We explore fundamental quantum physics with atoms, photons and phonons and harness it for applications in quantum metrology and quantum information. In our experiments we study many-particle entanglement in Bose-Einstein condensates and develop quantum interfaces between atoms and solid-state nanosystems such as mechanical oscillators and semiconductor quantum dots. Our research combines experiment with theory, employing techniques of laser cooling, atom chips, optomechanics, and nanofabrication. A common goal of our activities is to investigate quantum physics in systems of increasing size and complexity.
Have a look at our new review article on "Non-classical states of atomic ensembles: fundamentals and applications in quantum metrology", a joint work of L. Pezzè, A. Smerzi, M. K. Oberthaler, R. Schmied and P. Treutlein. Now published in Rev. Mod. Phys. 90, 035005 (2018).
By directly measuring the spin correlations between spatially separated parts of a spin-squeezed Bose-Einstein condensate we observe entanglement that is strong enough for Einstein-Podolsky-Rosen steering: We can predict measurement outcomes for noncommuting observables in one spatial region on the basis of corresponding measurements in another region with an inferred uncertainty product below the Heisenberg uncertainty bound. This method could be exploited for entanglement-enhanced imaging of electromagnetic field distributions and quantum information tasks. The results were reported in Science 360, 409-413.
We have observed the effects of collective atomic motion in a one-dimensional optical lattice coupled to an optomechanical system. In this hybrid atom-optomechanical system, the lattice light generates a coupling between the lattice atoms as well as between atoms and a micromechanical membrane oscillator. For large atom numbers we observe an instability in the coupled system, resulting in large-amplitude atom-membrane oscillations. We show that this behavior can be explained by light-mediated collective atomic motion in the lattice. These results were published in Physical Review Letters 120, 073602.
We have demonstrated a quantum memory in warm Rb vapor with on-demand storage and retrieval, based on electromagnetically induced transparency, and with an acceptance bandwidth of δf=0.66 GHz. This memory is suitable for single photons emitted by semiconductor quantum dots. In this regime, vapor cell memories offer an excellent compromise between storage efficiency, storage time, noise level, and experimental complexity, and atomic collisions have negligible influence on the optical coherences. These results were published in Physical Review Letters 119, 060502.
We congratulate Boris Décamps for winning a poster prize at the International Conference on Laser Spectroscopy 2017. His poster was entitled Coherence Times, EPR Entanglement, and Bell Correlations in a Bose-Einstein Condensate. He reported on violation of the EPR steering criteria by spatially separated regions of a spin squeezed BEC, as well as N-particle witnesses of Bell correlations, and quantitative models of decoherence that can be used to correct for phase noise.