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Jun 26, 2018
06/18

by
Caifeng Li; Jingtao Fan; Lixuan Yu; Gang Chen; Tian-Cai Zhang; Suotang Jia

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Ultracold atoms in an ultrahigh-finesse optical cavity are a powerful platform to produce spin squeezing since photon of cavity mode can induce nonlinear spin-spin interaction and thus generate a one-axis twisting Hamiltonian $H_{\text{OAT}}=qJ_{x}^{2}$, whose corresponding maximal squeezing factor scales as $N^{-2/3}$, where $N$ is the atomic number. On the contrary, for the other two-axis twisting Hamiltonian $H_{\text{TAT}}=q(J_{x}^{2}-J_{y}^{2})$, the maximal squeezing factor scales as...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1502.00470

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4.0

Jun 28, 2018
06/18

by
Nana Liu; Jayne Thompson; Christian Weedbrook; Seth Lloyd; Vlatko Vedral; Mile Gu; Kavan Modi

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Although quantum computers are capable of solving problems like factoring exponentially faster than the best-known classical algorithms, determining the resources responsible for their computational power remains unclear. An important class of problems where quantum computers possess an advantage is phase estimation, which includes applications like factoring. We introduce a new computational model based on a single squeezed state resource that can perform phase estimation, which we call the...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1510.04758

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0.0

Jun 30, 2018
06/18

by
A. Y. Klimenko

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The analysis conducted in this work indicates that interactions of a CP-violating (and CPT-preserving) quantum system with a thermodynamic environment can produce the impression of a CPT violation in the system. This conclusion is reasonably consistent with the results reported for decays of neutral K-mesons.

Topic: Quantum Physics

Source: http://arxiv.org/abs/1402.3864

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Jun 30, 2018
06/18

by
Vikesh Siddhu; Arvind

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Quantum Private Comparison (QPC) allows us to protect private information during its comparison. In the past various three-party quantum protocols have been proposed that claim to work well under noisy conditions. Here we tackle the problem of QPC under noise. We analyze the EPR-based protocol under depolarizing noise, bit flip and phase flip noise. We show how noise affects the robustness of the EPR-based protocol. We then present a straightforward protocol based on CSS codes to perform QPC...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1407.6323

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Jun 26, 2018
06/18

by
Paulo E. M. F. Mendonca; Marcelo A. Marchiolli; Gerard J. Milburn

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For every N-qubit density matrix written in the computational basis, an associated "X-density matrix" can be obtained by vanishing all entries out of the main- and anti-diagonals. It is very simple to compute the genuine multipartite (GM) concurrence of this associated N-qubit X-state, which, moreover, lower bounds the GM-concurrence of the original (non-X) state. In this paper, we rely on these facts to introduce and benchmark a heuristic for estimating the GM-concurrence of an...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1501.07026

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Jun 28, 2018
06/18

by
Hayato Goto

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The dynamics of nonlinear systems qualitatively change depending on their parameters, which is called bifurcation. A quantum-mechanical nonlinear oscillator can yield a quantum superposition of two oscillation states, known as a Schr\"odinger cat state, via quantum adiabatic evolution through its bifurcation point. Here we propose a quantum computer comprising such quantum nonlinear oscillators, instead of quantum bits, to solve hard combinatorial optimization problems. The nonlinear...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1510.02566

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Jun 29, 2018
06/18

by
Yu Yokotera; Naoki Yamamoto

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Engineering a sensor system for detecting an extremely tiny signal such as the gravitational-wave force is a very important subject in quantum physics. A major obstacle to this goal is that, in a simple detection setup, the measurement noise is lower bounded by the so-called standard quantum limit (SQL), which is originated from the intrinsic mechanical back-action noise. Hence, the sensor system has to be carefully engineered so that it evades the back-action noise and eventually beats the...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1609.04524

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Jun 30, 2018
06/18

by
P. Giannakeas; F. Robicheaux; Chris H. Greene

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Two-photon ionization of an alkali-metal atom in the presence of a uniform electric field is investigated using a standardized form of local frame transformation and generalized quantum defect theory. The relevant long-range quantum defect parameters in the combined Coulombic plus Stark potential is calculated with eigenchannel R-matrix theory applied in the downstream parabolic coordinate $\eta$. The present formulation permits us to express the corresponding microscopy observables in terms of...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1410.5360

