Speaker: Wolfgang Tittel (University of Calgary)

Title: Photon-Echo Quantum Memory and Controlled State Manipulation

Coauthors: A. Delfan, E. Saglamyurek, and C. La Mela

Quantum memories, as a part of a quantum repeater, are key elements to extend quantum communication beyond its current distance limit of around 100 km. In addition to memories, quantum repeaters also require the distribution of entangled photons as well as state manipulation, which is generally accomplished by means of interferometric optical setups. We experimentally investigate a novel approach based on photon-echo type atom light-interaction that allows combining storage with controlled transformation of quantum states [1,2]. As an example, we perform a proof-of-principle demonstration of unambiguous state discrimination in an Er:LiNbO3 waveguides cooled to 3K using states encoded into pulses of light in superposition of different temporal modes. Our approach can easily be extended to any unitary transformation. The high robustness and flexibility compared to current optical setups for state manipulation makes it promising for quantum communication and computation protocols that require storage and manipulation of photons, in particular quantum repeaters.

[1] W. Tittel, M. Afzelius, T. Chanelière, R. Cone, S. Kröll, S.A. Moiseev, and M. Sellars, Laser & Photonics Reviews, DOI 10.1002/lpor.200810056 (2009).

[2] A. Delfan, C. La Mela and W. Tittel, in Proceedings of SPIE 6903: 690308 (6 pp.), San Jose, United States of America (SPIE , Bellingham, United States of America, 2008).

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Speaker: Thomas Jennewein (Institute for Quantum Computing)

Title: Quantum Communication and Information Processing with Photons - Experiments and Outlook

Photons are good candidates for quantum information processing, and they have been widely used in implementations of quantum communication and quantum information processing. I will outline recent experimental results on long distance quantum communication with entangled photons, and the ongoing activities towards performing satellite based quantum networks. Furthermore, I will present the results of theoretical studies on the actual requirements for photon sources and detectors in order to perform photonic quantum computing outside the coincidence basis, which will be an important next experimental step towards scalable quantum information processing with photons.

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Speaker: Jeff Lundeen (National Research Council, Institute for National Measurement Standards)

Title: Designed photons from birefrigent waveguides

Coauthors: Offir Cohen, Pierre Mahou, Brian J. Smith, and Ian A. Walmsley

The capability to produce photon pairs and non-classical states of light, such as squeezed states, with controlled spatial and temporal mode structure is a crucial requirement for optical quantum technologies such as photonic quantum information processing, quantum cryptography, and quantum metrology. We develop a theoretical model of photon pair generation by spontaneous four-wave mixing in birefringent waveguides, such as optical fibers. The model demonstrates that a wide variety of spectral correlations can be designed into the photon pairs. We present experimental results in photonic crystal fiber and birefringent standard fiber where we eliminate all correlations, enabling the heralding of single photons in pure quantum state, which is a requirement for high-fidelity operation of photonic quantum logic gates.

Paper reference: http://dx.doi.org/10.1103/PhysRevLett.102.123603

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Speaker: Alberto M. Marino (NIST)

Title: Applications of Four-Wave Mixing in Quantum Information

Coauthors: Raphael C. Pooser Vincent Boyer Paul D. Lett

One of the most important resources in quantum mechanics is entanglement, which is at the basis of applications such as quantum cryptography, quantum imaging, teleportation, etc. In order to fully take advantage of this resource, it is necessary to develop a number of tools to manipulate and control it. We show that non-degenerate four-wave mixing in rubidium vapor is a good candidate for the implementation of some of those tools. Its dispersive properties make it possible to control the propagation velocity of light. We have used this property to delay entanglement without a significant degradation, effectively implementing a short term quantum memory. In addition, its operation as an almost ideal amplifier has allowed us to clone one of the beams of an entangled state of light.

Paper reference: Nature 457, 859 (2009) and PRL 103, 010501 (2009)