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PRA: Quantum information

Recently published articles in Phys. Rev. A in the Table of Content section "Quantum information"

Published: 2018-02-16T23:02:43+00:00


Entanglement and extreme planar spin squeezing


Author(s): G. Vitagliano, G. Colangelo, F. Martin Ciurana, M. W. Mitchell, R. J. Sewell, and G. Tóth

We introduce an entanglement-depth criterion optimized for planar quantum-squeezed (PQS) states. It is connected with the sensitivity of such states for estimating a phase generated by rotations about an axis orthogonal to its polarization. We compare numerically our criterion with the well-known ex...

[Phys. Rev. A 97, 020301(R)] Published Thu Feb 15, 2018

Distance scaling of electric-field noise in a surface-electrode ion trap


Author(s): J. A. Sedlacek, A. Greene, J. Stuart, R. McConnell, C. D. Bruzewicz, J. M. Sage, and J. Chiaverini

The electric-field noise affecting quantum logic gates in surface-electrode ion traps is studied as a function of trapping frequency, electrode temperature, and distance d between ion and surface. The finding that the noise scales as 1/d4 eliminates various surface-noise models that have been proposed to explain the anomalous ion heating observed in this type of trap.

[Phys. Rev. A 97, 020302(R)] Published Thu Feb 15, 2018

Diffusion Monte Carlo approach versus adiabatic computation for local Hamiltonians


Author(s): Jacob Bringewatt, William Dorland, Stephen P. Jordan, and Alan Mink

Most research regarding quantum adiabatic optimization has focused on stoquastic Hamiltonians, whose ground states can be expressed with only real non-negative amplitudes and thus for whom destructive interference is not manifest. This raises the question of whether classical Monte Carlo algorithms ...

[Phys. Rev. A 97, 022323] Published Thu Feb 15, 2018

Passive quantum error correction of linear optics networks through error averaging


Author(s): Ryan J. Marshman, Austin P. Lund, Peter P. Rohde, and Timothy C. Ralph

We propose and investigate a method of error detection and noise correction for bosonic linear networks using a method of unitary averaging. The proposed error averaging does not rely on ancillary photons or control and feedforward correction circuits, remaining entirely passive in its operation. We...

[Phys. Rev. A 97, 022324] Published Thu Feb 15, 2018

Dissipative environment may improve the quantum annealing performances of the ferromagnetic $p$-spin model


Author(s): G. Passarelli, G. De Filippis, V. Cataudella, and P. Lucignano

We investigate the quantum annealing of the ferromagnetic $p$-spin model in a dissipative environment ($p=5$ and $p=7$). This model, in the large-$p$ limit, codifies Grover's algorithm for searching in an unsorted database [L. K. Grover, Proceedings of the 28th Annual ACM Symposium on Theory of Comp...

[Phys. Rev. A 97, 022319] Published Wed Feb 14, 2018

Optimal discrimination of optical coherent states cannot always be realized by interfering with coherent light, photon counting, and feedback


Author(s): Kenji Nakahira, Kentaro Kato, and Tsuyoshi Sasaki Usuda

A method is developed to analyze the performance of sequential measurements, thus providing a way to benchmark various optical receivers. In particular, it is proved that a Dolinar-like receiver cannot realize a “minimum error quantum measurement” when dealing with ternary coherent states.

[Phys. Rev. A 97, 022320] Published Wed Feb 14, 2018

Experimental investigation of environment-induced entanglement using an all-optical setup


Author(s): M. H. M. Passos, W. F. Balthazar, A. Z. Khoury, M. Hor-Meyll, L. Davidovich, and J. A. O. Huguenin

We investigate the generation of entanglement between two noninteracting qubits coupled to a common reservoir. An experimental setup was conceived to encode one qubit on the polarization of an optical beam and another qubit on its transverse mode. The action of the reservoir is implemented as condit...

[Phys. Rev. A 97, 022321] Published Wed Feb 14, 2018

Entanglement measures in embedding quantum simulators with nuclear spins


Author(s): Tao Xin, Julen S. Pedernales, Enrique Solano, and Gui-Lu Long

We implement an embedding quantum simulator (EQS) in nuclear spin systems. The experiment consists of a simulator of up to three qubits, plus a single ancillary qubit, where we are able to efficiently measure the concurrence and the three-tangle of two-qubit and three-qubit systems as they undergo e...

[Phys. Rev. A 97, 022322] Published Wed Feb 14, 2018

Coherent control and storage of a microwave pulse in a one-dimensional array of artificial atoms using the Autler-Townes effect and electromagnetically induced transparency


Author(s): M. Q. Ayaz, Mohsin Waqas, Sajid Qamar, and Shahid Qamar

In this paper we propose a scheme for coherent control and storage of a microwave pulse in superconducting circuits exploiting the idea of electromagnetically induced transparency (EIT) and the Aulter-Townes (AT) effect. We show that superconducting artificial atoms in a four-level tripod configurat...

[Phys. Rev. A 97, 022318] Published Tue Feb 13, 2018

Bang-bang shortcut to adiabaticity in trapped-ion quantum simulators


Author(s): S. Balasubramanian, Shuyang Han, B. T. Yoshimura, and J. K. Freericks

We model the bang-bang optimization protocol as a shortcut to adiabaticity in the ground-state preparation of a trapped-ion quantum simulator. Compared to a locally adiabatic evolution, the bang-bang protocol typically produces a lower ground-state probability, but its implementation is so much simp...

[Phys. Rev. A 97, 022313] Published Mon Feb 12, 2018

Optimal resource states for local state discrimination


Author(s): Somshubhro Bandyopadhyay, Saronath Halder, and Michael Nathanson

We study the problem of locally distinguishing pure quantum states using shared entanglement as a resource. For a given set of locally indistinguishable states, we define a resource state to be useful if it can enhance local distinguishability and optimal if it can distinguish the states as well as ...

[Phys. Rev. A 97, 022314] Published Mon Feb 12, 2018

Continuous-variable quantum Gaussian process regression and quantum singular value decomposition of nonsparse low-rank matrices


Author(s): Siddhartha Das, George Siopsis, and Christian Weedbrook

With the significant advancement in quantum computation during the past couple of decades, the exploration of machine-learning subroutines using quantum strategies has become increasingly popular. Gaussian process regression is a widely used technique in supervised classical machine learning. Here w...

