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Jun 27, 2018
06/18

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Priyanka Chowdhury; Tanumoy Pramanik; Archan S. Majumdar

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We derive a fine-grained uncertainty relation for the measurement of two incompatible observables on a single quantum system of continuous variables, and show that continuous variable systems are more uncertain than discrete variable systems. Using the derived fine-grained uncertainty relation, we formulate stronger steering criterion that is able to reveal the steerability of N00N states that has hitherto not been possible using other criteria. We further obtain a monogamy relation for our...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1503.04697

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Jun 30, 2018
06/18

by
H R Baghshahi; M K Tavassoly; A Behjat

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The interaction between a $\diamondsuit$-type four-level atom and a single-mode field in the presence of Kerr medium with intensity-dependent coupling involving multi-photon processes has been studied. Using the generalized (nonlinear) Jaynes-Cummings model, the exact analytical solution of the wave function for the considered system under particular condition, has been obtained when the atom is initially excited to the topmost level and the field is in a coherent state. Some physical...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1408.2968

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Jun 30, 2018
06/18

by
L. G. Helt; M. J. Steel

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We show that a useful connection exists between spontaneous parametric downconversion (SPDC) and sum frequency generation in nonlinear optical waveguides with arbitrary scattering loss, while the same does not hold true for SPDC and difference frequency generation. This result deepens the relationship between quantum and classical second-order nonlinear optical processes in waveguides, and identifies the most accurate characterization of their quantum performance in the presence of loss based...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1412.3186

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Jun 29, 2018
06/18

by
Chong Chen; Chun-Jie Yang; Jun-Hong An

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Decoherence-free state (DFS) encoding supplies a useful way to avoid the detrimental influence of the environment on quantum information processing. The DFS was previously well established in either the two subsystems locating at the same spatial position or the dynamics under the Born--Markovian approximation. Here, we investigate the exact DFS of two spatially separated quantum systems consisting of two-level systems or harmonic oscillators coupled to a common non-Markovian zero-temperature...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1601.02303

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Jun 30, 2018
06/18

by
G. S. Vasilev; N. V. Vitanov

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The aim of this paper is to analyze the MS transformation in the case of weak deviation of the condition for equal detunings, which in necessary for factorization towards set of two-state systems and set of decouple states. Some elements concerning the general solution of the MS transformation will be also discussed.

Topic: Quantum Physics

Source: http://arxiv.org/abs/1402.5673

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Jun 30, 2018
06/18

by
Gangcheng Wang; Chunfang Sun; Chunfeng Wu; Bo Liu; Yan Zhang; Kang Xue

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We investigate the generalized braid relation ($d-$level $N-$body braid relation) and its application to quantum entanglement. By means of finite-dimensional representations of Heisenberg-Weyl algebra, a set of $d^{N}\times d^{N}$ unitary matrix representations satisfying the generalized braid relation can be constructed. Such generalized braid matrices can entangle $d-$level $N-$partite quantum states. Acting the generalized braid matrices on the standard basis, one can obtain a set of...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1404.4897

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Jun 30, 2018
06/18

by
Rúben Sousa; Yasser Omar

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The XX model with uniform couplings represents the most natural choice for quantum state transfer through spin chains. Given that it has long been established that single-qubit states cannot be transferred with perfect fidelity in this model, the notion of pretty good state transfer has been recently introduced as a relaxation of the constraints on fidelity. In this paper, we study the transfer of multi-qubit entangled and unentangled states through unmodulated spin chains, and we prove that it...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1405.1296

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Jun 30, 2018
06/18

by
Tzu-Chieh Wei; Ying Li; Leong Chuan Kwek

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We construct two spin models on lattices (both two and three-dimensional) to study the capability of quantum computational power as a function of temperature and the system parameter. There exists a finite region in the phase diagram such that the thermal equilibrium states are capable of providing a universal fault-tolerant resource for measurement-based quantum computation. Moreover, in such a region the thermal resource states on the 3D lattices can enable topological protection for quantum...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1402.4390

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Jun 29, 2018
06/18

by
Fabio Benatti; Dariusz Chruściński; Sergey Filippov

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The are several non-equivalent notions of Markovian quantum evolution. In this paper we show that the one based on the so-called CP-divisibility of the corresponding dynamical map enjoys the following stability property: the dynamical map $\Lambda_t$ is CP-divisible iff the second tensor power $\Lambda_t\otimes\Lambda_t$ is CP-divisible as well. Moreover, the P-divisibility of the map $\Lambda_t\otimes\Lambda_t$ is equivalent to the CP-divisibility of the map $\Lambda_t$. Interestingly, the...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1610.04634

