Tunable linear-optical phase amplification

We combine lossless, phase-only transformations with fully transmitting linear-optical scatterers to define the principle of linear-optical phase amplification. This enables a physical phase shift φ to be nonlinearly mapped to a new space γ(φ) using linear optics, resulting in a completely general and enhanced phase shifter that can replace any standard one. A particular phase amplifier is experimentally realized, allowing the phase enhancement parameter dγ/dφ to be continuously tuned. Placing this enhanced phase shifter in one arm of a Mach-Zehnder interferometer led to an intensity-phase slope more than 20 times steeper than what can be obtained with its unamplified counterpart.