[Phys. Rev. A 97, 022315] Published Mon Feb 12, 2018

Integrating machine learning to achieve an automatic parameter prediction for practical continuous-variable quantum key distribution


Author(s): Weiqi Liu, Peng Huang, Jinye Peng, Jianping Fan, and Guihua Zeng

For supporting practical quantum key distribution (QKD), it is critical to stabilize the physical parameters of signals, e.g., the intensity, phase, and polarization of the laser signals, so that such QKD systems can achieve better performance and practical security. In this paper, an approach is de...

[Phys. Rev. A 97, 022316] Published Mon Feb 12, 2018

Universal entanglement timescale for Rényi entropies


Author(s): Jesse C. Cresswell

Recently it was shown that the growth of entanglement in an initially separable state, as measured by the purity of subsystems, can be characterized by a timescale that takes a universal form for any Hamiltonian. We show that the same timescale governs the growth of entanglement for all Rényi entrop...

[Phys. Rev. A 97, 022317] Published Mon Feb 12, 2018

Dynamics of open quantum systems by interpolation of von Neumann and classical master equations, and its application to quantum annealing


Author(s): Tadashi Kadowaki

We propose a method to interpolate dynamics of von Neumann and classical master equations with an arbitrary mixing parameter to investigate the thermal effects in quantum dynamics. The two dynamics are mixed by intervening to continuously modify their solutions, thus coupling them indirectly instead...

[Phys. Rev. A 97, 022312] Published Fri Feb 09, 2018

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


Author(s): Akshay Gaikwad, Diksha Rehal, Amandeep Singh, Arvind, and Kavita Dorai

We present the NMR implementation of a scheme for selective and efficient quantum process tomography without ancilla. We generalize this scheme such that it can be implemented efficiently using only a set of measurements involving product operators. The method allows us to estimate any element of th...

[Phys. Rev. A 97, 022311] Published Wed Feb 07, 2018

Fully device-independent conference key agreement


Author(s): Jérémy Ribeiro, Gláucia Murta, and Stephanie Wehner

We present a security analysis of conference key agreement (CKA) in the most adversarial model of device independence (DI). Our protocol can be implemented by any experimental setup that is capable of performing Bell tests [specifically, the Mermin-Ardehali-Belinskii-Klyshko (MABK) inequality], and ...

[Phys. Rev. A 97, 022307] Published Tue Feb 06, 2018

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


Author(s): Walter Vinci and Daniel A. Lidar

Nested quantum annealing correction (NQAC) is an error-correcting scheme for quantum annealing that allows for the encoding of a logical qubit into an arbitrarily large number of physical qubits. The encoding replaces each logical qubit by a complete graph of degree $C$. The nesting level $C$ repres...

[Phys. Rev. A 97, 022308] Published Tue Feb 06, 2018

Multiqubit subradiant states in $N$-port waveguide devices: ε-and-μ-near-zero hubs and nonreciprocal circulators


Author(s): Iñigo Liberal and Nader Engheta

Quantum emitters interacting through a waveguide setup have been proposed as a promising platform for basic research on light-matter interactions and quantum information processing. We propose to augment waveguide setups with the use of multiport devices. Specifically, we demonstrate theoretically t...

[Phys. Rev. A 97, 022309] Published Tue Feb 06, 2018

Security proof of continuous-variable quantum key distribution using three coherent states


Author(s): Kamil Brádler and Christian Weedbrook

We introduce a ternary quantum key distribution (QKD) protocol and asymptotic security proof based on three coherent states and homodyne detection. Previous work had considered the binary case of two coherent states and here we nontrivially extend this to three. Our motivation is to leverage the pra...

[Phys. Rev. A 97, 022310] Published Tue Feb 06, 2018

Quantum machine learning with glow for episodic tasks and decision games


Author(s): Jens Clausen and Hans J. Briegel

We consider a general class of models, where a reinforcement learning (RL) agent learns from cyclic interactions with an external environment via classical signals. Perceptual inputs are encoded as quantum states, which are subsequently transformed by a quantum channel representing the agent's memor...

[Phys. Rev. A 97, 022303] Published Mon Feb 05, 2018

Quantum approximate optimization algorithm for MaxCut: A fermionic view


Author(s): Zhihui Wang, Stuart Hadfield, Zhang Jiang, and Eleanor G. Rieffel

Farhi et al. recently proposed a class of quantum algorithms, the quantum approximate optimization algorithm (QAOA), for approximately solving combinatorial optimization problems (E. Farhi et al., arXiv:1411.4028; arXiv:1412.6062; arXiv:1602.07674). A level-$p$ QAOA circuit consists of $p$ steps; in...

[Phys. Rev. A 97, 022304] Published Mon Feb 05, 2018

Universal quantum computing using ${({\mathbb{Z}}_{d})}^{3}$ symmetry-protected topologically ordered states


Author(s): Yanzhu Chen, Abhishodh Prakash, and Tzu-Chieh Wei

Measurement-based quantum computation describes a scheme where entanglement of resource states is utilized to simulate arbitrary quantum gates via local measurements. Recent works suggest that symmetry-protected topologically nontrivial, short-ranged entangled states are promising candidates for suc...

[Phys. Rev. A 97, 022305] Published Mon Feb 05, 2018

Spin-1 models in the ultrastrong-coupling regime of circuit QED


Author(s): F. Albarrán-Arriagada, L. Lamata, E. Solano, G. Romero, and J. C. Retamal

We propose a superconducting circuit platform for simulating spin-1 models. To this purpose we consider a chain of $N$ ultrastrongly coupled qubit-resonator systems interacting through a grounded superconducting quantum interference device (SQUID). The anharmonic spectrum of the qubit-resonator syst...