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Jun 29, 2018
06/18

by
Jing-Ling Chen; Changliang Ren; Changbo Chen; Xiang-Jun Ye; Arun Kumar Pati

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Recently quantum nonlocality has been classified into three distinct types: quantum entanglement, Einstein-Podolsky-Rosen steering, and Bell's nonlocality. Among which, Bell's nonlocality is the strongest type. Bell's nonlocality for quantum states is usually detected by violation of some Bell's inequalities, such as Clause-Horne-Shimony-Holt inequality for two qubits. Steering is a manifestation of nonlocality intermediate between entanglement and Bell's nonlocality. This peculiar feature has...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1606.07060

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Jun 29, 2018
06/18

by
Yamen Hamdouni

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We show that the probability distribution corresponding to a fully random tracial state of a system of spin-S particles satisfies a diffusion-like equation. The diffusion coefficient turns out to be equal to $S(S+1)/6$, where $S$ is the magnitude of the spin of each particle. We also introduce a bosonization scheme for the lowering and raising operators.

Topic: Quantum Physics

Source: http://arxiv.org/abs/1611.00753

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Jun 30, 2018
06/18

by
A. Soare; H. Ball; D. Hayes; J. Sastrawan; M. C. Jarratt; J. J. McLoughlin; X. Zhen; T. J. Green; M. J. Biercuk

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Instabilities due to extrinsic interference are routinely faced in systems engineering, and a common solution is to rely on a broad class of $\textit{filtering}$ techniques in order to afford stability to intrinsically unstable systems. For instance, electronic systems are frequently designed to incorporate electrical filters composed of, $\textit{e.g.}$ RLC components, in order to suppress the effects of out-of-band fluctuations that interfere with desired performance. Quantum coherent systems...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1404.0820

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Jun 29, 2018
06/18

by
Itsik Cohen; Nati Aharon; Alex Retzker

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Resilience to noise and to decoherence processes is an important ingredient for the implementation of quantum information processing, and quantum technologies. To this end, techniques such as pulsed and continuous dynamical decoupling have been proposed to reduce noise effects. In this paper, we suggest a new approach to implementing continuous dynamical decoupling techniques, that uses an extra control parameter; namely, the ability to shape the time dependence of the detuning. This approach...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1606.03960

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Jun 30, 2018
06/18

by
Charles Ci Wen Lim; Boris Korzh; Anthony Martin; Felix Bussieres; Rob Thew; Hugo Zbinden

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Recently, a quantum key distribution (QKD) scheme based on entanglement swapping, called measurement-device-independent QKD (mdiQKD), was proposed to bypass all detector side-channel attacks. While mdiQKD is conceptually elegant and offers a supreme level of security, the experimental complexity is challenging for practical systems. For instance, it requires interference between two widely separated independent single-photon sources, and the rates are dependent on detecting two photons - one...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1410.1850

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Jun 30, 2018
06/18

by
Jin-Xing Hou; Yun-Long Su; Si-Yuan Liu; Xiao-Hui Wang

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Two-qubit Bell-diagonal states can be depicted as a tetrahedron in three dimensions. We investigate the structure of quantum resources, including coherence and quantum discord, in the tetrahedron. The ordering of different resources measures is a common problem in resource theories, and which measure should be chosen to investigate the structure of resources is still an open question. We consider the structure of quantum resources which is not affected by the choice of measure. Our work...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1704.02180

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Jun 30, 2018
06/18

by
Katarzyna Macieszczak

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We prove the Zeno limit $N^{3/2}$ of the quantum Fisher information for frequency estimation with a general initial state of $N$ two-level atoms in the presence of local non-Markovian dephasing noise, which was demonstrated for a GHZ state by A. W. Chin, S. F. Huelga, M. B. Plenio (2012). For collective dephasing we prove that non-Markovian noise allows for better scaling for both correlated and uncorelated states. The quantum enhancement in precision is at least as good as in the local case.

