Engineering biphoton spectral wavefunction in a silicon micro-ring resonator with split resonances

TL;DR

This paper demonstrates a silicon micro-ring resonator capable of generating and controlling biphoton spectral wavefunctions, including separable and entangled states, with high spectral purity for quantum information applications.

Contribution

It introduces a novel method to engineer biphoton spectral wavefunctions in silicon micro-ring resonators with split resonances, enabling independent control of spectral properties without post-manipulation.

Findings

Achieved 95.5% spectral purity for separable states

Controlled entangled states with two- or four-peaked joint spectral intensities

Developed a semi-analytical model matching experimental results

Abstract

Frequency-time is a degree of freedom suitable for photonic high-dimensional entanglement, with advantages such as compatibility with single-mode devices and insensitivity to dispersion. The engineering control of the frequency-time amplitude of a photon's electric field has been demonstrated on platforms with second-order optical nonlinearity. For integrated photonic platforms with only third-order optical nonlinearity, the engineered generation of the state remains unexplored. Here, we demonstrate a cavity-enhanced photon-pair source on the silicon-on-insulator (SOI) platform that can generate both separable states and controllable entangled states in the frequency domain without post-manipulation. By choosing different resonance combinations and employing on-chip optical field differentiation, we achieve independent control over two functions that affect the joint spectral intensity (JSI) of the state. A semi-analytical model is derived to simulate the biphoton spectral wavefunction in the presence of resonance splitting and pump differentiation, and its parameters can be fully determined through fitting-based parameter extraction from the resonator's measured linear response. The measured spectral purity for the separable state is $95.5\pm 1.2\%$, while the measured JSIs for the entangled states show two- or four-peaked functions in two-dimensional frequency space. The experiments and simulations demonstrate the capacity to manipulate the frequency-domain wavefunction in a silicon-based device, which is promising for applications like quantum information processing using pulsed temporal-mode encoding or long-distance quantum key distribution.