Networking plays a ubiquitous role in quantum technology. It is an integral
part of quantum communication and has significant potential for upscaling
quantum computer technologies that are otherwise not scalable. Recently, it was
realized that sensing of multiple spatially distributed parameters may also
benefit from an entangled quantum network. Here we experimentally demonstrate
how sensing of an averaged phase shift among four distributed nodes benefits
from an entangled quantum network. Using a four-mode entangled continuous

The decoy-state method has been developed rapidly in quantum key distribution
(QKD) since it is immune to photon-number splitting attacks. However, two basis
detector efficiency asymmetry, which exists in realistic scenarios, has been
ignored in the prior results. By using the recent 4-intensity decoy-state
optimization protocol, we report the first implementation of high-rate QKD with
asymmetric basis detector efficiency, demonstrating 1.9 to 33.2 times higher

We show that detection of single photons is not subject to the fundamental
limitations that accompany quantum linear amplification of bosonic mode
amplitudes, even though a photodetector does amplify a few-photon input signal
to a macroscopic output signal. Alternative limits are derived for
\emph{nonlinear} photon-number amplification schemes with optimistic
implications for single-photon detection. Four commutator-preserving
transformations are presented: one idealized (which is optimal) and three more

We propose a profound consequence of symmetry towards the axiomatic
derivation of Hilbert space quantum theory. Specifically, we show that the
symmetry of information gain in minimal error state discrimination induces a
non-trivial proviso on the state space structure of a physical theory. The
symmetry considered here puts a restriction on the means of optimal guessing of
a system's state from that of an ensemble. We coin the term information
symmetry (IS) since it constrains the way optimal information gain occurs in

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.