The authors experimentally demonstrate that, counterintuitively, the heralding of zero photons in an ancillary mode can reduce the mean photon number in an optical mode despite the fact that no photons have been removed from the system. This scheme finds an immediate application in the process of noiseless attenuation.
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.
Single-photon subtraction (SPS) is useful for engineering optical quantum states and can be accomplished experimentally by heralding on the detection of one photon in the output port of a beamsplitter. Alternatively, conditioning on zero reflected photons modifies states by “zero-photon subtraction” (ZPS). Here we experimentally demonstrate that ZPS reduces the mean photon number of superpositions/mixtures of Fock states. The observed trends in attenuation show a dependence on the Mandel Q parameter for various input states, resulting in complementary behavior between SPS and ZPS. Theoretical results also show higher-order effects on the photon number distribution, beyond reduction in mean photon number.