Berlin 2014 – scientific programme

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A: Fachverband Atomphysik

A 58: Characterization and control of complex quantum systems SYQS 3 (with Q, MO, MS, MP, AGjDPG)

A 58.2: Talk

Friday, March 21, 2014, 16:45–17:00, Audimax

Tomography of squeezed and oversqueezed states of mesoscopic atomic ensembles — •Baptiste Allard, Roman Schmied, Caspar F. Ockeloen, and Philipp Treutlein — Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland

The experimental characterization of the quantum state of a mesoscopic ensemble of particles is a major challenge in quantum physics, especially when multi-particle entanglement is present.

We experimentally demonstrate tomographic state reconstruction of non-classical many-body (pseudo-)spin states. The system consists of a two-component ⁸⁷Rb Bose-Einstein condensate of a few hundred atoms created on an atom-chip [1]. A state-selective potential gives rise to a S_z² interaction term in the Hamiltonian in the collective spin representation. Using this one-axis twisting dynamics [2], we prepare non-classical spin states such as spin-squeezed and spin-oversqueezed states.

Using well-controlled Rabi rotations and projective measurements, we perform a Stern-Gerlach-type analysis to characterize the many-body quantum states. From the results of measurements along many quantization axes, we determine the most likely positive-semidefinite density matrix; this represents an improvement over our previously published backprojection technique [3].

[1] M. F. Riedel, et al., Nature 464, 1170 (2010). [2] M. Kitagawa and M. Ueda, Phys. Rev. A 47, 5138-5143 (1993). [3] R. Schmied and P. Treutlein, New J. Phys. 13, 065019 (2011).