Quantum nondemotion tracking of a resonator’s phase
Bernard Yurke, D. S. Creywall, Paul Busch +1 more
Resonators driven to self-oscillation by active feedback play an important role in technology. The laser is an example of such a device. Generally, the feedback that sustains self-oscillation is contaminated with amplifier noise, which leads to phase diffusion. Here we show that under suitable conditions phase noise from the feedback amplifier can be evaded, allowing one to track the resonator's phase in a quantum nondemolition manner. In particular, we consider a resonator with a Kerr nonlinearity. The output of the resonator is fed into a linear amplifier, phase shifted, fed through an amplitude limiter, and then fed back into the resonator. Stable operation is achieved, even on portions of the resonance curve for which the resonator would exhibit optical bistability under open-loop conditions. By operating the system at a point on the resonance curve for which the slope of the phase versus frequency is infinite, the long-term phase stability of the oscillator becomes insensitive to the amplifier's output noise. In addition, the amplifier's input-port noise can be evaded by making the coupling between the resonator and the amplifier sufficiently weak.
•May 8, 1994•0 citations