3,909 research outputs found
Phase Diagrams of Three-Component Attractive Ultracold Fermions in One-Dimension
We investigate trions, paired states and quantum phase transitions in
one-dimensional SU(3) attractive fermions in external fields by means of the
Bethe ansatz and the dressed energy formalism. Analytical results for the
ground state energy, critical fields and complete phase diagrams are presented
for weak and strong regimes. Numerical solutions of the dressed energy
equations allow us to examine how the different phase boundaries modify by
varying the inter-component coupling throughout the whole attractive regimes.
The pure trionic phase reduces smoothly by decreasing this coupling until the
weak limit is reached. In this weak regime, a pure BCS-paired phase can be
sustained under certain nonlinear Zeeman splittings. Finally we confirm that
the analytic expressions for the physical quantities and resulting phase
diagrams are highly accurate in the weak and strong coupling regimes.Comment: 12 pages, 3 figures, revised version, accepted in New J. Phy
Fate of topological states in incommensurate generalized Aubry-Andr\'e models
We study one-dimensional optical lattices described by generalized
Aubry-Andr\'e models that include both commensurate and incommensurate
modulations of the hopping amplitude. This brings together two interesting
features of this class of systems: Anderson localization and the existence of
topological edge states. We follow changes of the single-particle energy
spectrum induced by variations of the system parameters, with focus on the
survival of topological states in the localized regime.Comment: 5 pages, 5 figure
Finite-size effects in Anderson localization of one-dimensional Bose-Einstein condensates
We investigate the disorder-induced localization transition in Bose-Einstein
condensates for the Anderson and Aubry-Andre models in the non-interacting
limit using exact diagonalization. We show that, in addition to the standard
superfluid fraction, other tools such as the entanglement and fidelity can
provide clear signatures of the transition. Interestingly, the fidelity
exhibits good sensitivity even for small lattices. Effects of the system size
on these quantities are analyzed in detail, including the determination of a
finite-size-scaling law for the critical disorder strength in the case of the
Anderson model.Comment: 15 pages, 7 figure
Universality class of quantum criticality for strongly repulsive spin-1 bosons with antiferromagnetic spin-exchange interaction
Using the thermodynamic Bethe ansatz equations we study the quantum phase
diagram, thermodynamics and criticality of one-dimensional spin-1 bosons with
strongly repulsive density-density and antiferromagnetic spin-exchange
interactions. We analytically derive a high precision equation of state from
which the Tomonaga-Luttinger liquid physics and quantum critical behavior of
the system are computed. We obtain explicit forms for the scaling functions
near the critical points yielding the dynamical exponent and correlation
length exponent for the quantum phase transitions driven by either
the chemical potential or the magnetic field. Consequently, we further
demonstrate that quantum criticality of the system can be mapped out from the
finite temperature density and magnetization profiles of the 1D trapped gas.
Our results provide the physical origin of quantum criticality in a 1D
many-body system beyond the Tomonaga-Luttinger liquid description.Comment: 12 pages, 11 figure
Ordering in a frustrated pyrochlore antiferromagnet proximate to a spin liquid
We perform a general study of spin ordering on the pyrochlore lattice with a
3:1 proportionality of two spin polarizations. Equivalently, this describes
valence bond solid conformations of a quantum dimer model on the diamond
lattice. We determine the set of likely low temperature ordered phases, on the
assumption that the ordering is weak, i.e the system is close to a ``U(1)''
quantum spin liquid in which the 3:1 proportionality is maintained but the
spins are strongly fluctuating. The nature of the 9 ordered states we find is
determined by a ``projective symmetry'' analysis. All the phases exhibit
translational and rotational symmetry breaking, with an enlarged unit cell
containing 4 to 64 primitive cells of the underlying pyrochlore. The simplest
of the 9 phases is the same ``R'' state found earlier in a theoretical study of
the ordering on the magnetization plateau in the materials \cdaf and
\hgaf. We suggest that the spin/dimer model proposed therein undergoes a direct
transition from the spin liquid to the R state, and describe a field theory for
the universal properties of this critical point, at zero and non-zero
temperatures
Wilson ratio of Fermi gases in one dimension
We calculate the Wilson ratio of the one-dimensional Fermi gas with spin
imbalance. The Wilson ratio of attractively interacting fermions is solely
determined by the density stiffness and sound velocity of pairs and of excess
fermions for the two-component Tomonaga-Luttinger liquid (TLL) phase. The ratio
exhibits anomalous enhancement at the two critical points due to the sudden
change in the density of states. Despite a breakdown of the quasiparticle
description in one dimension, two important features of the Fermi liquid are
retained, namely the specific heat is linearly proportional to temperature
whereas the susceptibility is independent of temperature. In contrast to the
phenomenological TLL parameter, the Wilson ratio provides a powerful parameter
for testing universal quantum liquids of interacting fermions in one, two and
three dimensions.Comment: 5+2 pages, 4+1 figures, Eq. (4) is proved, figures were refine
Integrable multiparametric quantum spin chains
Using Reshetikhin's construction for multiparametric quantum algebras we
obtain the associated multiparametric quantum spin chains. We show that under
certain restrictions these models can be mapped to quantum spin chains with
twisted boundary conditions. We illustrate how this general formalism applies
to construct multiparametric versions of the supersymmetric t-J and U models.Comment: 17 pages, RevTe
Local Communication Protocols for Learning Complex Swarm Behaviors with Deep Reinforcement Learning
Swarm systems constitute a challenging problem for reinforcement learning
(RL) as the algorithm needs to learn decentralized control policies that can
cope with limited local sensing and communication abilities of the agents.
