Quantum control and measurement of spins in laser cooled gases

Ivan Deutsch

Florian Schreck, N. J. van Druten

Wei Qi, Ming-Cheng Liang, Han Zhang +4 more

Abstract We report the experimental realization of quantum degenerate Fermi gases of 87Sr atoms under controlled 10- and dual-nuclear-spin configurations. Based on laser cooling and evaporative cooling, we achieve an ultracold Fermi gas of 105 atoms equally distributed over 10 spin states, with a temperature of T/TF=0.21. We further prepare a dual-spin gas by optically pumping atoms to the mF=9/2 and mF=7/2 states and observe a slightly lower T/TF than that for a 10-spin gas under the same trapping condition, showing efficient evaporative cooling under a decreasing number N of spin states ( N ≥ 2 ) despite the increasing importance of Pauli exclusion. Given that rethermalization becomes less efficient with N approaching unity, we evaporatively cool an almost polarized gas to 130 nK. The simple and efficient preparation of ultracold Fermi gases of 87Sr with tunable spin configurations provides a first step towards engineering topological quantum systems.

Philipp Hauke, R. J. Sewell, Morgan W. Mitchell +1 more

We describe a new technique for preparing and detecting spatial spin-correlations and multipartite entanglement in a quantum lattice gas based on entropic cooling via quantum non-demolition (QND) measurement and feedback.

N. Behbood, Giorgio Colangelo, Ferran Martin Ciurana +3 more

We apply entropy removal by measurement and feedback to a cold atomic spin ensemble. Using quantum nondemolition probing by Faraday rotation measurement, and feedback by weak optical pumping, we drive the initially random collective spin variable F toward the origin F=0. We use input-output relations and ensemble quantum noise models to describe this quantum control process and identify an optimal two-round control procedure. We observe 12 dB of spin noise reduction, or a factor-of-63 reduction in phase-space volume. The method offers a nonthermal route to generation of exotic entangled states in ultracold gases, including macroscopic singlet states and strongly correlated states of quantum lattice gases.

Ivan Deutsch, Poul Jessen