Research

The theme of this project is the investigation of optomechanics – light coupled to mechanical motion at the microscale – using superconducting circuits in the microwave domain. The idea is to create an inductor-capacitor circuit made out of a thin film superconductor where the capacitor is mechanically compliant, i.e. one of its electrodes is a suspended membrane. As this membrane vibrates, it modulates the capacitance and, in turn, the resonance frequency of the microwave cavity. The microwave field also exerts pressure on the capacitor plates. The superconducting circuit architecture provides an agile platform to extend standard optomechanics to multimode optomechanics, where multiple microwave modes are coupled to the same mechanical mode (or to multiple mechanical modes). It also connects optomechanics to circuit quantum electrodynamics, a field which has gained a lot of momentum due to its potential for a scalable quantum computer.

The development of optical frequency combs, and notably self-referencing, has revolutionized precision measurements over the past decade, and enabled counting of the cycles of light. Frequency combs, for which Hall and Haensch shared the Physics Nobel Prize in 2005 has enabled dramatic advances in timekeeping, metrology and spectroscopy. In 2007, research on microresonators resulted in the discovery of a novel method to generate optical frequency combs using parametric frequency conversion in optical microresonators. This unexpected observation broke with the conventional dogma that optical combs can only be generated with mode locked pulsed laser sources. Instead this work showed that a CW laser can be converted into a broadband frequency comb, using parametric frequency conversion, overcoming passive cavity dispersion. The Kippenberg laboratory demonstrated with his group the accuracy of the mode spacing to be better than 1 part in 10(17) – hence unambiguously proving the comb nature.

Although mechanical oscillator are ubiquitous in our modern information technology, and used in time-keeping, MEMS accelerometers or in radio frequency filters in cell-phones, yet their quantum control had remained an outstanding challenge. The ability to achieve such quantum control has been a longstanding challenge of condensed matter Physics and quantum optics alike. In contrast to trapped ions no efficient manipulation techniques were available. Over the past decade, this has become a reality: Following quantum control of individual isolated quantum systems, the latter has now been extended to macroscopic, engineered mechanical oscillators, owing to the advances in the field of cavity optomechanics.