Physical Review Letters
Optical Decoherence in Er 3 + -Doped Silicate Fiber: Evidence for Coupled Spin-Elastic Tunneling Systems
R. M. Macfarlane, Yiwen Sun, Peter B. Sellin, R. L. Cone
Abstract
We measured the optical decoherence times T2, or, equivalently, the homogeneous line width, in an Er-doped optical fiber at low temperature as a function of external magnetic field and temperature using two-pulse photon echoes. The decoherence times were up to 230 ns at fields above 3 T. The magnitude of the line narrowing induced by a magnetic field of 3 T is 2.5 MHz, which is anomalously large compared to that typical for oxide crystals with similar Er3+ concentration. This is interpreted as evidence for dephasing by coupled spin-elastic tunneling modes where the normal glass tunneling modes acquire a magnetic character by coupling to the Er3+ spin.