Bulletin of the American Physical Society
49th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 63, Number 5
Monday–Friday, May 28–June 1 2018; Ft. Lauderdale, Florida
Session S03: Focus Session: Bose and Fermi Polarons |
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Chair: Chris Vale, Swinburne University Room: Grand B |
Thursday, May 31, 2018 2:00PM - 2:30PM |
S03.00001: Universality of an impurity in a Bose-Einstein condensate Invited Speaker: Meera Parish We consider the simplest strongly interacting Bose system, where an impurity particle (polaron) resonantly interacts with a Bose-Einstein condensate (BEC). Focusing on the ground state, we will introduce a variational wave function for the polaron that goes beyond previous work and includes up to three Bogoliubov excitations of the BEC, thus allowing us to capture both Efimov trimers and associated tetramers. We show that the length scale associated with Efimov trimers (i.e., the three-body parameter) can strongly affect the polaron's behaviour, even at densities where there are no well-defined Efimov states. However, by comparing our results with recent quantum Monte Carlo calculations, we argue that the polaron energy is a \emph{universal} function of the Efimov three-body parameter for sufficiently low boson densities. [Preview Abstract] |
Thursday, May 31, 2018 2:30PM - 3:00PM |
S03.00002: Polaron dynamics in strongly correlated systems Invited Speaker: Frederic Chevy The polaron problem describes the behavior of a single impurity immersed in a many-body background. Introduced first to describe the interaction of an electron with the acoustic excitations of a lattice, it is more generally the simplest, non-trivial many-body system and can be used as a test-bed for advanced quantum-many body theories. In this talk I will describe recent experiments on the interaction of a bosonic impurity with a strongly-correlated fermionic superfluid. In the regime of weak interspecies coupling, I will show that the study of the dynamics [1,2] as well as the lifetime of the impurity [3] can be used as a quantitative probe of both macroscopic and microscopic properties of the surrounding medium. [1] I. Ferrier-Barbut, M. Delehaye, S. Laurent, A.T. Grier, M. Pierce, B.S. Rem, F. Chevy, C. Salomon, Science 345, 1035 (2014) [2] M. Delehaye, S. Laurent, I. Ferrier-Barbut, S. Jin, F. Chevy, C. Salomon, Phys. Rev. Lett. 115, 265303 (2015 [3] S. Laurent, M. Pierce, M. Delehaye, T. Yefsah, F. Chevy, C. Salomon, Phys. Rev. Lett. 118, 103403 (2017) [Preview Abstract] |
Thursday, May 31, 2018 3:00PM - 3:12PM |
S03.00003: A heavy impurity immersed in a Bose-Einstein Condensate Zoe Yan, Carsten Robens, Yiqi Ni, Martin Zwierlein Impurities immersed in a bosonic bath represent a fundamental problem in many-body physics. These Bose polarons give rise to a wealth of new quantum phenomena, both in solid state systems and in ultracold atomic mixtures. We report on the creation and study of Bose polarons using degenerate fermionic 40K atoms immersed in a Bose-Einstein condensate (BEC) of 23Na. We observe the formation of the quasiparticles (the Bose polarons) and measure their energy landscape via radio-frequency ejection spectroscopy. Energies are measured across a variety of interaction strengths by tuning an interspecies magnetic Feshbach resonance. Besides measuring static properties such as polaron energy, we study collective oscillations between the majority BEC atoms and the impurities, demonstrating a strong locking of the two species' motion when their interaction strengths approach the unitary limit. Such measurements of polaron properties will inform work on a wide range of quantum phenomena, including high-Tc superconductivity and superfluid helium mixtures. [Preview Abstract] |
Thursday, May 31, 2018 3:12PM - 3:24PM |
S03.00004: Repulsive polarons in alkaline-earth(-like) atoms across an orbital Feshbach resonance Tian-Shu Deng, Zhuo-Cheng Lu, Yue-Ran Shi, Jin-Ge Chen, Wei Zhang, Wei Yi We characterize properties of the so-called repulsive polaron across the recently discovered orbital Feshbach resonance in alkaline-earth(-like) atoms. Being a metastable quasiparticle excitation at the positive energy, the repulsive polaron is induced by the interaction between an impurity atom and a Fermi sea. By analyzing in detail the energy, the polaron residue, the effective mass, and the decay rate of the repulsive polaron, we reveal interesting features that are uniquely related to the two-channel nature of the orbital Feshbach resonance. In particular, we demonstrate that the life time of the repulsive polaron is non-monotonic in the Zeeman-field detuning bewteen the two channels, and has a maximum on the BEC-side of the resonance. By considering the stability of a mixture of the impurity and the majority atoms against phase separation, we show that the itinerant ferromagnetism may exist near the orbital Feshbach resonance at large atomic densities. Our results can be readily probed experimentally, and have interesting implications for the observation of itinerant ferromagnetism near an orbital Feshbach resonance. [Preview Abstract] |
Thursday, May 31, 2018 3:24PM - 3:36PM |
S03.00005: Resonant quantum impurities in a Fermi gas: From the classical limit to Fermi polarons Zhenjie Yan, Biswaroop Mukherjee, Parth Patel, Airlia Shaffer-Moag, Cedric Wilson, Lev Kendrick, Richard Fletcher, Julian Struck, Martin Zwierlein The fate of impurities immersed in a quantum environment is a paradigmatic problem in many-body physics. We prepare a highly imbalanced, homogeneous spin mixture of fermions with resonant interactions and study the emergence of Fermi polarons upon cooling. The energy, lifetime and coherence of the Fermi polarons are extracted from radio-frequency spectra. Upon cooling the gas from non-degenerate temperatures, we first observe an increase in the spectral width of the impurity particles, revealing their shortened mean-free path. As impurities dress into Fermi polarons, the spectra narrow again. Furthermore, we measure the pressure temperature relation of these imbalanced spin mixtures. The equation of state shows a good agreement with a simple Fermi liquid pressure ansatz at low temperature while it can be described by a Virial expansion in the high temperature regime. [Preview Abstract] |
Thursday, May 31, 2018 3:36PM - 3:48PM |
S03.00006: Quantum dynamics of impurities coupled to a Fermi sea Jesper Levinsen, Meera Parish We consider the dynamics of an impurity atom immersed in an ideal Fermi gas at zero temperature. We focus on the coherent quantum evolution of the impurity following a quench to strong impurity-fermion interactions, where the interactions are assumed to be short range like in cold-atom experiments. To approximately model the many-body time evolution, we use a truncated basis method, where at most two particle-hole excitations of the Fermi sea are included. When the system is initially non-interacting, we show that our method exactly captures the short-time dynamics following the quench, and we find that the overlap between initial and final states displays a universal non-analytic dependence on time in this limit. We further demonstrate how our method can be used to compute the impurity spectral function, as well as describe many-body phenomena involving coupled impurity spin states, such as Rabi oscillations in a medium or highly engineered quantum quenches. [Preview Abstract] |
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