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Optics Letters

Generating entangled photons via enhanced spontaneous parametric downconversion in AlGaAs microring resonators

Zhenshan S. Yang, John E. Sipe

Published Nov 5, 2007• 46 citations
Publisher

Abstract

Spontaneous parametric downconversion (SPDC) can be enhanced in double-channel side-coupled microring resonator structures, generating entangled photons spatially separated in different channels. The enhancement is even more drastic in single-channel side-coupled microring resonator structures, although the generated entangled photons are not spatially separated, and it might be most interesting to use a ring tuned for nondegenerate SPDC.

DOI
10.1364/ol.32.003296

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Spontaneous parametric downconversion (SPDC) can be enhanced in double-channel side-coupled microring resonator structures, generating entangled photons spatially separated in different channels. The enhancement is even more drastic in single-channel side-coupled microring resonator structures, although the generated entangled photons are not spatially separated, and it might be most interesting to use a ring tuned for nondegenerate SPDC.
The ability to engineer pairs of entangled photons is essential to quantum information science, and generating these states using spontaneous parametric down-conversion (SPDC) in nano- and micrometer-scale materials offers numerous advantages. To properly engineer such sources, a reliable model describing nano- and micrometer-scale SPDC is necessary; however, such a theoretical description remains a challenge. Here, we propose and derive a simplified model to describe SPDC in resonant structures, which considers the generation of photon pairs and the resonant enhancement of spectral bands to be separate processes, even though they actually occur simultaneously. We compare our simplified model to both the rigorous theory of SPDC in an etalon - a simple example of a resonant structure - and our experiments on SPDC in etalons and find agreement for low-gain SPDC. By simplifying the calculations required to generate photon pairs, our model promises to make designing complex resonant structures easier, and it promises to hasten the iteration of designs across the field of quantum state engineering.
In this Letter, we theoretically study spontaneous parametric downconversion (SPDC) in a periodically poled structure composed of two linearly uncoupled resonators that are nonlinearly coupled via a Mach-Zehnder interferometer. The device does not require dispersion engineering to achieve efficient doubly resonant SPDC, and, unlike the case of a single resonator, one can reconfigure the system to generate photon pairs over a bandwidth of hundreds of nm. We consider the case of SPDC pumped at 775 nm in a periodically poled lithium niobate (PPLN) device compatible with up-to-date technological platforms. We calculated pair generation rates of up to 250 MHz/mW pump power for a single resonance and integrated pair generation rates of up to 100 THz/mW pump power over 170 nm. When properly reconfigured, a single device can efficiently generate over a bandwidth of some 300 nm, covering the S, C, L, and U infrared bands.
In spontaneous parametric downconversion (SPDC), a pump photon spontaneously splits into signal and idler photons in media with quadratic nonlinearity. This phenomenon is the most widely utilized source of entangled photons with multiple applications in quantum information technology. SPDC on a chip is usually treated as a local process, meaning that signal and idler photons are created in the same position at which the pump photon is destroyed. We reveal that this locality condition can be violated in an array of coupled waveguides. By utilizing higher-order modes of individual waveguides, it is possible to destroy a pump photon in one waveguide and to generate signal and idler photons in other waveguides. This phenomenon of nonlocal photon-pair generation opens new opportunities for the engineering of spatial photon entanglement.