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European Quantum Electronics Conference (EQEC)

Conditions for a QND measurement of spin in cold /sup 87/Rb

S.R. de Echaniz, Marcin Kubasik, Herbert Crepaz, Morgan W. Mitchell, Jürgen Eschner

Published Jan 18, 2006• 0 citations
Publisher

Abstract

A scheme to generate spin squeezing via a quantum non-demolition (QND) measurement in a cold sample of /sup 87/Rb atoms is proposed using the /sup 5/S/sub 1/2/ (F = 1) hyperfine ground state. In this system it is expected to have a much higher signal to noise ratio. Suitable Zeeman substates and operators to perform the QND interaction in this scheme are identified, together with the possible sources of error and noise arising from these choices.

DOI
10.1109/eqec.2005.1567442

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•Apr 15, 2011•1 citation
A scheme to generate spin squeezing via a quantum non-demolition (QND) measurement in a cold sample of /sup 87/Rb atoms is proposed using the /sup 5/S/sub 1/2/ (F = 1) hyperfine ground state. In this system it is expected to have a much higher signal to noise ratio. Suitable Zeeman substates and operators to perform the QND interaction in this scheme are identified, together with the possible sources of error and noise arising from these choices.
We study the conditions for generating spin squeezing via a quantum non-demolition measurement in an ensemble of cold 87 Rb atoms. By considering the interaction of atoms in the 5S 1/2 ( F = 1) ground state with probe light tuned near the D 2 transition, we show that, for large detunings, this system is equivalent to a spin-1/2 system when suitable Zeeman substates and quantum operators are used to define a pseudo-spin. The degree of squeezing is derived for the rubidium system in the presence of scattering causing decoherence and loss. We describe how the system can decohere and lose atoms, and predict as much as 75% spin squeezing for atomic densities typical of optical dipole traps.
We demonstrate spin squeezing and entanglement in a large-spin system via quantum non-demolition measurement. We make non-destructive, projection-noise-limited collective spin measurements on an ensemble of up to in 8.4 × 105 laser-cooled 87Rb atoms in the f = 1 hyperfine ground state. A dynamically-decoupled probing scheme [Phys. Rev. Lett. 105, 093602 (2010)] prevents probe-induced decoherence. Repeated measurements show correlations beyond the standard quantum limit, indicating generation of a spin-squeezed state with up to −3.6 dB of noise reduction and −2.6 dB of metrologically-relevant squeezing.
We have demonstrated a quantum non‐demolition (QND) measurement with a collective spin of cold ytterbium atoms (171Yb) via Faraday rotation interaction, and have observed 1.8−1.5+2.4 dB spin squeezing. Since 171Yb atoms have only a nuclear spin of one‐half in the ground state, the system constitutes the simplest spin ensemble and is thus robust against decoherence. Furthermore, we have considered the atomic quantum swapping gate as a quantum information device using multiple Faraday rotation interactions, and have found that we can realize the quantum‐domain performance for a realistic experimental condition.
This thesis investigates the generation of atomic spin-squeezed states by quantum non-demolition (QND) measurements in a high-finesse optical cavity. Cold atom interferometry has demonstrated state of the art performance for the measurement of tiny rotations, accelerations and time. The sensitivity of atom interferometers has already reached the atomic shot noise level, a limit that could be overcome by the use of non-classical atomic states. In this context, we developed a crossed high-finesse cavity resonating both at 1560 nm and 780 nm. Laser light at 1560 nm injected in the cavity generates a far off resonance optical dipole trap where Rb 87 cold atoms are loaded from a magneto-optical trap. The lifetime of the atoms in this dipole trap is limited by the residual background collisions, indicating that further evaporation process should be effective. The concepts of QND measurement are introduced and a wavefunction formalism that describes the spin-squeezing dynamics of the atomic state is discussed. This formalism is applied to practical measurement apparatus that are the Mach-Zehnder interferometer and the heterodyne detection. Experimentally, this non-destructive measurement was implemented at 780 nm in a frequency modulation scheme strongly immune to noise. The influence of this non-demolition probe on the atomic sample has been characterized in single pass and this tool has been applied to follow in real time the state of atomic interferometers. In addition to this work, a narrow linewidth Raman laser suitable for high precision spectroscopy was implemented with cold atoms as the gain medium.