Measurement of Spectral Functions of Ultracold Atoms in Disordered Potentials

Valentin V. Volchkov (1) , Michael Pasek (2, 1) , Vincent Denechaud (1, 3) , Musawwadah Mukhtar (1) , Alain Aspect (1) , Dominique Delande (2) , Vincent Josse (1)

1 Laboratoire Charles Fabry / Optique atomique
2 LKB (Jussieu) - Laboratoire Kastler Brossel
3 Safran Tech

We report on the measurement of the spectral functions of non-interacting ultra-cold atoms in a three-dimensional disordered potential resulting from an optical speckle field. Varying the disorder strength by two orders of magnitude, we observe the crossover from the " quantum " perturbative regime of low disorder to the " classical " regime at higher disorder strength, and find an excellent agreement with numerical simulations. The method relies on the use of state-dependent disorder and the controlled transfer of atoms to create well-defined energy states. This opens new avenues for experimental investigations of three-dimensional Anderson localization. Introduction.— The spectral function provides essential information on the energy-momentum relation of one-particle excitations in complex systems. This relation takes a non-trivial form in the presence of random scatterers or inter-particle interactions [1]. The direct measurement of the spectral function via angle-resolved photoemission spectroscopy (ARPES) [2] in strongly correlated electronic systems has led to significant progress in the understanding of high-T c superconductivity [3]. More recently, the ability to measure and exploit spectral functions in ultracold atomic systems has also been widely demonstrated, for instance using radio-frequency spectroscopy [4, 5] to reveal the presence of a pseudo-gap in strongly interacting Fermi gases [6, 7], or to probe the Mott insulator and superfluid regimes of interacting Bose gases in periodic lattices using Bragg spectroscopy [8–10].

Domains: Quantum Gases [cond-mat.quant-gas]; Atomic Physics [physics.atom-ph]; Disordered Systems and Neural Networks [cond-mat.dis-nn]

Valentin V. Volchkov, Michael Pasek, Vincent Denechaud, Musawwadah Mukhtar, Alain Aspect, et al.. Measurement of Spectral Functions of Ultracold Atoms in Disordered Potentials. Physical Review Letters, 2018, 120 (6), pp.060404. ⟨10.1103/PhysRevLett.120.060404⟩. ⟨hal-01760034⟩