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Topological defects (kinks) in a relativistic $\phi^{4}$ scalar field theory
in $D=(1+1)$ are studied using the matrix product state tensor network. The one
kink state is approximated as a matrix product state and the kink mass is
calculated. The approach used is quite general and can be applied to a variety
of theories and tensor networks. Additionally, the contribution of
kink-antikink excitations to the ground state is examined and a general method
to estimate the scalar mass from equal time ground state observables is

We demonstrate optical spin polarization of the neutrally-charged
silicon-vacancy defect in diamond ($\mathrm{SiV^{0}}$), an $S=1$ defect which
emits with a zero-phonon line at 946 nm. The spin polarization is found to be
most efficient under resonant excitation, but non-zero at below-resonant
energies. We measure an ensemble spin coherence time $T_2>100~\mathrm{\mu s}$
at low-temperature, and a spin relaxation limit of $T_1>25~\mathrm{s}$. Optical

Phase-squeezed light can enhance the precision of optical phase estimation.
The larger the photon numbers are and the stronger the squeezing is, the better
the precision will be. We propose an experimental scheme for generating
phase-squeezed light pulses with large coherent amplitudes. In our scheme, one
arm of a single-photon Mach-Zehnder interferometer interacts with coherent
light via a non-linear optical Kerr medium to generate a coherent superposition

We give an exposition of the Horn inequalities and their triple role
characterizing tensor product invariants, eigenvalues of sums of Hermitian
matrices, and intersections of Schubert varieties. We follow Belkale's
geometric method, but assume only basic representation theory and algebraic
geometry, aiming for self-contained, concrete proofs. In particular, we do not
assume the Littlewood-Richardson rule nor an a priori relation between
intersections of Schubert cells and tensor product invariants. Our motivation

Global quantum quench with a finite quench rate which crosses critical points
is known to lead to universal scaling of correlation functions as functions of
the quench rate. In this work, we explore scaling properties of the
entanglement entropy of a subsystem in a harmonic chain during a mass quench
which asymptotes to finite constant values at early and late times and for
which the dynamics is exactly solvable. When the initial state is the ground
state, we find that for large enough subsystem sizes the entanglement entropy

There exist zero-temperature states in quantum many-body systems that are
fully factorized, thereby possessing vanishing entanglement, and hence being of
no use as resource in quantum information processing tasks. Such states can
become useful for quantum protocols when the temperature of the system is
increased, and when the system is allowed to evolve under either the influence
of an external environment, or a closed unitary evolution driven by its own
Hamiltonian due to a sudden change in the system parameters. Using the

In this work we develop an experimental procedure to interrogate the single-
and multi-photon scattering matrices of an unknown quantum object interacting
with propagating photons. Our proposal requires coherent state laser or
microwave inputs and homodyne detection at the scatterer's output, and provides
simultaneous information about multiple ---elastic and inelastic--- segments of
the scattering matrix. The method is resilient to detector noise and its errors

The measurement device independent (MDI) Quantum Key Distribution (QKD) is a
practically implementable method for transmitting secret keys between
respective partners performing quantum communication. SARG04
(Scarani-Ac\`{i}n-Ribordy-Gisin 2004) is a protocol tailored to struggle
against photon number splitting (PNS) attacks by eavesdroppers and its MDI-QKD
version is reviewed and optimized from secret key bitrate versus communication
distance point of view. We consider the effect of several important factors

The high index contrast of the silicon-on-insulator (SOI) platform allows the
realization of ultra-compact photonic circuits. However, this high contrast
hinders the implementation of narrow-band Bragg filters. These typically
require corrugations widths of a few nanometers or double-etch geometries,
hampering device fabrication. Here we report, for the first time, on the
realization of SOI Bragg filters based on sub-wavelength index engineering in a
differential corrugation width configuration. The proposed double periodicity

Starting from the symmetric gauge and the zero modes of the monolayer
graphene Dirac equation, we develop a mechanism to construct the eigenvalues
and its eigenfunctions. Specifically, we show that for positive configurations
of magnetic fields, we can construct the successive eigenstates from the zero
energy state with negative chirality. We also show that for negative magnetic
fields, the eigenstates may be constructed form the zero mode with positive
quirality. In addition, we discuss the implications that the Aharonov-Casher