285 research outputs found
Quantum Typicality and Initial Conditions
If the state of a quantum system is sampled out of a suitable ensemble, the
measurement of some observables will yield (almost) always the same result.
This leads us to the notion of quantum typicality: for some quantities the
initial conditions are immaterial. We discuss this problem in the framework of
Bose-Einstein condensates.Comment: 8 page
General phase spaces: from discrete variables to rotor and continuum limits
We provide a basic introduction to discrete-variable, rotor, and
continuous-variable quantum phase spaces, explaining how the latter two can be
understood as limiting cases of the first. We extend the limit-taking
procedures used to travel between phase spaces to a general class of
Hamiltonians (including many local stabilizer codes) and provide six examples:
the Harper equation, the Baxter parafermionic spin chain, the Rabi model, the
Kitaev toric code, the Haah cubic code (which we generalize to qudits), and the
Kitaev honeycomb model. We obtain continuous-variable generalizations of all
models, some of which are novel. The Baxter model is mapped to a chain of
coupled oscillators and the Rabi model to the optomechanical radiation pressure
Hamiltonian. The procedures also yield rotor versions of all models, five of
which are novel many-body extensions of the almost Mathieu equation. The toric
and cubic codes are mapped to lattice models of rotors, with the toric code
case related to U(1) lattice gauge theory.Comment: 22 pages, 3 figures; part of special issue on Rabi model; v2 minor
change
Long-lived entanglement of two multilevel atoms in a waveguide
We study the presence of nontrivial bound states of two multilevel quantum
emitters and the photons propagating in a linear waveguide. We characterize the
conditions for the existence of such states and determine their general
properties, focusing in particular on the entanglement between the two
emitters, that increases with the number of excitations. We discuss the
relevance of the results for entanglement preservation and generation by
spontaneous relaxation processes.Comment: 6 pages, 1 figur
Huygens' principle and Dirac-Weyl equation
We investigate the validity of Huygens' principle for forward propagation in
the massless Dirac-Weyl equation. The principle holds for odd space dimension
n, while it is invalid for even n. We explicitly solve the cases n=1,2 and 3
and discuss generic . We compare with the massless Klein-Gordon equation and
comment on possible generalizations and applications.Comment: 7 pages, 1 figur
Typical observables in a two-mode Bose system
A class of k-particle observables in a two-mode system of Bose particles is
characterized by typicality: if the state of the system is sampled out of a
suitable ensemble, an experimental measurement of that observable yields
(almost) always the same result. We investigate the general features of typical
observables, the criteria to determine typicality and finally focus on the case
of density correlation functions, which are related to spatial distribution of
particles and interference.Comment: 8 pages, 1 figur
Phase Transitions in Gauge Models: Towards Quantum Simulations of the Schwinger-Weyl QED
We study the ground-state properties of a class of lattice
gauge theories in 1 + 1 dimensions, in which the gauge fields are coupled to
spinless fermionic matter. These models, stemming from discrete representations
of the Weyl commutator for the group, preserve the unitary
character of the minimal coupling, and have therefore the property of formally
approximating lattice quantum electrodynamics in one spatial dimension in the
large- limit. The numerical study of such approximated theories is important
to determine their effectiveness in reproducing the main features and
phenomenology of the target theory, in view of implementations of cold-atom
quantum simulators of QED. In this paper we study the cases by
means of a DMRG code that exactly implements Gauss' law. We perform a careful
scaling analysis, and show that, in absence of a background field, all
models exhibit a phase transition which falls in the Ising
universality class, with spontaneous symmetry breaking of the symmetry. We
then perform the large- limit and find that the asymptotic values of the
critical parameters approach the ones obtained for the known phase transition
the zero-charge sector of the massive Schwinger model, which occurs at negative
mass.Comment: 15 pages, 18 figure
Signal-to-noise properties of correlation plenoptic imaging with chaotic light
Correlation Plenoptic Imaging (CPI) is a novel imaging technique, that
exploits the correlations between the intensity fluctuations of light to
perform the typical tasks of plenoptic imaging (namely, refocusing out-of-focus
parts of the scene, extending the depth of field, and performing 3D
reconstruction), without entailing a loss of spatial resolution. Here, we
consider two different CPI schemes based on chaotic light, both employing ghost
imaging: the first one to image the object, the second one to image the
focusing element. We characterize their noise properties in terms of the
signal-to-noise ratio (SNR) and compare their performances. We find that the
SNR can be significantly higher and easier to control in the second CPI scheme,
involving standard imaging of the object; under adequate conditions, this
scheme enables reducing by one order of magnitude the number of frames for
achieving the same SNR.Comment: 12 pages, 3 figure
Split and overlapped binary solitons in optical lattices
We analyze the energetic and dynamical properties of bright-bright (BB)
soliton pairs in a binary mixture of Bose-Einstein condensates subjected to the
action of a combined optical lattice, acting as an external potential for the
first species, while modulating the intraspecies coupling constant of the
second. In particular, we use a variational approach and direct numerical
integrations to investigate the existence and stability of BB solitons in which
the two species are either spatially separated (split soliton) or located at
the same optical lattice site (overlapped soliton). The dependence of these
solitons on the interspecies interaction parameter is explicitly investigated.
For repulsive interspecies interaction we show the existence of a series of
critical values at which transitions from an initially overlapped soliton to
split solitons occur. For attractive interspecies interaction only single
direct transitions from split to overlapped BB solitons are found. The
possibility to use split solitons for indirect measurements of scattering
lengths is also suggested.Comment: 9 pages, 10 figure
Tricriticalities and Quantum Phases in Spin-Orbit-Coupled Spin- Bose Gases
We study the zero-temperature phase diagram of a spin-orbit-coupled
Bose-Einstein condensate of spin , with equally weighted Rashba and
Dresselhaus couplings. Depending on the antiferromagnetic or ferromagnetic
nature of the interactions, we find three kinds of striped phases with
qualitatively different behaviors in the modulations of the density profiles.
Phase transitions to the zero-momentum and the plane-wave phases can be induced
in experiments by independently varying the Raman coupling strength and the
quadratic Zeeman field. The properties of these transitions are investigated in
detail, and the emergence of tricritical points, which are the direct
consequence of the spin-dependent interactions, is explicitly discussed.Comment: 6 pages, 2 figures + Supplemental Material. Revised version,
published in PR
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