely high detection efficiency, over the counterpart photonic states comprised entirely of flying qubits. (paper)
Quantum coherence behaviors of fermionic system in non-inertial frame
Huang, Zhiming; Situ, Haozhen
2018-04-01
In this paper, we analyze the quantum coherence behaviors of a single qubit in the relativistic regime beyond the single-mode approximation. Firstly, we investigate the freezing condition of quantum coherence in fermionic system. We also study the quantum coherence tradeoff between particle and antiparticle sector. It is found that there exists quantum coherence transfer between particle and antiparticle sector, but the coherence lost in particle sector is not entirely compensated by the coherence generation of antiparticle sector. Besides, we emphatically discuss the cohering power and decohering power of Unruh channel with respect to the computational basis. It is shown that cohering power is vanishing and decohering power is dependent of the choice of Unruh mode and acceleration. Finally, we compare the behaviors of quantum coherence with geometric quantum discord and entanglement in relativistic setup. Our results show that this quantifiers in two region converge at infinite acceleration limit, which implies that this measures become independent of Unruh modes beyond the single-mode approximations. It is also demonstrated that the robustness of quantum coherence and geometric quantum discord are better than entanglement under the influence of acceleration, since entanglement undergoes sudden death.
A toy model of a macroscopic quantum coherent system
International Nuclear Information System (INIS)
Muñoz-Vega, R; Flores-Godoy, J J; Fernández-Anaya, G; Salinas-Hernández, E
2013-01-01
This paper deals with macroscopic quantum coherence while using only basic quantum mechanics. A square double well is used to illustrate Leggett–Caldeira oscillations. The effect of thermal radiation on two-level systems is discussed. The concept of decoherence is introduced at an elementary level. Reference values are deduced for the energy, temperature and time scales involved in macroscopic quantum coherence. (paper)
Note on transmitted complexity for quantum dynamical systems
Watanabe, Noboru; Muto, Masahiro
2017-10-01
Transmitted complexity (mutual entropy) is one of the important measures for quantum information theory developed recently in several ways. We will review the fundamental concepts of the Kossakowski, Ohya and Watanabe entropy and define a transmitted complexity for quantum dynamical systems. This article is part of the themed issue `Second quantum revolution: foundational questions'.
Fano Effect and Quantum Entanglement in Hybrid Semiconductor Quantum Dot-Metal Nanoparticle System.
He, Yong; Zhu, Ka-Di
2017-06-20
In this paper, we review the investigation for the light-matter interaction between surface plasmon field in metal nanoparticle (MNP) and the excitons in semiconductor quantum dots (SQDs) in hybrid SQD-MNP system under the full quantum description. The exciton-plasmon interaction gives rise to the modified decay rate and the exciton energy shift which are related to the exciton energy by using a quantum transformation method. We illustrate the responses of the hybrid SQD-MNP system to external field, and reveal Fano effect shown in the absorption spectrum. We demonstrate quantum entanglement between two SQD mediated by surface plasmon field. In the absence of a laser field, concurrence of quantum entanglement will disappear after a few ns. If the laser field is present, the steady states appear, so that quantum entanglement produced will reach a steady-state entanglement. Because one of all optical pathways to induce Fano effect refers to the generation of quantum entangled states, It is shown that the concurrence of quantum entanglement can be obtained by observation for Fano effect. In a hybrid system including two MNP and a SQD, because the two Fano quantum interference processes share a segment of all optical pathways, there is correlation between the Fano effects of the two MNP. The investigations for the light-matter interaction in hybrid SQD-MNP system can pave the way for the development of the optical processing devices and quantum information based on the exciton-plasmon interaction.
Fano Effect and Quantum Entanglement in Hybrid Semiconductor Quantum Dot-Metal Nanoparticle System
Directory of Open Access Journals (Sweden)
Yong He
2017-06-01
Full Text Available In this paper, we review the investigation for the light-matter interaction between surface plasmon field in metal nanoparticle (MNP and the excitons in semiconductor quantum dots (SQDs in hybrid SQD-MNP system under the full quantum description. The exciton-plasmon interaction gives rise to the modified decay rate and the exciton energy shift which are related to the exciton energy by using a quantum transformation method. We illustrate the responses of the hybrid SQD-MNP system to external field, and reveal Fano effect shown in the absorption spectrum. We demonstrate quantum entanglement between two SQD mediated by surface plasmon field. In the absence of a laser field, concurrence of quantum entanglement will disappear after a few ns. If the laser field is present, the steady states appear, so that quantum entanglement produced will reach a steady-state entanglement. Because one of all optical pathways to induce Fano effect refers to the generation of quantum entangled states, It is shown that the concurrence of quantum entanglement can be obtained by observation for Fano effect. In a hybrid system including two MNP and a SQD, because the two Fano quantum interference processes share a segment of all optical pathways, there is correlation between the Fano effects of the two MNP. The investigations for the light-matter interaction in hybrid SQD-MNP system can pave the way for the development of the optical processing devices and quantum information based on the exciton-plasmon interaction.
Cadiz, Fabian; Djeffal, Abdelhak; Lagarde, Delphine; Balocchi, Andrea; Tao, Bingshan; Xu, Bo; Liang, Shiheng; Stoffel, Mathieu; Devaux, Xavier; Jaffres, Henri; George, Jean-Marie; Hehn, Michel; Mangin, Stephane; Carrere, Helene; Marie, Xavier; Amand, Thierry; Han, Xiufeng; Wang, Zhanguo; Urbaszek, Bernhard; Lu, Yuan; Renucci, Pierre
2018-04-11
The emission of circularly polarized light from a single quantum dot relies on the injection of carriers with well-defined spin polarization. Here we demonstrate single dot electroluminescence (EL) with a circular polarization degree up to 35% at zero applied magnetic field. The injection of spin-polarized electrons is achieved by combining ultrathin CoFeB electrodes on top of a spin-LED device with p-type InGaAs quantum dots in the active region. We measure an Overhauser shift of several microelectronvolts at zero magnetic field for the positively charged exciton (trion X + ) EL emission, which changes sign as we reverse the injected electron spin orientation. This is a signature of dynamic polarization of the nuclear spins in the quantum dot induced by the hyperfine interaction with the electrically injected electron spin. This study paves the way for electrical control of nuclear spin polarization in a single quantum dot without any external magnetic field.
Parallel decoherence in composite quantum systems
Indian Academy of Sciences (India)
Home; Journals; Pramana – Journal of Physics; Volume 79; Issue 2 ... Quantum decoherence; quantum Brownian motion; quantum structure; entanglement relativity. ... For the standard quantum Brownian motion (QBM) model, we point out the occurrence of simultaneous (parallel), mutually irreducible and autonomous ...
Optimal dynamics for quantum-state and entanglement transfer through homogeneous quantum systems
International Nuclear Information System (INIS)
Banchi, L.; Apollaro, T. J. G.; Cuccoli, A.; Vaia, R.; Verrucchi, P.
2010-01-01
The capability of faithfully transmit quantum states and entanglement through quantum channels is one of the key requirements for the development of quantum devices. Different solutions have been proposed to accomplish such a challenging task, which, however, require either an ad hoc engineering of the internal interactions of the physical system acting as the channel or specific initialization procedures. Here we show that optimal dynamics for efficient quantum-state and entanglement transfer can be attained in generic quantum systems with homogeneous interactions by tuning the coupling between the system and the two attached qubits. We devise a general procedure to determine the optimal coupling, and we explicitly implement it in the case of a channel consisting of a spin-(1/2)XY chain. The quality of quantum-state and entanglement transfer is found to be very good and, remarkably, almost independent of the channel length.
Fischbach, Sarah; Schlehahn, Alexander; Thoma, Alexander; Srocka, Nicole; Gissibl, Timo; Ristok, Simon; Thiele, Simon; Kaganskiy, Arsenty; Strittmatter, André; Heindel, Tobias; Rodt, Sven; Herkommer, Alois; Giessen, Harald; Reitzenstein, Stephan
2017-06-21
Integrated single-photon sources with high photon-extraction efficiency are key building blocks for applications in the field of quantum communications. We report on a bright single-photon source realized by on-chip integration of a deterministic quantum dot microlens with a 3D-printed multilens micro-objective. The device concept benefits from a sophisticated combination of in situ 3D electron-beam lithography to realize the quantum dot microlens and 3D femtosecond direct laser writing for creation of the micro-objective. In this way, we obtain a high-quality quantum device with broadband photon-extraction efficiency of (40 ± 4)% and high suppression of multiphoton emission events with g (2) (τ = 0) < 0.02. Our results highlight the opportunities that arise from tailoring the optical properties of quantum emitters using integrated optics with high potential for the further development of plug-and-play fiber-coupled single-photon sources.
A two-qubit photonic quantum processor and its application to solving systems of linear equations
Barz, Stefanie; Kassal, Ivan; Ringbauer, Martin; Lipp, Yannick Ole; Dakić, Borivoje; Aspuru-Guzik, Alán; Walther, Philip
2014-01-01
Large-scale quantum computers will require the ability to apply long sequences of entangling gates to many qubits. In a photonic architecture, where single-qubit gates can be performed easily and precisely, the application of consecutive two-qubit entangling gates has been a significant obstacle. Here, we demonstrate a two-qubit photonic quantum processor that implements two consecutive CNOT gates on the same pair of polarisation-encoded qubits. To demonstrate the flexibility of our system, we implement various instances of the quantum algorithm for solving of systems of linear equations. PMID:25135432
The transition to chaos conservative classical systems and quantum manifestations
Reichl, Linda E
2004-01-01
This book provides a thorough and comprehensive discussion of classical and quantum chaos theory for bounded systems and for scattering processes Specific discussions include • Noether’s theorem, integrability, KAM theory, and a definition of chaotic behavior • Area-preserving maps, quantum billiards, semiclassical quantization, chaotic scattering, scaling in classical and quantum dynamics, dynamic localization, dynamic tunneling, effects of chaos in periodically driven systems and stochastic systems • Random matrix theory and supersymmetry The book is divided into several parts Chapters 2 through 4 deal with the dynamics of nonlinear conservative classical systems Chapter 5 and several appendices give a thorough grounding in random matrix theory and supersymmetry techniques Chapters 6 and 7 discuss the manifestations of chaos in bounded quantum systems and open quantum systems respectively Chapter 8 focuses on the semiclassical description of quantum systems with underlying classical chaos, and Chapt...
Integrable quantum Stäckel systems
International Nuclear Information System (INIS)
Błaszak, Maciej; Domański, Ziemowit; Sergyeyev, Artur; Szablikowski, Błażej M.
2013-01-01
The Stäckel separability of a Hamiltonian system is well known to ensure existence of a complete set of Poisson commuting integrals of motion quadratic in the momenta. We consider a class of Stäckel separable systems where the entries of the Stäckel matrix are monomials in the separation variables. We show that the only systems in this class for which the integrals of motion arising from the Stäckel construction keep commuting after quantization are, up to natural equivalence transformations, the so-called Benenti systems. Moreover, it turns out that the latter are the only quantum separable systems in the class under study.
Quantum-like behavior without quantum physics I : Kinematics of neural-like systems.
Selesnick, S A; Rawling, J P; Piccinini, Gualtiero
2017-09-01
Recently there has been much interest in the possible quantum-like behavior of the human brain in such functions as cognition, the mental lexicon, memory, etc., producing a vast literature. These studies are both empirical and theoretical, the tenets of the theory in question being mainly, and apparently inevitably, those of quantum physics itself, for lack of other arenas in which quantum-like properties are presumed to obtain. However, attempts to explain this behavior on the basis of actual quantum physics going on at the atomic or molecular level within some element of brain or neuronal anatomy (other than the ordinary quantum physics that underlies everything), do not seem to survive much scrutiny. Moreover, it has been found empirically that the usual physics-like Hilbert space model seems not to apply in detail to human cognition in the large. In this paper we lay the groundwork for a theory that might explain the provenance of quantum-like behavior in complex systems whose internal structure is essentially hidden or inaccessible. The approach is via the logic obeyed by these systems which is similar to, but not identical with, the logic obeyed by actual quantum systems. The results reveal certain effects in such systems which, though quantum-like, are not identical to the kinds of quantum effects found in physics. These effects increase with the size of the system.
The Conditional Entropy Power Inequality for Bosonic Quantum Systems
DEFF Research Database (Denmark)
de Palma, Giacomo; Trevisan, Dario
2018-01-01
We prove the conditional Entropy Power Inequality for Gaussian quantum systems. This fundamental inequality determines the minimum quantum conditional von Neumann entropy of the output of the beam-splitter or of the squeezing among all the input states where the two inputs are conditionally...... independent given the memory and have given quantum conditional entropies. We also prove that, for any couple of values of the quantum conditional entropies of the two inputs, the minimum of the quantum conditional entropy of the output given by the conditional Entropy Power Inequality is asymptotically...... achieved by a suitable sequence of quantum Gaussian input states. Our proof of the conditional Entropy Power Inequality is based on a new Stam inequality for the quantum conditional Fisher information and on the determination of the universal asymptotic behaviour of the quantum conditional entropy under...
Linear dynamical quantum systems analysis, synthesis, and control
Nurdin, Hendra I
2017-01-01
This monograph provides an in-depth treatment of the class of linear-dynamical quantum systems. The monograph presents a detailed account of the mathematical modeling of these systems using linear algebra and quantum stochastic calculus as the main tools for a treatment that emphasizes a system-theoretic point of view and the control-theoretic formulations of quantum versions of familiar problems from the classical (non-quantum) setting, including estimation and filtering, realization theory, and feedback control. Both measurement-based feedback control (i.e., feedback control by a classical system involving a continuous-time measurement process) and coherent feedback control (i.e., feedback control by another quantum system without the intervention of any measurements in the feedback loop) are treated. Researchers and graduates studying systems and control theory, quantum probability and stochastics or stochastic control whether from backgrounds in mechanical or electrical engineering or applied mathematics ...
Quantum revivals and magnetization tunneling in effective spin systems
Krizanac, M.; Altwein, D.; Vedmedenko, E. Y.; Wiesendanger, R.
2016-03-01
Quantum mechanical objects or nano-objects have been proposed as bits for information storage. While time-averaged properties of magnetic, quantum-mechanical particles have been extensively studied experimentally and theoretically, experimental investigations of the real time evolution of magnetization in the quantum regime were not possible until recent developments in pump-probe techniques. Here we investigate the quantum dynamics of effective spin systems by means of analytical and numerical treatments. Particular attention is paid to the quantum revival time and its relation to the magnetization tunneling. The quantum revival time has been initially defined as the recurrence time of a total wave-function. Here we show that the quantum revivals of wave-functions and expectation values in spin systems may be quite different which gives rise to a more sophisticated definition of the quantum revival within the realm of experimental research. Particularly, the revival times for integer spins coincide which is not the case for half-integer spins. Furthermore, the quantum revival is found to be shortest for integer ratios between the on-site anisotropy and an external magnetic field paving the way to novel methods of anisotropy measurements. We show that the quantum tunneling of magnetization at avoided level crossing is coherent to the quantum revival time of expectation values, leading to a connection between these two fundamental properties of quantum mechanical spins.
Scavenging quantum information: Multiple observations of quantum systems
Energy Technology Data Exchange (ETDEWEB)
Rapcan, P. [Research Center for Quantum Information, Institute of Physics, Slovak Academy of Sciences, Dubravska cesta 9, 845 11 Bratislava (Slovakia); Calsamiglia, J.; Munoz-Tapia, R. [Fisica Teorica: Informacio i Fenomens Quantics, Edifici Cn, Universitat Autonoma de Barcelona, E-08193 Bellaterra (Barcelona) (Spain); Bagan, E. [Fisica Teorica: Informacio i Fenomens Quantics, Edifici Cn, Universitat Autonoma de Barcelona, E-08193 Bellaterra (Barcelona) (Spain); Department of Physics, Hunter College of the City University of New York, 695 Park Avenue, New York, New York 10021 (United States); Physics Department, Brookhaven National Laboratory, Upton, New York 11973 (United States); Buzek, V. [Research Center for Quantum Information, Institute of Physics, Slovak Academy of Sciences, Dubravska cesta 9, 845 11 Bratislava (Slovakia); Faculty of Informatics, Masaryk University, Botanicka 68a, CZ-602 00 Brno (Czech Republic)
2011-09-15
Given an unknown state of a qudit that has already been measured optimally, can one still extract any information about the original unknown state? Clearly, after a maximally informative measurement, the state of the system collapses into a postmeasurement state from which the same observer cannot obtain further information about the original state of the system. However, the system still encodes a significant amount of information about the original preparation for a second observer who is unaware of the actions of the first one. We study how a series of independent observers can obtain, or can scavenge, information about the unknown state of a system (quantified by the fidelity) when they sequentially measure it. We give closed-form expressions for the estimation fidelity when one or several qudits are available to carry information about the single-qudit state, and we study the classical limit when an arbitrarily large number of observers can obtain (nearly) complete information on the system. In addition to the case where all observers perform most informative measurements, we study the scenario where a finite number of observers estimates the state with equal fidelity, regardless of their position in the measurement sequence and the scenario where all observers use identical measurement apparatuses (up to a mutually unknown orientation) chosen so that a particular observer's estimation fidelity is maximized.
