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Jun 29, 2018
06/18

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Giuseppe Sergioli; Antonio Ledda

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The standard theory of quantum computation relies on the idea that the basic information quantity is represented by a superposition of elements of the canonical basis and the notion of probability naturally follows from the Born rule. In this work we consider three valued quantum computational logics. More specifically, we will focus on the Hilbert space C^3, we discuss extensions of several gates to this space and, using the notion of effect probability, we provide a characterization of its...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1602.04299

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Jun 29, 2018
06/18

by
Krzysztof Chabuda; Ian Leroux; Rafal Demkowicz-Dobrzanski

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The instability of an atomic clock is characterized by the Allan variance, a measure widely used to describe the noise of frequency standards. We provide an explicit method to find the ultimate bound on the Allan variance of an atomic clock in the most general scenario where N atoms are prepared in an arbitrarily entangled state and arbitrary measurement and feedback are allowed, including those exploiting coherences between succeeding interrogation steps. While the method is rigorous and...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1601.01685

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2.0

Jun 27, 2018
06/18

by
Antonio Vassallo; Michael Esfeld

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Crull (2014) claims that by invoking decoherence it is possible (i) to obviate many ``fine grained'' issues often conflated under the common designation of measurement problem, and (ii) to make substantial progresses in the fields of quantum gravity and quantum cosmology, without any early incorporation of a particular interpretation in the quantum formalism. We point out that Crull is mistaken about decoherence and tacitly assumes some kind of interpretation of the quantum formalism.

Topic: Quantum Physics

Source: http://arxiv.org/abs/1504.02642

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Jun 30, 2018
06/18

by
Kamil Korzekwa; Paweł Machnikowski; Paweł Horodecki

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We propose a quantum-state transfer protocol in a spin chain that requires only the control of the spins at the ends of the quantum wire. The protocol is to a large extent insensitive to inhomogeneity caused by local magnetic fields and perturbation of exchange couplings. Moreover, apart from the free evolution regime, it allows one to induce an adiabatic spin transfer, which provides the possibility of performing the transfer on demand. We also show that the amount of information leaking into...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1403.7359

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Jun 28, 2018
06/18

by
Jun Jing; Dvira Segal; Baowen Li; Lian-Ao Wu

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Relying on an exact time evolution scheme, we identify a novel transient energy transfer phe- nomenon in an exactly-solvable quantum microscopic model consisting of a three-level system coupled to two non-Markovian zero-temperature bosonic baths through two separable quantum channels. The dynamics of this model can be solved exactly using the quantum-state-diffusion equation formalism, demonstrating finite intervals of unidirectional energy flow across the system, typically, from the...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1507.00816

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Jun 29, 2018
06/18

by
Yudong Cao; Sabre Kais

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From celestial mechanics to quantum theory of atoms and molecules, perturbation theory has played a central role in natural sciences. Particularly in quantum mechanics, the amount of information needed for specifying the state of a many-body system commonly scales exponentially as the system size. This poses a fundamental difficulty in using perturbation theory at arbitrary order. As one computes the terms in the perturbation series at increasingly higher orders, it is often important to...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1607.01374

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Jun 29, 2018
06/18

by
Alexandru Paler; Simon J. Devitt; Austin G. Fowler

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Given a quantum algorithm, it is highly nontrivial to devise an efficient sequence of physical gates implementing the algorithm on real hardware and incorporating topological quantum error correction. In this paper, we present a first step towards this goal, focusing on generating correct and simple arrangements of topological structures that correspond to a given quantum circuit and largely neglecting their efficiency. We detail the many challenges that will need to be tackled in the pursuit...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1604.08621

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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

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Jun 30, 2018
06/18

by
Elliott Tammaro

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The stability of dynamical systems against perturbations (variations in initial conditions/model parameters) is a property referred to as structural stability. The study of sensitivity to perturbation is essential because in experiment initial conditions are not fixed, nor are model parameters known, to arbitrarily high precision. Additionally, if a physical system under study exhibits stability (insensitivity to initial conditions) then a theoretical description of the system must exhibit...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1411.4578

