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## Superconductivity and charge order of confined Fermi systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

45.82%

The low-temperature properties of the two-dimensional attractive Hubbard
model are strongly influenced by the fermion density. Away from half-filling,
there is a finite-temperature transition to a phase with s-wave pairing order.
However, the critical temperature is suppressed to zero at half-filling, where
long-range charge-density-wave order also appears, degenerate with
superconductivity. This paper presents Determinant Quantum Monte Carlo
simulations of the attractive Hubbard model in the presence of a confining
potential V which makes the fermion density \rho{} inhomogeneous across the
lattice. Pair correlations are shown to be large at low temperatures in regions
of the trapped system with incommensurate filling, and to exhibit a minimum as
the local density \rho(i) passes through one fermion per site. In this ring of
\rho=1, charge order is enhanced. A comparison is made between treating V
within the local-density approximation (LDA) and in an ab initio manner. It is
argued that certain sharp features of the LDA result at integer filling do not
survive the proximity of doped sites. The critical temperature of confined
systems of fixed characteristic density is estimated.; Comment: 7 pages, 5 figures; minor changes from v1

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## Galilean invariance in confined quantum systems: Implications on spectral gaps, superfluid flow, and periodic order

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

55.84%

Galilean invariance leaves its imprint on the energy spectrum and eigenstates
of $N$ quantum particles, bosons or fermions, confined in a bounded domain. It
endows the spectrum with a recurrent structure which in capillaries or
elongated traps of length $L$ and cross-section area $s_\perp$ leads to
spectral gaps $n^2h^2s_\perp\rho/(2mL)$ at wavenumbers $2n\pi s_\perp\rho$,
where $\rho$ is the number density and $m$ is the particle mass. In zero
temperature superfluids, in toroidal geometries, it causes the quantization of
the flow velocity with the quantum $h/(mL)$ or that of the circulation along
the toroid with the known quantum $h/m$. Adding a "friction" potential which
breaks Galilean invariance, the Hamiltonian can have a superfluid ground state
at low flow velocities but not above a critical velocity which may be different
from the velocity of sound. In the limit of infinite $N$ and $L$, if
$N/L=s_\perp\rho$ is kept fixed, translation invariance is broken, the center
of mass has a periodic distribution, while superfluidity persists at low flow
velocities. This conclusion holds for the Lieb-Liniger model.; Comment: Improved, final version. Equation (22) is slightly more general than
in the publication. The upper bound for the critical velocity on p. 4 is
corrected

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## Storage of energy in confined quantum systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 22/09/2002

Relevância na Pesquisa

65.88%

#Quantum Physics#Condensed Matter - Statistical Mechanics#High Energy Physics - Theory#Physics - Atomic Physics

Using the non-perturbative method of {\it dressed} states introduced in
previous publications [N.P.Andion, A.P.C. Malbouisson and A. Mattos Neto,
J.Phys.{\bf A34}, 3735, (2001); G. Flores-Hidalgo, A.P.C. Malbouisson, Y.W.
Milla, Phys. Rev. A, {\bf 65}, 063314 (2002)], we study the evolution of a
confined quantum mechanical system embedded in a {\it ohmic} environment. Our
approach furnishes a theoretical mechanism to control inhibition of the decay
of excited quantum systems in cavities, in both weak and strong coupling
regimes.; Comment: 4 pages REVTEX, no figures

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## Nearly-linear light cones in long-range interacting quantum systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 13/10/2014

Relevância na Pesquisa

45.82%

In non-relativistic quantum theories with short-range Hamiltonians, a
velocity $v$ can be chosen such that the influence of any local perturbation is
approximately confined to within a distance $r$ until a time $t \sim r/v$,
thereby defining a linear light cone and giving rise to an emergent notion of
locality. In systems with power-law ($1/r^{\alpha}$) interactions, when
$\alpha$ exceeds the dimension $D$, an analogous bound confines influences to
within a distance $r$ only until a time $t\sim(\alpha/v)\log r$, suggesting
that the velocity, as calculated from the slope of the light cone, may grow
exponentially in time. We rule out this possibility; light cones of power-law
interacting systems are algebraic for $\alpha>2D$, becoming linear as
$\alpha\rightarrow\infty$. Our results impose strong new constraints on the
growth of correlations and the production of entangled states in a variety of
rapidly emerging, long-range interacting atomic, molecular, and optical
systems.; Comment: 5 pages, 3 figures, and Supplemental Material