[Phys. Rev. A 97, 022306] Published Mon Feb 05, 2018

Automated quantum operations in photonic qutrits


Author(s): G. F. Borges, R. D. Baldijão, J. G. L. Condé, J. S. Cabral, B. Marques, M. Terra Cunha, A. Cabello, and S. Pádua

We report an experimental implementation of automated state transformations on spatial photonic qutrits following the theoretical proposal made by Baldijão et al. [Phys. Rev. A 96, 032329 (2017)]. A qutrit state is simulated by using three Gaussian beams, and after some state operations, the transfo...

[Phys. Rev. A 97, 022301] Published Fri Feb 02, 2018

Evolution of tripartite entangled states in a decohering environment and their experimental protection using dynamical decoupling


Author(s): Harpreet Singh, Arvind, and Kavita Dorai

We embarked upon the task of experimental protection of different classes of tripartite entangled states, namely, the maximally entangled Greenberger-Horne-Zeilinger (GHZ) and W states and the tripartite entangled state called the $W\overline{W}$ state, using dynamical decoupling. The states were cr...

[Phys. Rev. A 97, 022302] Published Fri Feb 02, 2018

Device-independent secret-key-rate analysis for quantum repeaters


Author(s): Timo Holz, Hermann Kampermann, and Dagmar Bruß

The device-independent approach to quantum key distribution (QKD) aims to establish a secret key between two or more parties with untrusted devices, potentially under full control of a quantum adversary. The performance of a QKD protocol can be quantified by the secret key rate, which can be lower b...

[Phys. Rev. A 97, 012337] Published Wed Jan 31, 2018

Robust quantum network architectures and topologies for entanglement distribution


Author(s): Siddhartha Das, Sumeet Khatri, and Jonathan P. Dowling

Entanglement distribution is a prerequisite for several important quantum information processing and computing tasks, such as quantum teleportation, quantum key distribution, and distributed quantum computing. In this work, we focus on two-dimensional quantum networks based on optical quantum techno...

[Phys. Rev. A 97, 012335] Published Mon Jan 29, 2018

Generalized monogamy inequalities and upper bounds of negativity for multiqubit systems


Author(s): Yanmin Yang, Wei Chen, Gang Li, and Zhu-Jun Zheng

In this paper, we present some generalized monogamy inequalities and upper bounds of negativity based on convex-roof extended negativity (CREN) and CREN of assistance (CRENOA). These monogamy relations are satisfied by the negativity of $N$-qubit quantum systems $AB{C}_{1}⋯{C}_{N−2}$, under the part...

[Phys. Rev. A 97, 012336] Published Mon Jan 29, 2018

Negativity and tight constraints of multiqubit entanglement


Author(s): Jeong San Kim

We provide a characterization of multiqubit entanglement constraints in terms of negativity. By using the square of convex-roof extended negativity (SCREN) and the Hamming weight of the binary vector related with the distribution of subsystems, we show that the $α\mathrm{th}$ power of SCREN provides...

[Phys. Rev. A 97, 012334] Published Fri Jan 26, 2018

Approaches for approximate additivity of the Holevo information of quantum channels


Author(s): Felix Leditzky, Eneet Kaur, Nilanjana Datta, and Mark M. Wilde

We study quantum channels that are close to another channel with weakly additive Holevo information, and we derive upper bounds on their classical capacity. Examples of channels with weakly additive Holevo information are entanglement-breaking channels, unital qubit channels, and Hadamard channels. ...

[Phys. Rev. A 97, 012332] Published Thu Jan 25, 2018

Quantum state transfer in spin chains via shortcuts to adiabaticity


Author(s): Bi-Hua Huang, Yi-Hao Kang, Ye-Hong Chen, Zhi-Cheng Shi, Jie Song, and Yan Xia

Based on shortcuts to adiabaticity and quantum Zeno dynamics, we present a protocol to implement quantum state transfer (QST) in a quantum spin-$\frac{1}{2}$ chain. In the protocol, the complex Hamiltonian of an $N$-site system is simplified, and a simple effective Hamiltonian is present. It is show...

[Phys. Rev. A 97, 012333] Published Thu Jan 25, 2018

Quantum singular-value decomposition of nonsparse low-rank matrices


Author(s): Patrick Rebentrost, Adrian Steffens, Iman Marvian, and Seth Lloyd

We present a method to exponentiate nonsparse indefinite low-rank matrices on a quantum computer. Given access to the elements of the matrix, our method allows one to determine the singular values and their associated singular vectors in time exponentially faster in the dimension of the matrix than ...

[Phys. Rev. A 97, 012327] Published Wed Jan 24, 2018

Multipartite monogamous relations for entanglement and discord


Author(s): Jonhy S. S. Ferreira, Daví Filenga, Marcio F. Cornelio, and Felipe F. Fanchini

The distribution of quantum correlations in multipartite systems plays a significant role in several aspects of quantum information theory. While it is well known that these quantum correlations cannot be freely distributed, the way that they are shared in a multipartite system is an open problem ev...

[Phys. Rev. A 97, 012328] Published Wed Jan 24, 2018

Arbitrary control of entanglement between two nitrogen-vacancy-center ensembles coupling to a superconducting-circuit qubit


Author(s): Wan-Jun Su, Zhen-Biao Yang, and Zhi-Rong Zhong

We propose an effective scheme for realizing a Jaynes-Cummings model with the collective nitrogen-vacancy-center ensemble (NVE) bosonic modes in a hybrid system. Specifically, the controllable transmon qubit can alternatively interact with one of the two NVEs, which results in the production of $N$-...

[Phys. Rev. A 97, 012329] Published Wed Jan 24, 2018

Locality-preserving logical operators in topological stabilizer codes


Author(s): Paul Webster and Stephen D. Bartlett

Locality-preserving logical operators in topological codes are naturally fault tolerant, since they preserve the correctability of local errors. Using a correspondence between such operators and gapped domain walls, we describe a procedure for finding all locality-preserving logical operators admitt...

[Phys. Rev. A 97, 012330] Published Wed Jan 24, 2018

Unification of nonclassicality measures in interferometry


Author(s): Xiao Yuan, Hongyi Zhou, Mile Gu, and Xiongfeng Ma

From an operational perspective, nonclassicality characterizes the exotic behavior in a physical process which cannot be explained with Newtonian physics. There are several widely used measures of nonclassicality, including coherence, discord, and entanglement, each proven to be essential resources ...

