Many-Body Decay of the Gapped Lowest Excitation of a Bose-Einstein Condensate.
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We study the decay mechanism of the gapped lowest-lying axial excitation of a quasipure atomic Bose-Einstein condensate confined in a cylindrical box trap. Owing to the absence of accessible lower-energy modes, or direct coupling to an external bath, this excitation is protected against one-body (linear) decay, and the damping mechanism is exclusively nonlinear. We develop a universal theoretical model that explains this fundamentally nonlinear damping as a process whereby two quanta of the gapped lowest excitation mode couple to a higher-energy mode, which subsequently decays into a continuum. We find quantitative agreement between our experiments and the predictions of this model. Finally, by strongly driving the system below its (lowest) resonant frequency, we observe third-harmonic generation, a hallmark of nonlinear behavior.
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1079-7114
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European Research Council (682285)
Engineering and Physical Sciences Research Council (EP/P009565/1)
Engineering and Physical Sciences Research Council (EP/R043396/1)
Royal Society (RSWF/R1/191012)
Engineering and Physical Sciences Research Council (EP/K030094/1)