Attosecond Measurements via Quantum-Enhanced Interferometry

We report on our work towards attosecond-level temporal resolution via quantum interferometry. Unlike classical interference, Hong-Ou-Mandel (HOM) two-photon interference is robust against dispersion, optical noise, and unbalanced loss. However, high-resolution HOM interferometry is challenging, requiring either very high photon bandwidth or flux. As reported in the literature, a solution is to perform HOM interference with frequency-entangled photon pairs. In the entangled case, the resolution is dominated by the detuning between the two involved frequency modes. By utilizing a highly non-degenerate spontaneous parametric down-conversion source, we achieve a detuning of 1110 THz (810 and 1550 nm), two orders of magnitude greater than previous work. We discuss our dual-wavelength interferometer designed to attain a time resolution below 10 attoseconds with 10⁴ photon pairs, an improvement of approximately two orders of magnitude over the current state-of-the art for this technique. Our system will enable sensing on the attosecond (nanometer) scale via HOM interference without the need for ultra-broadband sources while benefitting from robustness against dispersion, noise, and loss.