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Jun 30, 2018
06/18

by
Durmus Ali Demir; Ozan Sargin

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As an application of the polymer quantization scheme, in this work we investigate the one dimensional quantum mechanical tunneling phenomenon from the perspective of polymer representation of a non-relativistic point particle and derive the transmission and reflection coefficients. Since any tunneling phenomenon inevitably evokes a tunneling time we attempt an analytical calculation of tunneling times by defining an operator well suited in discrete spatial geometry. The results that we come up...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1409.7224

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Jun 27, 2018
06/18

by
Arindam Mallick; Sibasish Ghosh

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Experimental detection of entanglement of an arbitrary state of a given bipartite system is crucial for exploring many areas of quantum information. But such a detection should be made in a device independent way if the preparation process of the state is considered to be faithful, in order to avoid detection of a separable state as entangled one. The recently developed scheme of detecting bipartite entanglement in a measurement device independent way [Phys. Rev. Lett {\bf 110}, 060405 (2013)]...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1506.03985

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Jun 28, 2018
06/18

by
Michael J. W. Hall

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A local and deterministic model of quantum correlations is always possible, as shown explicitly by Brans in 1988: one simply needs the physical systems being measured to have a suitable statistical correlation with the physical systems performing the measurement, via some common cause. Hence, to derive no-go results such as Bell inequalities, an assumption of measurement independence is crucial. It is a surprisingly strong assumption -- less than 1/15 bits of prior correlation suffice for a...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1511.00729

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1.0

Jun 30, 2018
06/18

by
Daniel Brox

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Quantum dot cellular automata (QCA) computing schemes use arrays of quantum dots as computational devices. Typically, these operate ideally by maintaining arrays in their ground state to ensure correct computational output. For large QCA circuits, thermal fluctuations make this impossible, so adiabatic clocking has been proposed as a means of dividing large circuit computations into subcircuit computations that are more reliable. In this report, it is shown that wires and inverters can transmit...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1704.03932

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Jun 30, 2018
06/18

by
Augusto C. Lobo; Yakir Aharonov; Jeff Tollaksen; Elizabeth M. Berrigan; Clyffe A. Ribeiro

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We address two major conceptual developments introduced by Aharonov and collaborators through a \textit{quantum phase space} approach: the concept of \textit{modular variables} devised to explain the phenomena of quantum dynamical non-locality and the \textit{two-state formalism} for Quantum Mechanics which is a retrocausal time-symmetric interpretation of quantum physics which led to the discovery of \textit{weak values.} We propose that a quantum phase space structure underlies these profound...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1409.2891

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Jun 28, 2018
06/18

by
Harald Atmanspacher; Peter beim Graben

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The concept of complementarity in combination with a non-Boolean calculus of propositions refers to a pivotal feature of quantum systems which has long been regarded as a key to their distinction from classical systems. But a non-Boolean logic of complementary features may also apply to classical systems, if their states and observables are defined by partitions of a classical state space. If these partitions do not satisfy certain stability criteria, complementary observables and non-Boolean...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1510.03325

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4.0

Jun 28, 2018
06/18

by
Roman Schnabel

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In 1935, Einstein, Podolsky and Rosen (EPR) considered two particles in an entangled state of motion to illustrate why they questioned the completeness of quantum theory. In the past decades, microscopic systems with entanglement in various degrees of freedom have successfully been generated, representing compelling evidence to support the completeness of quantum theory. Today, the generation of an EPR-entangled state of motion of two massive objects of up to the kilogram-scale seems feasible...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1508.06462

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5.0

Jun 26, 2018
06/18

by
Yu. P. Rybakov; T. F. Kamalov

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Entangled solitons construction being introduced in the nonlinear spinor field model, the Einstein|Podolsky|Rosen (EPR) spin correlation is calculated and shown to coincide with the quantum mechanical one for the 1/2-spin particles.

