Cooling radio waves to their quantum ground state

Credit: Delft University of Technology
Delft University of Technology researchers have discovered a way to cool radio waves down to their quantum ground states. They used circuits that used an analog of the laser cooling technique, which is commonly used to cool atomic samples. Photon pressure coupling is a newly developed technique that the researchers have used to detect ultra-weak magnetic resonance signals (MRI). It can also be used in quantum-sensing applications, which could help with the search for dark matter. Science Advances published the results.

Hot radio waves are the ones we hear in our day, like those we listen to in cars or those we send to our baby monitors at home. They contain noise from random motions of the atoms in their emitted objects and the antenna we use to listen to them. This is why static can be heard when your car tunes to a frequency without a radio station.

Cooling waves

Cooling down radio waves can reduce the noise, such as by cooling the antenna that receives them until they reach near absolute zero temperature. The noise level will decrease as the antenna's atoms will not be moving around as much. This is what happens in a superconducting computer that is cooled down to 10 mK in order to stop these jiggling atoms creating noise in the GHz signals they work with.

Ines Rodrigues (a researcher at TU Delft), says that "there are some applications such as NMR and dark matter detection, or radio astronomy that are interested in ultra-weak signals on MHz frequencies." These signals require cooling down to 10 mK. Even at such low temperatures, noise can still be added to radio waves by the random movement of atoms within an antenna or device. To get rid of any residual noise, you must cool the radio waves further. How do you do this?

Combining photons

The Delft researchers discovered a new method to reduce the noise from jiggling electrons. The authors used circuits that were analogous to the laser cooling technique, which is commonly used to cool atom cloud. They cooled radio waves in the device down to the quantum ground. Gary Steele, TU Delft group leader, says that the dominant noise in the circuit is due to quantum fluctuations. This noise comes from strange quantum jumps predicted quantum mechanics. Steele's group specializes in quantum sensing using superconducting quantum circuits.

Photon pressure coupling, a technique that was recently invented by the authors, was used to create the device. This technique is expected to be very useful in detecting ultra weak magnetic resonance (MRI) signals. It could also be used for quantum information processing applications that involve the rapidly changing field of quantum computation. It could also be used in quantum sensing applications. This could help to search for dark matter, an unusual type of particles yet to be discovered that could answer open questions about gravity and cosmology.

Continue exploring Listening to quantum radio

Information: I. C. Rodrigues and al., Cooling photon pressure circuits into quantum regime, Science Advances (2021). Journal information: Science Advances I. C. Rodrigues et al, Cooling photon-pressure circuits into the quantum regime,(2021). DOI: 10.1126/sciadv.abg6653