Abstract
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.
Highlights
Entangled photons are a fundamental resource in many applications of quantum optics [1]
Even when a chirped quasi-phase-matched (QPM) waveguide is used to satisfy phase-matching over a broad spectral range [23], temporal distinguishability brought by the large group birefringence still has to be compensated exactly, and spectral distinguishability still severely degrades the quality of polarization entanglement
The spectral brightness and total brightness of periodically poled silica fiber (PPSF) source is comparable to other nonlinear crystal or waveguide based spontaneous parametric downcoversion (SPDC) broadband polarization entanglement sources [13, 23, 40], but provide better entanglement quality
Summary
Entangled photons are a fundamental resource in many applications of quantum optics [1]. Entanglement sources based upon Sagnac interferometers [18,19,20] are immune to perturbation, but have technical difficulties such as requiring triple wavelength polarization beamsplitters and dual wavelength half-wave plates These challenges become even more difficult to solve for broadband polarization entanglement generation. Even when a chirped quasi-phase-matched (QPM) waveguide is used to satisfy phase-matching over a broad spectral range [23], temporal distinguishability brought by the large group birefringence still has to be compensated exactly, and spectral distinguishability still severely degrades the quality of polarization entanglement. Is it possible to generate high-quality broadband polarization entanglement directly, compensation-free? We experimentally demonstrate that broadband high quality polarization entanglement can be realized in a PPSF source
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