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## Multi-electron dynamics in the tunnel ionization of correlated quantum systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 11/06/2015

Relevância na Pesquisa

55.75%

The importance of multi-electron dynamics during the tunnel ionization of a
correlated quantum system is investigated. By comparison of the solution of the
time-dependent Schr\"odinger equation (TDSE) with the time-dependent
configuration interaction singles approach (TDCIS), we demonstrate the
importance of a multi-electron description of the tunnel ionization process
especially for weakly confined quantum systems. Within this context, we observe
that adiabatic driving by an intense light field can even enhance the
correlations between still trapped electrons.

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## Strong Local Passivity in Finite Quantum Systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

55.86%

Passive states of quantum systems are states from which no system energy can
be extracted by any cyclic (unitary) process. Gibbs states of all temperatures
are passive. Strong local (SL) passive states are defined to allow any general
quantum operation, but the operation is required to be local, being applied
only to a specific subsystem. Any mixture of eigenstates in a system-dependent
neighborhood of a nondegenerate, entangled ground state is found to be SL
passive. In particular, Gibbs states are SL passive with respect to a subsystem
only at or below a critical, system-dependent temperature. SL passivity is
associated in many-body systems with the presence of ground state entanglement
in a way suggestive of collective quantum phenomena such as quantum phase
transitions, superconductivity, and the quantum Hall effect. The presence of SL
passivity is detailed for some simple spin systems where it is found that SL
passivity is neither confined to systems of just a few particles nor limited to
the near vicinity of the ground state.; Comment: This newer version is longer and more detailed. Published 24 July
2014

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## Cavity mode entanglement in relativistic quantum information

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

45.82%

A central aim of relativistic quantum information (RQI) is the investigation
of quantum information tasks and resources taking into account the relativistic
aspects of nature. More precisely, it is of fundamental interest to understand
how the storage, manipulation, and transmission of information utilizing
quantum systems are influenced by the fact that these processes take place in a
relativistic spacetime. In particular, many studies in RQI have been focused on
the effects of non-uniform motion on entanglement, the main resource of quantum
information protocols. Early investigations in this direction were performed in
highly idealized settings that prompted questions as to the practical
accessibility of these results. To overcome these limitations it is necessary
to consider quantum systems that are in principle accessible to localized
observers. In this thesis we present such a model, the rigid relativistic
cavity, and its extensions, focusing on the effects of motion on entanglement
and applications such as quantum teleportation. We study cavities in (1+1)
dimensions undergoing non-uniform motion, consisting of segments of uniform
acceleration and inertial motion of arbitrary duration that allow the involved
velocities to become relativistic. The transitions between segments can be
sharp or smooth and higher dimensions can be incorporated. The primary focus
lies in the Bogoliubov transformations of the quantum fields...

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## WKB and MAF Quantization Rules for Spatially Confined Quantum Mechanical Systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 15/10/1999

Relevância na Pesquisa

55.86%

A formalism is developed to obtain the energy eigenvalues of spatially
confined quantum mechanical systems in the framework of The usual WKB and MAF
methods. The technique is applied to three different cases,viz one dimensional
Harmonic Oscillators,Quartic Oscillators and a boxed-in charged particle in
electric field.

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## Confined quantum Zeno dynamics of a watched atomic arrow

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

45.87%

In a quantum world, a watched arrow never moves. This is the Quantum Zeno
Effect (QZE). Repeatedly asking a quantum system "are you still in your initial
state?" blocks its coherent evolution through measurement back-action. Quantum
Zeno Dynamics (QZD) leaves more freedom to the system. Instead of pinning it to
a single state, it sets a border in its evolution space. Repeatedly asking the
system "did you cross the border?" makes it impenetrable. Since the border can
be designed at will by choosing the measured observable, QZD allows one to
tailor the system's evolution space. Recent proposals, particularly in the
Cavity Quantum Electrodynamics (CQED) context, highlight the interest of QZD
for quantum state engineering tasks, which are the key to quantumenabled
technologies and quantum information processing. We report the observation of
QZD in the 51-dimension Hilbert space of a large angular momentum J = 25.
Continuous selective interrogation limits the evolution of this angular
momentum to an adjustable multi-dimensional subspace. This confined dynamics
leads to the production of non-classical "Schr\"odinger cat" states, quantum
superpositions of angular momentums pointing in different directions. These
states are promising for sensitive metrology of electric and magnetic fields.
This QZD approach could be generalized to other systems...

