EPFL researchers design device for quantum cooling

This innovation could address a major challenge in the development of quantum computing technologies, which require extremely low temperatures for optimal operation.

Quantum computations rely on quantum bits (qubits) that need to be cooled to temperatures in the millikelvin range (close to -273°C) to reduce atomic motion and minimise noise. However, the electronics managing these quantum circuits generate heat, which is difficult to dissipate at such low temperatures. Current technologies often separate quantum circuits from their electronic components, leading to noise and inefficiencies that impede the scaling up of quantum systems beyond laboratory settings.

Researchers at EPFL’s Laboratory of Nanoscale Electronics and Structures (LANES), led by Andras Kis, have now developed a device that operates efficiently at extremely low temperatures, comparable to current technologies at room temperature.

“We are the first to create a device that matches the conversion efficiency of current technologies, but that operates at the low magnetic fields and ultra-low temperatures required for quantum systems. This work is truly a step ahead,” said Gabriele Pasquale, LANES PhD student.

The innovative device combines graphene's excellent electrical conductivity with indium selenide's semiconductor properties. Only a few atoms thick, it functions as a two-dimensional object, with this novel material and structural combination delivering unprecedented performance. The findings have been published in Nature Nanotechnology.

The device utilises the Nernst effect, a complex thermoelectric phenomenon that generates electrical voltage when a magnetic field is applied perpendicular to an object with a temperature gradient. The two-dimensional nature of the device allows for efficient control of this mechanism electrically. Fabricated at the EPFL Center for MicroNanoTechnology and the LANES lab, the device was tested using a laser as a heat source and a specialised dilution refrigerator to reach 100 millikelvin – colder than outer space. Converting heat to voltage at such low temperatures is typically very challenging, but this device's utilisation of the Nernst effect makes it possible, addressing a critical need in quantum technology.

“If you think of a laptop in a cold office, the laptop will still heat up as it operates, causing the temperature of the room to increase as well. 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 explained.

Pasquale, a physicist, highlights the significance of this research in understanding thermopower conversion at low temperatures, an underexplored area until now. Given its high conversion efficiency and use of potentially manufacturable electronic components, the LANES team believes their device could already be integrated into existing low-temperature quantum circuits.