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A simple model based on the dynamics of coupled charge density wave domains is proposed to account for the sudden onset of nonlinear conduction, hysteresis in the current voltage characteristics and time delay phenomena, often observed in several model compounds. We suggest that while the overdamped phase dynamics does not lead to hysteretic behavior in the single or infinite degree of freedom limit, finite degrees of freedom restore this phenomenon.

We study the overdamped phase dynamics of a charge-density wave (CDW) pinned by randomly located impurities fully including the internal degrees of freedom of the CDW. The current-field behavior, the threshold field, and the phase diagram (pinned versus unpinned) are characterized and discussed. The narrow-band noise is computed explicitly for the full many-body problem, and it is found to be of the type observed in Nb${\mathrm{Se}}_{3}$.

We present an experimental and theoretical study of the response of a dipolar supersolid to a Bragg excitation at high-energy defined by the impulse approximation regime. We experimentally observe a continuous reduction of the response when tuning the contact interaction from an ordinary Bose-Einstein condensate to a supersolid state and ultimately to an incoherent array of droplets. Already in the supersolid regime, the observed reduction is faster than the one theoretically predicted by the Bogoliubov--de Gennes theory. By comparing experiments and theories, we are able to attribute this discrepancy to the presence of coherent phase dynamics induced by the crossing of the phase transition. The phase variations are found to change character along the phase diagram and become predominantly incoherent only when reaching the incoherent-droplet regime.

We study experimentally and theoretically the dynamics of a spatially extended (along the propagation direction) oscillatory medium with coherent forcing. We observe abnormally high events, responsible for a different statistics of intensity and pulse height, in a regime where solitons and roll patterns are unstable. We focus on the formation of these high-peak events and their connection to the phase dynamics. Each abnormal event can be associated with a change in the slope of the phase time trace. Furthermore, the coexistence of ±2π phase rotations inside the cavity can be associated to the observation of abnormal events, similarly to recent predictions in bidimensional vortex turbulence.

To emulate a spiking neuron, a photonic component needs to be excitable. In this paper, we theoretically simulate and experimentally demonstrate cascadable excitability near a self-pulsation regime in high-Q-factor silicon-on-insulator microrings. For the theoretical study we use Coupled Mode Theory. While neglecting the fast energy and phase dynamics of the cavity light, we can still preserve the most important microring dynamics, by only keeping the temperature difference with the surroundings and the amount of free carriers as dynamical variables of the system. Therefore we can analyse the microring dynamics in a 2D phase portrait. For some wavelengths, when changing the input power, the microring undergoes a subcritical Andronov-Hopf bifurcation at the self-pulsation onset. As a consequence the system shows class II excitability. Experimental single ring excitability and self-pulsation behaviour follows the theoretic predictions. Moreover, simulations and experiments show that this excitation mechanism is cascadable.

We investigate the quantum dynamics for a molecular-state-model system interacting with a resonant two-mode squeezed coherent field, in which each mode is initially correlated. As an example, we consider a three-state molecular model, which mimics the electronic excited states of trans-octatetraene obtained by a full-configuration-interaction calculation using the Pariser-Parr-Pople Hamiltonian, interacting with a two-mode squeezed coherent field. For comparison, we also perform parallel studies, in which the initial fields are prepared in uncorrelated two-mode states, i.e., a two-mode coherent state and a two-mode thermal state. It is well known that the case of two-mode coherent field leads to the usual collapse-revival phenomena of the Rabi oscillations, while the case of a two-mode thermal state leads to an irregular evolution of them. Although the two-mode squeezed coherent field exhibits similar collapse-revival behavior to that for the two-mode coherent field, some differences are detected in the amplitudes and periods of collapse-revival oscillations. Further, the dynamics of off-diagonal molecular density matrices between the ground and second excited states for these two fields are found to be distinctively different from each other. Such attractive behavior is found to be closely associated with the two-mode photon-phase dynamics obtained by the Pegg-Barnett phase operator and the initial quasiprobability (Q function) distribution of photons. These differences in phase properties are also shown to significantly affect the dynamics of the information entropy for a molecule, i.e., molecular entropy, which represents the degree of entanglement between the molecule and photons.

