The problem of a particle in a box is probably the simplest problem in
quantum mechanics which allows for significant insight into the nature of
quantum systems and thus is a cornerstone in the teaching of quantum mechanics.
In relativistic quantum mechanics this problem allows also to highlight the
implications of special relativity for quantum physics, namely the effect that
spin has on the quantized energy spectra. To illustrate this point, we solve
the problem of a spin zero relativistic particle in a one- and

We analyze a modified Bose-Hubbard model, where two cavities having on-site
Kerr interactions are subject to two-photon driving and correlated dissipation.
We derive an exact solution for the steady state of this interacting
driven-dissipative system, and use it show that the system permits the
preparation and stabilization of pure entangled non-Gaussian states, so-called
entangled cat states. Unlike previous proposals for dissipative stabilization
of such states, our approach requires only a linear coupling to a single

Quantum metrology allows for a tremendous boost in the accuracy of
measurement of diverse physical parameters. The estimation of a rotation
constitutes a remarkable example of this quantum-enhanced precision. The
recently introduced Kings of Quantumness are especially germane for this task
when the rotation axis is unknown, as they have a sensitivity independent of
that axis and they achieve a Heisenberg-limit scaling. Here, we report the
experimental realization of these states by generating up to 21-dimensional

We provide a short proof of the quantisation of the Hall conductance for
gapped interacting quantum lattice systems on the two-dimensional torus. This
is not new and should be seen as an adaptation of the proof of [1], simplified
by making the stronger assumption that the Hamiltonian remains gapped when
threading the torus with fluxes. We argue why this assumption is very
plausible. The conductance is given by Berry's curvature and our key auxiliary
result is that the curvature is asymptotically constant across the torus of

We numerically investigate the link between the delocalization-localization
transition and bipartite entanglement entropy in a disordered long-range
hopping model of non-interacting spinless fermions by studying various static
and dynamical quantities. This includes the inverse paricipation ratio,
level-statistics, entanglement entropy and number fluctuations in the subsytem
along with quench and wave-packet dynamics. Finite systems show delocalized,
quasi-localized and localized phases. The delocalized phase shows strong

A method is proposed to characterize a high-dimensional quantum channel with
the aid of classical light. It uses a single nonseparable input optical field
that contains correlations between spatial modes and wavelength to determine
the effect of the channel on the spatial degrees of freedom. The channel
estimation process incorporates spontaneous parametric upconversion (sum
frequency generation) to perform the necessary measurements.

We introduce and analyze a new type of decoding algorithm called General
Color Clustering (GCC), based on renormalization group methods, to be used in
qudit color codes. The performance of this decoder is analyzed under code
capacity depolarizing noise, and is used to obtain the first fault-tolerant
threshold estimates for qudit 6-6-6 color codes. The proposed decoder is
compared with similar decoding schemes for qudit surface codes as well as the
current leading qubit decoders for both sets of codes. We find that, as with

Quantum coherence is of potential applications from quantum computation using
simple atoms to optimized energy transports in biomolecular complexes. Here, a
time-resolved spectroscopic protocol exploiting a terahertz-assisted field
locked with the probe pulse is proposed for full observations of the evolution
of elements in transient density matrix. Coherence contributions of
off-diagonal elements are detectable in the spotlight. The coherence dynamics
for photoexcitation of hydrogen atom are explicitly demonstrated with

A triple-quantum-dot system can be operated as either an exchange-only qubit
or a resonant-exchange qubit. While it is generally believed that the decisive
advantage of the resonant-exchange qubit is the suppression of charge noise
because it is operated at a sweet spot, we show that the leakage is also an
important factor. Through molecular-orbital-theoretic calculations, we show
that when the system is operated in the exchange-only scheme, the leakage to

We present a security proof for establishing private entanglement by means of
recurrence-type entanglement distillation protocols over noisy quantum
channels. We consider protocols where the local devices are imperfect, and show
that nonetheless a confidential quantum channel can be established, and used to
e.g. perform distributed quantum computation in a secure manner. While our
results are not fully device independent (which we argue to be unachievable in