Quantum Zeno effect for exponentially decaying systems
International Nuclear Information System (INIS)
Koshino, Kazuki; Shimizu, Akira
2004-01-01
The quantum Zeno effect - suppression of decay by frequent measurements - was believed to occur only when the response of the detector is so quick that the initial tiny deviation from the exponential decay law is detectable. However, we show that it can occur even for exactly exponentially decaying systems, for which this condition is never satisfied, by considering a realistic case where the detector has a finite energy band of detection. The conventional theories correspond to the limit of an infinite bandwidth. This implies that the Zeno effect occurs more widely than expected thus far
Negative quantum capacitance induced by midgap states in single-layer graphene.
Wang, Lin; Wang, Yang; Chen, Xiaolong; Zhu, Wei; Zhu, Chao; Wu, Zefei; Han, Yu; Zhang, Mingwei; Li, Wei; He, Yuheng; Xiong, Wei; Law, Kam Tuen; Su, Dangsheng; Wang, Ning
2013-01-01
We demonstrate that single-layer graphene (SLG) decorated with a high density of Ag adatoms displays the unconventional phenomenon of negative quantum capacitance. The Ag adatoms act as resonant impurities and form nearly dispersionless resonant impurity bands near the charge neutrality point (CNP). Resonant impurities quench the kinetic energy and drive the electrons to the Coulomb energy dominated regime with negative compressibility. In the absence of a magnetic field, negative quantum capacitance is observed near the CNP. In the quantum Hall regime, negative quantum capacitance behavior at several Landau level positions is displayed, which is associated with the quenching of kinetic energy by the formation of Landau levels. The negative quantum capacitance effect near the CNP is further enhanced in the presence of Landau levels due to the magnetic-field-enhanced Coulomb interactions.
Toward quantum state tomography of a single polariton state of an atomic ensemble
DEFF Research Database (Denmark)
Christensen, S.L.; Béguin, J.B.; Sørensen, H.L.
2013-01-01
We present a proposal and a feasibility study for the creation and quantum state tomography of a single polariton state of an atomic ensemble. The collective non-classical and non-Gaussian state of the ensemble is generated by detection of a single forward-scattered photon. The state is subsequen...... the feasibility of the proposed method for the detection of a non-classical and non-Gaussian state of the mesoscopic atomic ensemble. This work represents the first attempt at hybrid discrete-continuous variable quantum state processing with atomic memories.......We present a proposal and a feasibility study for the creation and quantum state tomography of a single polariton state of an atomic ensemble. The collective non-classical and non-Gaussian state of the ensemble is generated by detection of a single forward-scattered photon. The state...
Workshop on quantum stochastic differential equations for the quantum simulation of physical systems
2016-09-22
and a milestone as ARL becomes a significant player in the development of mathematical tools for quantum systems of interest to the Army...Commun. Math . Phys. 104, 457 (1986). [5] M.-H. Chang, Quantum stochastics, Cambridge Series in Statistical and Probabilistic Mathematics (2014...Phys. A 28, 5401 (1995). [9] M. J. Kastoryano and K. Temme, Quantum logarithmic Sobolev inequalities and rapid mixing, J. Math . Phys. 54, 052202
Solving Systems of Linear Equations with a Superconducting Quantum Processor.
Zheng, Yarui; Song, Chao; Chen, Ming-Cheng; Xia, Benxiang; Liu, Wuxin; Guo, Qiujiang; Zhang, Libo; Xu, Da; Deng, Hui; Huang, Keqiang; Wu, Yulin; Yan, Zhiguang; Zheng, Dongning; Lu, Li; Pan, Jian-Wei; Wang, H; Lu, Chao-Yang; Zhu, Xiaobo
2017-05-26
Superconducting quantum circuits are a promising candidate for building scalable quantum computers. Here, we use a four-qubit superconducting quantum processor to solve a two-dimensional system of linear equations based on a quantum algorithm proposed by Harrow, Hassidim, and Lloyd [Phys. Rev. Lett. 103, 150502 (2009)PRLTAO0031-900710.1103/PhysRevLett.103.150502], which promises an exponential speedup over classical algorithms under certain circumstances. We benchmark the solver with quantum inputs and outputs, and characterize it by nontrace-preserving quantum process tomography, which yields a process fidelity of 0.837±0.006. Our results highlight the potential of superconducting quantum circuits for applications in solving large-scale linear systems, a ubiquitous task in science and engineering.
Quantum Hall states of atomic Bose gases: Density profiles in single-layer and multilayer geometries
International Nuclear Information System (INIS)
Cooper, N. R.; Lankvelt, F. J. M. van; Reijnders, J. W.; Schoutens, K.
2005-01-01
We describe the density profiles of confined atomic Bose gases in the high-rotation limit, in single-layer and multilayer geometries. We show that, in a local-density approximation, the density in a single layer shows a landscape of quantized steps due to the formation of incompressible liquids, which are analogous to fractional quantum Hall liquids for a two-dimensional electron gas in a strong magnetic field. In a multilayered setup we find different phases, depending on the strength of the interlayer tunneling t. We discuss the situation where a vortex lattice in the three-dimensional condensate (at large tunneling) undergoes quantum melting at a critical tunneling t c 1 . For tunneling well below t c 1 one expects weakly coupled or isolated layers, each exhibiting a landscape of quantum Hall liquids. After expansion, this gives a radial density distribution with characteristic features (cusps) that provide experimental signatures of the quantum Hall liquids
Quantum dynamics of quantum bits
International Nuclear Information System (INIS)
Nguyen, Bich Ha
2011-01-01
The theory of coherent oscillations of the matrix elements of the density matrix of the two-state system as a quantum bit is presented. Different calculation methods are elaborated in the case of a free quantum bit. Then the most appropriate methods are applied to the study of the density matrices of the quantum bits interacting with a classical pumping radiation field as well as with the quantum electromagnetic field in a single-mode microcavity. The theory of decoherence of a quantum bit in Markovian approximation is presented. The decoherence of a quantum bit interacting with monoenergetic photons in a microcavity is also discussed. The content of the present work can be considered as an introduction to the study of the quantum dynamics of quantum bits. (review)
Quantum simulation of strongly correlated condensed matter systems
Hofstetter, W.; Qin, T.
2018-04-01
We review recent experimental and theoretical progress in realizing and simulating many-body phases of ultracold atoms in optical lattices, which gives access to analog quantum simulations of fundamental model Hamiltonians for strongly correlated condensed matter systems, such as the Hubbard model. After a general introduction to quantum gases in optical lattices, their preparation and cooling, and measurement techniques for relevant observables, we focus on several examples, where quantum simulations of this type have been performed successfully during the past years: Mott-insulator states, itinerant quantum magnetism, disorder-induced localization and its interplay with interactions, and topological quantum states in synthetic gauge fields.
Liang, Lin-Mei; Sun, Shi-Hai; Jiang, Mu-Sheng; Li, Chun-Yan
2014-10-01
In general, quantum key distribution (QKD) has been proved unconditionally secure for perfect devices due to quantum uncertainty principle, quantum noncloning theorem and quantum nondividing principle which means that a quantum cannot be divided further. However, the practical optical and electrical devices used in the system are imperfect, which can be exploited by the eavesdropper to partially or totally spy the secret key between the legitimate parties. In this article, we first briefly review the recent work on quantum hacking on some experimental QKD systems with respect to imperfect devices carried out internationally, then we will present our recent hacking works in details, including passive faraday mirror attack, partially random phase attack, wavelength-selected photon-number-splitting attack, frequency shift attack, and single-photon-detector attack. Those quantum attack reminds people to improve the security existed in practical QKD systems due to imperfect devices by simply adding countermeasure or adopting a totally different protocol such as measurement-device independent protocol to avoid quantum hacking on the imperfection of measurement devices [Lo, et al., Phys. Rev. Lett., 2012, 108: 130503].
Energy Technology Data Exchange (ETDEWEB)
Dal Savio, C.
2006-02-20
Single InAs quantum dots (QDs) grown with the Stranski-Krastanov method in a In{sub 0.12}Ga{sub 0.88}As quantum well embedded in GaAs and emitting in the near infrared have been optically investigated. To perform QD spectroscopy at low temperatures a very stable micro-photoluminescence ({mu}-PL) microscope set-up fully integrated in a liquid helium (LHe) cryostate has been successfully developed. The system is based on the cold finger technique and a Fourier Transform (FT) spectrometer combined with a nitrogen cooled Ge detector. Photoluminescence of the QDs was excited non resonantly with a He-Ne laser and single dot spectroscopy was carried out at temperatures below 60 K. The experimental set-up allows mapping of the optical emission by recording spectra for every point of a scan grid. This mapping mode is used to acquire optical images and to locate a particular dot for investigation. Series of measurement on a single QD were normally performed over a long time (from a few days to a week), with the need of daily adjustment in the sub-micrometer range. At low excitation power a single sharp line (E{sub x}) arising from recombination of a single exciton in the dot is observed. Varying the excitation density the spectra become more complex, with appearance of the biexciton emission line (E{sub xx}) on the lower energies side of the E{sub x} line, followed by emission from excitons occupying higher shells in the dot. Measured biexciton binding energies and power dependence are in good agreement with values reported in the literature. The temperature dependence of the optical emission was investigated. The energy shows the characteristic decrease related to the shrinking of the semiconductor band gap, while the linewidth evolution is compatible with broadening due to coupling with acoustic and optical phonons. A statistics of biexciton binding energies over a dozen of dots was acquired and the results compared with single QD spectroscopy data available in the
Deterministic quantum teleportation with feed-forward in a solid state system.
Steffen, L; Salathe, Y; Oppliger, M; Kurpiers, P; Baur, M; Lang, C; Eichler, C; Puebla-Hellmann, G; Fedorov, A; Wallraff, A
2013-08-15
Engineered macroscopic quantum systems based on superconducting electronic circuits are attractive for experimentally exploring diverse questions in quantum information science. At the current state of the art, quantum bits (qubits) are fabricated, initialized, controlled, read out and coupled to each other in simple circuits. This enables the realization of basic logic gates, the creation of complex entangled states and the demonstration of algorithms or error correction. Using different variants of low-noise parametric amplifiers, dispersive quantum non-demolition single-shot readout of single-qubit states with high fidelity has enabled continuous and discrete feedback control of single qubits. Here we realize full deterministic quantum teleportation with feed-forward in a chip-based superconducting circuit architecture. We use a set of two parametric amplifiers for both joint two-qubit and individual qubit single-shot readout, combined with flexible real-time digital electronics. Our device uses a crossed quantum bus technology that allows us to create complex networks with arbitrary connecting topology in a planar architecture. The deterministic teleportation process succeeds with order unit probability for any input state, as we prepare maximally entangled two-qubit states as a resource and distinguish all Bell states in a single two-qubit measurement with high efficiency and high fidelity. We teleport quantum states between two macroscopic systems separated by 6 mm at a rate of 10(4) s(-1), exceeding other reported implementations. The low transmission loss of superconducting waveguides is likely to enable the range of this and other schemes to be extended to significantly larger distances, enabling tests of non-locality and the realization of elements for quantum communication at microwave frequencies. The demonstrated feed-forward may also find application in error correction schemes.
Quantum Tunneling of Magnetization in Single Molecular Magnets Coupled to Ferromagnetic Reservoirs
Misiorny, Maciej; Barnas, Józef
2006-01-01
The role of spin polarized reservoirs in quantum tunneling of magnetization and relaxation processes in a single molecular magnet (SMM) is investigated theoretically. The SMM is exchange-coupled to the reservoirs and also subjected to a magnetic field varying in time, which enables the quantum tunneling of magnetization (QTM). The spin relaxation times are calculated from the Fermi golden rule. The exchange interaction with tunneling electrons is shown to affect the spin reversal due to QTM. ...
Henderson, J. J.; Koo, C.; Feng, P. L.; del Barco, E.; Hill, S.; Tupitsyn, I. S.; Stamp, P. C. E.; Hendrickson, D. N.
2009-01-01
We present low temperature magnetometry measurements on a new Mn3 single-molecule magnet (SMM) in which the quantum tunneling of magnetization (QTM) displays clear evidence for quantum mechanical selection rules. A QTM resonance appearing only at elevated temperatures demonstrates tunneling between excited states with spin projections differing by a multiple of three: this is dictated by the C3 symmetry of the molecule, which forbids pure tunneling from the lowest metastable state. Resonances...
Channel analysis for single photon underwater free space quantum key distribution.
Shi, Peng; Zhao, Shi-Cheng; Gu, Yong-Jian; Li, Wen-Dong
2015-03-01
We investigate the optical absorption and scattering properties of underwater media pertinent to our underwater free space quantum key distribution (QKD) channel model. With the vector radiative transfer theory and Monte Carlo method, we obtain the attenuation of photons, the fidelity of the scattered photons, the quantum bit error rate, and the sifted key generation rate of underwater quantum communication. It can be observed from our simulations that the most secure single photon underwater free space QKD is feasible in the clearest ocean water.
Quantum tunneling of magnetization in single molecular magnets coupled to ferromagnetic reservoirs
Misiorny, M.; Barnas, J.
2007-04-01
The role of spin polarized reservoirs in quantum tunneling of magnetization and relaxation processes in a single molecular magnet (SMM) is investigated theoretically. The SMM is exchange-coupled to the reservoirs and also subjected to a magnetic field varying in time, which enables the quantum tunneling of magnetization. The spin relaxation times are calculated from the Fermi golden rule. The exchange interaction of SMM and electrons in the leads is shown to affect the spin reversal due to quantum tunneling of magnetization. It is shown that the switching is associated with transfer of a certain charge between the leads.
Open quantum system model of the one-dimensional Burgers equation with tunable shear viscosity
International Nuclear Information System (INIS)
Yepez, Jeffrey
2006-01-01
Presented is an analysis of an open quantum model of the time-dependent evolution of a flow field governed by the nonlinear Burgers equation in one spatial dimension. The quantum model is a system of qubits where there exists a minimum time interval in the time-dependent dynamics. Each temporally discrete unitary quantum-mechanical evolution is followed by state reduction of the quantum state. The mesoscopic behavior of this quantum model is described by a quantum Boltzmann equation with a naturally emergent entropy function and H theorem and the model obeys the detailed balance principle. The macroscopic-scale effective field theory for the quantum model is derived using a perturbative Chapman-Enskog expansion applied to the linearized quantum Boltzmann equation. The entropy function is consistent with the quantum-mechanical collision process and a Fermi-Dirac single-particle distribution function for the occupation probabilities of the qubit's energy eigenstates. Comparisons are presented between analytical predictions and numerical predictions and the agreement is excellent, indicating that the nonlinear Burgers equation with a tunable shear viscosity is the operative macroscopic scale effective field theory
Asymptotically open quantum systems; Asymptotisch offene Quantensysteme
Energy Technology Data Exchange (ETDEWEB)
Westrich, M.
2008-04-15
In the present thesis we investigate the structure of time-dependent equations of motion in quantum mechanics.We start from two coupled systems with an autonomous equation of motion. A limit, in which the dynamics of one of the two systems has a decoupled evolution and imposes a non-autonomous evolution for the second system is identified. A result due to K. Hepp that provides a classical limit for dynamics turns out to be part and parcel for this limit and is generalized in our work. The method introduced by J.S. Howland for the solution of the time-dependent Schroedinger equation is interpreted as such a limit. Moreover, we associate our limit with the modern theory of quantization. (orig.)
Solvable Hydrodynamics of Quantum Integrable Systems
Bulchandani, Vir B.; Vasseur, Romain; Karrasch, Christoph; Moore, Joel E.
