Phase shaping of single-photon wave packets

Although the phase of a coherent light field can be precisely known, this is not true for the phase of the individual photons that create the field, considered individually(1). Phase changes within single-photon wave packets, however, have observable effects. In fact, actively controlling the phase of individual photons has been identified as a powerful resource for quantum communication protocols(2,3). Here we demonstrate arbitrary phase control of a single photon. The phase modulation is applied without affecting the photon's amplitude profile and is verified by means of a two-photon quantum interference measurement(4,5), demonstrating fermionic spatial behaviour of photon pairs. Combined with previously demonstrated control of a single photon's amplitude(6-10), frequency(11), and polarization(12), the fully deterministic phase shaping presented here allows for the complete control of single-photon wave packets.