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Jun 29, 2018
06/18

by
Wei-Chen Wang; Mao-Fa Fang

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We have constructed a non-Hermitian two-level system (a PT -symmetric system) in dissipative environments, and investigated the quantum coherence in the non-Hermitian two-level system. Our results show that, quantum coherence can be created by PT -symmetric systems, even if the initial state of the twolevel system is incoherent state. Even though two-level system is interacted with dissipative environments, the quantum coherence exhibits a long-lived revival, and can be protected. We find that...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1612.08339

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Jun 29, 2018
06/18

by
Alexander E. Ulanov; Demid Sychev; Anastasia A. Pushkina; Ilya A. Fedorov; A. I. Lvovsky

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Transfer of quantum information between physical systems of a different nature is a central matter in quantum technologies. Particularly challenging is the transfer between discrete- and continuous degrees of freedom of various harmonic oscillator systems. Here we implement a protocol for teleporting a continuous-variable optical qubit, encoded by means of coherent states, onto a discrete-variable, single-rail qubit - a superposition of the vacuum- and single-photon optical states - via a...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1605.08649

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Jun 30, 2018
06/18

by
Lev Vaidman

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The counterfactuality of the recently proposed protocols for direct quantum communication is analyzed. It is argued that the protocols can be counterfactual only for one value of the transmitted bit. The protocols achieve a reduced probability of detection of the particle in the transmission channel by increasing the number of paths in the channel. However, this probability is not lower than the probability of detecting a particle actually passing through such a multi-path channel, which was...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1410.2723

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Jun 26, 2018
06/18

by
Jordan Cotler; Frank Wilczek

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Intensity interferometry (Hanbury Brown - Twiss effect) is an interesting and useful concept that is usually presented as a manifestation of the quantum statistics of indistinguishable particles. Here, by exploiting possibilities for project and entanglement, we substantially widen the scope of its central idea, removing the requirement of indistinguishability. We thereby potentially gain access to a host of new observables, including subtle polarization correlations and entanglement itself....

Topic: Quantum Physics

Source: http://arxiv.org/abs/1502.02477

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Jun 30, 2018
06/18

by
Jia-Min Gong; Zhan-Qiang Hui

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We study thermal quantum discord (TQD) in the Heisenberg chain with spin site or magnetic impurity. The former one of which may induce inhomogeneous exchange interactions between the neighboring spins, while the latter one modelling a spin chain with nonuniform magnetic field. In contrast with one's traditional understanding, we found that the spin impurity can be used to enhance the TQD greatly for all the bipartition schemes of the chain, while the magnetic impurity located on one spin can...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1401.3819

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Jun 29, 2018
06/18

by
Koji Azuma; Akihiro Mizutani; Hoi-Kwong Lo

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The quantum internet holds promise for performing quantum communication, such as quantum teleportation and quantum key distribution (QKD), freely between any parties all over the globe. Such a future quantum network, depending on the communication distance of the requesting parties, necessitates to invoke several classes of optical quantum communication such as point-to-point communication protocols, intercity QKD protocols and quantum repeater protocols. Recently, Takeoka, Guha and Wilde (TGW)...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1601.02933

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Jun 30, 2018
06/18

by
Zhu Cao; Zhen Zhang; Hoi-Kwong Lo; Xiongfeng Ma

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Coherent state photon sources are widely used in quantum information processing. In many applications, such as quantum key distribution (QKD), a coherent state is functioned as a mixture of Fock states by assuming its phase is continuously randomized. In practice, such a crucial assumption is often not satisfied and, therefore, the security of existing QKD experiments is not guaranteed. To bridge this gap, we provide a rigorous security proof of QKD with discrete-phase-randomized coherent state...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1410.3217

