Abstract
Generating entangled photons from a monolithic chip is a major milestone towards real-life applications of optical quantum information processing including quantum key distribution and quantum computing. Ultrabroadband entangled photons are of particular interest to various applications such as quantum metrology and multi-party entanglement distribution. In this work, we demonstrate the direct generation of broadband wavelength-multiplexed polarization entangled photons from a semiconductor chip for the first time. Without the use of any off-chip compensation or interferometry, entangled photons with a signal-idler separation as large as 95 nm in the telecom band were observed. The highest concurrence of 0.98±0.01 achieved in this work is also the highest, to the best of our knowledge, comparing to all previously demonstrated semiconductor waveguide sources. This work paves the way for fully integrated, ultrabroadband sources of polarization entangled photons.
Highlights
Generating entangled photons from a monolithic chip is a major milestone towards real-life applications of optical quantum information processing including quantum key distribution and quantum computing
This has been motivated by various applications in quantum optical technologies such as quantum optical coherence tomography (QOCT) [4] and quantum optical frequency comb sources (QOFC) [5, 6]
The source is a modal phase matched Bragg reflection waveguide (BRW) [16], consisting of multiple layers of AlGaAs, in which the pump light is guided by Bragg reflections from two periodic reflectors while the down-converted photons are guided by conventional total internal reflections
Summary
BRWs have been extensively studied in the past few year for classical wavelength conversions [21, 22] and entangled photon pair generations [16, 17, 23]. A high value of concurrence of at least 0.96 ± 0.02 and as high as 0.98 ± 0.01, as well as a highest fidelity of 0.97 t√o a maximally entangled state (|HV + exp (iφ) |V H )/ 2 could be observed for the signal-idler pairs from 1535.4 nm to 1575.6 nm, which approximately covers the whole C-band (1530 nm1565 nm) This corresponds to a total bandwidth of over 40 nm for the down-converted photons, and equivalently 26 pairs of wavelength channels if the channel spacing is 100 GHz. For signal and idler wavelengths further apart, the concurrence starts to decrease as well as the coincidence counts.
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