Increasing the sensitivity of future gravitational-wave detectors with double squeezed-input

We consider improving the sensitivity of future interferometric gravitational-wave detectors by simultaneously injecting two squeezed vacuums (light), filtered through a resonant Fabry-Perot cavity, into the dark port of the interferometer. The same scheme with single squeezed vacuum was first proposed and analyzed by Corbitt et al. [Phys. Rev. D 70, 022002 (2004).]. Here we show that the extra squeezed vacuum, together with an additional homodyne detection suggested previously by one of the authors [F. Ya. Khalili, Phys. Rev. D 77, 062003 (2008).], allows reduction of quantum noise over the entire detection band. To motivate future implementations, we take into account a realistic technical noise budget for Advanced LIGO and numerically optimize the parameters of both the filter and the interferometer for detecting gravitational-wave signals from two important astrophysics sources, namely, neutron-star–neutron-star binaries and bursts. Assuming the optical loss of the $\sim 30\mathrm{m}$ filter cavity to be 10 ppm per bounce and 10 dB squeezing injection, the corresponding quantum noise with optimal parameters lowers by a factor of 10 at high frequencies and goes below the technical noise at low and intermediate frequencies.

Figure 1

Schematic plot of the proposed configuration. Two squeezed vacuums $\widehat{\mathit{s}}$ and $\widehat{\mathit{p}}$ are injected from both sides of the filter cavity rather than the one which was considered in Refs. 21, 32. The signal is detected by the main homodyne detector (MHD) and an additional homodyne detector (AHD) is made in the idle port of the filter cavity. ETM: end test mass; ITM: input test mass; PRM: power recycling mirror; PBS: polarized beam splitter; IM: input mirror; EM: end mirror; SQZ: squeezed light.

Figure 2

Quantum-noise spectrums of different schemes with optimized parameters for detecting gravitational waves from NSNS binaries. The optimal values for the parameters are listed in Table. .

Figure 3

Quantum-noise spectrums of different schemes which are optimized for detecting gravitational waves from bursts. The optimal values for the parameters are listed in Table. .

Figure 4

Quantum-noise spectrums of different schemes using the same parameters as the optimal CMWA to show how different parameters affect sensitivity of the CMWA scheme.