Enabling Quantum Memory for Light

Montana State University, Bozeman MT

Investigators

Abstract

A recent Physics Today article and other scientific reviews highlight the importance of rare earth ion ensembles in the development of robust quantum memory for light. These solid-state systems store and recall the quantum states of light with high fidelity and have been shown to be competitive with or better than alternative approaches. Analysis and demonstrations by international groups have shown that rare-earth systems offer the potential to simultaneously achieve multimode quantum storage with 90% efficiency over timescales of seconds with GHz access bandwidths. Quantum memories that satisfy all these properties simultaneously are critical in the race to develop quantum networks, long-distance quantum communication and quantum cryptography, and linear optics quantum computing. This project focuses directly on the demonstration of efficient solid-state quantum memories through development of enabling triply ionized Thulium (Tm3+)-doped solid-state LiNbO3 optical waveguides in collaboration with the experimental quantum communication group of Prof. Wolfgang Tittel at the Institute for Quantum Information Science, University of Calgary, a leader in many of the quantum memory demonstrations. The broad goal of our work is to develop a solid-state material satisfying all requirements for quantum teleportation of quantum states between light and matter. In recent demonstrations of a high-fidelity solid-state quantum memory for entangled photons by Tittel, et al. (Nature, 2011), the 2% total system recall efficiency was limited by an unexplained excess decoherence in the Tm3+-doped LiNbO3 waveguide storage material. From our past decoherence studies of bulk Tm3+-doped LiNbO3 single crystals, it is known that excess decoherence that can be encountered in waveguides is not a fundamental limit of the material system. In this project, we are investigating and resolving the differences between the waveguide storage material used in the Nature demonstration by Calgary and the superior properties of our bulk crystals through coordinated experiments carried out in Montana and Calgary. Experimental study of optical decoherence combined with theoretical modeling of the material physics is used to reveal mechanisms for excess decoherence in the waveguide material to guide improvement in performance through routes including new LiNbO3 materials, alternate waveguide fabrication processes, material processing, and manipulation of properties through controlled external perturbations such as applied fields and temperature. This project's results have immediate applications in designing solid-state materials for quantum information processing, optical signal processing, laser frequency references, and laser materials. Quantum memories that enable long distance quantum key distribution for secure communication are of strategic importance given the need to transmit confidential information in a way that keeps it secure even 50 years from now. There is close collaboration with local groups in these areas at MSU, AdvR Inc., Scientific Materials Corp., and S2 Corp. -- a company whose technology was enabled by our scientific research. The techniques employed provide ideal educational programs for students at all stages, from undergraduates to post-doctoral researchers. This work offers students opportunities to gain proficiency with concepts and methods for research and development of optical materials in academic or industrial environments and is further enhanced by exchanges between MSU and Calgary. In particular, it provides a much-needed pool of skilled graduates for over twenty local Montana optical industries with whom close ties are maintained.