Optical decoherence in eR3+-doped silicate fiber: evidence for coupled spin-elastic tunneling systems.
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.
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Department of Physics, Montana State University, Bozeman, Montana 59717, USA and IBM Almaden Research Center, San Jose, California 95120, USA. macfarla@almaden.ibm.com
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