| 研究実績の概要 |
After the world first measurement of frequency dependent squeezing achieved at the end of FY2019, several degradation sources were identified: the major ones being the injection/readout optical losses and the filter cavity alignment and length stability. In FY2020, many degradation sources were addressed and solved.
On the FIS side, the optical losses were reduced from 25% to 18% allowing for the measurement of 6.5dB of squeezing. To further reduce this losses, new AR coating for the PPKTP crystal of the OPO was procured and the installation of the new OPO with reduced optical losses is ongoing. On the Injection/readout optical losses, the design of a new in vacuum Faraday isolator was finalized. The implementation of this new FI should reduce the optical losses of the injection/readout path by approximately 10%. For what concern the FC alignment, an auto-alignment system, based on radio-frequency demodulated quadrant photodiodes, was successfully implemented. With this AA system, the long term stability of the FC was greatly improved allowing for better measurement.
Finally, large fraction of FY2020 was devoted to the theoretical design, implementation and testing of a novel technique for FC length control. This technique is called Coherent Control of the Filter Cavity. The theoretical study was published on Physical Review D. This technique was successfully implemented in the FC experiment allowing for a length noise reduction of more than a factor of five. A paper on the experimental demonstration of this technique is being realized and will be submitted soon to PRD.
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