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arXiv:quant-ph/0311099 · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Coupling efficiencies in single-photon on-demand sources

Stefania Castelletto, Ivo Pietro Degiovanni, Michael J. Ware, Alan L. Migdall

Published Feb 3, 2004• 5 citations
arXivHTMLPDF

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.

DOI
10.1117/12.504773

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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.
We present the status of our work implementing a single photon on-demand source based on a multiplexed arrangement of parametric downconverters. An array of downconverters with multiplexed outputs makes it possible to create light pulses with increased probability of containing a single photon, while suppressing the probability of producing more than one photon. This is crucial for quantum cryptographic applications. Our current setup implements the scheme in a greatly simplified manner that produces photons along with a measure of the likelihood that the light pulse emitted is just a single photon. This implementation uses a virtual array of downconverters and an array of staggered length optical fibers allowing a single detector to measure a herald photon output by a series of downconverters. This single detector arrangement is a great savings considering the cost of such detectors. The timing of the herald tells us which path the herald took, which in turn, provides information on the single vs. multiphoton probabilities. So far, our work shows that the individual correlated photon peaks are clearly resolvable with our 2.4 ns delay line steps and the 1 ns full width half maximum (FWHM) of the correlated photon peaks, and that we can observe four correlated photon peaks simultaneously, a requirement to fully implement our scheme. Our current efforts are to increase the brightness and utility of the system for incorporation into a quantum communication testbed.
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. We present two possible models to describe single-mode fibres coupling with PDC light fields in a non-collinear configuration, that lead to two different results. These approaches include factors such as crystal length and walk-off, non-collinear phase-matching and transverse pump field distribution. We propose an experimental test to distinguish between the two. 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.
We investigate the coupling efficiency of parametric downconversion light (PDC) into single and multimode optical fibers as a function of the pump beam diameter, crystal length, and walk-off. We outline two different theoretical models for the preparation and collection of either single-mode or multimode PDC light (defined by, for instance, multimode fibers or apertures). Moreover, we define the mode-matching collection efficiency, important for realizing a single-photon source based on PDC output into a well-defined single mode. We also define a multimode collection efficiency that is useful for single-photon detector calibration applications.
We investigate the coupling efficiency of parametric downconversion light (PDC) into single and multi-mode optical fibers as a function of the pump beam diameter, crystal length and walk-off. We outline two different theoretical models for the preparation and collection of either single-mode or multi-mode PDC light (defined by, for instance, multi-mode fibers or apertures, corresponding to bucket detection). Moreover, we define the mode-matching collection efficiency, important for realizing a single-photon source based on PDC output into a well-defined single spatial mode. We also define a multimode collection efficiency that is useful for single-photon detector calibration applications. 1.
We investigate the coupling efficiency of parametric downconversion light (PDC) into single and multi-mode optical fibers as a function of the pump beam diameter, crystal length and walk-off. We outline two different theoretical models for the preparation and collection of either single-mode or multi-mode PDC light (defined by, for instance, multi-mode fibers or apertures, corresponding to bucket detection). Moreover, we define the mode-matching collection efficiency, important for realizing a single-photon source based on PDC output into a well-defined single spatial mode. We also define a multimode collection efficiency that is useful for single-photon detector calibration applications.