October 1, 2022

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The photon pressure circuit was constructed on a quantum scale.  What is this device?

The photon pressure circuit was constructed on a quantum scale. What is this device?

Scientists have created a photon pressure circuit in which the heat flow differs from the microscopic world.

Physicists at the Technical University of Delft (TU Delft), ETH Zurich and the University of Tübingen have built a heat pump made of light particles. This device brings scientists closer to the quantum limit of measuring radio frequency signals, which could be useful in the search for dark matter. Details have been published in the magazine science progress.

Photon pressure circuit on a quantum scale

If we connect two objects of different temperatures together, for example placing a warm thermos with tea in a cold cooler pack, then the heat usually flows in one direction – from hot (tea) to cold (cooler pack). If we wait too long, both substances will reach the same temperature, a process known in physics as thermodynamic equilibrium – the equilibrium between heat flow in both directions.

This balance can be disrupted and heat can flow in an apparently improper way – but only if some work is done. This is exactly what happens in refrigerators and heat pumps that can steal heat from the cold air outside to warm a home. Gary Steele’s team has introduced a quantum analogue of a heat pump – photons move “upstream” in it: from a hot object to a cold one.

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In a previous study, the unusual device was used as a cold bath for hot radiofrequency photons, but has now been converted into an amplifier at the same time. This makes the device more sensitive to radio frequency signals, similar to the amplified microwave signals emitted by superconducting quantum processors.

This is very exciting because we can approach the quantum limit of measuring radio frequency signals, which are frequencies that are difficult to measure otherwise. This new measuring tool could have a myriad of applications, one of which is looking for dark matter.Gary Steel

The device, known as a photon compression circuit, is made of superconducting coils and capacitors on a silicon chip cooled to a few millimeters above absolute zero. For some photons in the circuit, this temperature is high and excited by thermal energy. Physicists can link these excited photons to cold photons of higher frequency, which in previous experiments allowed them to cool hot photons to their quantum ground state.

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New work has shown that by sending an additional signal to a cold circuit, a motor can be created that amplifies and heats up cold photons. At the same time, the additional signal “pumps” photons preferentially in one direction between the two circuits. This allows photons in one part of the circuit to be cooled to a temperature cooler than the other, creating a quantum version of the photon heat pump in the superconducting circuit.