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Entangled Twin Atom Beams

Periodic Reporting for period 1 - ETAB (Entangled Twin Atom Beams)

Reporting period: 2015-04-01 to 2017-03-31

Many of the fascinating phenomena predicted by quantum mechanics, like non-local correlations and entanglement, were implemented with photons in the framework of quantum optics. It is today a mature field with applications emerging in cryptography, random number generation, and quantum computation. Based on the analogy between matter waves and electromagnetic waves and on particle-wave duality, quantum atom optics started to develop recently, thanks to the development of tools for matter wave manipulation. A crucial point for the success of quantum optics was the availability of twin-photon sources, based on a non-linear medium. At TU Wien, a source of twin-atom pairs has been developed in the previous years: Twin atoms are emitted from a quantum atomic gas when a population inversion of the atoms’ vibrational state is prepared.
The objectives of the ETAB project are i) the investigation of the non-equilibrium dynamics taking place after the vibrational state excitation and ii) the adaptation of this twin atom beam (TAB) source to a double-wells geometry where TAB should be produced in a Bell state. Objective i) was achieved by measuring the atom-atom correlations of the TAB and characterizing the relaxation of different superpositions of vibrational states. The main milestones towards objective ii) have been reached and we are currently working on the characterization of the TAB entanglement.
In order to separate the timescales of the vibrational state inversion and of the TAB emission, Optimal control was used to design a fast state preparation ramp. We implemented it successfully, obtaining a 99.3(6) % fidelity of the prepared state, and characterized its robustness. The results are described in van Frank et al, Scientific Reports 6, 34187 (2016). We investigated the atom-atom correlations of TAB and their time evolution for different regimes of emission, showing a spreading of correlations for the fast emission regime. We also investigated the dynamics after preparation of superpositions of the ground and first excited vibrational state, showing a strong dependence of the relaxation timescale on the atom number. These different results were presented at international workshop and conferences.
In order to trigger TAB emission in a double-well potential we developed a new optimal control scheme, based on modulation of the separation between the wells. Thanks to our extremely accurate control of the potential this scheme was successfully implemented, and emission of TAB with the expected momentum was observed. We elaborated a method for characterization of two-atom entanglement in our configuration, which we plan to use to demonstrate the entanglement of the TAB produced in the double wells.
Our mastering of optimal control of vibrational states, and the ability to prepare the target state faster than the dynamics to be studied opens further possibilities for preparation and investigation of non-equilibrium systems (for which we developed analysis method in the frame of the ETAB project). It could also be adapted to other configurations, for example in optical lattices.
For the first time TAB were observed in a double-well configuration. We expect that demonstrating a source of pairwise entangled atoms will have a large impact and allow applications in atom quantum optics.
Our experimental setup for manipulation and detection of the atomic quantum gas
In order to trigger twin atom beams emission we transfer the atoms to an excited vibrational state.