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The 56th Photo-molecular Science Forum

Lecture Title "Protected State Enhanced Quantum Metrology with Interacting Two-Level Ensembles"
Date Thursday 22 May 2014 16:00 to 17:00
Lecturer Claudiu Genes （the University of Innsbruck, Austria, independent senior researcher）
Place

Institute for Molecular Science, Research Building, Seminar Room, #201
Summary

 Ramsey interferometry is routinely used in quantum metrology for the most sensitive measurements of optical clockfrequencies. Spontaneous decay to the electromagnetic vacuum ultimately limits the interrogation time and thus sets a lower bound to the optimal frequency sensitivity. In dense ensembles of two-level systems, the presence of collective effects such as superradiance and dipole-dipole interaction tends to decrease the sensitivity even further. We show that by a redesign of the Ramsey-pulse sequence to include different rotations of individual spins that effectively fold the collective state onto a state close to the center of the Bloch sphere, partial protection from collective decoherence is possible
[1]. This allows a significant improvement in the sensitivity limit of a clock transition detection scheme over the conventional Ramsey method for interacting systems and even for noninteracting decaying atoms. Recent progress shows that this method might outperform results in scaling with number of particles obtained when employing quantum correlated states such as spin squeezed states. Moreover, protection of multiparticle entanglement such as used in quantum memories might as well be achieved.
[1] Laurin Ostermann, Helmut Ritsch, and Claudiu Genes, Phys. Rev. Lett. 111, 123601 (2013)
Contact

 Kenji Ohmori
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