Dissipative quantum error correction and application to quantum sensing with trapped ions.

Science.gov (United States)

Reiter, F; Sørensen, A S; Zoller, P; Muschik, C A

2017-11-28

Quantum-enhanced measurements hold the promise to improve high-precision sensing ranging from the definition of time standards to the determination of fundamental constants of nature. However, quantum sensors lose their sensitivity in the presence of noise. To protect them, the use of quantum error-correcting codes has been proposed. Trapped ions are an excellent technological platform for both quantum sensing and quantum error correction. Here we present a quantum error correction scheme that harnesses dissipation to stabilize a trapped-ion qubit. In our approach, always-on couplings to an engineered environment protect the qubit against spin-flips or phase-flips. Our dissipative error correction scheme operates in a continuous manner without the need to perform measurements or feedback operations. We show that the resulting enhanced coherence time translates into a significantly enhanced precision for quantum measurements. Our work constitutes a stepping stone towards the paradigm of self-correcting quantum information processing.

Experimental realization of quantum cheque using a five-qubit quantum computer

Science.gov (United States)

Behera, Bikash K.; Banerjee, Anindita; Panigrahi, Prasanta K.

2017-12-01

Quantum cheques could be a forgery-free way to make transaction in a quantum networked banking system with perfect security against any no-signalling adversary. Here, we demonstrate the implementation of quantum cheque, proposed by Moulick and Panigrahi (Quantum Inf Process 15:2475-2486, 2016), using the five-qubit IBM quantum computer. Appropriate single qubit, CNOT and Fredkin gates are used in an optimized configuration. The accuracy of implementation is checked and verified through quantum state tomography by comparing results from the theoretical and experimental density matrices.

Large-scale simulations of error-prone quantum computation devices

International Nuclear Information System (INIS)

Trieu, Doan Binh

2009-01-01

The theoretical concepts of quantum computation in the idealized and undisturbed case are well understood. However, in practice, all quantum computation devices do suffer from decoherence effects as well as from operational imprecisions. This work assesses the power of error-prone quantum computation devices using large-scale numerical simulations on parallel supercomputers. We present the Juelich Massively Parallel Ideal Quantum Computer Simulator (JUMPIQCS), that simulates a generic quantum computer on gate level. It comprises an error model for decoherence and operational errors. The robustness of various algorithms in the presence of noise has been analyzed. The simulation results show that for large system sizes and long computations it is imperative to actively correct errors by means of quantum error correction. We implemented the 5-, 7-, and 9-qubit quantum error correction codes. Our simulations confirm that using error-prone correction circuits with non-fault-tolerant quantum error correction will always fail, because more errors are introduced than being corrected. Fault-tolerant methods can overcome this problem, provided that the single qubit error rate is below a certain threshold. We incorporated fault-tolerant quantum error correction techniques into JUMPIQCS using Steane's 7-qubit code and determined this threshold numerically. Using the depolarizing channel as the source of decoherence, we find a threshold error rate of (5.2±0.2) x 10 -6 . For Gaussian distributed operational over-rotations the threshold lies at a standard deviation of 0.0431±0.0002. We can conclude that quantum error correction is especially well suited for the correction of operational imprecisions and systematic over-rotations. For realistic simulations of specific quantum computation devices we need to extend the generic model to dynamic simulations, i.e. time-dependent Hamiltonian simulations of realistic hardware models. We focus on today's most advanced technology, i

Distinguishing mixed quantum states: Minimum-error discrimination versus optimum unambiguous discrimination

International Nuclear Information System (INIS)

Herzog, Ulrike; Bergou, Janos A.

2004-01-01

We consider two different optimized measurement strategies for the discrimination of nonorthogonal quantum states. The first is ambiguous discrimination with a minimum probability of inferring an erroneous result, and the second is unambiguous, i.e., error-free, discrimination with a minimum probability of getting an inconclusive outcome, where the measurement fails to give a definite answer. For distinguishing between two mixed quantum states, we investigate the relation between the minimum-error probability achievable in ambiguous discrimination, and the minimum failure probability that can be reached in unambiguous discrimination of the same two states. The latter turns out to be at least twice as large as the former for any two given states. As an example, we treat the case where the state of the quantum system is known to be, with arbitrary prior probability, either a given pure state, or a uniform statistical mixture of any number of mutually orthogonal states. For this case we derive an analytical result for the minimum probability of error and perform a quantitative comparison with the minimum failure probability

Large-scale simulations of error-prone quantum computation devices

Energy Technology Data Exchange (ETDEWEB)

Trieu, Doan Binh

2009-07-01

The theoretical concepts of quantum computation in the idealized and undisturbed case are well understood. However, in practice, all quantum computation devices do suffer from decoherence effects as well as from operational imprecisions. This work assesses the power of error-prone quantum computation devices using large-scale numerical simulations on parallel supercomputers. We present the Juelich Massively Parallel Ideal Quantum Computer Simulator (JUMPIQCS), that simulates a generic quantum computer on gate level. It comprises an error model for decoherence and operational errors. The robustness of various algorithms in the presence of noise has been analyzed. The simulation results show that for large system sizes and long computations it is imperative to actively correct errors by means of quantum error correction. We implemented the 5-, 7-, and 9-qubit quantum error correction codes. Our simulations confirm that using error-prone correction circuits with non-fault-tolerant quantum error correction will always fail, because more errors are introduced than being corrected. Fault-tolerant methods can overcome this problem, provided that the single qubit error rate is below a certain threshold. We incorporated fault-tolerant quantum error correction techniques into JUMPIQCS using Steane's 7-qubit code and determined this threshold numerically. Using the depolarizing channel as the source of decoherence, we find a threshold error rate of (5.2{+-}0.2) x 10{sup -6}. For Gaussian distributed operational over-rotations the threshold lies at a standard deviation of 0.0431{+-}0.0002. We can conclude that quantum error correction is especially well suited for the correction of operational imprecisions and systematic over-rotations. For realistic simulations of specific quantum computation devices we need to extend the generic model to dynamic simulations, i.e. time-dependent Hamiltonian simulations of realistic hardware models. We focus on today's most advanced

Computation of Molecular Spectra on a Quantum Processor with an Error-Resilient Algorithm

Science.gov (United States)

Colless, J. I.; Ramasesh, V. V.; Dahlen, D.; Blok, M. S.; Kimchi-Schwartz, M. E.; McClean, J. R.; Carter, J.; de Jong, W. A.; Siddiqi, I.

2018-02-01

Harnessing the full power of nascent quantum processors requires the efficient management of a limited number of quantum bits with finite coherent lifetimes. Hybrid algorithms, such as the variational quantum eigensolver (VQE), leverage classical resources to reduce the required number of quantum gates. Experimental demonstrations of VQE have resulted in calculation of Hamiltonian ground states, and a new theoretical approach based on a quantum subspace expansion (QSE) has outlined a procedure for determining excited states that are central to dynamical processes. We use a superconducting-qubit-based processor to apply the QSE approach to the H2 molecule, extracting both ground and excited states without the need for auxiliary qubits or additional minimization. Further, we show that this extended protocol can mitigate the effects of incoherent errors, potentially enabling larger-scale quantum simulations without the need for complex error-correction techniques.

Role of memory errors in quantum repeaters

International Nuclear Information System (INIS)

Hartmann, L.; Kraus, B.; Briegel, H.-J.; Duer, W.

2007-01-01

We investigate the influence of memory errors in the quantum repeater scheme for long-range quantum communication. We show that the communication distance is limited in standard operation mode due to memory errors resulting from unavoidable waiting times for classical signals. We show how to overcome these limitations by (i) improving local memory and (ii) introducing two operational modes of the quantum repeater. In both operational modes, the repeater is run blindly, i.e., without waiting for classical signals to arrive. In the first scheme, entanglement purification protocols based on one-way classical communication are used allowing to communicate over arbitrary distances. However, the error thresholds for noise in local control operations are very stringent. The second scheme makes use of entanglement purification protocols with two-way classical communication and inherits the favorable error thresholds of the repeater run in standard mode. One can increase the possible communication distance by an order of magnitude with reasonable overhead in physical resources. We outline the architecture of a quantum repeater that can possibly ensure intercontinental quantum communication

Error suppression and error correction in adiabatic quantum computation: non-equilibrium dynamics

International Nuclear Information System (INIS)

Sarovar, Mohan; Young, Kevin C

2013-01-01

While adiabatic quantum computing (AQC) has some robustness to noise and decoherence, it is widely believed that encoding, error suppression and error correction will be required to scale AQC to large problem sizes. Previous works have established at least two different techniques for error suppression in AQC. In this paper we derive a model for describing the dynamics of encoded AQC and show that previous constructions for error suppression can be unified with this dynamical model. In addition, the model clarifies the mechanisms of error suppression and allows the identification of its weaknesses. In the second half of the paper, we utilize our description of non-equilibrium dynamics in encoded AQC to construct methods for error correction in AQC by cooling local degrees of freedom (qubits). While this is shown to be possible in principle, we also identify the key challenge to this approach: the requirement of high-weight Hamiltonians. Finally, we use our dynamical model to perform a simplified thermal stability analysis of concatenated-stabilizer-code encoded many-body systems for AQC or quantum memories. This work is a companion paper to ‘Error suppression and error correction in adiabatic quantum computation: techniques and challenges (2013 Phys. Rev. X 3 041013)’, which provides a quantum information perspective on the techniques and limitations of error suppression and correction in AQC. In this paper we couch the same results within a dynamical framework, which allows for a detailed analysis of the non-equilibrium dynamics of error suppression and correction in encoded AQC. (paper)

Computation of Molecular Spectra on a Quantum Processor with an Error-Resilient Algorithm

Directory of Open Access Journals (Sweden)

J. I. Colless

2018-02-01

Full Text Available Harnessing the full power of nascent quantum processors requires the efficient management of a limited number of quantum bits with finite coherent lifetimes. Hybrid algorithms, such as the variational quantum eigensolver (VQE, leverage classical resources to reduce the required number of quantum gates. Experimental demonstrations of VQE have resulted in calculation of Hamiltonian ground states, and a new theoretical approach based on a quantum subspace expansion (QSE has outlined a procedure for determining excited states that are central to dynamical processes. We use a superconducting-qubit-based processor to apply the QSE approach to the H_{2} molecule, extracting both ground and excited states without the need for auxiliary qubits or additional minimization. Further, we show that this extended protocol can mitigate the effects of incoherent errors, potentially enabling larger-scale quantum simulations without the need for complex error-correction techniques.

Entanglement and Quantum Error Correction with Superconducting Qubits

Science.gov (United States)

Reed, Matthew

2015-03-01

Quantum information science seeks to take advantage of the properties of quantum mechanics to manipulate information in ways that are not otherwise possible. Quantum computation, for example, promises to solve certain problems in days that would take a conventional supercomputer the age of the universe to decipher. This power does not come without a cost however, as quantum bits are inherently more susceptible to errors than their classical counterparts. Fortunately, it is possible to redundantly encode information in several entangled qubits, making it robust to decoherence and control imprecision with quantum error correction. I studied one possible physical implementation for quantum computing, employing the ground and first excited quantum states of a superconducting electrical circuit as a quantum bit. These ``transmon'' qubits are dispersively coupled to a superconducting resonator used for readout, control, and qubit-qubit coupling in the cavity quantum electrodynamics (cQED) architecture. In this talk I will give an general introduction to quantum computation and the superconducting technology that seeks to achieve it before explaining some of the specific results reported in my thesis. One major component is that of the first realization of three-qubit quantum error correction in a solid state device, where we encode one logical quantum bit in three entangled physical qubits and detect and correct phase- or bit-flip errors using a three-qubit Toffoli gate. My thesis is available at arXiv:1311.6759.

Achieving the Heisenberg limit in quantum metrology using quantum error correction.

Science.gov (United States)

Zhou, Sisi; Zhang, Mengzhen; Preskill, John; Jiang, Liang

2018-01-08

Quantum metrology has many important applications in science and technology, ranging from frequency spectroscopy to gravitational wave detection. Quantum mechanics imposes a fundamental limit on measurement precision, called the Heisenberg limit, which can be achieved for noiseless quantum systems, but is not achievable in general for systems subject to noise. Here we study how measurement precision can be enhanced through quantum error correction, a general method for protecting a quantum system from the damaging effects of noise. We find a necessary and sufficient condition for achieving the Heisenberg limit using quantum probes subject to Markovian noise, assuming that noiseless ancilla systems are available, and that fast, accurate quantum processing can be performed. When the sufficient condition is satisfied, a quantum error-correcting code can be constructed that suppresses the noise without obscuring the signal; the optimal code, achieving the best possible precision, can be found by solving a semidefinite program.

Practical, Reliable Error Bars in Quantum Tomography

OpenAIRE

Faist, Philippe; Renner, Renato

2015-01-01

Precise characterization of quantum devices is usually achieved with quantum tomography. However, most methods which are currently widely used in experiments, such as maximum likelihood estimation, lack a well-justified error analysis. Promising recent methods based on confidence regions are difficult to apply in practice or yield error bars which are unnecessarily large. Here, we propose a practical yet robust method for obtaining error bars. We do so by introducing a novel representation of...

Quantum secret sharing based on quantum error-correcting codes

International Nuclear Information System (INIS)

Zhang Zu-Rong; Liu Wei-Tao; Li Cheng-Zu

2011-01-01

Quantum secret sharing(QSS) is a procedure of sharing classical information or quantum information by using quantum states. This paper presents how to use a [2k − 1, 1, k] quantum error-correcting code (QECC) to implement a quantum (k, 2k − 1) threshold scheme. It also takes advantage of classical enhancement of the [2k − 1, 1, k] QECC to establish a QSS scheme which can share classical information and quantum information simultaneously. Because information is encoded into QECC, these schemes can prevent intercept-resend attacks and be implemented on some noisy channels. (general)

NP-hardness of decoding quantum error-correction codes

Science.gov (United States)

Hsieh, Min-Hsiu; Le Gall, François

2011-05-01

Although the theory of quantum error correction is intimately related to classical coding theory and, in particular, one can construct quantum error-correction codes (QECCs) from classical codes with the dual-containing property, this does not necessarily imply that the computational complexity of decoding QECCs is the same as their classical counterparts. Instead, decoding QECCs can be very much different from decoding classical codes due to the degeneracy property. Intuitively, one expects degeneracy would simplify the decoding since two different errors might not and need not be distinguished in order to correct them. However, we show that general quantum decoding problem is NP-hard regardless of the quantum codes being degenerate or nondegenerate. This finding implies that no considerably fast decoding algorithm exists for the general quantum decoding problems and suggests the existence of a quantum cryptosystem based on the hardness of decoding QECCs.

NP-hardness of decoding quantum error-correction codes

International Nuclear Information System (INIS)

Hsieh, Min-Hsiu; Le Gall, Francois

2011-01-01

Although the theory of quantum error correction is intimately related to classical coding theory and, in particular, one can construct quantum error-correction codes (QECCs) from classical codes with the dual-containing property, this does not necessarily imply that the computational complexity of decoding QECCs is the same as their classical counterparts. Instead, decoding QECCs can be very much different from decoding classical codes due to the degeneracy property. Intuitively, one expects degeneracy would simplify the decoding since two different errors might not and need not be distinguished in order to correct them. However, we show that general quantum decoding problem is NP-hard regardless of the quantum codes being degenerate or nondegenerate. This finding implies that no considerably fast decoding algorithm exists for the general quantum decoding problems and suggests the existence of a quantum cryptosystem based on the hardness of decoding QECCs.

Modeling coherent errors in quantum error correction

Science.gov (United States)

Greenbaum, Daniel; Dutton, Zachary

2018-01-01

Analysis of quantum error correcting codes is typically done using a stochastic, Pauli channel error model for describing the noise on physical qubits. However, it was recently found that coherent errors (systematic rotations) on physical data qubits result in both physical and logical error rates that differ significantly from those predicted by a Pauli model. Here we examine the accuracy of the Pauli approximation for noise containing coherent errors (characterized by a rotation angle ɛ) under the repetition code. We derive an analytic expression for the logical error channel as a function of arbitrary code distance d and concatenation level n, in the small error limit. We find that coherent physical errors result in logical errors that are partially coherent and therefore non-Pauli. However, the coherent part of the logical error is negligible at fewer than {ε }-({dn-1)} error correction cycles when the decoder is optimized for independent Pauli errors, thus providing a regime of validity for the Pauli approximation. Above this number of correction cycles, the persistent coherent logical error will cause logical failure more quickly than the Pauli model would predict, and this may need to be combated with coherent suppression methods at the physical level or larger codes.

Error Mitigation for Short-Depth Quantum Circuits

Science.gov (United States)

Temme, Kristan; Bravyi, Sergey; Gambetta, Jay M.

2017-11-01

Two schemes are presented that mitigate the effect of errors and decoherence in short-depth quantum circuits. The size of the circuits for which these techniques can be applied is limited by the rate at which the errors in the computation are introduced. Near-term applications of early quantum devices, such as quantum simulations, rely on accurate estimates of expectation values to become relevant. Decoherence and gate errors lead to wrong estimates of the expectation values of observables used to evaluate the noisy circuit. The two schemes we discuss are deliberately simple and do not require additional qubit resources, so to be as practically relevant in current experiments as possible. The first method, extrapolation to the zero noise limit, subsequently cancels powers of the noise perturbations by an application of Richardson's deferred approach to the limit. The second method cancels errors by resampling randomized circuits according to a quasiprobability distribution.

Quantum error correction with spins in diamond

NARCIS (Netherlands)

Cramer, J.

2016-01-01

Digital information based on the laws of quantum mechanics promisses powerful new ways of computation and communication. However, quantum information is very fragile; inevitable errors continuously build up and eventually all information is lost. Therefore, realistic large-scale quantum information

Tensor Networks and Quantum Error Correction

Science.gov (United States)

Ferris, Andrew J.; Poulin, David

2014-07-01

We establish several relations between quantum error correction (QEC) and tensor network (TN) methods of quantum many-body physics. We exhibit correspondences between well-known families of QEC codes and TNs, and demonstrate a formal equivalence between decoding a QEC code and contracting a TN. We build on this equivalence to propose a new family of quantum codes and decoding algorithms that generalize and improve upon quantum polar codes and successive cancellation decoding in a natural way.

Quantum error-correcting code for ternary logic

Science.gov (United States)

Majumdar, Ritajit; Basu, Saikat; Ghosh, Shibashis; Sur-Kolay, Susmita

2018-05-01

Ternary quantum systems are being studied because they provide more computational state space per unit of information, known as qutrit. A qutrit has three basis states, thus a qubit may be considered as a special case of a qutrit where the coefficient of one of the basis states is zero. Hence both (2 ×2 ) -dimensional and (3 ×3 ) -dimensional Pauli errors can occur on qutrits. In this paper, we (i) explore the possible (2 ×2 ) -dimensional as well as (3 ×3 ) -dimensional Pauli errors in qutrits and show that any pairwise bit swap error can be expressed as a linear combination of shift errors and phase errors, (ii) propose a special type of error called a quantum superposition error and show its equivalence to arbitrary rotation, (iii) formulate a nine-qutrit code which can correct a single error in a qutrit, and (iv) provide its stabilizer and circuit realization.

Topics in quantum cryptography, quantum error correction, and channel simulation

Science.gov (United States)

Luo, Zhicheng

In this thesis, we mainly investigate four different topics: efficiently implementable codes for quantum key expansion [51], quantum error-correcting codes based on privacy amplification [48], private classical capacity of quantum channels [44], and classical channel simulation with quantum side information [49, 50]. For the first topic, we propose an efficiently implementable quantum key expansion protocol, capable of increasing the size of a pre-shared secret key by a constant factor. Previously, the Shor-Preskill proof [64] of the security of the Bennett-Brassard 1984 (BB84) [6] quantum key distribution protocol relied on the theoretical existence of good classical error-correcting codes with the "dual-containing" property. But the explicit and efficiently decodable construction of such codes is unknown. We show that we can lift the dual-containing constraint by employing the non-dual-containing codes with excellent performance and efficient decoding algorithms. For the second topic, we propose a construction of Calderbank-Shor-Steane (CSS) [19, 68] quantum error-correcting codes, which are originally based on pairs of mutually dual-containing classical codes, by combining a classical code with a two-universal hash function. We show, using the results of Renner and Koenig [57], that the communication rates of such codes approach the hashing bound on tensor powers of Pauli channels in the limit of large block-length. For the third topic, we prove a regularized formula for the secret key assisted capacity region of a quantum channel for transmitting private classical information. This result parallels the work of Devetak on entanglement assisted quantum communication capacity. This formula provides a new family protocol, the private father protocol, under the resource inequality framework that includes the private classical communication without the assisted secret keys as a child protocol. For the fourth topic, we study and solve the problem of classical channel

Autonomous Quantum Error Correction with Application to Quantum Metrology

Science.gov (United States)

Reiter, Florentin; Sorensen, Anders S.; Zoller, Peter; Muschik, Christine A.

2017-04-01

We present a quantum error correction scheme that stabilizes a qubit by coupling it to an engineered environment which protects it against spin- or phase flips. Our scheme uses always-on couplings that run continuously in time and operates in a fully autonomous fashion without the need to perform measurements or feedback operations on the system. The correction of errors takes place entirely at the microscopic level through a build-in feedback mechanism. Our dissipative error correction scheme can be implemented in a system of trapped ions and can be used for improving high precision sensing. We show that the enhanced coherence time that results from the coupling to the engineered environment translates into a significantly enhanced precision for measuring weak fields. In a broader context, this work constitutes a stepping stone towards the paradigm of self-correcting quantum information processing.

A precise error bound for quantum phase estimation.

Directory of Open Access Journals (Sweden)

James M Chappell

Full Text Available Quantum phase estimation is one of the key algorithms in the field of quantum computing, but up until now, only approximate expressions have been derived for the probability of error. We revisit these derivations, and find that by ensuring symmetry in the error definitions, an exact formula can be found. This new approach may also have value in solving other related problems in quantum computing, where an expected error is calculated. Expressions for two special cases of the formula are also developed, in the limit as the number of qubits in the quantum computer approaches infinity and in the limit as the extra added qubits to improve reliability goes to infinity. It is found that this formula is useful in validating computer simulations of the phase estimation procedure and in avoiding the overestimation of the number of qubits required in order to achieve a given reliability. This formula thus brings improved precision in the design of quantum computers.

Unitary Application of the Quantum Error Correction Codes

International Nuclear Information System (INIS)

You Bo; Xu Ke; Wu Xiaohua

2012-01-01

For applying the perfect code to transmit quantum information over a noise channel, the standard protocol contains four steps: the encoding, the noise channel, the error-correction operation, and the decoding. In present work, we show that this protocol can be simplified. The error-correction operation is not necessary if the decoding is realized by the so-called complete unitary transformation. We also offer a quantum circuit, which can correct the arbitrary single-qubit errors.

Formulation of uncertainty relation of error and disturbance in quantum measurement by using quantum estimation theory

International Nuclear Information System (INIS)

Yu Watanabe; Masahito Ueda

2012-01-01

Full text: When we try to obtain information about a quantum system, we need to perform measurement on the system. The measurement process causes unavoidable state change. Heisenberg discussed a thought experiment of the position measurement of a particle by using a gamma-ray microscope, and found a trade-off relation between the error of the measured position and the disturbance in the momentum caused by the measurement process. The trade-off relation epitomizes the complementarity in quantum measurements: we cannot perform a measurement of an observable without causing disturbance in its canonically conjugate observable. However, at the time Heisenberg found the complementarity, quantum measurement theory was not established yet, and Kennard and Robertson's inequality erroneously interpreted as a mathematical formulation of the complementarity. Kennard and Robertson's inequality actually implies the indeterminacy of the quantum state: non-commuting observables cannot have definite values simultaneously. However, Kennard and Robertson's inequality reflects the inherent nature of a quantum state alone, and does not concern any trade-off relation between the error and disturbance in the measurement process. In this talk, we report a resolution to the complementarity in quantum measurements. First, we find that it is necessary to involve the estimation process from the outcome of the measurement for quantifying the error and disturbance in the quantum measurement. We clarify the implicitly involved estimation process in Heisenberg's gamma-ray microscope and other measurement schemes, and formulate the error and disturbance for an arbitrary quantum measurement by using quantum estimation theory. The error and disturbance are defined in terms of the Fisher information, which gives the upper bound of the accuracy of the estimation. Second, we obtain uncertainty relations between the measurement errors of two observables [1], and between the error and disturbance in the

Free-Space Quantum Communication with a Portable Quantum Memory

Science.gov (United States)

Namazi, Mehdi; Vallone, Giuseppe; Jordaan, Bertus; Goham, Connor; Shahrokhshahi, Reihaneh; Villoresi, Paolo; Figueroa, Eden

2017-12-01

The realization of an elementary quantum network that is intrinsically secure and operates over long distances requires the interconnection of several quantum modules performing different tasks. In this work, we report the realization of a communication network functioning in a quantum regime, consisting of four different quantum modules: (i) a random polarization qubit generator, (ii) a free-space quantum-communication channel, (iii) an ultralow-noise portable quantum memory, and (iv) a qubit decoder, in a functional elementary quantum network possessing all capabilities needed for quantum-information distribution protocols. We create weak coherent pulses at the single-photon level encoding polarization states |H ⟩ , |V ⟩, |D ⟩, and |A ⟩ in a randomized sequence. The random qubits are sent over a free-space link and coupled into a dual-rail room-temperature quantum memory and after storage and retrieval are analyzed in a four-detector polarization analysis akin to the requirements of the BB84 protocol. We also show ultralow noise and fully portable operation, paving the way towards memory-assisted all-environment free-space quantum cryptographic networks.

Ultrafast all-optical switching and error-free 10 Gbit/s wavelength conversion in hybrid InP-silicon on insulator nanocavities using surface quantum wells

Energy Technology Data Exchange (ETDEWEB)

Bazin, Alexandre; Monnier, Paul; Beaudoin, Grégoire; Sagnes, Isabelle; Raj, Rama [Laboratoire de Photonique et de Nanostructures (CNRS UPR20), Route de Nozay, Marcoussis 91460 (France); Lenglé, Kevin; Gay, Mathilde; Bramerie, Laurent [Université Européenne de Bretagne (UEB), 5 Boulevard Laënnec, 35000 Rennes (France); CNRS-Foton Laboratory (UMR 6082), Enssat, BP 80518, 22305 Lannion Cedex (France); Braive, Rémy; Raineri, Fabrice, E-mail: fabrice.raineri@lpn.cnrs.fr [Laboratoire de Photonique et de Nanostructures (CNRS UPR20), Route de Nozay, Marcoussis 91460 (France); Université Paris Diderot, Sorbonne Paris Cité, 75207 Paris Cedex 13 (France)

2014-01-06

Ultrafast switching with low energies is demonstrated using InP photonic crystal nanocavities embedding InGaAs surface quantum wells heterogeneously integrated to a silicon on insulator waveguide circuitry. Thanks to the engineered enhancement of surface non radiative recombination of carriers, switching time is obtained to be as fast as 10 ps. These hybrid nanostructures are shown to be capable of achieving systems level performance by demonstrating error free wavelength conversion at 10 Gbit/s with 6 mW switching powers.

Entanglement renormalization, quantum error correction, and bulk causality

Energy Technology Data Exchange (ETDEWEB)

Kim, Isaac H. [IBM T.J. Watson Research Center,1101 Kitchawan Rd., Yorktown Heights, NY (United States); Kastoryano, Michael J. [NBIA, Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 Copenhagen (Denmark)

2017-04-07

Entanglement renormalization can be viewed as an encoding circuit for a family of approximate quantum error correcting codes. The logical information becomes progressively more well-protected against erasure errors at larger length scales. In particular, an approximate variant of holographic quantum error correcting code emerges at low energy for critical systems. This implies that two operators that are largely separated in scales behave as if they are spatially separated operators, in the sense that they obey a Lieb-Robinson type locality bound under a time evolution generated by a local Hamiltonian.

Non-binary unitary error bases and quantum codes

Energy Technology Data Exchange (ETDEWEB)

Knill, E.

1996-06-01

Error operator bases for systems of any dimension are defined and natural generalizations of the bit-flip/ sign-change error basis for qubits are given. These bases allow generalizing the construction of quantum codes based on eigenspaces of Abelian groups. As a consequence, quantum codes can be constructed form linear codes over {ital Z}{sub {ital n}} for any {ital n}. The generalization of the punctured code construction leads to many codes which permit transversal (i.e. fault tolerant) implementations of certain operations compatible with the error basis.

Black Holes, Holography, and Quantum Error Correction

CERN Multimedia

CERN. Geneva

2017-01-01

How can it be that a local quantum field theory in some number of spacetime dimensions can "fake" a local gravitational theory in a higher number of dimensions?  How can the Ryu-Takayanagi Formula say that an entropy is equal to the expectation value of a local operator?  Why do such things happen only in gravitational theories?  In this talk I will explain how a new interpretation of the AdS/CFT correspondence as a quantum error correcting code provides satisfying answers to these questions, and more generally gives a natural way of generating simple models of the correspondence.  No familiarity with AdS/CFT or quantum error correction is assumed, but the former would still be helpful.  

Fast, efficient error reconciliation for quantum cryptography

International Nuclear Information System (INIS)

Buttler, W.T.; Lamoreaux, S.K.; Torgerson, J.R.; Nickel, G.H.; Donahue, C.H.; Peterson, C.G.

2003-01-01

We describe an error-reconciliation protocol, which we call Winnow, based on the exchange of parity and Hamming's 'syndrome' for N-bit subunits of a large dataset. The Winnow protocol was developed in the context of quantum-key distribution and offers significant advantages and net higher efficiency compared to other widely used protocols within the quantum cryptography community. A detailed mathematical analysis of the Winnow protocol is presented in the context of practical implementations of quantum-key distribution; in particular, the information overhead required for secure implementation is one of the most important criteria in the evaluation of a particular error-reconciliation protocol. The increase in efficiency for the Winnow protocol is largely due to the reduction in authenticated public communication required for its implementation

Tackling systematic errors in quantum logic gates with composite rotations

International Nuclear Information System (INIS)

Cummins, Holly K.; Llewellyn, Gavin; Jones, Jonathan A.

2003-01-01

We describe the use of composite rotations to combat systematic errors in single-qubit quantum logic gates and discuss three families of composite rotations which can be used to correct off-resonance and pulse length errors. Although developed and described within the context of nuclear magnetic resonance quantum computing, these sequences should be applicable to any implementation of quantum computation

Efficiently characterizing the total error in quantum circuits

Science.gov (United States)

Carignan-Dugas, Arnaud; Wallman, Joel J.; Emerson, Joseph

A promising technological advancement meant to enlarge our computational means is the quantum computer. Such a device would harvest the quantum complexity of the physical world in order to unfold concrete mathematical problems more efficiently. However, the errors emerging from the implementation of quantum operations are likewise quantum, and hence share a similar level of intricacy. Fortunately, randomized benchmarking protocols provide an efficient way to characterize the operational noise within quantum devices. The resulting figures of merit, like the fidelity and the unitarity, are typically attached to a set of circuit components. While important, this doesn't fulfill the main goal: determining if the error rate of the total circuit is small enough in order to trust its outcome. In this work, we fill the gap by providing an optimal bound on the total fidelity of a circuit in terms of component-wise figures of merit. Our bound smoothly interpolates between the classical regime, in which the error rate grows linearly in the circuit's length, and the quantum regime, which can naturally allow quadratic growth. Conversely, our analysis substantially improves the bounds on single circuit element fidelities obtained through techniques such as interleaved randomized benchmarking. This research was supported by the U.S. Army Research Office through Grant W911NF- 14-1-0103, CIFAR, the Government of Ontario, and the Government of Canada through NSERC and Industry Canada.

Efficient decoding of random errors for quantum expander codes

OpenAIRE

Fawzi , Omar; Grospellier , Antoine; Leverrier , Anthony

2017-01-01

We show that quantum expander codes, a constant-rate family of quantum LDPC codes, with the quasi-linear time decoding algorithm of Leverrier, Tillich and Z\\'emor can correct a constant fraction of random errors with very high probability. This is the first construction of a constant-rate quantum LDPC code with an efficient decoding algorithm that can correct a linear number of random errors with a negligible failure probability. Finding codes with these properties is also motivated by Gottes...

Efficiency of free-energy calculations of spin lattices by spectral quantum algorithms

International Nuclear Information System (INIS)

Master, Cyrus P.; Yamaguchi, Fumiko; Yamamoto, Yoshihisa

2003-01-01

Ensemble quantum algorithms are well suited to calculate estimates of the energy spectra for spin-lattice systems. Based on the phase estimation algorithm, these algorithms efficiently estimate discrete Fourier coefficients of the density of states. Their efficiency in calculating the free energy per spin of general spin lattices to bounded error is examined. We find that the number of Fourier components required to bound the error in the free energy due to the broadening of the density of states scales polynomially with the number of spins in the lattice. However, the precision with which the Fourier components must be calculated is found to be an exponential function of the system size

Decodoku: Quantum error rorrection as a simple puzzle game

Science.gov (United States)

Wootton, James

To build quantum computers, we need to detect and manage any noise that occurs. This will be done using quantum error correction. At the hardware level, QEC is a multipartite system that stores information non-locally. Certain measurements are made which do not disturb the stored information, but which do allow signatures of errors to be detected. Then there is a software problem. How to take these measurement outcomes and determine: a) The errors that caused them, and (b) how to remove their effects. For qubit error correction, the algorithms required to do this are well known. For qudits, however, current methods are far from optimal. We consider the error correction problem of qubit surface codes. At the most basic level, this is a problem that can be expressed in terms of a grid of numbers. Using this fact, we take the inherent problem at the heart of quantum error correction, remove it from its quantum context, and presented in terms of simple grid based puzzle games. We have developed three versions of these puzzle games, focussing on different aspects of the required algorithms. These have been presented and iOS and Android apps, allowing the public to try their hand at developing good algorithms to solve the puzzles. For more information, see www.decodoku.com. Funding from the NCCR QSIT.

Quantum teleportation and entanglement distribution over 100-kilometre free-space channels.

Science.gov (United States)

Yin, Juan; Ren, Ji-Gang; Lu, He; Cao, Yuan; Yong, Hai-Lin; Wu, Yu-Ping; Liu, Chang; Liao, Sheng-Kai; Zhou, Fei; Jiang, Yan; Cai, Xin-Dong; Xu, Ping; Pan, Ge-Sheng; Jia, Jian-Jun; Huang, Yong-Mei; Yin, Hao; Wang, Jian-Yu; Chen, Yu-Ao; Peng, Cheng-Zhi; Pan, Jian-Wei

2012-08-09

Transferring an unknown quantum state over arbitrary distances is essential for large-scale quantum communication and distributed quantum networks. It can be achieved with the help of long-distance quantum teleportation and entanglement distribution. The latter is also important for fundamental tests of the laws of quantum mechanics. Although quantum teleportation and entanglement distribution over moderate distances have been realized using optical fibre links, the huge photon loss and decoherence in fibres necessitate the use of quantum repeaters for larger distances. However, the practical realization of quantum repeaters remains experimentally challenging. Free-space channels, first used for quantum key distribution, offer a more promising approach because photon loss and decoherence are almost negligible in the atmosphere. Furthermore, by using satellites, ultra-long-distance quantum communication and tests of quantum foundations could be achieved on a global scale. Previous experiments have achieved free-space distribution of entangled photon pairs over distances of 600 metres (ref. 14) and 13 kilometres (ref. 15), and transfer of triggered single photons over a 144-kilometre one-link free-space channel. Most recently, following a modified scheme, free-space quantum teleportation over 16 kilometres was demonstrated with a single pair of entangled photons. Here we report quantum teleportation of independent qubits over a 97-kilometre one-link free-space channel with multi-photon entanglement. An average fidelity of 80.4 ± 0.9 per cent is achieved for six distinct states. Furthermore, we demonstrate entanglement distribution over a two-link channel, in which the entangled photons are separated by 101.8 kilometres. Violation of the Clauser-Horne-Shimony-Holt inequality is observed without the locality loophole. Besides being of fundamental interest, our results represent an important step towards a global quantum network. Moreover, the high

On superactivation of one-shot quantum zero-error capacity and the related property of quantum measurements

DEFF Research Database (Denmark)

Shirokov, M. E.; Shulman, Tatiana

2014-01-01

We give a detailed description of a low-dimensional quantum channel (input dimension 4, Choi rank 3) demonstrating the symmetric form of superactivation of one-shot quantum zero-error capacity. This property means appearance of a noiseless (perfectly reversible) subchannel in the tensor square...... of a channel having no noiseless subchannels. Then we describe a quantum channel with an arbitrary given level of symmetric superactivation (including the infinite value). We also show that superactivation of one-shot quantum zero-error capacity of a channel can be reformulated in terms of quantum measurement...

Analysis of quantum error-correcting codes: Symplectic lattice codes and toric codes

Science.gov (United States)

Harrington, James William

Quantum information theory is concerned with identifying how quantum mechanical resources (such as entangled quantum states) can be utilized for a number of information processing tasks, including data storage, computation, communication, and cryptography. Efficient quantum algorithms and protocols have been developed for performing some tasks (e.g. , factoring large numbers, securely communicating over a public channel, and simulating quantum mechanical systems) that appear to be very difficult with just classical resources. In addition to identifying the separation between classical and quantum computational power, much of the theoretical focus in this field over the last decade has been concerned with finding novel ways of encoding quantum information that are robust against errors, which is an important step toward building practical quantum information processing devices. In this thesis I present some results on the quantum error-correcting properties of oscillator codes (also described as symplectic lattice codes) and toric codes. Any harmonic oscillator system (such as a mode of light) can be encoded with quantum information via symplectic lattice codes that are robust against shifts in the system's continuous quantum variables. I show the existence of lattice codes whose achievable rates match the one-shot coherent information over the Gaussian quantum channel. Also, I construct a family of symplectic self-dual lattices and search for optimal encodings of quantum information distributed between several oscillators. Toric codes provide encodings of quantum information into two-dimensional spin lattices that are robust against local clusters of errors and which require only local quantum operations for error correction. Numerical simulations of this system under various error models provide a calculation of the accuracy threshold for quantum memory using toric codes, which can be related to phase transitions in certain condensed matter models. I also present

Activation of zero-error classical capacity in low-dimensional quantum systems

Science.gov (United States)

Park, Jeonghoon; Heo, Jun

2018-06-01

Channel capacities of quantum channels can be nonadditive even if one of two quantum channels has no channel capacity. We call this phenomenon activation of the channel capacity. In this paper, we show that when we use a quantum channel on a qubit system, only a noiseless qubit channel can generate the activation of the zero-error classical capacity. In particular, we show that the zero-error classical capacity of two quantum channels on qubit systems cannot be activated. Furthermore, we present a class of examples showing the activation of the zero-error classical capacity in low-dimensional systems.

Experimental demonstration of subcarrier multiplexed quantum key distribution system.

Science.gov (United States)

Mora, José; Ruiz-Alba, Antonio; Amaya, Waldimar; Martínez, Alfonso; García-Muñoz, Víctor; Calvo, David; Capmany, José

2012-06-01

We provide, to our knowledge, the first experimental demonstration of the feasibility of sending several parallel keys by exploiting the technique of subcarrier multiplexing (SCM) widely employed in microwave photonics. This approach brings several advantages such as high spectral efficiency compatible with the actual secure key rates, the sharing of the optical fainted pulse by all the quantum multiplexed channels reducing the system complexity, and the possibility of upgrading with wavelength division multiplexing in a two-tier scheme, to increase the number of parallel keys. Two independent quantum SCM channels featuring a sifted key rate of 10 Kb/s/channel over a link with quantum bit error rate <2% is reported.

Error Correction for Non-Abelian Topological Quantum Computation

Directory of Open Access Journals (Sweden)

James R. Wootton

2014-03-01

Full Text Available The possibility of quantum computation using non-Abelian anyons has been considered for over a decade. However, the question of how to obtain and process information about what errors have occurred in order to negate their effects has not yet been considered. This is in stark contrast with quantum computation proposals for Abelian anyons, for which decoding algorithms have been tailor-made for many topological error-correcting codes and error models. Here, we address this issue by considering the properties of non-Abelian error correction, in general. We also choose a specific anyon model and error model to probe the problem in more detail. The anyon model is the charge submodel of D(S_{3}. This shares many properties with important models such as the Fibonacci anyons, making our method more generally applicable. The error model is a straightforward generalization of those used in the case of Abelian anyons for initial benchmarking of error correction methods. It is found that error correction is possible under a threshold value of 7% for the total probability of an error on each physical spin. This is remarkably comparable with the thresholds for Abelian models.

Error Free Software

Science.gov (United States)

1985-01-01

A mathematical theory for development of "higher order" software to catch computer mistakes resulted from a Johnson Space Center contract for Apollo spacecraft navigation. Two women who were involved in the project formed Higher Order Software, Inc. to develop and market the system of error analysis and correction. They designed software which is logically error-free, which, in one instance, was found to increase productivity by 600%. USE.IT defines its objectives using AXES -- a user can write in English and the system converts to computer languages. It is employed by several large corporations.

Experimental all-optical one-way quantum computing

International Nuclear Information System (INIS)

Prevedel, R.

2009-01-01

strategy space, as they can also choose between superposition of classical input states while their choices get entangled. Evaluating the payoff function of this game for different strategy sets, we were able to experimentally show that the so-called 'dilemma', that occurs in the classical version of this game, can be resolved in the quantum domain. unfortunately, one of the main obstacles on the road towards the realization of large-scale quantum computers is decoherence, the ubiquitous loss of information encoded in a quantum system due to its uncontrollable interaction with an environment. One possible approach to overcome this challenge is to perform the computation in a so-called decoherence-free subspace (DFS). Building up on previous work on concepts of DFS we have been able to theoretically adapt these concepts to the model of one-way quantum computing. This allowed us to demonstrate for the first time the decoherence-free execution of a one-way quantum computing protocol while the photons were exposed to severe phase-damping noise. Remarkable protection of information was accomplished, delivering nearly ideal outcomes. Although the experiments presented in this thesis are proof-of-principle they are of great significance in the field of QIP and will hopefully pave the way for ever more exciting inventions and experimental demonstrations in the future. (author) [de

Experimental magic state distillation for fault-tolerant quantum computing.

Science.gov (United States)

Souza, Alexandre M; Zhang, Jingfu; Ryan, Colm A; Laflamme, Raymond

2011-01-25

Any physical quantum device for quantum information processing (QIP) is subject to errors in implementation. In order to be reliable and efficient, quantum computers will need error-correcting or error-avoiding methods. Fault-tolerance achieved through quantum error correction will be an integral part of quantum computers. Of the many methods that have been discovered to implement it, a highly successful approach has been to use transversal gates and specific initial states. A critical element for its implementation is the availability of high-fidelity initial states, such as |0〉 and the 'magic state'. Here, we report an experiment, performed in a nuclear magnetic resonance (NMR) quantum processor, showing sufficient quantum control to improve the fidelity of imperfect initial magic states by distilling five of them into one with higher fidelity.

