In their innovative study, X.-X. Wang et al. show that slow and stopped light in solids is extremely robust to decoherence. They do this by simultaneously stopping pulses of light from two laser beams in a solid and then demonstrating high visibility Young’s interference between the pulses after they are retrieved. Observing Young’s interference with high visibility is evidence of a high degree of spatial coherence. In contrast to previous methods, the authors are able to demonstrate that spatial coherence is preserved for all delays achievable by their apparatus; they observe a nearly constant visibility of 0.85 for delays up to 30 μs.
As with previous studies of stopped light in solids, the authors use electromagnetically-induced-transparency-driven stopped light based on ground-state coherence in a cryogenically cooled Praseodymium-doped Yttrium Silicate crystal (Pr:YSO). The angle between the two probe pulses is approximately 4 degrees and the probe pulses have identical frequencies with a common temporal length of 43 μs.
Though the present study investigates delays up to 30 μs, the authors note that much longer delays can be achieved by using an external magnetic field and employing dynamic decoupling techniques. Other researchers have already delayed 5 μs pulses by a full minute using these techniques. The prospect of pulses being delayed by 12 million pulse lengths with their spatial coherence preserved is truly an exciting possibility.
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