Atomic BECs with Interactions

Atomic Bose-Einstein condensates (BEC) are perhaps the cleanest system where a quantum state becomes macroscopically visible and controllable. So far, most BEC studies avoided strong many-body interactions to eliminate complications. Nevertheless, strong atom–atom interactions in BECs promote completely new classes of quantum processes to the macroscopic world. This prospect is more lucrative than ever because the Cornell-Jin group (JILA) reported in 2014 the first successful measurement where a BEC survived the strongest of atom–atom interactions, i.e. the so-called unitarity where atomic scattering length diverges.

We have discovered an intriguing semiconductor–BEC connection [P2-P4] that quantitatively describes quantum processes induced by strong atom-atom interactions in terms of atom-cluster formation. More specifically, found hyperbolic Bloch equations (HBE) as counterparts to the semiconductor Bloch equations in order the describe equilibrium many-body dynamics induced by interactions. Our HBE computations already explain the measured quantum kinetics in remarkable detail, which demonstrates a proof-of-principle that semiconductor quantum-dynamics knowhow also applies to a strongly interacting Bose gas. We are actively studying this connection, and possibility of extending BEC experiments to the realm typically studied in solids. This work will create complementary insights, beneficial for both semiconductor and atom-condensate experiments.

Selected references:

P. Makotyn, C.E. Klauss, D.L. Goldberger, E.A. Cornell, and D.S. Jin, Universal dynamics of a degenerate unitary Bose gas, Nature Phys. 10, 116 (2014).

M. Kira, Excitation picture of an interacting Bose gas, Ann. Phys. 351, 200 (2014).
M. Kira, Coherent quantum depletion of an interacting atom condensate, Nat. Comm. 6, 6624 (2015).

M. Kira, Hyperbolic Bloch equations: atom-cluster kinetics of an interacting Bose gas, Ann. Phys. 356, 185 (2015).