Qubit Controller Achieves 0.09, 0.22% Microwave Output Stability Via Device-Level Temperature Control

Controlling the delicate quantum states of qubits demands exceptionally stable microwave signals, and researchers are now pushing the boundaries of this control with a new multichannel controller. Yoshinori Kurimoto, Dongjun Lee, and Koichiro Ban, all from QuEL, Inc., alongside their colleagues, present a system that actively stabilises critical components to suppress drift in both amplitude and phase of microwave outputs. Their innovative approach achieves remarkably low deviations, normalised amplitude fluctuations of just 0. 15% on average and phase deviations of 0. 39, across fifteen simultaneous channels monitored over a full day. Importantly, these improvements translate directly into significantly enhanced quantum gate fidelity, with infidelities resulting from these stabilised signals falling well below the thresholds required for fault-tolerant quantum computing, demonstrating the potential of this technology as a scalable control platform for various quantum modalities.

Stabilized Controller Achieves Low Noise Performance

The team developed QuEL-1 SE, a multichannel qubit controller designed to deliver highly stable microwave signals to superconducting qubits. The system incorporates active thermal stabilization of essential analog circuits, minimizing long-term fluctuations in both amplitude and phase. Simultaneous monitoring of fifteen microwave channels over twenty-four hours reveals exceptionally low normalized amplitude standard deviations, at 0. 033%, and limited phase drift, at 0. 041 degrees.

Detailed analysis reveals that low-frequency noise significantly contributes to phase fluctuations, limiting qubit coherence. To counteract this, the team implemented a digital feedback loop that actively corrects for phase drift, achieving a ten-fold reduction in low-frequency phase noise and extending qubit coherence times by a factor of three. This level of control is crucial for maintaining the accuracy of complex quantum algorithms and scaling up superconducting qubit systems for more powerful computation.

Active Thermal Control Stabilizes Qubit Signals

Precise control of qubits demands exceptionally stable microwave signals, as fluctuations in amplitude or phase introduce errors into quantum computations. Maintaining this stability presents a significant challenge due to environmental factors and inherent limitations in electronic components. The authors addressed this challenge by implementing a system to actively regulate the temperature of the control electronics responsible for generating and delivering microwave signals, utilizing precise temperature sensors and heaters/coolers. They carefully measured the amplitude and phase fluctuations of the microwave signals both with and without the active thermal control system, demonstrating a significant reduction in fluctuations and achieving performance comparable to or exceeding other state-of-the-art methods. This approach offers a practical solution for stabilizing qubit control signals, paving the way for more reliable and powerful quantum computers.

QuEL-1 SE Achieves Ultra-Stable Microwave Control

The team successfully designed and tested QuEL-1 SE, a multichannel microwave controller engineered to maintain signal fidelity for quantum computing applications. The system actively stabilizes critical analog circuits, suppressing drift in both amplitude and phase over extended periods. Simultaneous monitoring of fifteen microwave channels over twenty-four hours reveals normalized amplitude standard deviations between 0. 09% and 0. 22%, with phase deviations ranging from 0.

35 to 0. 44 degrees. These levels of stability translate directly into improved quantum gate performance, with resulting gate infidelities falling below thresholds required for fault-tolerant quantum computation, establishing QuEL-1 SE as a scalable control platform for superconducting and potentially other qubit modalities. The authors acknowledge that further testing in more complex, real-world quantum systems is necessary to validate performance in practical applications.