At the same time, Quantum nanodevice can be a thermal engine and a fridge

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RIKEN engineers have created a multitasking nanomachine that can at the same time act as a heat engine and refrigerator.

The system is one of the first to examine how quantum effects could one day be used to enhance the performance of nanotechnologies, which control particle behavior on the smallest scale.

By mixing two pools of ice, traditional heat engines and refrigerators operate.

Compressing one pool heats its fluid, while the other pool cools its fluid by quickly expanding.

The pools exchange energy as these operations are done in a periodic cycle, and the machine can be used either as a heat engine or as a fridge.

In order to do both jobs at once, it would be difficult to create a macroscale computer – and engineers don’t want to, says Keiji Ono of the RIKEN Advanced System Laboratory. “If you combine a conventional heat engine with a refrigerator, the machine would be completely useless,” he says. “It wouldn’t know what to do.”

But when you scale down things, things are different. Physicists have created, often based on single atoms, ever-smaller devices.

They have to account for quantum theory on these tiny scales – the peculiar laws that suggest, for instance, that an electron can live at once in two places or have two different energies. To find out how such structures can behave, physicists are designing new theoretical frameworks and experiments.

In a transistor, the quantum version of the heat engine uses an electron.

The electron has two energy states that are possible.

By adding an electrical field and microwaves, the team may increase or decrease the distance between these energy states. This can be equivalent to a liquid’s periodic expansion-compression operation in a chamber,”This can be analogous to the periodic expansion-compression operation of a liquid in a chamber,”

As the electron moved from the high energy level to the lower one, the system also emitted microwaves.

The team initially demonstrated, by controlling whether the upper energy level was occupied, that the nanodevice could act as either a heat engine or a refrigerator.

But then they showed something even stranger – the nanomachine, which is a pure quantum effect, could behave as both at the same time.

By observing the occupancy of the upper energy stage, which together created a characteristic interference pattern, the researchers verified this. “There was an almost perfect match between the experimental interference pattern and the one predicted by theory,” Ono says.

Ono explains, “This could enable rapid switching between the two modes of operation,” “This capability could help create new applications with such systems in the future.”

Reference: K.’s “Analog of a Quantum Heat Engine Using a Single-Spin Qubit” Physical Review Letters.DOI: 10.1103/PhysRevLett.125.166802 Ono, S. N. Shevchenko, T. Mori, S. Moriyama, and Franco Nori, October 15, 2020.

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