Towards supersensitive optical phase measurement using a deterministic source of entangled multiphoton states

Precision measurements of optical phases have many applications in science and technology. Entangled multiphoton states have been suggested for performing such measurements with precision that significantly surpasses the shot-noise limit. Until recently, such states have been generated mainly using spontaneous parametric down-conversion-a process which is intrinsically probabilistic, counteracting the advantages that the entangled photon states might have. Here we use a semiconductor quantum dot to generate entangled multiphoton states in a deterministic manner, using periodic timed excitation of a confined spin. This way we entangle photons one by one at a rate which exceeds 300 MHz. We use the resulting multiphoton state to demonstrate super-resolved optical phase measurement. Our results open up a scalable way for realizing genuine quantum enhanced supersensitive measurements in the near future.