Decoherence of Matter-Wave Breathers

Solitons are non-dispersive wave packets which arise as solutions to the 1D non-linear Schrodinger equation (NLSE).  Higher-order solitons, known as breathers, can be formed from fundamental solitons by a specific interaction quench. An n-soliton breather is composed of constituent fundamental solitons with mass ratios 1:3:…:2n-1, and are formed when the attractive interactions are quenched by a factor of n², where n is an integer¹. A breather’s density profile oscillates in time at a frequency given by the chemical potential difference of its constituent solitons. Breathers are exactly integrable solutions to the NLSE in the mean-field (MF) limit. However, quantum many-body theory predicts that quantum fluctuations break integrability and can induce breather dissociation² or relaxation resulting in loss of coherence³. Using an interaction quench factor of 4 controlled through a magnetic Feshbach resonance, we experimentally produce second-order breathers from a Bose-Einstein condensate of ⁷Li atoms in a quasi-1D harmonic potential formed from a focused laser beam. We observe decoherence and dissociation of second-order breathers, but the rate of these processes is inconsistent with beyond MF effects.

[1] J. Satsuma et al. Prog. Theor. Phys. (Suppl.) 55, 284 (1974).

[2] O.V. Marchukov et al. , Phys. Rev. Lett. 125, 050405 (2020).

[3] B. Opanchuk et al.. Phys. Rev. A. 96, 053628 (2017).