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Ring-shaped spectra of parametric downconversion and entangled photons that never meet

Spasibko, K., Kopylov, D., Murzina, T., Gerd Leuchs, Chekhova, M.

Published Jan 1, 2016• 15 citations
OpenAlex

Abstract

We report on the observation of an unusual type of parametric downconversion. In the regime where collinear degenerate emission is in the anomalous range of group-velocity dispersion, its spectrum is restricted in both angle and wavelength. Detuning from exact collinear-degenerate phase-matching leads to a ring shape of the wavelength-angular spectrum, suggesting a new type of spatiotemporal coherence and entanglement of photon pairs. By imposing a phase varying in a specific way in both angle and wavelength, one can obtain an interesting state of an entangled photon pair, with the two photons being never at the same point at the same time. (C) 2016 Optical Society of America

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We report on the observation of an unusual type of parametric downconversion. In the regime where collinear degenerate emission is in the anomalous range of group-velocity dispersion, its spectrum is restricted in both angle and wavelength. Detuning from exact collinear-degenerate phase-matching leads to a ring shape of the wavelength-angular spectrum, suggesting a new type of spatiotemporal coherence and entanglement of photon pairs. By imposing a phase varying in a specific way in both angle and wavelength, one can obtain an interesting state of an entangled photon pair, with the two photons being never at the same point at the same time. (C) 2016 Optical Society of America
We report on the observation of an unusual type of parametric downconversion. In the regime where collinear degenerate emission is in the anomalous range of group-velocity dispersion, its spectrum is restricted in both angle and wavelength. Detuning from exact collinear-degenerate phase-matching leads to a ring shape of the wavelength-angular spectrum, suggesting a new type of spatiotemporal coherence and entanglement of photon pairs. By imposing a phase varying in a specific way in both angle and wavelength, one can obtain an interesting state of an entangled photon pair, with the two photons being never at the same point at the same time.
We report spontaneous parametric downconversion having an unusually wide spectral bandwidth. A collinear type 1 phase-matching configuration is employed with degeneracy near the zero group-velocity dispersion frequency. With a spectral width of 1080 nm and degenerate wavelength of 1885 nm, the source also emits a high flux of 3.4 x 10(11) s(-1)W(-1) photon pairs constrained to a cone of only approximately 2 degrees half-angle. A rigorous theoretical approach is developed that confirms the experimental observations. The source properties are consistent with an ultrashort photon-pair correlation time and, for a narrowband pump, extremely high-dimensional spectral entanglement.
We report the complete measurement of the spectral properties of entangled photon pairs generated via frequency-degenerate type-I spontaneous parametric down-conversion pumped by a cw laser in both the collinear and the noncollinear regimes. The measurement includes the single-photon spectra as well as the two-photon joint spectra. Our results reveal interesting yet subtle differences between the collinear and the noncollinear regimes of frequency-degenerate type-I spontaneous parametric down-conversion. The single-photon and two-photon spectral measurements are in good agreement with the numerical simulation taking into account the tuning curve and the experimental geometry.
The spectral properties of entangled photon pairs generated via quasi-phased matching in spontaneous parametric down-conversion are proposed and demonstrated experimentally.A general mathematical model for evaluating the spectral properties is developed to obtain the spectrum shape and range of down-converted photons.The model takes into account the effects of phase mismatching due to non-ideal pumping and the relationship between crystal periodic modulation function and the incidence angle of the pump beam.The spectrum curve shape is determined by the discrete Fourier transform of a Gaussian pump beam and the integration of parametric down-conversion generated by an individual plane wave.An experiment is carried out with a PPLN non-linear crystal and dispersing optics, which shows a good consistency in their spectral ranges and shapes with our model predictions within the spectrum of 600-633 nm.This therefore illustrates that both the simulation model and the experimental process are reasonable.This novel method has potential applications in high-accuracy calibration in the wide spectrum using correlated photons.
A method is presented for the separation of polarization-entangled, frequency-degenerate photon pairs based on inverse Hong-Ou-Mandel interference. Adjusting the phase between photon states is achieved by exploiting the wavelength dispersion of optical glass, for which process a complete mathematical description is given. To experimentally demonstrate the phenomenon, a custom photon pair source has been built using spontaneous parametric downconversion of type-0 phase matching and a Sagnac interferometer. The effect of phase tuning was characterized by the modulation of coincidence probability. The visibility of quantum interference was found to be 0.820 and 0.720 for photons being in purely horizontal or vertical polarization state. In case of polarization entanglement, the measured state fidelity with respect to the $|{\mathrm{\ensuremath{\Phi}}}^{\ensuremath{-}}\ensuremath{\rangle}$ Bell state was 0.914.