Speaker
Description
Quantum noise has been the limiting noise at high frequency and a relevant noise at low frequency for the sensitivity of current gravitational wave detectors. It is also expected to be a limiting noise source for future interferometric gravitational wave detectors across the whole frequency band. Squeezed vacuum has become a standard tool for reducing quantum noise and led to up to 65\% increase of detection rate for current gravitational wave detectors. To reduce quantum noise over a broad frequency band, current solution is to combine squeezed vacuum with a hundred-meter long, detuned, and over-coupled optical cavity, usually called filter cavity. However, there are many other quantum noise reduction techniques. For certain cases, the noise limitation from other noise sources is relatively high at low frequency, which makes the consideration of various quantum noise reduction technique necessary. In the context of KAGRA post O5, we have compared quantum noise reduction schemes, including single-mode squeezing technique (frequency independent squeezing, frequency dependent squeezing with filter cavity or amplitude filter cavity or frequency dependent beam splitter) and two-mode squeezing technique (EPR scheme). We find that the behavior of suspension thermal noise and mirror thermal noise plays crucial role for deciding which quantum noise reduction scheme is more suitable. We also analyzed the difference of filter cavity and EPR scheme when the losses and length of the filter cavity is varied.