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Jul 27

Vector light shift preprint on the arXiv

The Spinor Lab have released a preprint on measurement and cancellation of vector light shifts in optical dipole traps [1]. The optical dipole force was first used to trap neutral atoms by Chu, et al. 30 years ago [2]. The following decade, and three years after the realisation of Bose-Einstein condensates of dilute gases, optical dipole traps were used to confine BECs [3], heralding the study of spinor BECs. Unlocking the spin degree-of-freedom of the condensate relies on being able to confine multiple spin states simultaneously. When all spin states of a condensate are confined equally, the spin dynamics are largely decoupled from the spatial degree-of-freedom. However, this relies on a precisely linear polarisation state of the trapping light, imperfections of which can result in a spin-dependent energy shift. Such vector light shifts are apparent as a `fictitious’ magnetic field, and the same intensity curvature used to generate the trapping potential is manifest as an effective magnetic field gradient. These gradients are deleterious for preserving coherent spin evolution, and vector light shifts more generally are a hindrance for atomic magnetometry from nanokelvin to room temperatures. A significant part of Alex Wood’s PhD involved characterising and controlling this phenomenon using two spinor BECs in proximity to each other. This result also constitutes our first magnetically sensitive trapped-atom interferometer, with an interrogation time of 15 milliseconds.

Update (23/09/2016): This paper has been accepted by Physical Review A. Based on peer review, we added an appendix on thermally induced birefringence by the dipole trapping beams on glass vacuum windows.

[1] A. A. Wood, L. D. Turner, and R. P. Anderson. Measurement and extinction of vector light shifts using interferometry of spinor condensates. arXiv:1607.06898.
[2] S. Chu, J. E. Bjorkholm, A. Ashkin, and A. Cable. Phys. Rev. Lett. 57, 314 (1986).
[3] D. M. Stamper-Kurn, M. R. Andrews, A. P. Chikkatur, S. Inouye, H.-J. Miesner, J. Stenger, and W. Ketterle. Phys. Rev. Lett. 80, 2027 (1998)