5
5.0
Jun 27, 2018
06/18
by
M. T. Thomaz
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The geometric phase acquired by the vector states under an adiabatic evolution along a noncyclic path can be calculated correctly in any instantaneous basis of a Hamiltonian that varies in time due to a time-dependent classical field.
Topic: Quantum Physics
Source: http://arxiv.org/abs/1504.04872
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7.0
Jun 27, 2018
06/18
by
Jacopo Trapani; Berihu Teklu; Stefano Olivares; Matteo G. A. Paris
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We address quantum communication channels based on phase modulation of coherent states and analyze in details the effects of static and dynamical (stochastic) phase diffusion. We evaluate mutual information for an ideal phase receiver and for a covariant phase-space-based receiver, and compare their performances by varying the number of symbols in the alphabet and/or the overall energy of the channel. Our results show that phase communication channels are generally robust against phase noise,...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1505.03160
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9.0
Jun 27, 2018
06/18
by
Łukasz Rudnicki; Daniel S. Tasca; Stephen P. Walborn
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We present the uncertainty relation for the characteristic functions (ChUR) of the quantum mechanical position and momentum probability distributions. This inequality is more general than the Heisenberg Uncertainty Relation, and is saturated in two extremal cases for wavefunctions described by periodic Dirac combs. We further discuss a broad spectrum of applications of the ChUR, in particular, we constrain quantum optical measurements involving general detection apertures and provide the...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1505.04638
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13
Jun 27, 2018
06/18
by
J. Tura; R. Augusiak; A. B. Sainz; B. Lücke; C. Klempt; M. Lewenstein; A. Acín
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Contemporary understanding of correlations in quantum many-body systems and in quantum phase transitions is based to a large extent on the recent intensive studies of entanglement in many-body systems. In contrast, much less is known about the role of quantum nonlocality in these systems, mostly because the available multipartite Bell inequalities involve high-order correlations among many particles, which are hard to access theoretically, and even harder experimentally. Standard,...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1505.06740
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20
Jun 28, 2018
06/18
by
Tillmann Baumgratz; Animesh Datta
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We present a framework for the quantum enhanced estimation of multiple parameters corresponding to non-commuting unitary generators. Our formalism provides a recipe for the simultaneous estimation of all three components of a magnetic field. We propose a probe state that surpasses the precision of estimating the three components individually and discuss measurements that come close to attaining the quantum limit. Our study also reveals that too much quantum entanglement may be detrimental to...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1507.02956
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16
Jun 28, 2018
06/18
by
C. Jess Riedel
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Einstein-Smoluchowski diffusion, damped harmonic oscillations, and spatial decoherence are special cases of an elegant class of Markovian quantum Brownian motion models that is invariant under linear symplectic transformations. Here we prove that for each member of this class there is a preferred timescale such that the dynamics, considered stroboscopically, can be rewritten exactly as unitary evolution interrupted periodically by an entanglement-breaking measurement with respect to a fixed...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1507.04083
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14
Jun 28, 2018
06/18
by
David Hocker; Herschel Rabitz
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Simultaneous optimization of multiple quantum objectives is often considered a demanding task. However, a special circumstance arises when a primary objective is pitted against a set of secondary objectives, which we show leads to invariant behavior of the secondary objectives upon the primary one approaching its optimal value. Still, practical relationships among the objectives will generally lead to a threshold, beyond which system re-engineering is required to further increase the primary...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1507.05918
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17
Jun 28, 2018
06/18
by
C. Lopez
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eye 17
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The action reaction principle is violated by the projection of state in some simple quantum measurements. A formulation of Quantum Mechanics in an extended phase space is proposed in order to restore the action reaction principle. All predictions of the standard theory are reproduced. Observable effects of an accompanying de Broglie wave are also predicted.
