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Quantum Measurements with Bose-Einstein condensates strongly coupled to nanophotonic structures

Periodic Reporting for period 2 - QuantuM-nano (Quantum Measurements with Bose-Einstein condensates strongly coupled to nanophotonic structures)

Reporting period: 2017-08-14 to 2018-08-13

Quantum technologies have been recently recognized by the European Commission as a key resource for future applications in sensing, information processing, security and communications. In this context, this project aims at building quantum systems with a high degree of control and coherence, as an experimental resource to explore some of the abovementioned applications. As an elementary resource for quantum information, we are using ultracold neutral in optical traps. Along a first line, we are investigating how these atoms can be coupled to the field of nanophotonic structure with potential applications in sensing and metrology. Along a second closely related line, we have build a reconfigurable platform to create defect-free arrays of more than 50 individually-controlled atoms interacting through their Rydberg states, with potential applications in quantum simulations and information processing. Along a third line, we are studying chains of atoms strongly coupled to a fiber-based optical cavity.

Conclusion of the action: the Rydberg atom array experiment turned out to be extremely successful at performing various tasks in quantum simulations, with up to 50 qubits and an unprecedented degree of fidelity, making it a very promising platform for future applications of the second quantum revolution.
The most striking result of this first period is the successful realization of a 51-atom qubit programmable quantum simulator with highly controlled neutral atoms. The basic principle is to create an array of 100 optical tweezers from the same AOD, which are then stochastically loaded with single atoms and rearranged to the desired configuration, before turning on Rydberg interactions. With this platform, we were able to explore the phase diagram of an Ising Hamiltonian by sweeping into various ordered phases, we could quantitatively study the associated phase transitions, we showed the preparation with high fidelity of the many-body ground state of a Rydberg crystal phase with up to 51 atoms (where classical simulations are no longer tractable) and we observed some intriguing many-body dynamics in the form of robust oscillations between complementary ordered states. We have also explored the critical dynamics accros quantum phase transitions by looking at the density of defects as a function of the frequency sweeping rate. In a second experiment, we have demonstrated the possibility to couple more than one atom to the evanescent field of a nanophotonic cavity, as a promising resource for quantum sensing and quantum networks. In a third experiment, we have observed strong coupling between a chain of atoms and a fiber-based cavity, and studied how the atomic qubits are protected from decoherence coming from inhomogeneities by strong coupling to the optical cavity.

Publications related to this project:
A. Keesling, A. Omran, H. Levine, H. Bernien, H. Pichler, S. Choi, R. Samajdar, S. Schwartz, P. Silvi, S. Sachdev, P. Zoller, M. Endres, M. Greiner, V. Vuletic and M. D. Lukin. Probing quantum critical dynamics on a programmable Rydberg simulator. arXiv:1809.05540 accepted for publication in Nature (April 2019).
H. Levine, A. Keesling, A. Omran, H. Bernien, S. Schwartz, A. S. Zibrov, M. Endres, M. Greiner, V. Vuletic and M. D. Lukin. High-fidelity control and entanglement of Rydberg atom qubits. Physical Review Letters 121, 123603 (2018).
H. Bernien, S. Schwartz, A. Keesling, H. Levine, A. Omran, H. Pichler, S. Choi, A. S. Zibrov, M. Endres, M. Greiner, V. Vuletic and M. D. Lukin, Probing many-body dynamics on a 51-atom quantum simulator, Nature 551, 579-584 (2017).

Link to the report in brief on the CORDIS website:
The results obtained on our quantum simulator significantly advance previous state-of-the-art in the field of quantum simulations.
They are also an experimental demonstration of the high degree of control that can be achieved over a 50-qubit platform with neutral atoms, holding great prospects for several applications of the second quantum revolution including quantum metrology and quantum optimization. If pushed even further in system size and fidelity, this technique might find applications in fields of broad general interest like material science or biology, solving problems that cannot be solved on any classical computer.
Artistic impression of an atom array undergoing a quantum phase transition.