1,103 research outputs found
Driven Bose-Hubbard dimer under nonlocal dissipation: A bistable time crystal
We investigate the critical behavior of the open coherently-driven
Bose-Hubbard dimer under nonlocal dissipation. A conserved quantity arises from
the nonlocal nature of the dissipation, rendering the dimer multistable. In the
weak-coupling semiclassical limit, the displayed criticality takes the form of
amplitude bistability and breaking of spatial and temporal symmetries. A
period-bistable time crystal is formed, consisting of Josephson-like
oscillations. Mean-field dynamics and quantum trajectories complement the
spectral analysis of the Liouvillian in the approach to the semiclassical
limit.Comment: Accepted in PRB. 6 pages, 2 figures. Supplemental material included.
Comments are welcom
Relaxation and hysteresis near Shapiro resonances in a driven spinor condensate
We study the coherent and dissipative aspects of a driven spin-1
Bose-Einstein condensate (BEC) when the Zeeman energy is modulated around a
static bias value. Resonances appear when the bias energy matches an integer
number of modulation quanta. They constitute the atomic counterpart of Shapiro
resonances observed in microwave-driven superconducting Josephson junctions.
The population dynamics near each resonance corresponds to slow and non-linear
secular oscillations on top of a rapid `micromotion'. At long times and in a
narrow window of modulation frequencies around each resonance, we observe a
relaxation to asymptotic states that are unstable without drive. These
stationary states correspond to phase-locked solutions of the Josephson
equations generalized to include dissipation, and are analogous to the
stationary states of driven superconducting junctions. We find that dissipation
is essential to understand this long-time behavior, and we propose a
phenomenological model to explain quantitatively the experimental results.
Finally, we demonstrate hysteresis in the asymptotic state of the driven spinor
BEC when sweeping the modulation frequency across a Shapiro resonance
Speeding-up a quantum refrigerator via counter-diabatic driving
We study the application of a counter-diabatic driving (CD) technique to
enhance the thermodynamic efficiency and power of a quantum Otto refrigerator
based on a superconducting qubit coupled to two resonant circuits. Although the
CD technique is originally designed to counteract non-adiabatic coherent
excitations in isolated systems, we find that it also works effectively in the
open system dynamics, improving the coherence-induced losses of efficiency and
power. We compare the CD dynamics with its classical counterpart, and find a
deviation that arises because the CD is designed to follow the energy
eigenbasis of the original Hamiltonian, but the heat baths thermalize the
system in a different basis. We also discuss possible experimental realizations
of our model.Comment: 9 pages, 8 figure
Nanoscale phase-engineering of thermal transport with a Josephson heat modulator
Macroscopic quantum phase coherence has one of its pivotal expressions in the
Josephson effect [1], which manifests itself both in charge [2] and energy
transport [3-5]. The ability to master the amount of heat transferred through
two tunnel-coupled superconductors by tuning their phase difference is the core
of coherent caloritronics [4-6], and is expected to be a key tool in a number
of nanoscience fields, including solid state cooling [7], thermal isolation [8,
9], radiation detection [7], quantum information [10, 11] and thermal logic
[12]. Here we show the realization of the first balanced Josephson heat
modulator [13] designed to offer full control at the nanoscale over the
phase-coherent component of thermal currents. Our device provides
magnetic-flux-dependent temperature modulations up to 40 mK in amplitude with a
maximum of the flux-to-temperature transfer coefficient reaching 200 mK per
flux quantum at a bath temperature of 25 mK. Foremost, it demonstrates the
exact correspondence in the phase-engineering of charge and heat currents,
breaking ground for advanced caloritronic nanodevices such as thermal splitters
[14], heat pumps [15] and time-dependent electronic engines [16-19].Comment: 6+ pages, 4 color figure
Time Delay Effects on Coupled Limit Cycle Oscillators at Hopf Bifurcation
We present a detailed study of the effect of time delay on the collective
dynamics of coupled limit cycle oscillators at Hopf bifurcation. For a simple
model consisting of just two oscillators with a time delayed coupling, the
bifurcation diagram obtained by numerical and analytical solutions shows
significant changes in the stability boundaries of the amplitude death, phase
locked and incoherent regions. A novel result is the occurrence of amplitude
death even in the absence of a frequency mismatch between the two oscillators.
Similar results are obtained for an array of N oscillators with a delayed mean
field coupling and the regions of such amplitude death in the parameter space
of the coupling strength and time delay are quantified. Some general analytic
results for the N tending to infinity (thermodynamic) limit are also obtained
and the implications of the time delay effects for physical applications are
discussed.Comment: 20 aps formatted revtex pages (including 13 PS figures); Minor
changes over the previous version; To be published in Physica
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