Error of quantum-logic simulation via vector-soliton collisions

International Nuclear Information System (INIS)

Janutka, Andrzej

2007-01-01

In a concept of simulating the quantum logic with vector solitons by the author (Janutka 2006 J. Phys. A: Math. Gen. 39 12505), the soliton polarization is thought of as a state vector of a system of cebits (classical counterparts of qubits) switched via collisions with other solitons. The advantage of this method of information processing compared to schemes using linear optics is the possibility of the determination of the information-register state in a single measurement. Minimization of the information-processing error for different optical realizations of the logical systems is studied in the framework of a quantum analysis of soliton fluctuations. The problem is considered with relevance to general difficulties of the quantum error-correction schemes for the classical analogies of the quantum-information processing

Continuous time quantum random walks in free space

Science.gov (United States)

Eichelkraut, Toni; Vetter, Christian; Perez-Leija, Armando; Christodoulides, Demetrios; Szameit, Alexander

2014-05-01

We show theoretically and experimentally that two-dimensional continuous time coherent random walks are possible in free space, that is, in the absence of any external potential, by properly tailoring the associated initial wave function. These effects are experimentally demonstrated using classical paraxial light. Evidently, the usage of classical beams to explore the dynamics of point-like quantum particles is possible since both phenomena are mathematically equivalent. This in turn makes our approach suitable for the realization of random walks using different quantum particles, including electrons and photons. To study the spatial evolution of a wavefunction theoretically, we consider the one-dimensional paraxial wave equation (i∂z +1/2 ∂x2) Ψ = 0 . Starting with the initially localized wavefunction Ψ (x , 0) = exp [ -x2 / 2σ2 ] J0 (αx) , one can show that the evolution of such Gaussian-apodized Bessel envelopes within a region of validity resembles the probability pattern of a quantum walker traversing a uniform lattice. In order to generate the desired input-field in our experimental setting we shape the amplitude and phase of a collimated light beam originating from a classical HeNe-Laser (633 nm) utilizing a spatial light modulator.

Erratum: Synthesis of Cd-free InP/ZnS Quantum Dots Suitable for Biomedical Applications.

Science.gov (United States)

2016-02-29

A correction was made to: Synthesis of Cd-free InP/ZnS Quantum Dots Suitable for Biomedical Applications. There was an error with an author's given name. The author's name was corrected to: Katye M. Fichter from: Kathryn M. Fichter.

Iterative optimization of quantum error correcting codes

International Nuclear Information System (INIS)

Reimpell, M.; Werner, R.F.

2005-01-01

We introduce a convergent iterative algorithm for finding the optimal coding and decoding operations for an arbitrary noisy quantum channel. This algorithm does not require any error syndrome to be corrected completely, and hence also finds codes outside the usual Knill-Laflamme definition of error correcting codes. The iteration is shown to improve the figure of merit 'channel fidelity' in every step

Group representations, error bases and quantum codes

Energy Technology Data Exchange (ETDEWEB)

Knill, E

1996-01-01

This report continues the discussion of unitary error bases and quantum codes. Nice error bases are characterized in terms of the existence of certain characters in a group. A general construction for error bases which are non-abelian over the center is given. The method for obtaining codes due to Calderbank et al. is generalized and expressed purely in representation theoretic terms. The significance of the inertia subgroup both for constructing codes and obtaining the set of transversally implementable operations is demonstrated.

Robust dynamical decoupling for quantum computing and quantum memory.

Science.gov (United States)

Souza, Alexandre M; Alvarez, Gonzalo A; Suter, Dieter

2011-06-17

Dynamical decoupling (DD) is a popular technique for protecting qubits from the environment. However, unless special care is taken, experimental errors in the control pulses used in this technique can destroy the quantum information instead of preserving it. Here, we investigate techniques for making DD sequences robust against different types of experimental errors while retaining good decoupling efficiency in a fluctuating environment. We present experimental data from solid-state nuclear spin qubits and introduce a new DD sequence that is suitable for quantum computing and quantum memory.

A Quantum Theoretical Explanation for Probability Judgment Errors

Science.gov (United States)

Busemeyer, Jerome R.; Pothos, Emmanuel M.; Franco, Riccardo; Trueblood, Jennifer S.

2011-01-01

A quantum probability model is introduced and used to explain human probability judgment errors including the conjunction and disjunction fallacies, averaging effects, unpacking effects, and order effects on inference. On the one hand, quantum theory is similar to other categorization and memory models of cognition in that it relies on vector…

[Analysis of intrusion errors in free recall].

Science.gov (United States)

Diesfeldt, H F A

2017-06-01

Extra-list intrusion errors during five trials of the eight-word list-learning task of the Amsterdam Dementia Screening Test (ADST) were investigated in 823 consecutive psychogeriatric patients (87.1% suffering from major neurocognitive disorder). Almost half of the participants (45.9%) produced one or more intrusion errors on the verbal recall test. Correct responses were lower when subjects made intrusion errors, but learning slopes did not differ between subjects who committed intrusion errors and those who did not so. Bivariate regression analyses revealed that participants who committed intrusion errors were more deficient on measures of eight-word recognition memory, delayed visual recognition and tests of executive control (the Behavioral Dyscontrol Scale and the ADST-Graphical Sequences as measures of response inhibition). Using hierarchical multiple regression, only free recall and delayed visual recognition retained an independent effect in the association with intrusion errors, such that deficient scores on tests of episodic memory were sufficient to explain the occurrence of intrusion errors. Measures of inhibitory control did not add significantly to the explanation of intrusion errors in free recall, which makes insufficient strength of memory traces rather than a primary deficit in inhibition the preferred account for intrusion errors in free recall.

Decoherence and the quantum-to-classical transition

International Nuclear Information System (INIS)

Schlosshauer, M.A.

2007-01-01

The ultimate introduction, textbook, and reference on decoherence and the quantum-to-classical transition. This detailed but accessible text describes the concepts, formalism, interpretation, and experimental observation of decoherence and explains how decoherence is responsible for the emergence, from the realm of quantum mechanics, of the classical world of our experience. Topics include: - Foundational problems at the quantum-classical border; - The role of the environment and entanglement; - Environment-induced loss of coherence and superselection; - Scattering-induced decoherence and spatial localization; - Master equations; - Decoherence models; - Experimental realization of ''Schroedinger's kittens'' and their decoherence; - Quantum computing, quantum error correction, and decoherence-free subspaces; - Implications of decoherence for interpretations of quantum mechanics and for the ''measurement problem''; - Decoherence in the brain. Written in a lucid and concise style that is accessible to all readers with a basic knowledge of quantum mechanics, this stimulating book tells the ''classical from quantum'' story in a comprehensive and coherent manner that brings together the foundational, technical, and experimental aspects of decoherence. It will be an indispensable resource for newcomers and experts alike. (orig.)

Loophole-free Einstein-Podolsky-Rosen experiment via quantum steering

International Nuclear Information System (INIS)

Wittmann, Bernhard; Ramelow, Sven; Zeilinger, Anton; Steinlechner, Fabian; Langford, Nathan K; Ursin, Rupert; Brunner, Nicolas; Wiseman, Howard M

2012-01-01

Tests of the predictions of quantum mechanics for entangled systems have provided increasing evidence against local realistic theories. However, there remains the crucial challenge of simultaneously closing all major loopholes—the locality, freedom-of-choice and detection loopholes—in a single experiment. An important sub-class of local realistic theories can be tested with the concept of ‘steering’. The term ‘steering’ was introduced by Schrödinger in 1935 for the fact that entanglement would seem to allow an experimenter to remotely steer the state of a distant system as in the Einstein-Podolsky-Rosen (EPR) argument. Einstein called this ‘spooky action at a distance’. EPR-steering has recently been rigorously formulated as a quantum information task opening it up to new experimental tests. Here, we present the first loophole-free demonstration of EPR-steering by violating three-setting quadratic steering inequality, tested with polarization-entangled photons shared between two distant laboratories. Our experiment demonstrates this effect while simultaneously closing all loopholes: both the locality loophole and a specific form of the freedom-of-choice loophole are closed by having a large separation of the parties and using fast quantum random number generators, and the fair-sampling loophole is closed by having high overall detection efficiency. Thereby, we exclude—for the first time loophole-free—an important class of local realistic theories considered by EPR. Besides its foundational importance, loophole-free steering also allows the distribution of quantum entanglement secure event in the presence of an untrusted party. (paper)

Loophole-free Einstein-Podolsky-Rosen experiment via quantum steering

Science.gov (United States)

Wittmann, Bernhard; Ramelow, Sven; Steinlechner, Fabian; Langford, Nathan K.; Brunner, Nicolas; Wiseman, Howard M.; Ursin, Rupert; Zeilinger, Anton

2012-05-01

Tests of the predictions of quantum mechanics for entangled systems have provided increasing evidence against local realistic theories. However, there remains the crucial challenge of simultaneously closing all major loopholes—the locality, freedom-of-choice and detection loopholes—in a single experiment. An important sub-class of local realistic theories can be tested with the concept of ‘steering’. The term ‘steering’ was introduced by Schrödinger in 1935 for the fact that entanglement would seem to allow an experimenter to remotely steer the state of a distant system as in the Einstein-Podolsky-Rosen (EPR) argument. Einstein called this ‘spooky action at a distance’. EPR-steering has recently been rigorously formulated as a quantum information task opening it up to new experimental tests. Here, we present the first loophole-free demonstration of EPR-steering by violating three-setting quadratic steering inequality, tested with polarization-entangled photons shared between two distant laboratories. Our experiment demonstrates this effect while simultaneously closing all loopholes: both the locality loophole and a specific form of the freedom-of-choice loophole are closed by having a large separation of the parties and using fast quantum random number generators, and the fair-sampling loophole is closed by having high overall detection efficiency. Thereby, we exclude—for the first time loophole-free—an important class of local realistic theories considered by EPR. Besides its foundational importance, loophole-free steering also allows the distribution of quantum entanglement secure event in the presence of an untrusted party.

Decoherence and the quantum-to-classical transition

CERN Document Server

Schlosshauer, Maximilian

2007-01-01

The ultimate introduction, textbook, and reference on decoherence and the quantum-to-classical transition. This detailed but accessible text describes the concepts, formalism, interpretation, and experimental observation of decoherence and explains how decoherence is responsible for the emergence, from the realm of quantum mechanics, of the classical world of our experience. Topics include: • Foundational problems at the quantum–classical border; • The role of the environment and entanglement; • Environment-induced loss of coherence and superselection; • Scattering-induced decoherence and spatial localization; • Master equations; • Decoherence models; • Experimental realization of "Schrödinger kittens" and their decoherence; • Quantum computing, quantum error correction, and decoherence-free subspaces; • Implications of decoherence for interpretations of quantum mechanics and for the "measurement problem"; • Decoherence in the brain. Written in a lucid and concise style that is accessib...

Gate errors in solid-state quantum-computer architectures

International Nuclear Information System (INIS)

Hu Xuedong; Das Sarma, S.

2002-01-01

We theoretically consider possible errors in solid-state quantum computation due to the interplay of the complex solid-state environment and gate imperfections. In particular, we study two examples of gate operations in the opposite ends of the gate speed spectrum, an adiabatic gate operation in electron-spin-based quantum dot quantum computation and a sudden gate operation in Cooper-pair-box superconducting quantum computation. We evaluate quantitatively the nonadiabatic operation of a two-qubit gate in a two-electron double quantum dot. We also analyze the nonsudden pulse gate in a Cooper-pair-box-based quantum-computer model. In both cases our numerical results show strong influences of the higher excited states of the system on the gate operation, clearly demonstrating the importance of a detailed understanding of the relevant Hilbert-space structure on the quantum-computer operations

Quantum states and their marginals. From multipartite entanglement to quantum error-correcting codes

International Nuclear Information System (INIS)

Huber, Felix Michael

2017-01-01

At the heart of the curious phenomenon of quantum entanglement lies the relation between the whole and its parts. In my thesis, I explore different aspects of this theme in the multipartite setting by drawing connections to concepts from statistics, graph theory, and quantum error-correcting codes: first, I address the case when joint quantum states are determined by their few-body parts and by Jaynes' maximum entropy principle. This can be seen as an extension of the notion of entanglement, with less complex states already being determined by their few-body marginals. Second, I address the conditions for certain highly entangled multipartite states to exist. In particular, I present the solution of a long-standing open problem concerning the existence of an absolutely maximally entangled state on seven qubits. This sheds light on the algebraic properties of pure quantum states, and on the conditions that constrain the sharing of entanglement amongst multiple particles. Third, I investigate Ulam's graph reconstruction problems in the quantum setting, and obtain legitimacy conditions of a set of states to be the reductions of a joint graph state. Lastly, I apply and extend the weight enumerator machinery from quantum error correction to investigate the existence of codes and highly entangled states in higher dimensions. This clarifies the physical interpretation of the weight enumerators and of the quantum MacWilliams identity, leading to novel applications in multipartite entanglement.

Bound on quantum computation time: Quantum error correction in a critical environment

International Nuclear Information System (INIS)

Novais, E.; Mucciolo, Eduardo R.; Baranger, Harold U.

2010-01-01

We obtain an upper bound on the time available for quantum computation for a given quantum computer and decohering environment with quantum error correction implemented. First, we derive an explicit quantum evolution operator for the logical qubits and show that it has the same form as that for the physical qubits but with a reduced coupling strength to the environment. Using this evolution operator, we find the trace distance between the real and ideal states of the logical qubits in two cases. For a super-Ohmic bath, the trace distance saturates, while for Ohmic or sub-Ohmic baths, there is a finite time before the trace distance exceeds a value set by the user.

Experimental quantum secret sharing and third-man quantum cryptography.

Science.gov (United States)

Chen, Yu-Ao; Zhang, An-Ning; Zhao, Zhi; Zhou, Xiao-Qi; Lu, Chao-Yang; Peng, Cheng-Zhi; Yang, Tao; Pan, Jian-Wei

2005-11-11

Quantum secret sharing (QSS) and third-man quantum cryptography (TQC) are essential for advanced quantum communication; however, the low intensity and fragility of the multiphoton entanglement source in previous experiments have made their realization an extreme experimental challenge. Here, we develop and exploit an ultrastable high intensity source of four-photon entanglement to report an experimental realization of QSS and TQC. The technology developed in our experiment will be important for future multiparty quantum communication.

Experimental quantum control landscapes: Inherent monotonicity and artificial structure

International Nuclear Information System (INIS)

Roslund, Jonathan; Rabitz, Herschel

2009-01-01

Unconstrained searches over quantum control landscapes are theoretically predicted to generally exhibit trap-free monotonic behavior. This paper makes an explicit experimental demonstration of this intrinsic monotonicity for two controlled quantum systems: frequency unfiltered and filtered second-harmonic generation (SHG). For unfiltered SHG, the landscape is randomly sampled and interpolation of the data is found to be devoid of landscape traps up to the level of data noise. In the case of narrow-band-filtered SHG, trajectories are taken on the landscape to reveal a lack of traps. Although the filtered SHG landscape is trap free, it exhibits a rich local structure. A perturbation analysis around the top of these landscapes provides a basis to understand their topology. Despite the inherent trap-free nature of the landscapes, practical constraints placed on the controls can lead to the appearance of artificial structure arising from the resultant forced sampling of the landscape. This circumstance and the likely lack of knowledge about the detailed local landscape structure in most quantum control applications suggests that the a priori identification of globally successful (un)constrained curvilinear control variables may be a challenging task.

Expedited Holonomic Quantum Computation via Net Zero-Energy-Cost Control in Decoherence-Free Subspace.

Science.gov (United States)

Pyshkin, P V; Luo, Da-Wei; Jing, Jun; You, J Q; Wu, Lian-Ao

2016-11-25

Holonomic quantum computation (HQC) may not show its full potential in quantum speedup due to the prerequisite of a long coherent runtime imposed by the adiabatic condition. Here we show that the conventional HQC can be dramatically accelerated by using external control fields, of which the effectiveness is exclusively determined by the integral of the control fields in the time domain. This control scheme can be realized with net zero energy cost and it is fault-tolerant against fluctuation and noise, significantly relaxing the experimental constraints. We demonstrate how to realize the scheme via decoherence-free subspaces. In this way we unify quantum robustness merits of this fault-tolerant control scheme, the conventional HQC and decoherence-free subspace, and propose an expedited holonomic quantum computation protocol.

Long-distance quantum teleportation assisted with free-space entanglement distribution

International Nuclear Information System (INIS)

Ji-Gang, Ren; Zhen-Huan, Yi; Fei, Zhou; Cheng-Zhi, Peng; Jian-Wei, Pan; Bin, Yang; Kai, Chen

2009-01-01

Faithful long-distance quantum teleportation necessitates prior entanglement distribution between two communicated locations. The particle carrying on the unknown quantum information is then combined with one particle of the entangled states for Bell-state measurements, which leads to a transfer of the original quantum information onto the other particle of the entangled states. However in most of the implemented teleportation experiments nowadays, the Bell-state measurements are performed even before successful distribution of entanglement. This leads to an instant collapse of the quantum state for the transmitted particle, which is actually a single-particle transmission thereafter. Thus the true distance for quantum teleportation is, in fact, only in a level of meters. In the present experiment we design a novel scheme which has overcome this limit by utilizing fiber as quantum memory. A complete quantum teleportation is achieved upon successful entanglement distribution over 967 meters in public free space. Active feed-forward control techniques are developed for real-time transfer of quantum information. The overall experimental fidelities for teleported states are better than 89.6%, which signify high-quality teleportation. (rapid communications)

Experimental quantum verification in the presence of temporally correlated noise

Science.gov (United States)

Mavadia, S.; Edmunds, C. L.; Hempel, C.; Ball, H.; Roy, F.; Stace, T. M.; Biercuk, M. J.

2018-02-01

Growth in the capabilities of quantum information hardware mandates access to techniques for performance verification that function under realistic laboratory conditions. Here we experimentally characterise the impact of common temporally correlated noise processes on both randomised benchmarking (RB) and gate-set tomography (GST). Our analysis highlights the role of sequence structure in enhancing or suppressing the sensitivity of quantum verification protocols to either slowly or rapidly varying noise, which we treat in the limiting cases of quasi-DC miscalibration and white noise power spectra. We perform experiments with a single trapped 171Yb+ ion-qubit and inject engineered noise (" separators="∝σ^ z ) to probe protocol performance. Experiments on RB validate predictions that measured fidelities over sequences are described by a gamma distribution varying between approximately Gaussian, and a broad, highly skewed distribution for rapidly and slowly varying noise, respectively. Similarly we find a strong gate set dependence of default experimental GST procedures in the presence of correlated errors, leading to significant deviations between estimated and calculated diamond distances in the presence of correlated σ^ z errors. Numerical simulations demonstrate that expansion of the gate set to include negative rotations can suppress these discrepancies and increase reported diamond distances by orders of magnitude for the same error processes. Similar effects do not occur for correlated σ^ x or σ^ y errors or depolarising noise processes, highlighting the impact of the critical interplay of selected gate set and the gauge optimisation process on the meaning of the reported diamond norm in correlated noise environments.

Quantum mean-field decoding algorithm for error-correcting codes

International Nuclear Information System (INIS)

Inoue, Jun-ichi; Saika, Yohei; Okada, Masato

2009-01-01

We numerically examine a quantum version of TAP (Thouless-Anderson-Palmer)-like mean-field algorithm for the problem of error-correcting codes. For a class of the so-called Sourlas error-correcting codes, we check the usefulness to retrieve the original bit-sequence (message) with a finite length. The decoding dynamics is derived explicitly and we evaluate the average-case performance through the bit-error rate (BER).

Experimental quantum forgery of quantum optical money

Czech Academy of Sciences Publication Activity Database

Bartkiewicz, K.; Černoch, Antonín; Chimczak, G.; Lemr, K.; Miranowicz, A.; Nori, F.

2017-01-01

Roč. 3, Mar (2017), s. 1-8, č. článku 7. ISSN 2056-6387 R&D Projects: GA ČR GAP205/12/0382 Institutional support: RVO:68378271 Keywords : experimental quantum forgery * quantum optical money Subject RIV: BH - Optics, Masers, Lasers OBOR OECD: Optics (including laser optics and quantum optics) Impact factor: 9.111, year: 2016

Initialization Errors in Quantum Data Base Recall

OpenAIRE

Natu, Kalyani

2016-01-01

This paper analyzes the relationship between initialization error and recall of a specific memory in the Grover algorithm for quantum database search. It is shown that the correct memory is obtained with high probability even when the initial state is far removed from the correct one. The analysis is done by relating the variance of error in the initial state to the recovery of the correct memory and the surprising result is obtained that the relationship between the two is essentially linear.

Prospects for Studies of the Free Fall and Gravitational Quantum States of Antimatter

Directory of Open Access Journals (Sweden)

G. Dufour

2015-01-01

Full Text Available Different experiments are ongoing to measure the effect of gravity on cold neutral antimatter atoms such as positronium, muonium, and antihydrogen. Among those, the project GBAR at CERN aims to measure precisely the gravitational fall of ultracold antihydrogen atoms. In the ultracold regime, the interaction of antihydrogen atoms with a surface is governed by the phenomenon of quantum reflection which results in bouncing of antihydrogen atoms on matter surfaces. This allows the application of a filtering scheme to increase the precision of the free fall measurement. In the ultimate limit of smallest vertical velocities, antihydrogen atoms are settled in gravitational quantum states in close analogy to ultracold neutrons (UCNs. Positronium is another neutral system involving antimatter for which free fall under gravity is currently being investigated at UCL. Building on the experimental techniques under development for the free fall measurement, gravitational quantum states could also be observed in positronium. In this contribution, we report on the status of the ongoing experiments and discuss the prospects of observing gravitational quantum states of antimatter and their implications.

QSPIN: A High Level Java API for Quantum Computing Experimentation

Science.gov (United States)

Barth, Tim

2017-01-01

QSPIN is a high level Java language API for experimentation in QC models used in the calculation of Ising spin glass ground states and related quadratic unconstrained binary optimization (QUBO) problems. The Java API is intended to facilitate research in advanced QC algorithms such as hybrid quantum-classical solvers, automatic selection of constraint and optimization parameters, and techniques for the correction and mitigation of model and solution errors. QSPIN includes high level solver objects tailored to the D-Wave quantum annealing architecture that implement hybrid quantum-classical algorithms [Booth et al.] for solving large problems on small quantum devices, elimination of variables via roof duality, and classical computing optimization methods such as GPU accelerated simulated annealing and tabu search for comparison. A test suite of documented NP-complete applications ranging from graph coloring, covering, and partitioning to integer programming and scheduling are provided to demonstrate current capabilities.

Hardware-efficient bosonic quantum error-correcting codes based on symmetry operators

Science.gov (United States)

Niu, Murphy Yuezhen; Chuang, Isaac L.; Shapiro, Jeffrey H.

2018-03-01

We establish a symmetry-operator framework for designing quantum error-correcting (QEC) codes based on fundamental properties of the underlying system dynamics. Based on this framework, we propose three hardware-efficient bosonic QEC codes that are suitable for χ(2 )-interaction based quantum computation in multimode Fock bases: the χ(2 ) parity-check code, the χ(2 ) embedded error-correcting code, and the χ(2 ) binomial code. All of these QEC codes detect photon-loss or photon-gain errors by means of photon-number parity measurements, and then correct them via χ(2 ) Hamiltonian evolutions and linear-optics transformations. Our symmetry-operator framework provides a systematic procedure for finding QEC codes that are not stabilizer codes, and it enables convenient extension of a given encoding to higher-dimensional qudit bases. The χ(2 ) binomial code is of special interest because, with m ≤N identified from channel monitoring, it can correct m -photon-loss errors, or m -photon-gain errors, or (m -1 )th -order dephasing errors using logical qudits that are encoded in O (N ) photons. In comparison, other bosonic QEC codes require O (N2) photons to correct the same degree of bosonic errors. Such improved photon efficiency underscores the additional error-correction power that can be provided by channel monitoring. We develop quantum Hamming bounds for photon-loss errors in the code subspaces associated with the χ(2 ) parity-check code and the χ(2 ) embedded error-correcting code, and we prove that these codes saturate their respective bounds. Our χ(2 ) QEC codes exhibit hardware efficiency in that they address the principal error mechanisms and exploit the available physical interactions of the underlying hardware, thus reducing the physical resources required for implementing their encoding, decoding, and error-correction operations, and their universal encoded-basis gate sets.

Remote one-qubit information concentration and decoding of operator quantum error-correction codes

International Nuclear Information System (INIS)

Hsu Liyi

2007-01-01

We propose the general scheme of remote one-qubit information concentration. To achieve the task, the Bell-correlated mixed states are exploited. In addition, the nonremote one-qubit information concentration is equivalent to the decoding of the quantum error-correction code. Here we propose how to decode the stabilizer codes. In particular, the proposed scheme can be used for the operator quantum error-correction codes. The encoded state can be recreated on the errorless qubit, regardless how many bit-flip errors and phase-flip errors have occurred

Intrinsic errors in transporting a single-spin qubit through a double quantum dot

Science.gov (United States)

Li, Xiao; Barnes, Edwin; Kestner, J. P.; Das Sarma, S.

2017-07-01

Coherent spatial transport or shuttling of a single electron spin through semiconductor nanostructures is an important ingredient in many spintronic and quantum computing applications. In this work we analyze the possible errors in solid-state quantum computation due to leakage in transporting a single-spin qubit through a semiconductor double quantum dot. In particular, we consider three possible sources of leakage errors associated with such transport: finite ramping times, spin-dependent tunneling rates between quantum dots induced by finite spin-orbit couplings, and the presence of multiple valley states. In each case we present quantitative estimates of the leakage errors, and discuss how they can be minimized. The emphasis of this work is on how to deal with the errors intrinsic to the ideal semiconductor structure, such as leakage due to spin-orbit couplings, rather than on errors due to defects or noise sources. In particular, we show that in order to minimize leakage errors induced by spin-dependent tunnelings, it is necessary to apply pulses to perform certain carefully designed spin rotations. We further develop a formalism that allows one to systematically derive constraints on the pulse shapes and present a few examples to highlight the advantage of such an approach.

Optical waveform sampling and error-free demultiplexing of 1.28 Tbit/s serial data in a silicon nanowire

DEFF Research Database (Denmark)

Ji, Hua; Hu, Hao; Galili, Michael

2010-01-01

We experimentally demonstrate 640 Gbit/s and 1.28 Tbit/s serial data optical waveform sampling and 640-to-10 Gbit/s and 1.28 Tbit/s-to-10 Gbit/s error-free demultiplexing using four-wave mixing in a 300nm$$450nm$$5mm silicon nanowire.......We experimentally demonstrate 640 Gbit/s and 1.28 Tbit/s serial data optical waveform sampling and 640-to-10 Gbit/s and 1.28 Tbit/s-to-10 Gbit/s error-free demultiplexing using four-wave mixing in a 300nm$$450nm$$5mm silicon nanowire....

Effects of systematic phase errors on optimized quantum random-walk search algorithm

International Nuclear Information System (INIS)

Zhang Yu-Chao; Bao Wan-Su; Wang Xiang; Fu Xiang-Qun

2015-01-01

This study investigates the effects of systematic errors in phase inversions on the success rate and number of iterations in the optimized quantum random-walk search algorithm. Using the geometric description of this algorithm, a model of the algorithm with phase errors is established, and the relationship between the success rate of the algorithm, the database size, the number of iterations, and the phase error is determined. For a given database size, we obtain both the maximum success rate of the algorithm and the required number of iterations when phase errors are present in the algorithm. Analyses and numerical simulations show that the optimized quantum random-walk search algorithm is more robust against phase errors than Grover’s algorithm. (paper)

Quantum cryptography: individual eavesdropping with the knowledge of the error-correcting protocol

International Nuclear Information System (INIS)

Horoshko, D B

2007-01-01

The quantum key distribution protocol BB84 combined with the repetition protocol for error correction is analysed from the point of view of its security against individual eavesdropping relying on quantum memory. It is shown that the mere knowledge of the error-correcting protocol changes the optimal attack and provides the eavesdropper with additional information on the distributed key. (fifth seminar in memory of d.n. klyshko)

Error-Free Software

Science.gov (United States)

1989-01-01

001 is an integrated tool suited for automatically developing ultra reliable models, simulations and software systems. Developed and marketed by Hamilton Technologies, Inc. (HTI), it has been applied in engineering, manufacturing, banking and software tools development. The software provides the ability to simplify the complex. A system developed with 001 can be a prototype or fully developed with production quality code. It is free of interface errors, consistent, logically complete and has no data or control flow errors. Systems can be designed, developed and maintained with maximum productivity. Margaret Hamilton, President of Hamilton Technologies, also directed the research and development of USE.IT, an earlier product which was the first computer aided software engineering product in the industry to concentrate on automatically supporting the development of an ultrareliable system throughout its life cycle. Both products originated in NASA technology developed under a Johnson Space Center contract.

Experimental realization of Shor's quantum factoring algorithm using nuclear magnetic resonance.

Science.gov (United States)

Vandersypen, L M; Steffen, M; Breyta, G; Yannoni, C S; Sherwood, M H; Chuang, I L

The number of steps any classical computer requires in order to find the prime factors of an l-digit integer N increases exponentially with l, at least using algorithms known at present. Factoring large integers is therefore conjectured to be intractable classically, an observation underlying the security of widely used cryptographic codes. Quantum computers, however, could factor integers in only polynomial time, using Shor's quantum factoring algorithm. Although important for the study of quantum computers, experimental demonstration of this algorithm has proved elusive. Here we report an implementation of the simplest instance of Shor's algorithm: factorization of N = 15 (whose prime factors are 3 and 5). We use seven spin-1/2 nuclei in a molecule as quantum bits, which can be manipulated with room temperature liquid-state nuclear magnetic resonance techniques. This method of using nuclei to store quantum information is in principle scalable to systems containing many quantum bits, but such scalability is not implied by the present work. The significance of our work lies in the demonstration of experimental and theoretical techniques for precise control and modelling of complex quantum computers. In particular, we present a simple, parameter-free but predictive model of decoherence effects in our system.

Linear free energy relationships between aqueous phase hydroxyl radical reaction rate constants and free energy of activation.

Science.gov (United States)

Minakata, Daisuke; Crittenden, John

2011-04-15

The hydroxyl radical (HO(•)) is a strong oxidant that reacts with electron-rich sites on organic compounds and initiates complex radical chain reactions in aqueous phase advanced oxidation processes (AOPs). Computer based kinetic modeling requires a reaction pathway generator and predictions of associated reaction rate constants. Previously, we reported a reaction pathway generator that can enumerate the most important elementary reactions for aliphatic compounds. For the reaction rate constant predictor, we develop linear free energy relationships (LFERs) between aqueous phase literature-reported HO(•) reaction rate constants and theoretically calculated free energies of activation for H-atom abstraction from a C-H bond and HO(•) addition to alkenes. The theoretical method uses ab initio quantum mechanical calculations, Gaussian 1-3, for gas phase reactions and a solvation method, COSMO-RS theory, to estimate the impact of water. Theoretically calculated free energies of activation are found to be within approximately ±3 kcal/mol of experimental values. Considering errors that arise from quantum mechanical calculations and experiments, this should be within the acceptable errors. The established LFERs are used to predict the HO(•) reaction rate constants within a factor of 5 from the experimental values. This approach may be applied to other reaction mechanisms to establish a library of rate constant predictions for kinetic modeling of AOPs.

Practical experimental certification of computational quantum gates using a twirling procedure.

Science.gov (United States)

Moussa, Osama; da Silva, Marcus P; Ryan, Colm A; Laflamme, Raymond

2012-08-17

Because of the technical difficulty of building large quantum computers, it is important to be able to estimate how faithful a given implementation is to an ideal quantum computer. The common approach of completely characterizing the computation process via quantum process tomography requires an exponential amount of resources, and thus is not practical even for relatively small devices. We solve this problem by demonstrating that twirling experiments previously used to characterize the average fidelity of quantum memories efficiently can be easily adapted to estimate the average fidelity of the experimental implementation of important quantum computation processes, such as unitaries in the Clifford group, in a practical and efficient manner with applicability in current quantum devices. Using this procedure, we demonstrate state-of-the-art coherent control of an ensemble of magnetic moments of nuclear spins in a single crystal solid by implementing the encoding operation for a 3-qubit code with only a 1% degradation in average fidelity discounting preparation and measurement errors. We also highlight one of the advances that was instrumental in achieving such high fidelity control.

Model-free and model-based reward prediction errors in EEG.

Science.gov (United States)

Sambrook, Thomas D; Hardwick, Ben; Wills, Andy J; Goslin, Jeremy

2018-05-24

Learning theorists posit two reinforcement learning systems: model-free and model-based. Model-based learning incorporates knowledge about structure and contingencies in the world to assign candidate actions with an expected value. Model-free learning is ignorant of the world's structure; instead, actions hold a value based on prior reinforcement, with this value updated by expectancy violation in the form of a reward prediction error. Because they use such different learning mechanisms, it has been previously assumed that model-based and model-free learning are computationally dissociated in the brain. However, recent fMRI evidence suggests that the brain may compute reward prediction errors to both model-free and model-based estimates of value, signalling the possibility that these systems interact. Because of its poor temporal resolution, fMRI risks confounding reward prediction errors with other feedback-related neural activity. In the present study, EEG was used to show the presence of both model-based and model-free reward prediction errors and their place in a temporal sequence of events including state prediction errors and action value updates. This demonstration of model-based prediction errors questions a long-held assumption that model-free and model-based learning are dissociated in the brain. Copyright © 2018 Elsevier Inc. All rights reserved.

Direct observation of free-exciton thermalization in quantum-well structures

DEFF Research Database (Denmark)

Umlauff, M.; Hoffmann, J.; Kalt, H.

1998-01-01

We report on a direct observation of free-exciton thermalization in quantum-well structures. A narrow energy distribution of free 1s excitons is created in ZnSe-based quantum wells by emission of one LO phonon after optical excitation of the continuum stales with picosecond laser pulses. The subs......We report on a direct observation of free-exciton thermalization in quantum-well structures. A narrow energy distribution of free 1s excitons is created in ZnSe-based quantum wells by emission of one LO phonon after optical excitation of the continuum stales with picosecond laser pulses...

Magnitude of pseudopotential localization errors in fixed node diffusion quantum Monte Carlo.

Science.gov (United States)

Krogel, Jaron T; Kent, P R C

2017-06-28

Growth in computational resources has lead to the application of real space diffusion quantum Monte Carlo to increasingly heavy elements. Although generally assumed to be small, we find that when using standard techniques, the pseudopotential localization error can be large, on the order of an electron volt for an isolated cerium atom. We formally show that the localization error can be reduced to zero with improvements to the Jastrow factor alone, and we define a metric of Jastrow sensitivity that may be useful in the design of pseudopotentials. We employ an extrapolation scheme to extract the bare fixed node energy and estimate the localization error in both the locality approximation and the T-moves schemes for the Ce atom in charge states 3+ and 4+. The locality approximation exhibits the lowest Jastrow sensitivity and generally smaller localization errors than T-moves although the locality approximation energy approaches the localization free limit from above/below for the 3+/4+ charge state. We find that energy minimized Jastrow factors including three-body electron-electron-ion terms are the most effective at reducing the localization error for both the locality approximation and T-moves for the case of the Ce atom. Less complex or variance minimized Jastrows are generally less effective. Our results suggest that further improvements to Jastrow factors and trial wavefunction forms may be needed to reduce localization errors to chemical accuracy when medium core pseudopotentials are applied to heavy elements such as Ce.

Experimental quantum cryptography with qutrits

Science.gov (United States)

Gröblacher, Simon; Jennewein, Thomas; Vaziri, Alipasha; Weihs, Gregor; Zeilinger, Anton

2006-05-01

We produce two identical keys using, for the first time, entangled trinary quantum systems (qutrits) for quantum key distribution. The advantage of qutrits over the normally used binary quantum systems is an increased coding density and a higher security margin. The qutrits are encoded into the orbital angular momentum of photons, namely Laguerre Gaussian modes with azimuthal index l + 1, 0 and -1, respectively. The orbital angular momentum is controlled with phase holograms. In an Ekert-type protocol the violation of a three-dimensional Bell inequality verifies the security of the generated keys. A key is obtained with a qutrit error rate of approximately 10%.

A quantum byte with 10{sup -4} crosstalk for fault-tolerant quantum computing

Energy Technology Data Exchange (ETDEWEB)

Piltz, Christian; Sriarunothai, Theeraphot; Varon, Andres; Wunderlich, Christof [Department Physik, Universitaet Siegen, 57068 Siegen (Germany)

2014-07-01

A prerequisite for fault-tolerant and thus scalable operation of a quantum computer is the use of quantum error correction protocols. Such protocols come with a maximum tolerable gate error, and there is consensus that an error of order 10{sup -4} is an important threshold. This threshold was already breached for single-qubit gates with trapped ions using microwave radiation. However, crosstalk - the error that is induced in qubits within a quantum register, when one qubit (or a subset of qubits) is coherently manipulated, still prevents the realization of a scalable quantum computer. The application of a quantum gate - even if the gate error itself is low - induces errors in other qubits within the quantum register. We present an experimental study using quantum registers consisting of microwave-driven trapped {sup 171}Yb{sup +} ions in a static magnetic gradient. We demonstrate a quantum register of three qubits with a next-neighbour crosstalk of 6(1) . 10{sup -5} that for the first time breaches the error correction threshold. Furthermore, we present a quantum register of eight qubits - a quantum byte - with a next-neighbour crosstalk error better than 2.9(4) . 10{sup -4}. Importantly, our results are obtained with thermally excited ions far above the motional ground state.

Error analysis and assessment of unsteady forces acting on a flapping wing micro air vehicle: free flight versus wind-tunnel experimental methods.

Science.gov (United States)

Caetano, J V; Percin, M; van Oudheusden, B W; Remes, B; de Wagter, C; de Croon, G C H E; de Visser, C C

2015-08-20

An accurate knowledge of the unsteady aerodynamic forces acting on a bio-inspired, flapping-wing micro air vehicle (FWMAV) is crucial in the design development and optimization cycle. Two different types of experimental approaches are often used: determination of forces from position data obtained from external optical tracking during free flight, or direct measurements of forces by attaching the FWMAV to a force transducer in a wind-tunnel. This study compares the quality of the forces obtained from both methods as applied to a 17.4 gram FWMAV capable of controlled flight. A comprehensive analysis of various error sources is performed. The effects of different factors, e.g., measurement errors, error propagation, numerical differentiation, filtering frequency selection, and structural eigenmode interference, are assessed. For the forces obtained from free flight experiments it is shown that a data acquisition frequency below 200 Hz and an accuracy in the position measurements lower than ± 0.2 mm may considerably hinder determination of the unsteady forces. In general, the force component parallel to the fuselage determined by the two methods compares well for identical flight conditions; however, a significant difference was observed for the forces along the stroke plane of the wings. This was found to originate from the restrictions applied by the clamp to the dynamic oscillations observed in free flight and from the structural resonance of the clamped FWMAV structure, which generates loads that cannot be distinguished from the external forces. Furthermore, the clamping position was found to have a pronounced influence on the eigenmodes of the structure, and this effect should be taken into account for accurate force measurements.

Small-scale quantum information processing with linear optics

International Nuclear Information System (INIS)

Bergou, J.A.; Steinberg, A.M.; Mohseni, M.

2005-01-01

Full text: Photons are the ideal systems for carrying quantum information. Although performing large-scale quantum computation on optical systems is extremely demanding, non scalable linear-optics quantum information processing may prove essential as part of quantum communication networks. In addition efficient (scalable) linear-optical quantum computation proposal relies on the same optical elements. Here, by constructing multirail optical networks, we experimentally study two central problems in quantum information science, namely optimal discrimination between nonorthogonal quantum states, and controlling decoherence in quantum systems. Quantum mechanics forbids deterministic discrimination between nonorthogonal states. This is one of the central features of quantum cryptography, which leads to secure communications. Quantum state discrimination is an important primitive in quantum information processing, since it determines the limitations of a potential eavesdropper, and it has applications in quantum cloning and entanglement concentration. In this work, we experimentally implement generalized measurements in an optical system and demonstrate the first optimal unambiguous discrimination between three non-orthogonal states with a success rate of 55 %, to be compared with the 25 % maximum achievable using projective measurements. Furthermore, we present the first realization of unambiguous discrimination between a pure state and a nonorthogonal mixed state. In a separate experiment, we demonstrate how decoherence-free subspaces (DFSs) may be incorporated into a prototype optical quantum algorithm. Specifically, we present an optical realization of two-qubit Deutsch-Jozsa algorithm in presence of random noise. By introduction of localized turbulent airflow we produce a collective optical dephasing, leading to large error rates and demonstrate that using DFS encoding, the error rate in the presence of decoherence can be reduced from 35 % to essentially its pre

Correcting errors in a quantum gate with pushed ions via optimal control

International Nuclear Information System (INIS)

Poulsen, Uffe V.; Sklarz, Shlomo; Tannor, David; Calarco, Tommaso

2010-01-01

We analyze in detail the so-called pushing gate for trapped ions, introducing a time-dependent harmonic approximation for the external motion. We show how to extract the average fidelity for the gate from the resulting semiclassical simulations. We characterize and quantify precisely all types of errors coming from the quantum dynamics and reveal that slight nonlinearities in the ion-pushing force can have a dramatic effect on the adiabaticity of gate operation. By means of quantum optimal control techniques, we show how to suppress each of the resulting gate errors in order to reach a high fidelity compatible with scalable fault-tolerant quantum computing.

Error Correction using Quantum Quasi-Cyclic Low-Density Parity-Check(LDPC) Codes

Science.gov (United States)

Jing, Lin; Brun, Todd; Quantum Research Team

Quasi-cyclic LDPC codes can approach the Shannon capacity and have efficient decoders. Manabu Hagiwara et al., 2007 presented a method to calculate parity check matrices with high girth. Two distinct, orthogonal matrices Hc and Hd are used. Using submatrices obtained from Hc and Hd by deleting rows, we can alter the code rate. The submatrix of Hc is used to correct Pauli X errors, and the submatrix of Hd to correct Pauli Z errors. We simulated this system for depolarizing noise on USC's High Performance Computing Cluster, and obtained the block error rate (BER) as a function of the error weight and code rate. From the rates of uncorrectable errors under different error weights we can extrapolate the BER to any small error probability. Our results show that this code family can perform reasonably well even at high code rates, thus considerably reducing the overhead compared to concatenated and surface codes. This makes these codes promising as storage blocks in fault-tolerant quantum computation. Error Correction using Quantum Quasi-Cyclic Low-Density Parity-Check(LDPC) Codes.

Scalable Quantum Simulation of Molecular Energies

Directory of Open Access Journals (Sweden)

P. J. J. O’Malley

2016-07-01

Full Text Available We report the first electronic structure calculation performed on a quantum computer without exponentially costly precompilation. We use a programmable array of superconducting qubits to compute the energy surface of molecular hydrogen using two distinct quantum algorithms. First, we experimentally execute the unitary coupled cluster method using the variational quantum eigensolver. Our efficient implementation predicts the correct dissociation energy to within chemical accuracy of the numerically exact result. Second, we experimentally demonstrate the canonical quantum algorithm for chemistry, which consists of Trotterization and quantum phase estimation. We compare the experimental performance of these approaches to show clear evidence that the variational quantum eigensolver is robust to certain errors. This error tolerance inspires hope that variational quantum simulations of classically intractable molecules may be viable in the near future.

