Author(s): Philippe Allard Guérin, Giulia Rubino, and Časlav Brukner

In a recent series of works [Ebler et al., Phys. Rev. Lett. 120, 120502 (2018); arXiv:1809.06655v2; arXiv:1810.10457v2], it has been shown that the quantum superposition of causal order—the quantum switch—offers an enhancement of classical and quantum channel capacity through noisy channels, a phen...

Author(s): Sudipto Singha Roy and Himadri Shekhar Dhar

It is well known that the notions of spatial locality are often lost in quantum systems with long-range interactions, as exhibited by the emergence of phases with exotic long-range order and faster propagation of quantum correlations. We demonstrate here that such induced “quasinonlocal” effects do ...

[Phys. Rev. A 99, 062318] Published Mon Jun 17, 2019

Author(s): Timo Simnacher, Nikolai Wyderka, Cornelia Spee, Xiao-Dong Yu, and Otfried Gühne

Quantum memories are an important building block for quantum information processing. Ideally, these memories preserve the quantum properties of the input. We present general criteria for measures to evaluate the quality of quantum memories. Then we introduce a quality measure based on coherence sati...

[Phys. Rev. A 99, 062319] Published Mon Jun 17, 2019

Author(s): Chang-Kang Hu, Alan C. Santos, Jin-Ming Cui, Yun-Feng Huang, Marcelo S. Sarandy, Chuan-Feng Li, and Guang-Can Guo

Suppressing undesired nonunitary effects is a major challenge in quantum computation and quantum control. In this paper, by considering the adiabatic dynamics in the presence of a surrounding environment, we theoretically and experimentally analyze the robustness of adiabaticity in open quantum syst...

[Phys. Rev. A 99, 062320] Published Mon Jun 17, 2019

Let $H$ be a non trivial subgroup of index $d$ of a free group $G$ and $N$

the normal closure of $H$ in $G$. The coset organization in a subgroup $H$ of

$G$ provides a group $P$ of permutation gates whose common eigenstates are

either stabilizer states of the Pauli group or magic states for universal

quantum computing. A subset of magic states consists of MIC states associated

to minimal informationally complete measurements. It is shown that, in most

cases, the existence of a MIC state entails that the two conditions (i) $N=G$

We present OpenMP versions of C and Fortran programs for solving the

Gross-Pitaevskii equation for a rotating trapped Bose-Einstein condensate (BEC)

in two (2D) and three (3D) spatial dimensions. The programs can be used to

generate vortex lattices and study dynamics of rotating BECs. We use the

split-step Crank-Nicolson algorithm for imaginary- and real-time propagation to

calculate stationary states and BEC dynamics, respectively. The programs

propagate the condensate wave function and calculate several relevant physical

It is shown that Schrodinger's equation and Born's rule are sufficient to

ensure that the states of macroscopic collective coordinate subsystems are

microscopically localized in phase space and that the localized state follows

the classical trajectory with random quantum noise that is indistinguishable

from the pseudo-random noise of classical Brownian motion. This happens because

in realistic systems the localization rate determined by the coupling to the

environment is greater than the Lyapunov exponent that governs chaotic

Cavity optomechanical system involving an optical parametric amplifier (OPA)

can exhibit rich classical and quantum dynamical behaviors. By simply

modulating the frequency of the laser pumping the OPA, we find two interesting

parameter regimes, with one of them enabling to study quantum-classical

correspondence in system dynamics, while there exist no classical counterparts

of the quantum features for the other. For the former regime, as the parametric

gain of OPA increases to a critical value, the classical dynamics of the

Although highly successful, the truncated Wigner approximation (TWA) leaves

out many-body quantum interference between mean-field Gross-Pitaevskii

solutions as well as other quantum effects, and is therefore essentially

classical. Turned around, this implies that if a system's quantum properties

deviate from TWA, they must be exhibiting some quantum phenomenon, such as

localization, diffraction, or tunneling. Here, we consider in detail a

particular interference effect arising from discrete symmetries, which can lead

When a quantum system is divided into two local subsystems, measurements on

the two subsystems can exhibit correlations beyond those possible in a

classical joint probability distribution; these are partially explained by

entanglement, and more generally by a wider class of measures such as the

quantum discord. In this work, I introduce a simple thought experiment defining

a new measure of quantum correlations, which I call the accord, and write the

result as a minimax optimization over unitary matrices. I find the exact result

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