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Study demonstrates integration of 1,024 silicon quantum dots with on-chip electronics all operating at low temperatures

Quantum computers have the potential of outperforming classical computers on some optimization tasks. Yet scaling up quantum computers leveraging existing fabrication processes while also maintaining good performances and energy-efficiencies has so far proved challenging, which in turn limits their widespread adoption.

Researchers at Quantum Motion in London recently demonstrated the integration of 1,024 independent silicon quantum dots with on-chip digital and analog electronics, to produce a quantum computing system that can operate at extremely low temperatures. This system, outlined in a paper in Nature Electronics, links properties of devices at cryogenic temperatures with those observed at room temperature, opening new possibilities for the development of silicon qubit-based technologies.

"As quantum processors grow in complexity, new challenges arise such as the management of device variability and the interface with supporting electronics," Edward J. Thomas, Virginia N. Ciriano-Tejel and their colleagues wrote in their paper.

"Spin qubits in silicon quantum dots can potentially address these challenges given their control fidelities and potential for compatibility with large-scale integration. We report the integration of 1,024 independent silicon quantum dot devices with on-chip digital and analog electronics, all operating below 1 K."

Quantum dots are nanoscale semiconductor-based structures that can be used to confine and manipulate single electrons. These structures have proved promising for the development of quantum technologies relying on spin qubits (i.e., qubits that store information by leveraging the spin of electrons).

Thomas, Ciriano-Tejel and their colleagues created a system that operates at extremely low temperatures, combining 1,024 silicon-based quantum dots with on-chip electronics. To rapidly characterize all the quantum dots in this system, they used a technique known as radio frequency (RF) reflectometry.

"A high-frequency analog multiplexer provides fast access to all devices with minimal electrical connections, allowing characteristic data across the quantum dot array to be acquired and analyzed in under 10 min," wrote Thomas, Ciriano-Tejel and their colleagues. "This is achieved by leveraging radio-frequency reflectometry with state-of-the-art signal integrity, characterized by a typical signal-to-noise voltage ratio in excess of 75 for an integration time of 3.18 μs."

The researchers also developed new tools that can be used to extract information about the performance of quantum dots and assess their potential for integration in quantum technologies. These tools could be used to assess other types of quantum dot-based systems, including systems with coupled quantum dots, which are the basis of existing semiconductor-based quantum computers.

"We extract key quantum dot parameters by automated machine learning routines to assess quantum dot yield and understand the impact of device design," wrote the researchers. "We find correlations between quantum dot parameters and room-temperature transistor behavior that could be used as a proxy for in-line process monitoring."

Notably, the researchers observed that the cryogenic parameters of silicon quantum dots can be predicted from room-temperature behavior. This finding could have interesting implications for the future development of quantum technologies, as it could help to reduce the time and resources necessary to optimize these technologies.

"Further development of pre-cryogenic methods and analysis tools could allow wider industry engagement and a substantial cost reduction in technology development, particularly if further correlations can be extracted when complex unit cells are studied," wrote the authors.