Slowing and stopping light using an optomechanical crystal array

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New Journal of Physics The open–access journal for physics Slowing and stopping light using an optomechanical crystal array D E Chang 1,4 , A H Safavi-Naeini 2,4 , M Hafezi 3 and O Painter 2,5 1 Institute for Quantum Information and Center for the Physics of Information, California Institute of Technology, Pasadena, CA 91125, USA 2 Thomas J Watson, Sr, Laboratory of Applied Physics, California Institute of Technology, Pasadena, CA 91125, USA 3 Joint Quantum Institute and Department of Physics, University of Maryland, College Park, MD 20742, USA E-mail: opainter@caltech.edu New Journal of Physics 13 (2011) 023003 (26pp) Received 24 November 2010 Published 1 February 2011 Online at http://www.njp.org/ doi:10.1088/1367-2630/13/2/023003 Abstract. One of the major advances needed to realize all-optical information processing of light is the ability to delay or coherently store and retrieve optical information in a rapidly tunable manner. In the classical domain, this optical buffering is expected to be a key ingredient of managing the flow of information over complex optical networks. Such a system also has profound implications for quantum information processing, serving as a long-term memory that can store the full quantum information contained in an optical pulse. Here, we suggest a novel approach to light storage involving an optical waveguide coupled to an optomechanical crystal array, where light in the waveguide can be dynamically and coherently transferred into long-lived mechanical vibrations of the array. Under realistic conditions, this system is capable of achieving large bandwidths and storage/delay times in a compact, on-chip platform. 4 These authors contributed equally to this work. 5 Author to whom any correspondence should be addressed. New Journal of Physics 13 (2011) 023003 1367-2630/11/023003+26$33.00 © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft
2 Contents 1. Introduction 2 2. Description of the system: an optomechanical crystal (OMC) array 3 3. Slowing and stopping light 5 3.1. Static regime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.2. Storage of optical pulse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.3. Imperfections in storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4. OMC design 10 5. Outlook 13 Acknowledgments 13 Appendix A. Equations of motion for an OMC array 13 Appendix B. Transfer matrix analysis of propagation 15 Appendix C. Optical noise power 16 Appendix D. The band structure analysis 17 Appendix E. Implementation in an OMC 20 References 24 1. Introduction Light is a natural candidate for transmitting information across large networks owing to its high speed and low propagation losses. A major obstacle to building more advanced optical networks is the lack of an all-optically controlled device that can robustly delay or store optical wave packets over a tunable amount of time. In the classical domain, such a device would enable alloptical buffering and switching, bypassing the need to convert an optical pulse to an electronic signal. In the quantum realm, such a device could serve as a memory to store the full quantum information contained in a light pulse until it can be passed to a processing node at some later time. A number of schemes to coherently delay and store optical information are being actively explored. These range from tunable coupled resonator optical waveguide (CROW) structures [1, 2], where the propagation of light is dynamically altered by modulating the refractive index of the system, to electromagnetically induced transparency (EIT) in atomic media [3, 4], where the optical pulse is reversibly mapped into internal atomic degrees of freedom. While these schemes have been demonstrated in a number of remarkable experiments [5]–[8], they remain difficult to implement in a practical setting. Here, we present a novel approach to store or stop an optical pulse propagating through a waveguide, wherein coupling between the waveguide and a nearby nanomechanical resonator array enables one to map the optical field into long-lived mechanical excitations. This process is completely quantum coherent and allows the delay and release of pulses to be rapidly and all-optically tuned. Our scheme combines many of the best attributes of previously proposed approaches, in that it simultaneously allows for large bandwidths of operation, on-chip integration, relatively long delay/storage times and ease of external control. Beyond light storage, this work opens up the intriguing possibility of a platform for quantum or classical all-optical information processing using mechanical systems. New Journal of Physics 13 (2011) 023003 (http://www.njp.org/)
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