Superconducting Quantum Circuits
Group of Gerhard Kirchmair
Gerhard Kirchmair und Oriol Romero-Isart

In the journal Physical Review Letters, Gerhard Kirchmair’s and Oriol Romero-Isart’s research team has presented a new proposal for the coupling between a micro-mechanic oscillator and a superconducting quantum circuit. The experiment will soon be implemented in Innsbruck, offering new insights into the quantum properties of macroscopic mechanical systems.

The laws of quantum physics not only apply to elementary quantum systems such as photons, electrons and atoms but also to miniscule mechanically oscillating objects when they are close to absolute zero temperature. Worldwide, physicists have been investigating the properties of this type of mechanical systems experimentally. Theoretical physicists Oriol Romero-Isart and Guillem Via and experimental physicist Gerhard Kirchmair have now proposed an experiment that could help in mastering the shortcomings of previous approaches. While in previous experiments the coupling between the mechanical oscillator and the quantum circuit was achieved via electrical fields, the physicists in Innsbruck suggest magnetic coupling between the two systems.  

Quantum effects in mechanical systems

To achieve magnetomechanical coupling, a small superconducting strip is deposited on the tip of a cantilever, which looks like a miniscule diving board. “One of the characteristics of a superconductor is that it repels magnetic fields,” explains Oriol Romero-Isart. “In physics this is known as Meissner effect. When the tip of the cantilever with the superconductor on top moves, the surrounding magnetic field is displaced.” These extremely minimal changes in the magnetic field can be detected with high precision through a superconducting quantum interference device (SQUID), also used in magnetoenzephalography devices, which is part of the superconducting circuit. Gerhard Kirchmair is convinced: “With this approach we should be able to achieve strong coupling between the mechanical oscillator and the superconducting quantum circuit, which is important for observing quantum effects.” Kirchmair has established the technique of superconducting quantum circuits in Innsbruck in the last few years.
If the experiment succeeds, the physicists will be able to cool the mechanical oscillator into the ground state and transfer it into exotic quantum states. “For example, we would like to create Schroedinger cat-like states, where the oscillator moves in both directions simultaneously,” says Kirchmair, who is going to start preparing the set up for the experiments in the upcoming weeks. In the future this new system could be applied to build high-precision force sensors and accelerometers.
The researchers have presented their proposal in the journal Physical Review Letters. They are financially supported by the European Research Council and the Austrian Federal Ministry of Science, Research and Economy.

A future scientific career model

In 2013 Gerhard Kirchmair and Oriol Romero-Isart started a temporary 5-year professorship at the University of Innsbruck. They are also Junior Research Directors at the Institute for Quantum Optics and Quantum Information (IQOQI) at the Austrian Academy of Sciences. The establishment of these research groups goes back to Peter Zoller’ intiative to establish an example for a tenure-track process, which is to provide junior scientists with better opportunities at Austrian Universities.

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