BYU Physics and Astronomy

Abstract: Photon-based quantum information schemes have increased the need for light sources that produce individual photons, with many such schemes relying on optical parametric down-conversion (PDC). Practical realizations of this technology require that the PDC light be collected into a single spatial mode defined by an optical fibre. In this paper, we present two possible models to describe single-mode fibres coupling with PDC light fields in a non-collinear configuration, leading to two different results. These approaches include factors such as crystal length and walk-off, non-collinear phase-matching and also transverse pump field distribution. We propose an experimental test to distinguish between the two models. The goal is to help clarify open issues, such as how to extend the theory beyond the simplest experimental arrangements and, more importantly, to suggest ways to improve the collection efficiency.

Abstract: Correlated photons can be used to directly measure the detection efficiency of photon counting detectors without any ties to externally calibrated standards. An overview of the history of this technique is given and the paper reviews how to implement it in a practical lab setting. Some of the sources of uncertainty in the technique and how they can be minimized and quantified are discussed. The intent is to provide the information necessary to encourage the movement of this technique from the metrology lab into the general photon-counting detector community.

Abstract: Many quantum computation and communication schemes require, or would significantly benefit from, true sources of single photon on-demand (SPOD). Unfortunately, such sources do not exist. It is becoming increasingly clear that coupling photons out of a SPOD source will be a limiting factor in many SPOD implementations. In particular, coupling these source outputs into optical fibers (usually single mode fibers) is often the preferred method for handling this light. We investigate the practical limits to this coupling as relates to parametric downconversion, an important starting point for many SPOD schemes. We also explored whether it is possible to optimize the engineering of the downconversion sources to improve on this coupling. We present our latest results in this area.