  The detection of kilohertz-band gravitational waves promises discoveries in
astrophysics, exotic matter, and cosmology. To improve the kilohertz quantum
noise-limited sensitivity of interferometric gravitational-wave detectors, we
investigate nondegenerate internal squeezing: optical parametric oscillation
inside the signal-recycling cavity with distinct signal-mode and idler-mode
frequencies. We use an analytic Hamiltonian model to show that this stable,
all-optical technique is tolerant to decoherence from optical detection loss
and that it, with its optimal readout scheme, is feasible for broadband
sensitivity enhancement.
