Cryogenic Wavelength-Multiplexed Eight-Channel Optical-to-Microwave Converter

Area of Science:

• Quantum Computing
• Cryogenic Engineering
• Photonics

Background:

• Superconducting quantum computers require numerous cryogenic interconnects, limiting scalability.
• Photonic links, particularly with wavelength multiplexing, offer a solution to reduce cable density.
• A cryogenic multichannel optical-to-microwave converter is crucial for demultiplexing and signal conversion within cryostats.

Purpose of the Study:

• To demonstrate the first cryogenic eight-channel optical-to-microwave converter.
• To address the missing experimental validation for photonic interconnect solutions in quantum computing.

Main Methods:

• Integrated an arrayed waveguide grating (silicon photonics) with eight waveguide-integrated plasmonic graphene photodetectors.
• Designed for compact footprint (1.75 mm × 0.71 mm) enabling dense integration.
• Characterized device performance at 4 K.

Main Results:

• Achieved electrical crosstalk below 30 dB across all eight channels.
• Demonstrated high bandwidth (>45 GHz) and subnanoampere dark current.
• Observed 4-5x increased responsivity at 4 K compared to room temperature.
• Proof-of-concept: simultaneous transfer of two RF signals with >50 dB crosstalk isolation.

Conclusions:

• The developed device is the first cryogenic multichannel optical-to-microwave converter.
• Wavelength-multiplexed photonic links show significant potential for overcoming cryogenic interconnect bottlenecks.
• Enables scalable and dense integration for next-generation quantum computers.