In the project, we aim to explore quantum superpositions of mechanical resonators: mechanical objects, like a coffee cup or a football, that are in two different places at the same time. By doing so, we want to answer questions like: can massive objects really behave in a quantum way? In pursing this, we will push the boundaries of our understanding of the physical world, and in particular touch on topics of how to combine quantum mechanics and gravitational forces, which until now is still an open question.
So far, we have been developing the tools we need to take on these challenging questions: adapting the toolbox of the superconducting quantum computer to give us quantum control over heavy objects. This requires us to push these tools to new regimes.
We recently made a significant step in this direction by extending the frequencies that the quantum control these circuits enable down to the MHz regime where our mechanical resonators oscillate, a crucial step in bring the quantum world to mechanical objects.
The results that came out of this project include new insights and understanding of how to use extreme light matter coupling to bridge the frequency gap between circuit QED and heavy mechanical devices, disseminated via high profile publications, press releases, and invited talks at conferences, several of which have now been recorded and made publicly available on youtube (links can be found on steelelab.tudelft.nl). The identification of techniques to apply these to mechanical devices has been analysed in detail, which is currently under review but which is already available green-open-access on the arxiv. The next significant result is the detailed analysis of the platforms compatible with circuit QED in the context of testing quantum gravity, from which clear conclusions can be drawn about the platforms most relevant for this aim. Another significant result is the further development of the silicon nitride membrane platform itself, including the identification of the technical limitations of the complex assembly and how to reliably and reproducibly create these devices. This result has not yet been disseminated, but is currently being written up as part of the thesis of the second PhD student in the project for his thesis, which is expected to be submitted in mid-August, and shortly thereafter the results should be also available green-open-access via the arxiv. The last result I would like to emphasise here is the use of this platform for the systematic measurement of cryogenic vibrations over a wide frequency range: in particular, we have performed a detailed analysis of the cavity sideband noise induced by vibrations in our cryostat and used our calibrations to provide an absolute measure of the acceleration experienced by the device, highly valuable feedback for the manufacturers and crucial for the optimisation of the vibrations in the system. This we also plan to publish as a technical publication to share this knowledge with others. Finally, all of our publications are available (green) open access, and we furthermore pursue a high level of open data publication, combining the raw data files, the measurement scripts, and the analysis scripts used to generate all figures in the reports. We believe this level of openness will accelerate science by enabling researchers in the future to see exactly how everything was done, and even re-use the code we have written in their own analysis.