Topic: Quantum Physics

Source: http://arxiv.org/abs/1403.1333

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Jun 30, 2018
06/18

by
Tommaso Lunghi; Jędrzej Kaniewski; Felix Bussieres; Raphael Houlmann; Marco Tomamichel; Stephanie Wehner; Hugo Zbinden

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Bit commitment is a fundamental cryptographic primitive in which Alice wishes to commit a secret bit to Bob. Perfectly secure bit commitment between two mistrustful parties is impossible through asynchronous exchange of quantum information. Perfect security is however possible when Alice and Bob each split into several agents exchanging classical information at times and locations suitably chosen to satisfy specific relativistic constraints. In this Letter we first revisit a previously proposed...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1411.4917

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Jun 30, 2018
06/18

by
Boyan T. Torosov; Nikolay V. Vitanov

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We present a method to construct high-fidelity quantum phase gates, which are insensitive to errors in various experimental parameters. The phase gates consist of a pair of two sequential broadband composite pulses, with a phase difference $\pi+\alpha/2$ between them, where $\alpha$ is the desired gate phase. By using composite pulses which compensate systematic errors in the pulse area, the frequency detuning, or both the area and the detuning, we thereby construct composite phase gates which...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1409.6410

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Jun 30, 2018
06/18

by
Vlatko Vedral

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This paper summarizes the basics of the notion of quantum discord and how it relates to other types of correlations in quantum physics. We take the fundamental information theoretic approach and illustrate our exposition with a number of simple examples.

Topic: Quantum Physics

Source: http://arxiv.org/abs/1702.01327

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Jun 28, 2018
06/18

by
Xue-Ke Song; Hao Zhang; Qing Ai; Jing Qiu; Fu-Guo Deng

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By using transitionless quantum driving algorithm (TQDA), we present an efficient scheme for the shortcuts to the holonomic quantum computation (HQC). It works in decoherence-free subspace (DFS) and the adiabatic process can be speeded up in the shortest possible time. More interestingly, we give a physical implementation for our shortcuts to HQC with nitrogen-vacancy centers in diamonds dispersively coupled to a whispering-gallery mode microsphere cavity. It can be efficiently realized by...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1509.00097

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Jun 30, 2018
06/18

by
Xian-Peng Zhang; Li-Tuo Shen; Zhang-Qi Yin; Huai-Zhi Wu; Zhen-Biao Yang

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We demonstrate quantum bath engineering for preparation of any orbital state with controllable phase factor of a superconducting flux qubit assisted by a microwave coplanar waveguide resonator. We investigate the polarization efficiency of the arbitrary direction rotating on the Bloch sphere, and obtain an effective Rabi frequency by using the convergence condition of Markovian master equation. The processes of polarization can be implemented effectively in a dissipative environment created by...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1407.3337

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Jun 27, 2018
06/18

by
Ludovico Lami; Vittorio Giovannetti

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The set of Entanglement Saving (ES) quantum channels is introduced and characterized. These are completely positive, trace preserving transformations which when acting locally on a bipartite quantum system initially prepared into a maximally entangled configuration, preserve its entanglement even when applied an arbitrary number of times. In other words, a quantum channel $\psi$ is said to be ES if its powers $\psi^n$ are not entanglement-breaking for all integers $n$. We also characterize the...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1505.00461

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Jun 29, 2018
06/18

by
Chao Lei; Shijie Peng; Chenyong Ju; Man-Hong Yung; Jiangfeng Du

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Quantum mechanical systems lose coherence through interactions with external environments---a process known as decoherence. Although decoherence is detrimental for most of the tasks in quantum information processing, a substantial degree of decoherence is crucial for boosting the efficiency of quantum processes, for example, in quantum biology. The key to the success in simulating those open quantum systems is therefore the ability of controlling decoherence, instead of eliminating it. Here we...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1610.01875

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Jun 30, 2018
06/18

by
Jiangwei Shang; Hui Khoon Ng; Berthold-Georg Englert

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Because of the constraint that the estimators be bona fide physical states, any quantum state tomography scheme - including the widely used maximum likelihood estimation - yields estimators that may have a bias, although they are consistent estimators. Schwemmer et al. (arXiv:1310.8465 [quant-ph]) illustrate this by observing a systematic underestimation of the fidelity and an overestimation of entanglement in estimators obtained from simulated data. Further, these authors argue that the simple...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1405.5350

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Jun 28, 2018
06/18

by
Anton Wöllert; Heiko Bauke; Christoph H. Keitel

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Ultra strong electromagnetic fields can lead to spontaneous creation of single or multiple electron-positron pairs. A quantum field theoretical treatment of the pair creation process combined with numerical methods provides a description of the fermionic quantum field state, from which all observables of the multiple electron-positron pairs can be inferred. This allows to study the complex multi-particle dynamics of electron-positron pair creation in-depth, including multi-pair statistics as...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1511.07709

