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

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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.