| 概 要 |
Single atoms trapped in arrays of optical tweezers and excited to Rydberg states are considered as a promising platform for quantum simulation of spin models, quantum optimization of combinatorial problems and more generally for quantum computing [1]. At this Mesoscopic Science Forum, I will give a tutorial about this new artificial quantum system.
I will first introduce the concept of spin models, which can describe magnetic phenomena such as the phase transition between a paramagnetic and ferromagnetic state. These models are central in the field of quantum simulation, and they also apply to the optimization of combinatorial problems (e.g., the travelling salesman problem), and can further be though as an analog version of a digital quantum computer. We will identify the three ingredients to engineer a spin model, namely (i) an array of spin-1/2 (i.e. a two-level system, or qubit), (ii) arbitrary spin rotation and (iii) spin-spin coupling. After a review of platforms being developed to realize spin models, we will focus on cold Rydberg atoms in optical tweezers.
The second part of the talk will present a key technique of our apparatus: how to prepare up to 100 laser-cooled atoms in holographic 3D arrays of optical tweezers to encode the array of qubits [2-4]. After reviewing the principle of laser cooling and trapping of neutral atoms, I show how to trap, with 50 % success, a single atom in one tweezers. Large number of tweezers are obtained with computer-generated holograms, while the random loading of the traps is circumvented by re-ordering the atoms, one by one, with an automated moving tweezers. I will present our current work on improving these techniques.
The final part dives into the properties of the giant Rydberg orbitals of an atom. After discussing how to coherently excite the atoms to a Rydberg state, with cw- or pulsed-laser, we will be interested in the strong coupling between two Rydberg atoms. This coupling, mediated by the van der Walls [5] or the dipole-dipole interaction [6], can generate entanglement between two atomic qubits and can be mapped to a spin-spin coupling. I will demonstrate how to use these interacting Rydberg atoms to study phase of matter described by spin models [7,8], and finally give an overview of the research topics that we are currently exploring in the framework of the Q-LEAP program by MEXT in tight collaboration with Hamamatsu Photonics K.K. [9-11].
[1] A. Browaeys and T. Lahaye, “Many-body physics with individually controlled Rydberg atoms,” Nat. Phys. 16, 132 (2020).
[2] M. Endres et al., “Atom-by-atom assembly of defect-free one-dimensional cold atom arrays,” Science 354, 1024 (2016).
[3] D. Barredo, S. de Léséleuc, V. Lienhard, T. Lahaye and A. Browaeys, “An atom-by-atom assembler of defect-free arbitrary 2d atomic arrays,” Science 354, 1021 (2016).
[4] D. Barredo, V. Lienhard, S. de Léséleuc, T. Lahaye and A. Browaeys, “Synthetic three-dimensional atomic structures assembled atom by atom,” Nature 561, 79 (2018).
[5] L. Béguin, A. Vernier, R. Chicireanu, T. Lahaye, and A. Browaeys, “Direct measurement of the van der Waals interaction between two Rydberg atoms,” Phys. Rev. Lett. 110, 263201 (2013).
[6] S. de Léséleuc, D. Barredo, V. Lienhard, A. Browaeys and T. Lahaye, “Local optical control of the resonant dipole-dipole interaction between Rydberg atoms,” Phys. Rev. Lett. 119, 053202 (2017).
[7] V. Lienhard, S. de Léséleuc et al., “Observing the space- and time-dependent growth of correlations in dynamically tuned synthetic Ising antiferromagnets,” Phys. Rev. X 8, 021070 (2018).
[8] S. de Léséleuc, V. Lienhard et al., “Experimental realization of a symmetry protected topological phase of interacting bosons with Rydberg atoms,” Science 365, 775 (2019).
[9] N. Takei, C. Sommer, C. Genes, G. Pupillo, H. Goto, K. Koyasu, H. Chiba, M. Weidemüller, and K. Ohmori, “Direct observation of ultrafast many-body electron dynamics in an ultracold Rydberg gas,” Nat. Commun. 7, 13449 (2016).
[10] M. Mizoguchi et al., “Ultrafast creation of overlapping Rydberg electrons in an atomic BEC and Mott-insulator lattice,” arXiv:1910.05292.
[11] Patent Publication Number: US 2018/0292786 A1; JAPAN 2018-180179, “Quantum simulator and quantum simulation method,” H. Sakai (Hamamatsu Photonics K.K.), K. Ohmori (NINS) et al., Oct. 11, 2018 (US); Nov. 15, 2018 (JAPAN).
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