量子計算：超低温状態を脱した量子ビット

Quantum computing platforms that can operate at temperatures up to 15 times higher than existing technologies are demonstrated in two papers published in Nature this week. Although the relative temperature increase is quite small, it could make a big difference to the scalability of current prototypes into larger and more powerful quantum computers.

Quantum bits — the analogue to classical computing bits — can be realized by superconducting circuits or formed within semiconductors, such as silicon. These solid-state platforms require cooling to extremely low temperatures because vibrations generated by heat disrupt the qubits, which can impede performance. Typically, solid-state platforms need to operate at around 0.1 kelvin (−273.05 degrees Celsius), requiring expensive refrigeration approaches.

Two independent studies report proof-of-principle experiments with silicon-based quantum computing platforms operating at temperatures above 1 kelvin. Menno Veldhorst and colleagues produce a quantum circuit that operates at 1.1 kelvin, and Andrew Dzurak and co-workers demonstrate a system that operates at around 1.5 kelvin. Both studies use as qubits the spin of electrons confined in silicon, which are so well-isolated from the surrounding material that they are shown to be able to function well even at temperatures above 1 kelvin. At this temperature, fridges are powerful enough to allow the introduction of localized electronics for controlling the qubits, which the authors suggest is a pre-requisite for scaling up these quantum processors to millions of qubits.

Elevating the operating temperature beyond 1 kelvin is an important milestone, as cooling below this threshold is challenging and expensive. As temperatures rise above 1 kelvin, the cost drops substantially and the efficiency improves. In addition, using silicon-based platforms is attractive, as this can assist integration into classical systems that use existing silicon-based hardware.