Iterative Phase Optimization of Elementary Quantum Error Correcting Codes (Open Access, Publisher’s Version)

Science.gov (United States)

2016-08-24

to the seven-qubit Steane code [29] and also represents the smallest instance of a 2D topological color code [30]. Since the realized quantum error...Quantum Computations on a Topologically Encoded Qubit, Science 345, 302 (2014). [17] M. Cramer, M. B. Plenio, S. T. Flammia, R. Somma, D. Gross, S. D...Memory, J. Math . Phys. (N.Y.) 43, 4452 (2002). [20] B. M. Terhal, Quantum Error Correction for Quantum Memories, Rev. Mod. Phys. 87, 307 (2015). [21] D

Surface Traps in Colloidal Quantum Dots: A Combined Experimental and Theoretical Perspective.

Science.gov (United States)

Giansante, Carlo; Infante, Ivan

2017-10-19

Surface traps are ubiquitous to nanoscopic semiconductor materials. Understanding their atomistic origin and manipulating them chemically have capital importance to design defect-free colloidal quantum dots and make a leap forward in the development of efficient optoelectronic devices. Recent advances in computing power established computational chemistry as a powerful tool to describe accurately complex chemical species and nowadays it became conceivable to model colloidal quantum dots with realistic sizes and shapes. In this Perspective, we combine the knowledge gathered in recent experimental findings with the computation of quantum dot electronic structures. We analyze three different systems: namely, CdSe, PbS, and CsPbI 3 as benchmark semiconductor nanocrystals showing how different types of trap states can form at their surface. In addition, we suggest experimental healing of such traps according to their chemical origin and nanocrystal composition.

Experimental preparation and verification of quantum money

Science.gov (United States)

Guan, Jian-Yu; Arrazola, Juan Miguel; Amiri, Ryan; Zhang, Weijun; Li, Hao; You, Lixing; Wang, Zhen; Zhang, Qiang; Pan, Jian-Wei

2018-03-01

A quantum money scheme enables a trusted bank to provide untrusted users with verifiable quantum banknotes that cannot be forged. In this work, we report a proof-of-principle experimental demonstration of the preparation and verification of unforgeable quantum banknotes. We employ a security analysis that takes experimental imperfections fully into account. We measure a total of 3.6 ×106 states in one verification round, limiting the forging probability to 10-7 based on the security analysis. Our results demonstrate the feasibility of preparing and verifying quantum banknotes using currently available experimental techniques.

Reduced phase error through optimized control of a superconducting qubit

International Nuclear Information System (INIS)

Lucero, Erik; Kelly, Julian; Bialczak, Radoslaw C.; Lenander, Mike; Mariantoni, Matteo; Neeley, Matthew; O'Connell, A. D.; Sank, Daniel; Wang, H.; Weides, Martin; Wenner, James; Cleland, A. N.; Martinis, John M.; Yamamoto, Tsuyoshi

2010-01-01

Minimizing phase and other errors in experimental quantum gates allows higher fidelity quantum processing. To quantify and correct for phase errors, in particular, we have developed an experimental metrology - amplified phase error (APE) pulses - that amplifies and helps identify phase errors in general multilevel qubit architectures. In order to correct for both phase and amplitude errors specific to virtual transitions and leakage outside of the qubit manifold, we implement 'half derivative', an experimental simplification of derivative reduction by adiabatic gate (DRAG) control theory. The phase errors are lowered by about a factor of five using this method to ∼1.6 deg. per gate, and can be tuned to zero. Leakage outside the qubit manifold, to the qubit |2> state, is also reduced to ∼10 -4 for 20% faster gates.

Fault-tolerant quantum computing in the Pauli or Clifford frame with slow error diagnostics

Directory of Open Access Journals (Sweden)

Christopher Chamberland

2018-01-01

Full Text Available We consider the problem of fault-tolerant quantum computation in the presence of slow error diagnostics, either caused by measurement latencies or slow decoding algorithms. Our scheme offers a few improvements over previously existing solutions, for instance it does not require active error correction and results in a reduced error-correction overhead when error diagnostics is much slower than the gate time. In addition, we adapt our protocol to cases where the underlying error correction strategy chooses the optimal correction amongst all Clifford gates instead of the usual Pauli gates. The resulting Clifford frame protocol is of independent interest as it can increase error thresholds and could find applications in other areas of quantum computation.

Experimental quantum annealing: case study involving the graph isomorphism problem.

Science.gov (United States)

Zick, Kenneth M; Shehab, Omar; French, Matthew

2015-06-08

Quantum annealing is a proposed combinatorial optimization technique meant to exploit quantum mechanical effects such as tunneling and entanglement. Real-world quantum annealing-based solvers require a combination of annealing and classical pre- and post-processing; at this early stage, little is known about how to partition and optimize the processing. This article presents an experimental case study of quantum annealing and some of the factors involved in real-world solvers, using a 504-qubit D-Wave Two machine and the graph isomorphism problem. To illustrate the role of classical pre-processing, a compact Hamiltonian is presented that enables a reduced Ising model for each problem instance. On random N-vertex graphs, the median number of variables is reduced from N(2) to fewer than N log2 N and solvable graph sizes increase from N = 5 to N = 13. Additionally, error correction via classical post-processing majority voting is evaluated. While the solution times are not competitive with classical approaches to graph isomorphism, the enhanced solver ultimately classified correctly every problem that was mapped to the processor and demonstrated clear advantages over the baseline approach. The results shed some light on the nature of real-world quantum annealing and the associated hybrid classical-quantum solvers.

Neural network decoder for quantum error correcting codes

Science.gov (United States)

Krastanov, Stefan; Jiang, Liang

Artificial neural networks form a family of extremely powerful - albeit still poorly understood - tools used in anything from image and sound recognition through text generation to, in our case, decoding. We present a straightforward Recurrent Neural Network architecture capable of deducing the correcting procedure for a quantum error-correcting code from a set of repeated stabilizer measurements. We discuss the fault-tolerance of our scheme and the cost of training the neural network for a system of a realistic size. Such decoders are especially interesting when applied to codes, like the quantum LDPC codes, that lack known efficient decoding schemes.

Error estimates for discretized quantum stochastic differential inclusions

International Nuclear Information System (INIS)

Ayoola, E.O.

2001-09-01

This paper is concerned with the error estimates involved in the solution of a discrete approximation of a quantum stochastic differential inclusion (QSDI). Our main results rely on certain properties of the averaged modulus of continuity for multivalued sesquilinear forms associated with QSDI. We obtained results concerning the estimates of the Hausdorff distance between the set of solutions of the QSDI and the set of solutions of its discrete approximation. This extend the results of Dontchev and Farkhi concerning classical differential inclusions to the present noncommutative Quantum setting involving inclusions in certain locally convex space. (author)

Quantum entanglement in non-local games, graph parameters and zero-error information theory

NARCIS (Netherlands)

Scarpa, G.

2013-01-01

We study quantum entanglement and some of its applications in graph theory and zero-error information theory. In Chapter 1 we introduce entanglement and other fundamental concepts of quantum theory. In Chapter 2 we address the question of how much quantum correlations generated by entanglement can

Quantum Strategies: Proposal to Experimentally Test a Quantum Economics Protocol

Science.gov (United States)

2009-04-09

protocols can add security to competitive situations; and analyzing the feasibility of running multi-party quantum games over metro-distance optical... games of complete informa- tion. Physics Letters A, 272:291-303, August 2000. [21] D. A. Meyer. Quantum Communication in Games . In S. M. Barnett, E ...feasibility of quantum games , we proposed to implement a proof-of-principle quantum public goods game , and to experimentally demonstrate that the quantum

Quantum aspects of the free electron laser

Energy Technology Data Exchange (ETDEWEB)

Gaiba, R.

2007-03-15

We study the role of Quantum Mechanics in the physics of Free Electron Lasers. While the Free Electron Laser (FEL) is usually treated as a classical device, we review the advantages of a quantum formulation of the FEL. We then show the existence of a regime of operation of the FEL that can only be described using Quantum Mechanics: if the dimensionless quantum parameter anti {rho} is smaller than 1, then in the 1-dimensional approximation the Hamiltonian that describes the FEL becomes equivalent to the Hamiltonian of a two-level system coupled to a radiation field. We give analytical and numerical solutions for the photon statistics of a Free Electron Laser operating in the quantum regime under various approximations. Since in the quantum regime the momentum of the electrons is discrete, we give a description of the electrons in phase space by introducing the Discrete Wigner Function. We then drop the assumption of a mono-energetic electron beam and describe the general case of a initial electron energy spread G({gamma}). Numerical analysis shows that the FEL quantum regime is observed only when the width of the initial momentum distribution is smaller than the momentum of the emitted photons. Both the analytical results in the linear approximation and the numerical simulations show that only the electrons close to a certain resonant energy start to emit photons. This generates the so-called Hole-burning effect in the electrons energy distribution, as it can be seen in the simulations we provide. Finally, we present a brief discussion about a fundamental uncertainty relation that ties the electron energy spread and the electron bunching. (orig.)

Experimental quantum fingerprinting with weak coherent pulses

Science.gov (United States)

Xu, Feihu; Arrazola, Juan Miguel; Wei, Kejin; Wang, Wenyuan; Palacios-Avila, Pablo; Feng, Chen; Sajeed, Shihan; Lütkenhaus, Norbert; Lo, Hoi-Kwong

2015-10-01

Quantum communication holds the promise of creating disruptive technologies that will play an essential role in future communication networks. For example, the study of quantum communication complexity has shown that quantum communication allows exponential reductions in the information that must be transmitted to solve distributed computational tasks. Recently, protocols that realize this advantage using optical implementations have been proposed. Here we report a proof-of-concept experimental demonstration of a quantum fingerprinting system that is capable of transmitting less information than the best-known classical protocol. Our implementation is based on a modified version of a commercial quantum key distribution system using off-the-shelf optical components over telecom wavelengths, and is practical for messages as large as 100 Mbits, even in the presence of experimental imperfections. Our results provide a first step in the development of experimental quantum communication complexity.

Strictly contractive quantum channels and physically realizable quantum computers

International Nuclear Information System (INIS)

Raginsky, Maxim

2002-01-01

We study the robustness of quantum computers under the influence of errors modeled by strictly contractive channels. A channel T is defined to be strictly contractive if, for any pair of density operators ρ, σ in its domain, parallel Tρ-Tσ parallel 1 ≤k parallel ρ-σ parallel 1 for some 0≤k 1 denotes the trace norm). In other words, strictly contractive channels render the states of the computer less distinguishable in the sense of quantum detection theory. Starting from the premise that all experimental procedures can be carried out with finite precision, we argue that there exists a physically meaningful connection between strictly contractive channels and errors in physically realizable quantum computers. We show that, in the absence of error correction, sensitivity of quantum memories and computers to strictly contractive errors grows exponentially with storage time and computation time, respectively, and depends only on the constant k and the measurement precision. We prove that strict contractivity rules out the possibility of perfect error correction, and give an argument that approximate error correction, which covers previous work on fault-tolerant quantum computation as a special case, is possible

Automated searching for quantum subsystem codes

International Nuclear Information System (INIS)

Crosswhite, Gregory M.; Bacon, Dave

2011-01-01

Quantum error correction allows for faulty quantum systems to behave in an effectively error-free manner. One important class of techniques for quantum error correction is the class of quantum subsystem codes, which are relevant both to active quantum error-correcting schemes as well as to the design of self-correcting quantum memories. Previous approaches for investigating these codes have focused on applying theoretical analysis to look for interesting codes and to investigate their properties. In this paper we present an alternative approach that uses computational analysis to accomplish the same goals. Specifically, we present an algorithm that computes the optimal quantum subsystem code that can be implemented given an arbitrary set of measurement operators that are tensor products of Pauli operators. We then demonstrate the utility of this algorithm by performing a systematic investigation of the quantum subsystem codes that exist in the setting where the interactions are limited to two-body interactions between neighbors on lattices derived from the convex uniform tilings of the plane.

Experimental quantum fingerprinting with weak coherent pulses

Science.gov (United States)

Xu, Feihu; Arrazola, Juan Miguel; Wei, Kejin; Wang, Wenyuan; Palacios-Avila, Pablo; Feng, Chen; Sajeed, Shihan; Lütkenhaus, Norbert; Lo, Hoi-Kwong

2015-01-01

Quantum communication holds the promise of creating disruptive technologies that will play an essential role in future communication networks. For example, the study of quantum communication complexity has shown that quantum communication allows exponential reductions in the information that must be transmitted to solve distributed computational tasks. Recently, protocols that realize this advantage using optical implementations have been proposed. Here we report a proof-of-concept experimental demonstration of a quantum fingerprinting system that is capable of transmitting less information than the best-known classical protocol. Our implementation is based on a modified version of a commercial quantum key distribution system using off-the-shelf optical components over telecom wavelengths, and is practical for messages as large as 100 Mbits, even in the presence of experimental imperfections. Our results provide a first step in the development of experimental quantum communication complexity. PMID:26515586

Experimental Implementation of a Kochen-Specker Set of Quantum Tests

Directory of Open Access Journals (Sweden)

Vincenzo D’Ambrosio

2013-02-01

Full Text Available The conflict between classical and quantum physics can be identified through a series of yes-no tests on quantum systems, without it being necessary that these systems be in special quantum states. Kochen-Specker (KS sets of yes-no tests have this property and provide a quantum-versus-classical advantage that is free of the initialization problem that affects some quantum computers. Here, we report the first experimental implementation of a complete KS set that consists of 18 yes-no tests on four-dimensional quantum systems and show how to use the KS set to obtain a state-independent quantum advantage. We first demonstrate the unique power of this KS set for solving a task while avoiding the problem of state initialization. Such a demonstration is done by showing that, for 28 different quantum states encoded in the orbital-angular-momentum and polarization degrees of freedom of single photons, the KS set provides an impossible-to-beat solution. In a second experiment, we generate maximally contextual quantum correlations by performing compatible sequential measurements of the polarization and path of single photons. In this case, state independence is demonstrated for 15 different initial states. Maximum contextuality and state independence follow from the fact that the sequences of measurements project any initial quantum state onto one of the KS set’s eigenstates. Our results show that KS sets can be used for quantum-information processing and quantum computation and pave the way for future developments.

Experimental Implementation of a Kochen-Specker Set of Quantum Tests

Science.gov (United States)

D'Ambrosio, Vincenzo; Herbauts, Isabelle; Amselem, Elias; Nagali, Eleonora; Bourennane, Mohamed; Sciarrino, Fabio; Cabello, Adán

2013-01-01

The conflict between classical and quantum physics can be identified through a series of yes-no tests on quantum systems, without it being necessary that these systems be in special quantum states. Kochen-Specker (KS) sets of yes-no tests have this property and provide a quantum-versus-classical advantage that is free of the initialization problem that affects some quantum computers. Here, we report the first experimental implementation of a complete KS set that consists of 18 yes-no tests on four-dimensional quantum systems and show how to use the KS set to obtain a state-independent quantum advantage. We first demonstrate the unique power of this KS set for solving a task while avoiding the problem of state initialization. Such a demonstration is done by showing that, for 28 different quantum states encoded in the orbital-angular-momentum and polarization degrees of freedom of single photons, the KS set provides an impossible-to-beat solution. In a second experiment, we generate maximally contextual quantum correlations by performing compatible sequential measurements of the polarization and path of single photons. In this case, state independence is demonstrated for 15 different initial states. Maximum contextuality and state independence follow from the fact that the sequences of measurements project any initial quantum state onto one of the KS set’s eigenstates. Our results show that KS sets can be used for quantum-information processing and quantum computation and pave the way for future developments.

Topological quantum error correction in the Kitaev honeycomb model

Science.gov (United States)

Lee, Yi-Chan; Brell, Courtney G.; Flammia, Steven T.

2017-08-01

The Kitaev honeycomb model is an approximate topological quantum error correcting code in the same phase as the toric code, but requiring only a 2-body Hamiltonian. As a frustrated spin model, it is well outside the commuting models of topological quantum codes that are typically studied, but its exact solubility makes it more amenable to analysis of effects arising in this noncommutative setting than a generic topologically ordered Hamiltonian. Here we study quantum error correction in the honeycomb model using both analytic and numerical techniques. We first prove explicit exponential bounds on the approximate degeneracy, local indistinguishability, and correctability of the code space. These bounds are tighter than can be achieved using known general properties of topological phases. Our proofs are specialized to the honeycomb model, but some of the methods may nonetheless be of broader interest. Following this, we numerically study noise caused by thermalization processes in the perturbative regime close to the toric code renormalization group fixed point. The appearance of non-topological excitations in this setting has no significant effect on the error correction properties of the honeycomb model in the regimes we study. Although the behavior of this model is found to be qualitatively similar to that of the standard toric code in most regimes, we find numerical evidence of an interesting effect in the low-temperature, finite-size regime where a preferred lattice direction emerges and anyon diffusion is geometrically constrained. We expect this effect to yield an improvement in the scaling of the lifetime with system size as compared to the standard toric code.

From Einstein-Podolsky-Rosen paradox to quantum nonlocality: experimental investigation of quantum correlations

Science.gov (United States)

Xu, Jin-Shi; Li, Chuan-Feng; Guo, Guang-Can

2016-11-01

In 1935, Einstein, Podolsky and Rosen published their influential paper proposing a now famous paradox (the EPR paradox) that threw doubt on the completeness of quantum mechanics. Two fundamental concepts: entanglement and steering, were given in the response to the EPR paper by Schrodinger, which both reflect the nonlocal nature of quantum mechanics. In 1964, John Bell obtained an experimentally testable inequality, in which its violation contradicts the prediction of local hidden variable models and agrees with that of quantum mechanics. Since then, great efforts have been made to experimentally investigate the nonlocal feature of quantum mechanics and many distinguished quantum properties were observed. In this work, along with the discussion of the development of quantum nonlocality, we would focus on our recent experimental efforts in investigating quantum correlations and their applications with optical systems, including the study of entanglement-assisted entropic uncertainty principle, Einstein-Podolsky-Rosen steering and the dynamics of quantum correlations.

Optical Waveform Sampling and Error-Free Demultiplexing of 1.28 Tb/s Serial Data in a Nanoengineered Silicon Waveguide

DEFF Research Database (Denmark)

Ji, Hua; Pu, Minhao; Hu, Hao

2011-01-01

This paper presents the experimental demonstrations of using a pure nanoengineered silicon waveguide for 1.28 Tb/s serial data optical waveform sampling and 1.28 Tb/s–10 Gb/s error free demultiplexing. The 330-fs pulses are resolved in each 780-fs time slot in waveform sampling. Error...

Holographic quantum error-correcting codes: toy models for the bulk/boundary correspondence

Energy Technology Data Exchange (ETDEWEB)

Pastawski, Fernando; Yoshida, Beni [Institute for Quantum Information & Matter and Walter Burke Institute for Theoretical Physics,California Institute of Technology,1200 E. California Blvd., Pasadena CA 91125 (United States); Harlow, Daniel [Princeton Center for Theoretical Science, Princeton University,400 Jadwin Hall, Princeton NJ 08540 (United States); Preskill, John [Institute for Quantum Information & Matter and Walter Burke Institute for Theoretical Physics,California Institute of Technology,1200 E. California Blvd., Pasadena CA 91125 (United States)

2015-06-23

We propose a family of exactly solvable toy models for the AdS/CFT correspondence based on a novel construction of quantum error-correcting codes with a tensor network structure. Our building block is a special type of tensor with maximal entanglement along any bipartition, which gives rise to an isometry from the bulk Hilbert space to the boundary Hilbert space. The entire tensor network is an encoder for a quantum error-correcting code, where the bulk and boundary degrees of freedom may be identified as logical and physical degrees of freedom respectively. These models capture key features of entanglement in the AdS/CFT correspondence; in particular, the Ryu-Takayanagi formula and the negativity of tripartite information are obeyed exactly in many cases. That bulk logical operators can be represented on multiple boundary regions mimics the Rindler-wedge reconstruction of boundary operators from bulk operators, realizing explicitly the quantum error-correcting features of AdS/CFT recently proposed in http://dx.doi.org/10.1007/JHEP04(2015)163.

Capacity estimation and verification of quantum channels with arbitrarily correlated errors.

Science.gov (United States)

Pfister, Corsin; Rol, M Adriaan; Mantri, Atul; Tomamichel, Marco; Wehner, Stephanie

2018-01-02

The central figure of merit for quantum memories and quantum communication devices is their capacity to store and transmit quantum information. Here, we present a protocol that estimates a lower bound on a channel's quantum capacity, even when there are arbitrarily correlated errors. One application of these protocols is to test the performance of quantum repeaters for transmitting quantum information. Our protocol is easy to implement and comes in two versions. The first estimates the one-shot quantum capacity by preparing and measuring in two different bases, where all involved qubits are used as test qubits. The second verifies on-the-fly that a channel's one-shot quantum capacity exceeds a minimal tolerated value while storing or communicating data. We discuss the performance using simple examples, such as the dephasing channel for which our method is asymptotically optimal. Finally, we apply our method to a superconducting qubit in experiment.

Understanding the dynamics of correct and error responses in free recall: evidence from externalized free recall.

Science.gov (United States)

Unsworth, Nash; Brewer, Gene A; Spillers, Gregory J

2010-06-01

The dynamics of correct and error responses in a variant of delayed free recall were examined in the present study. In the externalized free recall paradigm, participants were presented with lists of words and were instructed to subsequently recall not only the words that they could remember from the most recently presented list, but also any other words that came to mind during the recall period. Externalized free recall is useful for elucidating both sampling and postretrieval editing processes, thereby yielding more accurate estimates of the total number of error responses, which are typically sampled and subsequently edited during free recall. The results indicated that the participants generally sampled correct items early in the recall period and then transitioned to sampling more erroneous responses. Furthermore, the participants generally terminated their search after sampling too many errors. An examination of editing processes suggested that the participants were quite good at identifying errors, but this varied systematically on the basis of a number of factors. The results from the present study are framed in terms of generate-edit models of free recall.

Machine-learning-assisted correction of correlated qubit errors in a topological code

Directory of Open Access Journals (Sweden)

Paul Baireuther

2018-01-01

Full Text Available A fault-tolerant quantum computation requires an efficient means to detect and correct errors that accumulate in encoded quantum information. In the context of machine learning, neural networks are a promising new approach to quantum error correction. Here we show that a recurrent neural network can be trained, using only experimentally accessible data, to detect errors in a widely used topological code, the surface code, with a performance above that of the established minimum-weight perfect matching (or blossom decoder. The performance gain is achieved because the neural network decoder can detect correlations between bit-flip (X and phase-flip (Z errors. The machine learning algorithm adapts to the physical system, hence no noise model is needed. The long short-term memory layers of the recurrent neural network maintain their performance over a large number of quantum error correction cycles, making it a practical decoder for forthcoming experimental realizations of the surface code.

Towards optimal experimental tests on the reality of the quantum state

International Nuclear Information System (INIS)

Knee, George C

2017-01-01

The Barrett–Cavalcanti–Lal–Maroney (BCLM) argument stands as the most effective means of demonstrating the reality of the quantum state. Its advantages include being derived from very few assumptions, and a robustness to experimental error. Finding the best way to implement the argument experimentally is an open problem, however, and involves cleverly choosing sets of states and measurements. I show that techniques from convex optimisation theory can be leveraged to numerically search for these sets, which then form a recipe for experiments that allow for the strongest statements about the ontology of the wavefunction to be made. The optimisation approach presented is versatile, efficient and can take account of the finite errors present in any real experiment. I find significantly improved low-cardinality sets which are guaranteed partially optimal for a BCLM test in low Hilbert space dimension. I further show that mixed states can be more optimal than pure states. (paper)

Free-space communication based on quantum cascade laser

International Nuclear Information System (INIS)

Liu Chuanwei; Zhai Shenqiang; Zhang Jinchuan; Zhou Yuhong; Jia Zhiwei; Liu Fengqi; Wang Zhanguo

2015-01-01

A free-space communication based on a mid-infrared quantum cascade laser (QCL) is presented. A room-temperature continuous-wave distributed-feedback (DFB) QCL combined with a mid-infrared detector comprise the basic unit of the communication system. Sinusoidal signals at a highest frequency of 40 MHz and modulated video signals with a carrier frequency of 30 MHz were successfully transmitted with this experimental setup. Our research has provided a proof-of-concept demonstration of space optical communication application with QCL. The highest operation frequency of our setup was determined by the circuit-limited modulation bandwidth. A high performance communication system can be obtained with improved modulation circuit system. (paper)

Correcting errors in a quantum gate with pushed ions via optimal control

DEFF Research Database (Denmark)

Poulsen, Uffe Vestergaard; Sklarz, Shlomo; Tannor, David

2010-01-01

We analyze in detail the so-called pushing gate for trapped ions, introducing a time-dependent harmonic approximation for the external motion. We show how to extract the average fidelity for the gate from the resulting semiclassical simulations. We characterize and quantify precisely all types...... of errors coming from the quantum dynamics and reveal that slight nonlinearities in the ion-pushing force can have a dramatic effect on the adiabaticity of gate operation. By means of quantum optimal control techniques, we show how to suppress each of the resulting gate errors in order to reach a high...

Minimum detection efficiency for the loophole-free confirmation of quantum contextuality

International Nuclear Information System (INIS)

Xiang Yang; Hong Fang-Yu

2013-01-01

Klyachko—Can—Binicioğlu—Shumovsky (KCBS) inequality is a Bell-like inequality, the violation of which can be used to confirm the existence of quantum contextuality. However, the imperfection of detection efficiency may cause the so-called loophole in actual KCBS's experiments. We derive an alternative KCBS inequality to deal with the loophole in actual KCBS's experiments. We prove that if the experimental data violate this KCBS inequality, the loophole-free violation of the original KCBS inequality will occur. We show that the minimum detection efficiency needed for a loophole-free violation of the KCBS inequality is about 0.9738

Experimental realization of nondestructive discrimination of Bell states using a five-qubit quantum computer

Science.gov (United States)

Sisodia, Mitali; Shukla, Abhishek; Pathak, Anirban

2017-12-01

A scheme for distributed quantum measurement that allows nondestructive or indirect Bell measurement was proposed by Gupta et al [1]. In the present work, Gupta et al.'s scheme is experimentally realized using the five-qubit super-conductivity-based quantum computer, which has been recently placed in cloud by IBM Corporation. The experiment confirmed that the Bell state can be constructed and measured in a nondestructive manner with a reasonably high fidelity. A comparison of the outcomes of this study and the results obtained earlier in an NMR-based experiment (Samal et al. (2010) [10]) has also been performed. The study indicates that to make a scalable SQUID-based quantum computer, errors introduced by the gates (in the present technology) have to be reduced considerably.

Quantum optical coherence can survive photon losses using a continuous-variable quantum erasure-correcting code

DEFF Research Database (Denmark)

Lassen, Mikael Østergaard; Sabuncu, Metin; Huck, Alexander

2010-01-01

A fundamental requirement for enabling fault-tolerant quantum information processing is an efficient quantum error-correcting code that robustly protects the involved fragile quantum states from their environment. Just as classical error-correcting codes are indispensible in today's information...... technologies, it is believed that quantum error-correcting code will play a similarly crucial role in tomorrow's quantum information systems. Here, we report on the experimental demonstration of a quantum erasure-correcting code that overcomes the devastating effect of photon losses. Our quantum code is based...... on linear optics, and it protects a four-mode entangled mesoscopic state of light against erasures. We investigate two approaches for circumventing in-line losses, and demonstrate that both approaches exhibit transmission fidelities beyond what is possible by classical means. Because in-line attenuation...

Experimental investigation of practical unforgeable quantum money

Science.gov (United States)

Bozzio, Mathieu; Orieux, Adeline; Trigo Vidarte, Luis; Zaquine, Isabelle; Kerenidis, Iordanis; Diamanti, Eleni

2018-01-01

Wiesner's unforgeable quantum money scheme is widely celebrated as the first quantum information application. Based on the no-cloning property of quantum mechanics, this scheme allows for the creation of credit cards used in authenticated transactions offering security guarantees impossible to achieve by classical means. However, despite its central role in quantum cryptography, its experimental implementation has remained elusive because of the lack of quantum memories and of practical verification techniques. Here, we experimentally implement a quantum money protocol relying on classical verification that rigorously satisfies the security condition for unforgeability. Our system exploits polarization encoding of weak coherent states of light and operates under conditions that ensure compatibility with state-of-the-art quantum memories. We derive working regimes for our system using a security analysis taking into account all practical imperfections. Our results constitute a major step towards a real-world realization of this milestone protocol.

Global Estimates of Errors in Quantum Computation by the Feynman-Vernon Formalism

Science.gov (United States)

Aurell, Erik

2018-04-01

The operation of a quantum computer is considered as a general quantum operation on a mixed state on many qubits followed by a measurement. The general quantum operation is further represented as a Feynman-Vernon double path integral over the histories of the qubits and of an environment, and afterward tracing out the environment. The qubit histories are taken to be paths on the two-sphere S^2 as in Klauder's coherent-state path integral of spin, and the environment is assumed to consist of harmonic oscillators initially in thermal equilibrium, and linearly coupled to to qubit operators \\hat{S}_z . The environment can then be integrated out to give a Feynman-Vernon influence action coupling the forward and backward histories of the qubits. This representation allows to derive in a simple way estimates that the total error of operation of a quantum computer without error correction scales linearly with the number of qubits and the time of operation. It also allows to discuss Kitaev's toric code interacting with an environment in the same manner.

Global Estimates of Errors in Quantum Computation by the Feynman-Vernon Formalism

Science.gov (United States)

Aurell, Erik

2018-06-01

The operation of a quantum computer is considered as a general quantum operation on a mixed state on many qubits followed by a measurement. The general quantum operation is further represented as a Feynman-Vernon double path integral over the histories of the qubits and of an environment, and afterward tracing out the environment. The qubit histories are taken to be paths on the two-sphere S^2 as in Klauder's coherent-state path integral of spin, and the environment is assumed to consist of harmonic oscillators initially in thermal equilibrium, and linearly coupled to to qubit operators \\hat{S}_z. The environment can then be integrated out to give a Feynman-Vernon influence action coupling the forward and backward histories of the qubits. This representation allows to derive in a simple way estimates that the total error of operation of a quantum computer without error correction scales linearly with the number of qubits and the time of operation. It also allows to discuss Kitaev's toric code interacting with an environment in the same manner.

Experimental demonstration of quantum contextuality with nonentangled photons

International Nuclear Information System (INIS)

Liu, B. H.; Huang, Y. F.; Gong, Y. X.; Sun, F. W.; Zhang, Y. S.; Li, C. F.; Guo, G. C.

2009-01-01

We present an experimental test of quantum contextuality by using two-photon product states. The experimental results show that the noncontextual hidden-variable theories are violated by nonentangled states in spite of the local hidden-variable theories can be violated or not. We find that the Hong-Ou-Mandel-type quantum interference effect causes the quantum contextuality.

Quantum mechanics of a free particle beyond differential equations ...

African Journals Online (AJOL)

With Feynman's path- integral method we can obtain the quantum mechanics of a quantum system like a free particle outside Schroedinger's method of differential equations and Heisenberg's method of algebra. The work involves obtaining the quantum propagator Kf, of the system which leads to summation over infinite ...

Error modelling of quantum Hall array resistance standards

Science.gov (United States)

Marzano, Martina; Oe, Takehiko; Ortolano, Massimo; Callegaro, Luca; Kaneko, Nobu-Hisa

2018-04-01

Quantum Hall array resistance standards (QHARSs) are integrated circuits composed of interconnected quantum Hall effect elements that allow the realization of virtually arbitrary resistance values. In recent years, techniques were presented to efficiently design QHARS networks. An open problem is that of the evaluation of the accuracy of a QHARS, which is affected by contact and wire resistances. In this work, we present a general and systematic procedure for the error modelling of QHARSs, which is based on modern circuit analysis techniques and Monte Carlo evaluation of the uncertainty. As a practical example, this method of analysis is applied to the characterization of a 1 MΩ QHARS developed by the National Metrology Institute of Japan. Software tools are provided to apply the procedure to other arrays.

High-speed noise-free optical quantum memory

Science.gov (United States)

Kaczmarek, K. T.; Ledingham, P. M.; Brecht, B.; Thomas, S. E.; Thekkadath, G. S.; Lazo-Arjona, O.; Munns, J. H. D.; Poem, E.; Feizpour, A.; Saunders, D. J.; Nunn, J.; Walmsley, I. A.

2018-04-01

Optical quantum memories are devices that store and recall quantum light and are vital to the realization of future photonic quantum networks. To date, much effort has been put into improving storage times and efficiencies of such devices to enable long-distance communications. However, less attention has been devoted to building quantum memories which add zero noise to the output. Even small additional noise can render the memory classical by destroying the fragile quantum signatures of the stored light. Therefore, noise performance is a critical parameter for all quantum memories. Here we introduce an intrinsically noise-free quantum memory protocol based on two-photon off-resonant cascaded absorption (ORCA). We demonstrate successful storage of GHz-bandwidth heralded single photons in a warm atomic vapor with no added noise, confirmed by the unaltered photon-number statistics upon recall. Our ORCA memory meets the stringent noise requirements for quantum memories while combining high-speed and room-temperature operation with technical simplicity, and therefore is immediately applicable to low-latency quantum networks.

Quantum teleportation and entanglement. A hybrid approach to optical quantum information procesing

Energy Technology Data Exchange (ETDEWEB)

Furusawa, Akira [Tokyo Univ. (Japan). Dept. of Applied Physics; Loock, Peter van [Erlangen-Nuernberg Univ. (Germany). Lehrstuhl fuer Optik

2011-07-01

Unique in that it is jointly written by an experimentalist and a theorist, this monograph presents universal quantum computation based on quantum teleportation as an elementary subroutine and multi-party entanglement as a universal resource. Optical approaches to measurement-based quantum computation are also described, including schemes for quantum error correction, with most of the experiments carried out by the authors themselves. Ranging from the theoretical background to the details of the experimental realization, the book describes results and advances in the field, backed by numerous illustrations of the authors' experimental setups. Aimed at researchers, physicists, and graduate and PhD students in physics, theoretical quantum optics, quantum mechanics, and quantum information. (orig.)

Experimental quantum computing without entanglement.

Science.gov (United States)

Lanyon, B P; Barbieri, M; Almeida, M P; White, A G

2008-11-14

Deterministic quantum computation with one pure qubit (DQC1) is an efficient model of computation that uses highly mixed states. Unlike pure-state models, its power is not derived from the generation of a large amount of entanglement. Instead it has been proposed that other nonclassical correlations are responsible for the computational speedup, and that these can be captured by the quantum discord. In this Letter we implement DQC1 in an all-optical architecture, and experimentally observe the generated correlations. We find no entanglement, but large amounts of quantum discord-except in three cases where an efficient classical simulation is always possible. Our results show that even fully separable, highly mixed, states can contain intrinsically quantum mechanical correlations and that these could offer a valuable resource for quantum information technologies.

Do Free Quantum-Mechanical Wave Packets Always Spread?

Science.gov (United States)

Klein, James R.

1980-01-01

The spreading or shrinking of free three-dimensional quantum-mechanical wave packets is addressed. A seeming paradox concerning the time evolution operator and nonspreading wave packets is discussed, and the necessity of taking into account the appropriate mathematical structure of quantum mechanics is emphasized. Teaching implications are given.…

Quantum Computing in Decoherence-Free Subspace Constructed by Triangulation

OpenAIRE

Bi, Qiao; Guo, Liu; Ruda, H. E.

2010-01-01

A formalism for quantum computing in decoherence-free subspaces is presented. The constructed subspaces are partial triangulated to an index related to environment. The quantum states in the subspaces are just projected states which are ruled by a subdynamic kinetic equation. These projected states can be used to perform ideal quantum logical operations without decoherence.

Experimental status of quantum electrodynamics

International Nuclear Information System (INIS)

Drell, S.D.

1980-01-01

The speech of Drell S. on the symposium dedicated to 60th anniversary of Schwinger J. is presented. The fundamental status of the hero of the day in quantum field theory, which turned into quantum electrodynamics, are stated. The theory has been perfectly experimentally confirmed and now is the main model permitting to explain weak and strong interactions. The attention is paid on the difference between theoretical and experimental values of the electron anomalous magnetic moment (asub(e)) obtained in the sixth order of perturbation theory. It is necessary to carry out calculations in the octic order of the perturbation theory in order to obtain more precise value of asub(e). The theory and the experimental difference is demonstrated on the example of estimation of fine and hyperfine structure of hydrogen, muonium, and positronium

Continuous quantum error correction for non-Markovian decoherence

International Nuclear Information System (INIS)

Oreshkov, Ognyan; Brun, Todd A.

2007-01-01

We study the effect of continuous quantum error correction in the case where each qubit in a codeword is subject to a general Hamiltonian interaction with an independent bath. We first consider the scheme in the case of a trivial single-qubit code, which provides useful insights into the workings of continuous error correction and the difference between Markovian and non-Markovian decoherence. We then study the model of a bit-flip code with each qubit coupled to an independent bath qubit and subject to continuous correction, and find its solution. We show that for sufficiently large error-correction rates, the encoded state approximately follows an evolution of the type of a single decohering qubit, but with an effectively decreased coupling constant. The factor by which the coupling constant is decreased scales quadratically with the error-correction rate. This is compared to the case of Markovian noise, where the decoherence rate is effectively decreased by a factor which scales only linearly with the rate of error correction. The quadratic enhancement depends on the existence of a Zeno regime in the Hamiltonian evolution which is absent in purely Markovian dynamics. We analyze the range of validity of this result and identify two relevant time scales. Finally, we extend the result to more general codes and argue that the performance of continuous error correction will exhibit the same qualitative characteristics

Quantum computing with trapped ions

International Nuclear Information System (INIS)

Haeffner, H.; Roos, C.F.; Blatt, R.

2008-01-01

Quantum computers hold the promise of solving certain computational tasks much more efficiently than classical computers. We review recent experimental advances towards a quantum computer with trapped ions. In particular, various implementations of qubits, quantum gates and some key experiments are discussed. Furthermore, we review some implementations of quantum algorithms such as a deterministic teleportation of quantum information and an error correction scheme

Quantum cryptography as a retrodiction problem.

Science.gov (United States)

Werner, A H; Franz, T; Werner, R F

2009-11-27

We propose a quantum key distribution protocol based on a quantum retrodiction protocol, known as the Mean King problem. The protocol uses a two way quantum channel. We show security against coherent attacks in a transmission-error free scenario, even if Eve is allowed to attack both transmissions. This establishes a connection between retrodiction and key distribution.

Error-Free Text Typing Performance of an Inductive Intra-Oral Tongue Computer Interface for Severely Disabled Individuals.

Science.gov (United States)

Andreasen Struijk, Lotte N S; Bentsen, Bo; Gaihede, Michael; Lontis, Eugen R

2017-11-01

For severely paralyzed individuals, alternative computer interfaces are becoming increasingly essential for everyday life as social and vocational activities are facilitated by information technology and as the environment becomes more automatic and remotely controllable. Tongue computer interfaces have proven to be desirable by the users partly due to their high degree of aesthetic acceptability, but so far the mature systems have shown a relatively low error-free text typing efficiency. This paper evaluated the intra-oral inductive tongue computer interface (ITCI) in its intended use: Error-free text typing in a generally available text editing system, Word. Individuals with tetraplegia and able bodied individuals used the ITCI for typing using a MATLAB interface and for Word typing for 4 to 5 experimental days, and the results showed an average error-free text typing rate in Word of 11.6 correct characters/min across all participants and of 15.5 correct characters/min for participants familiar with tongue piercings. Improvements in typing rates between the sessions suggest that typing ratescan be improved further through long-term use of the ITCI.

Quantum Computing in Decoherence-Free Subspace Constructed by Triangulation

Directory of Open Access Journals (Sweden)

Qiao Bi

2010-01-01

Full Text Available A formalism for quantum computing in decoherence-free subspaces is presented. The constructed subspaces are partial triangulated to an index related to environment. The quantum states in the subspaces are just projected states which are ruled by a subdynamic kinetic equation. These projected states can be used to perform ideal quantum logical operations without decoherence.

Practical scheme to share a secret key through a quantum channel with a 27.6% bit error rate

International Nuclear Information System (INIS)

Chau, H.F.

2002-01-01

A secret key shared through quantum key distribution between two cooperative players is secure against any eavesdropping attack allowed by the laws of physics. Yet, such a key can be established only when the quantum channel error rate due to eavesdropping or imperfect apparatus is low. Here, a practical quantum key distribution scheme by making use of an adaptive privacy amplification procedure with two-way classical communication is reported. Then, it is proven that the scheme generates a secret key whenever the bit error rate of the quantum channel is less than 0.5-0.1√(5)≅27.6%, thereby making it the most error resistant scheme known to date

Quantum-Enhanced Cyber Security: Experimental Computation on Quantum-Encrypted Data

Science.gov (United States)

2017-03-02

AFRL-AFOSR-UK-TR-2017-0020 Quantum-Enhanced Cyber Security: Experimental Computation on Quantum- Encrypted Data Philip Walther UNIVERSITT WIEN Final...on Quantum- Encrypted Data 5a.  CONTRACT NUMBER 5b.  GRANT NUMBER FA9550-16-1-0004 5c.  PROGRAM ELEMENT NUMBER 61102F 6. AUTHOR(S) Philip Walther 5d...1010 AT 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) EOARD Unit 4515 APO AE 09421-4515 10

Topological quantum computing with a very noisy network and local error rates approaching one percent.

Science.gov (United States)

Nickerson, Naomi H; Li, Ying; Benjamin, Simon C

2013-01-01

A scalable quantum computer could be built by networking together many simple processor cells, thus avoiding the need to create a single complex structure. The difficulty is that realistic quantum links are very error prone. A solution is for cells to repeatedly communicate with each other and so purify any imperfections; however prior studies suggest that the cells themselves must then have prohibitively low internal error rates. Here we describe a method by which even error-prone cells can perform purification: groups of cells generate shared resource states, which then enable stabilization of topologically encoded data. Given a realistically noisy network (≥10% error rate) we find that our protocol can succeed provided that intra-cell error rates for initialisation, state manipulation and measurement are below 0.82%. This level of fidelity is already achievable in several laboratory systems.

Free-space entangled quantum carpets

Science.gov (United States)

Barros, Mariana R.; Ketterer, Andreas; Farías, Osvaldo Jiménez; Walborn, Stephen P.

2017-04-01

The Talbot effect in quantum physics is known to produce intricate patterns in the probability distribution of a particle, known as "quantum carpets," corresponding to the revival and replication of the initial wave function. Recently, it was shown that one can encode a D -level qudit in such a way that the Talbot effect can be used to process the D -dimensional quantum information [Farías et al., Phys. Rev. A 91, 062328 (2015), 10.1103/PhysRevA.91.062328]. Here we introduce a scheme to produce free-propagating "entangled quantum carpets" with pairs of photons produced by spontaneous parametric down-conversion. First we introduce an optical device that can be used to synthesize arbitrary superposition states of Talbot qudits. Sending spatially entangled photon pairs through a pair of these devices produces an entangled pair of qudits. As an application, we show how the Talbot effect can be used to test a D -dimensional Bell inequality. Numerical simulations show that violation of the Bell inequality depends strongly on the amount of spatial correlation in the initial two-photon state. We briefly discuss how our optical scheme might be adapted to matter wave experiments.

