A 2D device for quantum cooling

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To perform quantum computations, quantum bits (qubits) must be cooled to temperatures in the millikelvin range (near -273 °C), to slow down atomic motion and minimize noise. However, the electronics used to drive these quantum circuits generate heat, which is difficult to dissipate at such low temperatures. Most current technologies therefore have to separate quantum circuits from their electronic components, leading to noise and inefficiencies that hamper the realization of larger quantum systems beyond the laboratory.

Researchers from the Laboratory of Electronics and Nanoscale Structures at EPFL (WAYS), led by Andras Kis of the School of Engineering, have now built a device that not only operates at extremely low temperatures, but does so with efficiency comparable to current room-temperature technologies.

“We are the first to have created a device with a conversion efficiency comparable to that of current technologies, but which operates with the weak magnetic fields and ultra-low temperatures required for quantum systems. This work represents a real breakthrough,” says Gabriele Pasquale, a doctoral student at LANES.

This innovative device combines the excellent electrical conductivity of graphene with the semiconducting properties of indium selenide. With a thickness of only a few atoms, it behaves like a two-dimensional object, and this new combination of materials and structure gives it unprecedented performance. This achievement was published in Natural nanotechnology.

Harness the Nernst effect

The device exploits the Nernst effect: a complex thermoelectric phenomenon that generates an electrical voltage when a magnetic field is applied perpendicular to an object whose temperature varies. The two-dimensional nature of the lab’s device allows the effectiveness of this mechanism to be electrically controlled.

The 2D structure was fabricated at EPFL’s Center for Micronanotechnology and the LANES laboratory. The experiments involved using a laser as a heat source and a specialized dilution refrigerator to reach 100 millikelvins, a temperature even colder than space. Converting heat to voltage at such low temperatures is typically extremely difficult, but the new device and its exploitation of the Nernst effect make it possible, filling a critical gap in quantum technology.

“If we take the example of a laptop in a cold office, it will still heat up during operation, which will also cause the room temperature to increase. In quantum computing systems, there is currently no mechanism to prevent this heat from disturbing the qubits. Our device could provide this necessary cooling,” Pasquale explains.

A physicist by training, Pasquale points out that this research is important because it allows us to better understand the conversion of thermal energy at low temperatures, a phenomenon that has been little studied until now. Given the high conversion efficiency and the use of potentially manufacturable electronic components, the LANES team also believes that their device could already be integrated into existing low-temperature quantum circuits.

“These results represent a major breakthrough in the field of nanotechnology and hold promise for the development of advanced cooling technologies that are essential for quantum computing at millikelvin temperatures,” says Pasquale. “We believe this breakthrough could revolutionize cooling systems for future technologies.”

Reference: Pasquale G, Sun Z, Migliato Marega G, Watanabe K, Taniguchi T, Kis A. Electrically tunable giant Nernst effect in two-dimensional van der Waals heterostructures. Nat Nanotechnology. 2024. doi: 10.1038/s41565-024-01717-y

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