# All

## Quantum circuit structure learning. (arXiv:1905.09692v1 [quant-ph])

We propose an efficient method for simultaneously learning both the structure
and parameter values of quantum circuits with only a small computational
overhead. Shallow circuits trained using structure learning perform
significantly better than circuits trained using parameter updates alone,
making this method particularly suitable for use on noisy intermediate-scale
quantum computers. We demonstrate the method for training a variational quantum
eigensolver for finding the ground states of Lithium Hydride and the Heisenberg

## Reduced Density-Matrix Approach to Strong Matter-Photon Interaction. (arXiv:1812.05562v2 [quant-ph] UPDATED)

We present a first-principles approach to electronic many-body systems
strongly coupled to cavity modes in terms of matter-photon one-body reduced
density matrices. The theory is fundamentally non-perturbative and thus
captures not only the effects of correlated electronic systems but accounts
also for strong interactions between matter and photon degrees of freedom. We
do so by introducing a higher-dimensional auxiliary system that maps the
coupled fermion-boson system to a dressed fermionic problem. This reformulation

## Characterization of an underwater channel for quantum communications in the Ottawa River. (arXiv:1905.09437v1 [quant-ph])

We examine the propagation of optical beams possessing different polarization
states and spatial modes through the Ottawa River in Canada. A Shack-Hartmann
wavefront sensor is used to record the distorted beam's wavefront. The
turbulence in the underwater channel is analysed, and associated Zernike
coefficients are obtained in real-time. Finally, we explore the feasibility of
transmitting polarization states as well as spatial modes through the
underwater channel for applications in quantum cryptography.

## Fine grained uncertainty determines preparation contextuality. (arXiv:1905.09695v1 [quant-ph])

The optimal success probability of a communication game reveals the
fundamental limitations of an operational theory. Quantum advantage of parity
oblivious random access code (PORAC), a communication game, over classical
resources reveals the preparation contextuality of quantum theory [Phys. Rev.
Lett. {\bf{102}}, 010401 (2009)]. Optimal quantum bound for N-dit PORAC game
for any finite dimension was an open problem. Here, we show that the degree of
uncertainty allowed in an operational theory determines the amount of

## Single-layer tensor network study of the Heisenberg model with chiral interactions on a kagome lattice. (arXiv:1812.11436v3 [cond-mat.str-el] UPDATED)

We study the antiferromagnetic kagome Heisenberg model with additional
scalar-chiral interaction by using the infinite projected entangled-pair state
(iPEPS) ansatz. We discuss in detail the implementation of optimization
algorithm in the framework of the single-layer tensor network based on the
corner-transfer matrix technique. Our benchmark based on the full-update
algorithm shows that the single-layer algorithm is stable, which leads to the
same level of accuracy as the double-layer ansatz but with much less

## Kochen-Specker sets in four-dimensional spaces. (arXiv:1905.09443v1 [math.CO])

For the first time we construct an infinite family of Kochen-Specker sets in
a space of fixed dimension, namely in R^4. While most of the previous
constructions of Kochen-Specker sets have been based on computer search, our
construction is analytical and it comes with a short, computer-free proof.

## Optimal Dispersive Readout of a Spin Qubit with a Microwave Cavity. (arXiv:1905.09702v1 [cond-mat.mes-hall])

Strong coupling of semiconductor spin qubits to superconducting microwave
cavities was recently demonstrated. These breakthroughs pave the way for
quantum information processing that combines the long coherence times of
solid-state spin qubits with the long-distance connectivity, fast control, and
fast high-fidelity quantum-non-demolition readout of existing superconducting
qubit implementations. Here, we theoretically analyze and optimize the
dispersive readout of a single spin in a semiconductor double quantum dot (DQD)

## Quantum Networks for Single Photon Detection. (arXiv:1901.09974v2 [quant-ph] UPDATED)

Single photon detection generally consists of several stages: the photon has
to interact with one or more charged particles, its excitation energy will be
converted into other forms of energy, and amplification to a macroscopic signal
must occur, thus leading to a "click." We focus here on the part of the
detection process before amplification (which we have studied in a separate
publication). We discuss how networks consisting of coupled discrete quantum

## Topological phase transition in non-Hermitian quasicrystals. (arXiv:1905.09460v1 [cond-mat.mes-hall])

The discovery of topological phases in non-Hermitian open classical and
quantum systems challenges our current understanding of topological order.
Non-Hermitian systems exhibit unique features with no counterparts in
topological Hermitian models, such as failure of the conventional bulk-boundary
correspondence and non-Hermitian skin effect. Advances in the understanding of
the topological properties of non-Hermitian lattices with translational
invariance have been reported in several recent studies, however little is

## Accuracy enhancing protocols for quantum clocks. (arXiv:1905.09707v1 [quant-ph])

The accuracy of the time information generated by clocks can be enhanced by
allowing them to communicate with each other. Here we consider a basic scenario
where a quantum clock receives a low-accuracy time signal as input and ask
whether it can generate an output of higher accuracy. We propose protocols
that, using a clock with a $d$-dimensional state space, achieve an accuracy
enhancement by a factor $d$ (in the limit of large $d$). If no feedback on the
input signal is allowed, this enhancement is temporary. Conversely, with