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Jun 26, 2018
06/18

by
Sarah Mostame; Joonsuk Huh; Christoph Kreisbeck; Andrew J Kerman; Takatoshi Fujita; Alexander Eisfeld; Alán Aspuru-Guzik

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With quantum computers being out of reach for now, quantum simulators are the alternative devices for efficient and more exact simulation of problems that are challenging on conventional computers. Quantum simulators are classified into analog and digital, with the possibility of constructing "hybrid" simulators by combining both techniques. In this paper, we focus on analog quantum simulators of open quantum systems and address the limit that they can beat classical computers. In...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1502.00962

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Jun 28, 2018
06/18

by
Jaewoo Joo; Eran Ginossar

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We propose a deterministic scheme for teleporting an unknown qubit through continuous-variable entangled states in superconducting circuits. The qubit is a superconducting two-level system and the bipartite quantum channel is a photonic entangled coherent state between two cavities. A Bell-type measurement performed on the hybrid state of solid and photonic states brings a discrete-variable unknown electronic state to a continuous-variable photonic cat state in a cavity mode. This scheme...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1509.02859

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Jun 29, 2018
06/18

by
Donghoon Ha; Younghun Kwon

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In this paper we consider the optimal discrimination of two mixed qubit states for a measurement that allows a fixed rate of inconclusive results(FRIR). Our strategy for the problem is to transform the FRIR of two qubit states into a minimum error discrimination for three qubit states by adding a specific quantum state $\rho_{0}$ and a prior probability $q_{0}$(which we will call an inconclusive degree), which we name the modified FRIR problem. First, we investigate special inconclusive degrees...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1608.02695

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Jun 29, 2018
06/18

by
E. G. Drukarev; A. I. Mikhailov

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We demonstrate that the high energy nonrelativistic asymptotic for the photoionization cross section in a central field $V(r)$ can be expressed in terms of the asymptotic of the Fourier transform $V(p)$ of the field. We show that the cross sections drop in the same way for the fields with the Coulomb short distance behavior. The character of the cross sections energy behavior is related to the analytical properties of the function $V(r)$. The cross sections exhibit power drop for the potentials...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1612.08833

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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 29, 2018
06/18

by
Valentin Averchenko; Denis Sych; Gerd Leuchs

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We propose a method to produce pure single photons with an arbitrary designed temporal shape in a heralded, lossless and scalable way. As the indispensable resource, the method uses pairs of time-energy entangled photons. To accomplish the shaping, one photon of a pair undergoes temporal modulation according to the desired shape. Subsequent frequency-resolving detection of the photon heralds its entangled counterpart in a pure quantum state with a temporal shape non-locally affected by the...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1610.03794

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Jun 30, 2018
06/18

by
Bo-xing Shang; Xi-qiang Xi

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A type of two qubits Josephson charge system is constructed in this paper, and properties of the quantum discord (QD) as well as the differences between thermal QD and thermal entanglement were investigated. A detailed calculation shows that the magnetic flux $\Phi_{Xk}$ is more efficient than the voltage $V_{Xi}$ in tuning QD. By choosing proper system parameters, one can realize the maximum QD in our two qubits Josephson charge system.

Topic: Quantum Physics

Source: http://arxiv.org/abs/1405.5002

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Jun 29, 2018
06/18

by
Dominic Verdon; Jamie Vicary

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We give a tight scheme for teleporting a quantum state between two parties whose reference frames are misaligned by an action of a finite symmetry group. Unlike previously proposed schemes, ours requires no additional tokens or data to be passed between the participants; the same amount of classical information is transferred as for ordinary quantum teleportation, and the Hilbert space of the entangled resource is of the same size. In the terminology of Peres and Scudo, our protocol relies on...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1603.08866

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Jun 29, 2018
06/18

by
Florian Boge

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Quantum mechanics notoriously faces the measurement problem, the problem that if read thoroughly, it implies the nonexistence of definite outcomes in measurement procedures. A plausible reaction to this and to related problems is to regard a system's quantum state $|\psi\rangle$ merely as an indication of our lack of knowledge about the system, i.e., to interpret it epistemically. However, there are radically different ways to spell out such an epistemic view of the quantum state. We here...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1603.09463

