We investigate the Unruh quantum Otto heat engine with level degeneracy. An

effectively two level system, where the ground state is non-degenerate and the

excited state is $n$-fold degenerate, is acting as the working substance, and

the vacuum of massless free scalar field serves as a thermal bath via the Unruh

effect. We calculate the heat and work at each step of the Unruh quantum Otto

cycle and study the features of the heat engine. The efficiency of the heat

# All

We theoretically investigate the simulation of moving cavities in a

superconducting circuit setup. In particular, we consider a recently proposed

experimental scenario where the phase of the cavity field is used as a moving

clock. By computing the error made when simulating the cavity trajectory with

SQUIDs, we identify parameter regimes where the correspondence holds, and where

time dilation, as well as corrections due to clock size and particle creation

coefficients, are observable. These findings may serve as a guideline when

Surface quantum error-correcting codes are the leading proposal for

fault-tolerance within quantum computers. There are different techniques for

implementing the surface code, and lattice surgery is considered the most

resource efficient method. Resource efficiency refers to the number of physical

qubits an the time necessary for executing a quantum computation. We present

OpenSurgery, a scalable tool for the preparation of lattice surgery implemented

quantum circuits. It is a first step towards techniques that aid quantum

High performance quantum information processing requires efficient control of

undesired decohering effects, which are present in realistic quantum dynamics.

To deal with this issue, a powerful strategy is to employ transitionless

quantum driving (TQD), where additional fields are added to speed up the

evolution of the quantum system, achieving a desired state in a short time in

comparison with the natural decoherence time scales. In this paper, we provide

Recently, apparent non-physical implications of non-Hermitian quantum

mechanics (NHQM) have been discussed in the literature. In particular, the

apparent violation of the non-signaling theorem, discrimination of

non-orthogonal states, and the increase of quantum entanglement by local

operations were reported and, therefore, NHQM was not considered as a

fundamental theory. Here we show that these and other no-go principles

(including the no-cloning and no-deleting theorems) of conventional quantum

A Markovian process of a system is defined classically as a process in which

the future state of the system is fully determined by only its present state,

not by its previous history. There have been several measures of

non-Markovianity to quantify the degrees of non-Markovian effect in a process

of an open quantum system based on information backflow from the environment to

the system. However, the condition for the witness of the system information

backflow does not coincide with the classical definition of a Markovian

We investigate a generic quantum walk starting in state $|\psi_\text{in}

\rangle$, on a finite graph, under repeated detection attempts aimed to find

the particle on node $|d\rangle$. For the corresponding classical random walk

the total detection probability $P_{{\rm det}}$ is unity. Due to destructive

interference one may find initial states $|\psi_\text{in}\rangle$ with $P_{{\rm

det}}<1$. We first obtain an uncertainty relation which yields insight on this

We investigate a form of quantum search, where a detector repeatedly probes

some quantum particle with fixed rate $1/\tau$ until it is first successful.

This is a quantum version of the first-passage problem. We focus on the total

probability, $P_\text{det}$, that the particle is eventually detected in some

state, for example on a node $r_\text{d}$ on a graph, after an arbitrary number

of detection attempts. For finite graphs, and more generally for systems with a

The establishment of a world-wide quantum communication network relies on the

synergistic integration of satellite-based links and fiber-based networks. The

first are helpful for long-distance communication, as the photon losses

introduced by the optical fibers are too detrimental for lengths greater than

about 200 km. This work aims at giving, on the one hand, a comprehensive and

fundamental model for the losses suffered by the quantum signals during the

propagation along an atmospheric free-space link. On the other hand, a

We propose to use the complex quantum dynamics of a massive particle in a

non-quadratic potential to reconstruct an initial unknown motional quantum

state. We theoretically show that the reconstruction can be efficiently done by

measuring the mean value and the variance of the position quantum operator at

different instances of time in a quartic potential. We train a neural network

to successfully solve this hard regression problem. We discuss the experimental

feasibility of the method by analyzing the impact of decoherence and