Advanced Photonic Quantum Information Processing

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

The nascent field of quantum information promises amazing and important capabilities, such as ultra-secure encryption, ultra-fast computation, and ultra-precise metrology. Photons are excellent carriers of quantum information, having been employed in numerous groundbreaking quantum information processing experiments. However, although many approaches to realizing a reliable periodic source of single photons - a critical resource for quantum applications - are being pursued, to date none operates at a level sufficient for realizing scalable optical quantum information processing. To date, nearly all experiments have been limited by inefficient photon-pair sources and detectors. Consequently, for example, a protocol needing five photons would be the equivalent of rolling five die and getting a "6" on each one, with the likelihood of only (1/6)(1/6)(1/6)(1/6)(1/6)= 0.00013. By incorporating time multiplexing of the photon source - making multiple attempts (~20) until we get a successful output, the success probability to create five photons is increased in principle to 88%. Large-scale quantum information processing also requires highly efficient detectors and high-fidelity photonic circuits. This project will solve these needs, combining advanced technologies for periodic single-/multi-photon sources, integrated photonic waveguide circuits, and highly efficient single-photon detectors. The net result will be a new capability for optical quantum information processing, greatly exceeding what has been possible until now. The realization of an efficient periodic source of indistinguishable photons is an enabling technology for many quantum information protocols, including one-way quantum computing, improved quantum cryptography, and quantum metrology. It would immediately enhance almost all existing quantum communication protocols, simultaneously increasing the possible rate while reducing the deleterious effects of multi-photon events. Spontaneous parametric downconversion is well known as a source of heralded single photons - detecting one of the daughter photons indicates the presence of the other one. However, the downconversion process itself is probabilistic, and therefore the resulting single photons are not on-demand; furthermore, using a brighter pump pulse to increase the likelihood of producing a pair automatically increases the unwanted probability of producing more than one pair. By employing temporal multiplexing, allowing photons created in any one of, e.g., 50 time slots to be mapped onto a single final time window, the net efficiency for single-photon creation can be greatly enhanced, while minimizing the likelihood of unwanted multi-photon events. The benefit becomes even greater when intentionally trying to create states with many photons: the methods developed here could enable rate enhancements over five orders of magnitude (and for one experiment up to 12 orders!). A similar improvement in optical circuitry (with regard to size and stability) is realized using custom-fabricated waveguides written into low-loss glass. One key feature of this work is the collaboration with Israeli researcher Yaron Silberberg, who will develop the required photonic waveguide circuitry, and work with the group on the final set of applications. The technology of 'integrating' a large number of waveguides and optics such as beamsplitters and phase shifters into a tiny glass substrate (approximately cross 5 centimeter area) will provide enhanced stability and interference between multiple photons. Thus, the unique bi-national connection in this proposal enables the development and implementation of sophisticated quantum photonic systems well beyond those that have been possible to date, until now limited to only a few photons. Combining the new source with optimized photonic waveguide circuitry, the project will then investigate several interesting photon-based quantum effects, including potentially scalable optical quantum logic and quantum walks.