[Phys. Rev. A 97, 012331] Published Wed Jan 24, 2018

Coherence, asymmetry, and quantum macroscopicity


Author(s): Hyukjoon Kwon, Chae-Yeun Park, Kok Chuan Tan, Daekun Ahn, and Hyunseok Jeong

We investigate a measure of quantum coherence and its extension to quantify quantum macroscopicity. The coherence measure can also quantify the asymmetry of a quantum state with respect to a given group transformation. We then show that a weighted sum of asymmetry in each mode can be applied as a me...

[Phys. Rev. A 97, 012326] Published Tue Jan 23, 2018

Continuous-variable quantum authentication of physical unclonable keys: Security against an emulation attack


Author(s): Georgios M. Nikolopoulos

We consider a recently proposed entity authentication protocol in which a physical unclonable key is interrogated by random coherent states of light, and the quadratures of the scattered light are analyzed by means of a coarse-grained homodyne detection. We derive a sufficient condition for the prot...

[Phys. Rev. A 97, 012324] Published Mon Jan 22, 2018

Efficient quantum repeater with respect to both entanglement-concentration rate and complexity of local operations and classical communication


Author(s): Zhaofeng Su, Ji Guan, and Lvzhou Li

Quantum entanglement is an indispensable resource for many significant quantum information processing tasks. However, in practice, it is difficult to distribute quantum entanglement over a long distance, due to the absorption and noise in quantum channels. A solution to this challenge is a quantum r...

[Phys. Rev. A 97, 012325] Published Mon Jan 22, 2018

Chiral spin currents in a trapped-ion quantum simulator using Floquet engineering


Author(s): Tobias Graß, Alessio Celi, Guido Pagano, and Maciej Lewenstein

The most typical ingredient of topologically protected quantum states is magnetic fluxes. In a system of spins, complex-valued interaction parameters give rise to a flux, if their phases do not add up to zero along a closed loop. Here we apply periodic driving, a powerful tool for quantum engineerin...

[Phys. Rev. A 97, 010302(R)] Published Fri Jan 19, 2018

Protecting the entanglement of twisted photons by adaptive optics


Author(s): Nina Leonhard, Giacomo Sorelli, Vyacheslav N. Shatokhin, Claudia Reinlein, and Andreas Buchleitner

Entanglement degradation of orbital-angular-momentum modes can be prevented using adaptive optics. The results prove the possibility of significantly reducing the crosstalk of modes, thereby making entanglement available even under moderate atmospheric turbulence conditions.

[Phys. Rev. A 97, 012321] Published Fri Jan 19, 2018

Ultimate entanglement robustness of two-qubit states against general local noises


Author(s): Sergey N. Filippov, Vladimir V. Frizen, and Daria V. Kolobova

We study the problem of optimal preparation of a bipartite entangled state, which remains entangled the longest time under action of local qubit noises. We show that for unital noises, such a state is always maximally entangled, whereas for nonunital noises, it is not. We develop a decomposition tec...

[Phys. Rev. A 97, 012322] Published Fri Jan 19, 2018

Qudit hypergraph states and their properties


Author(s): Fei-Lei Xiong, Yi-Zheng Zhen, Wen-Fei Cao, Kai Chen, and Zeng-Bing Chen

Hypergraph states, a generalization of graph states, constitute a large class of quantum states with intriguing nonlocal properties, and they have promising applications in quantum information science and technology. In this paper, we study some features of an independently proposed generalization o...

[Phys. Rev. A 97, 012323] Published Fri Jan 19, 2018

Quantum-key-distribution protocol with pseudorandom bases


Author(s): A. S. Trushechkin, P. A. Tregubov, E. O. Kiktenko, Y. V. Kurochkin, and A. K. Fedorov

Quantum key distribution (QKD) offers a way for establishing information-theoretical secure communications. An important part of QKD technology is a high-quality random number generator for the quantum-state preparation and for post-processing procedures. In this work, we consider a class of prepare...

[Phys. Rev. A 97, 012311] Published Tue Jan 16, 2018

Generating maximally-path-entangled number states in two spin ensembles coupled to a superconducting flux qubit


Author(s): Yusef Maleki and Aleksei M. Zheltikov

An ensemble of nitrogen-vacancy (NV) centers coupled to a circuit QED device is shown to enable an efficient, high-fidelity generation of high-N00N states. Instead of first creating entanglement and then increasing the number of entangled particles $N$, our source of high-N00N states first prepares ...

[Phys. Rev. A 97, 012312] Published Tue Jan 16, 2018

One-sided measurement-device-independent quantum key distribution


Author(s): Wen-Fei Cao, Yi-Zheng Zhen, Yu-Lin Zheng, Li Li, Zeng-Bing Chen, Nai-Le Liu, and Kai Chen

Measurement-device-independent quantum key distribution (MDI-QKD) protocol was proposed to remove all the detector side channel attacks, while its security relies on the trusted encoding systems. Here we propose a one-sided MDI-QKD (1SMDI-QKD) protocol, which enjoys detection loophole-free advantage...

[Phys. Rev. A 97, 012313] Published Tue Jan 16, 2018

Device-independent certification of two bits of randomness from one entangled bit and Gisin's elegant Bell inequality


Author(s): Ole Andersson, Piotr Badziąg, Irina Dumitru, and Adán Cabello

We prove that as conjectured by Acín et al. [Phys. Rev. A 93, 040102(R) (2016)], two bits of randomness can be certified in a device-independent way from one bit of entanglement using the maximal quantum violation of Gisin's elegant Bell inequality. This suggests a surprising connection between maxi...

[Phys. Rev. A 97, 012314] Published Tue Jan 16, 2018

Beating the classical limits of information transmission using a quantum decoder


Author(s): Robert J. Chapman, Akib Karim, Zixin Huang, Steven T. Flammia, Marco Tomamichel, and Alberto Peruzzo

Encoding schemes and error-correcting codes are widely used in information technology to improve the reliability of data transmission over real-world communication channels. Quantum information protocols can further enhance the performance in data transmission by encoding a message in quantum states...

