Reduction of quantum noise using the quantum locking with an optical spring for gravitational wave detectors

Highlights: • The quantum locking scheme is a promising method to reduce quantum noise. • We simulated an optical spring effect in the quantum locking scheme. • The simulation showed the quantum noise is reduced in a broader frequency band. • This method can improve the DECIGO sensitivity to the primordial gravitational waves. In our previous research, simulation showed that a quantum locking scheme with homodyne detection in sub-cavities is effective in surpassing the quantum noise limit for Deci-hertz Interferometer Gravitational Wave Observatory (DECIGO) in a limited frequency range. This time we have simulated an optical spring effect in the sub-cavities of the quantum locking scheme. We found that the optimized total quantum noise is reduced in a broader frequency band, compared to the case without the optical spring effect significantly improving the sensitivity of DECIGO to the primordial gravitational waves.