Ultracold Atoms Coupled to Ultracold Nano-mechanical Oscillators

• Applicants: Dr. Christoph Becker; Dr. Alexander Schwarz; Professor Dr. Klaus Sengstock; Professor Dr. Roland Wiesendanger
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2015 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 274978790

This proposal combines the expertise of two groups at the University of Hamburg with exceptional experience in quantum optics (QO-group: Dr. Christoph Becker; Prof. Sengstock) and scanning probe microscopy at cryogenic temperatures (SP-group: Dr. Alexander Schwarz; Prof. Wiesendanger). Our ambitious goal is to create a hybrid quantum system and study the interaction between its constituents. We will concentrate on a hybrid system comprised of cold atoms or a Bose Einstein condensate (BEC) on the one hand and a cryogenically cooled nano-mechanical oscillator on the other hand. The latter is usually regarded as a classical system, but its behavior turns quantum as well, if cooled to sufficiently low temperatures. Three regimes can be studied with this kind of hybrid system: (i) the interaction between a quantum and a classical system, (ii) the transition between classical and quantum, where the nano-mechanical oscillator is on the brink of reaching its quantum mechanical ground state and (iii) the interaction between two very different kinds of macroscopic quantum systems.We envisage two different types of experiments: (i) Indirect coupling via a light field between ultracold atoms trapped in an optical lattice and a spatially well separated nano-mechanical oscillator located in a dilution refrigerator and (ii) direct interaction of ultracold atoms with a nano-mechanical oscillator inside a dilution refrigerator. In this initial three-year proposal we will concentrate on the indirect ex-situ coupling experiment, using an adjustable all-fiber cavity with a membrane in the middle precooled to 100mK inside a dilution refrigerator. Applying opto-mechanical cooling techniques and developing advanced novel cooling schemes utilizing cold atoms as a thermal bath, we are confident to reach the motional ground state of the membrane. The hybrid quantum system can then be employed to create and study pure quantum phenomena like e.g. entanglement and squeezing.Finally, the already existing experimental set-up (dilution refrigerator plus BEC apparatus) is designed in a way to allow for the direct in-situ probing experiments after some modifications. Particularly, a magnetic transfer line is required to move cold atoms inside the cryostat as well as a trap to create and manipulate Bose Einstein condensates. In the framework of this proposal we present first concepts regarding these plans.

• DFG Programme: Research Grants