Observation of optical-fiber Kerr nonlinearity at the single-photon level

TL;DR

This paper reports the first experimental observation of optical Kerr nonlinearity at the single-photon level in an optical fiber, demonstrating measurable phase shifts induced by extremely weak light pulses, with implications for quantum information processing.

Contribution

It provides the first experimental evidence of optical nonlinearity at the single-photon level in fibers, using photonic crystal fibers with large nonlinearity and managed dispersion.

Findings

Measured very small conditional phase shifts (~10^(-7) to 10^(-8)) caused by single-photon-level pulses.

Phase shifts were detectable using much stronger probe pulses (~10^6 times more intense).

Discussed potential for quantum information processing with fiber-based Kerr nonlinearity.

Abstract

Optical fibers have been enabling numerous distinguished applications involving the operation and generation of light, such as soliton transmission, light amplification, all-optical switching and supercontinuum generation. The active function of optical fibers in the quantum regime is expected to be applicable to ultralow-power all-optical signal processing and quantum information processing. Here we demonstrate the first experimental observation of optical nonlinearity at the single-photon level in an optical fiber. Taking advantage of large nonlinearity and managed dispersion of a photonic crystal fiber, we have successfully measured very small (10^(-7) ~ 10^(-8)) conditional phase shifts induced by weak coherent pulses that contain one or less than one photon per pulse on average. In spite of its tininess, the phase shift was measurable using much (~10^6 times) stronger coherent probe pulses than the pump pulses. We discuss the feasibility of quantum information processing using optical fibers, taking into account the observed Kerr nonlinearity accompanied by ultrafast response time and low induced loss.