[Phys. Rev. A 97, 012315] Published Tue Jan 16, 2018

Emergence of entanglement with temperature and time in factorization-surface states


Author(s): Titas Chanda, Tamoghna Das, Debasis Sadhukhan, Amit Kumar Pal, Aditi Sen(De), and Ujjwal Sen

There exist zero-temperature states in quantum many-body systems that are fully factorized, thereby possessing vanishing entanglement, and hence being of no use as resource in quantum information processing tasks. Such states can become useful for quantum protocols when the temperature of the system...

[Phys. Rev. A 97, 012316] Published Tue Jan 16, 2018

Passive state preparation in the Gaussian-modulated coherent-states quantum key distribution


Author(s): Bing Qi, Philip G. Evans, and Warren P. Grice

In the Gaussian-modulated coherent-states (GMCS) quantum key distribution (QKD) protocol, Alice prepares quantum states actively: For each transmission, Alice generates a pair of Gaussian-distributed random numbers, encodes them on a weak coherent pulse using optical amplitude and phase modulators, ...

[Phys. Rev. A 97, 012317] Published Tue Jan 16, 2018

Measurement-free implementations of small-scale surface codes for quantum-dot qubits


Author(s): H. Ekmel Ercan, Joydip Ghosh, Daniel Crow, Vickram N. Premakumar, Robert Joynt, Mark Friesen, and S. N. Coppersmith

The performance of quantum-error-correction schemes depends sensitively on the physical realizations of the qubits and the implementations of various operations. For example, in quantum-dot spin qubits, readout is typically much slower than gate operations, and conventional surface-code implementati...

[Phys. Rev. A 97, 012318] Published Tue Jan 16, 2018

High resource of azimuthal entanglement in terms of Cartesian variables of noncollinear biphotons


Author(s): M. V. Fedorov

Single-particle and coincidence distributions of photons are analyzed for the noncollinear frequency-degenerate type-I regime of spontaneous parametric down-conversion. Noncollinearity itself is shown to provide a new mechanism of strong broadening of the single-particle distributions in Cartesian c...

[Phys. Rev. A 97, 012319] Published Tue Jan 16, 2018

Optimal entangling operations between deterministic blocks of qubits encoded into single photons


Author(s): Jake A. Smith and Lev Kaplan

Here, we numerically simulate probabilistic elementary entangling operations between rail-encoded photons for the purpose of scalable universal quantum computation or communication. We propose grouping logical qubits into single-photon blocks wherein single-qubit rotations and the controlled-not (cn...

[Phys. Rev. A 97, 012320] Published Tue Jan 16, 2018

Quantum-enhanced sensing from hyperentanglement


Author(s): S. P. Walborn, A. H. Pimentel, L. Davidovich, and R. L. de Matos Filho

Hyperentanglement—simultaneous entanglement between multiple degrees of freedom of two or more systems—has been used to enhance quantum information tasks such as quantum communication and photonic quantum computing. Here we show that hyperentanglement can lead to increased quantum advantage in metro...

[Phys. Rev. A 97, 010301(R)] Published Fri Jan 12, 2018

Finding paths in tree graphs with a quantum walk


Author(s): Daniel Koch and Mark Hillery

We analyze the potential for different types of searches using the formalism of scattering random walks on quantum computers. Given a particular type of graph consisting of nodes and connections, a “tree maze,” we would like to find a selected final node as quickly as possible, faster than any class...

[Phys. Rev. A 97, 012308] Published Fri Jan 12, 2018

Analysis of coined quantum walks with renormalization


Author(s): Stefan Boettcher and Shanshan Li

We introduce a framework to analyze quantum algorithms with the renormalization group (RG). To this end, we present a detailed analysis of the real-space RG for discrete-time quantum walks on fractal networks and show how deep insights into the analytic structure as well as generic results about the...

[Phys. Rev. A 97, 012309] Published Fri Jan 12, 2018

Pilot-multiplexed continuous-variable quantum key distribution with a real local oscillator


Author(s): Tao Wang, Peng Huang, Yingming Zhou, Weiqi Liu, and Guihua Zeng

We propose a pilot-multiplexed continuous-variable quantum key distribution (CVQKD) scheme based on a local local oscillator (LLO). Our scheme utilizes time-multiplexing and polarization-multiplexing techniques to dramatically isolate the quantum signal from the pilot, employs two heterodyne detecto...

[Phys. Rev. A 97, 012310] Published Fri Jan 12, 2018

Entanglement and dynamical phase transition in a spin-orbit-coupled Bose-Einstein condensate


Author(s): F. X. Sun, W. Zhang, Q. Y. He, and Q. H. Gong

Characterizing quantum phase transitions through quantum correlations has been deeply developed for a long time, while the connections between dynamical phase transitions (DPTs) and quantum entanglement is not yet well understood. In this work, we show that the time-averaged two-mode entanglement in...

[Phys. Rev. A 97, 012307] Published Thu Jan 11, 2018

Gaussian intrinsic entanglement for states with partial minimum uncertainty


Author(s): Ladislav Mišta, Jr. and Klára Baksová

We develop a recently proposed theory of a quantifier of bipartite Gaussian entanglement called Gaussian intrinsic entanglement (GIE) [L. Mišta, Jr. and R. Tatham, Phys. Rev. Lett. 117, 240505 (2016)]. Gaussian intrinsic entanglement provides a compromise between computable and physically meaningful...

[Phys. Rev. A 97, 012305] Published Wed Jan 10, 2018

Equivalence of qubit-environment entanglement and discord generation via pure dephasing interactions and the resulting consequences


Author(s): Katarzyna Roszak and Łukasz Cywiński

We find that when a qubit initialized in a pure state experiences pure dephasing due to interaction with an environment, separable qubit-environment states generated during the evolution also have zero quantum discord with respect to the environment. What follows is that the set of separable states ...

[Phys. Rev. A 97, 012306] Published Wed Jan 10, 2018

Magic angle for barrier-controlled double quantum dots


Author(s): Xu-Chen Yang and Xin Wang

We show that the exchange interaction of a singlet-triplet spin qubit confined in double quantum dots, when being controlled by the barrier method, is insensitive to a charged impurity lying along certain directions away from the center of the double-dot system. These directions differ from the pola...

