Optical Phase gradients in Cold Atoms

Multi-level atoms interfaces with closed excitation loops may enable large light phase-shifts that are all-optically tunable over length scales of several microns. The interface mechanism does not require a cavity and is illustrated here for two classical light pulses in cold trapped 87Rb atoms, where radian-level modulations of their relative-phase are predicted to occur even for very weak pulses. Such a light-by-light phase control interface may be relevant to new applications of all- optical low-light signal processing.