67 research outputs found
A dissipative time crystal with or without Z(2) symmetry breaking
We study an emergent semiclassical time crystal composed of two interacting driven-dissipative
bosonic modes. The system has a discrete Z2 spatial symmetry which, depending on the strength
of the drive, can be broken in the time-crystalline phase or it cannot. An exact semiclassical
mean-field analysis, numerical simulations in the quantum regime, and the spectral analysis of the
Liouvillian are combined to show the emergence of the time crystal and to prove the robustness of
the oscillation period against quantum fluctuations
Effect of a photonic band gap on the threshold and output power of solid-state lasers and light-emitting diodes
We present results for the operation of a three-level solid-state laser both with normal and with completely suppressed spontaneous emission between the lasing levels. The output power difference in these two cases drops as the pump rate is increased above threshold and is not greatly different at higher powers. The threshold pump power, although typically reduced by an order of magnitude, is not zero and our results thus throw further light on the concept of âthresholdlessâ lasing. The theory is also applicable to light-emitting diodes and amplifiers which function on the same principles as a laser
Non-equilibrium berezinskii-kosterlitz-thouless transition in driven-dissipative condensate
We study the two-dimensional phase transition of a driven-dissipative system of exciton-polaritons under non-resonant pumping. Stochastic calculations are used to investigate the Berezinskii-Kosterlitz-Thoulessâlike phase diagram for experimentally realistic parameters, with a special attention to the non-equilibrium features
Excitonic binding in coupled quantum wells
We study excitonic states in the presence of applied electric field in 8-nm GaAs coupled quantum wells (QWâs) separated by a 4-nm Al0.33Ga0.67As barrier and in 6-nm In0.1Ga0.9As coupled QWâs separated by a 4-nm GaAs barrier in which effects attributed to macroscopically ordered excitonic states have been recently reported. We discuss the differences in the nature of the states and in the origin of confinement which determines the change of excitonic properties with increase in the applied electric field in both structures. We have found that the indirect exciton binding energy for the field amplitude used in the experiment with InGaAs QWâs is around 3.5 meV, much less than the previously reported 10 meV value. This suggests that the optically induced ring structure, reported to persist to near 100 K, might not be caused by collective excitonic transport
Properties of the signal mode in the polariton optical parametric oscillator regime
Theoretical analyses of the polariton optical parametric oscillator (OPO) regime often rely on a mean-field approach based on the complex Gross-Pitaevskii equations in a three-mode approximation, where only three momentum states, the signal, pump, and idler, are assumed to be significantly occupied. This approximation, however, lacks a constraint to uniquely determine the signal and idler momenta. In contrast, multimode numerical simulations and experiments show a unique momentum structure for the OPO states. In this work we show that an estimate for the signal momentum chosen by the system can be found from a simple analysis of the pump-only configuration. We use this estimate to investigate how the chosen signal momentum depends on the properties of the drive
Critical slowing down in circuit quantum electrodynamics
Critical slowing down of the time it takes a system to reach equilibrium is a key signature of bistability in dissipative first-order phase transitions. Understanding and characterizing this process can shed light on the underlying many-body dynamics that occur close to such a transition. Here, we explore the rich quantum activation dynamics and the appearance of critical slowing down in an engineered superconducting quantum circuit. Specifically, we investigate the intermediate bistable regime of the generalized Jaynes-Cummings Hamiltonian (GJC), realized by a circuit quantum electrodynamics (cQED) system consisting of a transmon qubit coupled to a microwave cavity. We find a previously unidentified regime of quantum activation in which the critical slowing down reaches saturation and, by comparing our experimental results with a range of models, we shed light on the fundamental role played by the qubit in this regime
Dynamical Critical Exponents in Driven-Dissipative Quantum Systems
We study the phase ordering of parametrically and incoherently driven microcavity polaritons after an
infinitely rapid quench across the critical region. We confirm that the system, despite its driven-dissipative
