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

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