A micrometer-scale integrated silicon source of time-energy entangled photons (1409.4881v1)

Abstract: Entanglement is a fundamental resource in quantum information processing. Several studies have explored the integration of sources of entangled states on a silicon chip but the sources demonstrated so far require millimeter lengths and pump powers of the order of hundreds of mWs to produce an appreciable photon flux, hindering their scalability and dense integration. Microring resonators have been shown to be efficient sources of photon pairs, but entangled state emission has never been demonstrated. Here we report the first demonstration of a microring resonator capable of emitting time-energy entangled photons. We use a Franson experiment to show a violation of Bell's inequality by as much as 11 standard deviations. The source is integrated on a silicon chip, operates at sub-mW pump power, emits in the telecom band with a pair generation rate exceeding 10$^7$ Hz per $nm$, and outputs into a photonic waveguide. These are all essential features of an entangled states emitter for a quantum photonic networks.

• The paper presents a silicon microring resonator that produces time-energy entangled photons via spontaneous four-wave mixing at sub-mW pump power.
• It achieves a compact 10 μm footprint with a pair generation rate exceeding 10^7 Hz per nm in the telecom band.
• Experimental validation using a Franson interferometer confirmed robust entanglement with an 11-standard deviation violation of Bell’s inequality.

Integrated Silicon Source of Time-Energy Entangled Photons

The paper "A micrometer-scale integrated silicon source of time-energy entangled photons" investigates the development of a microring resonator capable of producing time-energy entangled photon pairs on a silicon chip, operating with sub-milliwatt pump power. This research represents a significant advancement toward scalable and efficient quantum photonic networks, addressing challenges in integrating photon pair sources on a silicon platform.

Entanglement, a crucial resource in quantum information processing, has often been challenging to achieve in integrated circuits due to the significant real estate and power required. Traditional sources typically necessitate millimeter-scale dimensions and hundreds of milliwatts of power, posing limitations in terms of scalability and integration density. In contrast, the microring resonator presented in this paper overcomes these constraints, achieving entanglement with a dramatically reduced footprint and pump power. The resonator's radius is a mere 10 micrometers, and it operates with a pair generation rate exceeding $10^7$ Hz per nm in the telecom band, making it particularly compatible with existing fiber optic infrastructures.

The experimental verification of entanglement was demonstrated using a Franson interferometer setup, which revealed a violation of Bell's inequality by up to 11 standard deviations. This substantial deviation is a testament to the robust entanglement of the photon pairs generated. The compactness of the device, combined with its efficient operation at telecom wavelengths, underscores its potential applicability in quantum communication and on-chip quantum processing systems.

Key contributions of this work include:

• The design and fabrication of a silicon-on-insulator microring resonator, which leverages third-order nonlinearities in silicon to achieve spontaneous four-wave mixing (SFWM). This nonlinear process is crucial for the generation of photon pairs, wherein two pump photons are converted into a signal and an idler photon.
• Successful operation at sub-mW pump power levels, with photon emission rates significantly exceeding prior silicon-based sources.
• Integration of the source into a photonic waveguide, facilitating direct interfacing with other on-chip optical components and potential large-scale quantum photonic circuits.

The implications of this research are multifold. Practically, it enables CMOS-compatible production of entangled photon sources, promising cost-effective and reliable deployment alongside conventional silicon electronics. Theoretically, it opens up new avenues for exploring complex photonic quantum circuits with enhanced scalability and integration. The demonstrated high brightness and telecommunication compatibility of the microring resonator suggest it could become a central element in developing robust quantum key distribution systems and other quantum network applications.

Looking forward, this technology paves the way for more advanced integrated quantum photonic systems, with potential applications extending to quantum metrology and computation. Future research might explore further optimization of the resonator's performance parameters, investigate its integration with various quantum devices, and expand its operational wavelength range. In conclusion, this paper contributes significantly to the advancement of integrated quantum photonics, positioning silicon-based microring resonators as a promising platform for future quantum technologies.