Southwest Quantum Information and Technology

Improved spin squeezing of an atomic ensemble through internal state control

Presenting Author: Daniel Hemmer, Arizona
Contributing Author(s): Senthilnathan Lingasamy, Ezad Shojaee, Ivan Deutsch, and Poul Jessen

Squeezing of collective atomic spins is typically generated by quantum backaction from a QND measurement of the relevant spin component. In this scenario the degree of squeezing is determined by the measurement resolution relative to the quantum projection noise (QPN) of a spin coherent state (SCS). When starting from a SCS our current experiment generates ~3dB of metrologically relevant spin squeezing, closely matching theoretical predictions. Going forward, our main objective is to use control of the internal atomic spin to improve squeezing. For example, we can coherently map the internal spins from the SCS to a “cat” state, which increases the QPN by a factor of 2f=8 relative to the SCS [1]. This leads to increased backaction and entanglement produced by our QND measurement. The squeezing generated in the cat state basis can in principle be mapped back to the SCS basis where it will correspond to squeezing of the physical spin. A preliminary experimental result suggests that up to 8dB of metrologically useful squeezing can be generated in this way. However, more complex internal state preparation brings additional vulnerability to control errors. The main source of error for internal state control in our experiment appears to be fluctuating background magnetic fields at frequencies up to tens of kHz. We are currently developing a toolbox of composite pulses in order to diagnose and compensate for their presence. [1] L.M. Norris et al., Phys. Rev. Lett. 109, 173603 (2012)

(Session 1 : Thursday from 9:30am - 10:00am)