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Optica Laser Congress (ASSL, LAC, LS&C)

An enabling source for quantum sensing and metrology: fiber-based broadband entangled photons

Li Qian

Published Jan 1, 2016• 0 citations
Publisher

Abstract

Due to the low birefringence and low differential group delay of the optical fiber, extremely broadband emission of spontaneous parametric downconverted photon pairs can be created in quasi phase-matched thermally-poled optical fibers.
DOI
10.1364/lsc.2016.ltu4b.2

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Quantum sources that provide broadband biphotons entangled in both polarization and time-energy degrees of freedom are a rich quantum resource that finds many applications in quantum communication, sensing, and metrology. Creating such a source while maintaining high entanglement quality over a broad spectral range is a challenge, which conventionally requires various compensation steps to erase temporal, spectral, or spatial distinguishabilities. Here, we point out that in fact compensation is not always necessary. The key to generate broadband polarization-entangled biphotons via type-II spontaneous parametric downcoversion (SPDC) without compensation is to use nonlinear materials with sufficiently low group birefringence that the biphoton bandwidth becomes dispersion-limited. Most nonlinear crystals or waveguides cannot meet this condition, but it is easily met in fiber-based systems. We reveal the interplay of group birefringence and dispersion on SPDC bandwidth and polarization entanglement quality. We show that periodically poled silica fiber (PPSF) is an ideal medium to generate high-concurrence (>0.977) polarization-entangled photons over a broad spectral range (>77nm), directly and without compensation. This is the highest polarization-entanglement concurrence reported that is maintained over a broad spectral range from a compensation-free source.
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