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

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(104) 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., , , # Data overview

The data is organized in folders as follows:

```
figures/
| - 1/
| | - 1b/
| | - 1c/
| | - 1d/
| - 2/
| - 3/
| - 4/
| | - 4a/
| | - 4b/
| - 5/
| | - 5a/
| | - 5b/
| - s4/
| - s6/
| - s8/
| - s10/
| - s13/
| - s14/
| - s15/
| - s16/
| - s17/
| - s18/
misc/
| - ellipsometer/
```

# Notes

Please refer to the main manuscript and supplementary text for additional details regarding the data files, e.g., the measurement and analysis protocols utilized.

Most of the data files may be readily loaded into a Python analysis script as pandas DataFrames. Please refer to pandas documentation for details.

Detector naming note: The 1550a, 1550b, 810a, and 810b labels in data files that contain them refer to the four detectors used in the experiment. \"1550a_810a\" therefore refers to coincidences between the 1550a and 810a detectors.

Three common types of \"counts\" appear in the data:

1. Single counts: Detection events on individual detectors.
2....,