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Jun 29, 2018
06/18

by
Le Bin Ho; Nobuyuki Imoto

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In contrast to that a weak value of an observable is usually divided into real and imaginary parts, here we show that separation into modulus and argument is important for modular values. We first show that modular values are expressed by the average of dynamic phase factors with complex conditional probabilities. We then relate, using the polar decomposition, the modulus of the modular value to the relative change in the qubit pointer post-selection probabilities, and relate the argument of...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1602.01594

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Jun 29, 2018
06/18

by
Kosuke Kakuyanagi; Yuichiro Matsuzaki; Corentin Deprez; Hiraku Toida; Kouichi Semba; Hiroshi Yamaguchi; William J. Munro; Shiro Saito

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The hybridization of distinct quantum systems is now seen as an effective way to engineer the properties of an entire system leading to applications in quantum metamaterials, quantum simulation, and quantum metrology. One well known example is superconducting circuits coupled to ensembles of microscopic natural atoms. In such cases, the properties of the individual atom are intrinsic, and so are unchangeable. However, current technology allows us to fabricate large ensembles of macroscopic...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1606.04222

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Jun 28, 2018
06/18

by
Joel J. Wallman; Joseph Emerson

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Quantum computers are poised to radically outperform their classical counterparts by manipulating coherent quantum systems. A realistic quantum computer will experience errors due to the environment and imperfect control. When these errors are even partially coherent, they present a major obstacle to achieving robust computation. Here, we propose a method for introducing independent random single-qubit gates into the logical circuit in such a way that the effective logical circuit remains...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1512.01098

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Jun 28, 2018
06/18

by
A. Boette; R. Rossignoli; N. Gigena; M. Cerezo

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We present a model of discrete quantum evolution based on quantum correlations between the evolving system and a reference quantum clock system. A quantum circuit for the model is provided, which in the case of a constant Hamiltonian is able to represent the evolution over $2^n$ time steps in terms of just $n$ time qubits and $n$ control gates. We then introduce the concept of system-time entanglement as a measure of distinguishable quantum evolution, based on the entanglement between the...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1512.07313

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Jun 29, 2018
06/18

by
Armin Tavakoli; Marek Zukowski

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Communication complexity problems (CCPs) are tasks in which separated parties attempt to compute a function whose inputs are distributed among the parties. Their communication is limited so that not all inputs can be sent. We show that broad classes of Bell inequalities can be mapped to CCPs and that a quantum violation of a Bell inequality is a necessary and sufficient condition for an enhancement of the related CCP beyond its classical limitation. However, one can implement CCPs by...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1611.00977

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Jun 28, 2018
06/18

by
Jing-Zheng Huang; Qin-Zheng Li; Chen Fang; Gui-Hua Zeng

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By exploiting the hyperentanglement, we propose a new concrete scheme to realize weak value amplification, which can be implemented by N hyperentangled photons along with coincidence detection. Our scheme can optimally increase the amplification factor by a factor of N compared to the usage of N uncorrelated photons, and achieve the Heisenberg limit for the purpose of parameter estimation. We expect our study can inspire a further investigation on the usage of hyperentanglement in weak...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1508.01268

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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 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 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 30, 2018
06/18

by
Shishan Dong; B. J. Falaye; A. E. Guerrero M.; Shi-Hai Dong

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The ladder operators for one dimensional quantum harmonic oscillator were constructed by Schr\"odinger in 1940s. We extend this method to a two dimensional uniform magnetic field and establish the ladder operators which depend on all spatial variables of quantum system. The Hamiltonian of quantum system can also be written by the velocity of the particle.

