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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