Spin-momentum coupled Bose-Einstein condensates with lattice band pseudospins.

M A Khamehchi,M E Mossman,Chuanwei Zhang,Chunlei Qu,P Engels

doi:10.1038/ncomms10867

M A Khamehchi, M E Mossman + Show 3 more

Open Access

https://doi.org/10.1038/ncomms10867

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Abstract

The quantum emulation of spin-momentum coupling, a crucial ingredient for the emergence of topological phases, is currently drawing considerable interest. In previous quantum gas experiments, typically two atomic hyperfine states were chosen as pseudospins. Here, we report the observation of a spin-momentum coupling achieved by loading a Bose-Einstein condensate into periodically driven optical lattices. The s and p bands of a static lattice, which act as pseudospins, are coupled through an additional moving lattice that induces a momentum-dependent coupling between the two pseudospins, resulting in s–p hybrid Floquet-Bloch bands. We investigate the band structures by measuring the quasimomentum of the Bose-Einstein condensate for different velocities and strengths of the moving lattice, and compare our measurements to theoretical predictions. The realization of spin-momentum coupling with lattice bands as pseudospins paves the way for engineering novel quantum matter using hybrid orbital bands.

Highlights

The quantum emulation of spin-momentum coupling, a crucial ingredient for the emergence of topological phases, is currently drawing considerable interest
In optical lattices filled with ultracold atoms, s- and p-orbital bands are separated by a large energy gap and can be defined as two pseudospin states
To generate the s–p band Spin-momentum coupling (SMC) and FB band structures, we begin with a 87Rb BoseEinstein condensate (BEC) composed of B5 Â 104 atoms confined in a crossed dipole trap

Summary

Results

For a given driving frequency, the coupling of the two bands is stronger for larger driving field strength (that is, larger depth of the moving lattice) so that the BEC is shifted to a larger absolute value of quasimomentum Floquet systems such as the one in our experiment are described by quasienergy bands. The position of the true minimum is uniquely determined by the moving velocity direction, moving lattice depth and driving frequency This minimal two-band model captures the essential physics of the driven lattices, as we have seen through the comparison of experimental measurements and theoretical values (Figs 2 and 3), demonstrating the observation of SMC between s–p band pseudospins.

Discussion

Methods

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