Ultra cold atoms are remarkable systems with a truly unprecedented level of experimental control and one application of this control is to engineer many body hamiltonians usually associated with condensed matter physics. To date this engineering has focused mostly on the real-space potential that the atoms experience, for example, multiple-well traps, optical lattice potentials, or even potentials depending on the internal state of the atom.
Here I present our experimental work creating artificial spin-orbit coupling. We couple two internal states of rubidium 87 via a momentum-selective Raman transition and load our system into the resulting adiabatic eigenstates. In agreement with theory, we observe that these dressed atoms have well-defined "dressed" spins upto a critical value of the Raman coupling strength.
In addition, we find that the artificial SO coupling modifies the interactions between the dressed atoms, and we observe a quantum phase transition between phase mixed, phase separated states. This transition is in agreement with our mean field calculations as a function of the Raman coupling strength and the detuning from Raman resonance. In addition, our results are in accord with a similar calculation by T.-L. Ho (in a coupling-strength - interaction strength phase space).
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