Quantum Computing Breakthrough: Real-Time Qubit Fluctuation Tracking Paves Way for More Stable Processors

Researchers at the Niels Bohr Institute in Copenhagen have achieved a significant advancement in quantum computing, developing a system capable of tracking changes in qubit states in real time. This breakthrough, approximately 100 times faster than previous methods, addresses a critical challenge in building reliable and scalable quantum computers – the inherent instability of qubits.

The Challenge of Qubit Instability

Qubits, the fundamental building blocks of quantum computers, are notoriously sensitive to environmental disturbances. Tiny defects within the materials used to construct them can cause fluctuations that alter a qubit’s energy levels and lead to information loss. Previously, standard testing methods were too slow to capture these rapid fluctuations, only providing an average energy loss rate and masking the true, often unstable, behavior of individual qubits. This limitation hindered efforts to identify and correct errors, a crucial step toward practical quantum computation.

FPGA-Powered Real-Time Monitoring

The research team, led by postdoctoral researcher Dr. Fabrizio Berritta from the Center for Quantum Devices and the Novo Nordisk Foundation Quantum Computing Programme, overcame this obstacle by implementing a real-time adaptive measurement system. This system tracks changes in qubit energy loss (relaxation) rate as they occur, utilizing a commercially available Field Programmable Gate Array (FPGA) from Quantum Machines, specifically the OPX1000 controller.¹

FPGAs are specialized processors designed for extremely fast operations. By running the experiment directly on the FPGA, the team could quickly generate a “best guess” of how fast the qubit was losing energy using only a few measurements, eliminating the delays associated with transferring data to a conventional computer. The controller updates its estimate of a qubit’s relaxation rate within milliseconds, matching the speed of the fluctuations themselves.

The team successfully updated the controller’s internal Bayesian model after every single qubit measurement, continually refining its understanding of the qubit’s condition in real time. This level of responsiveness allows for tighter integration between logic, measurements, and feedforward control, essential for the experiment’s success.³

Key Findings and Implications

The experiments revealed that even stable qubits can degrade in milliseconds – a previously unknown rate of fluctuation. This insight is crucial for developing strategies to stabilize and improve qubit performance. The research also highlights the importance of focusing on the “worst” qubits in a quantum processor, as overall performance is often limited by their instability.¹

According to Dr. Berritta, the novel algorithm and fast control hardware can pinpoint whether a qubit is “good” or “bad” in real time, and gather useful statistics on unstable qubits much faster than before. The team acknowledges that understanding and controlling the underlying physics of these fluctuations remains a significant challenge for scaling quantum processors to a practical size.

Collaboration and Future Outlook

This research was a collaborative effort involving scientists from the Niels Bohr Institute, the Norwegian University of Science and Technology, Leiden University, and Chalmers University. The integration of the FPGA controller with advanced quantum hardware was facilitated by close collaboration between the Niels Bohr Institute and Chalmers University, where the quantum processing unit was designed and fabricated.³

The development of real-time monitoring and adjustment techniques appears essential for improving the reliability of quantum computers, paving the way for more powerful and stable quantum processors. The Center for Quantum Devices at the Niels Bohr Institute continues to research methods for creating, controlling, measuring, and protecting quantum coherence and entanglement in solid-state electronic devices.²