Block-free optical quantum Banyan network based on quantum state fusion and fission

International Nuclear Information System (INIS)

Zhu Chang-Hua; Meng Yan-Hong; Quan Dong-Xiao; Zhao Nan; Pei Chang-Xing

2014-01-01

Optical switch fabric plays an important role in building multiple-user optical quantum communication networks. Owing to its self-routing property and low complexity, a banyan network is widely used for building switch fabric. While, there is no efficient way to remove internal blocking in a banyan network in a classical way, quantum state fusion, by which the two-dimensional internal quantum states of two photons could be combined into a four-dimensional internal state of a single photon, makes it possible to solve this problem. In this paper, we convert the output mode of quantum state fusion from spatial-polarization mode into time-polarization mode. By combining modified quantum state fusion and quantum state fission with quantum Fredkin gate, we propose a practical scheme to build an optical quantum switch unit which is block free. The scheme can be extended to building more complex units, four of which are shown in this paper. (general)

Long distance free-space quantum key distribution

International Nuclear Information System (INIS)

Schmitt-Manderbach, T.

2007-01-01

The aim of the presented experiment was to investigate the feasibility of satellite-based global quantum key distribution. In this context, a free-space quantum key distribution experiment over a real distance of 144 km was performed. The transmitter and the receiver were situated in 2500 m altitude on the Canary Islands of La Palma and Tenerife, respectively. The small and compact transmitter unit generated attenuated laser pulses, that were sent to the receiver via a 15-cm optical telescope. The receiver unit for polarisation analysis and detection of the sent pulses was integrated into an existing mirror telescope designed for classical optical satellite communications. To ensure the required stability and efficiency of the optical link in the presence of atmospheric turbulence, the two telescopes were equipped with a bi-directional automatic tracking system. Still, due to stray light and high optical attenuation, secure key exchange would not be possible using attenuated pulses in connection with the standard BB84 protocol. The photon number statistics of attenuated pulses follows a Poissonian distribution. Hence, by removing a photon from all pulses containing two or more photons, an eavesdropper could measure its polarisation without disturbing the polarisation state of the remaining pulse. In this way, he can gain information about the key without introducing detectable errors. To protect against such attacks, the presented experiment employed the recently developed method of using additional ''decoy'' states, i.e., the the intensity of the pulses created by the transmitter were varied in a random manner. By analysing the detection probabilities of the different pulses individually, a photon-number-splitting attack can be detected. Thanks to the decoy-state analysis, the secrecy of the resulting quantum key could be ensured despite the Poissonian nature of the emitted pulses. For a channel attenuation as high as 35 dB, a secret key rate of up to 250 bit

Long distance free-space quantum key distribution

Energy Technology Data Exchange (ETDEWEB)

Schmitt-Manderbach, T.

2007-10-16

The aim of the presented experiment was to investigate the feasibility of satellite-based global quantum key distribution. In this context, a free-space quantum key distribution experiment over a real distance of 144 km was performed. The transmitter and the receiver were situated in 2500 m altitude on the Canary Islands of La Palma and Tenerife, respectively. The small and compact transmitter unit generated attenuated laser pulses, that were sent to the receiver via a 15-cm optical telescope. The receiver unit for polarisation analysis and detection of the sent pulses was integrated into an existing mirror telescope designed for classical optical satellite communications. To ensure the required stability and efficiency of the optical link in the presence of atmospheric turbulence, the two telescopes were equipped with a bi-directional automatic tracking system. Still, due to stray light and high optical attenuation, secure key exchange would not be possible using attenuated pulses in connection with the standard BB84 protocol. The photon number statistics of attenuated pulses follows a Poissonian distribution. Hence, by removing a photon from all pulses containing two or more photons, an eavesdropper could measure its polarisation without disturbing the polarisation state of the remaining pulse. In this way, he can gain information about the key without introducing detectable errors. To protect against such attacks, the presented experiment employed the recently developed method of using additional 'decoy' states, i.e., the the intensity of the pulses created by the transmitter were varied in a random manner. By analysing the detection probabilities of the different pulses individually, a photon-number-splitting attack can be detected. Thanks to the decoy-state analysis, the secrecy of the resulting quantum key could be ensured despite the Poissonian nature of the emitted pulses. For a channel attenuation as high as 35 dB, a secret key rate of up to 250

Towards a quantum internet

Science.gov (United States)

Dür, Wolfgang; Lamprecht, Raphael; Heusler, Stefan

2017-07-01

A long-range quantum communication network is among the most promising applications of emerging quantum technologies. We discuss the potential of such a quantum internet for the secure transmission of classical and quantum information, as well as theoretical and experimental approaches and recent advances to realize them. We illustrate the involved concepts such as error correction, teleportation or quantum repeaters and consider an approach to this topic based on catchy visualizations as a context-based, modern treatment of quantum theory at high school.

The concept of free electromagnetic field in quantum domain

OpenAIRE

SHUMOVSKY, Alexander; MÜSTECAPLIOĞLU, Özgür

1999-01-01

By virtue of the consideration of polarization and phase properties of dipole radiation in the quantum domain, it is shown that the concept of free electromagnetic field should be considered as a quite risky approximation in the description of quantum fluctuations of some physical observables.

Experimental tests of quantum chromodynamics

International Nuclear Information System (INIS)

Dorfan, J.

1987-04-01

Experimental tests of quantum chromodynamics are discussed in the e + e - continuum, in pp and anti p p collisions, in measurements of α/sub s/ from Υ decays, in deep inelastic lepton scattering, and in the measurement of the photon structure function. A large body of data relating to the testing of quantum chromodynamics is reviewed, showing qualitative agreement between the data from a wide range of processes and QCD. 66 refs., 79 figs

Experimental realization of universal geometric quantum gates with solid-state spins.

Science.gov (United States)

Zu, C; Wang, W-B; He, L; Zhang, W-G; Dai, C-Y; Wang, F; Duan, L-M

2014-10-02

Experimental realization of a universal set of quantum logic gates is the central requirement for the implementation of a quantum computer. In an 'all-geometric' approach to quantum computation, the quantum gates are implemented using Berry phases and their non-Abelian extensions, holonomies, from geometric transformation of quantum states in the Hilbert space. Apart from its fundamental interest and rich mathematical structure, the geometric approach has some built-in noise-resilience features. On the experimental side, geometric phases and holonomies have been observed in thermal ensembles of liquid molecules using nuclear magnetic resonance; however, such systems are known to be non-scalable for the purposes of quantum computing. There are proposals to implement geometric quantum computation in scalable experimental platforms such as trapped ions, superconducting quantum bits and quantum dots, and a recent experiment has realized geometric single-bit gates in a superconducting system. Here we report the experimental realization of a universal set of geometric quantum gates using the solid-state spins of diamond nitrogen-vacancy centres. These diamond defects provide a scalable experimental platform with the potential for room-temperature quantum computing, which has attracted strong interest in recent years. Our experiment shows that all-geometric and potentially robust quantum computation can be realized with solid-state spin quantum bits, making use of recent advances in the coherent control of this system.

On lattices, learning with errors, cryptography, and quantum

International Nuclear Information System (INIS)

Regev, O.

2004-01-01

Full Text:Our main result is a reduction from worst-case lattice problems such as SVP and SIVP to a certain learning problem. This learning problem is a natural extension of the 'learning from parity with error' problem to higher moduli. It can also be viewed as the problem of decoding from a random linear code. This, we believe, gives a strong indication that these problems are hard. Our reduction, however, is quantum. Hence, an efficient solution to the learning problem implies a quantum algorithm for SVP and SIVP. A main open question is whether this reduction can be made classical. Using the main result, we obtain a public-key cryptosystem whose hardness is based on the worst-case quantum hardness of SVP and SIVP. Previous lattice-based public-key cryptosystems such as the one by Ajtai and Dwork were only based on unique-SVP, a special case of SVP. The new cryptosystem is much more efficient than previous cryptosystems: the public key is of size Ο((n 2 ) and encrypting a message increases its size by Ο((n) (in previous cryptosystems these values are Ο((n 4 ) and Ο(n 2 ), respectively)

Quantum phase transition of the transverse-field quantum Ising model on scale-free networks.

Science.gov (United States)

Yi, Hangmo

2015-01-01

I investigate the quantum phase transition of the transverse-field quantum Ising model in which nearest neighbors are defined according to the connectivity of scale-free networks. Using a continuous-time quantum Monte Carlo simulation method and the finite-size scaling analysis, I identify the quantum critical point and study its scaling characteristics. For the degree exponent λ=6, I obtain results that are consistent with the mean-field theory. For λ=4.5 and 4, however, the results suggest that the quantum critical point belongs to a non-mean-field universality class. Further simulations indicate that the quantum critical point remains mean-field-like if λ>5, but it continuously deviates from the mean-field theory as λ becomes smaller.

Error-Transparent Quantum Gates for Small Logical Qubit Architectures

Science.gov (United States)

Kapit, Eliot

2018-02-01

One of the largest obstacles to building a quantum computer is gate error, where the physical evolution of the state of a qubit or group of qubits during a gate operation does not match the intended unitary transformation. Gate error stems from a combination of control errors and random single qubit errors from interaction with the environment. While great strides have been made in mitigating control errors, intrinsic qubit error remains a serious problem that limits gate fidelity in modern qubit architectures. Simultaneously, recent developments of small error-corrected logical qubit devices promise significant increases in logical state lifetime, but translating those improvements into increases in gate fidelity is a complex challenge. In this Letter, we construct protocols for gates on and between small logical qubit devices which inherit the parent device's tolerance to single qubit errors which occur at any time before or during the gate. We consider two such devices, a passive implementation of the three-qubit bit flip code, and the author's own [E. Kapit, Phys. Rev. Lett. 116, 150501 (2016), 10.1103/PhysRevLett.116.150501] very small logical qubit (VSLQ) design, and propose error-tolerant gate sets for both. The effective logical gate error rate in these models displays superlinear error reduction with linear increases in single qubit lifetime, proving that passive error correction is capable of increasing gate fidelity. Using a standard phenomenological noise model for superconducting qubits, we demonstrate a realistic, universal one- and two-qubit gate set for the VSLQ, with error rates an order of magnitude lower than those for same-duration operations on single qubits or pairs of qubits. These developments further suggest that incorporating small logical qubits into a measurement based code could substantially improve code performance.

Experimental demonstration of deterministic one-way quantum computing on a NMR quantum computer

OpenAIRE

Ju, Chenyong; Zhu, Jing; Peng, Xinhua; Chong, Bo; Zhou, Xianyi; Du, Jiangfeng

2008-01-01

One-way quantum computing is an important and novel approach to quantum computation. By exploiting the existing particle-particle interactions, we report the first experimental realization of the complete process of deterministic one-way quantum Deutsch-Josza algorithm in NMR, including graph state preparation, single-qubit measurements and feed-forward corrections. The findings in our experiment may shed light on the future scalable one-way quantum computation.

Quantum computing with four-particle decoherence-free states in ion trap

OpenAIRE

Feng, Mang; Wang, Xiaoguang

2001-01-01

Quantum computing gates are proposed to apply on trapped ions in decoherence-free states. As phase changes due to time evolution of components with different eigenenergies of quantum superposition are completely frozen, quantum computing based on this model would be perfect. Possible application of our scheme in future ion-trap quantum computer is discussed.

Inhomogeneous effects in the quantum free electron laser

International Nuclear Information System (INIS)

Piovella, N.; Bonifacio, R.

2006-01-01

We include inhomogeneous effects in the quantum model of a free electron laser taking into account the initial energy spread of the electron beam. From a linear analysis, we obtain a generalized dispersion relation, from which the exponential gain can be explicitly calculated. We determine the maximum allowed initial energy spread in the quantum exponential regime and we discuss the limit of large energy spread

Integrated Quantum Optics: Experiments towards integrated quantum-light sources and quantum-enhanced sensing

DEFF Research Database (Denmark)

Hoff, Ulrich Busk

The work presented in this thesis is focused on experimental application and generation of continuous variable quantum correlated states of light in integrated dielectric structures. Squeezed states are among the most exploited continuous variable optical states for free-space quantum-enhanced se...... is presented and an optimized device design is proposed. The devices have been fabricated and tested optically and preliminary interrogations of the output quantum noise have been performed....

Macroscopic quantum mechanics: theory and experimental concepts of optomechanics

International Nuclear Information System (INIS)

Chen Yanbei

2013-01-01

Rapid experimental progress has recently allowed the use of light to prepare macroscopic mechanical objects into nearly pure quantum states. This research field of quantum optomechanics opens new doors towards testing quantum mechanics, and possibly other laws of physics, in new regimes. In the first part of this article, I will review a set of techniques of quantum measurement theory that are often used to analyse quantum optomechanical systems. Some of these techniques were originally designed to analyse how a classical driving force passes through a quantum system, and can eventually be detected with an optimal signal-to-noise ratio—while others focus more on the quantum-state evolution of a mechanical object under continuous monitoring. In the second part of this article, I will review a set of experimental concepts that will demonstrate quantum mechanical behaviour of macroscopic objects—quantum entanglement, quantum teleportation and the quantum Zeno effect. Taking the interplay between gravity and quantum mechanics as an example, I will review a set of speculations on how quantum mechanics can be modified for macroscopic objects, and how these speculations—and their generalizations—might be tested by optomechanics. (invited review)

Experimental demonstration of selective quantum process tomography on an NMR quantum information processor

Science.gov (United States)

Gaikwad, Akshay; Rehal, Diksha; Singh, Amandeep; Arvind, Dorai, Kavita

2018-02-01

We present the NMR implementation of a scheme for selective and efficient quantum process tomography without ancilla. We generalize this scheme such that it can be implemented efficiently using only a set of measurements involving product operators. The method allows us to estimate any element of the quantum process matrix to a desired precision, provided a set of quantum states can be prepared efficiently. Our modified technique requires fewer experimental resources as compared to the standard implementation of selective and efficient quantum process tomography, as it exploits the special nature of NMR measurements to allow us to compute specific elements of the process matrix by a restrictive set of subsystem measurements. To demonstrate the efficacy of our scheme, we experimentally tomograph the processes corresponding to "no operation," a controlled-NOT (CNOT), and a controlled-Hadamard gate on a two-qubit NMR quantum information processor, with high fidelities.

Statistical analysis of error rate of large-scale single flux quantum logic circuit by considering fluctuation of timing parameters

International Nuclear Information System (INIS)

Yamanashi, Yuki; Masubuchi, Kota; Yoshikawa, Nobuyuki

2016-01-01

The relationship between the timing margin and the error rate of the large-scale single flux quantum logic circuits is quantitatively investigated to establish a timing design guideline. We observed that the fluctuation in the set-up/hold time of single flux quantum logic gates caused by thermal noises is the most probable origin of the logical error of the large-scale single flux quantum circuit. The appropriate timing margin for stable operation of the large-scale logic circuit is discussed by taking the fluctuation of setup/hold time and the timing jitter in the single flux quantum circuits. As a case study, the dependence of the error rate of the 1-million-bit single flux quantum shift register on the timing margin is statistically analyzed. The result indicates that adjustment of timing margin and the bias voltage is important for stable operation of a large-scale SFQ logic circuit.

Statistical analysis of error rate of large-scale single flux quantum logic circuit by considering fluctuation of timing parameters

Energy Technology Data Exchange (ETDEWEB)

Yamanashi, Yuki, E-mail: yamanasi@ynu.ac.jp [Department of Electrical and Computer Engineering, Yokohama National University, Tokiwadai 79-5, Hodogaya-ku, Yokohama 240-8501 (Japan); Masubuchi, Kota; Yoshikawa, Nobuyuki [Department of Electrical and Computer Engineering, Yokohama National University, Tokiwadai 79-5, Hodogaya-ku, Yokohama 240-8501 (Japan)

2016-11-15

The relationship between the timing margin and the error rate of the large-scale single flux quantum logic circuits is quantitatively investigated to establish a timing design guideline. We observed that the fluctuation in the set-up/hold time of single flux quantum logic gates caused by thermal noises is the most probable origin of the logical error of the large-scale single flux quantum circuit. The appropriate timing margin for stable operation of the large-scale logic circuit is discussed by taking the fluctuation of setup/hold time and the timing jitter in the single flux quantum circuits. As a case study, the dependence of the error rate of the 1-million-bit single flux quantum shift register on the timing margin is statistically analyzed. The result indicates that adjustment of timing margin and the bias voltage is important for stable operation of a large-scale SFQ logic circuit.

Optimization of Trade-offs in Error-free Image Transmission

Science.gov (United States)

Cox, Jerome R.; Moore, Stephen M.; Blaine, G. James; Zimmerman, John B.; Wallace, Gregory K.

1989-05-01

The availability of ubiquitous wide-area channels of both modest cost and higher transmission rate than voice-grade lines promises to allow the expansion of electronic radiology services to a larger community. The band-widths of the new services becoming available from the Integrated Services Digital Network (ISDN) are typically limited to 128 Kb/s, almost two orders of magnitude lower than popular LANs can support. Using Discrete Cosine Transform (DCT) techniques, a compressed approximation to an image may be rapidly transmitted. However, intensity or resampling transformations of the reconstructed image may reveal otherwise invisible artifacts of the approximate encoding. A progressive transmission scheme reported in ISO Working Paper N800 offers an attractive solution to this problem by rapidly reconstructing an apparently undistorted image from the DCT coefficients and then subse-quently transmitting the error image corresponding to the difference between the original and the reconstructed images. This approach achieves an error-free transmission without sacrificing the perception of rapid image delivery. Furthermore, subsequent intensity and resampling manipulations can be carried out with confidence. DCT coefficient precision affects the amount of error information that must be transmitted and, hence the delivery speed of error-free images. This study calculates the overall information coding rate for six radiographic images as a function of DCT coefficient precision. The results demonstrate that a minimum occurs for each of the six images at an average coefficient precision of between 0.5 and 1.0 bits per pixel (b/p). Apparently undistorted versions of these six images can be transmitted with a coding rate of between 0.25 and 0.75 b/p while error-free versions can be transmitted with an overall coding rate between 4.5 and 6.5 b/p.

Towards experimental quantum-field tomography with ultracold atoms.

Science.gov (United States)

Steffens, A; Friesdorf, M; Langen, T; Rauer, B; Schweigler, T; Hübener, R; Schmiedmayer, J; Riofrío, C A; Eisert, J

2015-07-03

The experimental realization of large-scale many-body systems in atomic-optical architectures has seen immense progress in recent years, rendering full tomography tools for state identification inefficient, especially for continuous systems. To work with these emerging physical platforms, new technologies for state identification are required. Here we present first steps towards efficient experimental quantum-field tomography. Our procedure is based on the continuous analogues of matrix-product states, ubiquitous in condensed-matter theory. These states naturally incorporate the locality present in realistic physical settings and are thus prime candidates for describing the physics of locally interacting quantum fields. To experimentally demonstrate the power of our procedure, we quench a one-dimensional Bose gas by a transversal split and use our method for a partial quantum-field reconstruction of the far-from-equilibrium states of this system. We expect our technique to play an important role in future studies of continuous quantum many-body systems.

Experimental status of quantum electrodynamics

International Nuclear Information System (INIS)

Drell, S.D.

1978-10-01

This review of the experimental status of quantum electrodynamics covers the fine structure constant, the muon g-2 value, the Lamb shift in hydrogen, the finite proton radius, progress in muonium, and positronium. 37 references

Design of nanophotonic circuits for autonomous subsystem quantum error correction

Energy Technology Data Exchange (ETDEWEB)

Kerckhoff, J; Pavlichin, D S; Chalabi, H; Mabuchi, H, E-mail: jkerc@stanford.edu [Edward L Ginzton Laboratory, Stanford University, Stanford, CA 94305 (United States)

2011-05-15

We reapply our approach to designing nanophotonic quantum memories in order to formulate an optical network that autonomously protects a single logical qubit against arbitrary single-qubit errors. Emulating the nine-qubit Bacon-Shor subsystem code, the network replaces the traditionally discrete syndrome measurement and correction steps by continuous, time-independent optical interactions and coherent feedback of unitarily processed optical fields.

Information-preserving structures: A general framework for quantum zero-error information

International Nuclear Information System (INIS)

Blume-Kohout, Robin; Ng, Hui Khoon; Poulin, David; Viola, Lorenza

2010-01-01

Quantum systems carry information. Quantum theory supports at least two distinct kinds of information (classical and quantum), and a variety of different ways to encode and preserve information in physical systems. A system's ability to carry information is constrained and defined by the noise in its dynamics. This paper introduces an operational framework, using information-preserving structures, to classify all the kinds of information that can be perfectly (i.e., with zero error) preserved by quantum dynamics. We prove that every perfectly preserved code has the same structure as a matrix algebra, and that preserved information can always be corrected. We also classify distinct operational criteria for preservation (e.g., 'noiseless','unitarily correctible', etc.) and introduce two natural criteria for measurement-stabilized and unconditionally preserved codes. Finally, for several of these operational criteria, we present efficient (polynomial in the state-space dimension) algorithms to find all of a channel's information-preserving structures.

25 Gbit/s differential phase-shift-keying signal generation using directly modulated quantum-dot semiconductor optical amplifiers

International Nuclear Information System (INIS)

Zeghuzi, A.; Schmeckebier, H.; Stubenrauch, M.; Bimberg, D.; Meuer, C.; Schubert, C.; Bunge, C.-A.

2015-01-01

Error-free generation of 25-Gbit/s differential phase-shift keying (DPSK) signals via direct modulation of InAs quantum-dot (QD) based semiconductor optical amplifiers (SOAs) is experimentally demonstrated with an input power level of −5 dBm. The QD SOAs emit in the 1.3-μm wavelength range and provide a small-signal fiber-to-fiber gain of 8 dB. Furthermore, error-free DPSK modulation is achieved for constant optical input power levels from 3 dBm down to only −11 dBm for a bit rate of 20 Gbit/s. Direct phase modulation of QD SOAs via current changes is thus demonstrated to be much faster than direct gain modulation

Experimental quantum ratchets based on solid state nanostructures

International Nuclear Information System (INIS)

Linke, H.

1999-01-01

Ratchets are spatially asymmetric devices in which particles can move on average in one direction in the absence of external net forces or gradients. This is made possible by the rectification of fluctuations, which also provide the energy for the process. Interest in the physics of ratchets was revived in recent years when it emerged that the ratchet principle may be a suitable physical model for 'molecular motors', which are central to many fundamental biological processes, such as intracellular transport or muscle contraction. Most ratchets studied so far have relied on classical effects, but recently 'quantum ratchets', involving quantum effects, have also been studied. In the present article it is pointed out that semiconductor or metal nanostructures are very suitable systems for the realisation of experimental quantum ratchets. Recent experimental studies of a quantum ratchet based on an asymmetric quantum dot are reviewed. Copyright (1999) CSIRO Australia

Quantum money with nearly optimal error tolerance

Science.gov (United States)

Amiri, Ryan; Arrazola, Juan Miguel

2017-06-01

We present a family of quantum money schemes with classical verification which display a number of benefits over previous proposals. Our schemes are based on hidden matching quantum retrieval games and they tolerate noise up to 23 % , which we conjecture reaches 25 % asymptotically as the dimension of the underlying hidden matching states is increased. Furthermore, we prove that 25 % is the maximum tolerable noise for a wide class of quantum money schemes with classical verification, meaning our schemes are almost optimally noise tolerant. We use methods in semidefinite programming to prove security in a substantially different manner to previous proposals, leading to two main advantages: first, coin verification involves only a constant number of states (with respect to coin size), thereby allowing for smaller coins; second, the reusability of coins within our scheme grows linearly with the size of the coin, which is known to be optimal. Last, we suggest methods by which the coins in our protocol could be implemented using weak coherent states and verified using existing experimental techniques, even in the presence of detector inefficiencies.

Experimental verification of multidimensional quantum steering

Science.gov (United States)

Li, Che-Ming; Lo, Hsin-Pin; Chen, Liang-Yu; Yabushita, Atsushi

2018-03-01

Quantum steering enables one party to communicate with another remote party even if the sender is untrusted. Such characteristics of quantum systems not only provide direct applications to quantum information science, but are also conceptually important for distinguishing between quantum and classical resources. While concrete illustrations of steering have been shown in several experiments, quantum steering has not been certified for higher dimensional systems. Here, we introduce a simple method to experimentally certify two different kinds of quantum steering: Einstein-Podolsky-Rosen (EPR) steering and single-system (SS) steering (i.e., temporal steering), for dimensionality (d) up to d = 16. The former reveals the steerability among bipartite systems, whereas the latter manifests itself in single quantum objects. We use multidimensional steering witnesses to verify EPR steering of polarization-entangled pairs and SS steering of single photons. The ratios between the measured witnesses and the maximum values achieved by classical mimicries are observed to increase with d for both EPR and SS steering. The designed scenario offers a new method to study further the genuine multipartite steering of large dimensionality and potential uses in quantum information processing.

Discretization errors at free boundaries of the Grad-Schlueter-Shafranov equation

International Nuclear Information System (INIS)

Meyer-Spasche, R.; Fornberg, B.

1990-10-01

The numerical error of standard finite-difference schemes is analyzed at free boundaries of the Grad-Schlueter-Shafranov equation of plasma physics. A simple correction strategy is devised to eliminate (to leading order) the errors which arise as the free boundary crosses the rectangular grid at irregular locations. The resulting scheme can be solved by Gauss-Newton or Inverse iterations, or by multigrid iterations. Extrapolation (from 2nd to 3rd order of accuracy) is possible for the new scheme. (orig.)

Constitutive error based parameter estimation technique for plate structures using free vibration signatures

Science.gov (United States)

Guchhait, Shyamal; Banerjee, Biswanath

2018-04-01

In this paper, a variant of constitutive equation error based material parameter estimation procedure for linear elastic plates is developed from partially measured free vibration sig-natures. It has been reported in many research articles that the mode shape curvatures are much more sensitive compared to mode shape themselves to localize inhomogeneity. Complying with this idea, an identification procedure is framed as an optimization problem where the proposed cost function measures the error in constitutive relation due to incompatible curvature/strain and moment/stress fields. Unlike standard constitutive equation error based procedure wherein a solution of a couple system is unavoidable in each iteration, we generate these incompatible fields via two linear solves. A simple, yet effective, penalty based approach is followed to incorporate measured data. The penalization parameter not only helps in incorporating corrupted measurement data weakly but also acts as a regularizer against the ill-posedness of the inverse problem. Explicit linear update formulas are then developed for anisotropic linear elastic material. Numerical examples are provided to show the applicability of the proposed technique. Finally, an experimental validation is also provided.

A method for optical ground station reduce alignment error in satellite-ground quantum experiments

Science.gov (United States)

He, Dong; Wang, Qiang; Zhou, Jian-Wei; Song, Zhi-Jun; Zhong, Dai-Jun; Jiang, Yu; Liu, Wan-Sheng; Huang, Yong-Mei

2018-03-01

A satellite dedicated for quantum science experiments, has been developed and successfully launched from Jiuquan, China, on August 16, 2016. Two new optical ground stations (OGSs) were built to cooperate with the satellite to complete satellite-ground quantum experiments. OGS corrected its pointing direction by satellite trajectory error to coarse tracking system and uplink beacon sight, therefore fine tracking CCD and uplink beacon optical axis alignment accuracy was to ensure that beacon could cover the quantum satellite in all time when it passed the OGSs. Unfortunately, when we tested specifications of the OGSs, due to the coarse tracking optical system was commercial telescopes, the change of position of the target in the coarse CCD was up to 600μrad along with the change of elevation angle. In this paper, a method of reduce alignment error between beacon beam and fine tracking CCD is proposed. Firstly, OGS fitted the curve of target positions in coarse CCD along with the change of elevation angle. Secondly, OGS fitted the curve of hexapod secondary mirror positions along with the change of elevation angle. Thirdly, when tracking satellite, the fine tracking error unloaded on the real-time zero point position of coarse CCD which computed by the firstly calibration data. Simultaneously the positions of the hexapod secondary mirror were adjusted by the secondly calibration data. Finally the experiment result is proposed. Results show that the alignment error is less than 50μrad.

Local non-Calderbank-Shor-Steane quantum error-correcting code on a three-dimensional lattice

International Nuclear Information System (INIS)

Kim, Isaac H.

2011-01-01

We present a family of non-Calderbank-Shor-Steane quantum error-correcting code consisting of geometrically local stabilizer generators on a 3D lattice. We study the Hamiltonian constructed from ferromagnetic interaction of overcomplete set of local stabilizer generators. The degenerate ground state of the system is characterized by a quantum error-correcting code whose number of encoded qubits are equal to the second Betti number of the manifold. These models (i) have solely local interactions; (ii) admit a strong-weak duality relation with an Ising model on a dual lattice; (iii) have topological order in the ground state, some of which survive at finite temperature; and (iv) behave as classical memory at finite temperature.

Local non-Calderbank-Shor-Steane quantum error-correcting code on a three-dimensional lattice

Science.gov (United States)

Kim, Isaac H.

2011-05-01

We present a family of non-Calderbank-Shor-Steane quantum error-correcting code consisting of geometrically local stabilizer generators on a 3D lattice. We study the Hamiltonian constructed from ferromagnetic interaction of overcomplete set of local stabilizer generators. The degenerate ground state of the system is characterized by a quantum error-correcting code whose number of encoded qubits are equal to the second Betti number of the manifold. These models (i) have solely local interactions; (ii) admit a strong-weak duality relation with an Ising model on a dual lattice; (iii) have topological order in the ground state, some of which survive at finite temperature; and (iv) behave as classical memory at finite temperature.

Capacity of oscillatory associative-memory networks with error-free retrieval

International Nuclear Information System (INIS)

Nishikawa, Takashi; Lai Yingcheng; Hoppensteadt, Frank C.

2004-01-01

Networks of coupled periodic oscillators (similar to the Kuramoto model) have been proposed as models of associative memory. However, error-free retrieval states of such oscillatory networks are typically unstable, resulting in a near zero capacity. This puts the networks at disadvantage as compared with the classical Hopfield network. Here we propose a simple remedy for this undesirable property and show rigorously that the error-free capacity of our oscillatory, associative-memory networks can be made as high as that of the Hopfield network. They can thus not only provide insights into the origin of biological memory, but can also be potentially useful for applications in information science and engineering

Entangled photons and quantum communication

Energy Technology Data Exchange (ETDEWEB)

Yuan Zhensheng, E-mail: yuanzs@ustc.edu.c [Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Physikalisches Institut, Universitaet Heidelberg, Philosophenweg 12, 69120 Heidelberg (Germany); Bao Xiaohui [Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Physikalisches Institut, Universitaet Heidelberg, Philosophenweg 12, 69120 Heidelberg (Germany); Lu Chaoyang; Zhang Jun; Peng Chengzhi [Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Pan Jianwei, E-mail: pan@ustc.edu.c [Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Physikalisches Institut, Universitaet Heidelberg, Philosophenweg 12, 69120 Heidelberg (Germany)

2010-12-15

This article reviews the progress of quantum communication that utilizes photonic entanglement. We start with a survey of various methods for generating entangled photons, followed by an introduction of the theoretical principles and the experimental implementations of quantum key distribution. We then move on to a discussion of more involved quantum communication protocols including quantum dense coding, teleportation and quantum communication complexity. After that, we review the progress in free-space quantum communication, decoherence-free subspace, and quantum repeater protocols which are essential ingredients for long-distance quantum communication. Practical realizations of quantum repeaters, which require an interface between photons and quantum memories, are discussed briefly. Finally, we draw concluding remarks considering the technical challenges, and put forward an outlook on further developments of this field.

Entangled photons and quantum communication

International Nuclear Information System (INIS)

Yuan Zhensheng; Bao Xiaohui; Lu Chaoyang; Zhang Jun; Peng Chengzhi; Pan Jianwei

2010-01-01

This article reviews the progress of quantum communication that utilizes photonic entanglement. We start with a survey of various methods for generating entangled photons, followed by an introduction of the theoretical principles and the experimental implementations of quantum key distribution. We then move on to a discussion of more involved quantum communication protocols including quantum dense coding, teleportation and quantum communication complexity. After that, we review the progress in free-space quantum communication, decoherence-free subspace, and quantum repeater protocols which are essential ingredients for long-distance quantum communication. Practical realizations of quantum repeaters, which require an interface between photons and quantum memories, are discussed briefly. Finally, we draw concluding remarks considering the technical challenges, and put forward an outlook on further developments of this field.

Experimental entanglement of 25 individually accessible atomic quantum interfaces.

Science.gov (United States)

Pu, Yunfei; Wu, Yukai; Jiang, Nan; Chang, Wei; Li, Chang; Zhang, Sheng; Duan, Luming

2018-04-01

A quantum interface links the stationary qubits in a quantum memory with flying photonic qubits in optical transmission channels and constitutes a critical element for the future quantum internet. Entanglement of quantum interfaces is an important step for the realization of quantum networks. Through heralded detection of photon interference, we generate multipartite entanglement between 25 (or 9) individually addressable quantum interfaces in a multiplexed atomic quantum memory array and confirm genuine 22-partite (or 9-partite) entanglement. This experimental entanglement of a record-high number of individually addressable quantum interfaces makes an important step toward the realization of quantum networks, long-distance quantum communication, and multipartite quantum information processing.

Decoy-state quantum key distribution with both source errors and statistical fluctuations

International Nuclear Information System (INIS)

Wang Xiangbin; Yang Lin; Peng Chengzhi; Pan Jianwei

2009-01-01

We show how to calculate the fraction of single-photon counts of the 3-intensity decoy-state quantum cryptography faithfully with both statistical fluctuations and source errors. Our results rely only on the bound values of a few parameters of the states of pulses.

Investigations of fundamental phenomena in quantum mechanics with neutrons

International Nuclear Information System (INIS)

Hasegawa, Yuji

2014-01-01

Neutron interferometer and polarimeter are used for the experimental investigations of quantum mechanical phenomena. Interferometry exhibits clear evidence of quantum-contextuality and polarimetry demonstrates conflicts of a contextual model of quantum mechanics á la Leggett. In these experiments, entanglements are achieved between degrees of freedom in a single-particle: spin, path and energy degrees of freedom are manipulated coherently and entangled. Both experiments manifest the fact that quantum contextuality is valid for phenomena with matter waves with high precision. In addition, another experiment is described which deals with error-disturbance uncertainty relation: we have experimentally tested error-disturbance uncertainty relations, one is derived by Heisenberg and the other by Ozawa. Experimental results confirm the fact that the Heisenberg's uncertainty relation is often violated and that the new relation by Ozawa is always larger than the limit. At last, as an example of a counterfactual phenomenon of quantum mechanics, observation of so-called quantum Cheshire Cat is carried out by using neutron interferometer. Experimental results suggest that pre- and post-selected neutrons travel through one of the arms of the interferometer while their magnetic moment is located in the other arm.

Quantum Error Correction: Optimal, Robust, or Adaptive? Or, Where is The Quantum Flyball Governor?

Science.gov (United States)

Kosut, Robert; Grace, Matthew

2012-02-01

In The Human Use of Human Beings: Cybernetics and Society (1950), Norbert Wiener introduces feedback control in this way: ``This control of a machine on the basis of its actual performance rather than its expected performance is known as feedback ... It is the function of control ... to produce a temporary and local reversal of the normal direction of entropy.'' The classic classroom example of feedback control is the all-mechanical flyball governor used by James Watt in the 18th century to regulate the speed of rotating steam engines. What is it that is so compelling about this apparatus? First, it is easy to understand how it regulates the speed of a rotating steam engine. Secondly, and perhaps more importantly, it is a part of the device itself. A naive observer would not distinguish this mechanical piece from all the rest. So it is natural to ask, where is the all-quantum device which is self regulating, ie, the Quantum Flyball Governor? Is the goal of quantum error correction (QEC) to design such a device? Devloping the computational and mathematical tools to design this device is the topic of this talk.

One phonon resonant Raman scattering in free-standing quantum wires

International Nuclear Information System (INIS)

Zhao, Xiang-Fu; Liu, Cui-Hong

2007-01-01

The scattering intensity (SI) of a free-standing cylindrical semiconductor quantum wire for an electron resonant Raman scattering (ERRS) process associated with bulk longitudinal optical (LO) phonon modes and surface optical (SO) phonon modes is calculated separately for T=0 K. The Frohlich interaction is considered to illustrate the theory for GaAs and CdS systems. Electron states are confined within a free-standing quantum wire (FSW). Single parabolic conduction and valence bands are assumed. The selection rules are studied. Numerical results and a discussion are also presented for various radii of the cylindrical

Error tolerance in an NMR implementation of Grover's fixed-point quantum search algorithm

International Nuclear Information System (INIS)

Xiao Li; Jones, Jonathan A.

2005-01-01

We describe an implementation of Grover's fixed-point quantum search algorithm on a nuclear magnetic resonance quantum computer, searching for either one or two matching items in an unsorted database of four items. In this algorithm the target state (an equally weighted superposition of the matching states) is a fixed point of the recursive search operator, so that the algorithm always moves towards the desired state. The effects of systematic errors in the implementation are briefly explored

Blind topological measurement-based quantum computation.

Science.gov (United States)

Morimae, Tomoyuki; Fujii, Keisuke

2012-01-01

Blind quantum computation is a novel secure quantum-computing protocol that enables Alice, who does not have sufficient quantum technology at her disposal, to delegate her quantum computation to Bob, who has a fully fledged quantum computer, in such a way that Bob cannot learn anything about Alice's input, output and algorithm. A recent proof-of-principle experiment demonstrating blind quantum computation in an optical system has raised new challenges regarding the scalability of blind quantum computation in realistic noisy conditions. Here we show that fault-tolerant blind quantum computation is possible in a topologically protected manner using the Raussendorf-Harrington-Goyal scheme. The error threshold of our scheme is 4.3 × 10(-3), which is comparable to that (7.5 × 10(-3)) of non-blind topological quantum computation. As the error per gate of the order 10(-3) was already achieved in some experimental systems, our result implies that secure cloud quantum computation is within reach.

Multiconfiguration Pair-Density Functional Theory Is Free From Delocalization Error.

Science.gov (United States)

Bao, Junwei Lucas; Wang, Ying; He, Xiao; Gagliardi, Laura; Truhlar, Donald G

2017-11-16

Delocalization error has been singled out by Yang and co-workers as the dominant error in Kohn-Sham density functional theory (KS-DFT) with conventional approximate functionals. In this Letter, by computing the vertical first ionization energy for well separated He clusters, we show that multiconfiguration pair-density functional theory (MC-PDFT) is free from delocalization error. To put MC-PDFT in perspective, we also compare it with some Kohn-Sham density functionals, including both traditional and modern functionals. Whereas large delocalization errors are almost universal in KS-DFT (the only exception being the very recent corrected functionals of Yang and co-workers), delocalization error is removed by MC-PDFT, which bodes well for its future as a step forward from KS-DFT.

Assessment of the uncertainty associated with systematic errors in digital instruments: an experimental study on offset errors

International Nuclear Information System (INIS)

Attivissimo, F; Giaquinto, N; Savino, M; Cataldo, A

2012-01-01

This paper deals with the assessment of the uncertainty due to systematic errors, particularly in A/D conversion-based instruments. The problem of defining and assessing systematic errors is briefly discussed, and the conceptual scheme of gauge repeatability and reproducibility is adopted. A practical example regarding the evaluation of the uncertainty caused by the systematic offset error is presented. The experimental results, obtained under various ambient conditions, show that modelling the variability of systematic errors is more problematic than suggested by the ISO 5725 norm. Additionally, the paper demonstrates the substantial difference between the type B uncertainty evaluation, obtained via the maximum entropy principle applied to manufacturer's specifications, and the type A (experimental) uncertainty evaluation, which reflects actually observable reality. Although it is reasonable to assume a uniform distribution of the offset error, experiments demonstrate that the distribution is not centred and that a correction must be applied. In such a context, this work motivates a more pragmatic and experimental approach to uncertainty, with respect to the directions of supplement 1 of GUM. (paper)

Quantum engineering of continuous variable quantum states

Energy Technology Data Exchange (ETDEWEB)

Sabuncu, Metin

2009-10-29

Quantum information with continuous variables is a field attracting increasing attention recently. In continuous variable quantum information one makes use of the continuous information encoded into the quadrature of a quantized light field instead of binary quantities such as the polarization state of a single photon. This brand new research area is witnessing exciting theoretical and experimental achievements such as teleportation, quantum computation and quantum error correction. The rapid development of the field is mainly due higher optical data rates and the availability of simple and efficient manipulation tools in continuous-variable quantum information processing. We in this thesis extend the work in continuous variable quantum information processing and report on novel experiments on amplification, cloning, minimal disturbance and noise erasure protocols. The promising results we obtain in these pioneering experiments indicate that the future of continuous variable quantum information is bright and many advances can be foreseen. (orig.)

Quantum engineering of continuous variable quantum states

International Nuclear Information System (INIS)

Sabuncu, Metin

2009-01-01

Quantum information with continuous variables is a field attracting increasing attention recently. In continuous variable quantum information one makes use of the continuous information encoded into the quadrature of a quantized light field instead of binary quantities such as the polarization state of a single photon. This brand new research area is witnessing exciting theoretical and experimental achievements such as teleportation, quantum computation and quantum error correction. The rapid development of the field is mainly due higher optical data rates and the availability of simple and efficient manipulation tools in continuous-variable quantum information processing. We in this thesis extend the work in continuous variable quantum information processing and report on novel experiments on amplification, cloning, minimal disturbance and noise erasure protocols. The promising results we obtain in these pioneering experiments indicate that the future of continuous variable quantum information is bright and many advances can be foreseen. (orig.)

Experimental quantum simulations of many-body physics with trapped ions.

Science.gov (United States)

Schneider, Ch; Porras, Diego; Schaetz, Tobias

2012-02-01

Direct experimental access to some of the most intriguing quantum phenomena is not granted due to the lack of precise control of the relevant parameters in their naturally intricate environment. Their simulation on conventional computers is impossible, since quantum behaviour arising with superposition states or entanglement is not efficiently translatable into the classical language. However, one could gain deeper insight into complex quantum dynamics by experimentally simulating the quantum behaviour of interest in another quantum system, where the relevant parameters and interactions can be controlled and robust effects detected sufficiently well. Systems of trapped ions provide unique control of both the internal (electronic) and external (motional) degrees of freedom. The mutual Coulomb interaction between the ions allows for large interaction strengths at comparatively large mutual ion distances enabling individual control and readout. Systems of trapped ions therefore exhibit a prominent system in several physical disciplines, for example, quantum information processing or metrology. Here, we will give an overview of different trapping techniques of ions as well as implementations for coherent manipulation of their quantum states and discuss the related theoretical basics. We then report on the experimental and theoretical progress in simulating quantum many-body physics with trapped ions and present current approaches for scaling up to more ions and more-dimensional systems.

Methodology for bus layout for topological quantum error correcting codes

Energy Technology Data Exchange (ETDEWEB)

Wosnitzka, Martin; Pedrocchi, Fabio L.; DiVincenzo, David P. [RWTH Aachen University, JARA Institute for Quantum Information, Aachen (Germany)

2016-12-15

Most quantum computing architectures can be realized as two-dimensional lattices of qubits that interact with each other. We take transmon qubits and transmission line resonators as promising candidates for qubits and couplers; we use them as basic building elements of a quantum code. We then propose a simple framework to determine the optimal experimental layout to realize quantum codes. We show that this engineering optimization problem can be reduced to the solution of standard binary linear programs. While solving such programs is a NP-hard problem, we propose a way to find scalable optimal architectures that require solving the linear program for a restricted number of qubits and couplers. We apply our methods to two celebrated quantum codes, namely the surface code and the Fibonacci code. (orig.)

Modeling satellite-Earth quantum channel downlinks with adaptive-optics coupling to single-mode fibers

Science.gov (United States)

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.

