March 2014
Abstracts of the QSIT Lunch Seminar, March 6, 2014
Quantum interferometry with cold atoms on a chip
Baptiste Allard, Department of Physics, University of Basel
Ultra-cold atomic ensembles are very well-controlled quantum systems which can be used as sensitive probes for metrological applications or as a model system for studying entanglement and complex many-body quantum states. In our experiment, we explore two-component 87Rb Bose-Einstein condensates of a few hundred atoms created on an atom-chip [1]. A state-selective potential gives rise to a Sz² interaction term in the Hamiltonian in the collective spin representation. This one-axis twisting dynamics [2] creates non-classical spin states such as spin-squeezed or spin-oversqueezed states. We have used a spin-squeezed state on our chip for interferometric measurements of electromagnetic fields beyond the standard quantum limit [3]. More recently, we have used our setup to produce and characterize different many-particle entangled states beyond the concept of spin squeezing [4].
References:
[1] M. F. Riedel, et al., Nature 464, 1170 (2010).
[2] M. Kitagawa and M. Ueda, Phys. Rev. A 47, 5138-5143 (1993).
[3] C. F Ockeloen, et al., Phys. Rev. Lett. 111, 143001 (2013).
[4] R. Schmied and P. Treutlein, New J. Phys. 13, 065019 (2011).
Sequential quantum-enhanced measurement with an atomic ensemble
Andrey Lebedev, Institute for theoretical Physics, ETH Zurich
We propose a quantum-enhanced iterative (with K steps) measurement scheme based on an ensemble of N two-level probes which asymptotically approaches the Heisenberg limit δK ∝ R-K/(K+1), R the number of quantum resources. The protocol is inspired by Kitaev's phase estimation algorithm and involves only collective manipulation and measurement of the ensemble. The iterative procedure takes the shot-noise limited primary measurement with precision δ1 ∝ N-1/2 to increasingly precise results δK ∝ N-K/2. We propose an implementation of the algorithm for the measurement of a magnetic field using a two-component atomic cloud of Bosons.