Gerhard Rempe

Quantum Dynamics

Max Planck Institute of Quantum Optics

Hans-Kopfermann-Str. 1

85748 Garching

Tel. +49 89 3290 5711

rempe-office[at]mpq.mpg.de

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Description

Research focus: quantum optics, cavity QED, quantum informatics, ultracold molecules

The Quantum Dynamics Division, led by Gerhard Rempe at the Max Planck Institute of Quantum Optics, is well known for its broad range of activities, ranging from atomic to molecular physics, from quantum optics to quantum gases, and from cavity quantum electrodynamics to quantum information science. Dynamical effects occurring in driven dissipative systems play a pivotal role, in particular when the system constituents are strongly coupled to each other.

Cavity QED and quantum networks

Rempe_Fig2_QuantumNetwork
A paradigm example of our research is a single atom strongly coupled to a single photon inside an optical resonator of the highest possibly quality. This novel hybrid system is ideal to investigate fundamental nonlinear quantum phenomena of light-matter interaction like photon blockade or the deterministic generation of squeezed light or single photons by means of an atom with one-dimensional radiation characteristics. The system is also the scientifically most advanced implementation of a universal quantum network node capable to produce, store and distribute entanglement over large distances, to teleport information between material memories, and to make quantum computation and long-distance quantum communication with individual qubits scalable.


Bose-Einstein condensates

A complementary system to explore quantum-nonlinear phenomena of light-matter interaction at the level of single photons is an ultracold quantum gas of Bose-Einstein-condensed atoms. Here, the collective response of many atoms, all perfectly at rest, to impinging single photons, in combination with the giant nonlinearity provided by highly excited Rydberg atoms is utilized to realize all-optical information processing devices like single-photon switches and even single-photon transistors featuring gain. The novel ultracold Rydberg system is also perfect for the exploration of strongly correlated quantum systems and even molecules.


Trapped molecules

Rempe_Fig3_ElectricTrap
Molecules with their complex internal structure open up a plethora of exciting new avenues for research in quantum science including quantum-many body physics and quantum information processing. In fact, the many rotational and vibrational states as well as the permanent electric dipole moment in chemically stable molecules are yet unexplored treasures. Pioneering experiments have been performed in the group by electrically guiding and trapping naturally occurring molecules, by slowing them with a rapidly spinning centrifuge, by cooling them into the low millikelvin regime, corresponding to velocities around a meter per second, and most recently by producing pure low-entropy ensembles of trapped molecules.

Publications

Dark-time decay of the retrieval efficiency of light stored as a Rydberg excitation in a noninteracting ultracold gas

S. Schmidt-Eberle, T. Stolz, G. Rempe, and S.Dürr.

Physical Review A 101, 013421 (2020).

Show Abstract

We study the dark-time decay of the retrieval efficiency for light stored in a Rydberg state in an ultracold gas of 87Rb atoms based on electromagnetically induced transparency (EIT). Using low atomic density to avoid dephasing caused by atom-atom interactions, we measure a 1/e time of 30µs for the 80S state in free expansion. One of the dominant limitations is the combination of photon recoil and thermal atomic motion at 0.2µK. If the 1064-nm dipole trap is left on, then the 1/e time is reduced to 13 µs, in agreement with a model taking differential light shifts and gravitational sag into account. To characterize how coherent the retrieved light is, we overlap it with reference light and measure the visibility V of the resulting interference pattern, obtaining V>90% for short dark time. Our experimental work is accompanied by a detailed model for the dark-time decay of the retrieval efficiency of light stored in atomic ensembles. The model is generally applicable for photon storage in Dicke states, such as in EIT with $\lamda$-type or ladder-type level schemes and in Duan-Lukin-Cirac-Zoller single-photon sources. The model includes a treatment of the dephasing caused by thermal atomic motion combined with net photon recoil, as well as the influence of trapping potentials. It takes into account that the signal light field is typically not a plane wave. The model maps the retrieval efficiency to single-atom properties and shows that the retrieval efficiency is related to the decay of fringe visibility in Ramsey spectroscopy and to the spatial first-order coherence function of the gas.

DOI: 10.1103/PhysRevA.101.013421

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