Experimental plug and play quantum coin flipping

Science.gov (United States)

Pappa, Anna; Jouguet, Paul; Lawson, Thomas; Chailloux, André; Legré, Matthieu; Trinkler, Patrick; Kerenidis, Iordanis; Diamanti, Eleni

2014-04-01

Performing complex cryptographic tasks will be an essential element in future quantum communication networks. These tasks are based on a handful of fundamental primitives, such as coin flipping, where two distrustful parties wish to agree on a randomly generated bit. Although it is known that quantum versions of these primitives can offer information-theoretic security advantages with respect to classical protocols, a demonstration of such an advantage in a practical communication scenario has remained elusive. Here we experimentally implement a quantum coin flipping protocol that performs strictly better than classically possible over a distance suitable for communication over metropolitan area optical networks. The implementation is based on a practical plug and play system, developed by significantly enhancing a commercial quantum key distribution device. Moreover, we provide combined quantum coin flipping protocols that are almost perfectly secure against bounded adversaries. Our results offer a useful toolbox for future secure quantum communications.

Experimental quantum private queries with linear optics

International Nuclear Information System (INIS)

De Martini, Francesco; Giovannetti, Vittorio; Lloyd, Seth; Maccone, Lorenzo; Nagali, Eleonora; Sansoni, Linda; Sciarrino, Fabio

2009-01-01

The quantum private query is a quantum cryptographic protocol to recover information from a database, preserving both user and data privacy: the user can test whether someone has retained information on which query was asked and the database provider can test the amount of information released. Here we discuss a variant of the quantum private query algorithm that admits a simple linear optical implementation: it employs the photon's momentum (or time slot) as address qubits and its polarization as bus qubit. A proof-of-principle experimental realization is implemented.

Measurement-device-independent quantum key distribution with correlated source-light-intensity errors

Science.gov (United States)

Jiang, Cong; Yu, Zong-Wen; Wang, Xiang-Bin

2018-04-01

We present an analysis for measurement-device-independent quantum key distribution with correlated source-light-intensity errors. Numerical results show that the results here can greatly improve the key rate especially with large intensity fluctuations and channel attenuation compared with prior results if the intensity fluctuations of different sources are correlated.

Giersch International Symposion 2016 : Week 1 : Experimental Search for Quantum Gravity

CERN Document Server

Experimental Search for Quantum Gravity

2018-01-01

This book summarizes recent developments in the research area of quantum gravity phenomenology. A series of short and nontechnical essays lays out the prospects of various experimental possibilities and their current status. Finding observational evidence for the quantization of space-time was long thought impossible. In the last decade however, new experimental design and technological advances have changed the research landscape and opened new perspectives on quantum gravity. Formerly dominated by purely theoretical constructions, quantum gravity now has a lively phenomenology to offer. From high precision measurements using macroscopic quantum oscillators to new analysis methods of the cosmic microwave background, no stone is being left unturned in the experimental search for quantum gravity. This book sheds new light on the connection of astroparticle physics with the quantum gravity problem. Gravitational waves and their detection are covered. It illustrates findings from the interconnection between gene...

Hamiltonian formulation of quantum error correction and correlated noise: Effects of syndrome extraction in the long-time limit

Science.gov (United States)

Novais, E.; Mucciolo, Eduardo R.; Baranger, Harold U.

2008-07-01

We analyze the long-time behavior of a quantum computer running a quantum error correction (QEC) code in the presence of a correlated environment. Starting from a Hamiltonian formulation of realistic noise models, and assuming that QEC is indeed possible, we find formal expressions for the probability of a given syndrome history and the associated residual decoherence encoded in the reduced density matrix. Systems with nonzero gate times (“long gates”) are included in our analysis by using an upper bound on the noise. In order to introduce the local error probability for a qubit, we assume that propagation of signals through the environment is slower than the QEC period (hypercube assumption). This allows an explicit calculation in the case of a generalized spin-boson model and a quantum frustration model. The key result is a dimensional criterion: If the correlations decay sufficiently fast, the system evolves toward a stochastic error model for which the threshold theorem of fault-tolerant quantum computation has been proven. On the other hand, if the correlations decay slowly, the traditional proof of this threshold theorem does not hold. This dimensional criterion bears many similarities to criteria that occur in the theory of quantum phase transitions.

Experimental violation of local causality in a quantum network

Science.gov (United States)

Carvacho, Gonzalo; Andreoli, Francesco; Santodonato, Luca; Bentivegna, Marco; Chaves, Rafael; Sciarrino, Fabio

2017-03-01

Bell's theorem plays a crucial role in quantum information processing and thus several experimental investigations of Bell inequalities violations have been carried out over the years. Despite their fundamental relevance, however, previous experiments did not consider an ingredient of relevance for quantum networks: the fact that correlations between distant parties are mediated by several, typically independent sources. Here, using a photonic setup, we investigate a quantum network consisting of three spatially separated nodes whose correlations are mediated by two distinct sources. This scenario allows for the emergence of the so-called non-bilocal correlations, incompatible with any local model involving two independent hidden variables. We experimentally witness the emergence of this kind of quantum correlations by violating a Bell-like inequality under the fair-sampling assumption. Our results provide a proof-of-principle experiment of generalizations of Bell's theorem for networks, which could represent a potential resource for quantum communication protocols.

Gaussian Error Correction of Quantum States in a Correlated Noisy Channel

DEFF Research Database (Denmark)

Lassen, Mikael Østergaard; Berni, Adriano; Madsen, Lars Skovgaard

2013-01-01

Noise is the main obstacle for the realization of fault-tolerant quantum information processing and secure communication over long distances. In this work, we propose a communication protocol relying on simple linear optics that optimally protects quantum states from non-Markovian or correlated...... noise. We implement the protocol experimentally and demonstrate the near-ideal protection of coherent and entangled states in an extremely noisy channel. Since all real-life channels are exhibiting pronounced non-Markovian behavior, the proposed protocol will have immediate implications in improving...... the performance of various quantum information protocols....

Error-free 320 Gb/s simultaneous add-drop multiplexing

DEFF Research Database (Denmark)

Mulvad, Hans Christian Hansen; Oxenløwe, Leif Katsuo; Clausen, Anders

2007-01-01

We report on the first demonstration of error-free time-division add-drop multiplexing at 320 Gb/s. The add- and drop-operations are performed simultaneously in a non-linear optical loop mirror with only 100 m of highly non-linear fibre....

Secret Sharing of a Quantum State.

Science.gov (United States)

Lu, He; Zhang, Zhen; Chen, Luo-Kan; Li, Zheng-Da; Liu, Chang; Li, Li; Liu, Nai-Le; Ma, Xiongfeng; Chen, Yu-Ao; Pan, Jian-Wei

2016-07-15

Secret sharing of a quantum state, or quantum secret sharing, in which a dealer wants to share a certain amount of quantum information with a few players, has wide applications in quantum information. The critical criterion in a threshold secret sharing scheme is confidentiality: with less than the designated number of players, no information can be recovered. Furthermore, in a quantum scenario, one additional critical criterion exists: the capability of sharing entangled and unknown quantum information. Here, by employing a six-photon entangled state, we demonstrate a quantum threshold scheme, where the shared quantum secrecy can be efficiently reconstructed with a state fidelity as high as 93%. By observing that any one or two parties cannot recover the secrecy, we show that our scheme meets the confidentiality criterion. Meanwhile, we also demonstrate that entangled quantum information can be shared and recovered via our setting, which shows that our implemented scheme is fully quantum. Moreover, our experimental setup can be treated as a decoding circuit of the five-qubit quantum error-correcting code with two erasure errors.

Experimental superposition of orders of quantum gates

Science.gov (United States)

Procopio, Lorenzo M.; Moqanaki, Amir; Araújo, Mateus; Costa, Fabio; Alonso Calafell, Irati; Dowd, Emma G.; Hamel, Deny R.; Rozema, Lee A.; Brukner, Časlav; Walther, Philip

2015-01-01

Quantum computers achieve a speed-up by placing quantum bits (qubits) in superpositions of different states. However, it has recently been appreciated that quantum mechanics also allows one to ‘superimpose different operations'. Furthermore, it has been shown that using a qubit to coherently control the gate order allows one to accomplish a task—determining if two gates commute or anti-commute—with fewer gate uses than any known quantum algorithm. Here we experimentally demonstrate this advantage, in a photonic context, using a second qubit to control the order in which two gates are applied to a first qubit. We create the required superposition of gate orders by using additional degrees of freedom of the photons encoding our qubits. The new resource we exploit can be interpreted as a superposition of causal orders, and could allow quantum algorithms to be implemented with an efficiency unlikely to be achieved on a fixed-gate-order quantum computer. PMID:26250107

Minimizing Experimental Error in Thinning Research

Science.gov (United States)

C. B. Briscoe

1964-01-01

Many diverse approaches have been made prescribing and evaluating thinnings on an objective basis. None of the techniques proposed hasbeen widely accepted. Indeed. none has been proven superior to the others nor even widely applicable. There are at least two possible reasons for this: none of the techniques suggested is of any general utility and/or experimental error...

Optimization and experimental realization of the quantum permutation algorithm

Science.gov (United States)

Yalçınkaya, I.; Gedik, Z.

2017-12-01

The quantum permutation algorithm provides computational speed-up over classical algorithms for determining the parity of a given cyclic permutation. For its n -qubit implementations, the number of required quantum gates scales quadratically with n due to the quantum Fourier transforms included. We show here for the n -qubit case that the algorithm can be simplified so that it requires only O (n ) quantum gates, which theoretically reduces the complexity of the implementation. To test our results experimentally, we utilize IBM's 5-qubit quantum processor to realize the algorithm by using the original and simplified recipes for the 2-qubit case. It turns out that the latter results in a significantly higher success probability which allows us to verify the algorithm more precisely than the previous experimental realizations. We also verify the algorithm for the first time for the 3-qubit case with a considerable success probability by taking the advantage of our simplified scheme.

Towards scalable quantum communication and computation: Novel approaches and realizations

Science.gov (United States)

Jiang, Liang

Quantum information science involves exploration of fundamental laws of quantum mechanics for information processing tasks. This thesis presents several new approaches towards scalable quantum information processing. First, we consider a hybrid approach to scalable quantum computation, based on an optically connected network of few-qubit quantum registers. Specifically, we develop a novel scheme for scalable quantum computation that is robust against various imperfections. To justify that nitrogen-vacancy (NV) color centers in diamond can be a promising realization of the few-qubit quantum register, we show how to isolate a few proximal nuclear spins from the rest of the environment and use them for the quantum register. We also demonstrate experimentally that the nuclear spin coherence is only weakly perturbed under optical illumination, which allows us to implement quantum logical operations that use the nuclear spins to assist the repetitive-readout of the electronic spin. Using this technique, we demonstrate more than two-fold improvement in signal-to-noise ratio. Apart from direct application to enhance the sensitivity of the NV-based nano-magnetometer, this experiment represents an important step towards the realization of robust quantum information processors using electronic and nuclear spin qubits. We then study realizations of quantum repeaters for long distance quantum communication. Specifically, we develop an efficient scheme for quantum repeaters based on atomic ensembles. We use dynamic programming to optimize various quantum repeater protocols. In addition, we propose a new protocol of quantum repeater with encoding, which efficiently uses local resources (about 100 qubits) to identify and correct errors, to achieve fast one-way quantum communication over long distances. Finally, we explore quantum systems with topological order. Such systems can exhibit remarkable phenomena such as quasiparticles with anyonic statistics and have been proposed as

On the problem of non-zero word error rates for fixed-rate error correction codes in continuous variable quantum key distribution

International Nuclear Information System (INIS)

Johnson, Sarah J; Ong, Lawrence; Shirvanimoghaddam, Mahyar; Lance, Andrew M; Symul, Thomas; Ralph, T C

2017-01-01

The maximum operational range of continuous variable quantum key distribution protocols has shown to be improved by employing high-efficiency forward error correction codes. Typically, the secret key rate model for such protocols is modified to account for the non-zero word error rate of such codes. In this paper, we demonstrate that this model is incorrect: firstly, we show by example that fixed-rate error correction codes, as currently defined, can exhibit efficiencies greater than unity. Secondly, we show that using this secret key model combined with greater than unity efficiency codes, implies that it is possible to achieve a positive secret key over an entanglement breaking channel—an impossible scenario. We then consider the secret key model from a post-selection perspective, and examine the implications for key rate if we constrain the forward error correction codes to operate at low word error rates. (paper)

Experimental Greenberger-Horne-Zeilinger-Type Six-Photon Quantum Nonlocality.

Science.gov (United States)

Zhang, Chao; Huang, Yun-Feng; Wang, Zhao; Liu, Bi-Heng; Li, Chuan-Feng; Guo, Guang-Can

2015-12-31

Quantum nonlocality gives us deeper insight into quantum physics. In addition, quantum nonlocality has been further recognized as an essential resource for device-independent quantum information processing in recent years. Most experiments of nonlocality are performed using a photonic system. However, until now, photonic experiments of nonlocality have involved at most four photons. Here, for the first time, we experimentally demonstrate the six-photon quantum nonlocality in an all-versus-nothing manner based on a high-fidelity (88.4%) six-photon Greenberger-Horne-Zeilinger state. Our experiment pushes multiphoton nonlocality studies forward to the six-photon region and might provide a larger photonic system for device-independent quantum information protocols.

Development of the polarization tracking scheme for free-space quantum cryptography

Science.gov (United States)

Toyoshima, Morio; Takayama, Yoshihisa; Kunimori, Hiroo; Takeoka, Masahiro; Fujiwara, Mikio; Sasaki, Masahide

2008-04-01

Quantum cryptography is a new technique for transmitting quantum information. The information is securely transmitted due to the laws of physics. In such systems, the vehicle that transfers quantum information is a single photon. The problem with using photons is that the transmission distance is limited by the absorption of the photons by the optical fiber along which they pass. The maximum demonstrated range so far is approximately 100 km. Using free-space quantum cryptography between a ground station and a satellite is a possible way of sending quantum information farther than is possible with optical fibers. This is because there is no birefringence effect in the atmosphere. However, there is a complication in that the directions of the polarization basis between the transmitter and the receiver must coincide with each other. This polarization changes because the mobile terminals for free-space transmission continuously change their attitudes. If the transmission protocol is based on polarization, it is necessary to compensate for the change in attitude between the mobile terminals. We are developing a scheme to track the polarization basis between the transceivers. The preliminary result is presented.

Ideal quantum reading of optical memories

International Nuclear Information System (INIS)

Dall'Arno, Michele; Bisio, Alessandro; D'Ariano, Giacomo Mauro

2013-01-01

Quantum reading is the art of exploiting the quantum properties of light to retrieve classical information stored in an optical memory with low energy and high accuracy. Focusing on the ideal scenario where noise and loss are negligible, we review previous works on the optimal strategies for minimal-error retrieving of information (ambiguous quantum reading) and perfect but probabilistic retrieving of information (unambiguous quantum reading). The optimal strategies largely overcome the optimal coherent protocols (reminiscent of common CD readers), further allowing for perfect discrimination. Experimental proposals for optical implementations of optimal quantum reading are provided.

Equivalence principle for quantum systems: dephasing and phase shift of free-falling particles

Science.gov (United States)

Anastopoulos, C.; Hu, B. L.

2018-02-01

We ask the question of how the (weak) equivalence principle established in classical gravitational physics should be reformulated and interpreted for massive quantum objects that may also have internal degrees of freedom (dof). This inquiry is necessary because even elementary concepts like a classical trajectory are not well defined in quantum physics—trajectories originating from quantum histories become viable entities only under stringent decoherence conditions. From this investigation we posit two logically and operationally distinct statements of the equivalence principle for quantum systems. Version A: the probability distribution of position for a free-falling particle is the same as the probability distribution of a free particle, modulo a mass-independent shift of its mean. Version B: any two particles with the same velocity wave-function behave identically in free fall, irrespective of their masses. Both statements apply to all quantum states, including those without a classical correspondence, and also for composite particles with quantum internal dof. We also investigate the consequences of the interaction between internal and external dof induced by free fall. For a class of initial states, we find dephasing occurs for the translational dof, namely, the suppression of the off-diagonal terms of the density matrix, in the position basis. We also find a gravitational phase shift in the reduced density matrix of the internal dof that does not depend on the particle’s mass. For classical states, the phase shift has a natural classical interpretation in terms of gravitational red-shift and special relativistic time-dilation.

Description of quantum coherence in thermodynamic processes requires constraints beyond free energy

Science.gov (United States)

Lostaglio, Matteo; Jennings, David; Rudolph, Terry

2015-03-01

Recent studies have developed fundamental limitations on nanoscale thermodynamics, in terms of a set of independent free energy relations. Here we show that free energy relations cannot properly describe quantum coherence in thermodynamic processes. By casting time-asymmetry as a quantifiable, fundamental resource of a quantum state, we arrive at an additional, independent set of thermodynamic constraints that naturally extend the existing ones. These asymmetry relations reveal that the traditional Szilárd engine argument does not extend automatically to quantum coherences, but instead only relational coherences in a multipartite scenario can contribute to thermodynamic work. We find that coherence transformations are always irreversible. Our results also reveal additional structural parallels between thermodynamics and the theory of entanglement.

Interaction between an elastic structure and free-surface flows: experimental versus numerical comparisons using the PFEM

Science.gov (United States)

Idelsohn, S. R.; Marti, J.; Souto-Iglesias, A.; Oñate, E.

2008-12-01

The paper aims to introduce new fluid structure interaction (FSI) tests to compare experimental results with numerical ones. The examples have been chosen for a particular case for which experimental results are not much reported. This is the case of FSI including free surface flows. The possibilities of the Particle Finite Element Method (PFEM) [1] for the simulation of free surface flows is also tested. The simulations are run using the same scale as the experiment in order to minimize errors due to scale effects. Different scenarios are simulated by changing the boundary conditions for reproducing flows with the desired characteristics. Details of the input data for all the examples studied are given. The aim is to identifying benchmark problems for FSI including free surface flows for future comparisons between different numerical approaches.

Quantum spreading of a self-gravitating wave-packet in singularity free gravity

Science.gov (United States)

Buoninfante, Luca; Lambiase, Gaetano; Mazumdar, Anupam

2018-01-01

In this paper we will study for the first time how the wave-packet of a self-gravitating meso-scopic system spreads in theories beyond Einstein's general relativity. In particular, we will consider a ghost-free infinite derivative gravity, which resolves the 1 / r singularity in the potential - such that the gradient of the potential vanishes within the scale of non-locality. We will show that a quantum wave-packet spreads faster for a ghost-free and singularity-free gravity as compared to the Newtonian case, therefore providing us a unique scenario for testing classical and quantum properties of short-distance gravity in a laboratory in the near future.

Do free-falling quantum cats land on their feet?

International Nuclear Information System (INIS)

Chryssomalakos, C; Serrano-Ensástiga, E; Hernández-Coronado, H

2015-01-01

We present a quantum description of the mechanism by which a free-falling cat manages to reorient itself and land on its feet, having all along zero angular momentum. Our approach is geometrical, making use of the fiber bundle structure of the cat configuration space. We show how the classical picture can be recovered, but also point out a purely quantum scenario, that ends up with a Schroedinger cat. Finally, we sketch possible applications to molecular, nuclear, and nano-systems. (paper)

Scattering quantum random-walk search with errors

International Nuclear Information System (INIS)

Gabris, A.; Kiss, T.; Jex, I.

2007-01-01

We analyze the realization of a quantum-walk search algorithm in a passive, linear optical network. The specific model enables us to consider the effect of realistic sources of noise and losses on the search efficiency. Photon loss uniform in all directions is shown to lead to the rescaling of search time. Deviation from directional uniformity leads to the enhancement of the search efficiency compared to uniform loss with the same average. In certain cases even increasing loss in some of the directions can improve search efficiency. We show that while we approach the classical limit of the general search algorithm by introducing random phase fluctuations, its utility for searching is lost. Using numerical methods, we found that for static phase errors the averaged search efficiency displays a damped oscillatory behavior that asymptotically tends to a nonzero value

Efficient one-way quantum computations for quantum error correction

International Nuclear Information System (INIS)

Huang Wei; Wei Zhaohui

2009-01-01

We show how to explicitly construct an O(nd) size and constant quantum depth circuit which encodes any given n-qubit stabilizer code with d generators. Our construction is derived using the graphic description for stabilizer codes and the one-way quantum computation model. Our result demonstrates how to use cluster states as scalable resources for many multi-qubit entangled states and how to use the one-way quantum computation model to improve the design of quantum algorithms.

Experimental realization of a one-way quantum computer algorithm solving Simon's problem.

Science.gov (United States)

Tame, M S; Bell, B A; Di Franco, C; Wadsworth, W J; Rarity, J G

2014-11-14

We report an experimental demonstration of a one-way implementation of a quantum algorithm solving Simon's problem-a black-box period-finding problem that has an exponential gap between the classical and quantum runtime. Using an all-optical setup and modifying the bases of single-qubit measurements on a five-qubit cluster state, key representative functions of the logical two-qubit version's black box can be queried and solved. To the best of our knowledge, this work represents the first experimental realization of the quantum algorithm solving Simon's problem. The experimental results are in excellent agreement with the theoretical model, demonstrating the successful performance of the algorithm. With a view to scaling up to larger numbers of qubits, we analyze the resource requirements for an n-qubit version. This work helps highlight how one-way quantum computing provides a practical route to experimentally investigating the quantum-classical gap in the query complexity model.

Experimental implementation of a four-player quantum game

Energy Technology Data Exchange (ETDEWEB)

Schmid, C; Wieczorek, W; Kiesel, N; Weinfurter, H [Sektion Physik, Ludwig-Maximilians-Universitaet, D-80797 Muenchen (Germany); Flitney, A P; Hollenberg, L C L, E-mail: cschmid@eso.or [School of Physics, The University of Melbourne, Parkville, VIC 3010 (Australia)

2010-06-15

Game theory is central to the understanding of competitive interactions arising in many fields, from the social and physical sciences to economics. Recently, as the definition of information is generalized to include entangled quantum systems, quantum game theory has emerged as a framework for understanding the competitive flow of quantum information. Up till now, only two- and three-player quantum games have been demonstrated with restricted strategy sets. Here, we report the first experiment that implements a four-player quantum minority game over tunable four-partite entangled states encoded in the polarization of single photons. Experimental application of appropriate player strategies gives equilibrium payoff values well above those achievable in the classical game. These results are in excellent quantitative agreement with our theoretical analysis of the symmetric Pareto optimal strategies. Our results demonstrate for the first time how nontrivial equilibria can arise in a competitive situation involving quantum agents.

Key distillation in quantum cryptography

Science.gov (United States)

Slutsky, Boris Aron

1998-11-01

Quantum cryptography is a technique which permits two parties to communicate over an open channel and establish a shared sequence of bits known only to themselves. This task, provably impossible in classical cryptography, is accomplished by encoding the data on quantum particles and harnessing their unique properties. It is believed that no eavesdropping attack consistent with the laws of quantum theory can compromise the secret data unknowingly to the legitimate users of the channel. Any attempt by a hostile actor to monitor the data carrying particles while in transit reveals itself through transmission errors it must inevitably introduce. Unfortunately, in practice a communication is not free of errors even when no eavesdropping is present. Key distillation is a technique that permits the parties to overcome this difficulty and establish a secret key despite channel defects, under the assumption that every particle is handled independently from other particles by the enemy. In the present work, key distillation is described and its various aspects are studied. A relationship is derived between the average error rate resulting from an eavesdropping attack and the amount of information obtained by the attacker. Formal definition is developed of the security of the final key. The net throughput of secret bits in a quantum cryptosystem employing key distillation is assessed. An overview of quantum cryptographic protocols and related information theoretical results is also given.

Description of quantum coherence in thermodynamic processes requires constraints beyond free energy

Science.gov (United States)

Lostaglio, Matteo; Jennings, David; Rudolph, Terry

2015-01-01

Recent studies have developed fundamental limitations on nanoscale thermodynamics, in terms of a set of independent free energy relations. Here we show that free energy relations cannot properly describe quantum coherence in thermodynamic processes. By casting time-asymmetry as a quantifiable, fundamental resource of a quantum state, we arrive at an additional, independent set of thermodynamic constraints that naturally extend the existing ones. These asymmetry relations reveal that the traditional Szilárd engine argument does not extend automatically to quantum coherences, but instead only relational coherences in a multipartite scenario can contribute to thermodynamic work. We find that coherence transformations are always irreversible. Our results also reveal additional structural parallels between thermodynamics and the theory of entanglement. PMID:25754774

Experimental quantum teleportation and multiphoton entanglement via interfering narrowband photon sources

International Nuclear Information System (INIS)

Yang Jian; Zhang Han; Peng Chengzhi; Chen Zengbing; Bao Xiaohui; Chen Shuai; Pan Jianwei

2009-01-01

In this paper, we report a realization of synchronization-free quantum teleportation and narrowband three-photon entanglement through interfering narrowband photon sources. Since both the single-photon and the entangled photon pair utilized are completely autonomous, it removes the requirement of high-demanding synchronization techniques in long-distance quantum communication with pulsed spontaneous parametric down-conversion sources. The frequency linewidth of the three-photon entanglement realized is on the order of several MHz, which matches the requirement of atomic ensemble based quantum memories. Such a narrowband multiphoton source will have applications in some advanced quantum communication protocols and linear optical quantum computation.

Quantum spreading of a self-gravitating wave-packet in singularity free gravity

Energy Technology Data Exchange (ETDEWEB)

Buoninfante, Luca [Universita di Salerno, Dipartimento di Fisica ' ' E.R. Caianiello' ' , Fisciano (Italy); INFN-Sezione di Napoli, Gruppo Collegato di Salerno, Fisciano (Italy); University of Groningen, Van Swinderen Institute, Groningen (Netherlands); Lambiase, Gaetano [Universita di Salerno, Dipartimento di Fisica ' ' E.R. Caianiello' ' , Fisciano (Italy); INFN-Sezione di Napoli, Gruppo Collegato di Salerno, Fisciano (Italy); Mazumdar, Anupam [University of Groningen, Van Swinderen Institute, Groningen (Netherlands); University of Groningen, Kapteyn Astronomical Institute, Groningen (Netherlands)

2018-01-15

In this paper we will study for the first time how the wave-packet of a self-gravitating meso-scopic system spreads in theories beyond Einstein's general relativity. In particular, we will consider a ghost-free infinite derivative gravity, which resolves the 1/r singularity in the potential - such that the gradient of the potential vanishes within the scale of non-locality. We will show that a quantum wave-packet spreads faster for a ghost-free and singularity-free gravity as compared to the Newtonian case, therefore providing us a unique scenario for testing classical and quantum properties of short-distance gravity in a laboratory in the near future. (orig.)

Quantum key distribution with two-segment quantum repeaters

Energy Technology Data Exchange (ETDEWEB)

Kampermann, Hermann; Abruzzo, Silvestre; Bruss, Dagmar [Theoretische Physik III, Heinrich-Heine-Universitaet Duesseldorf (Germany)

2014-07-01

Quantum repeaters represent one possible way to achieve long-distance quantum key distribution. One way of improving the repeater rate and decreasing the memory coherence time is the usage of multiplexing. Motivated by the experimental fact that long-range connections are practically demanding, we extend the analysis of the quantum repeater multiplexing protocol to the case of short-range connections. We derive formulas for the repeater rate and we show that short-range connections lead to most of the benefits of a full-range multiplexing protocol. A less demanding QKD-protocol without quantum memories was recently introduced by Lo et al. We generalize this measurement-device-independent quantum key Distribution protocol to the scenario where the repeater Station contains also heralded quantum memories. We assume either single-photon sources or weak coherent pulse sources plus decay states. We show that it is possible to significantly outperform the original proposal, even in presence of decoherence of the quantum memory. We give formulas in terms of device imperfections i.e., the quantum bit error rate and the repeater rate.

High Quantum Yield Blue Emission from Lead-Free Inorganic Antimony Halide Perovskite Colloidal Quantum Dots.

Science.gov (United States)

Zhang, Jian; Yang, Ying; Deng, Hui; Farooq, Umar; Yang, Xiaokun; Khan, Jahangeer; Tang, Jiang; Song, Haisheng

2017-09-26

Colloidal quantum dots (QDs) of lead halide perovskite have recently received great attention owing to their remarkable performances in optoelectronic applications. However, their wide applications are hindered from toxic lead element, which is not environment- and consumer-friendly. Herein, we utilized heterovalent substitution of divalent lead (Pb 2+ ) with trivalent antimony (Sb 3+ ) to synthesize stable and brightly luminescent Cs 3 Sb 2 Br 9 QDs. The lead-free, full-inorganic QDs were fabricated by a modified ligand-assisted reprecipitation strategy. A photoluminescence quantum yield (PLQY) was determined to be 46% at 410 nm, which was superior to that of other reported halide perovskite QDs. The PL enhancement mechanism was unraveled by surface composition derived quantum-well band structure and their large exciton binding energy. The Br-rich surface and the observed 530 meV exciton binding energy were proposed to guarantee the efficient radiative recombination. In addition, we can also tune the inorganic perovskite QD (Cs 3 Sb 2 X 9 ) emission wavelength from 370 to 560 nm via anion exchange reactions. The developed full-inorganic lead-free Sb-perovskite QDs with high PLQY and stable emission promise great potential for efficient emission candidates.

Quantum computing with trapped ions, atoms and light

International Nuclear Information System (INIS)

Steane, Andrew M.

2001-01-01

We consider experimental issues relevant to quantum computing, and discuss the best way to achieve the essential requirements of reliable quantum memory and gate operations. Nuclear spins in trapped ions or atoms are a very promising candidate for the qubits. We estimate the parameters required to couple atoms using light via cavity QED in order to achieve quantum gates. We briefly comment on recent improvements to the Cirac-Zoller method for coupling trapped ions via their vibrational degree of freedom. Error processes result in a trade-off between quantum gate speed and failure probability. A useful quantum computer does appear to be feasible using a combination of ion trap and optical methods. The best understood method to stabilize a large computer relies on quantum error correction. The essential ideas of this are discussed, and recent estimates of the noise requirements in a quantum computing device are given

Prediction Errors of Molecular Machine Learning Models Lower than Hybrid DFT Error.

Science.gov (United States)

Faber, Felix A; Hutchison, Luke; Huang, Bing; Gilmer, Justin; Schoenholz, Samuel S; Dahl, George E; Vinyals, Oriol; Kearnes, Steven; Riley, Patrick F; von Lilienfeld, O Anatole

2017-11-14

evidence that ML model predictions deviate from DFT (B3LYP) less than DFT (B3LYP) deviates from experiment for all properties. Furthermore, out-of-sample prediction errors with respect to hybrid DFT reference are on par with, or close to, chemical accuracy. The results suggest that ML models could be more accurate than hybrid DFT if explicitly electron correlated quantum (or experimental) data were available.

Quantum light in coupled interferometers for quantum gravity tests.

Science.gov (United States)

Ruo Berchera, I; Degiovanni, I P; Olivares, S; Genovese, M

2013-05-24

In recent years quantum correlations have received a lot of attention as a key ingredient in advanced quantum metrology protocols. In this Letter we show that they provide even larger advantages when considering multiple-interferometer setups. In particular, we demonstrate that the use of quantum correlated light beams in coupled interferometers leads to substantial advantages with respect to classical light, up to a noise-free scenario for the ideal lossless case. On the one hand, our results prompt the possibility of testing quantum gravity in experimental configurations affordable in current quantum optics laboratories and strongly improve the precision in "larger size experiments" such as the Fermilab holometer; on the other hand, they pave the way for future applications to high precision measurements and quantum metrology.

Experimental non-classicality of an indivisible quantum system.

Science.gov (United States)

Lapkiewicz, Radek; Li, Peizhe; Schaeff, Christoph; Langford, Nathan K; Ramelow, Sven; Wieśniak, Marcin; Zeilinger, Anton

2011-06-22

In contrast to classical physics, quantum theory demands that not all properties can be simultaneously well defined; the Heisenberg uncertainty principle is a manifestation of this fact. Alternatives have been explored--notably theories relying on joint probability distributions or non-contextual hidden-variable models, in which the properties of a system are defined independently of their own measurement and any other measurements that are made. Various deep theoretical results imply that such theories are in conflict with quantum mechanics. Simpler cases demonstrating this conflict have been found and tested experimentally with pairs of quantum bits (qubits). Recently, an inequality satisfied by non-contextual hidden-variable models and violated by quantum mechanics for all states of two qubits was introduced and tested experimentally. A single three-state system (a qutrit) is the simplest system in which such a contradiction is possible; moreover, the contradiction cannot result from entanglement between subsystems, because such a three-state system is indivisible. Here we report an experiment with single photonic qutrits which provides evidence that no joint probability distribution describing the outcomes of all possible measurements--and, therefore, no non-contextual theory--can exist. Specifically, we observe a violation of the Bell-type inequality found by Klyachko, Can, Binicioğlu and Shumovsky. Our results illustrate a deep incompatibility between quantum mechanics and classical physics that cannot in any way result from entanglement.

The effects of field errors on low-gain free-electron lasers

International Nuclear Information System (INIS)

Esarey, E.; Tang, C.M.; Marable, W.P.

1991-01-01

This paper reports on the effects of random wiggler magnetic field errors on low-gain free-electron lasers that are examined analytically and numerically through the use of ensemble averaging techniques. Wiggler field errors perturb the electron beam as it propagates and lead to a random walk of the beam centroid δx, variations in the axial beam energy δ γz and deviations in the relative phase of the electrons in the ponderomotive wave δψ. In principle, the random walk may be kept as small as desired through the use of transverse focusing and beam steering. Transverse focusing of the electron beam is shown to be ineffective in reducing the phase deviation. Furthermore, it is shown that beam steering at the wiggler entrance reduces the average phase deviation at the end of the wiggler by 1/3. The effect of the field errors (via the phase deviation) on the gain in the low-gain regime is calculated. To avoid significant reduction in gain it is necessary for the phase deviation to be small compared to 2π. The detrimental effects of wiggler errors on low-gain free-electron lasers may be reduced by arranging the magnet poles in an optimal ordering such that the magnitude of the phase deviation is minimized

The quantum mechanical analysis of the free electron laser

International Nuclear Information System (INIS)

Dattoli, G.; Renieri, A.

1985-01-01

A quantum analysis of the Free Electron Laser is presented. The theory is developed both in single and longitudinal multimode regimes. Finally a self-consistent procedure to study the growth of the laser signal from the vacuum to the macroscopic level is presented

Strictly local one-dimensional topological quantum error correction with symmetry-constrained cellular automata

Directory of Open Access Journals (Sweden)

Nicolai Lang, Hans Peter Büchler

2018-01-01

Full Text Available Active quantum error correction on topological codes is one of the most promising routes to long-term qubit storage. In view of future applications, the scalability of the used decoding algorithms in physical implementations is crucial. In this work, we focus on the one-dimensional Majorana chain and construct a strictly local decoder based on a self-dual cellular automaton. We study numerically and analytically its performance and exploit these results to contrive a scalable decoder with exponentially growing decoherence times in the presence of noise. Our results pave the way for scalable and modular designs of actively corrected one-dimensional topological quantum memories.

Quantum gates by inverse engineering of a Hamiltonian

Science.gov (United States)

Santos, Alan C.

2018-01-01

Inverse engineering of a Hamiltonian (IEH) from an evolution operator is a useful technique for the protocol of quantum control with potential applications in quantum information processing. In this paper we introduce a particular protocol to perform IEH and we show how this scheme can be used to implement a set of quantum gates by using minimal quantum resources (such as entanglement, interactions between more than two qubits or auxiliary qubits). Remarkably, while previous protocols request three-qubit interactions and/or auxiliary qubits to implement such gates, our protocol requires just two-qubit interactions and no auxiliary qubits. By using this approach we can obtain a large class of Hamiltonians that allow us to implement single and two-qubit gates necessary for quantum computation. To conclude this article we analyze the performance of our scheme against systematic errors related to amplitude noise, where we show that the free parameters introduced in our scheme can be useful for enhancing the robustness of the protocol against such errors.

Quantum limitations on the sensitivity of gravitational wave detectors with free masses

International Nuclear Information System (INIS)

Tsyplyaev, S.A.

1989-01-01

The problem of recording a classical disturbance by tracking the coordinate of a free particle is examined within the scope of nonrelativistic quantum mechanics. The absence of the fundamental limitation on the sensitivity - the standard quantum limit - is proven. An arbitrarily small disturbance can be recorded with preparation of the system in a quantum state having a negative quantum correlation coefficient between the observable coordinate and momentum. It is shown that it belongs to the collective coherent states - the condensed states. Arguments are presented for the absence of fundamental quantum limits on the magnitude of the recordable disturbance in the measurement of an arbitrary observable with a continuous spectrum

Mysterious quantum Cheshire cat: an illusion

Science.gov (United States)

Michielsen, K.; Lippert, Th.; De Raedt, H.

2015-09-01

We provide a mystery-free explanation for the experimentally observed facts in the neutron interferometry quantum Cheshire cat experiment of Denkmayr et al. [Nat. Comm. 5, 4492, 2014] in terms of a discrete-event simulation model, demonstrating that the quantum Cheshire cat is an illusion.

Error bounds for molecular Hamiltonians inverted from experimental data

International Nuclear Information System (INIS)

Geremia, J.M.; Rabitz, Herschel

2003-01-01

Inverting experimental data provides a powerful technique for obtaining information about molecular Hamiltonians. However, rigorously quantifying how laboratory error propagates through the inversion algorithm has always presented a challenge. In this paper, we develop an inversion algorithm that realistically treats experimental error. It propagates the distribution of observed laboratory measurements into a family of Hamiltonians that are statistically consistent with the distribution of the data. This algorithm is built upon the formalism of map-facilitated inversion to alleviate computational expense and permit the use of powerful nonlinear optimization algorithms. Its capabilities are demonstrated by identifying inversion families for the X 1 Σ g + and a 3 Σ u + states of Na 2 that are consistent with the laboratory data

Quantum computing

International Nuclear Information System (INIS)

Steane, Andrew

1998-01-01

classical information theory and, arguably, quantum from classical physics. Basic quantum information ideas are next outlined, including qubits and data compression, quantum gates, the 'no cloning' property and teleportation. Quantum cryptography is briefly sketched. The universal quantum computer (QC) is described, based on the Church-Turing principle and a network model of computation. Algorithms for such a computer are discussed, especially those for finding the period of a function, and searching a random list. Such algorithms prove that a QC of sufficiently precise construction is not only fundamentally different from any computer which can only manipulate classical information, but can compute a small class of functions with greater efficiency. This implies that some important computational tasks are impossible for any device apart from a QC. To build a universal QC is well beyond the abilities of current technology. However, the principles of quantum information physics can be tested on smaller devices. The current experimental situation is reviewed, with emphasis on the linear ion trap, high-Q optical cavities, and nuclear magnetic resonance methods. These allow coherent control in a Hilbert space of eight dimensions (three qubits) and should be extendable up to a thousand or more dimensions (10 qubits). Among other things, these systems will allow the feasibility of quantum computing to be assessed. In fact such experiments are so difficult that it seemed likely until recently that a practically useful QC (requiring, say, 1000 qubits) was actually ruled out by considerations of experimental imprecision and the unavoidable coupling between any system and its environment. However, a further fundamental part of quantum information physics provides a solution to this impasse. This is quantum error correction (QEC). An introduction to QEC is provided. The evolution of the QC is restricted to a carefully chosen subspace of its Hilbert space. Errors are almost certain to

Quantum computing

Energy Technology Data Exchange (ETDEWEB)

Steane, Andrew [Department of Atomic and Laser Physics, University of Oxford, Clarendon Laboratory, Oxford (United Kingdom)

1998-02-01

classical information theory and, arguably, quantum from classical physics. Basic quantum information ideas are next outlined, including qubits and data compression, quantum gates, the 'no cloning' property and teleportation. Quantum cryptography is briefly sketched. The universal quantum computer (QC) is described, based on the Church-Turing principle and a network model of computation. Algorithms for such a computer are discussed, especially those for finding the period of a function, and searching a random list. Such algorithms prove that a QC of sufficiently precise construction is not only fundamentally different from any computer which can only manipulate classical information, but can compute a small class of functions with greater efficiency. This implies that some important computational tasks are impossible for any device apart from a QC. To build a universal QC is well beyond the abilities of current technology. However, the principles of quantum information physics can be tested on smaller devices. The current experimental situation is reviewed, with emphasis on the linear ion trap, high-Q optical cavities, and nuclear magnetic resonance methods. These allow coherent control in a Hilbert space of eight dimensions (three qubits) and should be extendable up to a thousand or more dimensions (10 qubits). Among other things, these systems will allow the feasibility of quantum computing to be assessed. In fact such experiments are so difficult that it seemed likely until recently that a practically useful QC (requiring, say, 1000 qubits) was actually ruled out by considerations of experimental imprecision and the unavoidable coupling between any system and its environment. However, a further fundamental part of quantum information physics provides a solution to this impasse. This is quantum error correction (QEC). An introduction to QEC is provided. The evolution of the QC is restricted to a carefully chosen subspace of its Hilbert space. Errors are almost certain to

Experimental test of quantum nonlocality in three-photon Greenberger-Horne-Zeilinger entanglement

Science.gov (United States)

Pan; Bouwmeester; Daniell; Weinfurter; Zeilinger

2000-02-03

Bell's theorem states that certain statistical correlations predicted by quantum physics for measurements on two-particle systems cannot be understood within a realistic picture based on local properties of each individual particle-even if the two particles are separated by large distances. Einstein, Podolsky and Rosen first recognized the fundamental significance of these quantum correlations (termed 'entanglement' by Schrodinger) and the two-particle quantum predictions have found ever-increasing experimental support. A more striking conflict between quantum mechanical and local realistic predictions (for perfect correlations) has been discovered; but experimental verification has been difficult, as it requires entanglement between at least three particles. Here we report experimental confirmation of this conflict, using our recently developed method to observe three-photon entanglement, or 'Greenberger-Horne-Zeilinger' (GHZ) states. The results of three specific experiments, involving measurements of polarization correlations between three photons, lead to predictions for a fourth experiment; quantum physical predictions are mutually contradictory with expectations based on local realism. We find the results of the fourth experiment to be in agreement with the quantum prediction and in striking conflict with local realism.

Focus on Quantum Cryptography

International Nuclear Information System (INIS)

Kwiat, Paul G.