Topic: Quantum Physics
Source: http://arxiv.org/abs/1507.07720
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12
Jun 28, 2018
06/18
by
Dmitry V. Zhdanov; Tamar Seideman
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eye 12
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The problems of optimizing the value of an arbitrary observable of the two-level system at both a fixed time and the shortest possible time is theoretically explored. Complete identification and classification along with comprehensive analysis of globally optimal control policies and traps (i.e. policies which are locally but not globally optimal) is presented. The central question addressed is whether the control landscape remains trap-free if control constraints of the inequality type are...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1507.08785
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11
Jun 28, 2018
06/18
by
F. Piacentini; M. P. Levi; A. Avella; E. Cohen; R. Lussana; F. Villa; A. Tosi; F. Zappa; M. Gramegna; G. Brida; I. P. Degiovanni; M. Genovese
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eye 11
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One of the most intriguing aspects of Quantum Mechanics is the impossibility of measuring at the same time observables corresponding to non-commuting operators. This impossibility can be partially relaxed when considering joint or sequential weak values evaluation. Indeed, weak measurements have been a real breakthrough in the quantum measurement framework that is of the utmost interest from both a fundamental and an applicative point of view. Here we show how we realized, for the first time, a...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1508.03220
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18
Jun 28, 2018
06/18
by
F. Yan; S. Gustavsson; A. Kamal; J. Birenbaum; A. P. Sears; D. Hover; D. Rosenberg; G. Samach; T. J. Gudmundsen; J. L. Yoder; T. P. Orlando; J. Clarke; A. J. Kerman; W. D. Oliver
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The scalable application of quantum information science will stand on reproducible and controllable high-coherence quantum bits (qubits). Here, we revisit the design and fabrication of the superconducting flux qubit, achieving a planar device with broad frequency tunability, strong anharmonicity, high reproducibility, and relaxation times in excess of $40\,\mu$s at its flux-insensitive point. Qubit relaxation times $T_1$ across 22 qubits are consistently matched with a single model involving...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1508.06299
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10.0
Jun 28, 2018
06/18
by
Se-Wan Ji; Jaehak Lee; Jiyong Park; Hyunchul Nha
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We derive steerability criteria applicable for both finite and infinite dimensional quantum systems using covariance matrices of local observables. We show that these criteria are useful to detect a wide range of entangled states particularly in high dimensional systems and that the Gaussian steering criteria for general M x N-modes of continuous variables are obtained as a special case. Extending from the approach of entanglement detection via covariance matrices, our criteria are based on the...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1509.02550
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20
Jun 28, 2018
06/18
by
Evgenii Glushkov; Anastasiia Glushkova; V. I. Man'ko
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We discuss the known construction of two interacting superconducting circuits, based on Josephson junctions, that can be precisely engineered and easily controlled. In particular, we use the parametric excitation of two circuits, realized by an instant change of the qubit coupling, to study entropic and information properties of the density matrix of the composite system. The density matrix is obtained from the initial thermal state and is then analyzed in the approximation of small...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1509.04341
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12
Jun 28, 2018
06/18
by
J. Rehacek; Z. Hradil; Y. S. Teo; L. L. Sanchez-Soto; H. K. Ng; J. H. Chai; B. -G. Englert
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Measuring incomplete sets of mutually unbiased bases constitutes a sensible approach to the tomography of high-dimensional quantum systems. The unbiased nature of these bases optimizes the uncertainty hypervolume. However, imposing unbiasedness on the probabilities for the unmeasured bases does not generally yield the estimator with the largest von Neumann entropy, a popular figure of merit in this context. Furthermore, this imposition typically leads to mock density matrices that are not even...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1509.07614
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8.0
Jun 28, 2018
06/18
by
Da-Bao Yang; Ji-Xuan Hou
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eye 8