While it is often difficult to directly define the behavior of the agents,
simple communication protocols can be defined more easily using prior knowledge
about the given task. In this paper, we propose a number of simple
communication protocols that can be exploited by deep reinforcement learning to
find decentralized control policies in a multi-robot swarm environment. The
protocols are based on histograms that encode the local neighborhood relations
of the agents and can also transmit task-specific information, such as the
shortest distance and direction to a desired target. In our framework, we use
an adaptation of Trust Region Policy Optimization to learn complex
collaborative tasks, such as formation building and building a communication
link. We evaluate our findings in a simulated 2D-physics environment, and
compare the implications of different communication protocols.Comment: 13 pages, 4 figures, version 2, accepted at ANTS 201
Intensity fluctuations in bimodal micropillar lasers enhanced by quantum-dot gain competition
We investigate correlations between orthogonally polarized cavity modes of a
bimodal micropillar laser with a single layer of self-assembled quantum dots in
the active region. While one emission mode of the microlaser demonstrates a
characteristic s-shaped input-output curve, the output intensity of the second
mode saturates and even decreases with increasing injection current above
threshold. Measuring the photon auto-correlation function g^{(2)}(\tau) of the
light emission confirms the onset of lasing in the first mode with g^{(2)}(0)
approaching unity above threshold. In contrast, strong photon bunching
associated with super-thermal values of g^{(2)}(0) is detected for the other
mode for currents above threshold. This behavior is attributed to gain
competition of the two modes induced by the common gain material, which is
confirmed by photon crosscorrelation measurements revealing a clear
anti-correlation between emission events of the two modes. The experimental
studies are in excellent qualitative agreement with theoretical studies based
on a microscopic semiconductor theory, which we extend to the case of two modes
interacting with the common gain medium. Moreover, we treat the problem by an
extended birth-death model for two interacting modes, which reveals, that the
photon probability distribution of each mode has a double peak structure,
indicating switching behavior of the modes for the pump rates around threshold.Comment: 11 pages, 5 figures, submitted to Phys. Rev.
Exploring the dynamic interplay of cognitive load and emotional arousal by using multimodal measurements: Correlation of pupil diameter and emotional arousal in emotionally engaging tasks
Multimodal data analysis and validation based on streams from
state-of-the-art sensor technology such as eye-tracking or emotion recognition
using the Facial Action Coding System (FACTs) with deep learning allows
educational researchers to study multifaceted learning and problem-solving
processes and to improve educational experiences. This study aims to
investigate the correlation between two continuous sensor streams, pupil
diameter as an indicator of cognitive workload and FACTs with deep learning as
an indicator of emotional arousal (RQ 1a), specifically for epochs of high,
medium, and low arousal (RQ 1b). Furthermore, the time lag between emotional
arousal and pupil diameter data will be analyzed (RQ 2). 28 participants worked
on three cognitively demanding and emotionally engaging everyday moral dilemmas
while eye-tracking and emotion recognition data were collected. The data were
pre-processed in Phyton (synchronization, blink control, downsampling) and
analyzed using correlation analysis and Granger causality tests. The results
show negative and statistically significant correlations between the data
streams for emotional arousal and pupil diameter. However, the correlation is
negative and significant only for epochs of high arousal, while positive but
non-significant relationships were found for epochs of medium or low arousal.
The average time lag for the relationship between arousal and pupil diameter
was 2.8 ms. In contrast to previous findings without a multimodal approach
suggesting a positive correlation between the constructs, the results
contribute to the state of research by highlighting the importance of
multimodal data validation and research on convergent vagility. Future research
should consider emotional regulation strategies and emotional valence.Comment: The first two authors contributed equally to the manuscrip
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