Cryogenic Optical-to-Microwave Conversion Using Si Photonic Integrated Circuit Ge Photodiodes

TL;DR

This paper demonstrates cryogenic optical-to-microwave conversion using a miniaturized, integrated Si photonic circuit with germanium photodiodes, showing promising performance for quantum control applications.

Contribution

It presents the first experimental characterization of a cryogenic integrated photonic circuit for optical-to-microwave conversion with high response and bandwidth, suitable for quantum technologies.

Findings

Peak conversion response of ~150 mA/W at 4.2 K

Diodes operate over 6 GHz bandwidth

Scalable integration with optical fiber arrays

Abstract

Integrated circuit technology enables the scaling of circuit complexity and functionality while maintaining manufacturability and reliability. Integration is expected to play an important role in quantum information technologies, including in the highly demanding task of producing the classical signals to control and measure quantum circuits at scales needed for fault-tolerant quantum computation. Here we experimentally characterize the cryogenic performance of a miniaturized photonic integrated circuit fabricated by a commercial foundry that down-converts classical optical signals to microwave signals. The circuit consists of waveguide-integrated germanium PIN photodiodes packaged using a scalable photonic wire bonding approach to a multi-channel optical fiber array that provides the optical excitation. We find the peak optical-to-microwave conversion response to be $\sim 150 \pm 13$ mA/W in the O-band at 4.2 K, well below the temperature the circuit was designed for and tested at in the past, for two different diode designs. The second diode design operates to over 6 GHz of 3 dB bandwidth making it suitable for controlling quantum circuits, with improvements in bandwidth and response expected from improved packaging. The demonstrated miniaturization and integration offers new perspectives for wavelength-division multiplexed control of microwave quantum circuits and scalable processors using light delivered by optical fiber arrays.