2017-12-01
The conventional theory of hydrodynamics describes the evolution in time of chaotic many-particle systems from local to global equilibrium. In a quantum integrable system, local equilibrium is characterized by a local generalized Gibbs ensemble or equivalently a local distribution of pseudomomenta. We study time evolution from local equilibria in such models by solving a certain kinetic equation, the "Bethe-Boltzmann" equation satisfied by the local pseudomomentum density. Explicit comparison with density matrix renormalization group time evolution of a thermal expansion in the XXZ model shows that hydrodynamical predictions from smooth initial conditions can be remarkably accurate, even for small system sizes. Solutions are also obtained in the Lieb-Liniger model for free expansion into vacuum and collisions between clouds of particles, which model experiments on ultracold one-dimensional Bose gases.
Solvable Hydrodynamics of Quantum Integrable Systems.
Bulchandani, Vir B; Vasseur, Romain; Karrasch, Christoph; Moore, Joel E
2017-12-01
The conventional theory of hydrodynamics describes the evolution in time of chaotic many-particle systems from local to global equilibrium. In a quantum integrable system, local equilibrium is characterized by a local generalized Gibbs ensemble or equivalently a local distribution of pseudomomenta. We study time evolution from local equilibria in such models by solving a certain kinetic equation, the "Bethe-Boltzmann" equation satisfied by the local pseudomomentum density. Explicit comparison with density matrix renormalization group time evolution of a thermal expansion in the XXZ model shows that hydrodynamical predictions from smooth initial conditions can be remarkably accurate, even for small system sizes. Solutions are also obtained in the Lieb-Liniger model for free expansion into vacuum and collisions between clouds of particles, which model experiments on ultracold one-dimensional Bose gases.
Quantum Accelerators for High-performance Computing Systems
Energy Technology Data Exchange (ETDEWEB)
Humble, Travis S. [ORNL; Britt, Keith A. [ORNL; Mohiyaddin, Fahd A. [ORNL
2017-11-01
We define some of the programming and system-level challenges facing the application of quantum processing to high-performance computing. Alongside barriers to physical integration, prominent differences in the execution of quantum and conventional programs challenges the intersection of these computational models. Following a brief overview of the state of the art, we discuss recent advances in programming and execution models for hybrid quantum-classical computing. We discuss a novel quantum-accelerator framework that uses specialized kernels to offload select workloads while integrating with existing computing infrastructure. We elaborate on the role of the host operating system to manage these unique accelerator resources, the prospects for deploying quantum modules, and the requirements placed on the language hierarchy connecting these different system components. We draw on recent advances in the modeling and simulation of quantum computing systems with the development of architectures for hybrid high-performance computing systems and the realization of software stacks for controlling quantum devices. Finally, we present simulation results that describe the expected system-level behavior of high-performance computing systems composed from compute nodes with quantum processing units. We describe performance for these hybrid systems in terms of time-to-solution, accuracy, and energy consumption, and we use simple application examples to estimate the performance advantage of quantum acceleration.
International Nuclear Information System (INIS)
Hoerhammer, C.
2007-01-01
In this thesis, non-Markovian dynamics, decoherence and entanglement in dissipative quantum systems are studied. In particular, applications to quantum information theory of continuous variable systems are considered. The non-Markovian dynamics are described by the Hu-Paz-Zhang master equation of quantum Brownian motion. In this context the focus is on non-Markovian effects on decoherence and separability time scales of various single- mode and two-mode continuous variable states. It is verified that moderate non-Markovian influences slow down the decay of interference fringes and quantum correlations, while strong non-Markovian effects resulting from an out-of-resonance bath can even accelerate the loss of coherence, compared to predictions of Markovian approximations. Qualitatively different scenarios including exponential, Gaussian or algebraic decay of the decoherence function are analyzed. It is shown that partial recurrence of coherence can occur in case of non-Lindblad-type dynamics. The time evolution of quantum correlations of entangled two-mode continuous variable states is examined in single-reservoir and two-reservoir models, representing noisy correlated or uncorrelated non-Markovian quantum channels. For this purpose the model of quantum Brownian motion is extended. Various separability criteria for Gaussian and non-Gaussian continuous variable systems are applied. In both types of reservoir models moderate non-Markovian effects prolong the separability time scales. However, in these models the properties of the stationary state may differ. In the two-reservoir model the initial entanglement is completely lost and both modes are finally uncorrelated. In a common reservoir both modes interact indirectly via the coupling to the same bath variables. Therefore, new quantum correlations may emerge between the two modes. Below a critical bath temperature entanglement is preserved even in the steady state. A separability criterion is derived, which depends
Quantum scattering theory of a single-photon Fock state in three-dimensional spaces.
Liu, Jingfeng; Zhou, Ming; Yu, Zongfu
2016-09-15
A quantum scattering theory is developed for Fock states scattered by two-level systems in three-dimensional free space. It is built upon the one-dimensional scattering theory developed in waveguide quantum electrodynamics. The theory fully quantizes the incident light as Fock states and uses a non-perturbative method to calculate the scattering matrix.
Stationary states of two-level open quantum systems
International Nuclear Information System (INIS)
Gardas, Bartlomiej; Puchala, Zbigniew
2011-01-01
A problem of finding stationary states of open quantum systems is addressed. We focus our attention on a generic type of open system: a qubit coupled to its environment. We apply the theory of block operator matrices and find stationary states of two-level open quantum systems under certain conditions applied on both the qubit and the surrounding.
Conditional quantum entropy power inequality for d-level quantum systems
Jeong, Kabgyun; Lee, Soojoon; Jeong, Hyunseok
2018-04-01
We propose an extension of the quantum entropy power inequality for finite dimensional quantum systems, and prove a conditional quantum entropy power inequality by using the majorization relation as well as the concavity of entropic functions also given by Audenaert et al (2016 J. Math. Phys. 57 052202). Here, we make particular use of the fact that a specific local measurement after a partial swap operation (or partial swap quantum channel) acting only on finite dimensional bipartite subsystems does not affect the majorization relation for the conditional output states when a separable ancillary subsystem is involved. We expect our conditional quantum entropy power inequality to be useful, and applicable in bounding and analyzing several capacity problems for quantum channels.
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.
Projective measurements in quantum and classical optical systems
CSIR Research Space (South Africa)
Roux, FS
2014-09-01
Full Text Available equally well to both classical and quantum optical systems. A projective measurement, in the context of quantum mechanics, is understood to be the process where a projection operator operates on some input state. Often this projection operator is composed...) Projective measurements in quantum and classical optical systems Filippus S. Roux* and Yingwen Zhang CSIR National Laser Centre, P.O. Box 395, Pretoria 0001, South Africa (Received 3 July 2014; published 22 September 2014) Experimental setups for the optical...
Constructing quantum games from a system of Bell's inequalities
International Nuclear Information System (INIS)
Iqbal, Azhar; Abbott, Derek
2010-01-01
We report constructing quantum games directly from a system of Bell's inequalities using Arthur Fine's analysis published in early 1980s. This analysis showed that such a system of inequalities forms a set of both necessary and sufficient conditions required to find a joint distribution function compatible with a given set of joint probabilities, in terms of which the system of Bell's inequalities is usually expressed. Using the setting of a quantum correlation experiment for playing a quantum game, and considering the examples of Prisoners' Dilemma and Matching Pennies, we argue that this approach towards constructing quantum games addresses some of their well-known criticisms.
Quantum statistical gravity: time dilation due to local information in many-body quantum systems
Sels, Dries; Wouters, Michiel
2017-08-01
We propose a generic mechanism for the emergence of a gravitational potential that acts on all classical objects in a quantum system. Our conjecture is based on the analysis of mutual information in many-body quantum systems. Since measurements in quantum systems affect the surroundings through entanglement, a measurement at one position reduces the entropy in its neighbourhood. This reduction in entropy can be described by a local temperature, that is directly related to the gravitational potential. A crucial ingredient in our argument is that ideal classical mechanical motion occurs at constant probability. This definition is motivated by the analysis of entropic forces in classical systems.
Li, Qian; Zhu, Changhua; Ma, Shuquan; Wei, Kejin; Pei, Changxing
2018-04-01
Measurement-device-independent quantum key distribution (MDI-QKD) is immune to all detector side-channel attacks. However, practical implementations of MDI-QKD, which require two-photon interferences from separated independent single-photon sources and a nontrivial reference alignment procedure, are still challenging with current technologies. Here, we propose a scheme that significantly reduces the experimental complexity of two-photon interferences and eliminates reference frame alignment by the combination of plug-and-play and reference frame independent MDI-QKD. Simulation results show that the secure communication distance can be up to 219 km in the finite-data case and the scheme has good potential for practical MDI-QKD systems.
Renner, R; Cirac, J I
2009-03-20
We show that the quantum de Finetti theorem holds for states on infinite-dimensional systems, provided they satisfy certain experimentally verifiable conditions. This result can be applied to prove the security of quantum key distribution based on weak coherent states or other continuous variable states against general attacks.
Quantum uncertainty in critical systems with three spins interaction
International Nuclear Information System (INIS)
Carrijo, Thiago M; Avelar, Ardiley T; Céleri, Lucas C
2015-01-01
In this article we consider two spin-1/2 chains described, respectively, by the thermodynamic limit of the XY model with the usual two site interaction, and an extension of this model (without taking the thermodynamics limit), called XYT, were a three site interaction term is presented. To investigate the critical behaviour of such systems we employ tools from quantum information theory. Specifically, we show that the local quantum uncertainty, a quantity introduced in order to quantify the minimum quantum share of the variance of a local measurement, can be used to indicate quantum phase transitions presented by these models at zero temperature. Due to the connection of this quantity with the quantum Fisher information, the results presented here may be relevant for quantum metrology and quantum thermodynamics. (paper)
Single-Shot Quantum Nondemolition Detection of Individual Itinerant Microwave Photons
Besse, Jean-Claude; Gasparinetti, Simone; Collodo, Michele C.; Walter, Theo; Kurpiers, Philipp; Pechal, Marek; Eichler, Christopher; Wallraff, Andreas
2018-04-01
Single-photon detection is an essential component in many experiments in quantum optics, but it remains challenging in the microwave domain. We realize a quantum nondemolition detector for propagating microwave photons and characterize its performance using a single-photon source. To this aim, we implement a cavity-assisted conditional phase gate between the incoming photon and a superconducting artificial atom. By reading out the state of this atom in a single shot, we reach an external (internal) photon-detection fidelity of 50% (71%), limited by transmission efficiency between the source and the detector (75%) and the coherence properties of the qubit. By characterizing the coherence and average number of photons in the field reflected off the detector, we demonstrate its quantum nondemolition nature. We envisage applications in generating heralded remote entanglement between qubits and for realizing logic gates between propagating microwave photons.
Quantum Transport in Strongly Correlated Systems
DEFF Research Database (Denmark)
Bohr, Dan
2007-01-01
the density matrix renormalization group (DMRG) method. We present two DMRG setups for calculating the linear conductance of strongly correlated nanostructures in the infinitesimal source-drain voltage regime. The first setup describes the leads by modified real-space tight-binding chains, whereas the second...... screening plays a much less significant role than in bulk systems due to the reduced size of the objects, therefore making it necessary to consider the importance of correlations between electrons. The work presented in this thesis deals with quantum transport through strongly correlated systems using....... Thus both coherence and correlation effects are important in this model, and the methods applied should be able to handle both these effects rigorously. We present the DMRG setup for this model and benchmark against existing Greens function results for the model. Then we present initial DMRG results...
Lippert, Kai-Alexander; Mukherjee, Chandan; Broschinski, Jan-Philipp; Lippert, Yvonne; Walleck, Stephan; Stammler, Anja; Bögge, Hartmut; Schnack, Jürgen; Glaser, Thorsten
2017-12-18
Single-molecule magnets (SMMs) retain a magnetization without applied magnetic field for a decent time due to an energy barrier U for spin-reversal. Despite the success to increase U, the difficult to control magnetic quantum tunneling often leads to a decreased effective barrier U eff and a fast relaxation. Here, we demonstrate the influence of the exchange coupling on the tunneling probability in two heptanuclear SMMs hosting the same spin-system with the same high spin ground state S t = 21/2. A chirality-induced symmetry reduction leads to a switch of the Mn III -Mn III exchange from antiferromagnetic in the achiral SMM [Mn III 6 Cr III ] 3+ to ferromagnetic in the new chiral SMM RR [Mn III 6 Cr III ] 3+ . Multispin Hamiltonian analysis by full-matrix diagonalization demonstrates that the ferromagnetic interactions in RR [Mn III 6 Cr III ] 3+ enforce a well-defined S t = 21/2 ground state with substantially less mixing of M S substates in contrast to [Mn III 6 Cr III ] 3+ and no tunneling pathways below the top of the energy barrier. This is experimentally verified as U eff is smaller than the calculated energy barrier U in [Mn III 6 Cr III ] 3+ due to tunneling pathways, whereas U eff equals U in RR [Mn III 6 Cr III ] 3+ demonstrating the absence of quantum tunneling.
Inelastic tunneling of electrons through a quantum dot with an embedded single molecular magnet
Chang, Bo; Liang, J.-Q.
2010-06-01
We report a theoretical analysis of electron transport through a quantum dot with an embedded biaxial single-molecule magnet (SMM) based on mapping of the many-body interaction-system onto a one-body problem by means of the non-equilibrium Green function technique. It is found that the conducting current exhibits a stepwise behavior and the nonlinear differential conductance displays additional peaks with variation of the sweeping speed and the magnitude of magnetic field. This observation can be interpreted by the interaction of electron-spin with the SMM and the quantum tunneling of magnetization. The inelastic conductance and the corresponding tunneling processes are investigated with normal as well as ferromagnetic electrodes. In the case of ferromagnetic configuration, the coupling to the SMM leads to an asymmetric tunneling magnetoresistance (TMR), which can be enhanced or suppressed greatly in certain regions. Moreover, a sudden TMR-switch with the variation of magnetic field is observed, which is seen to be caused by the inelastic tunneling.
Inelastic tunneling of electrons through a quantum dot with an embedded single molecular magnet
Energy Technology Data Exchange (ETDEWEB)
Chang Bo [Institute of Theoretical Physics and Department of Physics, Shanxi University, Taiyuan, Shanxi 030006 (China); Liang, J.-Q., E-mail: jqliang@sxu.edu.c [Institute of Theoretical Physics and Department of Physics, Shanxi University, Taiyuan, Shanxi 030006 (China)
2010-06-28
We report a theoretical analysis of electron transport through a quantum dot with an embedded biaxial single-molecule magnet (SMM) based on mapping of the many-body interaction-system onto a one-body problem by means of the non-equilibrium Green function technique. It is found that the conducting current exhibits a stepwise behavior and the nonlinear differential conductance displays additional peaks with variation of the sweeping speed and the magnitude of magnetic field. This observation can be interpreted by the interaction of electron-spin with the SMM and the quantum tunneling of magnetization. The inelastic conductance and the corresponding tunneling processes are investigated with normal as well as ferromagnetic electrodes. In the case of ferromagnetic configuration, the coupling to the SMM leads to an asymmetric tunneling magnetoresistance (TMR), which can be enhanced or suppressed greatly in certain regions. Moreover, a sudden TMR-switch with the variation of magnetic field is observed, which is seen to be caused by the inelastic tunneling.
Generation of robust tripartite entanglement with a single-cavity optomechanical system
Yang, Xihua; Ling, Yang; Shao, Xuping; Xiao, Min
2017-05-01
We present a proposal to generate robust tripartite optomechanical entanglement with a single-cavity optomechanical system driven by a single input laser field. The produced stationary tripartite entanglement among two longitudinal cavity modes and a mirror oscillation mode via radiation pressure force exhibits robustness to the variation of the environment temperature when the cavity free spectral range is close to the mechanical oscillation frequency. The present optomechanical system can serve as an alternative intermediary for quantum-state exchange between two microwave (or optical) fields as well as between photons and the macroscopic mechanical oscillator, and may be potentially useful for quantum information processing and quantum networks.
Longitudinal wave function control in single quantum dots with an applied magnetic field.
