  Photonic quantum technology increasingly uses frequency encoding to enable
higher quantum information density and noise resilience. Pulsed time-frequency
modes (TFM) represent a unique class of spectrally encoded quantum states of
light that enable a complete framework for quantum information processing.
Here, we demonstrate a technique for direct generation of entangled TFM-encoded
states in single-pass, tailored downconversion processes. We achieve
unprecedented quality in state generation---high rates, heralding efficiency
and state fidelity---as characterised via highly resolved time-of-flight fibre
spectroscopy and two-photon interference. We employ this technique in a
four-photon entanglement swapping scheme as a primitive for TFM-encoded quantum
protocols.