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Although the geometric phase for one-mode squeezed state had been studied in detail, the counterpart for two-mode squeezed state is vacant. It is be evaluated explicitly in this paper. Furthermore, the total phase factor is in an elegent form, which is just identical to one term of product of two squeezed operators. In addition, when this system undergoes cyclic evolutions, the corresponding geometric phase is obtained, which is just the sum of the counterparts of two isolated one-mode squeezed...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1510.00770
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7.0
Jun 28, 2018
06/18
by
Guilherme M. A. Almeida; Francesco Ciccarello; Tony J. G. Apollaro; Andre M. C. Souza
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We consider a coupled-cavity array, where each cavity interacts with an atom under the rotating-wave approximation. For a staggered pattern of inter-cavity couplings, a pair of field normal modes each bi-localized at the two array ends arise. A rich structure of dynamical regimes can hence be addressed depending on which resonance condition between the atom and field modes is set. We show that this can be harnessed to carry out high-fidelity quantum-state transfer (QST) of photonic, atomic or...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1510.02733
3
3.0
Jun 28, 2018
06/18
by
M. K. Olsen; J. F. Corney
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We examine one asymmetric adnd two fully symmetric Gaussian continuous-variable systems in terms of their tripartite and bipartite entanglement properties. We treat pure states and are able to find analytic solutions using the undepleted pump approximation for the Hamiltonian models, and standard beamsplitter relations for a model that mixes the outputs of optical parametric oscillators. Our two symmetric systems exhibit perfect tripartite correlations, but only in the unphysical limit of...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1510.04506
4
4.0
Jun 28, 2018
06/18
by
Vahid Azimi Mousolou
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eye 4
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Reliable quantum information processing requires high-fidelity universal manipulation of quantum systems within the characteristic coherence times. Non-adiabatic holonomic quantum computation offers a promising approach to implement fast, universal, and robust quantum logic gates particularly useful in nano-fabricated solid-state architectures, which typically have short coherence times. Here, we propose an experimentally feasible scheme to realize high-speed universal geometric quantum gates...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1510.05306
3
3.0
Jun 28, 2018
06/18
by
Marco Túlio Quintino; Joseph Bowles; Flavien Hirsch; Nicolas Brunner
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The observation of quantum nonlocality, i.e. quantum correlations violating a Bell inequality, implies the use of incompatible local quantum measurements. Here we consider the converse question. That is, can any set of incompatible measurements be used in order to demonstrate Bell inequality violation? Our main result is to construct a local hidden variable model for an incompatible set of qubit measurements. Specifically, we show that if Alice uses this set of measurements, then for any...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1510.06722
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6.0
Jun 28, 2018
06/18
by
Kai Sun; Xiang-Jun Ye; Jin-Shi Xu; Xiao-Ye Xu; Jian-Shun Tang; Yu-Chun Wu; Jing-Ling Chen; Chuan-Feng Li; Guang-Can Guo
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eye 6
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Einstein-Podolsky-Rosen (EPR) steering describes the ability of one observer to nonlocally "steer" the other observer's state through local measurements. It exhibits a unique asymmetric property, i.e., the steerability of one observer to steer the other's state could be different from each other, which can even lead to a one-way EPR steering, i.e., only one observer obtains the steerability in the two-observer case. This property is inherently different from the symmetric concepts of...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1511.01679
5
5.0
Jun 28, 2018
06/18
by
Leif Ove Hansen; Jan Myrheim
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eye 5
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We define an entanglement witness in a composite quantum system as an observable having nonnegative expectation value in every separable state. Then a state is entangled if and only if it has a negative expectation value of some entanglement witness. Equivalent representations of entanglement witnesses are as nonnegative biquadratic forms or as positive linear maps of Hermitian matrices. As reported elsewhere, we have studied extremal entanglement witnesses in dimension $3\times 3$ by...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1511.02110
4
4.0
Jun 28, 2018
06/18
by
Lan Zhou; Shi-Pu Gu; Xing-Fu Wang; Yu-Bo Sheng
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eye 4
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The concatenated Greenberger-Horne-Zeilinger (C-GHZ) state has great potential application in the future quantum network, for it is robust to the decoherence in a noisy environment. In the paper, we propose a complete C-GHZ state analysis protocol with the help of some auxiliary single atoms trapped in the low-quality cavities. In the protocol, we essentially make the parity check for the photonic states based on the photonic Faraday rotation effect, and complete the analysis task combined with...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1511.05302
