Radiofrequency-Photonic Control Interface for Scalable, High Speed Quantum Computing

Project Overview

Quantum computing (QC) has been hailed as the next big leap for the digital age with the potential to solve problems that classical binary computers cannot. However, in practice, these devices are yet to surpass classical computers in the problems they can solve due to the limited quantum volume. To overcome the scalability barrier and interface with QC systems at speeds beyond what is possible with state-of-the-art electronic control systems, we proposed a featureful, compact photonic quantum/classical interface using a Lawrence Livermore National Laboratory-developed photonics-based signal generator that can potentially operate at higher bandwidth and dynamic range. The photonic generation of the qubit drive signal enables seamless integration with the optical transport of the signal down to sub-millikelvin temperatures within the dilution refrigerator, thus replacing radio frequency (RF) cabling with optical fiber. We estimate replacing RF cabling with optics can improve scalability to >1000 qubit systems since optical fibers have lower thermal conductivity, large multiplexing capability, and reduce the need for attenuation, all of which dramatically alleviates thermalization. The goal of the project was to demonstrate qudit control using a laboratory prototype of the photonic digital-to-analog converter and photodetector at cryogenic temperatures, as a step towards a compact, featureful quantum/classical interface for large-scale (>1000) qubit systems. A PDAC prototype was integrated with the Quantum Design and Integration Testbed (QuDIT) and used the setup to evaluate qubit control performance with a photodiode at room temperature and cryogenic temperatures (3K). The prototype could generate 48-dB SINAD up to 10GHz at 1 GS/s, which was sufficient for two-level qudit control at cryogenic temperatures via a single photodetector. Over the course of the project, we demonstrated that the RF signals generated using the PDAC with Optical-to-Electrical (O/E) conversion at 3K achieve the same state population and energy decay times (T1 and T2) as a state-of-the-art RF system. The measurements showed that the PDAC prototype can achieve the same state population in the excited state without injecting more noise than the existing system. We also showed the potential of the PDAC to produce the wide range of microwave signals used for qudit manipulation by demonstrating optimal control of the qudit. While we utilized a commercial-off-the-shelf photodiode for preliminary cryogenic tests, we found that further improvement in the efficiency of the diodes at cryogenic temperatures is necessary to fully reach the potential of high dynamic range we can deliver to the qubit/qudit. Additionally, we demonstrated the scalability of the PDAC by taping out a 2-channel 4Gsps PDAC photonic integrated circuit and demonstrating amplitude and phase modulation needed for complex wideband signal generation.

Mission Impact

The project leverages Lawrence Livermore National Laboratory-developed RF-Photonic technology and applies it to the rapidly developing field of quantum computing. The National Quantum Initiative identifies quantum computing as a future foundation of information technology and area of international competition and places a high priority on enabling hardware for the next generation quantum computing systems. The project aligns with Laboratory missions for High Performance Computing and the Data Science Core Competency. The RF signal generation technologies and photonic integrated circuits effort support other applications related to next generation Communications, and Radar. 

Publications, Presentations, and Patents

Gowda, Apurva Shantharaj, et al. 2020. Radio Frequency Passband Signal Generation Using Photonics. U.S. Patent 11,209,714 B2. Filed Jan. 24, 2020 and issued December 28, 2021.  Non-Provisional Patent Application.