Fig. 5: Bandwidth compression of single photons.
a Experimental implementation and illustration of the temporal and spectral evolution of the photon. A waveshaper first applies a quadratic spectral phase (or group delay dispersion, GDD) to the input photon, which stretches the wavepacket in time. The TFLN modulator then adds a quasi-quadratic temporal phase to the photon by synchronizing the photon arrival time to the valley of the sinusoidal phase modulation. This modulation acts as a time lens and compresses the photon bandwidth. b Measured single-photon spectra with different GDDs. At the “focal point” (\({{{\mathrm{{\Phi}}}}} = 1/B\)), the 6.55 nm FWHM input photon (blue curve) was compressed to 0.35 nm (inset; black solid line: Gaussian fitting), corresponding to a compression factor of 18.7. c Extracted FWHM bandwidths (from Gaussian fitting) of the output photons with different GDDs. Spectra in the main panel of (b) and blue circles in (c) were measured using 20 km fiber, which has an instrument response function (IRF)-limited resolution of 0.53 nm; inset of (b) and purple star in (c) were measured using a high dispersion module made of a chirped fiber Bragg grating, which has an IRF-limited resolution of 0.11 nm. The TFLN modulator was driven at 13.6 GHz and 4.0 Vπ