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## Is there contextuality in behavioral and social systems?

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

45.83%

#Quantitative Biology - Neurons and Cognition#Mathematics - Probability#Quantum Physics#81P13, 81Q99, 60A99, 81P13, 81Q99, 60A99, 81P13, 81Q99, 60A99

Most behavioral and social experiments aimed at revealing contextuality are
confined to cyclic systems with binary outcomes. In quantum physics, this broad
class of systems includes as special cases
Klyachko-Can-Binicioglu-Shumovsky-type, Einstein-Podolsky-Rosen-Bell-type, and
Suppes-Zanotti-Leggett-Garg-type systems. The theory of contextuality known as
Contextuality-by-Default allows one to define and measure contextuality in all
such system, even if there are context-dependent errors in measurements, or if
something in the contexts directly interacts with the measurements. This makes
the theory especially suitable for behavioral and social systems, where direct
interactions of "everything with everything" are ubiquitous. For cyclic systems
with binary outcomes the theory provides necessary and sufficient conditions
for noncontextuality, and these conditions are known to be breached in certain
quantum systems. We review several behavioral and social data sets (from polls
of public opinion to visual illusions to conjoint choices to word combinations
to psychophysical matching), and none of these data provides any evidence for
contextuality. Our working hypothesis is that this may be a broadly applicable
rule: behavioral and social systems are noncontextual...

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## A geometrical approach to the mean density of states in many-body quantum systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 21/10/2012

Relevância na Pesquisa

45.88%

We present a novel analytical approach for the calculation of the mean
density of states in many-body systems made of confined indistinguishable and
non-interacting particles. Our method makes explicit the intrinsic geometry
inherent in the symmetrization postulate and, in the spirit of the usual Weyl
expansion for the smooth part of the density of states in single-particle
confined systems, our results take the form of a sum over clusters of particles
moving freely around manifolds in configuration space invariant under elements
of the group of permutations. Being asymptotic, our approximation gives
increasingly better results for large excitation energies and we formally
confirm that it coincides with the celebrated Bethe estimate in the appropriate
region. Moreover, our construction gives the correct high energy asymptotics
expected from general considerations, and shows that the emergence of the
fermionic ground state is actually a consequence of an extremely delicate large
cancellation effect. Remarkably, our expansion in cluster zones is naturally
incorporated for systems of interacting particles, opening the road to address
the fundamental problem about the interplay between confinement and
interactions in many-body systems of identical particles.; Comment: 45 pages...

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## Strongly interacting confined quantum systems in one dimension

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

55.84%

#Condensed Matter - Quantum Gases#Condensed Matter - Strongly Correlated Electrons#Mathematical Physics#Quantum Physics

In one dimension, the study of magnetism dates back to the dawn of quantum
mechanics when Bethe solved the famous Heisenberg model that describes quantum
behaviour in magnetic systems. In the last decade, one-dimensional systems have
become a forefront area of research driven by the realization of the
Tonks-Girardeau gas using cold atomic gases. Here we prove that one-dimensional
fermionic and bosonic systems with strong short-range interactions are solvable
in arbitrary confining geometries by introducing a new energy-functional
technique and obtaining the full spectrum of energies and eigenstates. As a
first application, we calculate spatial correlations and show how both ferro-
and anti-ferromagnetic states are present already for small system sizes that
are prepared and studied in current experiments. Our work demonstrates the
enormous potential for quantum manipulation of magnetic correlations at the
microscopic scale.; Comment: 11 pages, 2 figures, including methods, final version

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## Quantification and Control of non-Markovian Evolution in Finite Quantum Systems via Feedback

