Qubit entanglement between ring-resonator photon-pair sources on a silicon chip

Abstract

Entanglement—one of the most delicate phenomena in nature—is an essential resource for quantum information applications. Scalable photonic quantum devices must generate and control qubit entanglement on-chip, where quantum information is naturally encoded in photon path. Here we report a silicon photonic chip that uses resonant-enhanced photon-pair sources, spectral demultiplexers and reconfigurable optics to generate a path-entangled two-qubit state and analyse its entanglement. We show that ring-resonator-based spontaneous four-wave mixing photon-pair sources can be made highly indistinguishable and that their spectral correlations are small. We use on-chip frequency demultiplexers and reconfigurable optics to perform both quantum state tomography and the strict Bell-CHSH test, both of which confirm a high level of on-chip entanglement. This work demonstrates the integration of high-performance components that will be essential for building quantum devices and systems to harness photonic entanglement on the large scale.

CMOS-compatible photonic devices for single-photon generation

“…(iii) Owing to the narrow resonance bandwidth, they are usually pumped by narrow linewidth continuous wave (CW) lasers, which is not good for the multiplexing schemes discussed later in Section 4 because of the lack of a clock for the generated photons. (iv) The resonant wavelengths are extremely sensitive to environmental temperature and fabrication fluctuations, and so tunable elements such as micro-heaters are required to make two devices emit indistinguishable photons for high-visibility quantum interference [42]. (v) Once a microring or microdisk is fabricated, both pump and the generated photons can only be at the resonant wavelengths and thus lack flexibility.…”

Truly unentangled photon pairs without spectral filtering

“…Since heralded single photon sources can exploit parametric fluorescence in passive nonlinear optical mediaeither spontaneous four-wave mixing (SFWM) or spontaneous parametric down-conversion (SPDC) -they can be designed to operate at room temperature, and are readily implemented in integrated devices. Many integrated photon pair sources for single photon heralding have recently been demonstrated on the rapidly developing platform of silicon nanophotonics [3][4][5].…”

Generation and manipulation of entangled photons on silicon chips

“…To fully exploit the advantages of integrated photonics, it would be ideal to integrate these different components on a single substrate. Motivated by this, many researchers have recently demonstrated the hybrid integration of different quantum-optical components [103][104][105][106][107][108][109]. Hence, the stage of integrated quantum photonics research is now moving to hybrid integration on a chip.…”

“…Hence, the stage of integrated quantum photonics research is now moving to hybrid integration on a chip. Among the building blocks, quantum circuits can be realized by using integrated waveguides with cores made of silicon [18,108,110], GaAs [111], or silica-based materials [1,10,13,112]. Of these approaches, silica-based waveguide technology has realized planar lightwave circuits with a significantly large scale for classical optical communication [113,114]; this capability will facilitate the construction of large-scale quantum circuits.…”