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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

- Read more about Topological photonic orbital angular momentum switch. (arXiv:1706.08230v1 [quant-ph])
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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