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Jun 30, 2018
06/18

by
Hai-Rui Wei; Pei-Jin Zhu

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It is desirable to implement an efficient quantum information process demanding fewer quantum resources. We designed two compact quantum circuits for determinately implementing four-qubit Toffoli and Fredkin gates on single-photon systems in both the polarization and spatial degrees of freedom (DoFs) via diamond nitrogen-vacancy (NV) centers in resonators. The gates are heralded by the electron spins associated with the diamond NV centers. In contrast to the ones with one DoF, our...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1703.00274

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Jun 29, 2018
06/18

by
Paweł Mazurek; Michał Horodecki; Łukasz Czekaj; Paweł Horodecki

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We consider Bayesian estimate of static magnetic field, characterized by a prior Gaussian probability distribution, in systems of a few electron quantum dot spins interacting with infinite temperature spin environment via hyperfine interaction. Sudden transitions among optimal states and measurements are observed. Usefulness of measuring occupation levels is shown for all times of the evolution, together with the role of entanglement in the optimal scenario. For low values of magnetic field,...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1605.04279

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Jun 29, 2018
06/18

by
Carole Addis; Göktuğ Karpat; Chiara Macchiavello; Sabrina Maniscalco

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Memory effects play a fundamental role in the study of the dynamics of open quantum systems. There exist two conceptually distinct notions of memory discussed for quantum channels in the literature. In quantum information theory quantum channels with memory are characterised by the existence of correlations between successive applications of the channel on a sequence of quantum systems. In open quantum systems theory memory effects arise dynamically during the time evolution of quantum systems,...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1607.00134

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Jun 30, 2018
06/18

by
Ming-Liang Hu; Dong-Ping Tian

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Geometric description of quantum correlations are favored for their distinct physical significance. Geometric discord based on the trace distance and the Bures distance are shown to be well-defined quantum correlation measures. Here, we examine their particular dynamical behaviors under independent as well as common structured reservoirs, and reveal their robustness against decoherence. We showed that the two well-defined geometric discord may be preserved well, or even be improved and...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1402.0301

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Jun 29, 2018
06/18

by
M. Genkin; D. W. Schönleber; S. Wüster; A. Eisfeld

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We propose a setup of an open quantum system in which the environment can be tuned such that either Markovian or non-Markovian system dynamics can be achieved. The implementation uses ultracold Rydberg atoms, relying on their strong long-range interactions. Our suggestion extends the features available for quantum simulators of molecular systems employing Rydberg aggregates and presents a new test bench for fundamental studies of the classification of system-environment interactions and the...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1602.07981

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Jun 30, 2018
06/18

by
H. Bombin

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Topological stabilizer codes with different spatial dimensions have complementary properties. Here I show that the spatial dimension can be switched using gauge fixing. Combining 2D and 3D gauge color codes in a 3D qubit lattice, fault-tolerant quantum computation can be achieved with constant time overhead on the number of logical gates, up to efficient global classical computation, using only local quantum operations. Single-shot error correction plays a crucial role.

Topic: Quantum Physics

Source: http://arxiv.org/abs/1412.5079

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Jun 28, 2018
06/18

by
Luis A. Bru; Margarida Hinarejos; Fernando Silva; Germán J. de Valcárcel; Eugenio Roldán

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We study electric quantum walks in two dimensions considering Grover, Alternate, Hadamard, and DFT quantum walks. In the Grover walk the behaviour under an electric field is easy to summarize: when the field direction coincides with the x or y axes, it produces a transient trapping of the probability distribution along the direction of the field, while when it is directed along the diagonals, a perfect 2D trapping is frustrated. The analysis of the alternate walk helps to understand the...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1512.07433

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Jun 30, 2018
06/18

by
Toru Kawakubo; Katsuji Yamamoto

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We investigate interference of optical fields by examining the probability distribution of photon detection. The usual description of interference patterns in terms of superposition of classical mean fields with definite phases is elucidated in quantum fashion. Especially, for interference of two independent mixtures of number states with Poissonian or sub-Poissonian statistics, despite lack of intrinsic phases, it is found that the joint probability has a distinct peak manifold in the...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1401.0436

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Jun 30, 2018
06/18

by
Michael Epping; Hermann Kampermann; Dagmar Bruß

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We consider a subclass of bipartite CHSH-type Bell inequalities. We investigate operations, which leave their Tsirelson bound invariant, but change their classical bound. The optimal observables are unaffected except for a relative rotation of the two laboratories. We illustrate the utility of these operations by giving explicit examples: We prove that for a fixed quantum state and fixed measurement setup except for a relative rotation of the two laboratories, there is a Bell inequality that is...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1402.0378