Topic: Quantum Physics

Source: http://arxiv.org/abs/1701.03463

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Jun 29, 2018
06/18

by
Imran M. Mirza; John C. Schotland

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We study entanglement generation and control in bi-directional waveguide QED driven by a two photon Gaussian wavepacket. In particular, we focus on how increasing the number of qubits affects the overall average pairwise entanglement in the system. We also investigate how the presence of a second photon can introduce non-linearities, thereby manipulating the generated entanglement. In addition, we show that through the introduction of chirality and small decay rates, entanglement can be stored...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1604.03652

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Jun 29, 2018
06/18

by
Xuefeng Duan; Chi-Kwong Li; Diane Christine Pelejo

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We use projection methods to construct (global) quantum states with prescribed reduced (marginal) states, and possibly with some special properties such as having specific eigenvalues, having specific rank and extreme von Neumann or R\'{e}nyi entropy. Using convex analysis, optimization techniques on matrix manifolds, we obtain algorithms to solve the problem. Matlab programs are written based on these algorithms and numerical examples are illustrated. The numerical results reveal new patterns...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1604.08289

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Jun 29, 2018
06/18

by
Jin-Lei Wu; Xin Ji; Shou Zhang

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Recently, a novel three-dimensional entangled state called tree-type entanglement, which is likely to have applications for improving quantum communication security, was prepared via adiabatic passage by Song et al. [Phys. Rev. A 93, 062321 (2016)]. Here we propose two schemes for fast generations of tree-type three-dimensional entanglement among three spatially separated atoms via shortcuts to adiabatic passage. With the help of quantum Zeno dynamics, two kinds of different but equivalent...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1606.06796

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Jun 30, 2018
06/18

by
Tong Liu; Qi-Ping Su; Shao-Jie Xiong; Jin-Ming Liu; Chui-Ping Yang; Franco Nori

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$W$-type entangled states can be used as quantum channels for, e.g., quantum teleportation, quantum dense coding, and quantum key distribution. In this work, we propose a way to generate a macroscopic $W$-type entangled coherent state using quantum memories in circuit QED. The memories considered here are nitrogen-vacancy center ensembles (NVEs), each located in a different cavity. This proposal does not require initially preparing each NVE in a coherent state instead of a ground state, which...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1411.3102

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Jun 30, 2018
06/18

by
Marco Merkli; Haifeng Song; Gennady Berman

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We consider a three-level quantum system interacting with a bosonic thermal reservoir. Two energy levels of the system are nearly degenerate but well separated from the third one. The system-reservoir interaction constant is larger than the energy difference of the degenerate levels, but it is smaller than the separation between the latter and the remaining level. We show that the quasi-degeneracy of energy levels leads to the existence of a manifold of quasi-stationary states, and the dynamics...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1411.2934

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Jun 29, 2018
06/18

by
Terry Rudolph

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This is a short overview explaining how building a large-scale, silicon-photonic quantum computer has been reduced to the creation of good sources of 3-photon entangled states (and may simplify further). Given such sources, each photon need pass through a small, constant, number of components, interfering with at most 2 other spatially nearby photons, and current photonics engineering has already demonstrated the manufacture of thousands of components on two-dimensional semiconductor chips with...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1607.08535

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Jun 30, 2018
06/18

by
Leonardo Novo; Shantanav Chakraborty; Masoud Mohseni; Hartmut Neven; Yasser Omar

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Continuous time quantum walks provide an important framework for designing new algorithms and modelling quantum transport and state transfer problems. Often, the graph representing the structure of a problem contains certain symmetries that confine the dynamics to a smaller subspace of the full Hilbert space. In this work, we use invariant subspace methods, that can be computed systematically using Lanczos algorithm, to obtain the reduced set of states that encompass the dynamics of the problem...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1412.7209

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Jun 28, 2018
06/18

by
Vincent Debierre; Thomas Durt

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We investigate, in the case of the $2\mathrm{p}-1\mathrm{s}$ transition in atomic Hydrogen, the behaviour of the spontaneously emitted electromagnetic field in spacetime. We focus on Glauber's wave function for the emitted photon, a quantity which we find is nonzero outside the lightcone at all times after the start of the emission. We identify the uncertainty on the position of the decaying electron as a source of departure from causality in the naive sense of the term. We carry out a detailed...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1509.01475

