Quantum Nondemolition Measurement of the Spin Precession of Laser-Trapped

Quantum nondemolition (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 171Yb atoms held in an optical dipole trap, a transition that is simultaneously cycling, spinselective, and spin-preserving is created by introducing a circularly polarized beam of a 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 x 104 atoms in a bias magnetic field of 20 mG. This QND approach reduces the optical absorption detection noise by similar to 19 dB, to an inferred level of 2.3 dB below the atomic quantum projection noise. In addition to providing a general approach for efficient spinstate readout, this all-optical technique allows quick switching and real-time programming for quantum sensing and quantum information processing.

Automated summary

Quantum nondemolition (QND) measurement enhances detection efficiency and measurement fidelity in precision measurements and quantum information processing. A QND measurement scheme is proposed and demonstrated for the spin states of laser-trapped atoms. This approach utilizes a circularly polarized control laser to create a cycling, spin-selective, and spin-preserving transition on 171Yb atoms in an optical dipole trap.