2002-01-01

Full text: In our modern era of telecommunications and the Internet, information has become a valuable commodity. Sometimes it must therefore be protected against theft - in this case, loss of secret information to an eavesdropper. Most of today's transactions are protected using encryption unproven to be secure against a computational attack by a classical computer and, in fact, the standardly used encryption algorithms are provably vulnerable to the mind-boggling parallelism of a quantum computer, should one ever be physically realized. Enter quantum cryptography. Underlying nearly all forms of encryption is the necessity for a truly secret key, a random string of zeros and ones; the basic notion of quantum cryptography is to employ single photon transmissions (or the closest attainable approximation to these) to distribute the random key material, while removing the threat of an undetected eavesdropper. Now, nearly twenty years since the seminal quantum cryptography paper by Bennett and Brassard (Bennett C H and Brassard G 1984 Proc. IEEE Int. Conf. on Computers, Systems, and Signal Processing (Bangalore) (New York: IEEE) pp 175-9), we take a look at several state-of-the-art implementations, and glimpse how future quantum cryptosystems might look. We start with papers from three of the world's leading experimental quantum cryptography efforts: Stucki et al and Bethune and Risk describe working systems for quantum key distribution (QKD) over telecommunications fibres (at 1550 nanometres and 1300 nanometres, respectively). The former's achievement of quantum key exchange over 67 kilometres of optical fibre is a world record, as is the experimental demonstration by Hughes et al of daylight free-space QKD over a 10 km atmospheric range. Next, Luetkenhaus and Jahma explore the possible vulnerabilities of such systems (which employ attenuated laser pulses instead of actual single photon states) to conceivable future eavesdropping technologies. Enzer et al have

Experimental demonstration of squeezed-state quantum averaging

DEFF Research Database (Denmark)

Lassen, Mikael Østergaard; Madsen, Lars Skovgaard; Sabuncu, Metin

2010-01-01

We propose and experimentally demonstrate a universal quantum averaging process implementing the harmonic mean of quadrature variances. The averaged variances are prepared probabilistically by means of linear optical interference and measurement-induced conditioning. We verify that the implemented...

Reality, locality and all that: "experimental metaphysics" and the quantum foundations

Science.gov (United States)

Cavalcanti, Eric G.

2008-10-01

In recent decades there has been a resurge of interest in the foundations of quantum theory, partly motivated by new experimental techniques, partly by the emerging field of quantum information science. Old questions, asked since the seminal article by Einstein, Podolsky and Rosen (EPR), are being revisited. The work of John Bell has changed the direction of investigation by recognising that those fundamental philosophical questions can have, after all, input from experiment. Abner Shimony has aptly termed this new field of enquiry "experimental metaphysics". The objective of this Thesis is to contribute to that body of research, by formalising old concepts, proposing new ones, and finding new results in well-studied areas. Without losing from sight that the appeal of experimental metaphysics comes from the adjective, every major result is followed by clear experimental proposals for quantum-atom optical setups.

Experimental statistical signature of many-body quantum interference

Science.gov (United States)

Giordani, Taira; Flamini, Fulvio; Pompili, Matteo; Viggianiello, Niko; Spagnolo, Nicolò; Crespi, Andrea; Osellame, Roberto; Wiebe, Nathan; Walschaers, Mattia; Buchleitner, Andreas; Sciarrino, Fabio

2018-03-01

Multi-particle interference is an essential ingredient for fundamental quantum mechanics phenomena and for quantum information processing to provide a computational advantage, as recently emphasized by boson sampling experiments. Hence, developing a reliable and efficient technique to witness its presence is pivotal in achieving the practical implementation of quantum technologies. Here, we experimentally identify genuine many-body quantum interference via a recent efficient protocol, which exploits statistical signatures at the output of a multimode quantum device. We successfully apply the test to validate three-photon experiments in an integrated photonic circuit, providing an extensive analysis on the resources required to perform it. Moreover, drawing upon established techniques of machine learning, we show how such tools help to identify the—a priori unknown—optimal features to witness these signatures. Our results provide evidence on the efficacy and feasibility of the method, paving the way for its adoption in large-scale implementations.

Performing quantum computing experiments in the cloud

Science.gov (United States)

Devitt, Simon J.

2016-09-01

Quantum computing technology has reached a second renaissance in the past five years. Increased interest from both the private and public sector combined with extraordinary theoretical and experimental progress has solidified this technology as a major advancement in the 21st century. As anticipated my many, some of the first realizations of quantum computing technology has occured over the cloud, with users logging onto dedicated hardware over the classical internet. Recently, IBM has released the Quantum Experience, which allows users to access a five-qubit quantum processor. In this paper we take advantage of this online availability of actual quantum hardware and present four quantum information experiments. We utilize the IBM chip to realize protocols in quantum error correction, quantum arithmetic, quantum graph theory, and fault-tolerant quantum computation by accessing the device remotely through the cloud. While the results are subject to significant noise, the correct results are returned from the chip. This demonstrates the power of experimental groups opening up their technology to a wider audience and will hopefully allow for the next stage of development in quantum information technology.

Experimental quantum ratchets based on nanostructures

International Nuclear Information System (INIS)

Linke, H.; Loefgren, A.; Sheng, W.; Xu, H.; Svensson, A.; Omling, P.; Lindelof, P.E.

1999-01-01

Full text: A number of biological processes, for instance muscular contraction and intracellular transport, are based on a fascinating physical principle: In periodic, asymmetric potentials, so-called ratchets, the random motion of Brownian particles can be put to use by extracting energy from nonequilibrium fluctuations. These findings have recently revived interest in physics to explore the general principles of ratchet effects. So far, most ratchet systems studied assumed or used classical systems. In extension of this previous work, highly interesting and new physics can also be expected from ratchet mechanisms that rely on quantum processes. In this contribution, the requirements for experimental studies of quantum ratchet effects will be discussed, and it will be pointed out that these prerequisites are ideally fulfilled in semiconductor- and metal-nanostructures. As an example, experimental and theoretical results will be presented showing that phase-coherent, asymmetric (triangular) electron cavities can partially rectify an applied AC voltage. Using this effect, which is related to electron wave interference, an electron current can be generated without applied net field

Assessing the quantum physics impacts on future x-ray free-electron lasers

Energy Technology Data Exchange (ETDEWEB)

Schmitt, Mark J. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Anisimov, Petr Mikhaylovich [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2017-10-06

A new quantum mechanical theory of x-ray free electron lasers (XFELs) has been successfully developed that has placed LANL at the forefront of the understanding of quantum effects in XFELs. Our quantum theory describes the interaction of relativistic electrons with x-ray radiation in the periodic magnetic field of an undulator using the same mathematical formalism as classical XFEL theory. This places classical and quantum treatments on the same footing and allows for a continuous transition from one regime to the other eliminating the disparate analytical approaches previously used. Moreover, Dr. Anisimov, the architect of this new theory, is now considered a resource in the international FEL community for assessing quantum effects in XFELs.

Controlling qubit drift by recycling error correction syndromes

Science.gov (United States)

Blume-Kohout, Robin

2015-03-01

Physical qubits are susceptible to systematic drift, above and beyond the stochastic Markovian noise that motivates quantum error correction. This parameter drift must be compensated - if it is ignored, error rates will rise to intolerable levels - but compensation requires knowing the parameters' current value, which appears to require halting experimental work to recalibrate (e.g. via quantum tomography). Fortunately, this is untrue. I show how to perform on-the-fly recalibration on the physical qubits in an error correcting code, using only information from the error correction syndromes. The algorithm for detecting and compensating drift is very simple - yet, remarkably, when used to compensate Brownian drift in the qubit Hamiltonian, it achieves a stabilized error rate very close to the theoretical lower bound. Against 1/f noise, it is less effective only because 1/f noise is (like white noise) dominated by high-frequency fluctuations that are uncompensatable. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE

Free energies of binding from large-scale first-principles quantum mechanical calculations: application to ligand hydration energies.

Science.gov (United States)

Fox, Stephen J; Pittock, Chris; Tautermann, Christofer S; Fox, Thomas; Christ, Clara; Malcolm, N O J; Essex, Jonathan W; Skylaris, Chris-Kriton

2013-08-15

Schemes of increasing sophistication for obtaining free energies of binding have been developed over the years, where configurational sampling is used to include the all-important entropic contributions to the free energies. However, the quality of the results will also depend on the accuracy with which the intermolecular interactions are computed at each molecular configuration. In this context, the energy change associated with the rearrangement of electrons (electronic polarization and charge transfer) upon binding is a very important effect. Classical molecular mechanics force fields do not take this effect into account explicitly, and polarizable force fields and semiempirical quantum or hybrid quantum-classical (QM/MM) calculations are increasingly employed (at higher computational cost) to compute intermolecular interactions in free-energy schemes. In this work, we investigate the use of large-scale quantum mechanical calculations from first-principles as a way of fully taking into account electronic effects in free-energy calculations. We employ a one-step free-energy perturbation (FEP) scheme from a molecular mechanical (MM) potential to a quantum mechanical (QM) potential as a correction to thermodynamic integration calculations within the MM potential. We use this approach to calculate relative free energies of hydration of small aromatic molecules. Our quantum calculations are performed on multiple configurations from classical molecular dynamics simulations. The quantum energy of each configuration is obtained from density functional theory calculations with a near-complete psinc basis set on over 600 atoms using the ONETEP program.

Optical modeling based on mean free path calculations for quantum dot phosphors applied to optoelectronic devices.

Science.gov (United States)

Shin, Min-Ho; Kim, Hyo-Jun; Kim, Young-Joo

2017-02-20

We proposed an optical simulation model for the quantum dot (QD) nanophosphor based on the mean free path concept to understand precisely the optical performance of optoelectronic devices. A measurement methodology was also developed to get the desired optical characteristics such as the mean free path and absorption spectra for QD nanophosphors which are to be incorporated into the simulation. The simulation results for QD-based white LED and OLED displays show good agreement with the experimental values from the fabricated devices in terms of spectral power distribution, chromaticity coordinate, CCT, and CRI. The proposed simulation model and measurement methodology can be applied easily to the design of lots of optoelectronics devices using QD nanophosphors to obtain high efficiency and the desired color characteristics.

Information theoretic resources in quantum theory

Science.gov (United States)

Meznaric, Sebastian

Resource identification and quantification is an essential element of both classical and quantum information theory. Entanglement is one of these resources, arising when quantum communication and nonlocal operations are expensive to perform. In the first part of this thesis we quantify the effective entanglement when operations are additionally restricted to account for both fundamental restrictions on operations, such as those arising from superselection rules, as well as experimental errors arising from the imperfections in the apparatus. For an important class of errors we find a linear relationship between the usual and effective higher dimensional generalization of concurrence, a measure of entanglement. Following the treatment of effective entanglement, we focus on a related concept of nonlocality in the presence of superselection rules (SSR). Here we propose a scheme that may be used to activate nongenuinely multipartite nonlocality, in that a single copy of a state is not multipartite nonlocal, while two or more copies exhibit nongenuinely multipartite nonlocality. The states used exhibit the more powerful genuinely multipartite nonlocality when SSR are not enforced, but not when they are, raising the question of what is needed for genuinely multipartite nonlocality. We show that whenever the number of particles is insufficient, the degrading of genuinely multipartite to nongenuinely multipartite nonlocality is necessary. While in the first few chapters we focus our attention on understanding the resources present in quantum states, in the final part we turn the picture around and instead treat operations themselves as a resource. We provide our observers with free access to classical operations - ie. those that cannot detect or generate quantum coherence. We show that the operation of interest can then be used to either generate or detect quantum coherence if and only if it violates a particular commutation relation. Using the relative entropy, the

Decoherence-Free Interaction between Giant Atoms in Waveguide Quantum Electrodynamics.

Science.gov (United States)

Kockum, Anton Frisk; Johansson, Göran; Nori, Franco

2018-04-06

In quantum-optics experiments with both natural and artificial atoms, the atoms are usually small enough that they can be approximated as pointlike compared to the wavelength of the electromagnetic radiation with which they interact. However, superconducting qubits coupled to a meandering transmission line, or to surface acoustic waves, can realize "giant artificial atoms" that couple to a bosonic field at several points which are wavelengths apart. Here, we study setups with multiple giant atoms coupled at multiple points to a one-dimensional (1D) waveguide. We show that the giant atoms can be protected from decohering through the waveguide, but still have exchange interactions mediated by the waveguide. Unlike in decoherence-free subspaces, here the entire multiatom Hilbert space (2^{N} states for N atoms) is protected from decoherence. This is not possible with "small" atoms. We further show how this decoherence-free interaction can be designed in setups with multiple atoms to implement, e.g., a 1D chain of atoms with nearest-neighbor couplings or a collection of atoms with all-to-all connectivity. This may have important applications in quantum simulation and quantum computing.

Decoherence-Free Interaction between Giant Atoms in Waveguide Quantum Electrodynamics

Science.gov (United States)

Kockum, Anton Frisk; Johansson, Göran; Nori, Franco

2018-04-01

In quantum-optics experiments with both natural and artificial atoms, the atoms are usually small enough that they can be approximated as pointlike compared to the wavelength of the electromagnetic radiation with which they interact. However, superconducting qubits coupled to a meandering transmission line, or to surface acoustic waves, can realize "giant artificial atoms" that couple to a bosonic field at several points which are wavelengths apart. Here, we study setups with multiple giant atoms coupled at multiple points to a one-dimensional (1D) waveguide. We show that the giant atoms can be protected from decohering through the waveguide, but still have exchange interactions mediated by the waveguide. Unlike in decoherence-free subspaces, here the entire multiatom Hilbert space (2N states for N atoms) is protected from decoherence. This is not possible with "small" atoms. We further show how this decoherence-free interaction can be designed in setups with multiple atoms to implement, e.g., a 1D chain of atoms with nearest-neighbor couplings or a collection of atoms with all-to-all connectivity. This may have important applications in quantum simulation and quantum computing.

Characterizing a four-qubit planar lattice for arbitrary error detection

Science.gov (United States)

Chow, Jerry M.; Srinivasan, Srikanth J.; Magesan, Easwar; Córcoles, A. D.; Abraham, David W.; Gambetta, Jay M.; Steffen, Matthias

2015-05-01

Quantum error correction will be a necessary component towards realizing scalable quantum computers with physical qubits. Theoretically, it is possible to perform arbitrarily long computations if the error rate is below a threshold value. The two-dimensional surface code permits relatively high fault-tolerant thresholds at the ~1% level, and only requires a latticed network of qubits with nearest-neighbor interactions. Superconducting qubits have continued to steadily improve in coherence, gate, and readout fidelities, to become a leading candidate for implementation into larger quantum networks. Here we describe characterization experiments and calibration of a system of four superconducting qubits arranged in a planar lattice, amenable to the surface code. Insights into the particular qubit design and comparison between simulated parameters and experimentally determined parameters are given. Single- and two-qubit gate tune-up procedures are described and results for simultaneously benchmarking pairs of two-qubit gates are given. All controls are eventually used for an arbitrary error detection protocol described in separate work [Corcoles et al., Nature Communications, 6, 2015].

Experimental benchmarking of quantum control in zero-field nuclear magnetic resonance.

Science.gov (United States)

Jiang, Min; Wu, Teng; Blanchard, John W; Feng, Guanru; Peng, Xinhua; Budker, Dmitry

2018-06-01

Demonstration of coherent control and characterization of the control fidelity is important for the development of quantum architectures such as nuclear magnetic resonance (NMR). We introduce an experimental approach to realize universal quantum control, and benchmarking thereof, in zero-field NMR, an analog of conventional high-field NMR that features less-constrained spin dynamics. We design a composite pulse technique for both arbitrary one-spin rotations and a two-spin controlled-not (CNOT) gate in a heteronuclear two-spin system at zero field, which experimentally demonstrates universal quantum control in such a system. Moreover, using quantum information-inspired randomized benchmarking and partial quantum process tomography, we evaluate the quality of the control, achieving single-spin control for 13 C with an average fidelity of 0.9960(2) and two-spin control via a CNOT gate with a fidelity of 0.9877(2). Our method can also be extended to more general multispin heteronuclear systems at zero field. The realization of universal quantum control in zero-field NMR is important for quantum state/coherence preparation, pulse sequence design, and is an essential step toward applications to materials science, chemical analysis, and fundamental physics.

Two-quantum Doppler-free induced gamma emission

International Nuclear Information System (INIS)

Zadernovsky, A.A.

1999-01-01

Reported here is a theoretical study of an alternative way to remove the pernicious influence of chaotic motion of free nuclei by means of external ignition of two-quantum IGE process in counter-propagating intense photon beams. The performed analysis reveals the main advantages and drawbacks of this method. The following conclusions are underlined: 1. in contrast to single-quantum emission in an ensemble of nuclei with Doppler-broadened gain line, this method involves all nuclei regardless of there individual velocities; 2. a specific dynamic distributed feedback is in this case established in absence of any reflecting structures; 3. because of non-linearity of the feedback, with a coefficient proportional to the photon flux density of the igniting beam, the excitation of nuclei is released in an avalanche-like manner, which result in emission of a giant pulse of gamma quanta; 4. at present, the implementation of such a process is impeded by the absence of a source of igniting gamma quanta, with the sufficient photon flux density. Therefore the advantage of the propose technique may manifests themselves only in designing a final stage of a source of gamma quanta (e.g., in X-ray or gamma-ray laser, relativistic undulator, free electron laser, etc.) for production of short giant pulse of coherent gamma photons. (author)

Quantum theory for 1D X-ray free electron laser

Science.gov (United States)

Anisimov, Petr M.

2018-06-01

Classical 1D X-ray Free Electron Laser (X-ray FEL) theory has stood the test of time by guiding FEL design and development prior to any full-scale analysis. Future X-ray FELs and inverse-Compton sources, where photon recoil approaches an electron energy spread value, push the classical theory to its limits of applicability. After substantial efforts by the community to find what those limits are, there is no universally agreed upon quantum approach to design and development of future X-ray sources. We offer a new approach to formulate the quantum theory for 1D X-ray FELs that has an obvious connection to the classical theory, which allows for immediate transfer of knowledge between the two regimes. We exploit this connection in order to draw quantum mechanical conclusions about the quantum nature of electrons and generated radiation in terms of FEL variables.

Overcoming correlation fluctuations in two-photon interference experiments with differently bright and independently blinking remote quantum emitters

Science.gov (United States)

Weber, Jonas H.; Kettler, Jan; Vural, Hüseyin; Müller, Markus; Maisch, Julian; Jetter, Michael; Portalupi, Simone L.; Michler, Peter

2018-05-01

As a fundamental building block for quantum computation and communication protocols, the correct verification of the two-photon interference (TPI) contrast between two independent quantum light sources is of utmost importance. Here, we experimentally demonstrate how frequently present blinking dynamics and changes in emitter brightness critically affect the Hong-Ou-Mandel-type (HOM) correlation histograms of remote TPI experiments measured via the commonly utilized setup configuration. We further exploit this qualitative and quantitative explanation of the observed correlation dynamics to establish an alternative interferometer configuration, which is overcoming the discussed temporal fluctuations, giving rise to an error-free determination of the remote TPI visibility. We prove full knowledge of the obtained correlation by reproducing the measured correlation statistics via Monte Carlo simulations. As an exemplary system, we make use of two pairs of remote semiconductor quantum dots; however, the same conclusions apply for TPI experiments with flying qubits from any kind of remote solid-state quantum emitters.

Experimental characterization of a 400 Gbit/s orbital angular momentum multiplexed free-space optical link over 120 m.

Science.gov (United States)

Ren, Yongxiong; Wang, Zhe; Liao, Peicheng; Li, Long; Xie, Guodong; Huang, Hao; Zhao, Zhe; Yan, Yan; Ahmed, Nisar; Willner, Asher; Lavery, Martin P J; Ashrafi, Nima; Ashrafi, Solyman; Bock, Robert; Tur, Moshe; Djordjevic, Ivan B; Neifeld, Mark A; Willner, Alan E

2016-02-01

We experimentally demonstrate and characterize the performance of a 400-Gbit/s orbital angular momentum (OAM) multiplexed free-space optical link over 120 m on the roof of a building. Four OAM beams, each carrying a 100-Gbit/s quadrature-phase-shift-keyed channel are multiplexed and transmitted. We investigate the influence of channel impairments on the received power, intermodal crosstalk among channels, and system power penalties. Without laser tracking and compensation systems, the measured received power and crosstalk among OAM channels fluctuate by 4.5 dB and 5 dB, respectively, over 180 s. For a beam displacement of 2 mm that corresponds to a pointing error less than 16.7 μrad, the link bit error rates are below the forward error correction threshold of 3.8×10(-3) for all channels. Both experimental and simulation results show that power penalties increase rapidly when the displacement increases.

Quantum information processing and nuclear magnetic resonance

International Nuclear Information System (INIS)

Cummins, H.K.

2001-01-01

Quantum computers are information processing devices which operate by and exploit the laws of quantum mechanics, potentially allowing them to solve problems which are intractable using classical computers. This dissertation considers the practical issues involved in one of the more successful implementations to date, nuclear magnetic resonance (NMR). Techniques for dealing with systematic errors are presented, and a quantum protocol is implemented. Chapter 1 is a brief introduction to quantum computation. The physical basis of its efficiency and issues involved in its implementation are discussed. NMR quantum information processing is reviewed in more detail in Chapter 2. Chapter 3 considers some of the errors that may be introduced in the process of implementing an algorithm, and high-level ways of reducing the impact of these errors by using composite rotations. Novel general expressions for stabilising composite rotations are presented in Chapter 4 and a new class of composite rotations, tailored composite rotations, presented in Chapter 5. Chapter 6 describes some of the advantages and pitfalls of combining composite rotations. Experimental evaluations of the composite rotations are given in each case. An actual implementation of a quantum information protocol, approximate quantum cloning, is presented in Chapter 7. The dissertation ends with appendices which contain expansions of some equations and detailed calculations of certain composite rotation results, as well as spectrometer pulse sequence programs. (author)

Long-distance free-space distribution of quantum entanglement over Vienna

International Nuclear Information System (INIS)

Lindenthal, M.; Resch, K.; Blauensteiner, B.; Boehm, H.; Fedrizzi, A.; Kurtsiefer, C.; Poppe, A.; Schmitt-Manderbach, T.; Taraba, M.; Ursin, R.; Walther, P.; Weier, H.; Weinfurter, H.; Zeilinger, A.

2005-01-01

Full text: We have established a real-world free-space quantum channel over 7.8 km and demonstrate the distribution of entangled photons. The transmitter is placed at an observatory and the receiver on the 46th floor of an office skyscraper in Vienna, Austria. Using locally recorded time stamps and a public internet channel, coincident counts from correlated photons are demonstrated to violate a Bell inequality by 14 standard deviations. This confirms the high quality of the shared entanglement. In this experiment the horizontal freespace distance is chosen, so that the attenuation the light undergoes corresponds approximately to the attenuation from space to earth. This work is an encouraging step towards satellite-based distribution of quantum entanglement and future intra-city quantum networks. (author)

Tradeoff between energy and error in the discrimination of quantum-optical devices

Energy Technology Data Exchange (ETDEWEB)

Bisio, Alessandro; Dall' Arno, Michele; D' Ariano, Giacomo Mauro [Quit group, Dipartimento di Fisica ' ' A. Volta' ' , via Bassi 6, I-27100 Pavia (Italy) and Istituto Nazionale di Fisica Nucleare, Gruppo IV, via Bassi 6, I-27100 Pavia (Italy)

2011-07-15

We address the problem of energy-error tradeoff in the discrimination between two linear passive quantum optical devices with a single use. We provide an analytical derivation of the optimal strategy for beamsplitters and an iterative algorithm converging to the optimum in the general case. We then compare the optimal strategy with a simpler strategy using coherent input states and homodyne detection. It turns out that the former requires much less energy in order to achieve the same performances.

Tradeoff between energy and error in the discrimination of quantum-optical devices

International Nuclear Information System (INIS)

Bisio, Alessandro; Dall'Arno, Michele; D'Ariano, Giacomo Mauro

2011-01-01

We address the problem of energy-error tradeoff in the discrimination between two linear passive quantum optical devices with a single use. We provide an analytical derivation of the optimal strategy for beamsplitters and an iterative algorithm converging to the optimum in the general case. We then compare the optimal strategy with a simpler strategy using coherent input states and homodyne detection. It turns out that the former requires much less energy in order to achieve the same performances.

Separable and Error-Free Reversible Data Hiding in Encrypted Image with High Payload

Directory of Open Access Journals (Sweden)

Zhaoxia Yin

2014-01-01

Full Text Available This paper proposes a separable reversible data-hiding scheme in encrypted image which offers high payload and error-free data extraction. The cover image is partitioned into nonoverlapping blocks and multigranularity encryption is applied to obtain the encrypted image. The data hider preprocesses the encrypted image and randomly selects two basic pixels in each block to estimate the block smoothness and indicate peak points. Additional data are embedded into blocks in the sorted order of block smoothness by using local histogram shifting under the guidance of the peak points. At the receiver side, image decryption and data extraction are separable and can be free to choose. Compared to previous approaches, the proposed method is simpler in calculation while offering better performance: larger payload, better embedding quality, and error-free data extraction, as well as image recovery.

Optimal quantum error correcting codes from absolutely maximally entangled states

Science.gov (United States)

Raissi, Zahra; Gogolin, Christian; Riera, Arnau; Acín, Antonio

2018-02-01

Absolutely maximally entangled (AME) states are pure multi-partite generalizations of the bipartite maximally entangled states with the property that all reduced states of at most half the system size are in the maximally mixed state. AME states are of interest for multipartite teleportation and quantum secret sharing and have recently found new applications in the context of high-energy physics in toy models realizing the AdS/CFT-correspondence. We work out in detail the connection between AME states of minimal support and classical maximum distance separable (MDS) error correcting codes and, in particular, provide explicit closed form expressions for AME states of n parties with local dimension \

Demonstration of free-space reference frame independent quantum key distribution

International Nuclear Information System (INIS)

Wabnig, J; Bitauld, D; Li, H W; Niskanen, A O; Laing, A; O'Brien, J L

2013-01-01

Quantum key distribution (QKD) is moving from research laboratories towards applications. As computing becomes more mobile, cashless as well as cardless payment solutions are introduced. A possible route to increase the security of wireless communications is to incorporate QKD in a mobile device. Handheld devices present a particular challenge as the orientation and the phase of a qubit will depend on device motion. This problem is addressed by the reference frame independent (RFI) QKD scheme. The scheme tolerates an unknown phase between logical states that vary slowly compared to the rate of particle repetition. Here we experimentally demonstrate the feasibility of RFI QKD over a free-space link in a prepare and measure scheme using polarization encoding. We extend the security analysis of the RFI QKD scheme to be able to deal with uncalibrated devices and a finite number of measurements. Together these advances are an important step towards mass production of handheld QKD devices. (paper)

Complex Quantum Network Manifolds in Dimension d > 2 are Scale-Free

Science.gov (United States)

Bianconi, Ginestra; Rahmede, Christoph

2015-09-01

In quantum gravity, several approaches have been proposed until now for the quantum description of discrete geometries. These theoretical frameworks include loop quantum gravity, causal dynamical triangulations, causal sets, quantum graphity, and energetic spin networks. Most of these approaches describe discrete spaces as homogeneous network manifolds. Here we define Complex Quantum Network Manifolds (CQNM) describing the evolution of quantum network states, and constructed from growing simplicial complexes of dimension . We show that in d = 2 CQNM are homogeneous networks while for d > 2 they are scale-free i.e. they are characterized by large inhomogeneities of degrees like most complex networks. From the self-organized evolution of CQNM quantum statistics emerge spontaneously. Here we define the generalized degrees associated with the -faces of the -dimensional CQNMs, and we show that the statistics of these generalized degrees can either follow Fermi-Dirac, Boltzmann or Bose-Einstein distributions depending on the dimension of the -faces.

Minimum-error quantum distinguishability bounds from matrix monotone functions: A comment on 'Two-sided estimates of minimum-error distinguishability of mixed quantum states via generalized Holevo-Curlander bounds' [J. Math. Phys. 50, 032106 (2009)

International Nuclear Information System (INIS)

Tyson, Jon

2009-01-01

Matrix monotonicity is used to obtain upper bounds on minimum-error distinguishability of arbitrary ensembles of mixed quantum states. This generalizes one direction of a two-sided bound recently obtained by the author [J. Tyson, J. Math. Phys. 50, 032106 (2009)]. It is shown that the previously obtained special case has unique properties.

Experimental investigation of a four-qubit linear-optical quantum logic circuit.

Science.gov (United States)

Stárek, R; Mičuda, M; Miková, M; Straka, I; Dušek, M; Ježek, M; Fiurášek, J

2016-09-20

We experimentally demonstrate and characterize a four-qubit linear-optical quantum logic circuit. Our robust and versatile scheme exploits encoding of two qubits into polarization and path degrees of single photons and involves two crossed inherently stable interferometers. This approach allows us to design a complex quantum logic circuit that combines a genuine four-qubit C(3)Z gate and several two-qubit and single-qubit gates. The C(3)Z gate introduces a sign flip if and only if all four qubits are in the computational state |1〉. We verify high-fidelity performance of this central four-qubit gate using Hofmann bounds on quantum gate fidelity and Monte Carlo fidelity sampling. We also experimentally demonstrate that the quantum logic circuit can generate genuine multipartite entanglement and we certify the entanglement with the use of suitably tailored entanglement witnesses.

Quantum driving of a two level system: quantum speed limit and superadiabatic protocols – an experimental investigation

International Nuclear Information System (INIS)

Malossi, N; Arimondo, E; Ciampini, D; Mannella, R; Bason, M G; Viteau, M; Morsch, O

2013-01-01

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.

Proposed test of macroscopic quantum contextuality

International Nuclear Information System (INIS)

Cabello, Adan

2010-01-01

We show that, for any system with a number of levels which can be identified with n qubits, there is an inequality for the correlations between three compatible dichotomic measurements which must be satisfied by any noncontextual theory, but is violated by any quantum state. Remarkably, the violation grows exponentially with n, and the tolerated error per correlation also increases with n, showing that state-independent quantum contextuality is experimentally observable in complex systems.

Rigorous quantum limits on monitoring free masses and harmonic oscillators

Science.gov (United States)

Roy, S. M.

2018-03-01

There are heuristic arguments proposing that the accuracy of monitoring position of a free mass m is limited by the standard quantum limit (SQL): σ2( X (t ) ) ≥σ2( X (0 ) ) +(t2/m2) σ2( P (0 ) ) ≥ℏ t /m , where σ2( X (t ) ) and σ2( P (t ) ) denote variances of the Heisenberg representation position and momentum operators. Yuen [Phys. Rev. Lett. 51, 719 (1983), 10.1103/PhysRevLett.51.719] discovered that there are contractive states for which this result is incorrect. Here I prove universally valid rigorous quantum limits (RQL), viz. rigorous upper and lower bounds on σ2( X (t ) ) in terms of σ2( X (0 ) ) and σ2( P (0 ) ) , given by Eq. (12) for a free mass and by Eq. (36) for an oscillator. I also obtain the maximally contractive and maximally expanding states which saturate the RQL, and use the contractive states to set up an Ozawa-type measurement theory with accuracies respecting the RQL but beating the standard quantum limit. The contractive states for oscillators improve on the Schrödinger coherent states of constant variance and may be useful for gravitational wave detection and optical communication.

Phosphine-free synthesis and characterization of type-II ZnSe/CdS core-shell quantum dots

Science.gov (United States)

Ghasemzadeh, Roghayyeh; Armanmehr, Mohammad Hasan; Abedi, Mohammad; Fateh, Davood Sadeghi; Bahreini, Zaker

2018-01-01

A phosphine-free route for synthesis of type-II ZnSe/CdS core-shell quantum dots, using green, low cost and environmentally friendly reagents and phosphine-free solvents such as 1-octadecene (ODE) and liquid paraffin has been reported. Hot-injection technique has been used for the synthesis of ZnSe core quantum dots. The CdS shell quantum dots prepared by reaction of CdO precursor and S powder in 1-octadecene (ODE). The ZnSe/CdS core-shell quantum dots were synthesized via successive ion layer adsorption and reaction (SILAR) technique. The characterization of produced quantum dots were performed by absorption and fluorescence spectroscopy, X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). The results showed the formation of type-II ZnSe/CdS core-shell quantum dots with FWHM 32 nm and uniform size distribution.

Quantum computation and simulation with trapped ions using dissipation

International Nuclear Information System (INIS)

Schindler, P.

2013-01-01

Quantum information processing combines two of the most successful and fascinating ideas of the 20th century - quantum physics and computer science. A quantum computer promises to solve certain problems more efficient than classical computers. But building such a quantum computer is a cumbersome task as the quantum system needs to be manipulated with tremendous accuracy while being well shielded from the classical environment to preserve its quantum nature. An unwanted coupling to the surrounding environment manifests itself in computational errors. This coupling can be suppressed with the aid of quantum error correction schemes that are still a mainly theoretical construct. These error correcting protocols can only protect the information if they are applied multiple times subsequently. For this, it is necessary to remove the information about previous errors from the quantum system before performing the actual correction. However, this removal of information requires a controlled coupling to the environment which is beyond the standard set of operations available in a quantum computer. In this work, an experimental realization of repetitive quantum error correction in an ion-trap quantum information processor is presented, performing up to three consecutive rounds of correction. Moreover such an error correction algorithm can also be used to demonstrate a physical connection between information processing and quantum mechanics - computational errors are mapped onto quantum mechanical measurements. Therefore, a quantum error correction protocol is able to undo quantum measurements - a task that seemingly contradicts the foundations of quantum physics. In this work, we show that it is indeed possible to undo a partial measurement on a quantum register using an error correction protocol. After closer inspection it becomes obvious this does not violate the laws of quantum mechanics. However, the realization of a large-scale quantum computer lies in the far future as

All-optical XOR logic gate using intersubband transition in III-V quantum well materials.

Science.gov (United States)

Feng, Jijun; Akimoto, Ryoichi; Gozu, Shin-ichiro; Mozume, Teruo

2014-06-02

A monolithically integrated all-optical exclusive-OR (XOR) logic gate is experimentally demonstrated based on a Michelson interferometer (MI) gating device in InGaAs/AlAsSb coupled double quantum wells (CDQWs). The MI arms can convert the pump data with return-to-zero ON-OFF keying (RZ OOK) to binary phase-shift keying (BPSK) format, then two BPSK signals can interfere with each other for realizing a desired logical operation. All-optical format conversion from the RZ OOK to BPSK is based on the cross-phase modulation to the transverse electric (TE) probe wave, which is caused by the intersubband transition excited by the transverse magnetic (TM) pump light. Bit error rate measurements show that error free operation for both BPSK format conversion and XOR logical operation can be achieved.

Single-shot secure quantum network coding on butterfly network with free public communication

Science.gov (United States)

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.

Quantum reading of unitary optical devices

International Nuclear Information System (INIS)

Dall'Arno, Michele; Bisio, Alessandro; D'Ariano, Giacomo Mauro

2014-01-01

We address the problem of quantum reading of optical memories, namely the retrieving of classical information stored in the optical properties of a media with minimum energy. We present optimal strategies for ambiguous and unambiguous quantum reading of unitary optical memories, namely when one's task is to minimize the probability of errors in the retrieved information and when perfect retrieving of information is achieved probabilistically, respectively. A comparison of the optimal strategy with coherent probes and homodyne detection shows that the former saves orders of magnitude of energy when achieving the same performances. Experimental proposals for quantum reading which are feasible with present quantum optical technology are reported

Quantum tunneling of the magnetic moment in a free nanoparticle

International Nuclear Information System (INIS)

O'Keeffe, M.F.; Chudnovsky, E.M.; Garanin, D.A.

2012-01-01

We study tunneling of the magnetic moment in a particle that has full rotational freedom. Exact energy levels are obtained and the ground-state magnetic moment is computed for a symmetric rotor. The effect of mechanical freedom on spin tunneling manifests itself in a strong dependence of the magnetic moment on the moments of inertia of the rotor. The energy of the particle exhibits quantum phase transitions between states with different values of the magnetic moment. Particles of various shapes are investigated and the quantum phase diagram is obtained. - Highlights: ► We obtain an exact analytical solution of a tunneling spin in a mechanical rotator. ► The quantum phase diagram shows magnetic moment dependence on rotator shape and size. ► Our work explains magnetic properties of free atomic clusters and magnetic molecules.

Experimental Errors in QSAR Modeling Sets: What We Can Do and What We Cannot Do.

Science.gov (United States)

Zhao, Linlin; Wang, Wenyi; Sedykh, Alexander; Zhu, Hao

2017-06-30

Numerous chemical data sets have become available for quantitative structure-activity relationship (QSAR) modeling studies. However, the quality of different data sources may be different based on the nature of experimental protocols. Therefore, potential experimental errors in the modeling sets may lead to the development of poor QSAR models and further affect the predictions of new compounds. In this study, we explored the relationship between the ratio of questionable data in the modeling sets, which was obtained by simulating experimental errors, and the QSAR modeling performance. To this end, we used eight data sets (four continuous endpoints and four categorical endpoints) that have been extensively curated both in-house and by our collaborators to create over 1800 various QSAR models. Each data set was duplicated to create several new modeling sets with different ratios of simulated experimental errors (i.e., randomizing the activities of part of the compounds) in the modeling process. A fivefold cross-validation process was used to evaluate the modeling performance, which deteriorates when the ratio of experimental errors increases. All of the resulting models were also used to predict external sets of new compounds, which were excluded at the beginning of the modeling process. The modeling results showed that the compounds with relatively large prediction errors in cross-validation processes are likely to be those with simulated experimental errors. However, after removing a certain number of compounds with large prediction errors in the cross-validation process, the external predictions of new compounds did not show improvement. Our conclusion is that the QSAR predictions, especially consensus predictions, can identify compounds with potential experimental errors. But removing those compounds by the cross-validation procedure is not a reasonable means to improve model predictivity due to overfitting.

A Blueprint for Demonstrating Quantum Supremacy with Superconducting Qubits

Science.gov (United States)

Kechedzhi, Kostyantyn

2018-01-01

Long coherence times and high fidelity control recently achieved in scalable superconducting circuits paved the way for the growing number of experimental studies of many-qubit quantum coherent phenomena in these devices. Albeit full implementation of quantum error correction and fault tolerant quantum computation remains a challenge the near term pre-error correction devices could allow new fundamental experiments despite inevitable accumulation of errors. One such open question foundational for quantum computing is achieving the so called quantum supremacy, an experimental demonstration of a computational task that takes polynomial time on the quantum computer whereas the best classical algorithm would require exponential time and/or resources. It is possible to formulate such a task for a quantum computer consisting of less than a 100 qubits. The computational task we consider is to provide approximate samples from a non-trivial quantum distribution. This is a generalization for the case of superconducting circuits of ideas behind boson sampling protocol for quantum optics introduced by Arkhipov and Aaronson. In this presentation we discuss a proof-of-principle demonstration of such a sampling task on a 9-qubit chain of superconducting gmon qubits developed by Google. We discuss theoretical analysis of the driven evolution of the device resulting in output approximating samples from a uniform distribution in the Hilbert space, a quantum chaotic state. We analyze quantum chaotic characteristics of the output of the circuit and the time required to generate a sufficiently complex quantum distribution. We demonstrate that the classical simulation of the sampling output requires exponential resources by connecting the task of calculating the output amplitudes to the sign problem of the Quantum Monte Carlo method. We also discuss the detailed theoretical modeling required to achieve high fidelity control and calibration of the multi-qubit unitary evolution in the

Graphene quantum dot as a green and facile sensor for free chlorine in drinking water.

Science.gov (United States)

Dong, Yongqiang; Li, Geli; Zhou, Nana; Wang, Ruixue; Chi, Yuwu; Chen, Guonan

2012-10-02

Free chlorine was found to be able to destroy the passivated surface of the graphene quantum dots (GQDs) obtained by pyrolyzing citric acid, resulting in significant quenching of their fluorescence (FL) signal. After optimizing some experimental conditions (including response time, concentration of GQDs, and pH value of solution), a green and facile sensing system has been developed for the detection of free residual chlorine in water based on FL quenching of GQDs. The sensing system exhibits many advantages, such as short response time, excellent selectivity, wide linear response range, and high sensitivity. The linear response range of free chlorine (R(2) = 0.992) was from 0.05 to 10 μM. The detection limit (S/N = 3) was as low as 0.05 μM, which is much lower than that of the most widely used N-N-diethyl-p-phenylenediamine (DPD) colorimetric method. This sensing system was finally used to detect free residual chlorine in local tap water samples. The result agreed well with that by the DPD colorimetric method, suggesting the potential application of this new, green, sensitive, and facile sensing system in drinking water quality monitoring.

Efficiency of coherent-state quantum cryptography in the presence of loss: Influence of realistic error correction

International Nuclear Information System (INIS)

Heid, Matthias; Luetkenhaus, Norbert

2006-01-01

We investigate the performance of a continuous-variable quantum key distribution scheme in a practical setting. More specifically, we take a nonideal error reconciliation procedure into account. The quantum channel connecting the two honest parties is assumed to be lossy but noiseless. Secret key rates are given for the case that the measurement outcomes are postselected or a reverse reconciliation scheme is applied. The reverse reconciliation scheme loses its initial advantage in the practical setting. If one combines postselection with reverse reconciliation, however, much of this advantage can be recovered

Quantum metrology

International Nuclear Information System (INIS)

Xiang Guo-Yong; Guo Guang-Can

2013-01-01

The statistical error is ineluctable in any measurement. Quantum techniques, especially with the development of quantum information, can help us squeeze the statistical error and enhance the precision of measurement. In a quantum system, there are some quantum parameters, such as the quantum state, quantum operator, and quantum dimension, which have no classical counterparts. So quantum metrology deals with not only the traditional parameters, but also the quantum parameters. Quantum metrology includes two important parts: measuring the physical parameters with a precision beating the classical physics limit and measuring the quantum parameters precisely. In this review, we will introduce how quantum characters (e.g., squeezed state and quantum entanglement) yield a higher precision, what the research areas are scientists most interesting in, and what the development status of quantum metrology and its perspectives are. (topical review - quantum information)

Development of an Experimental Measurement System for Human Error Characteristics and a Pilot Test

International Nuclear Information System (INIS)

Jang, Tong-Il; Lee, Hyun-Chul; Moon, Kwangsu

2017-01-01

Some items out of individual and team characteristics were partially selected, and a pilot test was performed to measure and evaluate them using the experimental measurement system of human error characteristics. It is one of the processes to produce input data to the Eco-DBMS. And also, through the pilot test, it was tried to take methods to measure and acquire the physiological data, and to develop data format and quantification methods for the database. In this study, a pilot test to measure the stress and the tension level, and team cognitive characteristics out of human error characteristics was performed using the human error characteristics measurement and experimental evaluation system. In an experiment measuring the stress level, physiological characteristics using EEG was measured in a simulated unexpected situation. As shown in results, although this experiment was pilot, it was validated that relevant results for evaluating human error coping effects of workers’ FFD management guidelines and unexpected situation against guidelines can be obtained. In following researches, additional experiments including other human error characteristics will be conducted. Furthermore, the human error characteristics measurement and experimental evaluation system will be utilized to validate various human error coping solutions such as human factors criteria, design, and guidelines as well as supplement the human error characteristics database.

Quantum key distribution with an entangled light emitting diode

Energy Technology Data Exchange (ETDEWEB)

Dzurnak, B.; Stevenson, R. M.; Nilsson, J.; Dynes, J. F.; Yuan, Z. L.; Skiba-Szymanska, J.; Shields, A. J. [Toshiba Research Europe Limited, 208 Science Park, Milton Road, Cambridge CB4 0GZ (United Kingdom); Farrer, I.; Ritchie, D. A. [Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE (United Kingdom)

2015-12-28

Measurements performed on entangled photon pairs shared between two parties can allow unique quantum cryptographic keys to be formed, creating secure links between users. An advantage of using such entangled photon links is that they can be adapted to propagate entanglement to end users of quantum networks with only untrusted nodes. However, demonstrations of quantum key distribution with entangled photons have so far relied on sources optically excited with lasers. Here, we realize a quantum cryptography system based on an electrically driven entangled-light-emitting diode. Measurement bases are passively chosen and we show formation of an error-free quantum key. Our measurements also simultaneously reveal Bell's parameter for the detected light, which exceeds the threshold for quantum entanglement.