Cao, Shuo; Tang, Jing; Gao, Yunan; Sun, Yue; Qiu, Kangsheng; Zhao, Yanhui; He, Min; Shi, Jin-An; Gu, Lin; Williams, David A; Sheng, Weidong; Jin, Kuijuan; Xu, Xiulai
2015-01-27
Controlling single-particle wave functions in single semiconductor quantum dots is in demand to implement solid-state quantum information processing and spintronics. Normally, particle wave functions can be tuned transversely by an perpendicular magnetic field. We report a longitudinal wave function control in single quantum dots with a magnetic field. For a pure InAs quantum dot with a shape of pyramid or truncated pyramid, the hole wave function always occupies the base because of the less confinement at base, which induces a permanent dipole oriented from base to apex. With applying magnetic field along the base-apex direction, the hole wave function shrinks in the base plane. Because of the linear changing of the confinement for hole wave function from base to apex, the center of effective mass moves up during shrinking process. Due to the uniform confine potential for electrons, the center of effective mass of electrons does not move much, which results in a permanent dipole moment change and an inverted electron-hole alignment along the magnetic field direction. Manipulating the wave function longitudinally not only provides an alternative way to control the charge distribution with magnetic field but also a new method to tune electron-hole interaction in single quantum dots.
Correlation Functions in Open Quantum-Classical Systems
Directory of Open Access Journals (Sweden)
Chang-Yu Hsieh
2013-12-01
Full Text Available Quantum time correlation functions are often the principal objects of interest in experimental investigations of the dynamics of quantum systems. For instance, transport properties, such as diffusion and reaction rate coefficients, can be obtained by integrating these functions. The evaluation of such correlation functions entails sampling from quantum equilibrium density operators and quantum time evolution of operators. For condensed phase and complex systems, where quantum dynamics is difficult to carry out, approximations must often be made to compute these functions. We present a general scheme for the computation of correlation functions, which preserves the full quantum equilibrium structure of the system and approximates the time evolution with quantum-classical Liouville dynamics. Several aspects of the scheme are discussed, including a practical and general approach to sample the quantum equilibrium density, the properties of the quantum-classical Liouville equation in the context of correlation function computations, simulation schemes for the approximate dynamics and their interpretation and connections to other approximate quantum dynamical methods.
Investigating non-Markovian dynamics of quantum open systems
Chen, Yusui
Quantum open system coupled to a non-Markovian environment has recently attracted widespread interest for its important applications in quantum information processing and quantum dissipative systems. New phenomena induced by the non-Markovian environment have been discovered in variety of research areas ranging from quantum optics, quantum decoherence to condensed matter physics. However, the study of the non-Markovian quantum open system is known a difficult problem due to its technical complexity in deriving the fundamental equation of motion and elusive conceptual issues involving non-equilibrium dynamics for a strong coupled environment. The main purpose of this thesis is to introduce several new techniques of solving the quantum open systems including a systematic approach to dealing with non-Markovian master equations from a generic quantum-state diffusion (QSD) equation. In the first part of this thesis, we briefly introduce the non-Markovian quantum-state diffusion approach, and illustrate some pronounced non-Markovian quantum effects through numerical investigation on a cavity-QED model. Then we extend the non-Markovian QSD theory to an interesting model where the environment has a hierarchical structure, and find out the exact non-Markovian QSD equation of this model system. We observe the generation of quantum entanglement due to the interplay between the non-Markovian environment and the cavity. In the second part, we show an innovative method to obtain the exact non-Markovian master equations for a set of generic quantum open systems based on the corresponding non-Markovian QSD equations. Multiple-qubit systems and multilevel systems are discussed in details as two typical examples. Particularly, we derive the exact master equation for a model consisting of a three-level atom coupled to an optical cavity and controlled by an external laser field. Additionally, we discuss in more general context the mathematical similarity between the multiple
The Conditional Entropy Power Inequality for Bosonic Quantum Systems
De Palma, Giacomo; Trevisan, Dario
2018-01-01
We prove the conditional Entropy Power Inequality for Gaussian quantum systems. This fundamental inequality determines the minimum quantum conditional von Neumann entropy of the output of the beam-splitter or of the squeezing among all the input states where the two inputs are conditionally independent given the memory and have given quantum conditional entropies. We also prove that, for any couple of values of the quantum conditional entropies of the two inputs, the minimum of the quantum conditional entropy of the output given by the conditional Entropy Power Inequality is asymptotically achieved by a suitable sequence of quantum Gaussian input states. Our proof of the conditional Entropy Power Inequality is based on a new Stam inequality for the quantum conditional Fisher information and on the determination of the universal asymptotic behaviour of the quantum conditional entropy under the heat semigroup evolution. The beam-splitter and the squeezing are the central elements of quantum optics, and can model the attenuation, the amplification and the noise of electromagnetic signals. This conditional Entropy Power Inequality will have a strong impact in quantum information and quantum cryptography. Among its many possible applications there is the proof of a new uncertainty relation for the conditional Wehrl entropy.
Superconducting Qubit with Integrated Single Flux Quantum Controller Part I: Theory and Fabrication
Beck, Matthew; Leonard, Edward, Jr.; Thorbeck, Ted; Zhu, Shaojiang; Howington, Caleb; Nelson, Jj; Plourde, Britton; McDermott, Robert
As the size of quantum processors grow, so do the classical control requirements. The single flux quantum (SFQ) Josephson digital logic family offers an attractive route to proximal classical control of multi-qubit processors. Here we describe coherent control of qubits via trains of SFQ pulses. We discuss the fabrication of an SFQ-based pulse generator and a superconducting transmon qubit on a single chip. Sources of excess microwave loss stemming from the complex multilayer fabrication of the SFQ circuit are discussed. We show how to mitigate this loss through judicious choice of process workflow and appropriate use of sacrificial protection layers. Present address: IBM T.J. Watson Research Center.
Leonard, Edward, Jr.; Beck, Matthew; Thorbeck, Ted; Zhu, Shaojiang; Howington, Caleb; Nelson, Jj; Plourde, Britton; McDermott, Robert
We describe the characterization of a single flux quantum (SFQ) pulse generator cofabricated with a superconducting quantum circuit on a single chip. Resonant trains of SFQ pulses are used to induce coherent qubit rotations on the Bloch sphere. We describe the SFQ drive characteristics of the qubit at the fundamental transition frequency and at subharmonics (ω01 / n , n = 2 , 3 , 4 , ⋯). We address the issue of quasiparticle poisoning due to the proximal SFQ pulse generator, and we characterize the fidelity of SFQ-based rotations using randomized benchmarking. Present address: IBM T.J. Watson Research Center.
Extraction of the beta-factor for single quantum dots coupled to a photonic crystal waveguide
DEFF Research Database (Denmark)
Nielsen, Henri Thyrrestrup; Sapienza, Luca; Lodahl, Peter
2010-01-01
We present measurements of the β-factor, describing the coupling efficiency of light emitted by single InAs/GaAs semiconductor quantum dots into a photonic crystal waveguide mode. The β-factor is evaluated by means of time resolved frequency-dependent photoluminescence spectroscopy. The emission...... wavelength of single quantum dots is temperature tuned across the band edge of a photonic crystal waveguide and the spontaneous emission rate is recorded. Decay rates up to 5.7 ns−1, corresponding to a Purcell factor of 5.2, are measured and β-factors up to 85% are extracted. These results prove...
Quantum Liquid Crystal Phases in Strongly Correlated Fermionic Systems
Sun, Kai
2009-01-01
This thesis is devoted to the investigation of the quantum liquid crystal phases in strongly correlated electronic systems. Such phases are characterized by their partially broken spatial symmetries and are observed in various strongly correlated systems as being summarized in Chapter 1. Although quantum liquid crystal phases often involve…
Representation Theorem of Observables on a Quantum System
Nánásiová, Olga; Khrennikov, Andrei
2006-03-01
An orthomodular lattice (OML) with a conditional state can be used as a model for noncompatible events (a quantum system). In this paper we will study some properties of a conditional state and an s-map which are defined on an OML. We show conditions when a quantum system has the same properties as the classical probability space.
Tracking Quantum Jumps of Light with Repeated Single-Shot Parity Measurements
Sun, Luyan; Petrenko, Andrei; Leghtas, Zaki; Vlastakis, Brian; Kirchmair, Gerhard; Sliwa, Katrina; Narla, Anirudh; Hatridge, Michael; Shankar, Shyam; Blumoff, Jacob; Frunzio, Luigi; Mirrahimi, Mazyar; Devoret, Michel; Schoelkopf, Robert
2014-03-01
Quantum error correction (QEC) is required for a practical quantum computer because of the fragile nature of quantum information. A measurement-based QEC requires the measurement of error syndromes in a quantum non-demolition way and at a rate which is faster than errors occur. In a 3D circuit quantum electrodynamics architecture, we realize a parity measurement of a microwave field with about 90% fidelity by mapping its parity onto an ancilla qubit. The projective nature of the parity measurement onto a degenerate parity eigenspace, the cat states, is confirmed by Wigner tomography after a single parity measurement, showing 84% fidelity to ideal cats. The parity can therefore serve as an error syndrome for a recently proposed QEC scheme [Leghtas et.al. PRL (2013)]. We then demonstrate a tracking of quantum jumps of this error syndrome by repeated parity measurements. We will also discuss a quantum filter developed to mitigate the imperfections during the parity measurement for a best estimate of the photon state parity. The demonstrated extraction of error syndromes without perturbing the encoded information is essential for QEC. Current address: CQI, IIIS, Tsinghua University, Beijing, China.
Quantum jumps in a three-level system
International Nuclear Information System (INIS)
Javanainen, J.
1986-01-01
The authors study fluorescence in a scheme which is easy to treat theoretically: a two-level system driven by a laser and a third metastable state such that slow spontaneous transitions take place both from the excited state of a two-level system to the metastable state and from the metastable state to the ground state of the two-level system. With the aid of the quantum regression theorem the authors calculate the whole photon counting statistics at a detector which records scattering of the laser photons. In the limit of high intensity of the laser, the statistics of photon counts is found to be the same as the statistics of a two-state Markov jumps process. Thus, if the sequence of photon counts can be interpreted as a realization of a stochastic process, in a single experimental run the fluorescence should abruptly turn on and off for random intervals of time. The result is the same as given by the quantum-jump argument
Quantum chromodynamics in few-nucleon systems
International Nuclear Information System (INIS)
Brodsky, S.J.
1983-10-01
One of the most important implications of quantum chromodynamics (QCD) is that nuclear systems and forces can be described at a fundamental level. The theory provides natural explanations for the basic features of hadronic physics: the meson and baryon spectra, quark statistics, the structure of the weak and electromagnetic currents of hadrons, the scale-invariance of hadronic interactions at short distances, and evidently, color (i.e., quark and gluon) confinement at large distances. Many different and diverse tests have confirmed the basic predictions of QCD; however, since tests of quark and gluon interactions must be done within the confines of hadrons there have been few truly quantitative checks. Nevertheless, it appears likely that QCD is the fundamental theory of hadronic and nuclear interactions in the same sense that QED gives a precise description of electrodynamic interctions. Topics discussed include exclusive processes in QCD, the deuteron in QCD, reduced nuclear amplitudes, and limitations of traditional nuclear physics. 32 references
The problems of mapping in quantum systems
International Nuclear Information System (INIS)
Xu Gongou; Wang Wenge; Yang Yadian; Fu Deji
1992-01-01
The mapping from the state of Hamiltonian H(0) to that of H(λ) = H(0) + λ(H-H(0)) is established by means of Wigner-Brillion perturbation formula. An iterative perturbation calculation can be carried out to find the stable points set and to show that under what condition the iterative calculation is divergent(non convergent). Avoided crossing point is really a singularity-point showed clearly in such procedure. The topological invariant subspace endowed by corresponding Hamiltonian H(0) is destroyed after such avoided crossing point. It is similar to the classical invariant tori destruction. A quantum KAM theorem can be established in this manner. Numerical results of certain schematic systems are given as illustration
Anions, quantum particles in planar systems
International Nuclear Information System (INIS)
Monerat, Germano Amaral
2000-03-01
Our purpose here is to present a general review of the non-relativistic quantum-mechanical description of excitations that do not obey neither the Fermi-Dirac nor the Bose-Einstein statistics; they rather fulfill an intermediate statistics, the we called 'any-statistics'. As we shall see, this is a peculiarity of (1+1) and (1+2) dimensions, due to the fact that, in two space dimensions, the spin is not quantised, once the rotation group is Abelian. The relevance of studying theories in (1+2) dimensions is justified by the evidence that, in condensed matter physics, there are examples of planar systems, for which everything goes as if the third spatial dimension is frozen. (author)
Automated drawing system of quantum energy levels
Stampoultzis, M.; Sinatkas, J.; Tsakstara, V.; Kosmas, T. S.
2014-03-01
The purpose of this work is to derive an automated system that provides advantageous drawings of energy spectra for quantum systems (nuclei, atoms, molecules, etc.) required in various physical sciences. The automation involves the development of appropriate computational code and graphical imaging system based on raw data insertion, theoretical calculations and experimental or bibliographic data insertion. The system determines the appropriate scale to depict graphically with the best possible way in the available space. The presently developed code operates locally and the results are displayed on the screen and can be exported to a PostScript file. We note its main features to arrange and visualize in the available space the energy levels with their identity, taking care the existence in the final diagram the least auxiliary deviations. Future improvements can be the use of Java and the availability on the Internet. The work involves the automated plotting of energy levels in molecules, atoms, nuclei and other types of quantized energy spectra. The automation involves the development of an appropriate computational code and graphical imaging system.
Controlling open quantum systems: Tools, achievements, and limitations
Koch, Christiane P.
2016-01-01
The advent of quantum devices, which exploit the two essential elements of quantum physics, coherence and entanglement, has sparked renewed interest in the control of open quantum systems. Successful implementations face the challenge to preserve the relevant nonclassical features at the level of device operation. A major obstacle is decoherence which is caused by interaction with the environment. Optimal control theory is a tool that can be used to identify control strategies in the presence...
Interacting systems far from equilibrium quantum kinetic theory
Morawetz, Klaus
2018-01-01
This book presents an up-to-date formalism of non-equilibrium Green's functions covering different applications ranging from solid state physics, plasma physics, cold atoms in optical lattices up to relativistic transport and heavy ion collisions. Within the Green's function formalism, the basic sets of equations for these diverse systems are similar, and approximations developed in one field can be adapted to another field. The central object is the self-energy which includes all non-trivial aspects of the system dynamics. The focus is therefore on microscopic processes starting from elementary principles for classical gases and the complementary picture of a single quantum particle in a random potential. This provides an intuitive picture of the interaction of a particle with the medium formed by other particles, on which the Green's function is built on.
International Nuclear Information System (INIS)
Kouwenhoven, L.; Marcus, C.
1998-01-01
Quantum dots are man-made ''droplets'' of charge that can contain anything from a single electron to a collection of several thousand. Their typical dimensions range from nanometres to a few microns, and their size, shape and interactions can be precisely controlled through the use of advanced nanofabrication technology. The physics of quantum dots shows many parallels with the behaviour of naturally occurring quantum systems in atomic and nuclear physics. Indeed, quantum dots exemplify an important trend in condensed-matter physics in which researchers study man-made objects rather than real atoms or nuclei. As in an atom, the energy levels in a quantum dot become quantized due to the confinement of electrons. With quantum dots, however, an experimentalist can scan through the entire periodic table by simply changing a voltage. In this article the authors describe how quantum dots make it possible to explore new physics in regimes that cannot otherwise be accessed in the laboratory. (UK)
DEFF Research Database (Denmark)
Ding, Xing; He, Yu; Duan, Z.-C.
2016-01-01
Scalable photonic quantum technologies require on-demand single-photon sources with simultaneously high levels of purity, indistinguishability, and efficiency. These key features, however, have only been demonstrated separately in previous experiments. Here, by s-shell pulsed resonant excitation...... of a Purcellenhanced quantum dot-micropillar system, we deterministically generate resonance fluorescence single photons which, at π pulse excitation, have an extraction efficiency of 66%, single-photon purity of 99.1%, and photon indistinguishability of 98.5%. Such a single-photon source for the first time combines...... the features of high efficiency and near-perfect levels of purity and indistinguishabilty, and thus opens the way to multiphoton experiments with semiconductor quantum dots....
