Parametric down-conversion photon pair source on a nanophotonic chip (1603.03726v1)

Abstract: Quantum photonic chips, which integrate quantum light sources alongside active and passive optical elements, as well as single photon detectors, show great potential for photonic quantum information processing and quantum technology. Mature semiconductor nanofabrication processes allow for scaling such photonic integrated circuits to on-chip networks of increasing complexity. Second order nonlinear materials are the method of choice for generating photonic quantum states in the overwhelming part of linear optic experiments using bulk components but integration with waveguide circuitry on a nanophotonic chip proved to be challenging. Here we demonstrate such an on-chip parametric down-conversion source of photon pairs based on second order nonlinearity in an Aluminum nitride microring resonator. We show the potential of our source for quantum information processing by measuring high-visibility antibunching of heralded single photons with nearly ideal state purity. Our down conversion source operates with high brightness and low noise, yielding pairs of correlated photons at MHz-rates with high coincidence-to-accidental ratio. The generated photon pairs are spectrally far separated from the pump field, providing good potential for realizing sufficient on-chip filtering and monolithic integration of quantum light sources, waveguide circuits and single photon detectors.

• The paper demonstrates a high-efficiency AlN microring resonator producing photon pairs at a rate of over 20 MHz/mW.
• It reports near-ideal photon purity with a g(2)(0) value of 0.088, ensuring robust single-photon emission for quantum applications.
• The study highlights integration potential with telecom wavelengths, paving the way for scalable on-chip quantum photonic circuits.

Analysis of Parametric Down-Conversion Photon Pair Source on a Nanophotonic Chip

This paper presents a comprehensive paper of an integrated quantum photonic circuit leveraging parametric down-conversion (PDC) in an Aluminum Nitride (AlN) microring resonator to generate photon pairs. The research displays significant progress toward realizing compact, efficient quantum photonic devices on a chip. The demonstrated AlN-based microring resonators show high potential for integration in quantum information processing systems due to their efficient generation of photon pairs and compatibility with standard semiconductor nanofabrication techniques.

Key Findings and Contributions

The paper introduces an Aluminum Nitride microring resonator that exploits the second-order nonlinearity to produce entangled photon pairs through spontaneous parametric down-conversion. The photon pairs are generated with high brightness and low noise. The notable aspects of their implementation include:

1. Efficiency and Brightness: The resonators achieved a photon-pair generation rate of over 20 MHz/mW, aligning with contemporary bulk optic sources. The AlN microring devices surpass traditional waveguide or bulk crystal sources in terms of spectral brightness.
2. Quality Factor and Purity: The team measured a second-order correlation function value $g^{(2)}(0)$ of 0.088, indicative of strong antibunching and demonstrating emission of single photons with high purity. The generated photons possess nearly ideal state purity, a crucial feature for quantum computing applications.
3. Integration Potential: The spectral separation between pump and generated photons aids in effective filtering, showing great potential for monolithic integration of PDC sources alongside detectors and waveguide circuits on a single chip.
4. Compatibility with Telecom Band: By converting visible wavelength pump photons into telecom wavelength pairs, AlN resonators offer advantages in terms of interfacing with existing telecommunication infrastructure.

Techniques and Methodology

The microring resonator's design harnesses AlN's inherent second-order nonlinear optical properties. A visible pump field is converted through second harmonic generation (SHG) and difference frequency generation (DFG), leading to non-degenerate down-conversion at infrared wavelengths. The design ensures phase matching, enabling efficient nonlinear conversion. The photon pairs are characterized using superconducting single-photon detectors integrated in a separate chip, ensuring comprehensive analysis of photon statistics and correlation functions.

Implications and Future Outlook

The paper's findings reflect a significant step toward scalable quantum photonic technology. The use of AlN not only emphasizes the potential for more efficient nonlinear processes but also opens new avenues for integrating electro-optic modulation due to its EO properties. This integration is crucial for dynamic control of quantum states, providing a platform for future quantum computing and communication networks.

Looking forward, further optimization in resonator design could enhance quality factors and reduce device footprint, increasing the intrinsic efficiency of such photonic sources. The capability to integrate such devices with existing semiconductor technologies heralds a promising future for versatile quantum photonic circuits.

In conclusion, the paper lays a strong foundation for integrating nonlinear quantum optics with scalable semiconductor processes. It highlights the feasibility of developing compact, efficient quantum light sources that are integral to advancing quantum information processing technologies. The continuous improvement of such devices may soon enable fully operational quantum networks, paving the way for implementing complex quantum algorithms on-chip and enhancing the accessibility of quantum computing technologies.