In a many-body quantum system, local operators in Heisenberg picture $O(t) =
e^{i H t} O e^{-i H t}$ spread as time increases. Recent studies have attempted
to find features of that spreading which could distinguish between chaotic and
integrable dynamics. The operator entanglement - the entanglement entropy in
operator space - is a natural candidate to provide such a distinction. Indeed,
while it is believed that the operator entanglement grows linearly with time

Quantum Teleportation is the key communication functionality of the Quantum
Internet, allowing the ``transmission'' of qubits without either the physical
transfer of the particle storing the qubit or the violation of the quantum
mechanical principles. Quantum teleportation is facilitated by the action of
quantum entanglement, a somewhat counter-intuitive physical phenomenon with no
direct counterpart in the classical word. As a consequence, the very concept of

Self-testing refers to a device-independent way to uniquely identify the
state and the measurement for uncharacterized quantum devices. The only
information required comprises the number of measurements, the number of
outputs of each measurement, and the statistics of each measurement. Earlier
results on self-testing of multipartite state were restricted either to Dicke
states or graph states. In this paper, we propose self-testing schemes for a
large family of symmetric three-qubit states, namely the superposition of W

We derive the entanglement entropy of chiral fermions on the circle at
arbitrary temperature. The spin-sector contribution depends only on the total
length of the entangling region, regardless of the configuration of the
intervals. Thus three-partite information provides a global indicator for the
spin boundary conditions. Together with the modular Hamiltonian, our results
provide a systematic way of obtaining relative entropy on the torus.

We formulate an optimization problem of finding optimal Hamiltonians by
analogy to the variational principle. Given a variational ansatz for a
Hamiltonian we construct a loss function as a weighted sum of relevant
Hamiltonian properties specifying thereby the search query. Using fractional
quantum Hall effect as a test system we illustrate how the framework can be
used to determine a generating Hamiltonian of a finite-size model wavefunction
(Moore-Read Pfaffian and Read-Rezayi states) or to find optimal parameters for

We establish an important duality correspondence between topological order in
quantum many body systems and criticality in ferromagnetic classical spin
systems. We show how such a correspondence leads to a classical and simple
procedure for characterization of topological order in an important set of
quantum entangled states, namely the Calderbank-Shor-Steane (CSS) states. To
this end, we introduce a particular quantum Hamiltonian which allows us to
consider the existence of a topological phase transition from quantum CSS

Nonclassicality is studied through a quasidistribution of phases for the
Raman process under both weak and strong pump conditions. In the former case,
the solution is applicable to both resonant and off-resonant Raman processes,
while strong classical pump is assumed at resonance. Under weak pump conditions
(i.e., in a complete quantum treatment), the phase difference of phases
described by single nonclassical modes is required to be filtered to describe a

The quantum speed limit sets a bound on the minimum time required for a
quantum system to evolve between two states. For open quantum systems this
quantity depends on the dynamical map describing the time evolution in presence
of the environment, on the evolution time {\tau} , and on the initial state of
the system. We consider a general single qubit open dynamics and show that
there is no simple relationship between memory effects and the tightness of the

Quantum Ising model in a transverse field is of the simplest quantum many
body systems used for studying universal properties of quantum phase
transitions. Interestingly, it has been shown that such phase transitions can
be mapped to topological phase transitions in Toric code models by a dual
transformation [M. H. Zarei, Phys. Rev. B 96, 165146 (2017)]. Therefore, one
can expect that well-known properties of the transverse Ising model are used
for characterizing topological phase transition in Toric code model. In this

This paper proposes a multi-mode Gaussian modulated continuous variable
quantum key distribution (CV-QKD) scheme able to operate at high bandwidth
despite using conventional noisy, coherent detectors. We demonstrate
enhancement in shotnoise sensitivity as well as reduction in the electronic
noise variance of the coherent receiver of the multi-mode CV-QKD system. A
proof-of-concept simulation is presented using multiple modes; this
demonstrates an increase in signal-to-noise ratio and secure key rate at