Strong cross-Kerr nonlinearities have been long sought after for quantum information applications. Recent work has shown that they are intrinsically unreliable in traveling-wave configurations: cavity configurations avoid this, but require knowledge of both the nonlinearity and the loss. Here we present a detailed systematic study of cross-phase modulation and absorption in an Rb vapor confined within a hollow-core photonic crystal fiber. Using a two-photon transition, we observe phase modulations of up to $\pi$ rad with a signal power of 25 $\mu$W, corresponding to a nonlinear Kerr coefficient, $n_2$, of $0.8\times {10}^{-6}$ cm${}^2$/W, or $1.3\times {10}^{-6}$ rad per photon.

• Received 17 December 2012

DOI:https://doi.org/10.1103/PhysRevA.88.013819