Optimization Via Open System Quantum Annealing
2016-01-07
be solved by a quantum evolution from a strong transverse field to a spin glass Hamiltonian (also known as quantum annealing or QA). We have...reduced to Quadratic Unconstrained Binary Optimization (QUBO), which can be solved by a quantum evolution from a strong transverse field to a spin...Excellence grant for Education , Research and Engineering: The number of undergraduates funded by your agreement who graduated during this period and
Effects of symmetry breaking in finite quantum systems
Energy Technology Data Exchange (ETDEWEB)
Birman, J.L. [Department of Physics, City College, City University of New York, New York, NY 10031 (United States); Nazmitdinov, R.G. [Departament de Fisica, Universitat de les Illes Balears, Palma de Mallorca 07122 (Spain); Bogolubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation); Yukalov, V.I., E-mail: yukalov@theor.jinr.ru [Bogolubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation)
2013-05-15
The review considers the peculiarities of symmetry breaking and symmetry transformations and the related physical effects in finite quantum systems. Some types of symmetry in finite systems can be broken only asymptotically. However, with a sufficiently large number of particles, crossover transitions become sharp, so that symmetry breaking happens similarly to that in macroscopic systems. This concerns, in particular, global gauge symmetry breaking, related to Bose–Einstein condensation and superconductivity, or isotropy breaking, related to the generation of quantum vortices, and the stratification in multicomponent mixtures. A special type of symmetry transformation, characteristic only for finite systems, is the change of shape symmetry. These phenomena are illustrated by the examples of several typical mesoscopic systems, such as trapped atoms, quantum dots, atomic nuclei, and metallic grains. The specific features of the review are: (i) the emphasis on the peculiarities of the symmetry breaking in finite mesoscopic systems; (ii) the analysis of common properties of physically different finite quantum systems; (iii) the manifestations of symmetry breaking in the spectra of collective excitations in finite quantum systems. The analysis of these features allows for the better understanding of the intimate relation between the type of symmetry and other physical properties of quantum systems. This also makes it possible to predict new effects by employing the analogies between finite quantum systems of different physical nature.
Adiabatic response and quantum thermoelectrics for ac-driven quantum systems
Ludovico, María Florencia; Battista, Francesca; von Oppen, Felix; Arrachea, Liliana
2016-02-01
We generalize the theory of thermoelectrics to include coherent electron systems under adiabatic ac driving, accounting for quantum pumping of charge and heat, as well as for the work exchanged between the electron system and driving potentials. We derive the relevant response coefficients in the adiabatic regime and show that they obey generalized Onsager reciprocity relations. We analyze the consequences of our generalized thermoelectric framework for quantum motors, generators, heat engines, and heat pumps, characterizing them in terms of efficiencies and figures of merit. We illustrate these concepts in a model for a quantum pump.
Entangled Systems New Directions in Quantum Physics
Audretsch, Jürgen
2007-01-01
An introductory textbook for advanced students of physics, chemistry and computer science, covering an area of physics that has lately witnessed rapid expansion. The topics treated here include quantum information, quantum communication, quantum computing, teleportation and hidden parameters, thus imparting not only a well-founded understanding of quantum theory as such, but also a solid basis of knowledge from which readers can follow the rapid development of the topic or delve deeper into a more specialized branch of research. Commented recommendations for further reading as well as end-of-chapter problems help the reader to quickly access the theoretical basics of future key technologies
Quantum channel construction with circuit quantum electrodynamics
Shen, Chao; Noh, Kyungjoo; Albert, Victor V.; Krastanov, Stefan; Devoret, M. H.; Schoelkopf, R. J.; Girvin, S. M.; Jiang, Liang
2017-04-01
Quantum channels can describe all transformations allowed by quantum mechanics. We adapt two existing works [S. Lloyd and L. Viola, Phys. Rev. A 65, 010101 (2001), 10.1103/PhysRevA.65.010101 and E. Andersson and D. K. L. Oi, Phys. Rev. A 77, 052104 (2008), 10.1103/PhysRevA.77.052104] to superconducting circuits, featuring a single qubit ancilla with quantum nondemolition readout and adaptive control. This construction is efficient in both ancilla dimension and circuit depth. We point out various applications of quantum channel construction, including system stabilization and quantum error correction, Markovian and exotic channel simulation, implementation of generalized quantum measurements, and more general quantum instruments. Efficient construction of arbitrary quantum channels opens up exciting new possibilities for quantum control, quantum sensing, and information processing tasks.
Classical and quantum simulations of many-body systems
International Nuclear Information System (INIS)
Murg, Valentin
2008-01-01
This thesis is devoted to recent developments in the fields of classical and quantum simulations of many-body systems. We describe new classical algorithms that overcome problems apparent in conventional renormalization group and Monte Carlo methods. These algorithms make possible the detailed study of finite temperature properties of 2-D classical and 1-D quantum systems, the investigation of ground states of 2-D frustrated or fermionic systems and the analysis of time evolutions of 2-D quantum systems. Furthermore, we propose new ''analog'' quantum simulators that are able to realize interesting models such as a Tonks-Girardeau gas or a frustrated spin-1/2 XY model on a trigonal lattice. These quantum simulators make use of optical lattices and trapped ions and are technically feasible. In fact, the Tonks-Girardeau gas has been realized experimentally and we provide a detailed comparison between the experimental data and the theoretical predictions. (orig.)
Classical and quantum simulations of many-body systems
Energy Technology Data Exchange (ETDEWEB)
Murg, Valentin
2008-04-07
This thesis is devoted to recent developments in the fields of classical and quantum simulations of many-body systems. We describe new classical algorithms that overcome problems apparent in conventional renormalization group and Monte Carlo methods. These algorithms make possible the detailed study of finite temperature properties of 2-D classical and 1-D quantum systems, the investigation of ground states of 2-D frustrated or fermionic systems and the analysis of time evolutions of 2-D quantum systems. Furthermore, we propose new 'analog' quantum simulators that are able to realize interesting models such as a Tonks-Girardeau gas or a frustrated spin-1/2 XY model on a trigonal lattice. These quantum simulators make use of optical lattices and trapped ions and are technically feasible. In fact, the Tonks-Girardeau gas has been realized experimentally and we provide a detailed comparison between the experimental data and the theoretical predictions. (orig.)
The dynamical-quantization approach to open quantum systems
Bolivar, A. O.
2012-03-01
The dynamical-quantization approach to open quantum systems does consist in quantizing the Brownian motion starting directly from its stochastic dynamics under the framework of both Langevin and Fokker-Planck equations, without alluding to any model Hamiltonian. On the ground of this non-Hamiltonian quantization method, we can derive a non-Markovian Caldeira-Leggett quantum master equation as well as a non-Markovian quantum Smoluchowski equation. The former is solved for the case of a quantum Brownian particle in a gravitational field whilst the latter for a harmonic oscillator. In both physical situations, we come up with the existence of a non-equilibrium thermal quantum force and investigate its classical limit at high temperatures as well as its quantum limit at zero temperature. Further, as a physical application of our quantum Smoluchowski equation, we take up the tunneling phenomenon of a non-inertial quantum Brownian particle over a potential barrier. Lastly, we wish to point out, corroborating conclusions reached in our previous paper [A. O. Bolivar, Ann. Phys. 326 (2011) 1354], that the theoretical predictions in the present article uphold the view that our non-Hamiltonian quantum mechanics is able to capture novel features inherent in quantum Brownian motion, thereby overcoming shortcomings underlying the Caldeira-Leggett Hamiltonian model.
DEFF Research Database (Denmark)
Leosson, Kristjan
Semiconductor quantum dots ("solid-state atoms") are promising candidates for quantum computers and future electronic and optoelectronic devices. Quantum dots are zero-dimensional electronic systems and therefore have discrete energy levels, similar to atoms or molecules. The size distribution...... of quantum dots, however, results in a large inhomogeneous broadening of quantum dot spectra. Work on self-assembled InGaAs/GaAs quantum dots will be presented. Properties of atom-like single-dot states are investigated optically using high spatial and spectral resolution. Single-dot spectra can be used...
DEFF Research Database (Denmark)
Leosson, Kristjan
1999-01-01
Semiconductor quantum dots ("solid state atoms") are promising candidates for quantum computers and future electronic and optoelectronic devices. Quantum dots are zero-dimensional electronic systems and therefore have discrete energy levels, similar to atoms or molecules. The size distribution...... of quantum dots, however, results in a large inhomogeneous broadening of quantum dot spectra.Work on self-assembled InGaAs/GaAs quantum dots will be presented. Properties of atom-like single-dots states are investigated optically using high spatial and spectral resolution. Single-dot spectra can be used...
Vacuum Rabi splitting in a plasmonic cavity at the single quantum emitter limit.
Santhosh, Kotni; Bitton, Ora; Chuntonov, Lev; Haran, Gilad
2016-06-13
The strong interaction of individual quantum emitters with resonant cavities is of fundamental interest for understanding light-matter interactions. Plasmonic cavities hold the promise of attaining the strong coupling regime even under ambient conditions and within subdiffraction volumes. Recent experiments revealed strong coupling between individual plasmonic structures and multiple organic molecules; however, strong coupling at the limit of a single quantum emitter has not been reported so far. Here we demonstrate vacuum Rabi splitting, a manifestation of strong coupling, using silver bowtie plasmonic cavities loaded with semiconductor quantum dots (QDs). A transparency dip is observed in the scattering spectra of individual bowties with one to a few QDs, which are directly counted in their gaps. A coupling rate as high as 120 meV is registered even with a single QD, placing the bowtie-QD constructs close to the strong coupling regime. These observations are verified by polarization-dependent experiments and validated by electromagnetic calculations.
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%.
Quantum key distribution with a single photon from a squeezed coherent state
International Nuclear Information System (INIS)
Matsuoka, Masahiro; Hirano, Takuya
2003-01-01
Squeezing of the coherent state by optical parametric amplifier is shown to efficiently produce single-photon states with reduced multiphoton probabilities compared with the weak coherent light. It can be a better source for a longer-distance quantum key distribution and also for other quantum optical experiments. The necessary condition for a secure quantum key distribution given by Brassard et al. is analyzed as functions of the coherent-state amplitude and squeeze parameter. Similarly, the rate of the gained secure bits G after error correction and privacy amplification given by Luetkenhaus is calculated. Compared with the weak coherent light, it is found that G is about ten times larger and its high level continues on about two times longer distance. By improvement of the detector efficiency it is shown that the distance extends further. Measurement of the intensity correlation function and the relation to photon antibunching are discussed for the experimental verification of the single-photon generation
Macroscopic quantum coherence in a single molecular magnet and Kondo effect of electron transport
International Nuclear Information System (INIS)
Chang, Bo; Wang, Qiang; Xie, Haiqing; Liang, J.-Q.
2011-01-01
We report a Kondo-effect study of electron transport through a quantum dot with embedded biaxial single-molecule magnet based on slave boson mean-field theory and non-equilibrium Green-function technique. It is found the macroscopic quantum coherence of molecule-magnet results in the Kondo peak split of differential conductance due to interaction between electron and molecular magnet. It is also demonstrated that both the peak height and position can be controlled by the sweeping magnetic field and polarization of ferromagnetic electrodes. The characteristic peak split may be used to identify the macroscopic quantum coherence and develop molecule devices. -- Highlights: → Splits of Kondo peak are induced by the single molecular magnet. → Kondo effect can be controlled by magnetic field and its sweeping speed in our model. → The suppression and broadening of Kondo peaks is also observed with increase of temperature. → The peaks height and position is sensitive to polarization of the electrode.
Single-step fabrication of quantum funnels via centrifugal colloidal casting of nanoparticle films.
Kim, Jin Young
2015-07-13
Centrifugal casting of composites and ceramics has been widely employed to improve the mechanical and thermal properties of functional materials. This powerful method has yet to be deployed in the context of nanoparticles--yet size-effect tuning of quantum dots is among their most distinctive and application-relevant features. Here we report the first gradient nanoparticle films to be constructed in a single step. By creating a stable colloid of nanoparticles that are capped with electronic-conduction-compatible ligands we were able to leverage centrifugal casting for thin-films devices. This new method, termed centrifugal colloidal casting, is demonstrated to form films in a bandgap-ordered manner with efficient carrier funnelling towards the lowest energy layer. We constructed the first quantum-gradient photodiode to be formed in a single deposition step and, as a result of the gradient-enhanced electric field, experimentally measured the highest normalized detectivity of any colloidal quantum dot photodetector.
Control of quantum correlations in solid state systems
Berrada, K.
2015-11-01
The quantum correlations between two independent qubits immersed in an anisotropic and isotropic photonic band-gab (PBG) crystal have been studied without Born or Markovian approximation. We show that the amount of the entanglement and quantum discord between the qubits in the photonic crystal is greatly different from that of qubits in vacuum or that subjected to the usual non-Markovian reservoir. The results also show that, for PBG materials as environment, high values of quantum correlation trapping can be achieved and thus prevention of correlation sudden drop occurs, which seriously enhances the coherence and increase the amount of the correlations. Moreover, we show that the quantum correlations in the isotropic PBG are more easily preserved than that in the anisotropic PBG under the same condition. These features make the quantum systems in PBG materials as a good candidate for implementation of different schemes of quantum optics and information with high performance.
Anonymous voting for multi-dimensional CV quantum system
International Nuclear Information System (INIS)
Shi Rong-Hua; Xiao Yi; Shi Jin-Jing; Guo Ying; Lee, Moon-Ho
2016-01-01
We investigate the design of anonymous voting protocols, CV-based binary-valued ballot and CV-based multi-valued ballot with continuous variables (CV) in a multi-dimensional quantum cryptosystem to ensure the security of voting procedure and data privacy. The quantum entangled states are employed in the continuous variable quantum system to carry the voting information and assist information transmission, which takes the advantage of the GHZ-like states in terms of improving the utilization of quantum states by decreasing the number of required quantum states. It provides a potential approach to achieve the efficient quantum anonymous voting with high transmission security, especially in large-scale votes. (paper)
Single atom doping for quantum device development in diamond and silicon
Weis, C.D.; Schuh, A.; Batra, A.; Persaud, A.; Rangelow, I.W.; Bokor, J.; Lo, C.C.; Cabrini, S.; Sideras-Haddad, E.; Fuchs, G.D.; Hanson, R.; Awschalom, D.D.; Schenkel, T.
2008-01-01
The ability to inject dopant atoms with high spatial resolution, flexibility in dopant species, and high single ion detection fidelity opens opportunities for the study of dopant fluctuation effects and the development of devices in which function is based on the manipulation of quantum states in
DEFF Research Database (Denmark)
Wang, Qin; Stobbe, Søren; Nielsen, Henri Thyrrestrup
We have systematically measured the variation of the spontaneous emission rate with polarization for self-assembled single quantum dots in two-dimensional photonic crystal membranes and obtained a maximum anisotropy factor of 6 between the decay rates of the two nondegenerate bright exciton states....
Multiparty Quantum English Auction Scheme Using Single Photons as Message Carrier
Liu, Ge; Zhang, Jian-Zhong; Xie, Shu-Cui
2018-03-01
In this paper, a secure and economic multiparty english auction protocol using the single photons as message carrier of bids is proposed. In order to achieve unconditional security, fairness, undeniability and so on, we adopt the decoy photon checking technique and quantum encryption algorithm. Analysis result shows that our protocol satisfies all the characteristics of traditional english auction, meanwhile, it can resist malicious attacks.
Microwave testing of high-Tc based direct current to a single flux quantum converter
DEFF Research Database (Denmark)
Kaplunenko, V. K.; Fischer, Gerd Michael; Ivanov, Z. G.
1994-01-01
Design, simulation, and experimental investigations of a direct current to a single flux quantum converter loaded with a Josephson transmission line and driven by an external 70 GHz microwave oscillator are reported. The test circuit includes nine YBaCuO Josephson junctions aligned on the grain...
Multiparty Quantum English Auction Scheme Using Single Photons as Message Carrier
Liu, Ge; Zhang, Jian-Zhong; Xie, Shu-Cui
2017-11-01
In this paper, a secure and economic multiparty english auction protocol using the single photons as message carrier of bids is proposed. In order to achieve unconditional security, fairness, undeniability and so on, we adopt the decoy photon checking technique and quantum encryption algorithm. Analysis result shows that our protocol satisfies all the characteristics of traditional english auction, meanwhile, it can resist malicious attacks.
The exact solution of the Ising quantum chain with alternating single and sector defects
International Nuclear Information System (INIS)
Zhang Degang; Li Bozang; Li Yun
1992-10-01
The Ising quantum chain with alternating single and sector defects is solved exactly by using the technique of Lieb, Schultz and Mattis. The energy spectrum of this model is shown to have a tower structure if and only if these defects constitute a commensurate configuration. This means that conformal invariance is preserved under these circumstances. (author). 13 refs
Quantum interference effects at room temperature in OPV-based single-molecule junctions
Arroyo Rodriguez, C.; Frisenda, R.; Moth-Poulsen, K.; Seldenthuis, J.S.; Bjornholm, T.; Van der Zant, H.S.
