Quantum-correlated Photon Pair Generation Research Articles

Quantum-correlated photon-pair generation via cascaded nonlinearity in an ultra-compact lithium-niobate nano-waveguide.

We generate quantum-correlated photon pairs using cascaded χ(2):χ(2) traveling-wave interactions for second-harmonic generation (SHG) and spontaneous parametric down-conversion (SPDC) in a single periodically-poled thin-film lithium-niobate (TFLN) waveguide. When pulse-pumped at 50 MHz, a 4-mm-long poled region with nearly 300%/Wcm2 SHG peak efficiency yields a generated photon-pair probability of 7±0.2 × 10-4 with corresponding coincidence-to-accidental ratio (CAR) of 13.6±0.7. The CAR is found to be limited by Stokes/anti-Stokes Raman-scattering noise generated primarily in the waveguide. A Raman peak of photon counts at 250 cm-1 Stokes shift from the fundamental-pump wavenumber suggests most of the noise that limits the CAR originates within the lithium niobate material of the waveguide.

High-extinction ratio integrated photonic filters for silicon quantum photonics.

We present the generation of quantum-correlated photon pairs and subsequent pump rejection across two silicon-on-insulator photonic integrated circuits. Incoherently cascaded lattice filters are used to provide over 100 dB pass-band to stop-band contrast with no additional external filtering. Photon pairs generated in a microring resonator are successfully separated from the input pump, confirmed by temporal correlations measurements.

Quantum-correlated photon pairs generated in a commercial 45 nm complementary metal-oxide semiconductor microelectronic chip

Correlated photon pairs are a fundamental building block of quantum photonic systems. While pair sources have previously been integrated on silicon chips built using customized photonics manufacturing processes, these often take advantage of only a small fraction of the established techniques for microelectronics fabrication and have yet to be integrated in a process that also supports electronics. Here we report the first demonstration of quantum-correlated photon pair generation in a device fabricated in an unmodified advanced (sub-100-nm) complementary metal-oxide semiconductor (CMOS) process, alongside millions of working transistors. The microring resonator photon pair source is formed in the transistor layer structure, with the resonator core formed by the silicon layer typically used for the transistor body. With ultralow CW on-chip pump powers ranging from 4.8 to 400 μW, we demonstrate pair generation rates between 165 Hz and 332 kHz using >80% efficient WSi superconducting nanowire single-photon detectors. Coincidences-to-accidentals ratios consistently exceeding 40 were measured, with a maximum of 55. In the process of characterizing this source, we also accurately predict pair generation rates from the results of classical stimulated four-wave mixing measurements. This proof-of-principle device demonstrates the potential of commercial CMOS microelectronics as an advanced quantum photonics platform with the capability of large volumes and pristine process control, where state-of-the-art high-speed digital circuits could interact with quantum photonic circuits.

Integrated Source of Spectrally Filtered Correlated Photons for Large-Scale Quantum Photonic Systems

We demonstrate the generation of quantum-correlated photon-pairs combined with the spectral filtering of the pump field by more than 95dB using Bragg reflectors and electrically tunable ring resonators. Moreover, we perform demultiplexing and routing of signal and idler photons after transferring them via a fiber to a second identical chip. Non-classical two-photon temporal correlations with a coincidence-to-accidental ratio of 50 are measured without further off-chip filtering. Our system, fabricated with high yield and reproducibility in a CMOS process, paves the way toward truly large-scale quantum photonic circuits by allowing sources and detectors of single photons to be integrated on the same chip.

Slow light enhanced correlated photon pair generation in photonic-crystal coupled-resonator optical waveguides

We demonstrate the generation of quantum-correlated photon pairs from a Si photonic-crystal coupled-resonator optical waveguide. A slow-light supermode realized by the collective resonance of high-Q and small-mode-volume photonic-crystal cavities successfully enhanced the efficiency of the spontaneous four-wave mixing process. The generation rate of photon pairs was improved by two orders of magnitude compared with that of a photonic-crystal line defect waveguide without a slow-light effect.

Role of Absorption on the Generation of Quantum-Correlated Photon Pairs Through FWM

The impact of fiber absorption on the generation rate of quantum-correlated photon pairs through spontaneous four-wave mixing in optical fibers is studied theoretically. We quantify the impact of the loss through the analysis of the Cauchy-Schwarz correlation parameter and the Clauser, Horne, Shimony, and Holt inequality. Results show that fiber loss can improve the quantum-correlation between the photon pairs. This is a consequence of the decrease of the individual signal and idler photon-fluxes, which reduces the rate of uncorrelated photons generated through Raman scattering inside the optical fiber. Findings show that a high degree of polarization entanglement is obtained when the ratio of signal to idler photon-fluxes lies between 0.5 and 0.8, in a regime with high losses on the signal wave.

Quantum-correlated photon pair generation in tellurite microstructured optical fibers

We theoretically investigated the generation of quantum-correlated photon pair through spontaneous four-wave mixing in tellurite microstructured optical fiber (MOF). We evaluated the performance of photon pair generation in tellurite fibers based on Raman gain coefficient spectra. It was shown that the TBSN16P6W tellurite fiber provided a low Raman noise on correlation photon generation over a wide pump-idler detuning range. We can choose proper tellurite composition to obtain a low Raman gain window over wide range for correlated photon pair generation. We also designed the tellurite MOF structure to obtain a small dispersion value with high nonlinear coefficient at telecommunication wavelengths, thus realize efficient quantum-correlated photon pair generation.

Quantum-correlated photon pair generation in chalcogenide As_2S_3 waveguides

We theoretically investigate the generation of quantum-correlated photon pairs through spontaneous four-wave mixing in chalcogenide As(2)S(3) waveguides. For reasonable pump power levels, we show that such photonic-chip-based photon-pair sources can exhibit high brightness (approximately 1 x 10(9) pairs/s) and high correlation (approximately 100) if the waveguide length is chosen properly or the waveguide dispersion is engineered. Such a high correlation is possible in the presence of Raman scattering because the Raman profile exhibits a low gain window at a Stokes shift of 7.4 THz, though it is constrained due to multi-pair generation. As the proposed scheme is based on photonic chip technologies, it has the potential to become an integrated platform for the implementation of on-chip quantum technologies.

1.5-µm band quantum-correlated photon pair generation in dispersion-shifted fiber: suppression of noise photons by cooling fiber

Spontaneous four-wave mixing in a dispersion-shifted fiber (DSF) is a promising approach for generating quantum-correlated photon pairs in the 1.5 microm band. However, it has been reported that noise photons generated by the spontaneous Raman scattering process degrade the quantum correlation of the generated photons. This paper describes the characteristics of quantum-correlated photon pair generation in a DSF cooled by liquid nitrogen. With this technique, the number of noise photons was sufficiently suppressed and the ratio of true coincidence to accidental coincidence was increased to ~30.

Generation of Quantum-Correlated Photon Pairs in Optical Fiber: Influence of Spontaneous Raman Scattering

The generation of quantum-correlated photon pairs by spontaneous four-wave mixing (FWM) in an optical fiber is studied. After demonstrating the time correlation between signal and idler photons, the influence of spontaneous Raman scattering on extracting photon pairs is experimentally investigated. It is shown that a short pulse and a narrow filtering bandwidth are preferable for obtaining correlated photon pairs with a better signal-to-noise ratio via FWM in an optical fiber.