Large cross-phase modulations at the few-photon level

Zi Yu Liu, Yi Hsin Chen, Yen Chun Chen, Hsiang Yu Lo, Pin Ju Tsai, Ite A. Yu, Ying Cheng Chen, Yong Fan Chen

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47 Scopus citations


We demonstrate an efficient cross-phase modulation (XPM) based on a closed-loop double-Λ system. The property of the double-Λ medium can be controlled by changing the phases of the applied optical fields. This phase-dependent XPM scheme can achieve large phase modulations at low-light intensities without requiring cavities or tightly focusing laser beams. With this scheme, we observe a π-level phase shift with two pulses, both consisting of eight photons in cold rubidium atoms. Such a novel scheme provides a simple route to generate strong interactions between photons and may have potential applications in all-optical quantum signal processing.

Original languageEnglish
Article number203601
JournalPhysical Review Letters
Issue number20
StatePublished - 7 Nov 2016


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