The energy-time degree of freedom has emerged as a promising avenue for photonic quantum technologies due to its intrinsic robustness against decoherence; however, the timescales associated with energy-time entangled photons make for difficult measurement and manipulation. We implement two optical Kerr gates, in short (35 mm) pieces of single-mode fiber, to achieve ultrafast measurement of the time correlations of energy-time entangled photon pairs, with resolutions of $320\pm 30$ fs and $290\pm 30$ fs for signal and idler photons, respectively. These measurements, in addition to joint spectral measurements of the photon-pair state, are used to verify entanglement by means of the violation of a time-bandwidth inequality. Without the need for an interferometric setup or frequency conversion, the optical Kerr shutter is a valuable addition to the ultrafast quantum optics control and metrology toolbox.

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• Photon pairs & parametric down-conversion
• Quantum communication, protocols & technology
• Quantum information processing with continuous variables
• Quantum optics
• Quantum sensing
• Third order nonlinear optical processes
• Ultrafast optics
• Optical fibers
• Kerr effect