March 2017
Spotlight Summary by Filippo Miatto
All-order dispersion cancellation and energy-time entangled state
An energy-time entangled photon pair is a state where the timing of the photons is correlated and the frequency (techincally, the detuning) is anti-correlated. When we send such a state through a dispersive medium each frequency experiences a different group velocity which spreads out the individual pulses, but thanks to the frequency anti-correlation the time correlation is unaffected. This effect is known as "dispersion cancellation". The same happens for all the odd-order corrections to the dispersion relation, but how do we cancel out the even orders?
Steinberg proposed a clever solution by using a Hong-Ou-Mandel interference setup, where the photons (having been affected in the same way by the even-order effects) would bunch at the beam splitter and in fact no coincidences were observed. It was pointed out though that the same would happen regardless of entanglement, by the indistinguishability of the paths. So Ryu and colleagues added a Mach-Zehnder interferometer in the path of a photon, so that the average path length would match the path length of the other photon. The paths of non-entangled photons now are distinguishable, so the presence of a HOM dip can only be caused by the energy-time entanglement.
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Steinberg proposed a clever solution by using a Hong-Ou-Mandel interference setup, where the photons (having been affected in the same way by the even-order effects) would bunch at the beam splitter and in fact no coincidences were observed. It was pointed out though that the same would happen regardless of entanglement, by the indistinguishability of the paths. So Ryu and colleagues added a Mach-Zehnder interferometer in the path of a photon, so that the average path length would match the path length of the other photon. The paths of non-entangled photons now are distinguishable, so the presence of a HOM dip can only be caused by the energy-time entanglement.
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Article Information
All-order dispersion cancellation and energy-time entangled state
Jinsoo Ryu, Kiyoung Cho, Cha-Hwan Oh, and Hoonsoo Kang
Opt. Express 25(2) 1360-1380 (2017) View: Abstract | HTML | PDF