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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

High heralding-efficiency of near-IR fiber coupled photon pairs for quantum technologies

P. Ben Dixon, Ryan P. Murphy, Danna Rosenberg, Matthew E. Grein, Veronika Stelmakh, Ryan S. Bennink, Franco N. C. Wong

Published May 21, 2015• 0 citations
Publisher

Abstract

We report on the development and use of a high heralding-efficiency, single-mode-fiber coupled telecom-band source of entangled photons for quantum technology applications. The source development efforts consisted of theoretical and experimental efforts and we demonstrated a correlated-mode coupling efficiency of 97% ± 2%, the highest efficiency yet achieved for this type of system. We then incorporated these beneficial source development techniques in a Sagnac configured telecom-band entangled photon source that generates photon pairs entangled in both time/energy and polarization degrees of freedom. We made use of these highly desirable entangled states to investigate several promising quantum technologies.

DOI
10.1117/12.2178907

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We report on the development and use of a high heralding-efficiency, single-mode-fiber coupled telecom-band source of entangled photons for quantum technology applications. The source development efforts consisted of theoretical and experimental efforts and we demonstrated a correlated-mode coupling efficiency of 97% ± 2%, the highest efficiency yet achieved for this type of system. We then incorporated these beneficial source development techniques in a Sagnac configured telecom-band entangled photon source that generates photon pairs entangled in both time/energy and polarization degrees of freedom. We made use of these highly desirable entangled states to investigate several promising quantum technologies.
We report on a systematic experimental study of heralding efficiency and generation rate of telecom-band infrared photon pairs generated by spontaneous parametric down-conversion and coupled to single mode optical fibers. We define the correlated-mode coupling efficiency--an inherent source efficiency--and explain its relation to heralding efficiency. For our experiment, we developed a reconfigurable computer controlled pump-beam and collection-mode optical apparatus which we used to measure the generation rate and correlated-mode coupling efficiency. The use of low-noise, high-efficiency superconducting nanowire single-photon detectors in this setup allowed us to explore focus configurations with low overall photon flux. The measured data agree well with theory and we demonstrated a correlated-mode coupling efficiency of 97±2%97 \pm 2\%97±2%, which is the highest efficiency yet achieved for this type of system. These results confirm theoretical treatments and demonstrate that very high overall heralding efficiencies can, in principle, be achieved in quantum optical systems. It is expected that these results and techniques will be widely incorporated into future systems that require, or benefit from, a high heralding efficiency.
We report on a systematic experimental study of the heralding efficiency and generation rate of telecom-band infrared photon pairs generated by spontaneous parametric down-conversion and coupled to single-mode optical fibers. We define the correlated-mode coupling efficiency, an inherent source efficiency, and explain its relation to heralding efficiency. For our experiment, we developed a reconfigurable computer-controlled pump-beam and collection-mode optical apparatus which we used to measure the generation rate and correlated-mode coupling efficiency. The use of low-noise, high-efficiency superconducting nanowire single-photon detectors in this setup allowed us to explore focus configurations with low overall photon flux. The measured data agree well with theory, and we demonstrated a correlated-mode coupling efficiency of 9797%\ifmmode\pm\else\textpm\fi{}2%97, which is the highest efficiency yet achieved for this type of system. These results confirm theoretical treatments and demonstrate that very high overall heralding efficiencies can, in principle, be achieved in quantum optical systems. It is expected that these results and techniques will be widely incorporated into future systems that require, or benefit from, a high heralding efficiency.
Ultrabright sources of entangled photon pairs with high heralding efficiency are an important step in the pursuit of high-bit-rate entanglement-base quantum key distribution, as well as an enabling tool for loss-sensitive quantum optics experiments. Here, we present a robust single-mode fiber-coupled source of polarization-entangled photons around 810 nm with both high brightness and heralding efficiency. Our approach is based on quasi-phase-matched spontaneous parametric downconversion (SPDC) from periodically poled KTiOPO4 in a Sagnac loop configuration. We demonstrate a high degree of two-photon polarization entanglement for single-frequency-pumped type-0 and type-II SPDC, and conduct a conclusive comparison in terms of efficiency and spectral characteristics. In light of applications outside a laboratory environment, we evaluate the feasibility of pumping nonlinear crystals with free-running laser diodes.
The efforts of this research have been directed towards improving both the heralding efficiency and heralding rates of a high performance fiber-coupled single photon source based on an ultrafast pulsed beam-like Type-II parametric down conversion (PDC) source. Entangled photons generated from PDC are inherently broadband (many frequencies) and exit the nonlinear crystal at varying angles (different directions). This makes coupling the photons into single-mode fibers, a desirable feature for quantum computing, difficult. In response to these difficulties we have explored applying multi-layered thin film broadband anti-reflection coatings onto the ends of single-mode fibers using the technique of RF Planar Magnetron Sputtering in an effort to increase the coupling efficiency of the beam-like down converted photons. In addition, we have explored theoretically the broadband nature of novel phase matching geometries to increase heralding rates and minimize photon losses. With the ability to tailor coupling fibers to various down conversion sources we hope to increase both the heralding efficiency and heralding rate to levels needed for a broad range of future experiments.
This thesis explores a method to enhance the practical utility of hyper-entangled photons generatedin periodically poled silica fiber for quantum communication applications. Hyper-entanglement, which involves quantum correlations in multiple degrees of freedom simultaneously, offers increased information capacity per particle compared to single-degree entanglement. Periodically poled sil- ica fiber has shown promise in generating high-quality, broadband polarization-frequency hyper- entangled photon pairs collinearly through type-II spontaneous parametric down-conversion. How- ever, the collinear nature of these photon pairs poses a challenge for applications requiring hyper- entanglement, as they occupy the same spatial mode. This research develops a technique for sep- arating these photon pairs while preserving their information capacity, measures the resulting en- tanglement quality degradation, and discusses potential improvements. This work contributes to the development of efficient fiber-based hyper-entanglement sources, advancing the field of practical quantum technologies and long-distance quantum communication.