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6.0
Jun 28, 2018
06/18
by
Zhe Sun; Longwen Zhou; Gaoyang Xiao; Dario Poletti; Jiangbin Gong
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eye 6
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We investigate Landau-Zener processes modeled by a two-level quantum system, with its finite bias energy varied in time and in the presence of a single broadened cavity mode at zero temperature. By applying the hierarchy equation method to the Landau-Zener problem, we computationally study the survival fidelity of adiabatic states without Born, Markov, rotating-wave or other perturbative approximations. With this treatment it also becomes possible to investigate cases with very strong...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1511.07695
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10.0
Jun 28, 2018
06/18
by
Kaifeng Bu; Uttam Singh; Junde Wu
texts
eye 10
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Catalytic coherence transformations allow the otherwise impossible state transformations using only incoherent operations with the aid of an auxiliary system with finite coherence which is not being consumed in anyway. Here we find the necessary and sufficient conditions for the deterministic and stochastic catalytic coherence transformations between pair of pure quantum states. In particular, we show that the simultaneous decrease of a family of R\'enyi entropies of the diagonal parts of the...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1511.08071
5
5.0
Jun 29, 2018
06/18
by
Ching-Yi Chiu; Neill Lambert; Teh-Lu Liao; Franco Nori; Che-Ming Li
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eye 5
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Einstein-Podolsky-Rosen (EPR) steering allows two parties to verify their entanglement, even if one party's measurements are untrusted. This concept has not only provided new insights into the nature of non-local spatial correlations in quantum mechanics, but also serves as a resource for one-sided device-independent quantum information tasks. Here, we investigate how EPR steering behaves when one-half of a maximally-entangled pair of qudits (multidimensional quantum systems) is cloned by a...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1601.04407
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4.0
Jun 29, 2018
06/18
by
Francesc S. Roig
texts
eye 4
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Using the Gell-Mann and Hartle formalism of generalized quantum mechanics of closed systems, we study the classical limit of coarse-grained spacetime histories and their decoherence. The system under consideration is one-dimensional and consists of a particle coupled to a von Neumann apparatus that performs a measurement of the position of the particle during the finite time interval during which the histories of this system take place. We consider two cases: a free particle and a harmonic...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1601.04234
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4.0
Jun 29, 2018
06/18
by
Ana Belén Sainz; Leandro Aolita; Nicolas Brunner; Rodrigo Gallego; Paul Skrzypczyk
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Quantum steering is observed when performing appropriate local measurements on an entangled state. Here we discuss the possibility of simulating classically this effect, using classical communication instead of entanglement. We show that infinite communication is necessary for exactly simulating steering for any pure entangled state, as well as for a class of mixed entangled states. Moreover, we discuss the communication cost of steering for general entangled states, as well as approximate...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1603.05079
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6.0
Jun 29, 2018
06/18
by
Raj B. Patel; Joseph Ho; Franck Ferreyrol; Timothy C. Ralph; Geoff J. Pryde
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eye 6
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Key to realising quantum computers is minimising the resources required to build logic gates into useful processing circuits. While the salient features of a quantum computer have been shown in proof-of-principle experiments, difficulties in scaling quantum systems have made more complex operations intractable. This is exemplified in the classical Fredkin (controlled-SWAP) gate for which, despite theoretical proposals, no quantum analogue has been realised. By adding control to the SWAP...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1603.08086
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4.0
Jun 30, 2018
06/18
by
Olivia Di Matteo; Luis L. Sanchez-Soto; Gerd Leuchs; Markus Grassl
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We develop a systematic coarse graining procedure for systems of $N$ qubits. We exploit the underlying geometrical structures of the associated discrete phase space to produce a coarse-grained version with reduced effective size. Our coarse-grained spaces inherit key properties of the original ones. In particular, our procedure naturally yields a subset of the original measurement operators, which can be used to construct a coarse discrete Wigner function. These operators also constitute a...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1701.08630