Topic: Quantum Physics

Source: http://arxiv.org/abs/1501.05895

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5.0

Jun 27, 2018
06/18

by
Yuki Takeuchi; Keisuke Fujii; Rikizo Ikuta; Takashi Yamamoto; Nobuyuki Imoto

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Blind quantum computation (BQC) allows a client (Alice), who only possesses relatively poor quantum devices, to delegate universal quantum computation to a server (Bob) in such a way that Bob cannot know Alice's inputs, algorithm, and outputs. The quantum channel between Alice and Bob is noisy, and the loss over the long-distance quantum communication should also be taken into account. Here we propose to use decoherence-free subspace (DFS) to overcome the collective noise in the quantum channel...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1505.04248

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3.0

Jun 26, 2018
06/18

by
Biswanath Rath; P. Mallick

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We present a complete analysis on energy and wave function of Harmonic oscillator with simultaneous non-hermitian transformation of co-ordinate ($(x \rightarrow \frac{(x+ i\lambda p)}{\sqrt{(1+\beta \lambda)}}$ and momentum $(p \rightarrow \frac{(p+ i\beta x)}{\sqrt{(1+\beta \lambda)}}$ for getting energy eigenvalue using perturbation theory under iso-spectral condition. Further we notice that two different frequency of oscillation ($w_{1}, w_{2}$)correspond to same energy eigenvalue ,which can...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1501.06161

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4.0

Jun 27, 2018
06/18

by
Phillip Dukes

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We examine the time dependent amplitude $ \phi_{j}\left( t\right)$ at each vertex $j$ of a continuous-time quantum walk on the cycle $C_{n}$. In many cases the Lissajous curve of the real vs. imaginary parts of each $ \phi_{j}\left( t\right)$ reveals interesting shapes of the space of time-accessible amplitudes. We find two invariants of continuous-time quantum walks. First, considering the rate at which each amplitude evolves in time we find the quantity $T = \displaystyle\sum_{j=0}^{n-1}...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1506.03086

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2.0

Jun 28, 2018
06/18

by
Johan Noldus

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We propose two distinct interpretations of extended probabilities which are realistic for the physical world.

Topic: Quantum Physics

Source: http://arxiv.org/abs/1509.09281

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3.0

Jun 26, 2018
06/18

by
Feng Zhu; Wei Zhang; Yidong Huang

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We show that the perfect commutation graph is the sufficient tight condition for admitting the noncontextual description of each observable set satisfying it in the yes-no question scenario. With this condition, we propose a method for proving the monogamy relation between two informationtheoretic contextuality inequalities by decomposing the total commutation graph into perfect subgraphs. The results offer a powerful tool to investigate the contextuality and to understand quantum information...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1502.01098

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1.0

Jun 29, 2018
06/18

by
Martin Stefanak; Jaroslav Novotny; Igor Jex

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Coherent transport of excitations along chains of coupled quantum systems represents an interesting problem with a number of applications ranging from quantum optics to solar cell technology. A convenient tool for studying such processes are quantum walks. They allow to determine in a quantitative way all the process features. We study the survival probability and the transport efficiency on a simple, highly symmetric graph represented by a ring. The propagation of excitation is modeled by a...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1602.04678

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1.0

Jun 29, 2018
06/18

by
Namit Anand; Arun Kumar Pati

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Grover's search algorithm is the optimal quantum algorithm that can search an unstructured database quadratically faster than any known classical algorithm. The role of entanglement and correlations in the search algorithm have been studied in great detail and it is known that entanglement between the qubits is necessary to gain a quadratic speedup, for pure state implementation of the Grover search algorithm. Here, we systematically investigate the behavior of quantum coherence and monogamy of...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1611.04542

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0.0

Jun 29, 2018
06/18

by
Ihar Babushkin

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We consider a qubit governed by a sequence of weak measurements, with the measurement strength modified in a time- and state-dependent manner. The resulting trajectory of the qubit in the phase space can be weakly controlled without any direct action on the qubit (control-free control), even only one fixed observable is measured. Here we show a possibility of a weak form of a stochastic ratchet, allowing to create an additional "force" without changing the corresponding effective...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1601.08022

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0.0

Jun 30, 2018
06/18

by
Biswajit Paul; Kaushiki Mukherjee; Sumana Karmakar; Debasis Sarkar; Amit Mukherjee; Arup Roy; Some Sankar Bhattacharya

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Experimental demonstration of entanglement needs to have a precise control of experimentalist over the system on which the measurements are performed as prescribed by an appropriate entanglement witness. To avoid such trust problem, recently device-independent entanglement witnesses (\emph{DIEW}s) for genuine tripartite entanglement have been proposed where witnesses are capable of testing genuine entanglement without precise description of Hilbert space dimension and measured operators i.e...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1701.04114

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0.0

Jun 29, 2018
06/18

by
Jan Perina

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Intense spatio-spectral twin beams generated in the regime with pump depletion are analyzed applying a suggested quantum model that treats the signal, idler and pump fields in the same way. The model assumes the signal and idler fields in the form of the generalized superposition of signal and noise and reveals nonzero signal coherent components in both fields, contrary to the models developed earlier. The influence of coherent components on the properties of intense twin beams is elucidated....

