CMOS-compatible, multiplexed source of heralded photon pairs: towards integrated quantum combs (1403.6180v1)

Abstract: We report an integrated photon pair source based on a CMOS-compatible microring resonator that generates multiple, simultaneous, and independent photon pairs at different wavelengths in a frequency comb compatible with fiber communication wavelength division multiplexing channels (200 GHz channel separation) and with a linewidth that is compatible with quantum memories (110 MHz). It operates in a self-locked pump configuration, avoiding the need for active stabilization, making it extremely robust even at very low power levels.

• The paper introduces a CMOS-compatible microring resonator that uses a self-locked pumping configuration to stabilize photon pair generation without external lasers.
• It achieves ITU-compliant 200 GHz frequency spacing and a high Q-factor of 1.375 million, facilitating multiplexing for quantum communication protocols.
• The device generates narrow-linewidth (~110 MHz) photon pairs with heralding efficiencies around 10%, making it compatible with atomic-based quantum memories.

Integrated CMOS-Compatible Heralded Photon Pair Source for Quantum Technologies

The research by Christian Reimer et al. presents a sophisticated and self-stabilizing integrated photon pair source employing a CMOS-compatible microring resonator. This system is capable of generating multiple independent photon pairs at varying wavelengths, structured around a frequency comb that aligns with the International Telecommunication Union (ITU) channel spacing requirements of optical fiber communication networks.

Key Contributions

1. CMOS-Compatibility and Integration: The microring resonator is integrated on a platform compatible with CMOS technology, specifically fabricated with a high refractive index doped glass (Hydex) platform. This compatibility is crucial for potential large-scale integration in electronic-photonic systems.
2. Self-Locked Pumping Configuration: Unlike conventional systems that rely on external pump lasers needing stringent active stabilization, this device utilizes a self-locked pump mechanism that assures stability and robustness at sub-threshold power levels. This configuration negates the requirement for intricate thermal locking procedures and external feedback mechanisms.
3. Multiplexed Photon Pair Generation: The resonator efficiently produces photon pairs at multiple wavelengths concurrently, each separated by 200 GHz, matching the ITU-compliant frequency grid. This capability is essential for realizing frequency-multiplexed quantum communication protocols, particularly in quantum key distribution (QKD) systems.
4. Compatibility with Quantum Memories: The linewidth of the generated photon pairs is remarkably narrow, approximating 110 MHz, thus compatible with atomic-based quantum memory systems. This is a significant advancement over preceding sources where linewidths were often too broad.

Numerical and Experimental Results

• The microring resonator exhibits a Q-factor of 1.375 million and maintains a free spectral range (FSR) of 200 GHz. With this configuration, the team achieved a coincidence-to-accidental coincidence ratio (CAR) ranging from 10 to 14 across different channel pairs.
• Photon pair production rate per channel is reported between 286 and 346 kHz at the device's output.
• The experimental device achieved heralding efficiencies of approximately 10%, impacted predominantly by system losses.

Implications and Future Developments

The device's capability to operate stably over several days without any need for active stabilization paves the way for practical and scalable quantum communication devices. The achievement of high-quality heralded single-photon states further solidifies the potential utility of this device in various optical quantum technologies. Additionally, the ability to extend photon generation over the C and L telecom bands indicates significant prospects for large-scale multiplexing applications, essential for quantum networks accommodating high user numbers and high data rates.

Furthermore, the potential for integration of semiconductor optical amplifiers (SOAs) to replace erbium-doped fiber amplifiers (EDFAs) marks a pathway toward monolithic integration. Such integration could lead to a self-contained, chip-based solution, advancing the practical implementation of quantum technologies.

Overall, by addressing the major challenges of system stability and integration compatibility while demonstrating significant experimental results, this work serves as a vital step toward developing integrated quantum optics solutions in the framework of CMOS technology. This scalability offers numerous possibilities in the future landscape of quantum computing and secure communications.