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

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

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.

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

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

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.

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)

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

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

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