2013-01-01
Interference effects on charge transport through an individual molecule can lead to a notable modulation and suppression on its conductance. In this letter, we report the observation of quantum interference effects occurring at room temperature in single-molecule junctions based on
Wees, B.J. van; Kouwenhoven, L.P.; Enden, A. van der; Harmans, C.J.P.M.
1991-01-01
We describe transport experiments performed on ballistic submicron devices which are defined in the two dimensional electron gas of GaAs/AlGaAs heterostructures by means of metallic gates. Conductance measurements on single quantum dots reveal the formation of magnetically induced zero-dimensional
The Rabi Oscillation in Subdynamic System for Quantum Computing
Directory of Open Access Journals (Sweden)
Bi Qiao
2015-01-01
Full Text Available A quantum computation for the Rabi oscillation based on quantum dots in the subdynamic system is presented. The working states of the original Rabi oscillation are transformed to the eigenvectors of subdynamic system. Then the dissipation and decoherence of the system are only shown in the change of the eigenvalues as phase errors since the eigenvectors are fixed. This allows both dissipation and decoherence controlling to be easier by only correcting relevant phase errors. This method can be extended to general quantum computation systems.
Novel optical probe for quantum Hall system
Indian Academy of Sciences (India)
to 8 T using SPV spectroscopy. Keywords. Surface photovoltage spectroscopy; quantum Hall effect; Landau levels; edge states. PACS Nos 73.43.-f; 07.60.-j; 73.43.Fj. 1. Introduction. Integer quantum Hall effect (QHE) arises from quantization of energy of two- dimensional electron gas (2DEG) under perpendicular magnetic ...
Computational physics simulation of classical and quantum systems
Scherer, Philipp O J
2017-01-01
This textbook presents basic numerical methods and applies them to a large variety of physical models in multiple computer experiments. Classical algorithms and more recent methods are explained. Partial differential equations are treated generally comparing important methods, and equations of motion are solved by a large number of simple as well as more sophisticated methods. Several modern algorithms for quantum wavepacket motion are compared. The first part of the book discusses the basic numerical methods, while the second part simulates classical and quantum systems. Simple but non-trivial examples from a broad range of physical topics offer readers insights into the numerical treatment but also the simulated problems. Rotational motion is studied in detail, as are simple quantum systems. A two-level system in an external field demonstrates elementary principles from quantum optics and simulation of a quantum bit. Principles of molecular dynamics are shown. Modern bounda ry element methods are presented ...
Experimental quantum compressed sensing for a seven-qubit system.
Riofrío, C A; Gross, D; Flammia, S T; Monz, T; Nigg, D; Blatt, R; Eisert, J
2017-05-17
Well-controlled quantum devices with their increasing system size face a new roadblock hindering further development of quantum technologies. The effort of quantum tomography-the reconstruction of states and processes of a quantum device-scales unfavourably: state-of-the-art systems can no longer be characterized. Quantum compressed sensing mitigates this problem by reconstructing states from incomplete data. Here we present an experimental implementation of compressed tomography of a seven-qubit system-a topological colour code prepared in a trapped ion architecture. We are in the highly incomplete-127 Pauli basis measurement settings-and highly noisy-100 repetitions each-regime. Originally, compressed sensing was advocated for states with few non-zero eigenvalues. We argue that low-rank estimates are appropriate in general since statistical noise enables reliable reconstruction of only the leading eigenvectors. The remaining eigenvectors behave consistently with a random-matrix model that carries no information about the true state.
Quantum-Classical Connection for Hydrogen Atom-Like Systems
Syam, Debapriyo; Roy, Arup
2011-01-01
The Bohr-Sommerfeld quantum theory specifies the rules of quantization for circular and elliptical orbits for a one-electron hydrogen atom-like system. This article illustrates how a formula connecting the principal quantum number "n" and the length of the major axis of an elliptical orbit may be arrived at starting from the quantum…
Quantum interference of single photons from two remote nitrogen-vacancy centers in diamond
Goldman, Michael; Sipahigil, Alp; Togan, Emre; Chu, Yiwen; Markham, Mark; Twitchen, Daniel; Zibrov, Alexander; Kubanek, Alexander; Lukin, Mikhail
2012-06-01
The interference of two identical photons impinging on a beam splitter leads to perfect photon coalescence where both photons leave through the same output port. This effect, known as Hong-Ou-Mandel (HOM) interference, can be used to characterize the properties of quantum emitters with high accuracy. This is a particularly useful tool for quantum emitters embedded in a solid state matrix because their internal properties, unlike those of atoms in free space, differ substantially from emitter to emitter due to strong interactions with the environment. HOM interference can also be used to generate optically mediated entanglement between two remote quantum emitters, a crucial step toward the development of long-distance quantum communication and scalable quantum computation architectures. Here, we demonstrate this interference effect with single photons emitted from two single Nitrogen-Vacancy (NV) centers in diamond samples that are spatially separated by 2 meters [1]. The detuning of the photons can be tuned by applying a DC electric field to one NV center. We discuss current efforts toward optical entanglement of the two NV centers. [4pt] [1] A. Sipahigil, M. L. Goldman, E. Togan, Y. Chu, M. Markham, D. J. Twitchen, A. S. Zibrov, A. Kubanek, and M. D. Lukin, arXiv:1112.3975v1.
Excitons and trions in single and vertically coupled quantum dots under an electric field
Zhai, Li-Xue; Wang, Yan; An, Zhong
2017-08-01
We present a theoretical study of the exciton (X0), the positive and negative trions (X+ and X-) in single and vertically coupled configurations of self-assembled InGaAs quantum dots under an electric field. The quantum states of X0, X+ and X- have been investigated using a quasi-one-dimensional (Q1D) model within the effective-mass approximation. For the single quantum dots, the electric-field dependent energy levels and the average inter-particle distances for the exciton and trions have been calculated. For the coupled quantum dots, the ground and the excited states for X0, X+ and X- have also been calculated and discussed. It is found that either the hole or the electron can be tuned into resonance states by the electric field and that the transition energy spectra for both trions consequently show crossing and anticrossing patterns. The recombination probabilities of the exciton and trion optical transitions are also calculated. The theoretical results have been compared with previously reported photoluminescence data and qualitative agreement is obtained. The trion conditional wave functions are also plotted under different electric field intensities, and it is found that a molecular orbital can be formed at a critical electric field intensity. The evolution of the energy levels of the trions in coupled quantum dots can be explained by the interplay of particle transfer and the electric field.
Makarov, Nikolay S; Guo, Shaojun; Isaienko, Oleksandr; Liu, Wenyong; Robel, István; Klimov, Victor I
2016-04-13
Organic-inorganic lead-halide perovskites have been the subject of recent intense interest due to their unusually strong photovoltaic performance. A new addition to the perovskite family is all-inorganic Cs-Pb-halide perovskite nanocrystals, or quantum dots, fabricated via a moderate-temperature colloidal synthesis. While being only recently introduced to the research community, these nanomaterials have already shown promise for a range of applications from color-converting phosphors and light-emitting diodes to lasers, and even room-temperature single-photon sources. Knowledge of the optical properties of perovskite quantum dots still remains vastly incomplete. Here we apply various time-resolved spectroscopic techniques to conduct a comprehensive study of spectral and dynamical characteristics of single- and multiexciton states in CsPbX3 nanocrystals with X being either Br, I, or their mixture. Specifically, we measure exciton radiative lifetimes, absorption cross-sections, and derive the degeneracies of the band-edge electron and hole states. We also characterize the rates of intraband cooling and nonradiative Auger recombination and evaluate the strength of exciton-exciton coupling. The overall conclusion of this work is that spectroscopic properties of Cs-Pb-halide quantum dots are largely similar to those of quantum dots of more traditional semiconductors such as CdSe and PbSe. At the same time, we observe some distinctions including, for example, an appreciable effect of the halide identity on radiative lifetimes, considerably shorter biexciton Auger lifetimes, and apparent deviation of their size dependence from the "universal volume scaling" previously observed for many traditional nanocrystal systems. The high efficiency of Auger decay in perovskite quantum dots is detrimental to their prospective applications in light-emitting devices and lasers. This points toward the need for the development of approaches for effective suppression of Auger
Malossi, N.; Bason, M. G.; Viteau, M.; Arimondo, E.; Ciampini, D.; Mannella, R.; Morsch, O.
2013-06-01
A fundamental requirement in quantum information processing and in many other areas of science is the capability of precisely controlling a quantum system by preparing a quantum state with the highest fidelity and/or in the fastest possible way. Here we present an experimental investigation of a two level system, characterized by a time-dependent Landau-Zener Hamiltonian, aiming to test general and optimal high-fidelity control protocols. The experiment is based on a Bose-Einstein condensate (BEC) loaded into an optical lattice, then accelerated, which provides a high degree of control over the experimental parameters. We implement generalized Landau-Zener sweeps, comparing them with the well-known linear Landau-Zener sweep. We drive the system from an initial state to a final state with fidelity close to unity in the shortest possible time (quantum brachistochrone), thus reaching the ultimate speed limit imposed by quantum mechanics. On the opposite extreme of the quantum control spectrum, the aim is not to minimize the total transition time but to maximize the adiabaticity during the time-evolution, the system being constrained to the adiabatic ground state at any time. We implement such transitionless superadiabatic protocols by an appropriate transformation of the Hamiltonian parameters. This transformation is general and independent of the physical system.
Quantum Markov processes and applications in many-body systems
International Nuclear Information System (INIS)
Temme, P. K.
2010-01-01
This thesis is concerned with the investigation of quantum as well as classical Markov processes and their application in the field of strongly correlated many-body systems. A Markov process is a special kind of stochastic process, which is determined by an evolution that is independent of its history and only depends on the current state of the system. The application of Markov processes has a long history in the field of statistical mechanics and classical many-body theory. Not only are Markov processes used to describe the dynamics of stochastic systems, but they predominantly also serve as a practical method that allows for the computation of fundamental properties of complex many-body systems by means of probabilistic algorithms. The aim of this thesis is to investigate the properties of quantum Markov processes, i.e. Markov processes taking place in a quantum mechanical state space, and to gain a better insight into complex many-body systems by means thereof. Moreover, we formulate a novel quantum algorithm which allows for the computation of the thermal and ground states of quantum many-body systems. After a brief introduction to quantum Markov processes we turn to an investigation of their convergence properties. We find bounds on the convergence rate of the quantum process by generalizing geometric bounds found for classical processes. We generalize a distance measure that serves as the basis for our investigations, the chi-square divergence, to non-commuting probability spaces. This divergence allows for a convenient generalization of the detailed balance condition to quantum processes. We then devise the quantum algorithm that can be seen as the natural generalization of the ubiquitous Metropolis algorithm to simulate quantum many-body Hamiltonians. By this we intend to provide further evidence, that a quantum computer can serve as a fully-fledged quantum simulator, which is not only capable of describing the dynamical evolution of quantum systems, but
Photonic Quantum Information Processing
International Nuclear Information System (INIS)
Walther, P.
2012-01-01
The advantage of the photon's mobility makes optical quantum system ideally suited for delegated quantum computation. I will present results for the realization for a measurement-based quantum network in a client-server environment, where quantum information is securely communicated and computed. Related to measurement-based quantum computing I will discuss a recent experiment showing that quantum discord can be used as resource for the remote state preparation, which might shine new light on the requirements for quantum-enhanced information processing. Finally, I will briefly review recent photonic quantum simulation experiments of four frustrated Heisenberg-interactions spins and present an outlook of feasible simulation experiments with more complex interactions or random walk structures. As outlook I will discuss the current status of new quantum technology for improving the scalability of photonic quantum systems by using superconducting single-photon detectors and tailored light-matter interactions. (author)
Quantum spin systems on infinite lattices a concise introduction
Naaijkens, Pieter
2017-01-01
This course-based primer offers readers a concise introduction to the description of quantum mechanical systems with infinitely many degrees of freedom – and quantum spin systems in particular – using the operator algebraic approach. Here, the observables are modeled using elements of some operator algebra, usually a C*-algebra. This text introduces readers to the framework and the necessary mathematical tools without assuming much mathematical background, making it more accessible than advanced monographs. The book also highlights the usefulness of the so-called thermodynamic limit of quantum spin systems, which is the limit of infinite system size. For example, this makes it possible to clearly distinguish between local and global properties, without having to keep track of the system size. Together with Lieb-Robinson bounds, which play a similar role in quantum spin systems to that of the speed of light in relativistic theories, this approach allows ideas from relativistic field theories to be implemen...
Asymptotically Optimal Quantum Circuits for d-Level Systems
International Nuclear Information System (INIS)
Bullock, Stephen S.; O'Leary, Dianne P.; Brennen, Gavin K.
2005-01-01
Scalability of a quantum computation requires that the information be processed on multiple subsystems. However, it is unclear how the complexity of a quantum algorithm, quantified by the number of entangling gates, depends on the subsystem size. We examine the quantum circuit complexity for exactly universal computation on many d-level systems (qudits). Both a lower bound and a constructive upper bound on the number of two-qudit gates result, proving a sharp asymptotic of Θ(d 2n ) gates. This closes the complexity question for all d-level systems (d finite). The optimal asymptotic applies to systems with locality constraints, e.g., nearest neighbor interactions
Multi-particle correlations in quaternionic quantum systems
International Nuclear Information System (INIS)
Brumby, S.P.; Joshi, G.C.
1994-01-01
The authors investigated the outcomes of measurements on correlated, few-body quantum systems described by a quaternionic quantum mechanics that allows for regions of quaternionic curvature. It was found that a multi particles interferometry experiment using a correlated system of four nonrelativistic, spin-half particles has the potential to detect the presence of quaternionic curvature. Two-body systems, however, are shown to give predictions identical to those of standard quantum mechanics when relative angles are used in the construction of the operators corresponding to measurements of particle spin components. 15 refs
Magnetism of classical and quantum systems of localized spins
International Nuclear Information System (INIS)
Mariz, A.M.
1985-01-01
The static critical properties of localized are studied spin systems. Several models are discussed: (a) the anisotropic quantum Heisenberg ferromagnet on square lattice (with quenched bond-dilution and random anisotropy) and on simple cubic lattice; (b) the Z(4) ferromagnetic model on square lattice; (c) the Ising model on the Cayley tree, in the presence of competing interactions. The (a) and (b) problems are studied within a real-space Renormalisation Group (RG) approach. In both cases, methods to perform the relevant partial tracings, that are better than those available in the literature are developed. The critical frontiers obtained reproduce all known exact results, and they are high precision ones everywhere. Correlation lenght critical exponents (υ) and the crossover exponents (Φ) are also calculated. The values are, in degree of approximation, equal or superior to those obtained using the Migdal-Kadanoff RG. The (c) problem is investigated by constructing recursive relations (similar to RG); the resulting phase diagram (numerically exact) presents a set of modulated phases, besides the ferromagnetic, antiferromagnetic and paramagnetic ones. It is worth to stress the presence of metastability phenomena and the existence of the paramagnetic phase at arbitrary non-vanishing small temperatures. In addition to the previous works a study of the energy eigenvalues and the specific heat of a general anharmonic single quantum oscillator, by using the Turschner and WKB approximations was performed. Comparisons between them, exhibit the superiority of the Turschner approximation. (author) [pt
Time delays and advances in classical and quantum systems
Kolomeitsev, E. E.; Voskresensky, D. N.
2013-11-01
This article reviews positive and negative time delays in various processes of classical and quantum physics. In the beginning, we demonstrate how a time-shifted response of a system to an external perturbation appears in classical mechanics and classical electrodynamics. Then we quantify durations of various quantum mechanical processes. The duration of the quantum tunneling is studied, and an interpretation of the Hartmann paradox is suggested. Time delays and advances appearing in the three-dimensional scattering problem on a central potential are considered. We then discuss delays and advances appearing in quantum field theory and after that we focus on the issue of time delays and advancements in quantum kinetics. We discuss problems of the application of generalized kinetic equations in simulations of the system relaxation toward equilibrium and analyze the kinetic entropy flow. Possible measurements of time delays and advancements in experiments similar to the recent OPERA neutrino experiment are also discussed.
