Quantum heat pump: A new measuring tool for physicists


Researchers from the Universities of Tübingen, ETH Zürich, and TU Delft have created a heat pump that operates on the quantum scale using light particles. This tool helps researchers get closer to the radio frequency signal measurement quantum limit, which is helpful in projects like the search for dark matter. On August 26, Science Advances will publish an open-access publication based on their study.

Heat typically moves in one way, from hot (the wine) to cold (the chill pack), when two items of differing temperatures are brought together (the chill pack). The two will eventually achieve the same temperature, a process known in physics as reaching equilibrium: a balance between the heat flow in one direction and the other. If you wait long enough.

If you're prepared to put in some effort, you can upset this equilibrium and make heat flow in the incorrect direction. This idea underlies both effective heat pumps that may warm your home by stealing heat from the chilly outside air and your refrigerator, which keeps food cold. Gary Steele and his co-authors present a quantum equivalent of a heat pump in their work, in which photons, the fundamental quantum particles of light, go "against the flow" from a hot object to a cold one.

Dark matter indications

The scientists were able to concurrently transform their gadget into an amplifier even though they had previously employed it as a cool bath for hot radio-frequency photons in another investigation. The gadget is more responsive to radio-frequency impulses thanks to the integrated amplifier, which is similar to what happens with amplified microwave signals originating from superconducting quantum processors. This new measuring tool may have several uses, including the search for dark matter, according to Steele. "It's extremely interesting because we may get closer to the quantum limit of measuring the radio frequency signals, frequencies that are hard to measure normally," he says.

Unquantized heat pump

A silicon chip that has been cooled to just a few millidegrees above absolute zero temperature houses superconducting inductors and capacitors that make up the device, known as a photon pressure circuit. Even though it appears to be very cold, some of the photons in the circuit perceive it as being very hot, and they are activated by thermal energy. In prior studies, the researchers were able to cool the hot photons into their quantum ground state by coupling them to higher frequency cold photons using photon pressure.

The authors of this new work introduce a novel twist: they are able to develop a motor that amplifies the cold photons and heats them up by adding an additional signal to the cold circuit. The additional signal simultaneously "pumps" the photons between the two circuits preferentially in one direction. In order to create a quantum equivalent of a heat pump for photons in a superconducting circuit, the researchers are able to chill the photons in one part of the circuit to a temperature that is lower than the other section by pushing them harder in one direction than the other.

Reference: ScienceAdvances

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