A definition for the entanglement entropy in both Abelian and non-Abelian
gauge theories has been given in the literature, based on an extended Hilbert
space construction. The result can be expressed as a sum of two terms, a
classical term and a quantum term. It has been argued that only the quantum
term is extractable through the processes of quantum distillation and dilution.
Here we consider gauge theories in the continuum limit and argue that quite

We analyze vacuum tunneling in quantum field theory in a general formalism by
using the Wigner representation. In the standard instanton formalism, one
usually approximates the initial false vacuum state by an eigenstate of the
field operator, imposes Dirichlet boundary conditions on the initial field
value, and evolves in imaginary time. This approach does not have an obvious
physical interpretation. However, an alternative approach does have a physical
interpretation: in quantum field theory, tunneling can happen via classical

We realize Landau-Streater (LS) and Werner-Holevo (WH) quantum channels for
qutrits on the IBM quantum computers. These channels correspond to interaction
between the qutrit and its environment that result in the globally unitarily
covariant qutrit transformation violating multiplicativity of the maximal
$p$-norm. Our realization of LS and WH channels is based on embedding qutrit
states into states of two qubits and using single-qubit and two-qubit CNOT
gates to implement the specific interaction. We employ the standard quantum

We develop a rigorous theoretical approach for analyzing inelastic scattering
of photon pairs in arrays of two-level qubits embedded in a waveguide. Our
analysis reveals strong enhancement of the scattering when the energy of
incoming photons resonates with the double-excited subradiant states. We
identify the role of different double-excited states in the scattering such as
superradiant, subradiant, and twilight states, being a product of
single-excitation bright and subradiant states. Importantly, the N-excitation

The sending-or-not-sending (SNS) protocol of the twin-field quantum key
distribution (TFQKD) can tolerant large misalignment error and its key rate can
exceed the bound of repeaterless QKD. But the original SNS protocol requires
the two users to use the same source parameters. Here we propose a general
protocol with asymmetric source parameters and give the security proof of this
protocol. Our general protocol has a much better performance than that of the
original SNS protocol when the channel of the system is asymmetric.

We consider identical quantum bosons with weak contact interactions in a
two-dimensional isotropic harmonic trap. When the interactions are turned off,
the energy levels are equidistant and highly degenerate. At linear order in the
coupling parameter, these degenerate levels split, and we study the patterns of
this splitting. It turns out that the problem is mathematically identical to
diagonalizing the quantum resonant system of the two-dimensional
Gross-Pitaevskii equation, whose classical counterpart has been previously

We briefly summarize the main steps leading to the Faddeev-Yakubovsky
equations in configuration space for N=3, 4 and 5 interacting particles.

The standard benchmark for teleportation is the average fidelity of
teleportation and according to this benchmark not all states are useful for
teleportation. It was recently shown however that all entangled states lead to
non-classical teleportation, with there being no classical scheme able to
reproduce the states teleported to Bob. Here we study the operational
significance of this result. On the one hand we demonstrate that every state is
useful for teleportation if a generalisation of the average fidelity of

The quest to identify the best heat engine has been at the center of science
and technology. Thermoelectric nanoscale heat engines convert heat flows into
useful work in the form of electrical power and promise the realization of
on-chip power production. Considerable studies have so far revealed the
potentials to yield an enhanced efficiency originating from quantum confinement
effects and energy-dependent transport properties. However, the full benefit of

Steady-state thermoelectric machines convert heat into work by driving a
thermally-generated charge current against a voltage gradient. In this work, we
propose a new class of steady-state heat engines operating in the quantum
regime, where a quasi-periodic tight-binding model that features a mobility
edge forms the working medium. In particular, we focus on a generalization of
the paradigmatic Aubrey-Andr\'e-Harper (AAH) model, known to display a
single-particle mobility edge that separates the energy spectrum into regions