July 2015
Spotlight Summary by Curtis Broadbent
Preservation of transverse spatial coherence in the storage of double light pulses
Quantum technologies hold the promise of paradigm-shifting increases in computational power and communication security. However, challenges arising from loss and decoherence make it difficult to achieve the stringent gate requirements in computational settings and can drastically reduce the secret key rate and achievable distances in quantum communication technologies. One approach for alleviating some of these problems has been to use slow and stopped light to make more efficient use of photons as quantum information carriers. Unfortunately, many implementations of slow and stopped light have intrinsic sources of decoherence (both spatial and longitudinal) which belies their effectiveness as a quantum-assistive technology.
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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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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Article Information
Preservation of transverse spatial coherence in the storage of double light pulses
Xiao-Xiao Wang, Ai-Jun Li, Jia-Xiang Sun, Yuan-Hang Sun, Yi Chen, Xiao-Jun Zhang, Lei Wang, Hai-Hua Wang, and Jin-Yue Gao
J. Opt. Soc. Am. B 32(7) 1318-1322 (2015) View: Abstract | HTML | PDF