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Jun 28, 2018
06/18

by
Riccardo Messina; Paulo A. Maia Neto; Brahim Guizal; Mauro Antezza

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We derive the explicit expression for the Casimir energy between a sphere and a 1D grating, in terms of the sphere and grating reflection matrices, and valid for arbitrary materials, sphere radius, and grating geometric parameters. We then numerically calculate the Casimir energy between a metallic (gold) sphere and a dielectric (fused silica) lamellar grating at room temperature, and explore its dependence on the sphere radius, grating-sphere separation, and lateral displacement. We...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1510.06538

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Jun 27, 2018
06/18

by
Li-Bo Chen; Wen Yang; Zhang-Qi Yin

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We present a proposal for heralded entanglement between two quantum dots via Hong--Ou--Mandel effect. Each of the quantum dots, drived off-resonance by two lasers, can be entangled with the coherent cavity mode. The output photons from the two coherent cavity modes interfering by a beamsplitter, we could entangle the two QDs with nearly unit success probability. Our scheme requires neither direct coupling between qubits nor the detection of single photons. Moreover the quantum dots do not need...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1505.04476

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Jun 30, 2018
06/18

by
Bruno Bellomo; Mauro Antezza

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We study an ensemble of two-level quantum systems (qubits) interacting with a common electromagnetic field in proximity of a dielectric slab whose temperature is held different from that of some far surrounding walls. We show that the dissipative dynamics of the qubits driven by this stationary and out of thermal equilibrium (OTE) field, allows the production of steady many-body entangled states, differently from the case at thermal equilibrium where steady states are always non-entangled. By...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1409.7178

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Jun 30, 2018
06/18

by
Gilles Pütz; Denis Rosset; Tomer Jack Barnea; Yeong-Cherng Liang; Nicolas Gisin

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The use of Bell's theorem in any application or experiment relies on the assumption of free choice or, more precisely, measurement independence, meaning that the measurements can be chosen freely. Here, we prove that even in the simplest Bell test - one involving 2 parties each performing 2 binary-outcome measurements - an arbitrarily small amount of measurement independence is sufficient to manifest quantum nonlocality. To this end, we introduce the notion of measurement dependent locality and...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1407.5634

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Jun 26, 2018
06/18

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

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We address the problem of quantum reading of optical memories, namely the retrieving of classical information stored in the optical properties of a media with minimum energy. We present optimal strategies for ambiguous and unambiguous quantum reading of unitary optical memories, namely when one's task is to minimize the probability of errors in the retrieved information and when perfect retrieving of information is achieved probabilistically, respectively. A comparison of the optimal strategy...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1502.05787

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Jun 28, 2018
06/18

by
Jianwei Xu

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Coherence arises from the superposition principle and plays a key role in quantum mechanics. Recently, Baumgratz et al. [T. Baumgratz, M. Cramer, and M. B. Plenio, Phys. Rev. Lett. 113, 140401 (2014)] established a rigorous framework for quantifying the coherence of finite dimensional quantum states. In this work we provide a framework for quantifying the coherence of Gaussian states and explicitly give a coherence measure based on the relative entropy.

Topic: Quantum Physics

Source: http://arxiv.org/abs/1510.02916

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Jun 29, 2018
06/18

by
T. Ferreira da Silva; G. B. Xavier; G. C. Amaral; G. P. Temporão; J. P. von der Weid

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We propose and demonstrate a technique for quantum random number generation based on the random population of the output spatial modes of a beam splitter when both inputs are simultaneously fed with indistinguishable weak coherent states. We simulate and experimentally validate the probability of generation of random bits as a function of the average photon number per input, and compare it to the traditional approach of a single weak coherent state transmitted through a beam-splitter, showing...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1608.05155