Ultra broadband entangled photon pairs

The process of broadband spontaneous parametric down conversion produces photon pairs that are highly entangled in time-energy. The strong correlations of down converted light introduce a whole range of unusual phenomena observed in our research. We observe a classically inexplicable linear dependence of nonlinear sum frequency generation on input flux, when performed with down-converted light. We also demonstrate quantum interference between photon pairs generated at different crystals, allowing interferometric measurement of the two-photon wave function.


Due to the very low power limit of the quantum regime, less then one photon / (Hz sec), measurements are difficult to distinguish from noise. In order to intensify the measurements we use an ultra broadband spectrum spanning almost an octave (1400-2400nm) of down conversion. The broadband spectrum enables us to generate up to microwatts of down-converted light within the quantum regime of single photons.


Another aspect we research is the classical parametric behavior of the down conversion process in coupled optical parametric oscillators (OPO’s). In contrast to coupled regular lasers, who lock to a common phase relation that minimizes losses in the coupled cavity, an OPO’s phase is dictated by the pump field and is not free to evolve. The strong dependence of parametric amplification gain on phase produces many exceptional temporal oscillating modes, starting from frequency splitting to broad band oscillation of CW correlated fields (Paper, Poster).




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