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

55.8%

We consider the unitary time evolution of continuous quantum mechanical
systems confined to a cavity in contact with a finite bath of variable size.
Measures for Markovianity for such finite system-bath configurations are
developed in terms of Hilbert-Schmidt distances of time evolving wave packets.
The relevant time scales are identified, which characterize pseudo-Markovian
transient behavior, boundary scattering induced non-Markovian oscillations at
intermediate times, and non-Markovian rephasing events at long time scales. It
is shown how these time scales can be controlled by tunable parameters such as
the bath size and the strength of the system-bath coupling.; Comment: 7 pages, 7 figures, Revised version with text made more clear and
figure 1 improved. Author names changed from initials to full first names
title changed from 'Control of Pseudo-Markovian Evolution in Finite Quantum
Systems via Feedback'. Title later changed to current title. Minor revision
in third version at editors request

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## A scanning transmon qubit for strong coupling circuit quantum electrodynamics

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 04/03/2013

Relevância na Pesquisa

45.83%

Like a quantum computer designed for a particular class of problems, a
quantum simulator enables quantitative modeling of quantum systems that is
computationally intractable with a classical computer. Quantum simulations of
quantum many-body systems have been performed using ultracold atoms and trapped
ions among other systems. Superconducting circuits have recently been
investigated as an alternative system in which microwave photons confined to a
lattice of coupled resonators act as the particles under study with qubits
coupled to the resonators producing effective photon-photon interactions. Such
a system promises insight into the nonequilibrium physics of interacting bosons
but new tools are needed to understand this complex behavior. Here we
demonstrate the operation of a scanning transmon qubit and propose its use as a
local probe of photon number within a superconducting resonator lattice. We map
the coupling strength of the qubit to a resonator on a separate chip and show
that the system reaches the strong coupling regime over a wide scanning area.; Comment: 11 pages, 8 figures

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## Exactly solvable Richardson-Gaudin models for many-body quantum systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 05/05/2004

Relevância na Pesquisa

55.94%

#Nuclear Theory#Condensed Matter - Superconductivity#Nonlinear Sciences - Exactly Solvable and Integrable Systems#Quantum Physics

The use of exactly-solvable Richardson-Gaudin (R-G) models to describe the
physics of systems with strong pair correlations is reviewed. We begin with a
brief discussion of Richardson's early work, which demonstrated the exact
solvability of the pure pairing model, and then show how that work has evolved
recently into a much richer class of exactly-solvable models. We then show how
the Richardson solution leads naturally to an exact analogy between such
quantum models and classical electrostatic problems in two dimensions. This is
then used to demonstrate formally how BCS theory emerges as the large-N limit
of the pure pairing Hamiltonian and is followed by several applications to
problems of relevance to condensed matter physics, nuclear physics and the
physics of confined systems. Some of the interesting effects that are discussed
in the context of these exactly-solvable models include: (1) the crossover from
superconductivity to a fluctuation-dominated regime in small metallic grains,
(2) the role of the nucleon Pauli principle in suppressing the effects of high
spin bosons in interacting boson models of nuclei, and (3) the possibility of
fragmentation in confined boson systems. Interesting insight is also provided
into the origin of the superconducting phase transition both in two-dimensional
electronic systems and in atomic nuclei...

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## Quantum critical behavior and trap-size scaling of trapped bosons in a one-dimensional optical lattice

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 17/03/2010

Relevância na Pesquisa

45.88%

We study the quantum (zero-temperature) critical behaviors of confined
particle systems described by the one-dimensional (1D) Bose-Hubbard model in
the presence of a confining potential, at the Mott insulator to superfluid
transitions, and within the gapless superfluid phase. Specifically, we consider
the hard-core limit of the model, which allows us to study the effects of the
confining potential by exact and very accurate numerical results. We analyze
the quantum critical behaviors in the large trap-size limit within the
framework of the trap-size scaling (TSS) theory, which introduces a new trap
exponent theta to describe the dependence on the trap size. This study is
relevant for experiments of confined quasi 1D cold atom systems in optical
lattices. At the low-density Mott transition TSS can be shown analytically
within the spinless fermion representation of the hard-core limit. The
trap-size dependence turns out to be more subtle in the other critical regions,
when the corresponding homogeneous system has a nonzero filling f, showing an
infinite number of level crossings of the lowest states when increasing the
trap size. At the n=1 Mott transition this gives rise to a modulated TSS: the
TSS is still controlled by the trap-size exponent theta...

