We show that, by using the quantum orthogonal functions invariant, we are

able to solve a coupled of time dependent harmonic oscillators where all the

time dependent frequencies are arbitrary. We do so, by transforming the time

dependent Hamiltonian of the interaction by a set of unitary operators. In

passing, we show that $N$ time dependent and coupled oscillators have a

generalized orthogonal functions invariant from which we can write a

Ermakov-Lewis invariant.

# All

We investigate, in the framework of open quantum systems, the entanglement

dynamics of two circularly accelerated two-level atoms with the same

centripetal acceleration interacting with a bath of fluctuating electromagnetic

fields in the Minkowski vacuum. We assume that the two atoms rotate

synchronically with their separation perpendicular to the rotating plane, and

study the entanglement degradation, creation, revival, and enhancement by

solving the Markovian master equation. In contrast to the scalar-field case,

We present a scheme for engineering quantum transport dynamics of spin

excitations in a chain of laser-dressed Rydberg atoms, mediated by synthetic

spin-exchange arising from diagonal van der Waals interaction. The dynamic

tunability and long-range interaction feature of our scheme allows for the

exploration of transport physics unattainable in conventional spin systems. As

two concrete examples, we first demonstrate a topological exciton pumping

protocol that facilitates quantized entanglement transfer, and secondly we

Entangled states can be used as secure carriers of information much in the

same way as carriers are used in classical communications. In such protocols,

quantum states are uploaded to the carrier at one end and are downloaded from

it in safe form at the other end, leaving the carrier intact and ready for

reuse. Furthermore, protocols have been designed for performing quantum state

sharing in this way. In this work, we study the robustness of these protocols

Hybrid quantum-classical algorithms such as the quantum approximate

optimization algorithm (QAOA) are considered one of the most promising

approaches for leveraging near-term quantum computers for practical

applications. Such algorithms are often implemented in a variational form,

combining classical optimization methods with a quantum machine to find

parameters to maximize performance. The quality of the QAOA solution depends

heavily on quality of the parameters produced by the classical optimizer.

Entangling quantum systems with different characteristics through the

exchange of photons is a prerequisite for building future quantum networks.

Proving the presence of entanglement between quantum memories for light working

at different wavelengths furthers this goal. Here, we report on a series of

experiments with a thulium-doped crystal, serving as a quantum memory for 794

nm photons, an erbium-doped fibre, serving as a quantum memory for

telecommunication-wavelength photons at 1535 nm, and a source of photon pairs

We determine the quantum Cram\'er-Rao bound for the precision with which the

oscillator frequency and damping constant of a damped quantum harmonic

oscillator in an arbitrary Gaussian state can be estimated. This goes beyond

standard quantum parameter estimation of a single mode Gaussian state for which

typically a mode of fixed frequency is assumed. We present a scheme through

which the frequency estimation can nevertheless be based on the known results

for single-mode quantum parameter estimation with Gaussian states. Based on

We determine the maximum squashed entanglement achievable between sender and

receiver of the noiseless quantum Gaussian attenuators and amplifiers, and

prove that it is achieved sending half of an infinitely squeezed two-mode

vacuum state. The key ingredient of the proof is a lower bound to the squashed

entanglement of the quantum Gaussian states obtained applying a two-mode

squeezing operation to a quantum thermal Gaussian state tensored with the

vacuum state. This is the first lower bound to the squashed entanglement of a

Numerical techniques to efficiently model out-of-equilibrium dynamics in

interacting quantum many-body systems are key for advancing our capability to

harness and understand complex quantum matter. Here we propose a new numerical

approach which we refer to as GDTWA. It is based on a discrete semi-classical

phase-space sampling and allows to investigate quantum dynamics in lattice spin

systems with arbitrary $S\geq 1/2$. We show that the GDTWA can accurately

A number of noncontextual models exist which reproduce different subsets of

quantum theory and admit a no-cloning theorem. Therefore, if one chooses

noncontextuality as one's notion of classicality, no-cloning cannot be regarded

as a nonclassical phenomenon. In this work, however, we show that the

phenomenology of quantum state cloning is indeed nonclassical, but not for the

reasons usually given. Specifically, we focus on the task of state-dependent

cloning and prove that the optimal cloning fidelity predicted by quantum theory