Bohmian mechanics, open quantum systems and continuous measurements
Nassar, Antonio B
2017-01-01
This book shows how Bohmian mechanics overcomes the need for a measurement postulate involving wave function collapse. The measuring process plays a very important role in quantum mechanics. It has been widely analyzed within the Copenhagen approach through the Born and von Neumann postulates, with later extension due to Lüders. In contrast, much less effort has been invested in the measurement theory within the Bohmian mechanics framework. The continuous measurement (sharp and fuzzy, or strong and weak) problem is considered here in this framework. The authors begin by generalizing the so-called Mensky approach, which is based on restricted path integral through quantum corridors. The measuring system is then considered to be an open quantum system following a stochastic Schrödinger equation. Quantum stochastic trajectories (in the Bohmian sense) and their role in basic quantum processes are discussed in detail. The decoherence process is thereby described in terms of classical trajectories issuing from th...
Computing with a single qubit faster than the computation quantum speed limit
Sinitsyn, Nikolai A.
2018-02-01
The possibility to save and process information in fundamentally indistinguishable states is the quantum mechanical resource that is not encountered in classical computing. I demonstrate that, if energy constraints are imposed, this resource can be used to accelerate information-processing without relying on entanglement or any other type of quantum correlations. In fact, there are computational problems that can be solved much faster, in comparison to currently used classical schemes, by saving intermediate information in nonorthogonal states of just a single qubit. There are also error correction strategies that protect such computations.
Electroluminescence from a single InGaN quantum dot in the green spectral region up to 150 K
International Nuclear Information System (INIS)
Kalden, J; Sebald, K; Gutowski, J; Tessarek, C; Figge, S; Kruse, C; Hommel, D
2010-01-01
We present electrically driven luminescence from single InGaN quantum dots embedded into a light emitting diode structure grown by metal-organic vapor-phase epitaxy. Single sharp emission lines in the green spectral region can be identified. Temperature dependent measurements demonstrate thermal stability of the emission of a single quantum dot up to 150 K. These results are an important step towards applications like electrically driven single-photon emitters, which are a basis for applications incorporating plastic optical fibers as well as for modern concepts of free space quantum cryptography.
Controlled Rephasing of Single Collective Spin Excitations in a Cold Atomic Quantum Memory.
Albrecht, Boris; Farrera, Pau; Heinze, Georg; Cristiani, Matteo; de Riedmatten, Hugues
2015-10-16
We demonstrate active control of inhomogeneous dephasing and rephasing for single collective atomic spin excitations (spin waves) created by spontaneous Raman scattering in a quantum memory based on cold 87Rb atoms. The control is provided by a reversible external magnetic field gradient inducing an inhomogeneous broadening of the atomic hyperfine levels. We demonstrate experimentally that active rephasing preserves the single photon nature of the retrieved photons. Finally, we show that the control of the inhomogeneous dephasing enables the creation of time-separated spin waves in a single ensemble followed by a selective read-out in time. This is an important step towards the implementation of a functional temporally multiplexed quantum repeater node.
Does an onlooker stop an evolving quantum system?
International Nuclear Information System (INIS)
Toschek, P E
2007-01-01
The evolution of quantum mechanics has followed the critical analysis of 'gedanken' experiments. Many of these concrete speculations can become implemented today in the laboratory - thanks to now available techniques. A key experiment is concerned with the time evolution of a quantum system under repeated or continuing observation. Here, three problems overlap: 1. The microphysical measurement by a macroscopic device, 2. the system's temporal evolution, and 3. the emergence of macroscopic reality out of the microcosmos. A well-known calculation shows the evolution of a quantum system being slowed down, or even obstructed, when the system is merely observed.An experiment designed to demonstrate this 'quantum Zeno effect' and performed in the late eighties on an ensemble of identical atomic ions confirmed its quantum description, but turned out inconclusive with respect to the very origin of the impediment of evolution. During the past years, experiments on individualelectrodynamically stored and laser-cooled ions have been performed that unequivocally demonstrate the observed system's quantum evolution being impeded. Strategy and results exclude any physical reaction on the measured object, but reveal the effect of the gain of information as put forward by the particular correlation of the ion state with the detected signal. They shed light on the process of measurement as well as on the quantum evolution and allow an epistemological interpretation
Magnetic Quantum Tunneling in Single Molecule Magnets: Mn-12 and Others
del Barco, Enrique
2004-03-01
Magnetic quantum tunneling (MQT) has been studied in single molecule magnets (SMMs) using a micro-Hall effect magnetometer in a superconducting high field vector magnet system that incorporates the possibility of applying pulsed microwave fields. Mn_12-acetate has been studied extensively over the years. However, only recently the symmetry of MQT and the nature of the transverse interactions important to MQT have been determined [1,2]. Magnetic measurements in the pure quantum tunneling regime (0.6 K) illustrate that an average crystal fourfold MQT symmetry is due to local molecular environments of twofold symmetry that are rotated by 90 degrees with respect to one another, confirming that disorder which lowers the molecule symmetry is important to MQT. We have studied a subset of these lower site symmetry molecules and present evidence for a Berry phase that results from a combination of second and forth order contributions to the transverse magnetic anisotropy. These observations are consistent with high frequency EPR studies of the transverse interactions in Mn_12-acetate [3]. Finally, we discuss recent experiments in which microwave radiation is applied to modulate MQT and characterize the lifetimes and coherence times of states that are superpositions of "up" and "down" high spin-projections. [1] E. del Barco, et al., Phys. Rev. Lett. 91, 047203 (2003) [2] S. Hill, et al., Phys. Rev. Lett. 90, 217204 (2003). [3] E. del Barco, A, D. Kent, R. S. Edwards, S. I. Jones, S. Hill, J. M. North, N. S. Dalal, E. M. Rumnberger, D. N. Hendrickson and G. Christou, to be published.
Simulation of Quantum Tunnelling in an Open System
Fernández, Julio F.
2003-04-01
Magnetic clusters, such as Fe8 and Mn12, within large organic molecules, behave at low temperature T as large single spins S, that is, as single molecule magnets (SMM's). In crystals, magnetic anisotropy gives rise to energy barriers U, and quantum tunnelling is then the only available path for magnetic relaxation at vanishingly small temperatures. Even this path, however, would seem to be nearly closed by energy conservation requirements, given the existence of magnetic dipolar interactions among all SMM's in the crystal. Nevertheless, magnetic relaxation that is temperature independent has lately been observed for temperatures under 0.1 U/kBS for Fe8 and Mn12 (U ≈ 30 K and U ≈ 60 K, for Fe8 and Mn12, respectively, and S = 10 for both of them). Prokof'ev and Stamp (PS) were able to explain it by taking into account hyperfine interactions between the tunnelling electronic spins and nuclear spins. In the PS theory, the system of nuclear spins acts much as a heat bath providing a somewhat random magnetic field h(t) that acts on the otherwise closed system of interacting magnetic dipoles. Thus, the open nature of these systems plays an essential role in bringing tunnelling about. Their numerical simulations are explained, results that follow from the simulations are discussed, and a simple derivation of the tunnelling rate is given.
Energy Technology Data Exchange (ETDEWEB)
Heo, Jino [College of Electrical and Computer Engineering, Chungbuk National University, Chungdae-ro 1, Seowon-Gu, Cheongju (Korea, Republic of); Kang, Min-Sung [Center for Quantum Information, Korea Institute of Science and Technology (KIST), Seoul, 136-791 (Korea, Republic of); Hong, Chang-Ho [National Security Research Institute, P.O.Box 1, Yuseong, Daejeon, 34188 (Korea, Republic of); Choi, Seong-Gon [College of Electrical and Computer Engineering, Chungbuk National University, Chungdae-ro 1, Seowon-Gu, Cheongju (Korea, Republic of); Hong, Jong-Phil, E-mail: jongph@cbnu.ac.kr [College of Electrical and Computer Engineering, Chungbuk National University, Chungdae-ro 1, Seowon-Gu, Cheongju (Korea, Republic of)
2017-06-15
We propose a scheme for swapping two unknown states of a photon and electron spin confined to a charged quantum dot (QD) between two users by transferring a single photon. This scheme simultaneously transfers and teleports an unknown state (electron spin) between two users. For this bidirectional quantum communication, we utilize the interactions between a photonic and an electron-spin qubits of a QD located inside a single-sided optical cavity. Thus, our proposal using QD-cavity systems can obtain a certain success probability with high fidelity. Furthermore, compared to a previous scheme using cross-Kerr nonlinearities and homodyne detections, our scheme (using QD-cavity systems) can improve the feasibility under the decoherence effect in practice. - Highlights: • Design of Simultaneous quantum transmission and teleportation scheme via quantum dots and cavities. • We have developed the experimental feasibility of this scheme compared with the existing scheme. • Analysis of some benefits when our scheme is experimentally implemented using quantum dots and single-sided cavities.
Entanglement transfer from electrons to photons in quantum dots: an open quantum system approach
International Nuclear Information System (INIS)
Budich, Jan C; Trauzettel, Bjoern
2010-01-01
We investigate entanglement transfer from a system of two spin-entangled electron-hole pairs, each placed in a separate single mode cavity, to the photons emitted due to cavity leakage. Dipole selection rules and a splitting between the light hole and the heavy hole subbands are the crucial ingredients establishing a one-to-one correspondence between electron spins and circular photon polarizations. To account for the measurement of the photons as well as dephasing effects, we choose a stochastic Schroedinger equation and a conditional master equation approach, respectively. The influence of interactions with the environment as well as asymmetries in the coherent couplings on the photon entanglement is analysed for two concrete measurement schemes. The first one is designed to violate the Clauser-Horne-Shimony-Holt (CHSH) inequality, while the second one employs the visibility of interference fringes to prove the entanglement of the photons. Because of the spatial separation of the entangled electronic system over two quantum dots, a successful verification of entangled photons emitted by this system would imply the detection of nonlocal spin entanglement of massive particles in a solid state structure.
The Dalton quantum chemistry program system.
Aidas, Kestutis; Angeli, Celestino; Bak, Keld L; Bakken, Vebjørn; Bast, Radovan; Boman, Linus; Christiansen, Ove; Cimiraglia, Renzo; Coriani, Sonia; Dahle, Pål; Dalskov, Erik K; Ekström, Ulf; Enevoldsen, Thomas; Eriksen, Janus J; Ettenhuber, Patrick; Fernández, Berta; Ferrighi, Lara; Fliegl, Heike; Frediani, Luca; Hald, Kasper; Halkier, Asger; Hättig, Christof; Heiberg, Hanne; Helgaker, Trygve; Hennum, Alf Christian; Hettema, Hinne; Hjertenæs, Eirik; Høst, Stinne; Høyvik, Ida-Marie; Iozzi, Maria Francesca; Jansík, Branislav; Jensen, Hans Jørgen Aa; Jonsson, Dan; Jørgensen, Poul; Kauczor, Joanna; Kirpekar, Sheela; Kjærgaard, Thomas; Klopper, Wim; Knecht, Stefan; Kobayashi, Rika; Koch, Henrik; Kongsted, Jacob; Krapp, Andreas; Kristensen, Kasper; Ligabue, Andrea; Lutnæs, Ola B; Melo, Juan I; Mikkelsen, Kurt V; Myhre, Rolf H; Neiss, Christian; Nielsen, Christian B; Norman, Patrick; Olsen, Jeppe; Olsen, Jógvan Magnus H; Osted, Anders; Packer, Martin J; Pawlowski, Filip; Pedersen, Thomas B; Provasi, Patricio F; Reine, Simen; Rinkevicius, Zilvinas; Ruden, Torgeir A; Ruud, Kenneth; Rybkin, Vladimir V; Sałek, Pawel; Samson, Claire C M; de Merás, Alfredo Sánchez; Saue, Trond; Sauer, Stephan P A; Schimmelpfennig, Bernd; Sneskov, Kristian; Steindal, Arnfinn H; Sylvester-Hvid, Kristian O; Taylor, Peter R; Teale, Andrew M; Tellgren, Erik I; Tew, David P; Thorvaldsen, Andreas J; Thøgersen, Lea; Vahtras, Olav; Watson, Mark A; Wilson, David J D; Ziolkowski, Marcin; Agren, Hans
2014-05-01
Dalton is a powerful general-purpose program system for the study of molecular electronic structure at the Hartree-Fock, Kohn-Sham, multiconfigurational self-consistent-field, Møller-Plesset, configuration-interaction, and coupled-cluster levels of theory. Apart from the total energy, a wide variety of molecular properties may be calculated using these electronic-structure models. Molecular gradients and Hessians are available for geometry optimizations, molecular dynamics, and vibrational studies, whereas magnetic resonance and optical activity can be studied in a gauge-origin-invariant manner. Frequency-dependent molecular properties can be calculated using linear, quadratic, and cubic response theory. A large number of singlet and triplet perturbation operators are available for the study of one-, two-, and three-photon processes. Environmental effects may be included using various dielectric-medium and quantum-mechanics/molecular-mechanics models. Large molecules may be studied using linear-scaling and massively parallel algorithms. Dalton is distributed at no cost from http://www.daltonprogram.org for a number of UNIX platforms.
Quantum nernst effect in a bismuth single crystal
International Nuclear Information System (INIS)
Matsuo, M.; Endo, A.; Hatano, N.; Nakamura, H.; Shirasaki, R.; Sugihara, K.
2009-07-01
We calculate the phonon-drag contribution to the transverse (Nernst) thermoelectric power S yx in a bismuth single crystal subjected to a quantizing magnetic field. The calculated heights of the Nernst peaks originating from the hole Landau levels and their temperature dependence reproduce the right order of magnitude for those of the pronounced magneto-oscillations recently reported by Behnia et al. A striking experimental finding that S yx is much larger than the longitudinal (Seebeck) thermoelectric power S xx can be naturally explained as the effect of the phonon drag, combined with the well-known relation between the longitudinal and the Hall resistivity ρ xx >> |ρ yx | in a semi-metal bismuth. The calculation that includes the contribution of both holes and electrons suggests that some of the hitherto unexplained minor peaks located roughly at the fractional filling of the hole Landau levels are attributable to the electron Landau levels. (author)
Quantum systems that follow classical dynamics
Manfredi, G; Feix, M R
1993-01-01
For a special class of potentials, the dynamical evolution of any quantum wavepacket is entirely determined by the laws of classical mechanics. Here, the properties of this class are investigated both from the viewpoint of the Ehrenfest theorem (which provides the evolution of the average position and momentum), and the Wigner representation (which expresses quantum mechanics in a phase space formalism). Finally, these results are extended to the case of a charged particle in a uniform magnetic field. (author)
Single-mode quantum cascade lasers employing a candy-cane shaped monolithic coupled cavity
Liu, Peter Q.; Sladek, Kamil; Wang, Xiaojun; Fan, Jen-Yu; Gmachl, Claire F.
2011-12-01
We demonstrate single-mode quantum cascade lasers emitting at ˜4.5 μm by employing a monolithic "candy-cane" shaped coupled-cavity consisting of a straight section connecting at one end to a spiral section. The fabrication process is identical to those for simple Fabry-Perot-type ridge lasers. Continuously tunable single-mode emission across ˜8 cm-1 with side mode suppression ratio up to ˜25 dB and a single-mode operating current range of more than 70% above the threshold current is achieved when the lasers are operated in pulsed-mode from 80 K to 155 K.
Ultrafast quantum random access memory utilizing single Rydberg atoms in a Bose-Einstein condensate.
Patton, Kelly R; Fischer, Uwe R
2013-12-13
We propose a long-lived and rapidly accessible quantum memory unit, for which the operational Hilbert space is spanned by states involving the two macroscopically occupied hyperfine levels of a miscible binary atomic Bose-Einstein condensate and the Rydberg state of a single atom. It is shown that an arbitrary qubit state, initially prepared using a flux qubit, can be rapidly transferred to and from the trapped atomic ensemble in approximately 10 ns and with a large fidelity of 97%, via an effective two-photon process using an external laser for the transition to the Rydberg level. The achievable ultrafast transfer of quantum information therefore enables a large number of storage and retrieval cycles from the highly controllable quantum optics setup of a dilute ultracold gas, even within the typically very short flux qubit lifetimes of the order of microseconds.
