Periodic Reporting for period 1 - ExCOM-cCEO (Extremely Coherent Mechanical Oscillators and circuit Cavity Electro-Optics)
Reporting period: 2019-10-01 to 2021-03-31
Towards our efforts in objectives 3 and 4 of developing strain-engineered superconducting mechanical resonators, we developed a novel nano-fabrication process to explore ultracoherent mechanical resonators for superconducting circuits. Within the first year of the project, we purchased and installed a new cryogenic dilution fridge funded by ERC project. This fridge provides environment temperature of 8 mK that results in twice higher mechanical quality factors compared to our old system. We characterized the new devices using this fridge and measured the record of 18 million mechanical quality factor for a superconducting electromechanical system. We successfully performed quantum ground state cooling of the mechanical motion and measured 0.1 quanta occupation of mechanical motion. We established a time-domain experimental setup to conduct pulse sequential measurements on this device and currently are improving the efficiency of this approach.
We developed a new method to optically readout superconducting circuits via light. The cryogenic electro-optical interconnect we purposed was exploiting a commercial optical phase modulator to transduce microwave signals to light at 800 milli-Kelvin temperatures.
Shifting the window of operation to optical frequencies provides the advantages of a wider operations frequency range, low loss and compact transmission in optical fibers. We have analysed and proposed a new kind of device harnessing the strong piezoelectric coupling of microwave signals to a mechanical excitation, a high overtone bulk acoustic resonance (HBAR), parametrically interacting with optical supermodes of optically coupled ring cavities to realize a (quantum) coherent microwave-optical conversion. We also developed an ultra-low loss hybrid lithium niobate - silicon nitride integrated photonic platform. We used wafer bonding to combine low-loss waveguiding of our silicon nitride PICs with electro-optic properties of lithium niobate.
All data and experimental details of our publications are available on public repositories and libraries such as ZENODO (https://zenodo.org/) and arXiv (https://arxiv.org/). In addition, our group has developed and launched a new platform as part of and open science initiative at EPFL for collecting and sharing the details of nanofabrication processes (https://nanofab-net.org/) from tacit knowledge in the field. This comprises a collection of notes that will significantly reduce the time and resources spent in nanofabrication facilities by all researchers world-wide. This initiative upholds a culture of Open Science leading to higher transparency between the researchers and public society as well as increasing the reliability and reproducibility of our research.