Probing the collective excitations of a spinor polariton fluid

We propose a pump-probe setup to analyze the properties of the collective excitation spectrum of a spinor polariton fluid. By using a linear response approximation scheme, we carry on a complete classification of all excitation spectra, as well as their intrinsic degree of polarization, in terms of two experimentally tunable parameters only: themean-field polarization angle and a rescaled pump detuning.We evaluate the system response to the external probe, and show that the transmitted light can undergo a spin rotation along the dispersion for spectra that we classify as diffusivelike. We show that in this case, the spin flip predicted along the dispersion is enhanced when the system is close to a parametrically amplified instabilityM.V.R. gratefully acknowledges support in the form of a Ph.D. fellowship of the Research Foundation–Flanders (FWO). M.W. acknowledges financial support from the FWO-Odysseus program. F.M.M. acknowledges financial support from the Ministerio de Economíaa y Competitividad (MINECO) (Contract No. MAT2011-22997) and the Comunidad Autonoma de Madrid (CAM) (Contract No. S-2009/ESP-1503

Bose-Einstein condensation of Efimovian triples in the unitary Bose gas

In an atomic Bose-Einstein condensate quenched to the unitary regime, we predict the sequential formation of a significant fraction of condensed pairs and triples. At short-distances, we demonstrate the two-body and Efimovian character of the condensed pairs and triples, respectively. As the system evolves, the size of the condensed pairs and triples becomes comparable to the interparticle distance, such that many-body effects become significant. The structure of the condensed triples depends on the relative size of Efimov states to density scales. Unexpectedly, we find universal condensed triples in the limit where these scales are well-separated. Our findings provide a new framework for understanding dynamics in the unitary regime as the Bose-Einstein condensation of few-body composites

Cumulant theory of the unitary Bose gas: Prethermal and Efimovian dynamics

We study the quench of a degenerate ultracold Bose gas to the unitary regime, where interactions are as strong as allowed by quantum mechanics. We lay the foundations of a cumulant theory able to capture simultaneously the three-body Efimov effect and ergodic evolution. After an initial period of rapid quantum depletion, a universal prethermal stage is established characterized by a kinetic temperature and an emergent Bogoliubov dispersion law while the microscopic degrees of freedom remain far-from-equilibrium. Integrability is then broken by higher-order interaction terms in the many-body Hamiltonian, leading to a momentum-dependent departure from power law to decaying exponential behavior of the occupation numbers at large momentum. We find also signatures of the Efimov effect in the many-body dynamics and make a precise identification between the observed beating phenomenon and the binding energy of an Efimov trimer. Throughout the work, our predictions for a uniform gas are quantitatively compared with experimental results for quenched unitary Bose gases in uniform potentials.Comment: 34 pages, 12 figure

Cumulant theory of the unitary Bose gas: Prethermal and Efimovian dynamics

We study the quench of a degenerate ultracold Bose gas to the unitary regime, where interactions are as strong as allowed by quantum mechanics. We lay the foundations of a cumulant theory able to capture simultaneously the three-body Efimov effect and ergodic evolution. After an initial period of rapid quantum depletion, a universal prethermal stage is established characterized by a kinetic temperature and an emergent Bogoliubov dispersion law while the microscopic degrees of freedom remain far-from-equilibrium. Integrability is then broken by higher-order interaction terms in the many-body Hamiltonian, leading to a momentum-dependent departure from power law to decaying exponential behavior of the occupation numbers at large momentum. We find also signatures of the Efimov effect in the many-body dynamics and make a precise identification between the observed beating phenomenon and the binding energy of an Efimov trimer. Throughout the work, our predictions for a uniform gas are quantitatively compared with experimental results for quenched unitary Bose gases in uniform potentials

Cumulant SNEG Codes

This program is linked to the article V.E. Colussi et al. "Cumulant theory of the unitary Bose gas: Prethermal and Efimovian dynamics". It verifies the cumulant equations of motion Eqs. (46--50) and (124--135). It includes also J. van de Kraats, "Cumulant expansion for an ultracold quantum gas",TU/e Bachelor thesis 2019. Contact details: [email protected] / [email protected]