[Phys. Rev. A 97, 012304] Published Tue Jan 09, 2018

Mixed-state certification of quantum capacities for noisy communication channels


Author(s): Chiara Macchiavello and Massimiliano F. Sacchi

We extend a recent method to detect lower bounds to the quantum capacity of quantum communication channels by considering realistic scenarios with general input probe states and arbitrary detection procedures at the output. Realistic certification relies on a bound for the coherent information of a ...

[Phys. Rev. A 97, 012303] Published Fri Jan 05, 2018

Secure uniform random-number extraction via incoherent strategies


Author(s): Masahito Hayashi and Huangjun Zhu

To guarantee the security of uniform random numbers generated by a quantum random-number generator, we study secure extraction of uniform random numbers when the environment of a given quantum state is controlled by the third party, the eavesdropper. Here we restrict our operations to incoherent str...

[Phys. Rev. A 97, 012302] Published Thu Jan 04, 2018

Quantum state concentration and classification of multipartite entanglement


Author(s): S. M. Zangi, Jun-Li Li, and Cong-Feng Qiao

Entanglement is a unique feature of quantum theory and has tremendous potential for application. Nevertheless, the complexity of quantum entanglement grows exponentially with an increase in the number of entangled particles. Here we introduce a quantum state concentration scheme which decomposes the...

[Phys. Rev. A 97, 012301] Published Wed Jan 03, 2018

Exact dimension estimation of interacting qubit systems assisted by a single quantum probe


Author(s): Akira Sone and Paola Cappellaro

Estimating the dimension of an Hilbert space is an important component of quantum system identification. In quantum technologies, the dimension of a quantum system (or its corresponding accessible Hilbert space) is an important resource, as larger dimensions determine, e.g., the performance of quant...

[Phys. Rev. A 96, 062334] Published Fri Dec 29, 2017

Experimentally feasible protocol for semiquantum key distribution


Author(s): Michel Boyer, Matty Katz, Rotem Liss, and Tal Mor

Quantum key distribution (QKD) protocols make it possible for two quantum parties to generate a secret shared key. Semiquantum key distribution (SQKD) protocols, such as “QKD with classical Bob” and “QKD with classical Alice” (that have both been proven robust), achieve this goal even if one of the ...

[Phys. Rev. A 96, 062335] Published Fri Dec 29, 2017

Multiqubit Clifford groups are unitary 3-designs


Author(s): Huangjun Zhu

Unitary $t$-designs are a ubiquitous tool in many research areas, including randomized benchmarking, quantum process tomography, and scrambling. Despite the intensive efforts of many researchers, little is known about unitary $t$-designs with $t≥3$ in the literature. We show that the multiqubit Clif...

[Phys. Rev. A 96, 062336] Published Fri Dec 29, 2017

Effect of correlated decay on fault-tolerant quantum computation


Author(s): B. Lemberger and D. D. Yavuz

We analyze noise in the circuit model of quantum computers when the qubits are coupled to a common bosonic bath and discuss the possible failure of scalability of quantum computation. Specifically, we investigate correlated (super-radiant) decay between the qubit energy levels from a two- or three-d...

[Phys. Rev. A 96, 062337] Published Fri Dec 29, 2017

Quantifying entanglement in two-mode Gaussian states


Author(s): Spyros Tserkis and Timothy C. Ralph

Entangled two-mode Gaussian states are a key resource for quantum information technologies such as teleportation, quantum cryptography, and quantum computation, so quantification of Gaussian entanglement is an important problem. Entanglement of formation is unanimously considered a proper measure of...

[Phys. Rev. A 96, 062338] Published Fri Dec 29, 2017

Optimization and experimental realization of the quantum permutation algorithm


Author(s): İ. Yalçınkaya and Z. Gedik

The quantum permutation algorithm provides computational speed-up over classical algorithms for determining the parity of a given cyclic permutation. For its $n$-qubit implementations, the number of required quantum gates scales quadratically with $n$ due to the quantum Fourier transforms included. ...

[Phys. Rev. A 96, 062339] Published Fri Dec 29, 2017

Simulating the Lipkin-Meshkov-Glick model in a hybrid quantum system


Author(s): Yuan Zhou, Sheng-Li Ma, Bo Li, Xiao-Xiao Li, Fu-Li Li, and Peng-Bo Li

We propose an efficient scheme for simulating the Lipkin-Meshkov-Glick (LMG) model with nitrogen-vacancy (NV) center ensembles in diamond magnetically coupled to superconducting coplanar waveguide cavities. With the assistance of external microwave driving fields, we show that the interaction of the...

[Phys. Rev. A 96, 062333] Published Thu Dec 28, 2017

Ising formulation of associative memory models and quantum annealing recall


Author(s): Siddhartha Santra, Omar Shehab, and Radhakrishnan Balu

Associative memory models, in theoretical neuro- and computer sciences, can generally store at most a linear number of memories. Recalling memories in these models can be understood as retrieval of the energy minimizing configuration of classical Ising spins, closest in Hamming distance to an imperf...

[Phys. Rev. A 96, 062330] Published Wed Dec 27, 2017

Entanglement-assisted classical communication can simulate classical communication without causal order


Author(s): Seiseki Akibue, Masaki Owari, Go Kato, and Mio Murao

Phenomena induced by the existence of entanglement, such as nonlocal correlations, exhibit characteristic properties of quantum mechanics distinguishing from classical theories. When entanglement is accompanied by classical communication, it enhances the power of quantum operations jointly performed...

[Phys. Rev. A 96, 062331] Published Wed Dec 27, 2017

Coherence of assistance and regularized coherence of assistance


Author(s): Ming-Jing Zhao, Teng Ma, and Shao-Ming Fei

We study the relation between the coherence of assistance and the regularized coherence of assistance introduced by Chitambar et al. [E. Chitambar et al., Phys. Rev. Lett. 116, 070402 (2016)]. The necessary and sufficient conditions that these two quantities coincide are provided. Detailed examples...

