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Author(s): Victoria Lipinska, Gláucia Murta, and Stephanie Wehner

We consider the task of anonymously transmitting a quantum message in a network. We present a protocol that accomplishes this task using the $W$ state and we analyze its performance in a quantum network where some form of noise is present. We then compare the performance of our protocol with some of...

[Phys. Rev. A 98, 052320] Published Fri Nov 16, 2018

Author(s): Tanjung Krisnanda, Ray Ganardi, Su-Yong Lee, Jaewan Kim, and Tomasz Paterek

Noncommutativity is one of the most elementary nonclassical features of quantum observables. Here we propose a method to detect noncommutativity of interaction Hamiltonians of two probe objects coupled via a mediator. If these objects are open to their local environments, our method reveals nondecom...

[Phys. Rev. A 98, 052321] Published Fri Nov 16, 2018

Author(s): Max Schemmer and Isabelle Bouchoule

We report the demonstration of cooling by three-body losses in a Bose gas. We use a harmonically confined one-dimensional (1D) Bose gas in the quasicondensate regime and, as the atom number decreases under the effect of three-body losses, the temperature $T$ drops up to a factor of 4. The ratio ${k}...

[Phys. Rev. Lett. 121, 200401] Published Fri Nov 16, 2018

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We revisit the calculation of multi-interval modular Hamiltonians for free

fermions using a Euclidean path integral approach. We show how the

multi-interval modular flow is obtained by glueing together the single interval

modular flows. Using this relation, we obtain an exact expression for the

multi-interval modular Hamiltonian and entanglement entropy in agreement with

previous work. Our procedure allows for a simple derivation of the non-local

field theory describing the reduced density matrix, and makes manifest it's

We study theoretically entanglement and operator growth in a spin system

coupled to an environment, which is modeled with classical dephasing noise.

Using exact numerical simulations we show that the entanglement growth and its

fluctuations are described by the Kardar-Parisi-Zhang equation. Moreover, we

find that the wavefront in the out-of-time ordered correlator (OTOC), which is

a measure for the operator growth, propagates linearly with the butterfly

In 1939, von Neumann argued for the equivalence of the thermodynamic entropy

and $-\text{Tr}\rho\ln\rho$, since known as the von Neumann entropy. Hemmo and

Shenker (2006) recently challenged this argument by pointing out an alleged

discrepancy between the two entropies in the single particle case, concluding

that they must be distinct. In this article, their argument is shown to be

problematic as it a) allows for a violation of the second law of thermodynamics

and b) is based on an incorrect calculation of the von Neumann entropy.

Large scale quantum computing is highly anticipated, and quantum circuit

design automation needs to keep up with the transition from small scale to

large scale problems. Methods to support fast quantum circuit manipulations

(e.g.~gate replacement, wire reordering, etc.) or specific circuit analysis

operations have not been considered important and have been often implemented

in a naive manner thus far. For example, quantum circuits are usually

represented in term of one-dimensional gate lists or as directed acyclic

Nonadiabatic holonomic quantum computation has received increasing attention

due to its robustness against control errors as well as high-speed realization.

The original protocol of nonadiabatic holonomic one-qubit gates has been

experimentally demonstrated with superconducting transmon qutrit. However, the

original protocol requires two noncommuting gates to realize an arbitrary

one-qubit gate, which doubles the exposure time of gates to error sources and

therefore makes the gates vulnerable to environment-induced decoherence.

We evaluate the quantum witness based on the no-signaling-in-time condition

of a damped two-level system for nonselective generalized measurements of

varying strength. We explicitly compute its dependence on the measurement

strength for a generic example. We find a vanishing derivative for weak

measurements and an infinite derivative in the limit of projective

measurements. The quantum witness is hence mostly insensitive to the strength

of the measurement in the weak measurement regime and displays a singular,

The dynamics of mixedness and entanglement is examined by solving the

time-dependent Schr\"{o}dinger equation for three coupled harmonic oscillator

system with arbitrary time-dependent frequency and coupling constants

parameters. We assume that part of oscillators is inaccessible and remaining

oscillators accessible. We compute the dynamics of entanglement between

inaccessible and accessible oscillators. In order to show the dynamics

pictorially we introduce three quenched models. In the quenched models both