We study the direct experimental verification of continuous-variable (CV) energy-time entanglement, a crucial resource for long-distance quantum communication. Despite its potential advantages, including higher information capacity and robustness against noise, verifying energy-time CV entanglement under practical conditions has remained challenging. We find that nonlocal dispersion cancellation (NDC) provides an effective means to probe energy-time CV entanglement, successfully emulating photon propagation through a 379-km optical fiber at telecom wavelengths. By implementing NDC, we experimentally demonstrate that pairs of energy-time-entangled photons experience opposite dispersions, leaving the two-photon wave packet unbroadened, despite significant local dispersion acting individually on each photon. Our results show a violation of the separability criterion [Phys. Rev. A 82, 052120 (2010)] by 32 standard deviations, confirming energy-time CV entanglement independently of entanglement in other degrees of freedom. This work establishes a practical method for robustly verifying CV energy-time entanglement, facilitating advances in quantum information processing and secure long-distance quantum communication.

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• Optical tests of quantum theory
• Photon pairs & parametric down-conversion
• Quantum entanglement