We study the early-time dynamics of a degenerate Bose gas after a sudden quench of the interaction strength, starting from a weakly interacting gas. By making use of a time-dependent generalization of the Nozières-Saint-James variational formalism, we describe the crossover of the early-time dynamics from shallow to deep interaction quenches. We analyze the coherent oscillations that characterize both the density of excited states and the Tan's contact as a function of the final scattering length. For shallow quenches, the oscillatory behaviour is negligible and the dynamics is universally governed by the healing length and the mean-field interaction energy. By increasing the final scattering length to intermediate values, we reveal a universal regime where the period of the coherent atom-molecule oscillations is set by the molecule binding energy. For the largest scattering lengths we can numerically simulate in the unitary regime, we find a universal scaling behaviour of the typical growth time of the momentum distribution in agreement with recent experimental observations [C. Eigen et al., Nature 563, 221 (2018)]. * alberto.munnozd@estudiante.uam.es † francesca.marchetti@uam.es arXiv:1811.12135v1 [cond-mat.quant-gas]
We report on the demonstration of an effective, nonlinearity-induced non-reciprocal behavior in a single non-magnetic multi-mode Taiji resonator. Non-reciprocity is achieved by a combination of an intensity-dependent refractive index and of a broken spatial reflection symmetry. Continuous wave power dependent transmission experiments show non-reciprocity and a direction-dependent optical bistability loop. These can be explained in terms of the unidirectional mode coupling that causes an asymmetric power enhancement in the resonator. The observations are quantitatively reproduced by a numerical finite-element theory and physically explained by an analytical coupled-mode theory. This nonlinear Taiji resonator has the potential of being the building block of large arrays where to study topological and/or non-Hermitian physics. This represents an important step towards the miniaturization of nonreciprocal elements for photonic integrated networks.
We study the quantum dynamics of massive impurities embedded in a strongly interacting twodimensional atomic gas driven into the fractional quantum Hall (FQH) regime under the effect of a synthetic magnetic field. For suitable values of the atom-impurity interaction strength, each impurity can capture one or more quasi-hole excitations of the FQH liquid, forming a bound molecular state with novel physical properties. An effective Hamiltonian for such molecules is derived within the Born-Oppenheimer approximation, which provides renormalized values for the effective mass, charge and statistics of such anyonic molecules by combining the finite mass of the impurity and the fractional charge and anyonic statistics of the quasi-holes. The anyonic statistics is shown to provide a long-range Aharonov-Bohm-like interaction between molecules. The resulting relative phase of the direct and exchange scattering channels can be thus extracted from the angular position of the interference fringes in the scattering cross section of a pair of colliding molecules. Different configurations providing direct and quantitative insight on the fractional charge and the anyonic statistics of quasi-hole excitations in FQH liquids are highlighted for both cold atoms and photonic systems.
We develop a general formalism to study laser operation in active micro-ring resonators supporting two counterpropagating modes. Our formalism is based on the coupled-mode equations of motion for the field amplitudes in the two counterpropagating modes and a linearized analysis of the small perturbations around the steady state. We show that the devices including an additional S-shaped waveguide establishing an unidirectional coupling between both modes -the so-called "Taiji" resonators (TJR)-feature a preferred chirality on the laser emission and can ultimately lead to unidirectional lasing even in the presence of sizable backscattering. The efficiency of this mode selection process is further reinforced by the Kerr nonlinearity of the material. This stable unidirectional laser operation can be seen as an effective breaking of T -reversal symmetry dynamically induced by the breaking of the P-symmetry of the underlying device geometry. This mechanism appears as a promising building block to ensure non-reciprocal behaviors in integrated photonic networks and topological lasers without the need for magnetic elements.
We study the linear and nonlinear response of a unidirectional reflector where a nonlinear breaking of the Lorentz reciprocity is observed. The device under test consists of a racetrack microresonator, with an embedded S-shaped waveguide, coupled to an external bus waveguide (BW). This geometry of the microresonator is known as “taiji” microresonator (TJMR). Here, we show that a full description of the device needs to consider also the role of the BW, which introduces (i) Fabry-Perot oscillations (FPOs) due to reflections at its facets, and (ii) asymmetric losses, which depend on the actual position of the TJMR. At sufficiently low powers the asymmetric loss does not affect the unidirectional behavior, but the FP interference fringes can cancel the effect of the S-shaped waveguide. However, at high input power, both the asymmetric loss and the FPOs contribute to the redistribution of energy between counterpropagating modes within the TJMR. This strongly modifies the nonlinear response, giving rise to counter-intuitive features where, due to the FP effect and the asymmetric losses, the BW properties can determine the violation of the Lorentz reciprocity and, in particular, the difference between the transmittance in the two directions of excitation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.