3
3.0
Jun 30, 2018
06/18
by
Yong-Chang Zhang; Xiang-Fa Zhou; Xingxiang Zhou; Guang-Can Guo; Zheng-Wei Zhou
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eye 3
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We propose a scheme to realize the two-axis counter-twisting spin-squeezing Hamiltonian inside an optical cavity with the aid of phase-locked atom-photon coupling. By careful analysis and extensive simulation, we demonstrate that our scheme is robust against dissipation caused by cavity loss and atomic spontaneous emission, and it can achieve significantly higher squeezing than one axis twisting. We further show how our idea can be extended to generate two-mode spin-squeezed states in two...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1703.05662
5
5.0
Jun 30, 2018
06/18
by
Michael Zwolak; Wojciech H. Zurek
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eye 5
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The objective, classical world emerges from the underlying quantum substrate via the proliferation of redundant copies of selected information into the environment, which acts as a communication channel, transmitting that information to observers. These copies are independently accessible, allowing many observers to reach consensus about the state of a quantum system via its imprints in the environment. Quantum Darwinism recognizes that the redundancy of information is thus central to the...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1703.10096
3
3.0
Jun 30, 2018
06/18
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L. E. Oxman; A. Z. Khoury; F. C. Lombardo; P. I. Villar
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In this work, we study a bipartite system composed by a pair of entangled qudits coupled to an environment. Initially, we derive a master equation and show how the dynamics can be restricted to a "diagonal" sector that includes a maximally entangled state (MES). Next, we solve this equation for mixed qutrit pairs and analyze the $I$-concurrence $C(t)$ for the effective state, which is needed to compute the geometric phase when the initial state is pure. Unlike (locally operated)...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1704.01999
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5.0
Jun 30, 2018
06/18
by
Naila Amir; Shahid Iqbal
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eye 5
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We develop generalized coherent states for a class of nonlinear oscillators with position-dependent effective mass in the context of the Gazeau-Klauder formalism and discuss some of their properties. In order to investigate the temporal evolution we first explore the statistical properties by means of weighting distribution and the Mandel parameter. It is found that the temporal evolution of the coherent states may exhibit the phenomena of quantum revivals and fractional revivals for a...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1704.02650
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4.0
Jun 30, 2018
06/18
by
Scott E. Hoffmann
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We treat the nonrelativistic quantum mechanical scattering of a wavepacket (for a single, charged, spinless particle) of well-resolved momentum incident on a fixed Coulomb potential. To implement this, we calculate the incoming and outgoing probability amplitudes for normalized state vectors on the basis of eigenvectors of total momentum magnitude and total angular momentum. We show that the method of partial wave analysis becomes applicable for this long range potential with the use of...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1704.04305
3
3.0
Jun 30, 2018
06/18
by
Christian Arenz; Benjamin Russell; Daniel Burgarth; Herschel Rabitz
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In this work we derive a lower bound for the minimum time required to implement a target unitary transformation through a classical time-dependent field in a closed quantum system. The bound depends on the target gate, the strength of the internal Hamiltonian and the highest permitted control field amplitude. These findings reveal some properties of the reachable set of operations, explicitly analyzed for a single qubit. Moreover, for fully controllable systems, we identify a lower bound for...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1704.06289
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4.0
Jun 30, 2018
06/18
by
Kyunghyun Baek; Tristan Farrow; Wonmin Son
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In the history of quantum mechanics, various types of uncertainty relationships have been introduced to accommodate different operational meanings of Heisenberg uncertainty principle. We derive an optimized entropic uncertainty relation (EUR) that quantifies an amount of quantum uncertainty in the scenario of successive measurements. The EUR characterizes the limitation in the measurability of two different quantities of a quantum state when they are measured through successive measurements. We...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1401.1013
