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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

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

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