Scientists develop a new measurement tool for physicists, useful in the search for dark matter

Aug. 29 () –

A team of researchers have built a quantum-scale heat pump made of light particles, a device that brings scientists closer to the quantum limit of measuring radiofrequency signals, useful, for example, in the search for dark matteras published in the journal ‘Science Advances’.

The researchers explain that if two objects of different temperatures are brought together, such as putting a bottle of mulled white wine in a cold bag, the heat usually flows in one direction, from hot (the wine) to cold (the cold bag). and after a while both will reach the same temperature, in a process known in physics as reaching equilibrium: a balance between the flow of heat in one direction and the other.

But the authors of the study, physicists from the Technical University of Delft (TU Delft), in the Netherlands; the Federal Polytechnic School of Zurich (ETH Zürich), in Switzerland, and the University of Tübingen, in Germany, remember that you can upset this balance and cause heat to flow in the “wrong” direction.

This is the principle used in the refrigerator to keep food cold, and in efficient heat pumps that can steal heat from cold outside air to heat the house.

In their publication, TU Delft researcher Gary Steele and his co-authors demonstrate a quantum analog of a heat pump, causing elementary quantum particles of light, known as photons, to move “upstream” from one hot object to another. another cold.

Although the researchers had already used their device as a cold bath for hot radio-frequency photons in a previous study, they have now simultaneously turned it into an amplifier. With the built-in amplifier, the device is more sensitive to radio frequency signals, just like the amplified microwave signals coming out of superconducting quantum processors.

“It’s very exciting, because we can get close to the quantum limit of measuring radio frequency signals, frequencies that are otherwise difficult to measure. This new measurement tool could have many applications, one of them the search for dark matterSteele says.

The device, known as a photon pressure circuit, is made of superconducting inductors and capacitors on a silicon chip cooled to just a few millimeters above absolute zero temperature. Although this seems very cold, for some of the photons in the circuit, this temperature is very hot, and they are excited with thermal energy, the researchers explain.

Using the pressure of the photons, the researchers can couple these excited photons to colder photons of higher frequency.which in previous experiments allowed them to cool hot photons down to their quantum ground state.

In this new work, the authors add a new twist: by sending an extra signal to the cold circuit, they are able to create a motor that amplifies the cold photons and heats them up. At the same time, the extra signal “pumps” the photons preferentially in one direction between the two circuits.

By pushing photons harder in one direction than the other, the researchers are able to cool photons in one part of the circuit to a cooler temperature than the other.creating a quantum version of the heat pump for photons in a superconducting circuit.