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It was recently conjectured by Vivo, Pato, and Oshanin [Phys. Rev. E 93,
052106 (2016)] that for a quantum system of Hilbert dimension $mn$ in a pure
state, the variance of the von Neumann entropy of a subsystem of dimension
$m\leq n$ is given by \begin{equation*}
-\psi_{1}\left(mn+1\right)+\frac{m+n}{mn+1}\psi_{1}\left(n\right)-\frac{(m+1)(m+2n+1)}{4n^{2}(mn+1)},
\end{equation*} where $\psi_{1}(\cdot)$ is the trigamma function. We give a
proof of this formula.

We introduce the coherent state mapping ring-polymer molecular dynamics
(CS-RPMD), a new method that accurately describes electronic non-adiabatic
dynamics with explicit nuclear quantization. This new approach is derived by
using coherent state mapping representation for the electronic degrees of
freedom (DOF) and the ring-polymer path-integral representation for the nuclear
DOF. CS-RPMD Hamiltonian does not contain any inter-bead coupling term in the
state-dependent potential, which is a key feature that ensures correct

We demonstrate the irreversibility of asymptotic entanglement manipulation
under quantum operations that completely preserve the positivity of partial
transpose (PPT), resolving a major open problem in quantum information theory.
Our key tool is a new efficiently computable additive lower bound for the
asymptotic relative entropy of entanglement with respect to PPT states. We find
that for any rank-two mixed state supporting on the $3\otimes 3$ antisymmetric

We present reversible classical circuits for performing various arithmetic
operations aided by dirty ancillae (i.e. extra qubits in an unknown state that
must be restored before the circuit ends). We improve the number of clean
qubits needed to factor an n-bit number with Shor's algorithm from 2n+2 to n+2,
and the total number of qubits needed from 2n+2 to 2n+1, without increasing the
asymptotic size or depth of the circuit.

Stationary and slow light effects are of great interest for quantum
information applications. Using laser-cooled Rb87 atoms we have performed side
imaging of our atomic ensemble under slow and stationary light conditions,
which allows direct comparison with numerical models. The polaritions were
generated using electromagnetically induced transparency (EIT), with stationary
light generated using counter-propagating control fields. By controlling the
power ratio of the two control fields we show fine control of the group

Operational characterization of quantumness for a bipartite unsteerable
quantum correlation is captured by the notion of super-unsteerability.
Super-unsteerability refers to the requirement of a larger dimension of the
random variable in the classical simulation protocol than that of the quantum
states that generate the correlation. In the present study, this concept of
super-unsteerability has been generalized by defining the notion of
super-bi-unsteerability for tripartite correlations, which is unsteerable

Detailed analysis of the system of four interacting ultra-cold fermions
confined in a one-dimensional harmonic trap is performed. The analysis is done
in the framework of a simple variational ansatz for the many-body ground state
and its predictions are confronted with the results of numerically exact
diagonalization of the many-body Hamiltonian. Short discussion on the role of
the quantum statistics, i.e. Bose-Bose and Bose-Fermi mixtures is also
presented. It is concluded that the variational ansatz, although seemed to be

The large number of available orbital angular momentum (OAM) states of
photons provides a unique resource for many important applications in quantum
information and optical communications. However, conventional OAM switching
devices usually rely on precise parameter control and are limited by slow
switching rate and low efficiency. Here we propose a robust, fast and efficient
photonic OAM switch device based on a topological process, where photons are
adiabatically pumped to a target OAM state on demand. Such topological OAM

Quantum annealers aim at solving non-convex optimization problems by
exploiting cooperative tunneling effects to escape local minima. The underlying
idea consists in designing a classical energy function whose ground states are
the sought optimal solutions of the original optimization problem and add a
controllable quantum transverse field to generate tunneling processes. A key
challenge is to identify classes of non-convex optimization problems for which

We derive a monogamy inequality for entanglement and local contextuality, for
any finite bipartite system. It essentially results from the relations between
the purity of a local state and the entanglement of the global state, and
between the purity of a state and its ability to violate a given
noncontextuality inequality. We build an explicit entanglement monotone that
satisfies the found monogamy inequality. An important consequence of this
inequality, is that there are global states too entangled to violate the local