Finding the ground state energy of a Hamiltonian $H$, which describes a

quantum system of several interacting subsystems, is crucial as well for

many-body physics as for various optimization problems. Variety of algorithms

and simulation procedures (either hardware or software based) rely on the

separability approximation, in which one seeks for the minimal expectation

value of $H$ among all product states. We demonstrate that already for systems

with nearest neighbor interactions this approximation is inaccurate, which

# All

In Thouless pumping, although non-flat band has no effects on the

quantization of particle transport, it induces wave-packet dispersion which

hinders the practical applications of Thouless pumping. Indeed, we find that

the dispersion mainly arises from the dynamical phase difference between

individual Bloch states. Here we propose two efficient schemes to suppress the

dispersion in Thouless pumping: a re-localization echo protocol and a

high-order tunneling suppression protocol. In the re-localization echo

It is well-known that observing nonlocal correlations allows us to draw

conclusions about the quantum systems under consideration. In some cases this

yields a characterisation which is essentially complete, a phenomenon known as

self-testing. Self-testing becomes particularly interesting if we can make the

statement robust, so that it can be applied to a real experimental setup. For

the simplest self-testing scenarios the most robust bounds come from the method

In a special representation of complex action theory that we call

``future-included'', we study a harmonic oscillator model defined with a

non-normal Hamiltonian $\hat{H}$, in which a mass $m$ and an angular frequency

$\omega$ are taken to be complex numbers. In order for the model to be sensible

some restrictions on $m$ and $\omega$ are required. We draw a phase diagram in

the plane of the arguments of $m$ and $\omega$, according to which the model is

classified into several types. In addition, we formulate two pairs of

We derive an equation for the time evolution of the natural occupation

numbers for fermionic systems with more than two electrons. The evolution of

such numbers is connected with the symmetry-adapted generalized Pauli exclusion

principle, as well as with the evolution of the natural orbitals and a set of

many-body relative phases. We then relate the evolution of these phases to a

geometrical and a dynamical term, attached to each one of the Slater

determinants appearing in the configuration-interaction expansion of the wave

Bell's theorem implies that any completion of quantum mechanics which uses

hidden variables (that is, preexisting values of all observables) must be

nonlocal in the Einstein sense. This customarily indicates that knowledge of

the hidden variables would permit superluminal communication. Such superluminal

signaling, akin to the existence of a preferred reference frame, is to be

expected. However, here we provide a protocol that allows an observer with

knowledge of the hidden variables to communicate with her own causal past,

A three-state system subjected to a time-dependent Hamiltonian whose bare

energies undergo one or more crossings, depending on the relevant parameters,

is considered, also taking into account the role of dissipation in the

adiabatic following of the Hamiltonian eigenstates. Depending on the fact that

the bare energies are equidistant or not, the relevant population transfer

turns out to be very sensitive to the environmental interaction or relatively

robust. The physical mechanisms on the basis of this behavior are discussed in

Suppressing undesired nonunitary effects is a major challenge in quantum

computation and quantum control. In this work, by considering the adiabatic

dynamics in presence of a surrounding environment, we theoretically and

experimentally analyze the robustness of adiabaticity in open quantum systems.

More specifically, by considering a decohering scenario, we exploit the

validity conditions of the adiabatic approximation as well as its sensitiveness

to the resonance situation, which typically harm adiabaticity in closed

Colour centres with long-lived spins are established platforms for quantum

sensing and quantum information applications. Colour centres exist in different

charge states, each of them with distinct optical and spin properties.

Application to quantum technology requires the capability to access and

stabilize charge states for each specific task. Here, we investigate charge

state manipulation of individual silicon vacancies in silicon carbide, a system

which has recently shown a unique combination of long spin coherence time and

Motivated by recent developments in the realm of matter waves, we explore the

potential of creating solitary waves on the surface of a torus. This is an

intriguing perspective due to the role of curvature in the shape and dynamics

of the coherent structures. We find different families of bright solitary waves

for attractive nonlinearities including ones localized in both angular

directions, as well as waves localized in one direction and homogeneous in the

other. The waves localized in both angular directions have also been