  We describe a new axion search method based on measuring the variance in the
interference of the axion signal using injected photons with a power detector.
The need for a linear amplifier is eliminated by putting a strong signal into
the microwave cavity, to acquire not only the power excess but also measure the
variance of the output power. The interference of the external photons with the
axion to photon converted signal greatly enhances the variance at the
particular axion frequency, providing evidence of its existence. This method
has an advantage in that it can always obtain sensitivity near the quantum
noise limit even for a power detector with high dark count rate. We describe
the basic concept of this method both analytically and numerically, and we show
experimental results using a simple demonstration circuit.
