33 research outputs found
Interplay between Josephson and Aharonov-Bohm effects in Andreev interferometers
Proximity induced quantum coherence of electrons in multi-terminal
voltage-driven hybrid normal-superconducting nanostructures may result in a
non-trivial interplay between topology-dependent Josephson and Aharonov-Bohm
effects. We elucidate a trade-off between stimulation of the voltage-dependent
Josephson current due to non-equilibrium effects and quantum dephasing of
quasiparticles causing reduction of both Josephson and Aharonov-Bohm currents.
We also predict phase-shifted quantum coherent oscillations of the induced
electrostatic potential as a function of the externally applied magnetic flux.
Our results may be employed for engineering superconducting nanocircuits with
controlled quantum properties
Non-Gaussian correlations imprinted by local dephasing in fermionic wires
We study the behavior of an extended fermionic wire coupled to a local
stochastic field. Since the quantum jump operator is Hermitian and quadratic in
fermionic operators, it renders the model soluble, allowing investigation of
the properties of the non-equilibrium steady-state and the role of
dissipation-induced fluctuations. We derive a closed set of equations of motion
solely for the two-point correlator; on the other hand, we find, surprisingly,
that the many-body state exhibits non-Gaussian correlations. Density-density
correlation function demonstrates a crossover from a regime of weak dissipation
characterized by moderate heating and stimulated fluctuations to a quantum Zeno
regime ruled by strong dissipation, which tames quantum fluctuations. Instances
of soluble dissipative impurities represent an experimentally viable platform
to understand the interplay between dissipation and Hamiltonian dynamics in
many-body quantum systems.Comment: Accepted to Phys. Rev. B as rapid communicatio
Amplitude dynamics of charge density wave in LaTe: theoretical description of pump-probe experiments
We formulate a dynamical model to describe a photo-induced charge density
wave (CDW) quench transition and apply it to recent multi-probe experiments on
LaTe [A. Zong et al., Nat. Phys. 15, 27 (2019)]. Our approach relies on
coupled time-dependent Ginzburg-Landau equations tracking two order parameters
that represent the modulations of the electronic density and the ionic
positions. We aim at describing the amplitude of the order parameters under the
assumption that they are homogeneous in space. This description is supplemented
by a three-temperature model, which treats separately the electronic
temperature, temperature of the lattice phonons with stronger couplings to the
electronic subsystem, and temperature of all other phonons. The broad scope of
available data for LaTe and similar materials as well as the synergy
between different time-resolved spectroscopies allow us to extract model
parameters. The resulting calculations are in good agreement with ultra-fast
electron diffraction experiments, reproducing qualitative and quantitative
features of the CDW amplitude evolution during the initial few picoseconds
after photoexcitation.Comment: 21 pages, 14 figures; this version is almost identical to the
published version; comparing to the earlier arXiv submission, current version
contains a new figure (Fig.10), and a broader discussion of theoretical
results and approximation
Efficient variational approach to the Fermi polaron problem in two dimensions, both in and out of equilibrium
We develop a non-Gaussian variational approach that enables us to study both
equilibrium and far-from-equilibrium physics of the two-dimensional Fermi
polaron. This method provides an unbiased analysis of the polaron-to-molecule
phase transition without relying on truncations in the total number of
particle-hole excitations. Our results -- which include the ground state energy
and quasiparticle residue -- are in qualitative agreement with the known Monte
Carlo calculations. The main advantage of the non-Gaussian states compared to
conventional numerical methods is that they enable us to explore long-time
polaron evolution and, in particular, study various spectral properties
accessible to both solid-state and ultracold atom experiments. We design two
types of radiofrequency spectroscopies to measure polaronic and molecular
spectral functions. Depending on the parameter regime, we find that these
spectral functions and fermionic density profiles near the impurity display
either long-lived oscillations between the repulsive and attractive polaron
branches or exhibit fast relaxational dynamics to the molecular state.Comment: 12 pages, 7 figure
Self-similar dynamics of order parameter fluctuations in pump-probe experiments
Upon excitation by a laser pulse, broken-symmetry phases of a wide variety of
solids demonstrate similar order parameter dynamics characterized by a dramatic
slowing down of relaxation for stronger pump fluences. Motivated by this
recurrent phenomenology, we develop a simple non-perturbative effective model
of dynamics of collective bosonic excitations in pump-probe experiments. We
find that as the system recovers after photoexcitation, it shows universal
prethermalized dynamics manifesting a power-law, as opposed to exponential,
relaxation, explaining the slowing down of the recovery process. For strong
quenches, long-wavelength over-populated transverse modes dominate the
long-time dynamics; their distribution function exhibits universal scaling in
time and space, whose universal exponents can be computed analytically. Our
model offers a unifying description of order parameter fluctuations in a regime
far from equilibrium, and our predictions can be tested with available
time-resolved techniques
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Amplitude dynamics of the charge density wave in LaTe3: Theoretical description of pump-probe experiments
We formulate a dynamical model to describe a photo-induced charge density
wave (CDW) quench transition and apply it to recent multi-probe experiments on
LaTe [A. Zong et al., Nat. Phys. 15, 27 (2019)]. Our approach relies on
coupled time-dependent Ginzburg-Landau equations tracking two order parameters
that represent the modulations of the electronic density and the ionic
positions. We aim at describing the amplitude of the order parameters under the
assumption that they are homogeneous in space. This description is supplemented
by a three-temperature model, which treats separately the electronic
temperature, temperature of the lattice phonons with stronger couplings to the
electronic subsystem, and temperature of all other phonons. The broad scope of
available data for LaTe and similar materials as well as the synergy
between different time-resolved spectroscopies allow us to extract model
parameters. The resulting calculations are in good agreement with ultra-fast
electron diffraction experiments, reproducing qualitative and quantitative
features of the CDW amplitude evolution during the initial few picoseconds
after photoexcitation
Accelerating analysis of Boltzmann equations using Gaussian mixture models: Application to quantum Bose-Fermi mixtures
The Boltzmann equation is a powerful theoretical tool for modeling the
collective dynamics of quantum many-body systems subject to external
perturbations. Analysis of such a model gives access to linear response
properties such as collective modes and transport coefficients that
characterize a system, but often proves intractable due to computational costs
associated with multidimensional integrals describing collision processes.
Here, we present a method to resolve this bottleneck, enabling efficient study
of the linear response of a broad class of quantum many-body systems whose
behavior can be described using a Boltzmann equation. Specifically, we
demonstrate that a Gaussian mixture model can accurately represent equilibrium
distribution functions and, when combined with the variational method of
moments framework, allows efficient computation of collision integrals. We
apply this method to investigate the collective behavior of a quantum
Bose-Fermi mixture of cold atoms in a cigar-shaped trap, focusing on monopole
and quadrupole collective modes above the Bose-Einstein transition temperature.
We find a rich phenomenology that spans interference effects between bosonic
and fermionic collective modes, dampening of these modes, and the emergence of
hydrodynamics in various parameter regimes. Typical spectral functions exhibit
Fano interference profiles, systems with dilute fermions manifest behavior
reminiscent of Bose polarons, and systems with comparable bosonic and fermionic
densities display hallmarks of hydrodynamics such as mode-locking. These
effects are readily verifiable with modern cold-atom experiments, and the
method developed here opens the door to understanding the collective behavior
of many fundamental and technologically-relevant systems.Comment: 32 page (19 pages of the main text), 10 figures (7 are in the main
text