Topic: Quantum Physics

Source: http://arxiv.org/abs/1606.00733

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0.0

Jun 30, 2018
06/18

by
Vlad Gheorghiu; Marcos C. de Oliveira; Barry C. Sanders

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Quantum discord is the quantitative difference between two alternative expressions for bipartite mutual information, given respectively in terms of two distinct definitions for the conditional entropy. By constructing a stochastic model of shared states, classical discord can be similarly defined, quantifying the presence of some stochasticity in the measurement process. Therefore, discord can generally be understood as a quantification of the system's state disturbance due to local...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1407.5507

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0.0

Jun 30, 2018
06/18

by
A. C. S. Costa; R. M. Angelo; M. W. Beims

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We investigate the dynamics of information among the parties of tripartite systems. We start by proving two results concerning the monogamy of mutual information. The first one states that mutual information is monogamous for generic tripartite pure states. The second shows that in general mutual information is monogamous only if the amount of genuine tripartite correlations is large enough. Then, we analyze the internal dynamics of tripartite systems whose parties do not exchange energy. In...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1404.6433

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0.0

Jun 28, 2018
06/18

by
Wei Li; Xudong Yu; Jing Zhang

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We present the experimental measurement of a squeezed vacuum state by means of a bichromatic local oscillator (BLO). A pair of local oscillators at $\pm$5 MHz around the central frequency $\omega_{0}$ of the fundamental field with equal power are generated by three acousto-optic modulators and phase-locked, which are used as a BLO. The squeezed vacuum light are detected by a phase-sensitive balanced-homodyne detection with a BLO. The baseband signal around $\omega_{0}$ combined with a broad...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1510.09062

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Jun 28, 2018
06/18

by
Gan Gao

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Kang et al. [Chin. Phys. B 24 (2015) 090306] proposed a controlled mutual quantum entity authentication protocol. We find that the proposed protocol is not secure, that is, Charlie can eavesdrop the shared keys between Alice and Bob without being detected.

Topic: Quantum Physics

Source: http://arxiv.org/abs/1510.01347

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Jun 30, 2018
06/18

by
Yasunari Suzuki; Keisuke Fujii; Masato Koashi

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In order to realize fault-tolerant quantum computation, tight evaluation of error threshold under practical noise models is essential. While non-Clifford noise is ubiquitous in experiments, the error threshold under non-Clifford noise cannot be efficiently treated with known approaches. We construct an efficient scheme for estimating the error threshold of one-dimensional quantum repetition code under non-Clifford noise. To this end, we employ non-unitary free-fermionic formalism for efficient...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1703.03671

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0.0

Jun 29, 2018
06/18

by
A. P. Costa; Fernando Parisio

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Correlation boxes are hypothetical systems capable of producing the maximal algebraic violation of Bell inequalities, beyond the quantum bound and without superluminal signaling. The fact that these systems show stronger correlations than those presented by maximally entangled quantum states has been regarded as a demonstration that the former are more nonlocal than the latter. By employing an alternative, consistent measure of nonlocality, we show that this conclusion is not necessarily true....

Topic: Quantum Physics

Source: http://arxiv.org/abs/1605.04577

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Jun 28, 2018
06/18

by
Li-Die Wang; Li-Tao Wang; Mou Yang; Jing-Zhou Xu; Z. D. Wang; Yan-Kui Bai

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The maximally entangled state can be in a mixed state as well as the well-known pure state. Taking the negativity as a measure of entanglement, we study the entanglement dynamics of bipartite, mixed maximally entangled states (MMESs) in multipartite cavity-reservoir systems. It is found that the MMES can exhibit the phenomenon of entanglement sudden death, which is quite different from the asymptotic decay of the pure-Bell-state case. We also find that maximal entanglement cannot guarantee...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1506.06878

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Jun 30, 2018
06/18

by
Peter Janotta; Haye Hinrichsen

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The framework of generalized probabilistic theories is a powerful tool for studying the foundations of quantum physics. It provides the basis for a variety of recent findings that significantly improve our understanding of the rich physical structure of quantum theory. This review paper tries to present the framework and recent results to a broader readership in an accessible manner. To achieve this, we follow a constructive approach. Starting from few basic physically motivated assumptions we...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1402.6562

