High-Fidelity, Scalable Quantum Qubit Control Signal Generation

Apurva Gowda | 20-FS-017

Project Overview

Quantum computing (QC) has been hailed as the next big leap for the digital age; however, state-of-the-art QC devices have yet to surpass classical computers. One bottleneck is the number of quantum operations that can be done within a qubit lifetime, also known as the circuit depth. Circuit depths are currently limited by the control interface hardware to 10–100 operations due to uncontrolled coupling to the classical environment, infidelities in the qubit operations, and slow gate-operation times. In other words, a high-fidelity qubit control interface from a classical environment is essential to extend the circuit depth and scale quantum computing beyond the hardware limit of 10–100 operations.

To that end, our feasibility study investigated a novel radio frequency (RF) photonic implementation for a QC control interface. The all-optical generation and multiplexing of qubit control signals increases the signal dynamic range and bandwidth, which reduces the time per quantum gate operation and thus widens the circuit-depth bottleneck. Additionally, replacing RF cabling with optical fiber for transporting the control signals to the qubits at cryogenic temperatures reduces waste heat and alleviates thermalization issues common in traditional RF-cable approaches. This further improves scalability to larger qubit systems.

In this feasibility study we simulated a 6GHz RF-photonic signal generator that showed an order-of-magnitude improvement in dynamic range over state-of-the-art electronic signal generators. Additionally, our narrow-band (500MHz) laboratory prototype of the RF-photonic signal generator achieved a signal-to-noise-and-distortion ratio of  greater than 40 dB and demonstrated stability over 1.2 microseconds. We also experimentally demonstrated a method to optically suppress electronic noise that is introduced by the RF-driver. These results show the promise of an RF-photonic approach to high-fidelity, scalable, quantum control signal generation to next-generation, high-circuit-depth quantum computing systems.

Mission Impact

This project supports the Lawrence Livermore National Laboratory's core competency in high-performance computing, simulation, and data science, as well as the Laboratory's mission research challenge in quantum science and technology. The project leverages RF–photonic technology developed at Livermore, and applies it to the rapidly developing field of quantum computing. This feasibility study supports other quantum computing research at the Laboratory, including efforts to demonstrate control of the qubit using the RF-photonic signal-generator prototype demonstrated in this project. The RF signal-generation technologies also support other applications related to next-generation communications and radar. 

Publications, Presentations, and Patents

Chan, J., et al. 2020. "Wideband, High Fidelity RF Signal Generation using Photonics." Lawrence Livermore National Laboratory External Review Committee Poster Session. LLNL-POST-795748

——— 2020b. "High-Fidelity, Scalable Quantum–Classical Control Interface Using Photonics." APS March Meeting, Denver, CO, March 2020. LLNL-PRES-806544