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Based on the novel idea of twin-field quantum key distribution, we present a

sending-or-not-sending twin-field fault tolerant quantum key distribution

protocol. Our protocol can access a secure distance longer than 700 km even

though the misalignment error rate is $15\%$. In the case of zero alignment

error, our protocol can exceeds a secure distance of 800 km. Thanks to the

novel idea of TF-QKD !

The purpose of this paper is to present a network realization theory for a

class of mixed quantum-classical linear stochastic systems. Two forms, the

standard form and the general form, of this class of linear mixed

quantum-classical systems are proposed. Necessary and sufficient conditions for

their physical realizability are derived. Based on these physical realizability

conditions, a network synthesis theory for this class of linear mixed

quantum-classical systems is developed, which clearly exhibits the quantum

We introduce collective geometric phases of bosons and fermions interfering

on a linear unitary multiport, where each phase depends on the internal states

of the particles, not affected by the multiport, and corresponds to a cycle of

the symmetric group. We show that quantum interference of $N$ particles in

generic pure internal states, i.e., with no pair being orthogonal, is governed

by $(N-1)(N-2)/2$ independent triad phases (each involving only three

particles). The deterministic distinguishability, preventing quantum

We develop a theory to describe dynamics of a non-stationary open quantum

system interacting with a hybrid environment, which includes high-frequency and

low-frequency noise components. One part of the system-bath interaction is

treated in a perturbative manner, whereas the other part is considered exactly.

This approach allows us to derive a set of master equations where the

relaxation rates are expressed as convolutions of the Bloch-Redfield and Marcus

formulas. Our theory enables analysis of systems that have extremely small

Quantum machine learning carries the promise to revolutionize information and

communication technologies. While a number of quantum algorithms with potential

exponential speedups have been proposed already, it is quite difficult to

provide convincing evidence that quantum computers with quantum memories will

be in fact useful to solve real-world problems. Our work makes considerable

progress towards this goal.

The error in estimating the separation of a pair of incoherent sources from

radiation emitted by them and subsequently captured by an imager is

fundamentally bounded below by the inverse of the corresponding quantum Fisher

information (QFI) matrix. We calculate the QFI for estimating the full

three-dimensional (3D) pair separation vector, extending previous work on pair

separation in one and two dimensions. We also show that the pair-separation QFI

is, in fact, identical to source localization QFI, which underscores the

Processes that break molecular bonds are typically observed with molecules

occupying a mixture of quantum states and successfully described with

quasiclassical models, while a few studies have explored the distinctly quantum

mechanical low-energy regime. Here we use photodissociation of diatomic

strontium molecules to demonstrate the crossover from the ultracold, quantum

regime where the photofragment angular distributions strongly depend on the

kinetic energy, to the energy-independent quasiclassical regime. Using

We analyze a basis-independent definition of quantum coherence. The maximally

mixed state is used as the reference state, which allows for a way of defining

coherence that is invariant under arbitrary unitary transformations. The

basis-independent approach is applied to finding the distri- bution of the

coherence within a multipartite system, where the contributions due to

correlations between the subsystems and within each subsystem are isolated. The

use of the square root of the Jensen-Shannon divergence allows for inequality

We investigate the effects of disorder and lattice geometry against

localization phenomenon in a weakly interacting ultracold bosonic gas confined

in a 2D optical lattice. The behaviour of the quantum fluid is studied as a

function of disorder strength, considering lattices of sizes similar to current

experiments at the mean-field level. Performing computational experiments, we

find that the disorder induced localization transition strongly depends on the

geometry of the system. The coordination number determines how fast this

Quantum field theory (QFT) in classical spacetime has revealed interesting

and puzzling aspects about gravitational systems, in particular black hole

thermodynamics and its information processing. Although quantum gravitational

effects may be relevant for a better understanding of these topics, a commonly

accepted framework for studying QFT with quantum gravitational effects is

missing. We present a theory for studying quantum fields in the presence of

quantum indefinite causal structure. This theory incorporates quantum