Closed-Loop and Robust Control of Quantum Systems
Directory of Open Access Journals (Sweden)
Chunlin Chen
2013-01-01
Full Text Available For most practical quantum control systems, it is important and difficult to attain robustness and reliability due to unavoidable uncertainties in the system dynamics or models. Three kinds of typical approaches (e.g., closed-loop learning control, feedback control, and robust control have been proved to be effective to solve these problems. This work presents a self-contained survey on the closed-loop and robust control of quantum systems, as well as a brief introduction to a selection of basic theories and methods in this research area, to provide interested readers with a general idea for further studies. In the area of closed-loop learning control of quantum systems, we survey and introduce such learning control methods as gradient-based methods, genetic algorithms (GA, and reinforcement learning (RL methods from a unified point of view of exploring the quantum control landscapes. For the feedback control approach, the paper surveys three control strategies including Lyapunov control, measurement-based control, and coherent-feedback control. Then such topics in the field of quantum robust control as H∞ control, sliding mode control, quantum risk-sensitive control, and quantum ensemble control are reviewed. The paper concludes with a perspective of future research directions that are likely to attract more attention.
Theory and simulation of cavity quantum electro-dynamics in multi-partite quantum complex systems
Alidoosty Shahraki, Moslem; Khorasani, Sina; Aram, Mohammad Hasan
2014-05-01
The cavity quantum electrodynamics of various complex systems is here analyzed using a general versatile code developed in this research. Such quantum multi-partite systems normally consist of an arbitrary number of quantum dots in interaction with an arbitrary number of cavity modes. As an example, a nine-partition system is simulated under different coupling regimes, consisting of eight emitters interacting with one cavity mode. Two-level emitters (e.g. quantum dots) are assumed to have an arrangement in the form of a linear chain, defining the mutual dipole-dipole interactions. It was observed that plotting the system trajectory in the phase space reveals a chaotic behavior in the so-called ultrastrong-coupling regime. This result is mathematically confirmed by detailed calculation of the Kolmogorov entropy, as a measure of chaotic behavior. In order to study the computational complexity of our code, various multi-partite systems consisting of one to eight quantum dots in interaction with one cavity mode were solved individually. Computation run times and the allocated memory for each system were measured.
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
Geodesic paths and topological charges in quantum systems
Grangeiro Souza Barbosa Lima, Tiago Aecio
This dissertation focuses on one question: how should one drive an experimentally prepared state of a generic quantum system into a different target-state, simultaneously minimizing energy dissipation and maximizing the fidelity between the target and evolved-states? We develop optimal adiabatic driving protocols for general quantum systems, and show that these are geodesic paths. Geometric ideas have always played a fundamental role in the understanding and unification of physical phenomena, and the recent discovery of topological insulators has drawn great interest to topology from the field of condensed matter physics. Here, we discuss the quantum geometric tensor, a mathematical object that encodes geometrical and topological properties of a quantum system. It is related to the fidelity susceptibility (an important quantity regarding quantum phase transitions) and to the Berry curvature, which enables topological characterization through Berry phases. A refined understanding of the interplay between geometry and topology in quantum mechanics is of direct relevance to several emergent technologies, such as quantum computers, quantum cryptography, and quantum sensors. As a demonstration of how powerful geometric and topological ideas can become when combined, we present the results of an experiment that we recently proposed. This experimental work was done at the Google Quantum Lab, where researchers were able to visualize the topological nature of a two-qubit system in sharp detail, a startling contrast with earlier methods. To achieve this feat, the optimal protocols described in this dissertation were used, allowing for a great improvement on the experimental apparatus, without the need for technical engineering advances. Expanding the existing literature on the quantum geometric tensor using notions from differential geometry and topology, we build on the subject nowadays known as quantum geometry. We discuss how slowly changing a parameter of a quantum
Ordering due to disorder in frustrated quantum magnetic system
International Nuclear Information System (INIS)
Yildirim, T.
1999-01-01
The phenomenon of order by disorder in frustrated magnetic systems is reviewed. Disorder (thermal or quantum fluctuations) may sometimes give rise to long range ordering in systems with frustration, where one must often consider the selection among classically degenerate ground states which are not equivalent by any symmetry. The lowest order effects of quantum fluctuations in such frustrated systems usually resolves the continues degeneracy of the ground state manifold into discrete Ising-type degeneracy. A unique ground state selection out of this Ising degenerate manifold then occurs due to higher order effects of quantum fluctuations. For systems such as face-centered cubic and body-centered tetragonal antiferromagnets where the number of Ising parameters to describe the ground state manifold is not macroscopic, we show that quantum fluctuations choose a unique ground state at the first order in 1/S
Quantum Hall Ferroelectrics and Nematics in Multivalley Systems
Sodemann, Inti; Zhu, Zheng; Fu, Liang
2017-10-01
We study broken symmetry states at integer Landau-level fillings in multivalley quantum Hall systems whose low-energy dispersions are anisotropic. When the Fermi surface of individual pockets lacks twofold rotational symmetry, like in bismuth (111) [Feldman et al. , Observation of a Nematic Quantum Hall Liquid on the Surface of Bismuth, Science 354, 316 (2016), 10.1126/science.aag1715] and in Sn1 -xPbxSe (001) [Dziawa et al., Topological Crystalline Insulator States in Pb1 -xSnxSe , Nat. Mater. 11, 1023 (2012), 10.1038/nmat3449] surfaces, interactions tend to drive the formation of quantum Hall ferroelectric states. We demonstrate that the dipole moment in these states has an intimate relation to the Fermi surface geometry of the parent metal. In quantum Hall nematic states, like those arising in AlAs quantum wells, we demonstrate the existence of unusually robust Skyrmion quasiparticles.
Quantum correlations for bipartite continuous-variable systems
Ma, Ruifen; Hou, Jinchuan; Qi, Xiaofei; Wang, Yangyang
2018-04-01
Two quantum correlations Q and Q_P for (m+n)-mode continuous-variable systems are introduced in terms of average distance between the reduced states under the local Gaussian positive operator-valued measurements, and analytical formulas of these quantum correlations for bipartite Gaussian states are provided. It is shown that the product states do not contain these quantum correlations, and conversely, all (m+n)-mode Gaussian states with zero quantum correlations are product states. Generally, Q≥ Q_{P}, but for the symmetric two-mode squeezed thermal states, these quantum correlations are the same and a computable formula is given. In addition, Q is compared with Gaussian geometric discord for symmetric squeezed thermal states.
Chen, Ze-Sheng; Ma, Ben; Shang, Xiang-Jun; He, Yu; Zhang, Li-Chun; Ni, Hai-Qiao; Wang, Jin-Liang; Niu, Zhi-Chuan
2016-12-01
Single-photon emission in the telecommunication wavelength band is realized with self-assembled strain-coupled bilayer InAs quantum dots (QDs) embedded in a planar microcavity on GaAs substrate. Low-density large QDs in the upper layer active for ~1.3 μm emission are fabricated by precisely controlling the indium deposition amount and applying a gradient indium flux in both QD layers. Time-resolved photoluminescence (PL) intensity suggested that the radiative lifetime of their exciton emission is 1.5~1.6 ns. The second-order correlation function of g (2)(0) < 0.5 which demonstrates a pure single-photon emission.
The phase diagram of quantum systems: Heisenberg antiferromagnets
Gianinetti, Pietro; Parola, Alberto
2000-01-01
A novel approach for studying phase transitions in systems with quantum degrees of freedom is discussed. Starting from the microscopic hamiltonian of a quantum model, we first derive a set of exact differential equations for the free energy and the correlation functions describing the effects of fluctuations on the thermodynamics of the system. These equations reproduce the full renormalization group structure in the neighborhood of a critical point keeping, at the same time, full information...
N-Level Quantum Systems and Legendre Functions
Mazurenko, A. S.; Savva, V. A.
2001-01-01
An excitation dynamics of new quantum systems of N equidistant energy levels in a monochromatic field has been investigated. To obtain exact analytical solutions of dynamic equations an analytical method based on orthogonal functions of a real argument has been proposed. Using the orthogonal Legendre functions we have found an exact analytical expression for a population probability amplitude of the level n. Various initial conditions for the excitation of N-level quantum systems have been co...
Nanoscale thermal imaging of dissipation in quantum systems
Halbertal, Dorri; Cuppens, Jo; Shalom, Moshe Ben; Embon, Lior; Shadmi, Nitzan; Anahory, Yonathan; Naren, HR; Sarkar, Jayanta; Uri, Aviram; Ronen, Yuval; Myasoedov, Yury; Levitov, Leonid; Joselevich, Ernesto; Geim, Andre Konstantin; Zeldov, Eli
2016-01-01
Energy dissipation is a fundamental process governing the dynamics of physical, chemical and biological systems. It is also one of the main characteristics that distinguish quantum from classical phenomena. In particular, in condensed matter physics, scattering mechanisms, loss of quantum information or breakdown of topological protection are deeply rooted in the intricate details of how and where the dissipation occurs. Yet the microscopic behaviour of a system is usually not formulated in t...
Energy Technology Data Exchange (ETDEWEB)
Warming, Till
2009-02-20
The application of quantum-mechanical effects in semiconductor nanostructures enables the realization of novel opto-electronic devices. Examples are given by single-photon emitters and emitters of entangled photon pairs, both being essential for quantum cryptography, or for qubit systems as needed for quantum computing. InAs/GaAs quantum dots are one of the most promising candidates for such applications. A detailed knowledge of the electronic properties of quantum dots is a prerequisite for this development. The aim of this work is an experimental access to the detailed electronic structure of the excited states in single InAs/GaAs quantum dots including few-particle effects and in particular exchange interaction. The experimental approach is micro photoluminescence excitation spectroscopy ({mu}PLE). One of the main difficulties using {mu}PLE to probe single QDs is the unambiguous assignment of the observed resonances in the spectrum to specific transitions. By comparing micro photoluminescence ({mu}PL) and {mu}PLE spectra, the identification of the main resonances becomes possible. The key is given by the fine structure of the hot trion. Excitation spectroscopy on single charged QDs enables for the first time the complete observation of a non-trivial fine structure of an excitonic complex in a QD, the hot trion. Modelling based on eight-band k.p theory in combination with a configuration interaction scheme is in excellent agreement. Therewith the simulation also enables realistic predictions on the fine structure of the ground-state exciton which is of large importance for single quantum dot devices. Theory concludes from the observed transitions that the structural symmetry of the QDs is broken. Micro photoluminescence excitation spectroscopy combined with resonantly excited micro photoluminescence enables an optical access to the single particle states of the hole without the influence of few-particle coulomb interactions. Based on this knowledge the exciton
Quantum phase transitions of strongly correlated electron systems
International Nuclear Information System (INIS)
Imada, Masatoshi
1998-01-01
Interacting electrons in solids undergo various quantum phase transitions driven by quantum fluctuations. The quantum transitions take place at zero temperature by changing a parameter to control quantum fluctuations rather than thermal fluctuations. In contrast to classical phase transitions driven by thermal fluctuations, the quantum transitions have many different features where quantum dynamics introduces a source of intrinsic fluctuations tightly connected with spatial correlations and they have been a subject of recent intensive studies as we see below. Interacting electron systems cannot be fully understood without deep analyses of the quantum phase transitions themselves, because they are widely seen and play essential roles in many phenomena. Typical and important examples of the quantum phase transitions include metal-insulator transitions, (2, 3, 4, 5, 6, 7, 8, 9) metal-superconductor transitions, superconductor-insulator transitions, magnetic transitions to antiferromagnetic or ferromagnetic phases in metals as well as in Mott insulators, and charge ordering transitions. Here, we focus on three different types of transitions
Quantum dots for quantum information technologies
2017-01-01
This book highlights the most recent developments in quantum dot spin physics and the generation of deterministic superior non-classical light states with quantum dots. In particular, it addresses single quantum dot spin manipulation, spin-photon entanglement and the generation of single-photon and entangled photon pair states with nearly ideal properties. The role of semiconductor microcavities, nanophotonic interfaces as well as quantum photonic integrated circuits is emphasized. The latest theoretical and experimental studies of phonon-dressed light matter interaction, single-dot lasing and resonance fluorescence in QD cavity systems are also provided. The book is written by the leading experts in the field.
Quantum Sensing of Mechanical Motion with a Single InAs Quantum Dot
2017-03-01
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Applicability of transfer tensor method for open quantum system dynamics.
Gelzinis, Andrius; Rybakovas, Edvardas; Valkunas, Leonas
2017-12-21
Accurate simulations of open quantum system dynamics is a long standing issue in the field of chemical physics. Exact methods exist, but are costly, while perturbative methods are limited in their applicability. Recently a new black-box type method, called transfer tensor method (TTM), was proposed [J. Cerrillo and J. Cao, Phys. Rev. Lett. 112, 110401 (2014)]. It allows one to accurately simulate long time dynamics with a numerical cost of solving a time-convolution master equation, provided many initial system evolution trajectories are obtained from some exact method beforehand. The possible time-savings thus strongly depend on the ratio of total versus initial evolution lengths. In this work, we investigate the parameter regimes where an application of TTM would be most beneficial in terms of computational time. We identify several promising parameter regimes. Although some of them correspond to cases when perturbative theories could be expected to perform well, we find that the accuracy of such approaches depends on system parameters in a more complex way than it is commonly thought. We propose that the TTM should be applied whenever system evolution is expected to be long and accuracy of perturbative methods cannot be ensured or in cases when the system under consideration does not correspond to any single perturbative regime.
A cost-effective measurement-device-independent quantum key distribution system for quantum networks
Valivarthi, Raju; Zhou, Qiang; John, Caleb; Marsili, Francesco; Verma, Varun B.; Shaw, Matthew D.; Nam, Sae Woo; Oblak, Daniel; Tittel, Wolfgang
2017-12-01
We experimentally realize a measurement-device-independent quantum key distribution (MDI-QKD) system. It is based on cost-effective and commercially available hardware such as distributed feedback lasers and field-programmable gate arrays that enable time-bin qubit preparation and time-tagging, and active feedback systems that allow for compensation of time-varying properties of photons after transmission through deployed fiber. We examine the performance of our system, and conclude that its design does not compromise performance. Our demonstration paves the way for MDI-QKD-based quantum networks in star-type topology that extend over more than 100 km distance.
Growth and characterization of InP/In0.48Ga0.52P quantum dots optimized for single-photon emission
International Nuclear Information System (INIS)
Ugur, Asli
2012-01-01
In this work the growth of self-assembled InP/InGaP quantum dots, as well as their optical and structural properties are presented and discussed. The QDs were grown on In 0.48 Ga 0.52 P, lattice matched to GaAs. Self-assembled InP quantum dots are grown using gas-source molecular beam epitaxy over a wide range of InP deposition rates, using an ultra-low growth rate of about 0.01 atomic monolayers/s, a quantum-dot density of 1 dot/μm 2 is realized. The resulting isolated InP quantum dots are individually characterized without the need for lithographical patterning and masks on the substrate. Both excitonic and biexcitonic emissions are observed from single dots, appearing as doublets with a fine-structure splitting of 320 μeV. Hanbury Brown-Twiss correlation measurements for the excitonic emission under cw excitation show anti-bunching behavior with an autocorrelation value of g (2) (0)=0.2. This system is applicable as a single-photon source for applications such as quantum cryptography. The formation of well-ordered chains of InP quantum dots on GaAs (001) substrates by using self-organized In 0.48 Ga 0.52 P surface undulations as a template is also demonstrated. The ordering requires neither stacked layers of quantum dots nor substrate misorientation. The structures are investigated by polarization-dependent photoluminescence together with transmission electron microscopy. Luminescence from the In 0.48 Ga 0.52 P matrix is polarized in one crystallographic direction due to anisotropic strain arising from a lateral compositional modulation. The photoluminescence measurements show enhanced linear polarization in the alignment direction of quantum dots. A polarization degree of 66% is observed. The optical anisotropy is achieved with a straightforward heterostructure, requiring only a single layer of QDs.
Low-threshold room-temperature AlGaAs/GaAs nanowire/single-quantum-well heterostructure laser
Yan, Xin; Wei, Wei; Tang, Fengling; Wang, Xi; Li, Luying
2017-01-01
Near-infrared nanowire lasers are promising as ultrasmall, low-consumption light emitters in on-chip optical communications and computing systems. Here, we report on a room-temperature near-infrared nanolaser based on an AlGaAs/GaAs nanowire/single-quantum-well heterostructure grown by Au-catalyzed metal organic chemical vapor deposition. When subjects to pulsed optical excitation, the nanowire exhibits lasing, with a low threshold of 600 W/cm2, a narrow linewidth of 0.39 nm, and a high Q fac...