nature, satisfies the dynamical scaling hypothesis for both driving schemes by exhibiting self-similar
patterns for the two-point correlator at late times of the phase ordering. We show that polaritons are
characterized by the dynamical critical exponent z â 2 with topological defects playing a fundamental role
in the dynamics, giving logarithmic corrections both to the power-law decay of the number of vortices and
to the associated growth of the characteristic length scale
Quantum-fluid dynamics of microcavity polaritons
Semiconductor microcavities offer a unique system to investigate the physics
of weakly interacting bosons. Their elementary excitations, polaritons--a
mixture of excitons and photons--behave, in the low density limit, as bosons
that can undergo a phase transition to a regime characterised by long range
coherence. Condensates of polaritons have been advocated as candidates for
superfluidity; and the formation of vortices as well as elementary excitations
with a linear dispersion are actively sought after. In this work, we have
created and set in motion a macroscopically degenerate state of polaritons and
let it collide with a variety of defects present in the sample. Our experiments
show striking manifestations of a coherent light-matter packet that displays
features of a superfluid, although one of a highly unusual character as it
involves an out-of-equilibrium dissipative system where it travels at
ultra-fast velocity of the order of 1% the speed of light. Our main results are
the observation of i) a linear polariton dispersion accompanied with
diffusion-less motion, ii) flow without resistance when crossing an obstacle,
iii) suppression of Rayleigh scattering and iv) splitting into two fluids when
the size of the obstacle is comparable with the size of the wavepacket. This
work opens the way to the investigation of new phenomenology of
out-of-equilibrium condensates.Comment: 22 pages, 5 figure
Observation of Superfluidity of Polaritons in Semiconductor Microcavities
One of the most striking manifestations of quantum coherence in interacting
boson systems is superfluidity. Exciton-polaritons in semiconductor
microcavities are two-dimensional composite bosons predicted to behave as
particular quantum fluids. We report the observation of superfluid motion of
polaritons created by a laser in a semiconductor microcavity. Superfluidity is
investigated in terms of the Landau criterion and manifests itself as the
suppression of scattering from defects when the flow velocity is slower than
the speed of sound in the fluid. On the other hand, a Cerenkov-like wake
pattern is clearly observed when the flow velocity exceeds the speed of sound.
The experimental findings are in excellent quantitative agreement with the
predictions based on a generalized Gross-Pitaevskii theory, showing that
polaritons in microcavities constitute a very rich system for exploring the
physics of non-equilibrium quantum fluids.Comment: 14 pages, 3 figure
Characterizing the morbid genome of ciliopathies
Background Ciliopathies are clinically diverse disorders of the primary cilium. Remarkable progress has been made in understanding the molecular basis of these genetically heterogeneous conditions; however, our knowledge of their morbid genome, pleiotropy, and variable expressivity remains incomplete. Results We applied genomic approaches on a large patient cohort of 371 affected individuals from 265 families, with phenotypes that span the entire ciliopathy spectrum. Likely causal mutations in previously described ciliopathy genes were identified in 85% (225/265) of the families, adding 32 novel alleles. Consistent with a fully penetrant model for these genes, we found no significant difference in their âmutation loadâ beyond the causal variants between our ciliopathy cohort and a control non-ciliopathy cohort. Genomic analysis of our cohort further identified mutations in a novel morbid gene TXNDC15, encoding a thiol isomerase, based on independent loss of function mutations in individuals with a consistent ciliopathy phenotype (Meckel-Gruber syndrome) and a functional effect of its deficiency on ciliary signaling. Our study also highlighted seven novel candidate genes (TRAPPC3, EXOC3L2, FAM98C, C17orf61, LRRCC1, NEK4, and CELSR2) some of which have established links to ciliogenesis. Finally, we show that the morbid genome of ciliopathies encompasses many founder mutations, the combined carrier frequency of which accounts for a high disease burden in the study population. Conclusions Our study increases our understanding of the morbid genome of ciliopathies. We also provide the strongest evidence, to date, in support of the classical Mendelian inheritance of Bardet-Biedl syndrome and other ciliopathies
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