Nonlocal Pulse Shaping with Entangled Photon Pairs

Nonlocal shaping effects in the time or spectral profiles of an entangled photon pair emerging from a pulsed parametric down-converter are observed by spectrally or temporally filtering one of the twin beams. In particular, we demonstrate the appearance of fourth-order (“ghost”) interference fringes in the spectrum of one beam conditioned by photodetection at the output of an unbalanced Michelson interferometer placed in the path of the other beam. The coherence time of the pump is the limiting factor for the sharpness of the details in the shaped biphoton spectrum.

Figure 1

Simplified scheme of the experiment. See the text for details.

Figure 2

(a) Experimental visibility of fourth-order temporal interference fringes on the idler beam for different values of the monochromator output slit width in the signal channel (diamonds 1 mm; stars $500\mu \mathrm{m}$; triangles $250\mu \mathrm{m}$; circles $100\mu \mathrm{m}$; squares $50\mu \mathrm{m}$). The input slit width is set to $50\mu \mathrm{m}$. The solid line is the limit curve, calculated assuming a Gaussian pump spectrum with the measured bandwidth. (b) Coherence times of the idler photon. The solid curve is calculated from the experimentally available pump coherence time (horizontal dashed line) and monochromator dispersion (dotted line).

Figure 3

Fourth-order spectral interference fringes on the signal spectrum conditioned on the detection of an idler photon after the Michelson interferometer. Data are taken with monochromator slit widths of 100 (input) and $250\mu \mathrm{m}$ (output). Figures correspond to time delays between the interferometer arms of (a) $\sim 0\mathrm{f}\mathrm{s}$, (b) 700 fs, (c) 1000 fs, and (d) 2300 fs.