[Phys. Rev. A 96, 062332] Published Wed Dec 27, 2017

Protocol for generating multiphoton entangled states from quantum dots in the presence of nuclear spin fluctuations


Author(s): Emil V. Denning, Jake Iles-Smith, Dara P. S. McCutcheon, and Jesper Mork

Multiphoton entangled states are a crucial resource for many applications in quantum information science. Semiconductor quantum dots offer a promising route to generate such states by mediating photon-photon correlations via a confined electron spin, but dephasing caused by the host nuclear spin env...

[Phys. Rev. A 96, 062329] Published Tue Dec 26, 2017

Tomography and generative training with quantum Boltzmann machines


Author(s): Mária Kieferová and Nathan Wiebe

The promise of quantum neural nets, which utilize quantum effects to model complex data sets, has made their development an aspirational goal for quantum machine learning and quantum computing in general. Here we provide methods of training quantum Boltzmann machines. Our work generalizes existing m...

[Phys. Rev. A 96, 062327] Published Fri Dec 22, 2017

Determination of any pure spatial qudits from a minimum number of measurements by phase-stepping interferometry


Author(s): Quimey Pears Stefano, Lorena Rebón, Silvia Ledesma, and Claudio Iemmi

We present a proof-of-principle demonstration of a method to characterize any pure spatial qudit of arbitrary dimension $d$, which is based on the classic phase-shift interferometry technique. In the proposed scheme a total of only $4d$ measurement outcomes are needed, implying a significant reducti...

[Phys. Rev. A 96, 062328] Published Fri Dec 22, 2017

Enhancing coherence of a state by stochastic strictly incoherent operations


Author(s): C. L. Liu, Yan-Qing Guo, and D. M. Tong

In this paper, we address the issue of enhancing coherence of a state under stochastic strictly incoherent operations. Based on the ${l}_{1}$ norm of coherence, we obtain the maximal value of coherence that can be achieved for a state undergoing a stochastic strictly incoherent operation and the max...

[Phys. Rev. A 96, 062325] Published Thu Dec 21, 2017

Quantum state engineering using one-dimensional discrete-time quantum walks


Author(s): Luca Innocenti, Helena Majury, Taira Giordani, Nicolò Spagnolo, Fabio Sciarrino, Mauro Paternostro, and Alessandro Ferraro

Quantum state preparation in high-dimensional systems is an essential requirement for many quantum-technology applications. The engineering of an arbitrary quantum state is, however, typically strongly dependent on the experimental platform chosen for implementation, and a general framework is still...

[Phys. Rev. A 96, 062326] Published Thu Dec 21, 2017

Quantum supremacy in constant-time measurement-based computation: A unified architecture for sampling and verification


Author(s): Jacob Miller, Stephen Sanders, and Akimasa Miyake

While quantum speed-up in solving certain decision problems by a fault-tolerant universal quantum computer has been promised, a timely research interest includes how far one can reduce the resource requirement to demonstrate a provable advantage in quantum devices without demanding quantum error cor...

[Phys. Rev. A 96, 062320] Published Wed Dec 20, 2017

Verification of hypergraph states


Author(s): Tomoyuki Morimae, Yuki Takeuchi, and Masahito Hayashi

Hypergraph states are generalizations of graph states where controlled-$Z$ gates on edges are replaced with generalized controlled-$Z$ gates on hyperedges. Hypergraph states have several advantages over graph states. For example, certain hypergraph states, such as the Union Jack states, are universa...

[Phys. Rev. A 96, 062321] Published Wed Dec 20, 2017

Tree tensor network approach to simulating Shor's algorithm


Author(s): Eugene Dumitrescu

Constructively simulating quantum systems furthers our understanding of qualitative and quantitative features which may be analytically intractable. In this paper, we directly simulate and explore the entanglement structure present in the paradigmatic example for exponential quantum speedups: Shor's...

[Phys. Rev. A 96, 062322] Published Wed Dec 20, 2017

Analysis of a parametrically driven exchange-type gate and a two-photon excitation gate between superconducting qubits


Author(s): Marco Roth, Marc Ganzhorn, Nikolaj Moll, Stefan Filipp, Gian Salis, and Sebastian Schmidt

A current bottleneck for quantum computation is the realization of high-fidelity two-qubit quantum operations between two or more quantum bits in arrays of coupled qubits. Gates based on parametrically driven tunable couplers offer a convenient method to entangle multiple qubits by selectively activ...

[Phys. Rev. A 96, 062323] Published Wed Dec 20, 2017

Experimental realization of self-guided quantum coherence freezing


Author(s): Shang Yu, Yi-Tao Wang, Zhi-Jin Ke, Wei Liu, Wen-Hao Zhang, Geng Chen, Jian-Shun Tang, Chuan-Feng Li, and Guang-Can Guo

Quantum coherence is the most essential characteristic of quantum physics, specifcially, when it is subject to the resource-theoretical framework, it is considered as the most fundamental resource for quantum techniques. Other quantum resources, e.g., entanglement, are all based on coherence. Theref...

[Phys. Rev. A 96, 062324] Published Wed Dec 20, 2017

Upper bounds on secret-key agreement over lossy thermal bosonic channels


Author(s): Eneet Kaur and Mark M. Wilde

Upper bounds on the secret-key-agreement capacity of a quantum channel serve as a way to assess the performance of practical quantum-key-distribution protocols conducted over that channel. In particular, if a protocol employs a quantum repeater, achieving secret-key rates exceeding these upper bound...

[Phys. Rev. A 96, 062318] Published Tue Dec 19, 2017

Regularized maximum pure-state input-output fidelity of a quantum channel


Author(s): Moritz F. Ernst and Rochus Klesse

As a toy model for the capacity problem in quantum information theory we investigate finite and asymptotic regularizations of the maximum pure-state input-output fidelity $F(\mathcal{N})$ of a general quantum channel $\mathcal{N}$. We show that the asymptotic regularization $\stackrel{̃}{F}(\mathcal...

[Phys. Rev. A 96, 062319] Published Tue Dec 19, 2017

Evaluation of counterfactuality in counterfactual communication protocols


Author(s): D. R. M. Arvidsson-Shukur, A. N. O. Gottfries, and C. H. W. Barnes

We provide an in-depth investigation of parameter estimation in nested Mach-Zehnder interferometers (NMZIs) using two information measures: the Fisher information and the Shannon mutual information. Protocols for counterfactual communication have, so far, been based on two different definitions of c...

