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Home / / / / / / Electrical Engineering Baskin School of Engineering UC Santa Cruz
© 2007 H. Schmidt. All rights reserved. Contact
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Single-Photon Nonlinear Optics Recent work in quantum interference in alkali vapors has shown some spectacular and well-publicized results. This type of atomic quantum state control can be used to reduce the speed of light down to a few meters per second, temporarily store the quantum state of a photon in an atomic medium, render an opaque medium transparent, and realize phase modulation and optical switching with few or single photons [1]. Fig. 1 shows the generic four-level scheme that exhibits giant Kerr nonlinearities [2]. A coherent coupling field applied between levels 2 and 3 creates a quantum interference that leads to a constructive interference for the Kerr nonlinearity while eliminating linear absorption. As a result, the presence of a signal field denoted by WS imparts a large phase shift on the probe field WS through cross-phase modulation. The effect can be so strong that it may enable quantum non-demolition detection with single-photon signals. A slightly modified version of the scheme (Fig. 1, right)can be used to generate entangled photon pairs via parametric generation [3]. |
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This type of quantum interference is best observed in alkali vapors such as rubidium. In order to move quantum interference from fundamental physics towards practical device applications, alkali vapors need to be integrated into optical waveguides on a semiconductor chip. In addition, nonlinear quantum interference effects benefit from integration because much higher intensities can be achieved. Hence, an optical waveguide is required where light is guided in the low-index vapor. This has never been realized in atomic vapor, but can be achieved in antiresonant reflecting optical (ARROW) waveguides as shown in Fig. 2 [4,5]. |
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In this project, optical quantum interference is combined with design and fabrication of ARROW waveguides to develop an integrated atomic spectroscopy platform. We have recently demonstrated the first integrated rubidium cell for atomic spectroscopy on a chip [6]. Compared with conventional bulk cells, this compact portable cell has a vapor volume that is more than 7 orders of magnitude smaller. The simultaneous reduction in optical mode area makes this device ideal for low-level nonlinear optics. Fig. 3 shows an image of the chip along with the absorption spectrum from the ARROW chip compared to a conventional bulk cell. The newly gained capability of carrying out atomic spectroscopy on a chip can be used in a variety of applications as diverse as frequency stabilization, frequency references (atomic clocks) or gas detection. |
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Our main goal is to improve these chips for the use of quantum interference in alkali atoms for integrated optical devices in linear and nonlinear optics. Improvements in electronic decoherence times are necessary to demonstrate linear and nonlinear quantum interference effects. The ultimate goal is to build integrated optical devices relying on quantum state control on a chip. This work is funded by DARPA/AFOSR under the Slow Light Program, and the National Science Foundation (NSF). [1] S.E. Harris, Phys. Today, p. 36, July 1997, and references therein. [2] H. Schmidt and A. Imamoglu, Optics Letters, 21, 1936,(1996). [3] V. Balic et al., "Generation of paired photons with controllable waveforms", Phys. Rev. Lett., 94, 183601, (2005). M.D. Eisaman et al., Phys. Rev. Lett., 93, 233602 (2004). [4] D. Yin, J.P. Barber, A.R. Hawkins, and H. Schmidt, "Integrated ARROW waveguides with hollow cores", Optics Express, 12, 2710, (2004). |