  Rare earth doped crystals are promising systems for quantum information
processing. In particular paramagnetic rare earths could be used to build
coherent interfaces with optical and microwave photons. In addition, isotopes
with non zero nuclear spins could provide long lived states for quantum state
storage and processing. Yb3+ is particularly interesting in this respect since
it is the only paramagnetic rare earth with a spin 1/2 isotope, which
corresponds to the simplest possible level structure. In this paper, we report
on the optical and magnetic properties of Yb3+ in the two sites of Y2SiO5, a
commonly used crystal for quantum applications. We measured optical
inhomogeneous linewidths, peak absorption coefficients, oscillator strengths,
excited state lifetimes and fuorescence branching ratios. The Zeeman tensors
were also determined in the ground and excited states, as well as the ground
state hyperfine tensor for the 171Yb3+ (I = 1=2) isotope. These results suggest
that Yb3+:Y2SiO5 is a promising material for applications like solid state
optical and microwave quantum memories.