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5.0
Jun 30, 2018
06/18
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I. Sinayskiy; N. Pumulo; F. Petruccione
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The dynamics of simple qubit systems in a chain configuration coupled at both ends to separate bosonic baths at different temperatures is studied. An exact analytical solution of the master equation in the Born-Markov approximation for the reduced density matrix of the qubit system is constructed. The unique non-equilibrium stationary state for the long time behavior of the reduced density matrix in obtained. Dynamical and steady state properties of the concurrence between the first and the...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1401.2306
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8.0
Jun 30, 2018
06/18
by
K. Jensen; N. Leefer; A. Jarmola; Y. Dumeige; V. M. Acosta; P. Kehayias; B. Patton; D. Budker
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We demonstrate a cavity-enhanced room-temperature magnetic field sensor based on nitrogen-vacancy centers in diamond. Magnetic resonance is detected using absorption of light resonant with the 1042 nm spin-singlet transition. The diamond is placed in an external optical cavity to enhance the absorption, and significant absorption is observed even at room temperature. We demonstrate a magnetic field sensitivity of 2.5 nT/sqrt(Hz), and project a photon shot-noise-limited sensitivity of 70...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1401.2438
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6.0
Jun 30, 2018
06/18
by
C. Bernhard; B. Bessire; A. Montina; M. Pfaffhauser; A. Stefanov; S. Wolf
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The insight due to John Bell that the joint behavior of individually measured entangled quantum systems cannot be explained by shared information remains a mystery to this day. We describe an experiment, and its analysis, displaying non-locality of entangled qutrit pairs. The non-locality of such systems, as compared to qubit pairs, is of particular interest since it potentially opens the door for tests of bipartite non-local behavior independent of probabilistic Bell inequalities, but of...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1402.5026
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5.0
Jun 30, 2018
06/18
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Jürgen Volz; Michael Scheucher; Christian Junge; Arno Rauschenbeutel
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Realizing a strong interaction between individual optical photons is an important objective of research in quantum science and technology. Since photons do not interact directly, this goal requires, e.g., an optical medium in which the light experiences a phase shift that depends nonlinearly on the photon number. Once the additional phase shift for two photons reaches pi, such an ultra-strong nonlinearity could even enable the direct implementation of high-fidelity quantum logic operations....
Topic: Quantum Physics
Source: http://arxiv.org/abs/1403.1860
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5.0
Jun 30, 2018
06/18
by
Serge Massar; Manas K. Patra
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Generalized probabilistic theories (GPT) provide a framework in which one can formulate physical theories that includes classical and quantum theories, but also many other alternative theories. In order to compare different GPTs, we advocate an approach in which one views a state in a GPT as a resource, and quantifies the cost of interconverting between different such resources. We illustrate this approach on polygon theories (Janotta et al. New J. Phys 13, 063024, 2011) that interpolate (as...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1403.2509
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6.0
Jun 30, 2018
06/18
by
C. N. Gagatsos; J. Fiurasek; A. Zavatta; M. Bellini; N. J. Cerf
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We examine the behavior of non-Gaussian states of light under the action of probabilistic noiseless amplification and attenuation. Surprisingly, we find that the mean field amplitude may decrease in the process of noiseless amplification -- or increase in the process of noiseless attenuation, a counterintuitive effect that Gaussian states cannot exhibit. This striking phenomenon could be tested with experimentally accessible non-Gaussian states, such as single-photon added coherent states. We...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1403.6054
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6.0
Jun 30, 2018
06/18
by
Masanao Ozawa
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Heisenberg's uncertainty principle was originally formulated in 1927 as a quantitative relation between the "mean error" of a measurement of one observable and the disturbance thereby caused on another observable. Heisenberg derived this famous relation under an additional assumption on quantum measurements that has been abandoned in the modern theory, and its universal validity was questioned in a debate on the sensitivity limit to gravitational-wave detectors in 1980s. A universally...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1404.3388