Pseudorandom dynamics of frequency combs in free-running quantum cascade lasers

Science.gov (United States)

Henry, Nathan; Burghoff, David; Yang, Yang; Hu, Qing; Khurgin, Jacob B.

2018-01-01

Recent research has shown that free-running quantum cascade lasers are capable of producing frequency combs in midinfrared and THz regions of the spectrum. Unlike familiar frequency combs originating from mode-locked lasers, these do not require any additional optical elements inside the cavity and have temporal characteristics that are dramatically different from the periodic pulse train of conventional combs. Frequency combs from quantum cascade lasers are characterized by the absence of sharp pulses and strong frequency modulation, periodic with the cavity round trip time but lacking any periodicity within that period. To explicate for this seemingly perplexing behavior, we develop a model of the gain medium using optical Bloch equations that account for hole burning in spectral, spatial, and temporal domains. With this model, we confirm that the most efficient mode of operation of a free-running quantum cascade laser is indeed a pseudorandom frequency-modulated field with nearly constant intensity. We show that the optimum modulation period is commensurate with the gain recovery time of the laser medium and the optimum modulation amplitude is comparable to the gain bandwidth, behavior that has been observed in the experiments.

Uncertainties of predictions from parton distributions 1, experimental errors

CERN Document Server

Martin, A D; Stirling, William James; Thorne, R S; CERN. Geneva

2003-01-01

We determine the uncertainties on observables arising from the errors on the experimental data that are fitted in the global MRST2001 parton analysis. By diagonalizing the error matrix we produce sets of partons suitable for use within the framework of linear propagation of errors, which is the most convenient method for calculating the uncertainties. Despite the potential limitations of this approach we find that it can be made to work well in practice. This is confirmed by our alternative approach of using the more rigorous Lagrange multiplier method to determine the errors on physical quantities directly. As particular examples we determine the uncertainties on the predictions of the charged-current deep-inelastic structure functions, on the cross-sections for W production and for Higgs boson production via gluon--gluon fusion at the Tevatron and the LHC, on the ratio of W-minus to W-plus production at the LHC and on the moments of the non-singlet quark distributions. We discuss the corresponding uncertain...

The effect of experimental sleep fragmentation on error monitoring.

Science.gov (United States)

Ko, Cheng-Hung; Fang, Ya-Wen; Tsai, Ling-Ling; Hsieh, Shulan

2015-01-01

Experimental sleep fragmentation (SF) is characterized by frequent brief arousals without reduced total sleep time and causes daytime sleepiness and impaired neurocognitive processes. This study explored the impact of SF on error monitoring. Thirteen adults underwent auditory stimuli-induced high-level (H) and low-level (L) SF nights. Flanker task performance and electroencephalogram data were collected in the morning following SF nights. Compared to LSF, HSF induced more arousals and stage N1 sleep, decreased slow wave sleep and rapid-eye-movement sleep (REMS), decreased subjective sleep quality, increased daytime sleepiness, and decreased amplitudes of P300 and error-related positivity (Pe). SF effects on N1 sleep were negatively correlated with SF effects on the Pe amplitude. Furthermore, as REMS was reduced by SF, post-error accuracy compensations were greatly reduced. In conclusion, attentional processes and error monitoring were impaired following one night of frequent sleep disruptions, even when total sleep time was not reduced. Copyright © 2014 Elsevier B.V. All rights reserved.

Scalable implementation of ancilla-free optimal 1→M phase-covariant quantum cloning by combining quantum Zeno dynamics and adiabatic passage

International Nuclear Information System (INIS)

Shao, Xiao-Qiang; Zheng, Tai-Yu; Zhang, Shou

2011-01-01

A scalable way for implementation of ancilla-free optimal 1→M phase-covariant quantum cloning (PCC) is proposed by combining quantum Zeno dynamics and adiabatic passage. An optimal 1→M PCC can be achieved directly from the existed optimal 1→(M-1) PCC without excited states population during the whole process. The cases for optimal 1→3 (4) PCCs are discussed detailedly to show that the scheme is robust against the effect of decoherence. Moreover, the time for carrying out each cloning transformation is regular, which may reduce the complexity for achieving the optimal PCC in experiment. -- Highlights: → We implement the ancilla-free optimal 1→M phase-covariant quantum cloning machine. → This scheme is robust against the cavity decay and the spontaneous emission of atom. → The time for carrying out each cloning transformation is regular.

Scalable implementation of ancilla-free optimal 1→M phase-covariant quantum cloning by combining quantum Zeno dynamics and adiabatic passage

Energy Technology Data Exchange (ETDEWEB)

Shao, Xiao-Qiang, E-mail: xqshao83@yahoo.cn [School of Physics, Northeast Normal University, Changchun 130024 (China); Zheng, Tai-Yu, E-mail: zhengty@nenu.edu.cn [School of Physics, Northeast Normal University, Changchun 130024 (China); Zhang, Shou [Department of Physics, College of Science, Yanbian University, Yanji, Jilin 133002 (China)

2011-09-19

A scalable way for implementation of ancilla-free optimal 1→M phase-covariant quantum cloning (PCC) is proposed by combining quantum Zeno dynamics and adiabatic passage. An optimal 1→M PCC can be achieved directly from the existed optimal 1→(M-1) PCC without excited states population during the whole process. The cases for optimal 1→3 (4) PCCs are discussed detailedly to show that the scheme is robust against the effect of decoherence. Moreover, the time for carrying out each cloning transformation is regular, which may reduce the complexity for achieving the optimal PCC in experiment. -- Highlights: → We implement the ancilla-free optimal 1→M phase-covariant quantum cloning machine. → This scheme is robust against the cavity decay and the spontaneous emission of atom. → The time for carrying out each cloning transformation is regular.

Quantum measurements of atoms using cavity QED

International Nuclear Information System (INIS)

Dada, Adetunmise C.; Andersson, Erika; Jones, Martin L.; Kendon, Vivien M.; Everitt, Mark S.

2011-01-01

Generalized quantum measurements are an important extension of projective or von Neumann measurements in that they can be used to describe any measurement that can be implemented on a quantum system. We describe how to realize two nonstandard quantum measurements using cavity QED. The first measurement optimally and unambiguously distinguishes between two nonorthogonal quantum states. The second example is a measurement that demonstrates superadditive quantum coding gain. The experimental tools used are single-atom unitary operations effected by Ramsey pulses and two-atom Tavis-Cummings interactions. We show how the superadditive quantum coding gain is affected by errors in the field-ionization detection of atoms and that even with rather high levels of experimental imperfections, a reasonable amount of superadditivity can still be seen. To date, these types of measurements have been realized only on photons. It would be of great interest to have realizations using other physical systems. This is for fundamental reasons but also since quantum coding gain in general increases with code word length, and a realization using atoms could be more easily scaled than existing realizations using photons.

Experimental characterization of quantum correlated triple beams generated by cascaded four-wave mixing processes

Science.gov (United States)

Qin, Zhongzhong; Cao, Leiming; Jing, Jietai

2015-05-01

Quantum correlations and entanglement shared among multiple modes are fundamental ingredients of most continuous-variable quantum technologies. Recently, a method used to generate multiple quantum correlated beams using cascaded four-wave mixing (FWM) processes was theoretically proposed and experimentally realized by our group [Z. Qin et al., Phys. Rev. Lett. 113, 023602 (2014)]. Our study of triple-beam quantum correlation paves the way to showing the tripartite entanglement in our system. Our system also promises to find applications in quantum information and precision measurement such as the controlled quantum communications, the generation of multiple quantum correlated images, and the realization of a multiport nonlinear interferometer. For its applications, the degree of quantum correlation is a crucial figure of merit. In this letter, we experimentally study how various parameters, such as the cell temperatures, one-photon, and two-photon detunings, influence the degree of quantum correlation between the triple beams generated from the cascaded two-FWM configuration.

High-fidelity quantum gates on quantum-dot-confined electron spins in low-Q optical microcavities

Science.gov (United States)

Li, Tao; Gao, Jian-Cun; Deng, Fu-Guo; Long, Gui-Lu

2018-04-01

We propose some high-fidelity quantum circuits for quantum computing on electron spins of quantum dots (QD) embedded in low-Q optical microcavities, including the two-qubit controlled-NOT gate and the multiple-target-qubit controlled-NOT gate. The fidelities of both quantum gates can, in principle, be robust to imperfections involved in a practical input-output process of a single photon by converting the infidelity into a heralded error. Furthermore, the influence of two different decay channels is detailed. By decreasing the quality factor of the present microcavity, we can largely increase the efficiencies of these quantum gates while their high fidelities remain unaffected. This proposal also has another advantage regarding its experimental feasibility, in that both quantum gates can work faithfully even when the QD-cavity systems are non-identical, which is of particular importance in current semiconductor QD technology.

Quantum tunneling of the magnetic moment in a free nanoparticle

Energy Technology Data Exchange (ETDEWEB)

O' Keeffe, M.F. [Physics Department, Lehman College, City University of New York, 250 Bedford Park Boulevard West, Bronx, New York, 10468-1589 (United States); Chudnovsky, E.M., E-mail: eugene.chudnovsky@lehman.cuny.edu [Physics Department, Lehman College, City University of New York, 250 Bedford Park Boulevard West, Bronx, New York, 10468-1589 (United States); Garanin, D.A. [Physics Department, Lehman College, City University of New York, 250 Bedford Park Boulevard West, Bronx, New York, 10468-1589 (United States)

2012-09-15

We study tunneling of the magnetic moment in a particle that has full rotational freedom. Exact energy levels are obtained and the ground-state magnetic moment is computed for a symmetric rotor. The effect of mechanical freedom on spin tunneling manifests itself in a strong dependence of the magnetic moment on the moments of inertia of the rotor. The energy of the particle exhibits quantum phase transitions between states with different values of the magnetic moment. Particles of various shapes are investigated and the quantum phase diagram is obtained. - Highlights: Black-Right-Pointing-Pointer We obtain an exact analytical solution of a tunneling spin in a mechanical rotator. Black-Right-Pointing-Pointer The quantum phase diagram shows magnetic moment dependence on rotator shape and size. Black-Right-Pointing-Pointer Our work explains magnetic properties of free atomic clusters and magnetic molecules.

Quantum random number generation for loophole-free Bell tests

Science.gov (United States)

Mitchell, Morgan; Abellan, Carlos; Amaya, Waldimar

2015-05-01

We describe the generation of quantum random numbers at multi-Gbps rates, combined with real-time randomness extraction, to give very high purity random numbers based on quantum events at most tens of ns in the past. The system satisfies the stringent requirements of quantum non-locality tests that aim to close the timing loophole. We describe the generation mechanism using spontaneous-emission-driven phase diffusion in a semiconductor laser, digitization, and extraction by parity calculation using multi-GHz logic chips. We pay special attention to experimental proof of the quality of the random numbers and analysis of the randomness extraction. In contrast to widely-used models of randomness generators in the computer science literature, we argue that randomness generation by spontaneous emission can be extracted from a single source.

Experimental motivation and empirical consistency in minimal no-collapse quantum mechanics

International Nuclear Information System (INIS)

Schlosshauer, Maximilian

2006-01-01

We analyze three important experimental domains (SQUIDs, molecular interferometry, and Bose-Einstein condensation) as well as quantum-biophysical studies of the neuronal apparatus to argue that (i) the universal validity of unitary dynamics and the superposition principle has been confirmed far into the mesoscopic and macroscopic realm in all experiments conducted thus far; (ii) all observed 'restrictions' can be correctly and completely accounted for by taking into account environmental decoherence effects; (iii) no positive experimental evidence exists for physical state-vector collapse; (iv) the perception of single 'outcomes' is likely to be explainable through decoherence effects in the neuronal apparatus. We also discuss recent progress in the understanding of the emergence of quantum probabilities and the objectification of observables. We conclude that it is not only viable, but moreover compelling to regard a minimal no-collapse quantum theory as a leading candidate for a physically motivated and empirically consistent interpretation of quantum mechanics

Blow-up of the quantum potential for a free particle in one dimension

International Nuclear Information System (INIS)

Devillanova, G.; Maddalena, F.; Florio, G.

2013-01-01

We derive a non-linear differential equation that must be satisfied by the quantum potential, in the context of the Madelung equations, in one dimension for a particular class of wave functions. In this case, we exhibit explicit conditions leading to the blow-up of the quantum potential of a free particle at the boundary of the compact support of the probability density.

Computation of Hydration Free Energies Using the Multiple Environment Single System Quantum Mechanical/Molecular Mechanical Method.

Science.gov (United States)

König, Gerhard; Mei, Ye; Pickard, Frank C; Simmonett, Andrew C; Miller, Benjamin T; Herbert, John M; Woodcock, H Lee; Brooks, Bernard R; Shao, Yihan

2016-01-12

A recently developed MESS-E-QM/MM method (multiple-environment single-system quantum mechanical molecular/mechanical calculations with a Roothaan-step extrapolation) is applied to the computation of hydration free energies for the blind SAMPL4 test set and for 12 small molecules. First, free energy simulations are performed with a classical molecular mechanics force field using fixed-geometry solute molecules and explicit TIP3P solvent, and then the non-Boltzmann-Bennett method is employed to compute the QM/MM correction (QM/MM-NBB) to the molecular mechanical hydration free energies. For the SAMPL4 set, MESS-E-QM/MM-NBB corrections to the hydration free energy can be obtained 2 or 3 orders of magnitude faster than fully converged QM/MM-NBB corrections, and, on average, the hydration free energies predicted with MESS-E-QM/MM-NBB fall within 0.10-0.20 kcal/mol of full-converged QM/MM-NBB results. Out of five density functionals (BLYP, B3LYP, PBE0, M06-2X, and ωB97X-D), the BLYP functional is found to be most compatible with the TIP3P solvent model and yields the most accurate hydration free energies against experimental values for solute molecules included in this study.

A measurement strategy and an error-compensation model for the on-machine laser measurement of large-scale free-form surfaces

International Nuclear Information System (INIS)

Li, Bin; Li, Feng; Liu, Hongqi; Cai, Hui; Mao, Xinyong; Peng, Fangyu

2014-01-01

This study presents a novel measurement strategy and an error-compensation model for the measurement of large-scale free-form surfaces in on-machine laser measurement systems. To improve the measurement accuracy, the effects of the scan depth, surface roughness, incident angle and azimuth angle on the measurement results were investigated experimentally, and a practical measurement strategy considering the position and orientation of the sensor is presented. Also, a semi-quantitative model based on geometrical optics is proposed to compensate for the measurement error associated with the incident angle. The normal vector of the measurement point is determined using a cross-curve method from the acquired surface data. Then, the azimuth angle and incident angle are calculated to inform the measurement strategy and error-compensation model, respectively. The measurement strategy and error-compensation model are verified through the measurement of a large propeller blade on a heavy machine tool in a factory environment. The results demonstrate that the strategy and the model are effective in increasing the measurement accuracy. (paper)

Concatenated quantum codes

Energy Technology Data Exchange (ETDEWEB)

Knill, E.; Laflamme, R.

1996-07-01

One main problem for the future of practial quantum computing is to stabilize the computation against unwanted interactions with the environment and imperfections in the applied operations. Existing proposals for quantum memories and quantum channels require gates with asymptotically zero error to store or transmit an input quantum state for arbitrarily long times or distances with fixed error. This report gives a method which has the property that to store or transmit a qubit with maximum error {epsilon} requires gates with errors at most {ital c}{epsilon} and storage or channel elements with error at most {epsilon}, independent of how long we wish to store the state or how far we wish to transmit it. The method relies on using concatenated quantum codes and hierarchically implemented recovery operations. The overhead of the method is polynomial in the time of storage or the distance of the transmission. Rigorous and heuristic lower bounds for the constant {ital c} are given.

Experimental multiplexing of quantum key distribution with classical optical communication

International Nuclear Information System (INIS)

Wang, Liu-Jun; Chen, Luo-Kan; Ju, Lei; Xu, Mu-Lan; Zhao, Yong; Chen, Kai; Chen, Zeng-Bing; Chen, Teng-Yun; Pan, Jian-Wei

2015-01-01

We demonstrate the realization of quantum key distribution (QKD) when combined with classical optical communication, and synchronous signals within a single optical fiber. In the experiment, the classical communication sources use Fabry-Pérot (FP) lasers, which are implemented extensively in optical access networks. To perform QKD, multistage band-stop filtering techniques are developed, and a wavelength-division multiplexing scheme is designed for the multi-longitudinal-mode FP lasers. We have managed to maintain sufficient isolation among the quantum channel, the synchronous channel and the classical channels to guarantee good QKD performance. Finally, the quantum bit error rate remains below a level of 2% across the entire practical application range. The proposed multiplexing scheme can ensure low classical light loss, and enables QKD over fiber lengths of up to 45 km simultaneously when the fibers are populated with bidirectional FP laser communications. Our demonstration paves the way for application of QKD to current optical access networks, where FP lasers are widely used by the end users

Qubits in phase space: Wigner-function approach to quantum-error correction and the mean-king problem

International Nuclear Information System (INIS)

Paz, Juan Pablo; Roncaglia, Augusto Jose; Saraceno, Marcos

2005-01-01

We analyze and further develop a method to represent the quantum state of a system of n qubits in a phase-space grid of NxN points (where N=2 n ). The method, which was recently proposed by Wootters and co-workers (Gibbons et al., Phys. Rev. A 70, 062101 (2004).), is based on the use of the elements of the finite field GF(2 n ) to label the phase-space axes. We present a self-contained overview of the method, we give insights into some of its features, and we apply it to investigate problems which are of interest for quantum-information theory: We analyze the phase-space representation of stabilizer states and quantum error-correction codes and present a phase-space solution to the so-called mean king problem

Experimental implementation of the Bacon-Shor code with 10 entangled photons

Science.gov (United States)

Gimeno-Segovia, Mercedes; Sanders, Barry C.

The number of qubits that can be effectively controlled in quantum experiments is growing, reaching a regime where small quantum error-correcting codes can be tested. The Bacon-Shor code is a simple quantum code that protects against the effect of an arbitrary single-qubit error. In this work, we propose an experimental implementation of said code in a post-selected linear optical setup, similar to the recently reported 10-photon GHZ generation experiment. In the procedure we propose, an arbitrary state is encoded into the protected Shor code subspace, and after undergoing a controlled single-qubit error, is successfully decoded. BCS appreciates financial support from Alberta Innovates, NSERC, China's 1000 Talent Plan and the Institute for Quantum Information and Matter, which is an NSF Physics Frontiers Center(NSF Grant PHY-1125565) with support of the Moore Foundation(GBMF-2644).

Intermixing of InGaAs/GaAs quantum wells and quantum dots using sputter-deposited silicon oxynitride capping layers

International Nuclear Information System (INIS)

McKerracher, Ian; Fu Lan; Hoe Tan, Hark; Jagadish, Chennupati

2012-01-01

Various approaches can be used to selectively control the amount of intermixing in III-V quantum well and quantum dot structures. Impurity-free vacancy disordering is one technique that is favored for its simplicity, however this mechanism is sensitive to many experimental parameters. In this study, a series of silicon oxynitride capping layers have been used in the intermixing of InGaAs/GaAs quantum well and quantum dot structures. These thin films were deposited by sputter deposition in order to minimize the incorporation of hydrogen, which has been reported to influence impurity-free vacancy disordering. The degree of intermixing was probed by photoluminescence spectroscopy and this is discussed with respect to the properties of the SiO x N y films. This work was also designed to monitor any additional intermixing that might be attributed to the sputtering process. In addition, the high-temperature stress is known to affect the group-III vacancy concentration, which is central to the intermixing process. This stress was directly measured and the experimental values are compared with an elastic-deformation model.

Fermion-induced quantum critical points.

Science.gov (United States)

Li, Zi-Xiang; Jiang, Yi-Fan; Jian, Shao-Kai; Yao, Hong

2017-08-22

A unified theory of quantum critical points beyond the conventional Landau-Ginzburg-Wilson paradigm remains unknown. According to Landau cubic criterion, phase transitions should be first-order when cubic terms of order parameters are allowed by symmetry in the Landau-Ginzburg free energy. Here, from renormalization group analysis, we show that second-order quantum phase transitions can occur at such putatively first-order transitions in interacting two-dimensional Dirac semimetals. As such type of Landau-forbidden quantum critical points are induced by gapless fermions, we call them fermion-induced quantum critical points. We further introduce a microscopic model of SU(N) fermions on the honeycomb lattice featuring a transition between Dirac semimetals and Kekule valence bond solids. Remarkably, our large-scale sign-problem-free Majorana quantum Monte Carlo simulations show convincing evidences of a fermion-induced quantum critical points for N = 2, 3, 4, 5 and 6, consistent with the renormalization group analysis. We finally discuss possible experimental realizations of the fermion-induced quantum critical points in graphene and graphene-like materials.Quantum phase transitions are governed by Landau-Ginzburg theory and the exceptions are rare. Here, Li et al. propose a type of Landau-forbidden quantum critical points induced by gapless fermions in two-dimensional Dirac semimetals.

Experimental probes of emergent symmetries in the quantum Hall system

CERN Document Server

Lutken, C A

2011-01-01

Experiments studying renormalization group flows in the quantum Hall system provide significant evidence for the existence of an emergent holomorphic modular symmetry Gamma(0)(2). We briefly review this evidence and show that, for the lowest temperatures, the experimental determination of the position of the quantum critical points agrees to the parts per mille level with the prediction from Gamma(0)(2). We present evidence that experiments giving results that deviate substantially from the symmetry predictions are not cold enough to be in the quantum critical domain. We show how the modular symmetry extended by a non-holomorphic particle hole duality leads to an extensive web of dualities related to those in plateau insulator transitions, and we derive a formula relating dual pairs (B, B(d)) of magnetic field strengths across any transition. The experimental data obtained for the transition studied so far is in excellent agreement with the duality relations following from this emergent symmetry, and rule out...

EXPERIMENTAL VALIDATION OF CUMULATIVE SURFACE LOCATION ERROR FOR TURNING PROCESSES

Directory of Open Access Journals (Sweden)

Adam K. Kiss

2016-02-01

Full Text Available The aim of this study is to create a mechanical model which is suitable to investigate the surface quality in turning processes, based on the Cumulative Surface Location Error (CSLE, which describes the series of the consecutive Surface Location Errors (SLE in roughing operations. In the established model, the investigated CSLE depends on the currently and the previously resulted SLE by means of the variation of the width of cut. The phenomenon of the system can be described as an implicit discrete map. The stationary Surface Location Error and its bifurcations were analysed and flip-type bifurcation was observed for CSLE. Experimental verification of the theoretical results was carried out.

Influence of experimental parameters inherent to optical fibers on Quantum Key Distribution, the protocol BB84

Directory of Open Access Journals (Sweden)

L. Bouchoucha

2018-03-01

Full Text Available In this work, we represent the principle of quantum cryptography (QC that is based on fundamental laws of quantum physics. QC or Quantum Key Distribution (QKD uses various protocols to exchange a secret key between two communicating parties. This research paper focuses and examines the quantum key distribution by using the protocol BB84 in the case of encoding on the single-photon polarization and shows the influence of optical components parameters on the quantum key distribution. We also introduce Quantum Bit Error Rate (QBER to better interpret our results and show its relationship with the intrusion of the eavesdropper called Eve on the optical channel to exploit these vulnerabilities.

Correct mutual information, quantum bit error rate and secure transmission efficiency in Wojcik's eavesdropping scheme on ping-pong protocol

OpenAIRE

Zhang, Zhanjun

2004-01-01

Comment: The wrong mutual information, quantum bit error rate and secure transmission efficiency in Wojcik's eavesdropping scheme [PRL90(03)157901]on ping-pong protocol have been pointed out and corrected

An asymptotic formula for the free energy density of ideal quantum gases

International Nuclear Information System (INIS)

Mackowiak, J.

1988-01-01

It is shown that the expressions for the free energy density of ideal quantum gases in the canonical and grand canonical ensembles, are identical up to additive terms which vanish in the thermodynamic limit. (orig.)

Efficient experimental design of high-fidelity three-qubit quantum gates via genetic programming

Science.gov (United States)

Devra, Amit; Prabhu, Prithviraj; Singh, Harpreet; Arvind; Dorai, Kavita

2018-03-01

We have designed efficient quantum circuits for the three-qubit Toffoli (controlled-controlled-NOT) and the Fredkin (controlled-SWAP) gate, optimized via genetic programming methods. The gates thus obtained were experimentally implemented on a three-qubit NMR quantum information processor, with a high fidelity. Toffoli and Fredkin gates in conjunction with the single-qubit Hadamard gates form a universal gate set for quantum computing and are an essential component of several quantum algorithms. Genetic algorithms are stochastic search algorithms based on the logic of natural selection and biological genetics and have been widely used for quantum information processing applications. We devised a new selection mechanism within the genetic algorithm framework to select individuals from a population. We call this mechanism the "Luck-Choose" mechanism and were able to achieve faster convergence to a solution using this mechanism, as compared to existing selection mechanisms. The optimization was performed under the constraint that the experimentally implemented pulses are of short duration and can be implemented with high fidelity. We demonstrate the advantage of our pulse sequences by comparing our results with existing experimental schemes and other numerical optimization methods.

Adaptive hybrid optimal quantum control for imprecisely characterized systems.

Science.gov (United States)

Egger, D J; Wilhelm, F K

2014-06-20

Optimal quantum control theory carries a huge promise for quantum technology. Its experimental application, however, is often hindered by imprecise knowledge of the input variables, the quantum system's parameters. We show how to overcome this by adaptive hybrid optimal control, using a protocol named Ad-HOC. This protocol combines open- and closed-loop optimal control by first performing a gradient search towards a near-optimal control pulse and then an experimental fidelity estimation with a gradient-free method. For typical settings in solid-state quantum information processing, adaptive hybrid optimal control enhances gate fidelities by an order of magnitude, making optimal control theory applicable and useful.

Competing quantum effects in the free energy profiles and diffusion rates of hydrogen and deuterium molecules through clathrate hydrates.

Science.gov (United States)

Cendagorta, Joseph R; Powers, Anna; Hele, Timothy J H; Marsalek, Ondrej; Bačić, Zlatko; Tuckerman, Mark E

2016-11-30

Clathrate hydrates hold considerable promise as safe and economical materials for hydrogen storage. Here we present a quantum mechanical study of H 2 and D 2 diffusion through a hexagonal face shared by two large cages of clathrate hydrates over a wide range of temperatures. Path integral molecular dynamics simulations are used to compute the free-energy profiles for the diffusion of H 2 and D 2 as a function of temperature. Ring polymer molecular dynamics rate theory, incorporating both exact quantum statistics and approximate quantum dynamical effects, is utilized in the calculations of the H 2 and D 2 diffusion rates in a broad temperature interval. We find that the shape of the quantum free-energy profiles and their height relative to the classical free energy barriers at a given temperature, as well as the rate of diffusion, are strongly affected by competing quantum effects: above 25 K, zero-point energy (ZPE) perpendicular to the reaction path for diffusion between cavities decreases the quantum rate compared to the classical rate, whereas at lower temperatures tunneling outcompetes the ZPE and as a result the quantum rate is greater than the classical rate.

Integer, fractional, and anomalous quantum Hall effects explained with Eyring's rate process theory and free volume concept.

Science.gov (United States)

Hao, Tian

2017-02-22

The Hall effects, especially the integer, fractional and anomalous quantum Hall effects, have been addressed using Eyring's rate process theory and free volume concept. The basic assumptions are that the conduction process is a common rate controlled "reaction" process that can be described with Eyring's absolute rate process theory; the mobility of electrons should be dependent on the free volume available for conduction electrons. The obtained Hall conductivity is clearly quantized as with prefactors related to both the magnetic flux quantum number and the magnetic quantum number via the azimuthal quantum number, with and without an externally applied magnetic field. This article focuses on two dimensional (2D) systems, but the approaches developed in this article can be extended to 3D systems.

Ergodic Capacity Analysis of Free-Space Optical Links with Nonzero Boresight Pointing Errors

KAUST Repository

Ansari, Imran Shafique; Alouini, Mohamed-Slim; Cheng, Julian

2015-01-01

A unified capacity analysis of a free-space optical (FSO) link that accounts for nonzero boresight pointing errors and both types of detection techniques (i.e. intensity modulation/ direct detection as well as heterodyne detection) is addressed

Discrete-Event Simulation Unmasks the Quantum Cheshire Cat

Science.gov (United States)

Michielsen, Kristel; Lippert, Thomas; Raedt, Hans De

2017-05-01

It is shown that discrete-event simulation accurately reproduces the experimental data of a single-neutron interferometry experiment [T. Denkmayr {\\sl et al.}, Nat. Commun. 5, 4492 (2014)] and provides a logically consistent, paradox-free, cause-and-effect explanation of the quantum Cheshire cat effect without invoking the notion that the neutron and its magnetic moment separate. Describing the experimental neutron data using weak-measurement theory is shown to be useless for unravelling the quantum Cheshire cat effect.

An Experimental and Quantum Chemical Study of the Electronic Spectrum of the HBCl Free Radical

Science.gov (United States)

Gharaibeh, Mohammed A.; Nagarajan, Ramya; Clouthier, Dennis J.; Tarroni, Ricardo

2012-06-01

The chloroborane (HBCl) free radical has a complex electronic spectrum in the visible that involves a transition from a bent ground state to a linear excited state, both of which are the Renner-Teller components of what would be a ^2π state at linearity. We have used the synchronous-scan LIF and single vibronic level emission techniques to untangle the many overlapping vibronic bands and assign upper state K quantum numbers for jet-cooled HBCl and DBCl. The radicals were produced in a pulsed electric discharge jet using a precursor mixture of boron trichloride (BCl_3) and hydrogen or deuterium in high-pressure argon. As an important aid to understanding the data, the ground and excited state high level ab initio potential energy surfaces (PES) have been calculated and the vibrational levels obtained variationally. The calculated ground state levels are in excellent agreement with the emission data validating the quality of the PES. Aside from an approximately 100 cm-1 shift in the upper state electronic term value, the calculated excited state vibrational energy levels and isotope shifts match the LIF data very well, allowing the observed bands to be assigned with confidence.

Experimental investigation of the generation of harmonic photons from the interaction of free electrons with intense laser radiation

International Nuclear Information System (INIS)

Englert, T.J.

1983-01-01

An experimental investigation of the generation of second harmonic photons through the interaction of free electrons with an intense laser beam has been performed. Second harmonic photons with a wavelength of 530nm generated from the interaction of free electrons with 1060nm photons from a neodymium-glass laser are implied by observing Doppler shifted photons with wavelengths of 490nm and 507nm. The observed photon wavelengths results from a Doppler shift of the laser photon wavelengths as viewed in the rest frame of the electrons combined with a Doppler shift of the second harmonic photons emitted from 1600eV and 500eV electrons. Comparison of experimental results with those predicted by cross sections, derived using classical and quantum electrodynamics, shows reasonable agreement with both theories. Although second harmonic photons are created, the dynamics of second harmonic photon generation (accelerated electron motion due to the electromagnetic field or actual two-photon interaction with the electron) cannot be resolved without further experiment

Entropic Barriers for Two-Dimensional Quantum Memories

Science.gov (United States)

Brown, Benjamin J.; Al-Shimary, Abbas; Pachos, Jiannis K.

2014-03-01

Comprehensive no-go theorems show that information encoded over local two-dimensional topologically ordered systems cannot support macroscopic energy barriers, and hence will not maintain stable quantum information at finite temperatures for macroscopic time scales. However, it is still well motivated to study low-dimensional quantum memories due to their experimental amenability. Here we introduce a grid of defect lines to Kitaev's quantum double model where different anyonic excitations carry different masses. This setting produces a complex energy landscape which entropically suppresses the diffusion of excitations that cause logical errors. We show numerically that entropically suppressed errors give rise to superexponential inverse temperature scaling and polynomial system size scaling for small system sizes over a low-temperature regime. Curiously, these entropic effects are not present below a certain low temperature. We show that we can vary the system to modify this bound and potentially extend the described effects to zero temperature.

Impact of errors in experimental parameters on reconstructed breast images using diffuse optical tomography.

Science.gov (United States)

Deng, Bin; Lundqvist, Mats; Fang, Qianqian; Carp, Stefan A

2018-03-01

Near-infrared diffuse optical tomography (NIR-DOT) is an emerging technology that offers hemoglobin based, functional imaging tumor biomarkers for breast cancer management. The most promising clinical translation opportunities are in the differential diagnosis of malignant vs. benign lesions, and in early response assessment and guidance for neoadjuvant chemotherapy. Accurate quantification of the tissue oxy- and deoxy-hemoglobin concentration across the field of view, as well as repeatability during longitudinal imaging in the context of therapy guidance, are essential for the successful translation of NIR-DOT to clinical practice. The ill-posed and ill-condition nature of the DOT inverse problem makes this technique particularly susceptible to model errors that may occur, for example, when the experimental conditions do not fully match the assumptions built into the image reconstruction process. To evaluate the susceptibility of DOT images to experimental errors that might be encountered in practice for a parallel-plate NIR-DOT system, we simulated 7 different types of errors, each with a range of magnitudes. We generated simulated data by using digital breast phantoms derived from five actual mammograms of healthy female volunteers, to which we added a 1-cm tumor. After applying each of the experimental error types and magnitudes to the simulated measurements, we reconstructed optical images with and without structural prior guidance and assessed the overall error in the total hemoglobin concentrations (HbT) and in the HbT contrast between the lesion and surrounding area vs. the best-case scenarios. It is found that slight in-plane probe misalignment and plate rotation did not result in large quantification errors. However, any out-of-plane probe tilting could result in significant deterioration in lesion contrast. Among the error types investigated in this work, optical images were the least likely to be impacted by breast shape inaccuracies but suffered the

Potts glass reflection of the decoding threshold for qudit quantum error correcting codes

Science.gov (United States)

Jiang, Yi; Kovalev, Alexey A.; Pryadko, Leonid P.

We map the maximum likelihood decoding threshold for qudit quantum error correcting codes to the multicritical point in generalized Potts gauge glass models, extending the map constructed previously for qubit codes. An n-qudit quantum LDPC code, where a qudit can be involved in up to m stabilizer generators, corresponds to a ℤd Potts model with n interaction terms which can couple up to m spins each. We analyze general properties of the phase diagram of the constructed model, give several bounds on the location of the transitions, bounds on the energy density of extended defects (non-local analogs of domain walls), and discuss the correlation functions which can be used to distinguish different phases in the original and the dual models. This research was supported in part by the Grants: NSF PHY-1415600 (AAK), NSF PHY-1416578 (LPP), and ARO W911NF-14-1-0272 (LPP).

Feedback Control in Quantum Optics: An Overview of Experimental Breakthroughs and Areas of Application

OpenAIRE

Alessio Serafini

2012-01-01

We present a broad summary of research involving the application of quantum feedback control techniques to optical set-ups, from the early enhancement of optical amplitude squeezing to the recent stabilisation of photon number states in a microwave cavity, dwelling mostly on the latest experimental advances. Feedback control of quantum optical continuous variables, quantum non-demolition memories, feedback cooling, quantum state control, adaptive quantum measurements and coherent feedback str...

Scalable effective-temperature reduction for quantum annealers via nested quantum annealing correction

Science.gov (United States)

Vinci, Walter; Lidar, Daniel A.

2018-02-01

Nested quantum annealing correction (NQAC) is an error-correcting scheme for quantum annealing that allows for the encoding of a logical qubit into an arbitrarily large number of physical qubits. The encoding replaces each logical qubit by a complete graph of degree C . The nesting level C represents the distance of the error-correcting code and controls the amount of protection against thermal and control errors. Theoretical mean-field analyses and empirical data obtained with a D-Wave Two quantum annealer (supporting up to 512 qubits) showed that NQAC has the potential to achieve a scalable effective-temperature reduction, Teff˜C-η , with 0 temperature of a quantum annealer. Such effective-temperature reduction is relevant for machine-learning applications. Since we demonstrate that NQAC achieves error correction via a reduction of the effective-temperature of the quantum annealing device, our results address the problem of the "temperature scaling law for quantum annealers," which requires the temperature of quantum annealers to be reduced as problems of larger sizes are attempted to be solved.

Proof-of-principle experimental realization of a qubit-like qudit-based quantum key distribution scheme

Science.gov (United States)

Wang, Shuang; Yin, Zhen-Qiang; Chau, H. F.; Chen, Wei; Wang, Chao; Guo, Guang-Can; Han, Zheng-Fu

2018-04-01

In comparison to qubit-based protocols, qudit-based quantum key distribution ones generally allow two cooperative parties to share unconditionally secure keys under a higher channel noise. However, it is very hard to prepare and measure the required quantum states in qudit-based protocols in general. One exception is the recently proposed highly error tolerant qudit-based protocol known as the Chau15 (Chau 2015 Phys. Rev. A 92 062324). Remarkably, the state preparation and measurement in this protocol can be done relatively easily since the required states are phase encoded almost like the diagonal basis states of a qubit. Here we report the first proof-of-principle demonstration of the Chau15 protocol. One highlight of our experiment is that its post-processing is based on practical one-way manner, while the original proposal in Chau (2015 Phys. Rev. A 92 062324) relies on complicated two-way post-processing, which is a great challenge in experiment. In addition, by manipulating time-bin qudit and measurement with a variable delay interferometer, our realization is extensible to qudit with high-dimensionality and confirms the experimental feasibility of the Chau15 protocol.

Experimental quantum Hamiltonian learning

NARCIS (Netherlands)

Wang, J.; Paesani, S.; Santagati, R.; Knauer, S.; Gentile, A.A.; Wiebe, N.; Petruzzella, M.; O’Brien, J.L.; Rarity, J.G.; Laing, A.; Thompson, M.G.

2017-01-01

The efficient characterization of quantum systems1, 2, 3, the verification of the operations of quantum devices4, 5, 6 and the validation of underpinning physical models7, 8, 9, are central challenges for quantum technologies10, 11, 12 and fundamental physics13, 14. The computational cost of such

Mean Field Analysis of Quantum Annealing Correction.

Science.gov (United States)

Matsuura, Shunji; Nishimori, Hidetoshi; Albash, Tameem; Lidar, Daniel A

2016-06-03

Quantum annealing correction (QAC) is a method that combines encoding with energy penalties and decoding to suppress and correct errors that degrade the performance of quantum annealers in solving optimization problems. While QAC has been experimentally demonstrated to successfully error correct a range of optimization problems, a clear understanding of its operating mechanism has been lacking. Here we bridge this gap using tools from quantum statistical mechanics. We study analytically tractable models using a mean-field analysis, specifically the p-body ferromagnetic infinite-range transverse-field Ising model as well as the quantum Hopfield model. We demonstrate that for p=2, where the phase transition is of second order, QAC pushes the transition to increasingly larger transverse field strengths. For p≥3, where the phase transition is of first order, QAC softens the closing of the gap for small energy penalty values and prevents its closure for sufficiently large energy penalty values. Thus QAC provides protection from excitations that occur near the quantum critical point. We find similar results for the Hopfield model, thus demonstrating that our conclusions hold in the presence of disorder.

Gluon Green functions free of quantum fluctuations

Directory of Open Access Journals (Sweden)

A. Athenodorou

2016-09-01

Full Text Available This letter reports on how the Wilson flow technique can efficaciously kill the short-distance quantum fluctuations of 2- and 3-gluon Green functions, remove the ΛQCD scale and destroy the transition from the confining non-perturbative to the asymptotically-free perturbative sector. After the Wilson flow, the behavior of the Green functions with momenta can be described in terms of the quasi-classical instanton background. The same behavior also occurs, before the Wilson flow, at low-momenta. This last result permits applications as, for instance, the detection of instanton phenomenological properties or a determination of the lattice spacing only from the gauge sector of the theory.

Generating higher-order quantum dissipation from lower-order parametric processes

Science.gov (United States)

Mundhada, S. O.; Grimm, A.; Touzard, S.; Vool, U.; Shankar, S.; Devoret, M. H.; Mirrahimi, M.

2017-06-01

The stabilisation of quantum manifolds is at the heart of error-protected quantum information storage and manipulation. Nonlinear driven-dissipative processes achieve such stabilisation in a hardware efficient manner. Josephson circuits with parametric pump drives implement these nonlinear interactions. In this article, we propose a scheme to engineer a four-photon drive and dissipation on a harmonic oscillator by cascading experimentally demonstrated two-photon processes. This would stabilise a four-dimensional degenerate manifold in a superconducting resonator. We analyse the performance of the scheme using numerical simulations of a realisable system with experimentally achievable parameters.

Quantum mechanical free energy profiles with post-quantization restraints: Binding free energy of the water dimer over a broad range of temperatures.

Science.gov (United States)

Bishop, Kevin P; Roy, Pierre-Nicholas

2018-03-14

Free energy calculations are a crucial part of understanding chemical systems but are often computationally expensive for all but the simplest of systems. Various enhanced sampling techniques have been developed to improve the efficiency of these calculations in numerical simulations. However, the majority of these approaches have been applied using classical molecular dynamics. There are many situations where nuclear quantum effects impact the system of interest and a classical description fails to capture these details. In this work, path integral molecular dynamics has been used in conjunction with umbrella sampling, and it has been observed that correct results are only obtained when the umbrella sampling potential is applied to a single path integral bead post quantization. This method has been validated against a Lennard-Jones benchmark system before being applied to the more complicated water dimer system over a broad range of temperatures. Free energy profiles are obtained, and these are utilized in the calculation of the second virial coefficient as well as the change in free energy from the separated water monomers to the dimer. Comparisons to experimental and ground state calculation values from the literature are made for the second virial coefficient at higher temperature and the dissociation energy of the dimer in the ground state.

Experimental Quantum-Walk Revival with a Time-Dependent Coin

Science.gov (United States)

Xue, P.; Zhang, R.; Qin, H.; Zhan, X.; Bian, Z. H.; Li, J.; Sanders, Barry C.

2015-04-01

We demonstrate a quantum walk with time-dependent coin bias. With this technique we realize an experimental single-photon one-dimensional quantum walk with a linearly ramped time-dependent coin flip operation and thereby demonstrate two periodic revivals of the walker distribution. In our beam-displacer interferometer, the walk corresponds to movement between discretely separated transverse modes of the field serving as lattice sites, and the time-dependent coin flip is effected by implementing a different angle between the optical axis of half-wave plate and the light propagation at each step. Each of the quantum-walk steps required to realize a revival comprises two sequential orthogonal coin-flip operators, with one coin having constant bias and the other coin having a time-dependent ramped coin bias, followed by a conditional translation of the walker.

An in fiber experimental approach to photonic quantum digital signatures that does not require quantum memory

Science.gov (United States)

Collins, Robert J.; Donaldon, Ross J.; Dunjko, Vedran; Wallden, Petros; Clarke, Patrick J.; Andersson, Erika; Jeffers, John; Buller, Gerald S.

2014-10-01

Classical digital signatures are commonly used in e-mail, electronic financial transactions and other forms of electronic communications to ensure that messages have not been tampered with in transit, and that messages are transferrable. The security of commonly used classical digital signature schemes relies on the computational difficulty of inverting certain mathematical functions. However, at present, there are no such one-way functions which have been proven to be hard to invert. With enough computational resources certain implementations of classical public key cryptosystems can be, and have been, broken with current technology. It is nevertheless possible to construct information-theoretically secure signature schemes, including quantum digital signature schemes. Quantum signature schemes can be made information theoretically secure based on the laws of quantum mechanics, while classical comparable protocols require additional resources such as secret communication and a trusted authority. Early demonstrations of quantum digital signatures required quantum memory, rendering them impractical at present. Our present implementation is based on a protocol that does not require quantum memory. It also uses the new technique of unambiguous quantum state elimination, Here we report experimental results for a test-bed system, recorded with a variety of different operating parameters, along with a discussion of aspects of the system security.

