Quantum heat pump: a new measuring tool for physicists

News - 26 August 2022 - Communication TNW

Physicists from TU Delft, ETH Zürich and the University of Tübingen have built a quantum scale heat pump made from particles of light. This device brings scientists closer to the quantum limit of measuring radio frequency signals, useful in for example the hunt for dark matter. Their work was published as an open-access article in Science Advances last Friday.

If you bring two objects of different temperatures together, such as putting a warm bottle of white wine into a cold chill pack, heat usually flows in one direction, from hot (the wine) to cold (the chill pack). And if you wait long enough, the two will both reach the same temperature, a process known in physics as reaching equilibrium: a balance between the heat flow one way and the other. 

If you are willing to do some work, you can break this balance and cause heat to flow in the “wrong” way. This is the principle used in your refrigerator to keep your food cold, and in efficient heat pumps that can steal heat from the cold air outside to warm your house. In their publication, Gary Steele and his co-authors demonstrate a quantum analog of a heat pump, causing the elementary quantum particles of light, known as photons, to move “against the flow” from a hot object to a cold one. 

Dark matter signals

While the researchers had already used their device as cold bath for hot radio-frequency photons in a previous study, they have now managed to simultaneously turn it into an amplifier. With the built-in amplifier, the device is more sensitive to radio-frequency signals, just like what happens with amplified microwave signals coming out of superconducting quantum processors. “It’s very exciting, because we can get closer to the quantum limit of measuring the radio frequency signals, frequencies that are hard to measure otherwise. This new measuring tool might have lots of applications, one of them being to look for dark matter,” Steele says.

An illustration of the device, which consists of two superconducting circuits: a cold high frequency circuit (in blue) and a hot low frequency circuit (in red). Here, the current that flows in the red circuit generates an oscillating magnetic field which leads to the photon-pressure coupling. By sending in a strong signal to the blue high-frequency circuit, this one is transformed into an amplifier capable of detecting radio-frequency photons flowing in the red circuit with much higher sensitivity.

Gary Steele

Professor

Ines C. Rodrigues

Postdoc (Former PhD Student in Steele Lab)

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