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Jun 30, 2018
06/18

by
Pietro Liuzzo-Scorpo; Alessandro Cuccoli; Paola Verrucchi

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In this work we investigate the relation between quantum measurements and decoherence, in order to formally express the necessity of the latter for obtaining an informative output from the former. To this aim, referring to the Von Neumann scheme for ideal quantum measurements, we first look for the minimal structure that the interaction between principal system and measurement apparatus must have for properly describing the process, beyond the quantum measurement limit, and then analyze the...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1411.2797

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Jun 28, 2018
06/18

by
Stefan Schütz; Simon B. Jäger; Giovanna Morigi

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We theoretically characterize the semiclassical dynamics of an ensemble of atoms after a sudden quench across a driven-dissipative second-order phase transition. The atoms are driven by a laser and interact via conservative and dissipative long-range forces mediated by the photons of a single-mode cavity. These forces can cool the motion and, above a threshold value of the laser intensity, induce spatial ordering. We show that the relaxation dynamics following the quench exhibits a long...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1512.05243

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Jun 27, 2018
06/18

by
Richard D. Gill

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Pearle (1970) gave an example of a local hidden variables model which exactly reproduced the singlet correlations of quantum theory, through the device of data-rejection: particles can fail to be detected in a way which depends on the hidden variables carried by the particles and on the measurement settings. If the experimenter computes correlations between measurement outcomes of particle pairs for which both particles are detected, he is actually looking at a subsample of particle pairs,...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1505.04431

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Jun 28, 2018
06/18

by
Jean-Philippe Bourgoin; Nikolay Gigov; Brendon L. Higgins; Zhizhong Yan; Evan Meyer-Scott; Amir K. Khandani; Norbert Lütkenhaus; Thomas Jennewein

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Quantum key distribution (QKD) has the potential to improve communications security by offering cryptographic keys whose security relies on the fundamental properties of quantum physics. The use of a trusted quantum receiver on an orbiting satellite is the most practical near-term solution to the challenge of achieving long-distance (global-scale) QKD, currently limited to a few hundred kilometers on the ground. This scenario presents unique challenges, such as high photon losses and restricted...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1512.05789

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Jun 29, 2018
06/18

by
Agata Chęcińska; Krzysztof Lorek; Andrzej Dragan

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We show that the operational definition of non-classicality of a quantum state depends on the motion of the observer. We use the relativistic Unruh-DeWitt detector model to witness nonclassicality of the probed field state. It turns out that the witness based on the properties of the P-representation of the quantum state depends on the trajectory of the detector. Inertial and noninertial motion of the device have qualitatively different impact on the performance of the witness.

Topic: Quantum Physics

Source: http://arxiv.org/abs/1604.03845

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Jun 29, 2018
06/18

by
Ilaria Siloi; Claudia Benedetti; Enrico Piccinini; Jyrki Piilo; Sabrina Maniscalco; Matteo G. A. Paris; Paolo Bordone

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We investigate the dynamics of continuous-time two-particle quantum walks on a one-dimensional noisy lattice. Depending on the initial condition, we show how the interplay between particle indistinguishability and interaction determines distinct propagation regimes. A realistic model for the environment is considered by introducing non-Gaussian noise as time-dependent fluctuations of the tunneling amplitudes between adjacent sites. We observe that the combined effect of particle interaction and...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1610.04180

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Jun 30, 2018
06/18

by
Susanna Kirchhoff; Torsten Keßler; Per J. Liebermann; Elie Assémat; Shai Machnes; Felix Motzoi; Frank K. Wilhelm

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The cross-resonant gate is an entangling gate for fixed frequency superconducting qubits introduced for untunable qubits. While being simple and extensible, it suffers from long duration and limited fidelity. Using two different optimal control algorithms, we probe the quantum speed limit for a CNOT gate in this system. We show that the ability to approach this limit depends strongly on the ansatz used to describe the optimal control pulse. A piecewise constant ansatz with a single carrier...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1701.01841

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Jun 30, 2018
06/18

by
Srinivasan Arunachalam; Nathaniel Johnston; Vincent Russo

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The absolute separability problem asks for a characterization of the quantum states $\rho \in M_m\otimes M_n$ with the property that $U\rho U^\dagger$ is separable for all unitary matrices $U$. We investigate whether or not it is the case that $\rho$ is absolutely separable if and only if $U\rho U^\dagger$ has positive partial transpose for all unitary matrices $U$. In particular, we develop an easy-to-use method for showing that an entanglement witness or positive map is unable to detect...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1405.5853

