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

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