Enhanced cooling method developed for the quantum world
A team of researchers led by Innsbruck physicist Gerhard Kirchmair has 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 an order of a magnitude.
With optomechanical experiments, scientists are trying to explore the limits of the quantum world and to create a foundation for the development of sensitive quantum sensors. In these experiments, objects visible to the naked eye are coupled to superconducting circuits via electromagnetic fields. To get functioning superconductors, such experiments take place in cryostats at a template of approximately 100 millikelvin. However, this is far from sufficient to really dive into the quantum world.
In order to observe quantum effects on macroscopic objects, they must be cooled to nearly absolute zero using sophisticated cooling methods. Physicists led by Gerhard Kirchmair from the Department 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 as well.
In the current paper, the researchers coupled the mechanical object — 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 micrometres long. When the magnet moves, it changes the magnetic flux through the circuit, the heart of which is a co-called SQUID (a superconducting quantum inference device). 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. David Zöpfl from Kirchmair’s team said the change in the resonant frequency of the SQUID circuit as a function of microwave power is not linear. “As a consequence, we can cool the massive object by an order of magnitude more for the same power,” Zöpfl said.
This new, simple method is also suitable for cooling more massive mechanical objects. Zöpfl and Kirchmair believe that this could be the foundation for the search of quantum properties in larger macroscopic objects.
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