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Jun 30, 2018
06/18

by
C. E. Susa; J. H. Reina; R. Hildner

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We show how to generate and control the correlations in a set of two distant quantum emitters coupled to a one-dimensional dissipative plasmonic waveguide. An external laser field enhances the dimer's steady-state correlations and allows an active control (switching on/off) of nonclassical correlations. The plasmon-assisted dipolar-interacting qubits exhibit persistent correlations, which in turn can be decoupled and made to evolve independently from each other. The setup enables long-distance...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1405.3325

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Jun 30, 2018
06/18

by
Nikolay L. Chuprikov

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It is shown that in the state space of a quantum particle involved in a one-dimensional completed scattering (OCS) there is a superselection rule (SSR) induced by the dichotomous physical context that determines the properties of a quantum ensemble of scattering particles in the disjoint spatial regions located on the different sides of the potential barrier at asymptotically large distances from it. At the initial stage of the OCS this context is associated, in the general case, with two...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1412.7657

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Jun 30, 2018
06/18

by
Edmond Jonckheere; Frank Langbein; Sophie Schirmer

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Spin networks are endowed with an Information Transfer Fidelity (ITF), which defines an absolute upper bound on the probability of transmission of an excitation from one spin to another. The ITF is easily computable but the bound can be reached asymptotically in time only under certain conditions. General conditions for attainability of the bound are established and the process of achiev-ing the maximum transfer probability is given a dynamical model, the translation on the torus. The time to...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1408.3765

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Jun 30, 2018
06/18

by
Giuseppe Bimonte; Thorsten Emig; Mehran Kardar

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We use a derivative expansion for gently curved surfaces to compute the leading and the next-to-leading curvature corrections to the Casimir-Polder interaction between a polarizable small particle and a non-planar surface. While our methods apply to any homogeneous and isotropic surface, explicit results are presented here for perfect conductors. We show that the derivative expansion of the Casimir-Polder potential follows from a resummation of its perturbative series, for small in-plane...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1409.6993

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Jun 30, 2018
06/18

by
A. S. Sheremet; D. F. Kornovan; L. V. Gerasimov; B. Gouraud; J. Laurat; D. V. Kupriyanov

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Light transport in a dense and disordered cold atomic ensemble, where the cooperation of atomic dipoles essentially modifies their coupling with the radiation modes, offers an alternative approach to light-matter interfacing protocols. Here, we show how the cooperativity and quasi-static dipole interaction affect the process of light propagation under the conditions of electromagnetically-induced transparency (EIT). We perform comparative analysis of the self-consistent approach with ab-initio...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1411.4771

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Jun 30, 2018
06/18

by
Sharad Joshi; Abhishek Shukla; Hemant Katiyar; Anirban Hazra; T. S. Mahesh

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Interaction of molecules with light may lead to electronic transitions and simultaneous vibrational excitations. Franck-Condon factors (FCFs) play an important role in quantifying the intensities of such vibronic transitions occurring during molecular photo-excitations. In this article, we describe a general method for estimating FCFs using a quantum information processor. The method involves the application of a translation operator followed by the measurement of certain projections. We also...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1405.2400

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Jun 30, 2018
06/18

by
Daniel Mills; Anna Pappa; Theodoros Kapourniotis; Elham Kashefi

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We propose a new composable and information-theoretically secure protocol to verify that a server has the power to sample from a sub-universal quantum machine implementing only commuting gates. By allowing the client to manipulate single qubits, we exploit properties of Measurement based Blind Quantum Computing to prove security against a malicious Server and therefore certify quantum supremacy without the need for a universal quantum computer.

Topic: Quantum Physics

Source: http://arxiv.org/abs/1704.01998

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Jun 30, 2018
06/18

by
Łukasz Rudnicki; Zbigniew Puchała; Karol Życzkowski

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We analyze entropic uncertainty relations in a finite dimensional Hilbert space and derive several strong bounds for the sum of two entropies obtained in projective measurements with respect to any two orthogonal bases. We improve the recent bounds by Coles and Piani, which are known to be stronger than the well known result of Maassen and Uffink. Furthermore, we find a novel bound based on majorization techniques, which also happens to be stronger than the recent results involving largest...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1402.0129

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Jun 28, 2018
06/18

by
M. Daoud; R. Ahl Laamara; S. Seddik

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The Hilbert-Schmidt distance between a mixed three-qubit state and its closest state is used to quantify the amount of pairwise quantum correlations in a tripartite system. Analytical expressions of geometric quantum discord are derived. A particular attention is devoted to two special classes of three-qubit $X$ states. They include three-qubit states of ${\rm W}$, ${\rm GHZ}$ and Bell type. We also discuss the monogamy property of geometric quantum discord in some mixed three-qubit systems.