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Jun 30, 2018
06/18

by
N. G. de Almeida

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We present a method to engineer the unitary charge conjugation operator, as given by quantum field theory, in the highly controlled context of quantum optics, thus allowing one to simulate the creation of charged particles with well-defined momenta simultaneously with their respective antiparticles. Our method relies on trapped ions driven by a laser field and interacting with a single mode of a light field in a high Q cavity.

Topic: Quantum Physics

Source: http://arxiv.org/abs/1401.5746

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Jun 30, 2018
06/18

by
M. Bordag

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We consider a flat lattice of dipoles modeled by harmonic oscillators interacting with the electromagnetic field in dipole approximation. Eliminating the variables from the coupled equations of motion, we come to effective Maxwell equations. These allow for taking the lattice spacing $a$ to zero. As a result, we obtain reflection coefficients for the scattering of electromagnetic waves off the sheet. These are a generalization of that known from the hydrodynamic model. For instance, we get a...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1404.4842

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Jun 30, 2018
06/18

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Michal Horodecki; Marcin Marciniak; Zhi Yin

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In \cite{JP2011,JPPVW2010} the operator space theory was applied to study bipartite Bell inequalities. The aim of the paper is to follow this line of research and use the operator space technique to analyze the steering scenario. We obtain a bipartite steering functional with unbounded largest violation of steering inequality, as well as we can construct all ingredients explicitly. It turns out that the unbounded largest violation is obtained by non maximally entangled state. Moreover, we focus...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1405.1945

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Jun 29, 2018
06/18

by
Yigit Subasi; Christopher Jarzynski

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The need for Hamiltonians with many-body interactions arises in various applications of quantum computing. However, interactions beyond two-body are difficult to realize experimentally. Perturbative gadgets were introduced to obtain arbitrary many-body effective interactions using Hamiltonians with two-body interactions only. Although valid for arbitrary $k$-body interactions, their use is limited to small $k$ because the strength of interaction is $k$'th order in perturbation theory. In this...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1601.02922

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Jun 30, 2018
06/18

by
Ashley M. Stephens

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Topological color codes defined by the 4.8.8 semiregular lattice feature geometrically local check operators and admit transversal implementation of the entire Clifford group, making them promising candidates for fault-tolerant quantum computation. Recently, several efficient algorithms for decoding the syndrome of color codes were proposed. Here, we modify one of these algorithms to account for errors affecting the syndrome, applying it to the family of triangular 4.8.8 color codes encoding...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1402.3037

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Jun 27, 2018
06/18

by
Jesni Shamsul Shaari; Stefano Mancini

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Quantum cryptographic protocols solve the longstanding problem of distributing a shared secret string to two distant users by typically making use of one-way quantum channel. However, alternative protocols exploiting two-way quantum channel have been proposed for the same goal and with potential advantages. Here we overview a security proof for two-way quantum key distribution protocols, against the most general eavesdropping attack, that utilize an entropic uncertainty relation. Then, by...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1503.01498

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Jun 28, 2018
06/18

by
M. Ghalaii; M. Afsary; S. Alipour; A. T. Rezakhani

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We show that how a recent experiment of quantum imaging with undetected photons can basically be described as a (partial) ancilla-assisted process tomography. We propose a simplified quantum circuit version of this scenario, which also enables to recast quantum imaging in quantum computation language. Our analogy and analysis may help better understand the role of classical and/or quantum correlations in imaging experiments.

Topic: Quantum Physics

Source: http://arxiv.org/abs/1509.02031

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Jun 30, 2018
06/18

by
L. Motka; B. Stoklasa; J. Rehacek; Z. Hradil; V. Karasek; D. Mogilevtsev; G. Harder; C. Silberhorn; L. L. Sanchez-Soto

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We give a detailed account of an efficient search algorithm for the data pattern tomography proposed by J. Rehacek, D. Mogilevtsev, and Z. Hradil [Phys. Rev. Lett.~\textbf{105}, 010402 (2010)], where the quantum state of a system is reconstructed without a priori knowledge about the measuring setup. The method is especially suited for experiments involving complex detectors, which are difficult to calibrate and characterize. We illustrate the approach with the case study of the homodyne...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1407.0959