Quantum optical coherence tomography (QOCT) was proposed two decades ago, as a quantum-enabled alternative to its classical counterpart, or OCT. Two main advantages were identified for QOCT over OCT: a factor-of-two improvement in the axial resolution for a given source bandwidth, and even-order dispersion cancellation. In their recent contribution, Hayama et al. have on the one hand obtained the best axial QOCT resolution to date (2.2 μm), and on the other hand have performed a beautiful comparison of QOCT vs OCT. For a plain mirror in place of a sample, they have shown that while the OCT trace is seriously degraded by dispersion (introduced by a ZnSe window), the QOCT interferogram remains essentially unaffected; the same data shows the quantum-enabled resolution enhancement. The authors then go on to employ a QOCT sample involving two depth levels with a 30 μm difference between them. They show that while the QOCT interferogram shows unwanted artifacts, the steps can be clearly resolved despite the presence of dispersion. In comparison, in the case of OCT the two retrieved depth levels become so broadened that they in fact overlap. This timely contribution no doubt represents a significant step forward for QOCT as it matures towards a usable technology.

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