Architectural design for a topological cluster state quantum computer

International Nuclear Information System (INIS)

Devitt, Simon J; Munro, William J; Nemoto, Kae; Fowler, Austin G; Stephens, Ashley M; Greentree, Andrew D; Hollenberg, Lloyd C L

2009-01-01

The development of a large scale quantum computer is a highly sought after goal of fundamental research and consequently a highly non-trivial problem. Scalability in quantum information processing is not just a problem of qubit manufacturing and control but it crucially depends on the ability to adapt advanced techniques in quantum information theory, such as error correction, to the experimental restrictions of assembling qubit arrays into the millions. In this paper, we introduce a feasible architectural design for large scale quantum computation in optical systems. We combine the recent developments in topological cluster state computation with the photonic module, a simple chip-based device that can be used as a fundamental building block for a large-scale computer. The integration of the topological cluster model with this comparatively simple operational element addresses many significant issues in scalable computing and leads to a promising modular architecture with complete integration of active error correction, exhibiting high fault-tolerant thresholds.

Experimental demonstration of macroscopic quantum coherence in Gaussian states

DEFF Research Database (Denmark)

Marquardt, C.; Andersen, Ulrik Lund; Leuchs, G.

2007-01-01

We witness experimentally the presence of macroscopic coherence in Gaussian quantum states using a recently proposed criterion [E. G. Cavalcanti and M. D. Reid, Phys. Rev. Lett. 97 170405 (2006)]. The macroscopic coherence stems from interference between macroscopically distinct states in phase...

High-Efficiency Quantum Interrogation Measurements via the Quantum Zeno Effect

International Nuclear Information System (INIS)

Kwiat, P. G.; White, A. G.; Mitchell, J. R.; Nairz, O.; Weihs, G.; Weinfurter, H.; Zeilinger, A.

1999-01-01

The phenomenon of quantum interrogation allows one to optically detect the presence of an absorbing object, without the measuring light interacting with it. In an application of the quantum Zeno effect, the object inhibits the otherwise coherent evolution of the light, such that the probability that an interrogating photon is absorbed can in principle be arbitrarily small. We have implemented this technique, achieving efficiencies of up to 73% , and consequently exceeding the 50% theoretical maximum of the original ''interaction-free'' measurement proposal. We have also predicted and experimentally verified a previously unsuspected dependence on loss. (c) 1999 The American Physical Society

Toward quantum-limited position measurements using optically levitated microspheres

International Nuclear Information System (INIS)

Libbrecht, Kenneth G.; Black, Eric D.

2004-01-01

We propose the use of optically levitated microspheres as test masses in experiments aimed at reaching and potentially exceeding the standard quantum limit for position measurements. Optically levitated microspheres have low mass and are essentially free of suspension thermal noise, making them well suited for experimentally testing our understanding of quantum-limited measurements

Toward quantum-limited position measurements using optically levitated microspheres

Energy Technology Data Exchange (ETDEWEB)

Libbrecht, Kenneth G.; Black, Eric D

2004-01-26

We propose the use of optically levitated microspheres as test masses in experiments aimed at reaching and potentially exceeding the standard quantum limit for position measurements. Optically levitated microspheres have low mass and are essentially free of suspension thermal noise, making them well suited for experimentally testing our understanding of quantum-limited measurements.

Towards room temperature solid state quantum devices at the edge of quantum chaos for long-living quantum states

International Nuclear Information System (INIS)

Prati, Enrico

2015-01-01

Long living coherent quantum states have been observed in biological systems up to room temperature. Light harvesting in chromophoresis realized by excitonic systems living at the edge of quantum chaos, where energy level distribution becomes semi-Poissonian. On the other hand, artificial materials suffer the loss of coherence of quantum states in quantum information processing, but semiconductor materials are known to exhibit quantum chaotic conditions, so the exploitation of similar conditions are to be considered. The advancements of nanofabrication, together with the control of implantation of individual atoms at nanometric precision, may open the experimental study of such special regime at the edge of the phase transitions for the electronic systems obtained by implanting impurity atoms in a silicon transistor. Here I review the recent advancements made in the field of theoretical description of the light harvesting in biological system in its connection with phase transitions at the few atoms scale and how it would be possible to achieve transition point to quantum chaotic regime. Such mechanism may thus preserve quantum coherent states at room temperature in solid state devices, to be exploited for quantum information processing as well as dissipation-free quantum electronics. (paper)

High speed and adaptable error correction for megabit/s rate quantum key distribution.

Science.gov (United States)

Dixon, A R; Sato, H

2014-12-02

Quantum Key Distribution is moving from its theoretical foundation of unconditional security to rapidly approaching real world installations. A significant part of this move is the orders of magnitude increases in the rate at which secure key bits are distributed. However, these advances have mostly been confined to the physical hardware stage of QKD, with software post-processing often being unable to support the high raw bit rates. In a complete implementation this leads to a bottleneck limiting the final secure key rate of the system unnecessarily. Here we report details of equally high rate error correction which is further adaptable to maximise the secure key rate under a range of different operating conditions. The error correction is implemented both in CPU and GPU using a bi-directional LDPC approach and can provide 90-94% of the ideal secure key rate over all fibre distances from 0-80 km.

Quantum tomography via compressed sensing: error bounds, sample complexity and efficient estimators

International Nuclear Information System (INIS)

Flammia, Steven T; Gross, David; Liu, Yi-Kai; Eisert, Jens

2012-01-01

Intuitively, if a density operator has small rank, then it should be easier to estimate from experimental data, since in this case only a few eigenvectors need to be learned. We prove two complementary results that confirm this intuition. Firstly, we show that a low-rank density matrix can be estimated using fewer copies of the state, i.e. the sample complexity of tomography decreases with the rank. Secondly, we show that unknown low-rank states can be reconstructed from an incomplete set of measurements, using techniques from compressed sensing and matrix completion. These techniques use simple Pauli measurements, and their output can be certified without making any assumptions about the unknown state. In this paper, we present a new theoretical analysis of compressed tomography, based on the restricted isometry property for low-rank matrices. Using these tools, we obtain near-optimal error bounds for the realistic situation where the data contain noise due to finite statistics, and the density matrix is full-rank with decaying eigenvalues. We also obtain upper bounds on the sample complexity of compressed tomography, and almost-matching lower bounds on the sample complexity of any procedure using adaptive sequences of Pauli measurements. Using numerical simulations, we compare the performance of two compressed sensing estimators—the matrix Dantzig selector and the matrix Lasso—with standard maximum-likelihood estimation (MLE). We find that, given comparable experimental resources, the compressed sensing estimators consistently produce higher fidelity state reconstructions than MLE. In addition, the use of an incomplete set of measurements leads to faster classical processing with no loss of accuracy. Finally, we show how to certify the accuracy of a low-rank estimate using direct fidelity estimation, and describe a method for compressed quantum process tomography that works for processes with small Kraus rank and requires only Pauli eigenstate preparations

Quantum steganography with noisy quantum channels

International Nuclear Information System (INIS)

Shaw, Bilal A.; Brun, Todd A.

2011-01-01

Steganography is the technique of hiding secret information by embedding it in a seemingly ''innocent'' message. We present protocols for hiding quantum information by disguising it as noise in a codeword of a quantum error-correcting code. The sender (Alice) swaps quantum information into the codeword and applies a random choice of unitary operation, drawing on a secret random key she shares with the receiver (Bob). Using the key, Bob can retrieve the information, but an eavesdropper (Eve) with the power to monitor the channel, but without the secret key, cannot distinguish the message from channel noise. We consider two types of protocols: one in which the hidden quantum information is stored locally in the codeword, and another in which it is embedded in the space of error syndromes. We analyze how difficult it is for Eve to detect the presence of secret messages, and estimate rates of steganographic communication and secret key consumption for specific protocols and examples of error channels. We consider both the case where there is no actual noise in the channel (so that all errors in the codeword result from the deliberate actions of Alice), and the case where the channel is noisy and not controlled by Alice and Bob.

Experimental simulation and limitations of quantum walks with trapped ions

International Nuclear Information System (INIS)

Matjeschk, R; Schneider, Ch; Enderlein, M; Huber, T; Schmitz, H; Glueckert, J; Schaetz, T

2012-01-01

We examine the prospects of discrete quantum walks (QWs) with trapped ions. In particular, we analyze in detail the limitations of the protocol of Travaglione and Milburn (2002 Phys. Rev. A 65 032310) that has been implemented by several experimental groups in recent years. Based on the first realization in our group (Schmitz et al 2009 Phys. Rev. Lett. 103 090504), we investigate the consequences of leaving the scope of the approximations originally made, such as the Lamb-Dicke approximation. We explain the consequential deviations from the idealized QW for different experimental realizations and an increasing number of steps by taking into account higher-order terms of the quantum evolution. It turns out that these already become significant after a few steps, which is confirmed by experimental results and is currently limiting the scalability of this approach. Finally, we propose a new scheme using short laser pulses, derived from a protocol from the field of quantum computation. We show that this scheme is not subject to the above-mentioned restrictions and analytically and numerically evaluate its limitations, based on a realistic implementation with our specific setup. Implementing the protocol with state-of-the-art techniques should allow for substantially increasing the number of steps to 100 and beyond and should be extendable to higher-dimensional QWs. (paper)

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

FIRST EXPERIMENTAL RESULTS FROM DEGAS, THE QUANTUM LIMITED BRIGHTNESS ELECTRON SOURCE

International Nuclear Information System (INIS)

Zolotorev, Max S.; Commins, Eugene D.; Oneill, James; Sannibale, Fernando; Tremsin, Anton; Wan, Weishi

2008-01-01

The construction of DEGAS (DEGenerate Advanced Source), a proof of principle for a quantum limited brightness electron source, has been completed at the Lawrence Berkeley National Laboratory. The commissioning and the characterization of this source, designed to generate coherent single electron 'bunches' with brightness approaching the quantum limit at a repetition rate of few MHz, has been started. In this paper the first experimental results are described

Quantum computers and quantum computations

International Nuclear Information System (INIS)

Valiev, Kamil' A

2005-01-01

This review outlines the principles of operation of quantum computers and their elements. The theory of ideal computers that do not interact with the environment and are immune to quantum decohering processes is presented. Decohering processes in quantum computers are investigated. The review considers methods for correcting quantum computing errors arising from the decoherence of the state of the quantum computer, as well as possible methods for the suppression of the decohering processes. A brief enumeration of proposed quantum computer realizations concludes the review. (reviews of topical problems)

Organic molecule fluorescence as an experimental test-bed for quantum jumps in thermodynamics.

Science.gov (United States)

Browne, Cormac; Farrow, Tristan; Dahlsten, Oscar C O; Taylor, Robert A; Vlatko, Vedral

2017-08-01

We demonstrate with an experiment how molecules are a natural test bed for probing fundamental quantum thermodynamics. Single-molecule spectroscopy has undergone transformative change in the past decade with the advent of techniques permitting individual molecules to be distinguished and probed. We demonstrate that the quantum Jarzynski equality for heat is satisfied in this set-up by considering the time-resolved emission spectrum of organic molecules as arising from quantum jumps between states. This relates the heat dissipated into the environment to the free energy difference between the initial and final state. We demonstrate also how utilizing the quantum Jarzynski equality allows for the detection of energy shifts within a molecule, beyond the relative shift.

Exploring Interacting Quantum Many-Body Systems by Experimentally Creating Continuous Matrix Product States in Superconducting Circuits

Directory of Open Access Journals (Sweden)

C. Eichler

2015-12-01

Full Text Available Improving the understanding of strongly correlated quantum many-body systems such as gases of interacting atoms or electrons is one of the most important challenges in modern condensed matter physics, materials research, and chemistry. Enormous progress has been made in the past decades in developing both classical and quantum approaches to calculate, simulate, and experimentally probe the properties of such systems. In this work, we use a combination of classical and quantum methods to experimentally explore the properties of an interacting quantum gas by creating experimental realizations of continuous matrix product states—a class of states that has proven extremely powerful as a variational ansatz for numerical simulations. By systematically preparing and probing these states using a circuit quantum electrodynamics system, we experimentally determine a good approximation to the ground-state wave function of the Lieb-Liniger Hamiltonian, which describes an interacting Bose gas in one dimension. Since the simulated Hamiltonian is encoded in the measurement observable rather than the controlled quantum system, this approach has the potential to apply to a variety of models including those involving multicomponent interacting fields. Our findings also hint at the possibility of experimentally exploring general properties of matrix product states and entanglement theory. The scheme presented here is applicable to a broad range of systems exploiting strong and tunable light-matter interactions.

Quantum information processing beyond ten ion-qubits

International Nuclear Information System (INIS)

Monz, T.

2011-01-01

Successful processing of quantum information is, to a large degree, based on two aspects: a) the implementation of high-fidelity quantum gates, as well as b) avoiding or suppressing decoherence processes that destroy quantum information. The presented work shows our progress in the field of experimental quantum information processing over the last years: the implementation and characterisation of several quantum operations, amongst others the first realisation of the quantum Toffoli gate in an ion-trap based quantum computer. The creation of entangled states with up to 14 qubits serves as basis for investigations of decoherence processes. Based on the realised quantum operations as well as the knowledge about dominant noise processes in the employed apparatus, entanglement swapping as well as quantum operations within a decoherence-free subspace are demonstrated. (author) [de

Fluctuation theorems in feedback-controlled open quantum systems: Quantum coherence and absolute irreversibility

Science.gov (United 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.

Experimental metaphysics2 : The double standard in the quantum-information approach to the foundations of quantum theory

Science.gov (United States)

Hagar, Amit

Among the alternatives of non-relativistic quantum mechanics (NRQM) there are those that give different predictions than quantum mechanics in yet-untested circumstances, while remaining compatible with current empirical findings. In order to test these predictions, one must isolate one's system from environmental induced decoherence, which, on the standard view of NRQM, is the dynamical mechanism that is responsible for the 'apparent' collapse in open quantum systems. But while recent advances in condensed-matter physics may lead in the near future to experimental setups that will allow one to test the two hypotheses, namely genuine collapse vs. decoherence, hence make progress toward a solution to the quantum measurement problem, those philosophers and physicists who are advocating an information-theoretic approach to the foundations of quantum mechanics are still unwilling to acknowledge the empirical character of the issue at stake. Here I argue that in doing so they are displaying an unwarranted double standard.

Development of an Abbe Error Free Micro Coordinate Measuring Machine

Directory of Open Access Journals (Sweden)

Qiangxian Huang

2016-04-01

Full Text Available A micro Coordinate Measuring Machine (CMM with the measurement volume of 50 mm × 50 mm × 50 mm and measuring accuracy of about 100 nm (2σ has been developed. In this new micro CMM, an XYZ stage, which is driven by three piezo-motors in X, Y and Z directions, can achieve the drive resolution of about 1 nm and the stroke of more than 50 mm. In order to reduce the crosstalk among X-, Y- and Z-stages, a special mechanical structure, which is called co-planar stage, is introduced. The movement of the stage in each direction is detected by a laser interferometer. A contact type of probe is adopted for measurement. The center of the probe ball coincides with the intersection point of the measuring axes of the three laser interferometers. Therefore, the metrological system of the CMM obeys the Abbe principle in three directions and is free from Abbe error. The CMM is placed in an anti-vibration and thermostatic chamber for avoiding the influence of vibration and temperature fluctuation. A series of experimental results show that the measurement uncertainty within 40 mm among X, Y and Z directions is about 100 nm (2σ. The flatness of measuring face of the gauge block is also measured and verified the performance of the developed micro CMM.

Quantum Dot Laser for a Light Source of an Athermal Silicon Optical Interposer

Directory of Open Access Journals (Sweden)

Nobuaki Hatori

2015-04-01

Full Text Available This paper reports a hybrid integrated light source fabricated on a silicon platform using a 1.3 μm wavelength quantum dot array laser. Temperature insensitive characteristics up to 120 °C were achieved by the optimum quantum dot structure and laser structure. Light output power was obtained that was high enough to achieve an optical error-free link of a silicon optical interposer. Furthermore, we investigated a novel spot size convertor in a silicon waveguide suitable for a quantum dot laser for lower energy cost operation of the optical interposer.

Error Modelling for Multi-Sensor Measurements in Infrastructure-Free Indoor Navigation

Directory of Open Access Journals (Sweden)

Laura Ruotsalainen

2018-02-01

Full Text Available The long-term objective of our research is to develop a method for infrastructure-free simultaneous localization and mapping (SLAM and context recognition for tactical situational awareness. Localization will be realized by propagating motion measurements obtained using a monocular camera, a foot-mounted Inertial Measurement Unit (IMU, sonar, and a barometer. Due to the size and weight requirements set by tactical applications, Micro-Electro-Mechanical (MEMS sensors will be used. However, MEMS sensors suffer from biases and drift errors that may substantially decrease the position accuracy. Therefore, sophisticated error modelling and implementation of integration algorithms are key for providing a viable result. Algorithms used for multi-sensor fusion have traditionally been different versions of Kalman filters. However, Kalman filters are based on the assumptions that the state propagation and measurement models are linear with additive Gaussian noise. Neither of the assumptions is correct for tactical applications, especially for dismounted soldiers, or rescue personnel. Therefore, error modelling and implementation of advanced fusion algorithms are essential for providing a viable result. Our approach is to use particle filtering (PF, which is a sophisticated option for integrating measurements emerging from pedestrian motion having non-Gaussian error characteristics. This paper discusses the statistical modelling of the measurement errors from inertial sensors and vision based heading and translation measurements to include the correct error probability density functions (pdf in the particle filter implementation. Then, model fitting is used to verify the pdfs of the measurement errors. Based on the deduced error models of the measurements, particle filtering method is developed to fuse all this information, where the weights of each particle are computed based on the specific models derived. The performance of the developed method is

Quantum information. Teleportation - cryptography - quantum computer

International Nuclear Information System (INIS)

Koenneker, Carsten

2012-01-01

The following topics are dealt with: Reality in the test facility, quantum teleportation, the reality of quanta, interaction-free quantum measurement, rules for quantum computers, quantum computers with ions, spintronics with diamond, the limits of the quantum computers, a view in the future of quantum optics. (HSI)

Free NH3 quantum rotations in Hofmann clathrates: structure factors and line widths studied by inelastic neutron scattering

International Nuclear Information System (INIS)

Sobolev, O.; Vorderwisch, P.; Desmedt, A.

2005-01-01

Quantum rotations of NH 3 groups in Hofmann clathrates Ni-Ni-C 6 H 6 and Ni-Ni-C 12 H 10 have been studied using inelastic neutron scattering. Calculations of the dynamical structure factor for a free uniaxial quantum rotor reproduce the neutron scattering data with respect to their Q- and T-dependence as well as the relative intensities for the 0 → 1, 0 → 2 and 1 → 2 transitions. Though the effective NH 3 rotation constant is different from the gas phase value, the effective radius of rotation (i.e., the average distance of protons from the rotation axis) is equal or very close to the geometrical value r = 0.94 A for a NH 3 group. Comparing the experimental data with the calculated dynamical structure factor for the 0 → 3 transition it could be shown, that the corresponding transition line, in contrast to transitions between j = 0,1,2 levels measured so far, has a finite width at T = 0 K

Influence of the nanoparticles agglomeration state in the quantum-confinement effects: Experimental evidences

Energy Technology Data Exchange (ETDEWEB)

Lorite, I., E-mail: lorite@physik.uni-leipzig.de [Electroceramic Department, Instituto de Cerámica y Vidrio, CSIC, Kelsen 5, 28049, Madrid (Spain); Division of Superconductivity and Magnetism, Faculty of Physics and Earth Sciences, Linnestrasse 5, D-04103 Leipzig (Germany); Romero, J. J.; Fernandez, J. F. [Electroceramic Department, Instituto de Cerámica y Vidrio, CSIC, Kelsen 5, 28049, Madrid (Spain)

2015-03-15

The agglomeration state facilitates particle-particle interaction which produces important effects in the phonon confinement effects at the nanoscale. A partial phonon transmission between close nanoparticles yields a lower momentum conservation relaxation than in a single isolated nanoparticle. It means a larger red shift and broadening of the Raman modes than the expected ones for Raman quantum confinement effects. This particle-particle interaction can drive to error when Raman responses are used to estimate the size of the nanoscaled materials. In this work different corrections are suggested to overtake this source of error.

Influence of the nanoparticles agglomeration state in the quantum-confinement effects: Experimental evidences

International Nuclear Information System (INIS)

Lorite, I.; Romero, J. J.; Fernandez, J. F.

2015-01-01

The agglomeration state facilitates particle-particle interaction which produces important effects in the phonon confinement effects at the nanoscale. A partial phonon transmission between close nanoparticles yields a lower momentum conservation relaxation than in a single isolated nanoparticle. It means a larger red shift and broadening of the Raman modes than the expected ones for Raman quantum confinement effects. This particle-particle interaction can drive to error when Raman responses are used to estimate the size of the nanoscaled materials. In this work different corrections are suggested to overtake this source of error

The classicality and quantumness of a quantum ensemble

International Nuclear Information System (INIS)

Zhu Xuanmin; Pang Shengshi; Wu Shengjun; Liu Quanhui

2011-01-01

In this Letter, we investigate the classicality and quantumness of a quantum ensemble. We define a quantity called ensemble classicality based on classical cloning strategy (ECCC) to characterize how classical a quantum ensemble is. An ensemble of commuting states has a unit ECCC, while a general ensemble can have a ECCC less than 1. We also study how quantum an ensemble is by defining a related quantity called quantumness. We find that the classicality of an ensemble is closely related to how perfectly the ensemble can be cloned, and that the quantumness of the ensemble used in a quantum key distribution (QKD) protocol is exactly the attainable lower bound of the error rate in the sifted key. - Highlights: → A quantity is defined to characterize how classical a quantum ensemble is. → The classicality of an ensemble is closely related to the cloning performance. → Another quantity is also defined to investigate how quantum an ensemble is. → This quantity gives the lower bound of the error rate in a QKD protocol.

Quantum solitonic wave-packet of a meso-scopic system in singularity free gravity

Science.gov (United States)

Buoninfante, Luca; Lambiase, Gaetano; Mazumdar, Anupam

2018-06-01

In this paper we will discuss how to localise a quantum wave-packet due to self-gravitating meso-scopic object by taking into account gravitational self-interaction in the Schrödinger equation beyond General Relativity. In particular, we will study soliton-like solutions in infinite derivative ghost free theories of gravity, which resolves the gravitational 1 / r singularity in the potential. We will show a unique feature that the quantum spread of such a gravitational system is larger than that of the Newtonian gravity, therefore enabling us a window of opportunity to test classical and quantum properties of such theories of gravity in the near future at a table-top experiment.

Ultraviolet and soft X-ray free-electron lasers introduction to physical principles, experimental results, technological challenges

CERN Document Server

Schmüser, Peter; Rossbach, Jörg; Fujimori, A; Kühn, J; Müller, T; Steiner, F; Trümper, J; Varma, C; Wölfle, P

2008-01-01

In the introduction accelerator-based light sources are considered and a comparison is made between free-electron lasers and conventional quantum lasers. The motion and radiation of relativistic electrons in undulator magnets is discussed. The principle of a low-gain free-electron laser is explained and the pendulum equations are introduced that characterize the electron dynamics in the field of a light wave. The differential equations of the high-gain FEL are derived from the Maxwell equations of electrodynamics. Analytical and numerical solutions of the FEL equations are presented and important FEL parameters are defined, such as gain length, FEL bandwidth and saturation power. A detailed numerical study of the all-important microbunching process is presented. The mechanism of Self Amplified Spontaneous Emission is described theoretically and illustrated with numerous experimental results. Three-dimensional effects such as betatron oscillations and optical diffraction are addressed and their impact on the F...

Characterizing multi-photon quantum interference with practical light sources and threshold single-photon detectors

Science.gov (United States)

Navarrete, Álvaro; Wang, Wenyuan; Xu, Feihu; Curty, Marcos

2018-04-01

The experimental characterization of multi-photon quantum interference effects in optical networks is essential in many applications of photonic quantum technologies, which include quantum computing and quantum communication as two prominent examples. However, such characterization often requires technologies which are beyond our current experimental capabilities, and today's methods suffer from errors due to the use of imperfect sources and photodetectors. In this paper, we introduce a simple experimental technique to characterize multi-photon quantum interference by means of practical laser sources and threshold single-photon detectors. Our technique is based on well-known methods in quantum cryptography which use decoy settings to tightly estimate the statistics provided by perfect devices. As an illustration of its practicality, we use this technique to obtain a tight estimation of both the generalized Hong‑Ou‑Mandel dip in a beamsplitter with six input photons and the three-photon coincidence probability at the output of a tritter.

Assessing the Progress of Trapped-Ion Processors Towards Fault-Tolerant Quantum Computation

Science.gov (United States)

Bermudez, A.; Xu, X.; Nigmatullin, R.; O'Gorman, J.; Negnevitsky, V.; Schindler, P.; Monz, T.; Poschinger, U. G.; Hempel, C.; Home, J.; Schmidt-Kaler, F.; Biercuk, M.; Blatt, R.; Benjamin, S.; Müller, M.

2017-10-01

A quantitative assessment of the progress of small prototype quantum processors towards fault-tolerant quantum computation is a problem of current interest in experimental and theoretical quantum information science. We introduce a necessary and fair criterion for quantum error correction (QEC), which must be achieved in the development of these quantum processors before their sizes are sufficiently big to consider the well-known QEC threshold. We apply this criterion to benchmark the ongoing effort in implementing QEC with topological color codes using trapped-ion quantum processors and, more importantly, to guide the future hardware developments that will be required in order to demonstrate beneficial QEC with small topological quantum codes. In doing so, we present a thorough description of a realistic trapped-ion toolbox for QEC and a physically motivated error model that goes beyond standard simplifications in the QEC literature. We focus on laser-based quantum gates realized in two-species trapped-ion crystals in high-optical aperture segmented traps. Our large-scale numerical analysis shows that, with the foreseen technological improvements described here, this platform is a very promising candidate for fault-tolerant quantum computation.

Fast and robust approach to long-distance quantum communication with atomic ensembles

International Nuclear Information System (INIS)

Jiang, L.; Lukin, M. D.; Taylor, J. M.

2007-01-01

Quantum repeaters create long-distance entanglement between quantum systems while overcoming difficulties such as the attenuation of single photons in a fiber. Recently, an implementation of a repeater protocol based on single qubits in atomic ensembles and linear optics has been proposed [Duan et al., Nature (London) 414, 413 (2001)]. Motivated by rapid experimental progress towards implementing that protocol, here we develop a more efficient scheme compatible with active purification of arbitrary errors. Using similar resources as the earlier protocol, our approach intrinsically purifies leakage out of the logical subspace and all errors within the logical subspace, leading to greatly improved performance in the presence of experimental inefficiencies. Our analysis indicates that our scheme could generate approximately one pair per 3 min over 1280 km distance with fidelity (F≥78%) sufficient to violate Bell's inequality

Energy levels and quantum states of [Leu]enkephalin conformations based on theoretical and experimental investigations

DEFF Research Database (Denmark)

Abdali, Salim; Jensen, Morten Østergaard; Bohr, Henrik

2003-01-01

This paper describes a theoretical and experimental study of [Leu]enkephalin conformations with respect to the quantum estates of the atomic structure of the peptide. Results from vibrational absorption measurements and quantum calculations are used to outline a quantum picture and to assign vibr...

Design and experimental realization of an optimal scheme for teleportation of an n-qubit quantum state

Science.gov (United States)

Sisodia, Mitali; Shukla, Abhishek; Thapliyal, Kishore; Pathak, Anirban

2017-12-01

An explicit scheme (quantum circuit) is designed for the teleportation of an n-qubit quantum state. It is established that the proposed scheme requires an optimal amount of quantum resources, whereas larger amount of quantum resources have been used in a large number of recently reported teleportation schemes for the quantum states which can be viewed as special cases of the general n-qubit state considered here. A trade-off between our knowledge about the quantum state to be teleported and the amount of quantum resources required for the same is observed. A proof-of-principle experimental realization of the proposed scheme (for a 2-qubit state) is also performed using 5-qubit superconductivity-based IBM quantum computer. The experimental results show that the state has been teleported with high fidelity. Relevance of the proposed teleportation scheme has also been discussed in the context of controlled, bidirectional, and bidirectional controlled state teleportation.

Randomized benchmarking of single- and multi-qubit control in liquid-state NMR quantum information processing

International Nuclear Information System (INIS)

Ryan, C A; Laforest, M; Laflamme, R

2009-01-01

Being able to quantify the level of coherent control in a proposed device implementing a quantum information processor (QIP) is an important task for both comparing different devices and assessing a device's prospects with regards to achieving fault-tolerant quantum control. We implement in a liquid-state nuclear magnetic resonance QIP the randomized benchmarking protocol presented by Knill et al (2008 Phys. Rev. A 77 012307). We report an error per randomized π/2 pulse of 1.3±0.1x10 -4 with a single-qubit QIP and show an experimentally relevant error model where the randomized benchmarking gives a signature fidelity decay which is not possible to interpret as a single error per gate. We explore and experimentally investigate multi-qubit extensions of this protocol and report an average error rate for one- and two-qubit gates of 4.7±0.3x10 -3 for a three-qubit QIP. We estimate that these error rates are still not decoherence limited and thus can be improved with modifications to the control hardware and software.

Robust Learning Control Design for Quantum Unitary Transformations.

Science.gov (United States)

Wu, Chengzhi; Qi, Bo; Chen, Chunlin; Dong, Daoyi

2017-12-01

Robust control design for quantum unitary transformations has been recognized as a fundamental and challenging task in the development of quantum information processing due to unavoidable decoherence or operational errors in the experimental implementation of quantum operations. In this paper, we extend the systematic methodology of sampling-based learning control (SLC) approach with a gradient flow algorithm for the design of robust quantum unitary transformations. The SLC approach first uses a "training" process to find an optimal control strategy robust against certain ranges of uncertainties. Then a number of randomly selected samples are tested and the performance is evaluated according to their average fidelity. The approach is applied to three typical examples of robust quantum transformation problems including robust quantum transformations in a three-level quantum system, in a superconducting quantum circuit, and in a spin chain system. Numerical results demonstrate the effectiveness of the SLC approach and show its potential applications in various implementation of quantum unitary transformations.

A simple route for making surfactant free lead sulfide (PbS) quantum dots

Energy Technology Data Exchange (ETDEWEB)

Alam, Firoz; Kumar, Neetesh; Dutta, Viresh, E-mail: vdutta@ces.iitd.ac.in

2015-05-15

Highlights: • Surfactant free PbS NCs were successfully synthesised using CoSP technique. • The technique eliminates the requirements of washing to remove the ligands. • Grinding using mortar and pestle creates well separated PbS QDs. • Surfactant free PbS NCs are stable and do not show any degradation with time. - Abstract: An efficient, cost effective and less time consuming method suitable for mass production of surfactant free quantum dots (QDs) of lead sulfide (PbS) is reported. PbS nanocrystals (NCs) are first synthesised by continuous spray pyrolysis (CoSP) technique and de-agglomeration into PbS quantum dots (QDs) is achieved by vigorous mechanical grinding using mortar and pestle. Lead acetate and thiourea were used as the precursor materials for preparation of surfactant free PbS NCs. The broadening in XRD peaks of ground NCs as compared to as synthesized PbS NCs clearly indicated the reduction in particle size to be QDs of PbS. The TEM images also showed that ground PbS NCs were nearly spherical in shape having an average diameter in the range of 4–6 nm. The shift in optical gap from 0.41 eV to 1.47 eV supported the QD formation.

Experimental verification of quantum discord in continuous-variable states

International Nuclear Information System (INIS)

Hosseini, S; Haw, J Y; Assad, S M; Chrzanowski, H M; Janousek, J; Symul, T; Lam, P K; Rahimi-Keshari, S; Ralph, T C

2014-01-01

We introduce a simple and efficient technique to verify quantum discord in unknown Gaussian states and a certain class of non-Gaussian states. We show that any separation in the peaks of the marginal distributions of one subsystem conditioned on two different outcomes of homodyne measurements performed on the other subsystem indicates correlation between the corresponding quadratures, and hence nonzero discord. We also apply this method to non-Gaussian states that are prepared by overlapping a statistical mixture of coherent and vacuum states on a beam splitter. We experimentally demonstrate this technique by verifying nonzero quantum discord in a bipartite Gaussian and certain non-Gaussian states. (paper)

Converging ligand-binding free energies obtained with free-energy perturbations at the quantum mechanical level.

Science.gov (United States)

Olsson, Martin A; Söderhjelm, Pär; Ryde, Ulf

2016-06-30

In this article, the convergence of quantum mechanical (QM) free-energy simulations based on molecular dynamics simulations at the molecular mechanics (MM) level has been investigated. We have estimated relative free energies for the binding of nine cyclic carboxylate ligands to the octa-acid deep-cavity host, including the host, the ligand, and all water molecules within 4.5 Å of the ligand in the QM calculations (158-224 atoms). We use single-step exponential averaging (ssEA) and the non-Boltzmann Bennett acceptance ratio (NBB) methods to estimate QM/MM free energy with the semi-empirical PM6-DH2X method, both based on interaction energies. We show that ssEA with cumulant expansion gives a better convergence and uses half as many QM calculations as NBB, although the two methods give consistent results. With 720,000 QM calculations per transformation, QM/MM free-energy estimates with a precision of 1 kJ/mol can be obtained for all eight relative energies with ssEA, showing that this approach can be used to calculate converged QM/MM binding free energies for realistic systems and large QM partitions. © 2016 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc. © 2016 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc.

From quantum chemical formation free energies to evaporation rates

Directory of Open Access Journals (Sweden)

I. K. Ortega

2012-01-01

Full Text Available Atmospheric new particle formation is an important source of atmospheric aerosols. Large efforts have been made during the past few years to identify which molecules are behind this phenomenon, but the actual birth mechanism of the particles is not yet well known. Quantum chemical calculations have proven to be a powerful tool to gain new insights into the very first steps of particle formation. In the present study we use formation free energies calculated by quantum chemical methods to estimate the evaporation rates of species from sulfuric acid clusters containing ammonia or dimethylamine. We have found that dimethylamine forms much more stable clusters with sulphuric acid than ammonia does. On the other hand, the existence of a very deep local minimum for clusters with two sulfuric acid molecules and two dimethylamine molecules hinders their growth to larger clusters. These results indicate that other compounds may be needed to make clusters grow to larger sizes (containing more than three sulfuric acid molecules.

Quantum mechanics versus relativity: an experimental test of the structure of spacetime

International Nuclear Information System (INIS)

Emelyanov, S A

2012-01-01

We have performed an experimental test under the conditions in which quantum mechanics predicts spatially discontinuous single-particle transport. The transport is beyond the relativistic paradigm of movement in Cartesian space and therefore may well be nonlocal. Our test has demonstrated that such transport does exist. This fact opens the door for a realistic interpretation of quantum mechanics in so far as the requirement of Lorentz invariance appears inapplicable to any version of quantum theory. Moreover, as quantum mechanics proposes a particle dynamics beyond relativity, it automatically requires an adequate ‘quantum’ concept of spacetime, for which the relativistic concept is only a limiting case. The quantum concept allows absolute simultaneity and hence revives the notion of absolute time. It also goes beyond the relativistic curvilinear Cartesian order of space to account for quantum phenomena such as discontinuity and nonlocality in the spirit of Bohm's concept of the implicate order.

Experimental reversion of the optimal quantum cloning and flipping processes

International Nuclear Information System (INIS)

Sciarrino, Fabio; Secondi, Veronica; De Martini, Francesco

2006-01-01

The quantum cloner machine maps an unknown arbitrary input qubit into two optimal clones and one optimal flipped qubit. By combining linear and nonlinear optical methods we experimentally implement a scheme that, after the cloning transformation, restores the original input qubit in one of the output channels, by using local measurements, classical communication, and feedforward. This nonlocal method demonstrates how the information on the input qubit can be restored after the cloning process. The realization of the reversion process is expected to find useful applications in the field of modern multipartite quantum cryptography

Quantum stopwatch: how to store time in a quantum memory.

Science.gov (United States)

Yang, Yuxiang; Chiribella, Giulio; Hayashi, Masahito

2018-05-01

Quantum mechanics imposes a fundamental trade-off between the accuracy of time measurements and the size of the systems used as clocks. When the measurements of different time intervals are combined, the errors due to the finite clock size accumulate, resulting in an overall inaccuracy that grows with the complexity of the set-up. Here, we introduce a method that, in principle, eludes the accumulation of errors by coherently transferring information from a quantum clock to a quantum memory of the smallest possible size. Our method could be used to measure the total duration of a sequence of events with enhanced accuracy, and to reduce the amount of quantum communication needed to stabilize clocks in a quantum network.

Equation of state of dense plasmas: Orbital-free molecular dynamics as the limit of quantum molecular dynamics for high-Z elements

Energy Technology Data Exchange (ETDEWEB)

Danel, J.-F.; Blottiau, P.; Kazandjian, L.; Piron, R.; Torrent, M. [CEA, DAM, DIF, 91297 Arpajon (France)

2014-10-15

The applicability of quantum molecular dynamics to the calculation of the equation of state of a dense plasma is limited at high temperature by computational cost. Orbital-free molecular dynamics, based on a semiclassical approximation and possibly on a gradient correction, is a simulation method available at high temperature. For a high-Z element such as lutetium, we examine how orbital-free molecular dynamics applied to the equation of state of a dense plasma can be regarded as the limit of quantum molecular dynamics at high temperature. For the normal mass density and twice the normal mass density, we show that the pressures calculated with the quantum approach converge monotonically towards those calculated with the orbital-free approach; we observe a faster convergence when the orbital-free approach includes the gradient correction. We propose a method to obtain an equation of state reproducing quantum molecular dynamics results up to high temperatures where this approach cannot be directly implemented. With the results already obtained for low-Z plasmas, the present study opens the way for reproducing the quantum molecular dynamics pressure for all elements up to high temperatures.

On the robustness of bucket brigade quantum RAM

Science.gov (United States)

Arunachalam, Srinivasan; Gheorghiu, Vlad; Jochym-O'Connor, Tomas; Mosca, Michele; Varshinee Srinivasan, Priyaa

2015-12-01

We study the robustness of the bucket brigade quantum random access memory model introduced by Giovannetti et al (2008 Phys. Rev. Lett.100 160501). Due to a result of Regev and Schiff (ICALP ’08 733), we show that for a class of error models the error rate per gate in the bucket brigade quantum memory has to be of order o({2}-n/2) (where N={2}n is the size of the memory) whenever the memory is used as an oracle for the quantum searching problem. We conjecture that this is the case for any realistic error model that will be encountered in practice, and that for algorithms with super-polynomially many oracle queries the error rate must be super-polynomially small, which further motivates the need for quantum error correction. By contrast, for algorithms such as matrix inversion Harrow et al (2009 Phys. Rev. Lett.103 150502) or quantum machine learning Rebentrost et al (2014 Phys. Rev. Lett.113 130503) that only require a polynomial number of queries, the error rate only needs to be polynomially small and quantum error correction may not be required. We introduce a circuit model for the quantum bucket brigade architecture and argue that quantum error correction for the circuit causes the quantum bucket brigade architecture to lose its primary advantage of a small number of ‘active’ gates, since all components have to be actively error corrected.

Gaussian Hypothesis Testing and Quantum Illumination.

Science.gov (United States)

Wilde, Mark M; Tomamichel, Marco; Lloyd, Seth; Berta, Mario

2017-09-22

Quantum hypothesis testing is one of the most basic tasks in quantum information theory and has fundamental links with quantum communication and estimation theory. In this paper, we establish a formula that characterizes the decay rate of the minimal type-II error probability in a quantum hypothesis test of two Gaussian states given a fixed constraint on the type-I error probability. This formula is a direct function of the mean vectors and covariance matrices of the quantum Gaussian states in question. We give an application to quantum illumination, which is the task of determining whether there is a low-reflectivity object embedded in a target region with a bright thermal-noise bath. For the asymmetric-error setting, we find that a quantum illumination transmitter can achieve an error probability exponent stronger than a coherent-state transmitter of the same mean photon number, and furthermore, that it requires far fewer trials to do so. This occurs when the background thermal noise is either low or bright, which means that a quantum advantage is even easier to witness than in the symmetric-error setting because it occurs for a larger range of parameters. Going forward from here, we expect our formula to have applications in settings well beyond those considered in this paper, especially to quantum communication tasks involving quantum Gaussian channels.

Experimental quantum 'Guess my Number' protocol using multiphoton entanglement

International Nuclear Information System (INIS)

Zhang, Jun; Bao, Xiao-Hui; Chen, Teng-Yun; Yang, Tao; Cabello, Adan; Pan, Jian-Wei

2007-01-01

We present an experimental demonstration of a modified version of the entanglement-assisted 'Guess my Number' protocol for the reduction of communication complexity among three separated parties. The results of experimental measurements imply that the separated parties can compute a function of distributed inputs by exchanging less classical information than by using any classical strategy. And the results also demonstrate the advantages of entanglement-enhanced communication, which is very close to quantum communication. The advantages are based on the properties of Greenberger-Horne-Zeilinger states

Quantification of the Impact of Photon Distinguishability on Measurement-Device- Independent Quantum Key Distribution

Directory of Open Access Journals (Sweden)

Garrett K. Simon

2018-04-01

Full Text Available Measurement-Device-Independent Quantum Key Distribution (MDI-QKD is a two-photon protocol devised to eliminate eavesdropping attacks that interrogate or control the detector in realized quantum key distribution systems. In MDI-QKD, the measurements are carried out by an untrusted third party, and the measurement results are announced openly. Knowledge or control of the measurement results gives the third party no information about the secret key. Error-free implementation of the MDI-QKD protocol requires the crypto-communicating parties, Alice and Bob, to independently prepare and transmit single photons that are physically indistinguishable, with the possible exception of their polarization states. In this paper, we apply the formalism of quantum optics and Monte Carlo simulations to quantify the impact of small errors in wavelength, bandwidth, polarization and timing between Alice’s photons and Bob’s photons on the MDI-QKD quantum bit error rate (QBER. Using published single-photon source characteristics from two-photon interference experiments as a test case, our simulations predict that the finite tolerances of these sources contribute ( 4.04 ± 20 / N sifted % to the QBER in an MDI-QKD implementation generating an N sifted -bit sifted key.

Experimental realization of the quantum duel game using linear optical circuits

International Nuclear Information System (INIS)

Balthazar, W F; Passos, M H M; Schmidt, A G M; Huguenin, J A O; Caetano, D P

2015-01-01

We report on the experimental realization of the quantum duel game for two players, Alice and Bob. Using an all optical approach, we have encoded Alice and Bob states in transverse modes and polarization degrees of freedom of a laser beam, respectively. By setting Alice and Bob input states and considering the possibility of Alice performing two shots, we demonstrated the quantum features of the game as well as we recovered the classical version of the game. (paper)

State-independent error-disturbance trade-off for measurement operators

International Nuclear Information System (INIS)