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Observation of the Quantum Boomerang Effect

Roshan Sajjad, Jeremy L. Tanlimco, Hector Mas, Alec Cao, Eber Nolasco-Martinez, Ethan Q. Simmons, Flávio L. N. Santos, Patrizia Vignolo, Tommaso Macrì, and David M. Weld
Phys. Rev. X 12, 011035 – Published 23 February 2022
Physics logo See synopsis: A Bose-Einstein-Condensate Boomerang

Abstract

A particle in an Anderson-localized system, if launched in any direction, should, on average, return to its starting point and stay there. Despite the central role played by Anderson localization in the modern understanding of condensed matter, this “quantum boomerang” effect, an essential feature of the localized state, was only recently theoretically predicted. We report the experimental observation of the quantum boomerang effect. Using a degenerate gas and a phase-shifted pair of optical lattices, we not only confirm the predicted dependence of the boomerang effect on Floquet gauge but also elucidate the crucial role of initial-state symmetries. Highlighting the key role of localization, we observe that as stochastic kicking destroys dynamical localization, the quantum boomerang effect also disappears. Measured dynamics are in agreement with numerical models and with predictions of an analytical theory we present which clarifies the connection between time-reversal symmetry and boomerang dynamics. These results showcase a unique experimental probe of the underlying quantum nature of Anderson localized matter.

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  • Received 1 September 2021
  • Accepted 25 January 2022

DOI:https://doi.org/10.1103/PhysRevX.12.011035

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Atomic, Molecular & OpticalCondensed Matter, Materials & Applied PhysicsGeneral Physics

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A Bose-Einstein-Condensate Boomerang

Published 23 February 2022

After being pushed in one direction, the average momentum of a Bose-Einstein condensate is seen to slow and return to its original value.

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Authors & Affiliations

Roshan Sajjad1, Jeremy L. Tanlimco1, Hector Mas1, Alec Cao1, Eber Nolasco-Martinez1, Ethan Q. Simmons1, Flávio L. N. Santos2, Patrizia Vignolo3, Tommaso Macrì2, and David M. Weld1,*

  • 1Department of Physics, University of California, Santa Barbara, California 93106, USA
  • 2Departamento de Física Teórica e Experimental, Universidade Federal do Rio Grande do Norte, 59072-970 Natal, Rio Grande do Norte, Brazil
  • 3Université Côte d’Azur, CNRS, Institut de Physique de Nice, 06560 Valbonne, France

  • *Corresponding author. weld@ucsb.edu

Popular Summary

According to a celebrated 1958 result of condensed-matter physics, disorder induces insulating behavior, a phenomenon known as Anderson localization. A particle in an Anderson-localized system, if launched in any direction, should, on average, return to its starting point and stay there. Despite the central role played by Anderson localization in the modern understanding of condensed matter, this “quantum boomerang” effect, an essential feature of the localized state, was only recently theoretically predicted and has not previously been observed. We report the experimental observation and characterization of this surprising quantum-mechanical phenomenon.

In our experiments, we expose a gas of ultracold lithium atoms to a phase-shifted pair of optical lattices to realize a “quantum kicked rotor,” a momentum-space realization of Anderson-localized matter. Following the dynamics of the average momentum, we observe the characteristic departure from and return to the origin that is the key signature of the boomerang effect. Detailed characterization reveals the key dependence of the boomerang effect on time-reversal symmetry and localization: We observe that disruption of either of these conditions destroys the boomerang dynamics.

These experiments validate a powerful dynamical probe of the uniquely quantum-mechanical nature of the localized state, applicable to a general class of disordered systems. The results suggest a variety of intriguing topics for future exploration, including tunable boomerang phenomena in higher-dimensional and interacting systems and implications for ultrafast electron dynamics in disordered solids.

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Vol. 12, Iss. 1 — January - March 2022

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