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## Vortices in quantum droplets: Analogies between boson and fermion systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 09/06/2010

Relevância na Pesquisa

45.85%

The main theme of this review is the many-body physics of vortices in quantum
droplets of bosons or fermions, in the limit of small particle numbers. Systems
of interest include cold atoms in traps as well as electrons confined in
quantum dots. When set to rotate, these in principle very different quantum
systems show remarkable analogies. The topics reviewed include the structure of
the finite rotating many-body state, universality of vortex formation and
localization of vortices in both bosonic and fermionic systems, and the
emergence of particle-vortex composites in the quantum Hall regime. An overview
of the computational many-body techniques sets focus on the configuration
interaction and density-functional methods. Studies of quantum droplets with
one or several particle components, where vortices as well as coreless vortices
may occur, are reviewed, and theoretical as well as experimental challenges are
discussed.; Comment: Review article, 53 pages, 53 figures

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## Energy gaps and interaction blockade in confined quantum systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 09/02/2007

Relevância na Pesquisa

65.97%

Many-body effects in confined quantum systems pose a challenging problem due
to the simultaneous presence of particle-particle interactions and spatial
inhomogeneity. Here we investigate universal properties of strongly confined
particles that turn out to be dramatically different from what is observed for
electrons in atoms and molecules. We show that for a large class of
harmonically confined systems, including small quantum dots and optically
trapped atoms, many-body particle addition and removal energies, and energy
gaps, can accurately be obtained from single-particle eigenvalues. Transport
blockade phenomena are related to the derivative discontinuity of the
exchange-correlation functional. This implies that they occur very generally,
with Coulomb blockade being a particular realization of a more general
phenomenon. In particular, we predict van-der-Waals blockade in cold atom gases
in traps.

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## Energy eigenvalues for free and confined triple-well potentials

Fonte: Sociedad Mexicana de Física
Publicador: Sociedad Mexicana de Física

Tipo: Artigo de Revista Científica
Formato: text/html

Publicado em 01/02/2011
EN

Relevância na Pesquisa

55.79%

#One-dimensional triple-well potentials#energy eigenvalues and eigenfunctions#confined quantum systems

Some confined and unconfined (free) one-dimensional triple-well potentials are analyzed with two different numerical approaches. Confinement is achieved by enclosing the potential between two impenetrable walls. The unconfined (free) system is recovered as the positions of the walls move to infinity. The numerical solutions of the Schrodinger equation for the symmetric and asymmetric potentials without confinement, are comparable in precision with those obtained anaylitically. For the symmetric triple-well potentials, V (x) = αx2 - βx4 + x6, it is found that there are sets of two or three quasi-degenerate eigenvalues depending on the parameters a and ¡3. A heuristic analysis shows that if the conditions α= (β2 /4) ± 1 (with α > 0 and β > 0) are satisfied, then there are sets of three eigenvalues with similar energy. An interesting behavior is found when one impenetrable wall is fixed and the other is moved to different positions. In summary, the number of local minima that the potential has in the confined region determines a two- or three-fold degeneracy.

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## Color centers envisioned as confined quantum systems: the case of F, F' and F+2 centers

Fonte: Sociedad Mexicana de Física
Publicador: Sociedad Mexicana de Física

Tipo: Artigo de Revista Científica
Formato: text/html

Publicado em 01/06/2008
EN

Relevância na Pesquisa

75.99%

Color centers in alkali halides, as well as point defects with dimensions of a few nanometers, have been considered to be confined systems and were studied with a variational formalism within a semi-continuum model. This new approach was applied to the well-known F, F' and F+2 centers, which are assumed to be cavities of a determined shape that can trap one or two electrons. Inside of the cavity, the electron is subject to a constant potential (V0) related to the Madelung energy and outside of it, the potential is Coulomb type due to a continuum polarizable medium. Because the F, F' and F+2confined systems were considered to be hydrogen-like, helium-like and F+2-like molecular ion systems, respectively, the ansatz functions were constructed from wave functions corresponding to these kinds of systems. For these systems, the energy transition (ΔΕ) from the ground state to the first excited state in KCl crystals was calculated and compared with experimental and calculated values obtained from the literature. The ΔΕ behavior is shown for different values of V0. It is worth mentioning that the formalism presented in this work would be useful for both graduate and undergraduate students embarking on the study of some properties of confined quantum systems...

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