[Phys. Rev. A 96, 062316] Published Mon Dec 18, 2017

Classical multiparty computation using quantum resources


Author(s): Marco Clementi, Anna Pappa, Andreas Eckstein, Ian A. Walmsley, Elham Kashefi, and Stefanie Barz

In this work, we demonstrate a way to perform classical multiparty computing among parties with limited computational resources. Our method harnesses quantum resources to increase the computational power of the individual parties. We show how a set of clients restricted to linear classical processin...

[Phys. Rev. A 96, 062317] Published Mon Dec 18, 2017

Dissipative preparation of steady Greenberger-Horne-Zeilinger states for Rydberg atoms with quantum Zeno dynamics


Author(s): X. Q. Shao, J. H. Wu, X. X. Yi, and Gui-Lu Long

Inspired by a recent work [F. Reiter, D. Reeb, and A. S. Sørensen, Phys. Rev. Lett. 117, 040501 (2016)], we present a simplified proposal for dissipatively preparing a Greenberger-Horne-Zeilinger (GHZ) state of three Rydberg atoms in a cavity. The $Z$ pumping is implemented under the action of the s...

[Phys. Rev. A 96, 062315] Published Fri Dec 15, 2017

Experimental study of a quantum random-number generator based on two independent lasers


Author(s): Shi-Hai Sun and Feihu Xu

A quantum random-number generator (QRNG) can produce true randomness by utilizing the inherent probabilistic nature of quantum mechanics. Recently, the spontaneous-emission quantum phase noise of the laser has been widely deployed for quantum random-number generation, due to its high rate, its low c...

[Phys. Rev. A 96, 062314] Published Thu Dec 14, 2017

Steady many-body entanglements in dissipative systems


Author(s): G. D. de Moraes Neto, V. F. Teizen, V. Montenegro, and E. Vernek

We propose a dissipative method for the preparation of many-body steady entangled states in spin and fermionic chains. The scheme is accomplished by means of an engineered set of Lindbladians acting over the eigenmodes of the system, whose spectrum is assumed to be resolvable. We apply this idea to ...

[Phys. Rev. A 96, 062313] Published Wed Dec 13, 2017

Evolution of entanglement under an Ising-like Hamiltonian with particle losses


Author(s): Konrad Szymański and Krzysztof Pawłowski

We present an analytical compact solution for the density matrix and all correlation functions of two collective-macroscopic spins evolving via an Ising-like Hamiltonian in the presence of particle losses. The losses introduce nonlocal phase noise which destroys highly entangled states arising in th...

[Phys. Rev. A 96, 062312] Published Tue Dec 12, 2017

Detecting Gaussian entanglement via extractable work


Author(s): Matteo Brunelli, Marco G. Genoni, Marco Barbieri, and Mauro Paternostro

We show how the presence of entanglement in a bipartite Gaussian state can be detected by the amount of work extracted by a continuous-variable Szilard-like device, where the bipartite state serves as the working medium of the engine. We provide an expression for the work extracted in such a process...

[Phys. Rev. A 96, 062311] Published Mon Dec 11, 2017

Symmetric three-qubit-state invariants


Author(s): Alexander Meill and David A. Meyer

For pure symmetric three-qubit states there are only three algebraically independent entanglement measures; one choice is the pairwise concurrence $\mathcal{C}$, the three-tangle $τ$, and the Kempe invariant $κ$. Using a canonical form for symmetric $n$-qubit states derived from their Majorana repre...

[Phys. Rev. A 96, 062310] Published Fri Dec 08, 2017

Continuous-variable quantum key distribution with a leakage from state preparation


Author(s): Ivan Derkach, Vladyslav C. Usenko, and Radim Filip

We address side-channel leakage in a trusted preparation station of continuous-variable quantum key distribution with coherent and squeezed states. We consider two different scenarios: multimode Gaussian modulation, directly accessible to an eavesdropper, or side-channel loss of the signal states pr...

[Phys. Rev. A 96, 062309] Published Thu Dec 07, 2017

Triangle inequalities in coherence measures and entanglement concurrence


Author(s): Yue Dai, Wenlong You, Yuli Dong, and Chengjie Zhang

We provide detailed proofs of triangle inequalities in coherence measures and entanglement concurrence. If a rank-2 state $ϱ$ can be expressed as a convex combination of two pure states, i.e., $ϱ={p}_{1}|{ψ}_{1}〉〈{ψ}_{1}|+{p}_{2}|{ψ}_{2}〉〈{ψ}_{2}|$, a triangle inequality can be established as $|E(|{...

[Phys. Rev. A 96, 062308] Published Wed Dec 06, 2017

Continuous-variable sampling from photon-added or photon-subtracted squeezed states


Author(s): U. Chabaud, T. Douce, D. Markham, P. van Loock, E. Kashefi, and G. Ferrini

We introduce a family of quantum circuits in continuous variables and we show that, relying on the widely accepted conjecture that the polynomial hierarchy of complexity classes does not collapse, their output probability distribution cannot be efficiently simulated by a classical computer. These ci...

[Phys. Rev. A 96, 062307] Published Tue Dec 05, 2017

Practical resources and measurements for lossy optical quantum metrology


Author(s): Changhun Oh, Su-Yong Lee, Hyunchul Nha, and Hyunseok Jeong

We study the sensitivity of phase estimation in a lossy Mach-Zehnder interferometer (MZI) using two general, and practical, resources generated by a laser and a nonlinear optical medium with passive optimal elements, which are readily available in the laboratory: One is a two-mode separable coherent...

[Phys. Rev. A 96, 062304] Published Mon Dec 04, 2017

Reliable computation from contextual correlations


Author(s): André L. Oestereich and Ernesto F. Galvão

An operational approach to the study of computation based on correlations considers black boxes with one-bit inputs and outputs, controlled by a limited classical computer capable only of performing sums modulo-two. In this setting, it was shown that noncontextual correlations do not provide any ext...

[Phys. Rev. A 96, 062305] Published Mon Dec 04, 2017