Niels Bohr Institute Develops Real-Time Qubit Monitoring System, Accelerating Path to Stable Quantum Computers

Researchers at the Niels Bohr Institute (NBI) at the University of Copenhagen have developed a real-time monitoring system that tracks the state of quantum bits (qubits) approximately 100 times faster than previous methods. This breakthrough provides an unprecedented view into the rapid fluctuations that destabilize qubits, addressing a core challenge in the development of scalable and reliable quantum computers. The new technique can identify when a qubit’s performance degrades in milliseconds, a crucial insight for building fault-tolerant quantum machines.

The Challenge of Qubit Instability

Qubits, the fundamental units of quantum computers, are notoriously fragile. Their quantum states are easily disrupted by environmental noise, such as microscopic defects in the materials from which they are made. These defects can move hundreds of times per second, causing a qubit’s energy loss rate (or relaxation rate) to change in fractions of a second. Until now, measurement techniques were too slow, taking up to a minute to characterize a qubit’s performance. This meant scientists could only see an averaged, and often misleading, picture of the qubit’s behavior, masking the rapid changes that lead to computational errors.

A High-Speed Adaptive Solution

The NBI system overcomes this hurdle with an adaptive measurement technology built on a high-speed Field Programmable Gate Array (FPGA) controller. The technology uses a commercially available OPX1000 controller from Quantum Machines, which is programmed in a Python-like language, making it accessible to research groups worldwide. The system employs a Bayesian model, which updates its estimate of the qubit’s relaxation rate after each measurement. This adaptive feedback loop allows it to track the qubit’s state almost instantaneously, collecting statistics on unstable qubits in seconds rather than hours.

The experiment, a collaboration with the Norwegian University of Science and Technology, Leiden University, and Chalmers University of Technology, where the quantum processor was fabricated, revealed that even seemingly stable qubits can degrade in milliseconds. “The surprise from our work is that a ‘good’ qubit can turn into a ‘bad’ one in fractions of a second, rather than minutes or hours,” said Dr. Fabrizio Berritta, a postdoctoral researcher who led the team.

Implications for the Future of Quantum Computing

This ability to perform real-time calibration and monitoring is critical for the reliability of future quantum computers. As the industry moves from simply adding more qubits to improving system quality and error correction, the focus is shifting toward stability and coherence. The NBI team’s discovery enables scientists to quickly identify and potentially correct for “bad” qubits, a vital step for scaling processors and enhancing performance. This could fundamentally change how quantum processors are tested and calibrated. Instead of judging a system by its best-performing qubits, reliability will be determined by the ability to monitor and manage the worst-performing ones in real time. This advancement represents a significant leap toward the era of fault-tolerant quantum computing.