Fast quantum interferometry at the nanometer and attosecond scales with energy-entangled photons

TL;DR

This paper demonstrates a quantum interferometry technique using energy-entangled photons that achieves nanometer and attosecond resolution in loss and background environments, enabling rapid, non-destructive measurements.

Contribution

It introduces a novel method of enhancing two-photon interference with highly non-degenerate energy entanglement for high-resolution, loss-tolerant optical measurements.

Findings

Achieved nanometer and attosecond resolution with ~10,000 photon pairs.

Measurement resolution is unaffected by background and loss.

Validated non-destructive thickness measurement against atomic force microscopy.

Abstract

In classical optical interferometry, loss and background complicate achieving fast nanometer-resolution measurements with illumination at low light levels. Conversely, quantum two-photon interference is unaffected by loss and background, but nanometer-scale resolution is physically difficult to realize. As a solution, we enhance two-photon interference with highly non-degenerate energy entanglement featuring photon frequencies separated by 177 THz. We observe measurement resolution at the nanometer (attosecond) scale with only $O(10^4)$ photon pairs, despite the presence of background and loss. Our non-destructive thickness measurement of a metallic thin film agrees with atomic force microscopy, which often achieves better resolution via destructive means. With contactless, non-destructive measurements in seconds or faster, our instrument enables metrological studies in optically challenging contexts where background, loss, or photosensitivity are factors.