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5.0
Jun 30, 2018
06/18
by
Stefan Putz; Dmitry O. Krimer; Robert. Amsüss; Abhilash Valookaran; Tobias Nöbauer; Jörg Schmiedmayer; Stefan Rotter; Johannes Majer
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Hybrid quantum systems based on spin ensembles coupled to superconducting microwave cavities are promising candidates for robust experiments in cavity quantum electrodynamics (QED) and for future technologies employing quantum mechanical effects. Currently the main source of decoherence in these systems is inho- mogeneous spin broadening, which limits their performance for the coherent transfer and storage of quantum information. Here we study the dynamics of a superconducting cavity strongly...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1404.4169
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5.0
Jun 30, 2018
06/18
by
M. Feng; Y. P. Zhong; T. Liu; L. L. Yan; W. L. Yang; J. Twamley; H. Wang
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Quantum phase transitions play an important role in many-body systems and have been a research focus in conventional condensed matter physics over the past few decades. Artificial atoms, such as superconducting qubits that can be individually manipulated, provide a new paradigm of realising and exploring quantum phase transitions by engineering an on-chip quantum simulator. Here we demonstrate experimentally the quantum critical behaviour in a highly-controllable superconducting circuit,...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1406.1436
5
5.0
Jun 30, 2018
06/18
by
J. J. M. Varga; L. Rebón; M. A. Solís-Prosser; L. Neves; S. Ledesma; C. Iemmi
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We present a method for preparing arbitrary pure states of spatial qudits, namely, D-dimensional (D > 2) quantum systems carrying information in the transverse momentum and position of single photons. For this purpose, a set of D slits with complex transmission are displayed on a spatial light modulator (SLM). In a recent work we have shown a method that requires a single phase-only SLM to control independently the complex coefficients which define the quantum state of dimension D. The...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1406.3596
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5.0
Jun 30, 2018
06/18
by
Cosmo Lupo; Seth Lloyd
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Quantum data locking is a protocol that allows for a small secret key to (un)lock an exponentially larger amount of information, hence yielding the strongest violation of the classical one-time pad encryption in the quantum setting. This violation mirrors a large gap existing between two security criteria for quantum cryptography quantified by two entropic quantities: the Holevo information and the accessible information. We show that the latter becomes a sensible security criterion if an upper...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1406.4418
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4.0
Jun 30, 2018
06/18
by
İ. Yalçınkaya; Z. Gedik
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We propose a scheme for perfect transfer of an unknown qubit state via the discrete-time quantum walk on a line or a circle. For this purpose, we introduce an additional coin operator which is applied at the end of the walk. This operator does not depend on the state to be transferred. We show that perfect state transfer over an arbitrary distance can be achieved only if the walk is driven by an identity or a flip coin operator. Other biased coin operators and Hadamard coin allow perfect state...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1407.0689
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4.0
Jun 30, 2018
06/18
by
Dorian Baguette; Thierry Bastin; John Martin
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We present a comprehensive study of maximally entangled symmetric states of arbitrary numbers of qubits in the sense of the maximal mixedness of the one-qubit reduced density operator. A general criterion is provided to easily identify whether given symmetric states are maximally entangled in that respect or not. We show that these maximally entangled symmetric (MES) states are the only symmetric states for which the expectation value of the associated collective spin of the system vanishes, as...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1407.1738
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9.0
Jun 30, 2018
06/18
by
Laura Mančinska; Stephanie Wehner
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Bell's inequality fundamentally changed our understanding of quantum mechanics. Bell's insight that non-local correlations between quantum systems cannot be explained classically can be verified experimentally, and has numerous applications in modern quantum information. Today, the CHSH inequality is probably the most well-known Bell inequality and it has given us a wealth of understanding in what differentiates the classical from the quantum world. Yet, there are certainly other means of...
Topic: Quantum Physics
Source: http://arxiv.org/abs/1407.2320
