Reducing Collective Quantum State Rotation Errors with Reversible Dephasing

TL;DR

This paper demonstrates that reversible dephasing can significantly reduce collective quantum state rotation errors, enabling enhanced spin state measurements and entanglement generation in a large atomic ensemble.

Contribution

The authors show that inhomogeneous broadening-based reversible dephasing effectively suppresses rotation errors, leading to improved quantum measurement precision and entanglement.

Findings

Rotation errors suppressed by over 21 dB

Spin state populations resolved 13 dB below quantum projection noise

Achieved 9.5 dB spectroscopic enhancement (squeezing)

Abstract

We demonstrate that reversible dephasing via inhomogeneous broadening can greatly reduce collective quantum state rotation errors, and observe the suppression of rotation errors by more than 21 dB in the context of collective population measurements of the spin states of an ensemble of $2.1 \times 10^5$ laser cooled and trapped $^{87}$Rb atoms. The large reduction in rotation noise enables direct resolution of spin state populations 13(1) dB below the fundamental quantum projection noise limit. Further, the spin state measurement projects the system into an entangled state with 9.5(5) dB of directly observed spectroscopic enhancement (squeezing) relative to the standard quantum limit, whereas no enhancement would have been obtained without the suppression of rotation errors.