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Optics Letters

Bidirectional multiplexing of heralded single photons from a silicon chip

Chunle Xiong, Trung D. Vo, Matthew J. Collins, Jun Li, Thomas F. Krauss, Michael J. Steel, Alex S. Clark, Benjamin J. Eggleton

Published Nov 25, 2013• 35 citations
Publisher

Abstract

We demonstrate integrated spatial multiplexing of heralded single photons generated from a single 96 μm long silicon photonic crystal waveguide in a bidirectional pump configuration. By using a low-loss fiber-coupled opto-ceramic switch, the multiplexing technique enhances the brightness of the single photon source by 51.2±4.0% while maintaining the coincidence-to-accidental ratio. Compared with the demonstration of multiplexing two individual sources, the bidirectional pump scheme represents a twofold reduction in the footprint of nonlinear devices for future large-scale integration of on-chip single photon sources. The 51.2±4.0% gain will make any quantum operation requiring n photons 1.5(n) times faster.

DOI
10.1364/ol.38.005176

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Silicon-based integrated spiral waveguides are extensively used as on-chip single-photon sources. However, inherent uncertainties and limitations in single-photon fidelity pose significant theoretical performance bottlenecks. These challenges often necessitate the multiplexing of multiple sources. In this paper, we propose a novel scheme for spatial multiplexing using bidirectional spirals. By pumping a spiral waveguide bidirectionally, photon pairs are generated in both clockwise (cw) and counterclockwise (ccw) directions, each producing signal-idler photon pairs in a two-mode squeezed state. Consequently, a single spiral waveguide can function as two spatially multiplexed sources. Using CMOS fabrication technology, we constructed a bidirectional spiral waveguide structure. We measured the coincidence count rates, heralded second-order correlation function, and coincidence to accidental ratio (CAR) as functions of pump power, both before and after multiplexing. Our experimental results demonstrated a 1.67-fold increase in performance post-multiplexing. This finding underscores the potential of bidirectional spirals as spatially multiplexed sources, paving the way for the largescale integration of future photonic quantum chips.
The non-deterministic nature of photon sources is a key limitation for single-photon quantum processors. Spatial multiplexing overcomes this by enhancing the heralded single-photon yield without enhancing the output noise. Here the intrinsic statistical limit of an individual source is surpassed by spatially multiplexing two monolithic silicon-based correlated photon pair sources in the telecommunications band, demonstrating a 62.4% increase in the heralded single-photon output without an increase in unwanted multipair generation. We further demonstrate the scalability of this scheme by multiplexing photons generated in two waveguides pumped via an integrated coupler with a 63.1% increase in the heralded photon rate. This demonstration paves the way for a scalable architecture for multiplexing many photon sources in a compact integrated platform and achieving efficient two-photon interference, required at the core of optical quantum computing and quantum communication protocols. Photonic quantum technologies will require efficient single-photon sources and spatial multiplexing has been explored as a route to achieve this. Here, the authors present a scheme to integrate several single-photon sources using spatial multiplexing for on-chip applications at telecommunications wavelengths.
The non-deterministic nature of photon sources poses a fundamental challenge to scaling single-photon quantum processors. While multiplexing in space, time, and frequency can enhance heralding efficiency, key bottlenecks remain in the efficiency of the on-chip resource unit and the speed of the external control system. Here, we demonstrate a high-count-rate, spatially multiplexed single-photon source on a silicon chip. By implementing a bidirectional pumping scheme, our architecture halves the number of required photon sources, creating a compact, optimized unit for future large-scale multiplexing sources. In addition, we implement a control system based on a Random-Access Memory First-In-First-Out module to improve the count rate limitation. Experimental results demonstrate a coincidence count rate gain of 1.67 under both pulsed and continuous-wave pumping regimes in our system. This work provides a scalable unit design and a robust control strategy for high-rate quantum photonic circuits.
We demonstrate room temperature heralded single photon generation in a CMOS-compatible silicon nanophotonic device. The strong modal confinement and slow group velocity provided by a coupled resonator optical waveguide produced a large four-wave-mixing nonlinearity coefficient γeff≈4100 W−1 m−1 at telecommunications wavelengths. Spontaneous four-wave-mixing using a degenerate pump beam at 1549.6 nm created photon pairs at 1529.5 nm and 1570.5 nm with a coincidence-to-accidental ratio exceeding 20. A photon correlation measurement of the signal (1529.5 nm) photons heralded by the detection of the idler (1570.5 nm) photons showed antibunching with g(2)(0)=0.19±0.03. The demonstration of a single photon source within a silicon platform holds promise for future integrated quantum photonic circuits.