We demonstrate an observation of zero to $\pi$ continuously controllable cross-phase-modulation based on an $N$-type electromagnetically-induced-transparency scheme in a room-temperature ${}^{87}\mathrm{Rb}$ vapor. We theoretically and experimentally show that the signal field acquires a $\pi$ phase shift compared with the reference light in the presence of the phase-control field. Using the method of the optical Mach-Zehnder interferometer, we demonstrate that a zero to $\pi$ continuously controllable phase gate can be built by modulating the phase-control field. In addition, our theoretical calculation agrees well with the experimental observation, and the results presented in this work hold potential applications for the orthogonal polarization or vector gate in quantum information processing.

• Received 16 June 2015

DOI:https://doi.org/10.1103/PhysRevA.92.043838