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

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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