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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

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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