We discuss the Kirillov method for massless Wigner particles, usually (mis)named ‘continuous spin’
or ‘infinite spin’ particles. These appear in Wigner’s classification of the unitary representations
of the Poincaré group, labelled by elements of the enveloping algebra of the Poincaré Lie algebra.
Now, the coadjoint orbit procedure introduced by Kirillov is a prelude to quantization. Here we
exhibit for those particles the classical Casimir functions on phase space, in parallel to quantum

We present and study a two-particle quantum walk on the line in which the two
particles interact via a long-range Coulombian-like interaction. We obtain the
spectrum of the system as well as study the type of molecules that form,
attending to the bosonic or fermionic nature of the walkers. The usual loss of
distinction between attractive and repulsive forces does not entirely apply in
our model because of the long-range of the interaction.

We report the first experimental observation of multiple transitions showing
the emergence and disappearance of slowly decaying eigenmodes in a dissipative,
Floquet electronic system with synthetic components. Conventional wisdom has it
that such transitions occur at exceptional points, and avoided-level-crossing
driven phenomena in purely dissipative systems are formerly unexplored.
Remarkably, in our system, the slowly decaying eigenmodes emerge without
exceptional points. Our experimental setup makes use of an LC oscillator

Atomic many-body phase transitions and quantum criticality have recently
attracted much attention in non-standard optical lattices. Here we perform an
experimental study of finite-temperature superfluid transition of bosonic atoms
confined in a three dimensional triangular lattice, whose structure can be
continuously deformed to dimensional crossover regions including quasi-one and
two dimensions. This non-standard lattice system provides a versatile platform

In this paper, we mainly consider the local indistinguishability of the set
of mutually orthogonal bipartite generalized Bell states (GBSs). We construct
small sets of GBSs with cardinality smaller than $d$ which are not
distinguished by one-way local operations and classical communication (1-LOCC)
in $d\otimes d$. The constructions, based on linear system and Vandermonde
matrix, is simple and effective. The results give a unified upper bound for the
minimum cardinality of 1-LOCC indistinguishable set of GBSs, and greatly

We study a class of anomalies associated with time-reversal and spatial
reflection symmetry in (2+1)D topological phases of matter. In these systems,
the topological quantum numbers of the quasiparticles, such as the fusion rules
and braiding statistics, possess a $\mathbb{Z}_2$ symmetry which can be
associated with either time-reversal (denoted $\mathbb{Z}_2^{\bf T})$ or
spatial reflections. Under this symmetry, correlation functions of all Wilson
loop operators in the low energy topological quantum field theory (TQFT) are

Since inflationary perturbations must generically couple to all degrees of
freedom present in the early Universe, it is more realistic to view these
fluctuations as an open quantum system interacting with an environment. Then,
on very general grounds, their evolution can be modelled with a Lindblad
equation. This modified evolution leads to quantum decoherence of the system,
as well as to corrections to observables such as the power spectrum of
curvature fluctuations. On one hand, current cosmological observations

Typical studies of quantum error correction assume probabilistic Pauli noise,
largely because it is relatively easy to analyze and simulate. Consequently,
the effective logical noise due to physically realistic coherent errors is
relatively unknown. Here we prove that encoding a system in a stabilizer code
and measuring error syndromes decoheres errors, that is, converts coherent
errors to probabilistic Pauli errors, even when no recovery operations are
applied. Two practical consequences are that the error rate in a logical

We present a detailed theoretical description of an atomic scanning
microscope in a cavity QED setup proposed in Phys. Rev. Lett. 120, 133601
(2018). The microscope continuously observes atomic densities with optical
subwavelength resolution in a nondestructive way. The super-resolution is
achieved by engineering an internal atomic dark state with a sharp spatial
variation of population of a ground level dispersively coupled to the cavity
field. Thus, the atomic position encoded in the internal state is revealed as a

A quantum dot coupled to an optical cavity has recently proven to be an
excellent source of on-demand single photons. Typically, applications require
simultaneous high efficiency of the source and quantum indistinguishability of
the extracted photons. While much progress has been made both in suppressing
background sources of decoherence and utilizing cavity-quantum electrodynamics
to overcome fundamental limitations set by the intrinsic exciton-phonon
scattering inherent in the solid-state platform, the role of the excitation