is now generally realized that the exploitation of fundamentally
quantum-mechanical phenomena can enable significant, and in some cases,
tremendous, improvement for a variety of tasks important to emergent
technologies. Building on decades
of successes in the experimental demonstration of such fundamental phenomena, it
is not surprising that photonics is playing a preeminent role in this nascent
endeavor. Many of the objectives of
quantum technologies are inherently suited to optics (e.g., communications,
metrology), while others may have a strong optical component (e.g., distributed
quantum computing, quantum repeaters). In
order for quantum information technology to attain its full potential,
instrumentation by which quantum systems may be created, stored, manipulated and
characterized must be developed.
Our multi-institutional project started in 2003 aims at the development of the technological tools to further the realization of quantum information processing in the optical domain. Specifically, we investigate the following instrumentation technologies: on-demand and periodic single-photon and entangled-photon sources; high-efficiency detectors that can discriminate incident photon number; tunable sources of arbitrary entangled states and the means to characterize them via state tomography; optical quantum memories and repeaters; and the possibility of full Bell-state analysis. Material systems, designs, and techniques that we investigate will enable to perform these essential functions at wavelengths ranging from ultraviolet to infrared. In addition, our approach allows coupling of generated photons into optical fibers at high data rates (presently at 76 MHz and potentially higher than 10 GHz), and combining of individual components into integrated quantum information systems.
We will develop the sources of single and entangled photons on demand based on variety of techniques: from pulsed excitation of a single semiconductor quantum dot exciton or a single quantum well impurity bound exciton in a photonic crystal microcavity, to parametric down conversion in bulk nonlinear optical materials or periodically poled waveguides. A range of materials will be explored for this purpose: InGaAs/GaAs quantum dots and acceptor impurity doped GaAs and InGaAs quantum wells, as well as lithium niobate (LiNbO3), KTP and BBO for parametric down-conversion. Proposed detectors of single photons and photon pairs include a number of techniques, ranging from visible light photon counters (VLPC), solid-state photo-multipliers (SSPM), and silicon avalanche photodiodes (Si APD) combined with quantum state transducers, to superconducting bolometric detectors. The capability to make a wide variety of entangled states with very high precision will be extended to include multiple degrees of freedom, and the brightness of our systems will be optimized by incorporating periodically-poled materials and recycling the pulsed pump light. We will also improve our current methods of quantum state tomography to incorporate an adaptive routine, thereby optimizing the information obtained for a given number of photons. Three systems will be investigated for efficient photon storage and release: specially designed, switchable optical storage cavities, a quantum dot exciton or quantum well impurity bound-exciton strongly coupled to a cavity, and stopped-light in solid-state systems. We will also design, theoretically investigate, and begin proof-of-principle experiments on a solid-state implementation of a quantum repeater that could eventually perform cascades of entanglement swaps between pairs of previously unentangled photons. Finally, we will explore the possibility of Bell state analysis based on combining the use of two-photon transitions with our high efficiency atomic vapor scheme for photon-number counting detectors.
The breadth of our approach, the variety of used materials and techniques, and the range of operating wavelengths of the resulting quantum devices are the key features of this project. We are purposely pursuing multiple approaches to each problem in parallel, which will allow us to directly compare the options and maximize the likelihood of success. The established history of fruitful collaboration between several members of the groups will be further enhanced by the fact that nearly every project will have participation of at least two groups. Our coherent efforts will enable us to engineer a new generation of tools for photonic quantum information science, with applications to other areas such as optical metrology, biophysics, and even security (e.g., very low-light level imaging). By the end of the five-year period, we will not only demonstrate these basic components and employ them for quantum information science, but also deliver recipes that will allow other scientists and engineers to replicate our devices in their labs.