Quantum Non-Demolition Measurement on the Spin Precession of Laser-Trapped $^{171}$Yb Atoms

TL;DR

This paper demonstrates a quantum non-demolition measurement technique for laser-trapped $^{171}$Yb atoms that improves detection efficiency and fidelity, enabling real-time quantum sensing and information processing.

Contribution

It introduces a novel all-optical QND measurement scheme for atomic spin states that reduces noise below quantum projection limits.

Findings

Reduces optical detection noise by ~19 dB

Achieves measurement noise 2.3 dB below atomic quantum projection noise

Enables fast, real-time spin state readout for quantum applications

Abstract

Quantum non-demolition (QND) measurement enhances the detection efficiency and measurement fidelity, and is highly desired for its applications in precision measurements and quantum information processing. We propose and demonstrate a QND measurement scheme for the spin states of laser-trapped atoms. On $^{171}$Yb atoms held in an optical dipole trap, a transition that is simultaneously cycling, spin-state selective, and spin-state preserving is created by introducing a circularly polarized beam of control laser to optically dress the spin states in the excited level, while leaving the spin states in the ground level unperturbed. We measure the phase of spin precession of $5\times10^{4}$ atoms in a bias magnetic field of 20 mG. This QND approach reduces the optical absorption detection noise by $\sim$19 dB, to a level of 2.3 dB below the atomic quantum projection noise. In addition to providing a general approach for efficient spin-state readout, this all-optical technique allows quick switching and real-time programming for quantum sensing and quantum information processing.