2D device turns heat into electricity, can keep quantum ops cool

You might be hearing a lot about quantum computing nowadays but the world has yet to see a fully operational, powerful quantum computer that could perform large-scale calculations.

A big reason we haven’t been able to build one so far is that we don’t have the technology to keep quantum computers cool. 

For instance, qubits, the fundamental unit of quantum computers require temperatures below 100 millikelvin (about -460 °F) to function. This is even colder than the temperatures in deep regions of outer space. However, without achieving such ultra-low temperatures, we can’t make a quantum system work. 

Surprisingly, researchers at the Swiss Federal Institute of Technology Lausanne (EPFL) have developed a 2D micrometer-sized thermoelectric device that can efficiently convert heat into electricity at temperatures suitable for qubits to operate. 

“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,” Gabriele Pasquale, lead researcher and a PhD student at EPFL, said.

Cooling the qubits using the Nernst effect

Even if you make a device powerful enough to cool down qubits there’s another big challenge. Many electrical components that make quantum circuits and qubits work, continuously produce heat, making it difficult to maintain ultra-low temperatures.

Many conventional quantum cooling methods work by isolating such electrical components from the quantum circuit. However, this approach results in inefficient outputs that prevent quantum computers from working outside lab settings.  

Interestingly, the newly developed 2D device overcomes these challenges by harnessing the Nernst effect, a 127-year-old phenomenon that explains how a magnetic field influences the electrical voltage generated by heat flow in an object. 

This effect enables the 2D device to efficiently generate electrical voltage in a quantum system in response to temperature changes when a perpendicular magnetic field is applied. Moreover, the device is made using graphene, which is known for high electrical conductivity, and indium selenide which offers excellent semiconductor properties. 

These properties combined with the Nernst effect, make the thermoelectric device capable of cooling down a quantum system and effectively managing the heat produced by the components of its quantum circuit. 

“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,” Pasquale said.

Testing the thermoelectric device

The researchers performed an interesting experiment to check whether their 2D device could make a system efficiently work at extremely cool temperatures when the system is exposed to a heating source. 

They used their device with a dilution refrigerator having a stable temperature of 100 millikelvins (the temperature at which qubits work) and then used a laser to heat the system. The 2D device was successful in turning heat into electricity at such ultra-low temperatures.

“Our study presents the demonstration of a micrometer-sized thermoelectric device harnessing the photoinduced Nernst effect, displaying exceptional performance even at ultralow temperatures of 100 mK, which were previously unattainable,” the researchers note.

This experiment shows that it is indeed possible to achieve the cooling technologies that make a quantum system work. Hopefully, this interesting development will bring us closer to feasible and scalable quantum computing applications.

The study is published in the journal Nature Nanotechnology.