Topic: Quantum Physics

Source: http://arxiv.org/abs/1512.01772

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Jun 28, 2018
06/18

by
C. Valverde; V. G. Gonçalves; B. Baseia

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We employ a more realistic treatment to investigate the entropy and the excitation-inversion of a coupled system that consists of a nanomechanical resonator and a superconducting Cooper pair box. The procedure uses the Buck-Sukumar model in the microwave domain, considers the nanoresonator with a time dependent frequency and both subsystems in the presence of losses. Interesting results were found for the temporal evolutions of the entropy of each subsystem and of the excitation-inversion in...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1506.07102

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Jun 27, 2018
06/18

by
Siddharth Muthukrishnan; Tameem Albash; Daniel A. Lidar

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We provide and analyze examples that counter the widely made claim that tunneling is needed for a quantum speedup in optimization problems. The examples belong to the class of perturbed Hamming-weight optimization problems. In one case, featuring a plateau in the cost function in Hamming weight space, we find that the adiabatic dynamics that make tunneling possible, while superior to simulated annealing, result in a slowdown compared to a diabatic cascade of avoided level-crossings. This, in...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1505.01249

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Jun 26, 2018
06/18

by
Yuan-yuan Zhao; Neng-kun Yu; Pawe Kurzynski; Guo-yong Xiang; Chuan-Feng Li; Guang-Can Guo

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We report an experimental implementation of a single-qubit generalised measurement scenario(POVM) based on a quantum walk model. The qubit is encoded in a single-photon polarisation. The photon performs a quantum walk on an array of optical elements, where the polarisation-dependent translation is performed via birefringent beam displacers and a change of the polarisation is implemented with the help of wave-plates. We implement: (i) Trine-POVM, i.e., the POVM elements uniformly distributed on...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1501.05096

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Jun 29, 2018
06/18

by
Charles H. Baldwin; Ivan H. Deutsch; Amir Kalev

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We consider the problem of quantum-state tomography under the assumption that the state is pure, and more generally that its rank is bounded by a given value $r$. In this scenario two notions of informationally complete measurements emerge: rank-$r$ complete measurements and rank-$r$ strictly-complete measurements. Whereas in the first notion, a rank-$r$ state is uniquely identified from within the set of rank-$r$ states, in the second notion the same state is uniquely identified from within...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1605.02109

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Jun 27, 2018
06/18

by
Anubhav Chaturvedi; Maharshi Ray; Ryszard Veynar; Marcin Pawlowski

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While fully device-independent security in BB84-like one way QKD is impossible, it can be guaranteed against individual attacks in a semi device-independent scenario, where no assumptions on the characteristics of the hardware used are made except for the communication channel for which an upper bound on capacity is put. This approach is meaningful especially in the context of recent {\it quantum hacking} attacks in which the eavesdroppers are able to remotely alter the behaviour of the devices...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1504.00939

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Jun 29, 2018
06/18

by
Liwei Duan; You-Fei Xie; Daniel Braak; Qing-Hu Chen

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The two-photon quantum Rabi model with quadratic coupling is studied using extended squeezed states and we derive $G$-functions for Bargmann index $q=1/4$ and $3/4$. The simple singularity structure of the $G$-function allows to draw conclusions about the distribution of eigenvalues along the real axis. The previously found picture of the spectral collapse at critical coupling $g_{\mathrm{c}}$ has to be modified regarding the low lying states, especially the ground state: We obtain a finite gap...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1603.04503

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Jun 29, 2018
06/18

by
Fengzheng Zhu; Teng Zhao; Hebin Zhang; Gao-xiang Li; Zbigniew Ficek

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We examine conditions under which an open quantum system composed of a driven degenerated parametric oscillator cavity and a driven two-level atom coupled to a waveguide could decay to a pure dark state rather than the expected mixed state. The calculations are carried out analytically in a low dimensional Hilbert space truncated at the double-excitation states of the combined system. The validity of the truncation is confirmed by the exact numerical analysis. It is found that one way to...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1612.02124