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.

Above-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.

A quantum heat pump
The device, known as a photon pressure circuit, is made from superconducting inductors and capacitors on a silicon chip cooled to only a few millidegrees above absolute zero temperature. While this sounds very cold, for some of photons in the circuit, this temperature is very hot, and they are excited with thermal energy. Using photon pressure, the researchers can couple these excited photons to higher frequency cold photons, which in previous experiments allowed them to cool the hot photons into their quantum ground state.