Zero-photon subtraction: a useful tool for quantum communication

The process of single-photon subtraction --essentially an implementation of the annihilation operator-- is known to be a useful tool for manipulating quantum optical states. Somewhat surprisingly, subtracting zero photons can also alter the properties of certain quantum states, and forms the bases of a noiseless attenuation process that is useful for quantum communication. Here we review our recent experimental work in this area, which uses parametric down-conversion sources and heralding signals based on the active detection of zero photons.