Driven-dissipative systems in two dimensions can differ substantially from their equilibrium counterparts. In particular, a dramatic loss of off-diagonal algebraic order and superfluidity has been predicted to occur due to the interplay between coherent dynamics and external drive and dissipation in the thermodynamic limit. We show here that the order adopted by the system can be substantially altered by a simple, experimentally viable, tuning of the driving process. More precisely, by considering the long-wavelength phase dynamics of a polariton quantum fluid in the optical parametric oscillator regime, we demonstrate that simply changing the strength of the pumping mechanism in an appropriate parameter range can substantially alter the level of effective spatial anisotropy induced by the driving laser, and move the system into distinct scaling regimes. These include: (i) the classic algebraically ordered superfluid below the Berezinskii-Kosterlitz-Thouless (BKT) transition, as in equilibrium; (ii) the non-equilibrium, long-wave-length fluctuation dominated Kardar-Parisi-Zhang (KPZ) phase; and the two associated topological defect dominated disordered phases caused by proliferation of (iii) entropic BKT vortex-antivortex pairs or (iv) repelling vortices in the KPZ phase. Further, by analysing the renormalization group flow in a finite system, we examine the length scales associated with these phases, and assess their observability in current experimental conditions., Comment: 18 pages, 11 figures

© 2017 [Optical Society of America]. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved. The generation of extreme intensity pulses in an optically injected semiconductor laser is studied numerically by using a well-known rate equation model. We show that step-up perturbations of the laser pump current can trigger extreme pulses. We study the perturbation parameters (amplitude, duration) that are more likely to trigger a extreme pulse, and compare the properties of the generated extreme pulses with those spontaneous emitted, which are due to the intrinsic deterministic dynamics of the laser. We study how the phase of the optical field evolves during the pulses and compare both types of pulses (generated by external perturbations and generated by intrinsic nonlinear dynamics). We find that in both cases the phase dynamics is similar with an abrupt rise and fall: as an extreme pulse begins, the phase grows abruptly and reaches a local maximum at the peak of the pulse, then, when the pulse is over, the phase falls down to a value which is similar to the one before the pulse started.

Driven-dissipative systems in two dimensions can differ substantially from their equilibrium counterparts. In particular, a dramatic loss of off-diagonal algebraic order and superfluidity has been predicted to occur because of the interplay between coherent dynamics and external drive and dissipation in the thermodynamic limit. We show here that the order adopted by the system can be substantially altered by a simple, experimentally viable tuning of the driving process. More precisely, by considering the long-wavelength phase dynamics of a polariton quantum fluid in the optical parametric oscillator regime, we demonstrate that simply changing the strength of the pumping mechanism in an appropriate parameter range can substantially alter the level of effective spatial anisotropy induced by the driving laser and move the system into distinct scaling regimes. These include (i) the classic algebraically ordered superfluid below the Berezinskii-Kosterlitz-Thouless (BKT) transition, as in equilibrium; (ii) the nonequilibrium, long-wavelength-fluctuation-dominated Kardar-Parisi-Zhang (KPZ) phase; and the two associated topological-defect-dominated disordered phases caused by proliferation of (iii) entropic BKT vortex-antivortex pairs or (iv) repelling vortices in the KPZ phase. Furthermore, by analyzing the renormalization group flow in a finite system, we examine the length scales associated with these phases and assess their observability in current experimental conditions.

We study the transverse-mode dynamics of vertical-cavity surface-emitting lasers with weak optical feedback. We use a model that takes into account the spatial dependence of the transverse modes and of two carrier density profiles, associated with confined carriers in the quantum well region of the laser and unconfined carriers in the barrier region. Optical feedback is included as in the Lang-Kobayashi model. We find that for adequate parameter values antiphase dynamics occurs. As the injection current varies, the antiphase dynamics is destroyed through a sequence of periodic mixed states leading to in-phase dynamics. In these mixed states there are time intervals in which the modes are in phase, followed by time intervals in which they are in antiphase. We study the origin of the antiphase dynamics, assessing the role of the different spatial profiles. We show that the competition between the different profiles leads to the observed antiphase behavior. 5555 2002 The American Physical Society., SCOPUS: ar.j, info:eu-repo/semantics/published

The chaotically driven circle map is considered as the simplest model of phase synchronization of a chaotic continuous-time oscillator by external periodic force. The phase dynamics is analyzed via phase-locking regions of the periodic cycles embedded in the strange attractor. It is shown that full synchronization, where all the periodic cycles are phase locked, disappears via the attractor-repeller collision. Beyond the transition an intermittent regime with exponentially rare phase slips, resulting from the trajectory's hits on an eyelet, is observed.

We report on the observation of spontaneous coherent oscillations in a microcavity polariton bosonic Josephson junction. The condensation of exciton polaritons takes place under incoherent excitation in a disordered environment, where double potential wells tend to appear in the disordered landscape. Coherent oscillations set on at an excitation power well above the condensation threshold. The time resolved population and phase dynamics reveal the analogy with the AC Josephson effect. We have introduced a theoretical two-mode model to describe the observed effects, which allows us to explain how the different realizations of the pulsed experiment have a similar phase relation.