Blast Chiller for the Quantum World

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Blast Chiller Superconducting circuit (white) on a silicon substrate fixed in a Blast Chiller Superconducting circuit (white) on a silicon substrate fixed in a copper holder. The chip (silver) with the micromechanical oscillator is attached to the silicon substrate. The close-up shows the so-called SQUID in the center of the circuit and directly above it the micromechanical oscillator with a magnet on its underside. A ballpoint pen serves as a size comparison. IQOQI Innsbruck

The quantum nature of objects visible to the naked eye is currently a much-discussed research question. A team led by Innsbruck physicist Gerhard Kirchmair has now demonstrated a new method in the laboratory that could make the quantum properties of macroscopic objects more accessible than before. With the method, the researchers were able to increase the efficiency of an established cooling method by a factor of 10.

With optomechanical experiments, science is trying to explore the limits of the quantum world and create a basis for the development of highly sensitive quantum sensors. In these experiments, objects visible to the naked eye are coupled to superconducting circuits via electromagnetic fields. For superconductors to work properly, such experiments take place in cryostats at a temperature of around 100 millikelvin. But this is still not nearly enough to really dive into the quantum world. In order to observe quantum effects on macroscopic objects, they must be cooled to just below absolute zero using special cooling methods. Physicists led by Gerhard Kirchmair from the Institute of Experimental Physics at the University of Innsbruck and the Institute of Quantum Optics and Quantum Information (IQOQI) have now demonstrated a nonlinear cooling mechanism with which even massive objects can be cooled well.

Cooling capacity increases disproportionately

In the experiment, the Innsbruck scientists couple the mechanical object - in their case a vibrating beam - to the superconducting circuit via a magnetic field. To do this, they attached a magnet to the beam, which is about 100 micrometers long. When the magnet moves, it changes the magnetic flux through the circuit, the heart of which is a so-called SQUID, a superconducting quantum interferometer. Its resonant frequency changes depending on the magnetic flux, which is measured using microwave signals. In this way, the micromechanical oscillator can be cooled to near the quantum mechanical ground state. Furthermore, David Zpfl from Gerhard Kirchmair’s team explains, "The change in the resonant frequency of the SQUID circuit as a function of microwave power is not linear. As a result, we can cool the massive object by a factor of 10 more for the same power." This new, simple method is particularly interesting for cooling more massive mechanical objects. It could be the basis for the search for the quantum properties of larger macroscopic objects, Zpfl and Kirchmair are CONVINCED.

The work was carried out in collaboration with scientists in Canada and Germany and has now been published in the journal Physical Review Letters. The research was financially supported by the Austrian Science Fund FWF and the European Union, among others. Co-authors Christian Schneider and Lukas Deeg are or were members of the FWF Doctoral Program Atoms, Light and Molecules (DK-ALM).

Publication: Kerr enhanced backaction cooling in magnetomechanics. D. Zoepfl, M. L. Juan, N. Diaz-Naufal, C. M. F. Schneider, L. F. Deeg, A. Sharafiev, A. Metelmann, and G. Kirchmair. Phys. Rev. Lett. 130, 033601 DOI: https://doi.org/10.1103/PhysRevLett.130.033601