Frequency-multiplexed photon storage and read-out on demand using an atomic frequency comb-based quantum memory

Optical quantum memories require the ability to reversibly map quantum states between photons and atoms [1]. When employed for quantum repeaters [2], quantum memories are key to enabling long-distance quantum communication. Towards this end, quantum memories require recall on demand with high fidelity and efficiency, long storage times, and the possibility to simultaneously store multiple carriers of quantum information. The combination of a quantum state storage protocol based on an atomic frequency comb (AFC) [3] with rare-earth-ion doped crystals cooled to cryogenic temperatures as storage materials [4] has been shown to meet many of these requirements. In particular, it is well suited for storage of temporally multiplexed photons [5,6]. Yet, despite first proof-of-principle demonstrations [7], recalling quantum information at a desired time (i.e. read-out on demand) with broadband, single-photon-level pulses remains an outstanding challenge. We will present the first experimental demonstration of frequency-multiplexed storage of attenuated laser pulses followed by read-out on demand in the frequency domain. Our work is based on the AFC protocol and employs a Tm-doped LiNbO3 waveguide [8,9]. We will argue that, in view of a quantum repeater, our approach is equivalent to temporal multiplexing and read-out on demand in the temporal domain. This overcomes one further obstacle to building quantum repeaters using rare-earth-ion doped crystals as memory devices. [1] A. I. Lvovsky, B. C. Sanders and W. Tittel. “Optical Quantum Memory”, Nature Photonics 3, 2009, 706. [2] N. Sangouard et al. “Quantum repeaters based on atomic ensembles and linear optics”, Rev. Mod. Phys. 83, 2011, 33. [3] M. Afzelius et al. “Multimode quantum memory based on atomic frequency combs”, Phys. Rev. A 79, 2009, 052329. [4] W. Tittel et al. “Photon-echo quantum memory in solid state systems”, Las. Phot. Rev. 4 (2), 2010, 244. [5] I. Usmani et al. “Mapping multiple photonic qubits into and out of one solid-state atomic ensemble”, Nature Commun. 1, 2010, 12. [6] M. Bonarota, J.-L. Le Gouet, and T. Chaneličre. “Highly multimode storage in a crystal”, New J. Phys. 13, 2011, 013013. [7] M. Afzelius et al. “Demonstration of Atomic Frequency Comb Memory for Light with Spin- Wave Storage”, Phys. Rev. Lett. 104, 2010, 040503. [8] E. Saglamyurek et al. “Broadband waveguide quantum memory for entangled photons”, Nature 469, 2011, 512. [9] N. Sinclair et al. “Spectroscopic investigations of a Ti:Tm:LiNbO3 waveguide for photon-echo quantum memory”, J. Lumin. 130, 2010, 1586.