QSE Quantum Seminar: Emergence of non-Gaussian correlations in strongly-interacting ultracold Bose gases

Please join us for the QSE Center Quantum Seminar with Prof. David Clément from the Institute d’optique graduate school, who will speak Tuesday January 30 on "Emergence of non-Gaussian correlations in strongly-interacting ultracold Bose gases".
Location: CE 1 100

Pizzas will be available before the seminar at 12:00. All PhDs, postdocs, students, and PIs are welcome to join us.

TITLE: Emergence of non-Gaussian correlations in strongly-interacting ultracold Bose gases

ABSTRACT: 
Strongly correlated quantum matter is characterised by properties that cannot be understood in terms of linear fluctuations and theory of free quasi-particles. Quantum fluctuations in such systems are large and generically exhibit non-Gaussian statistics -- a property captured only by inspecting high-order correlations, whose quantitative reconstruction poses a formidable challenge to both experiments and theory alike. A prime example of correlated quantum matter is the strongly interacting Bose fluid, realized by superfluid Helium and, more recently, ultra-cold atoms. In this talk, I will report on our work to understand the emergence of non-Gaussian correlations in interacting bosons realised with ultracold Helium atoms. 
I will first discuss the weakly-interacting regime where Bogoliubov theory treats fluctuations as linear and predicts that interactions promotes pairs of bosons with opposite momenta outside the condensate, the quantum depletion. Exploiting the capability to detect individual metastable Helium atoms after a long free-fall expansion [1], we confirm this microscopic prediction [2]. I will then address the strongly-interacting regime that we enter using an optical lattice [3]. We observe that the Bogoliubov pairing is suppressed as interactions become stronger. This departure from the predictions of Bogoliubov theory signals the onset of the strongly correlated regime, as confirmed by numerical simulations that highlight the role of non-linear quantum fluctuations in our system. Additionally, our measurements unveil a non-zero four-operator cumulant at even stronger interactions, which is a direct signature of non-Gaussian correlations [4].
[1] H. Cayla et al. Physical Review A 97, 061609(R) (2018); A. Tenart et al. Physical Review Research 2, 013017 (2020).
[2] A. Tenart et al. Nature Physics 17, 1364 (2021).
[3] C. Carcy et al. Physical Review Letters 126, 045301(2021).
[4] J.-P. Bureik et al. In preparation (2024).

BIO: David Clément is a Professor at the Institute d’optique graduate school in Palaiseau in France. Previously he was a junior member of the university of France and a post doc in Florence in Italy. He did his PhD from 2004-2007 with Alan Aspect.