Group Seminar via Zoom:Sub-nanosecond control of optical spin waves in a disordered atomic gas

September 08, 2020

Yizun He, Postdoc candidate
Group meeting via video conference (Zoom)
Tuesday, September 8th, 09:00 (MEZ)

Dealing with the unique situation of partial lock downs worldwide and home office solutions at our Institute due to the current spreading of the Covid 19 virus, we are now holding our group seminars and journal clubs via video conference. This procedure enables us to continue our research, enhance discussions and exchange important information.


Quantum light-matter interfaces [1], based upon ensembles of cold atoms or other quantum emitters, are being actively pursued as a platform for various quantum technologies. It has been pointed out that a shared, collective atomic excitation, in the form of an electric dipole spin wave with well-defined wavevector k, will radiate efficiently into a narrow spatial mode centered around the direction of k rather than into all directions, when the wavevector is ``phase-matched’’ to the dispersion relation of electromagnetic radiation. However, its ``phase-mismatched’’ counterparts, which are recently attracting significant interests, tend to de-couple from light and be difficult to excite with traditional methods. Recently, we experimentally demonstrate a technique to coherently and all-optically convert between matched and mismatched dipole spin waves using a laser-cooled 87Rb gas, overcoming the natural tendency for mismatched excitations to de-couple from light [2]. Enabled by this novel technique, we realize high-efficiency phase-mismatched excitations and observe a spin-wave dephasing effect due to strong dipole-dipole interactions of the close-by atoms, which is extremely hard to observe in the phase-matched excitations. Our work represents a first step of controlling the interacting electric dipole spin dynamics in the optical domain, where the long-range interactions compete with near-field interactions to govern the many-body dynamics. A deep understanding of such optical spin system is of fundamental importance and may help to unlock quantum resources beyond conventional mean-field pictures at photon-atom interfaces.

[1] Klemens Hammerer, Anders S Sørensen, and Eugene S Polzik. Quantum interface between light and atomic ensembles. Rev. Mod. Phys., 82(June):1041–1093, 2010.

[2] Yizun He, Lingjing Ji, Yuzhuo Wang, Liyang Qiu, Jian Zhao, Yudi Ma, Xing Huang, Saijun Wu and Darrick E. Chang, “Geometric control of collective spontaneous emission,” arXiv:1910.02289v2.

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