Spectral domain nonlinear quantum interferometry with pulsed laser excitation

Nonlinear quantum interferometry is widely used in photonic quantum sensing applications to perform measurements with undetected photons. While continuous wave (cw) lasers are typically used to generate correlated photon pairs, pulsed laser pumping can enhance the generation efficiency for photon pairs and enable time-resolved measurements. However, the finite spectral linewidth of pulsed lasers leads to imperfect frequency correlation between generated photon pairs, which can affect the sensitivity of nonlinear interferometry. In this work, we investigate the effect of the finite linewidth of a pump laser on the visibility of spectral domain interference in a nonlinear quantum interferometer where signal photons are detected using a dispersive spectrometer. The proposed theory quantitatively predicts the visibility as a function of optical path difference for a pump source with arbitrary spectrum. As a demonstration, we construct an experimental setup to obtain quantum interference using both cw and pulsed laser excitations under the same experimental conditions. At large optical path differences, a fine interference fringe pattern with high contrast is observed with cw laser excitation, whereas with pulsed laser pumping, the visibility decreases as the optical path delay increases, and the interference fringes appear almost washed out. Our quantitative analysis is useful for determining appropriate pulsed laser parameters for designing nonlinear interferometers for quantum sensing applications using a dispersive spectrometer.