Test by NMR of the Phase Coherence of Electromagnetically Induced

K.V.R.M. Murali, Hyung-Bin Son, Matthias Steffen, Patrick Judeinstein, and Isaac L. Chuang
Phys. Rev. Lett. 93 , 3, 033601 (2004)

Electromagnetically induced transparency is an effect observed in atomic systems, originating from quantum interference, in which electromagnetically transitions to and from a certain quantum state become suppressed. This dark state is also characterized by a quantum phase, relative to other states, which theoretically should stop evolving, but remain phase coherent, during transparency. We test this theoretical prediction using techniques developed for liquid-state nuclear magnetic resonance quantum computation, applied to a spin-7/2 nuclear spin system. A sequence of quantum operations is applied to create the dark state, and during transparency its phase evolution is measured relative to a reference state using Ramsey interferometry. Experimental measurements of the fringe visibility are in excellent agreement with theoretical expectations, taking into account measured decoherence rates.