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arXiv:2512.05961

Entanglement-Enhanced Quantum Nano-Vibrometry

Colin P. Lualdi, Joshua Rapp, Spencer J. Johnson, Michael Vayninger, Paul G. Kwiat

quant-phSubmitted Dec 5, 2025• Announced Dec 8, 2025• 0 citations
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Abstract

The study of dynamic systems at the nanometer scale can benefit from the loss and background resilience offered by quantum two-photon interference. However, fast measurements with the required resolution are difficult to realize. As a solution, we introduce extreme energy entanglement between the photons undergoing interference. Using a flux probing analysis technique, we recover vibrational signals with frequencies as high as 21 kHz. Along with validating nanometer-scale precision and accuracy, we observe a significant quantum advantage when measuring in the presence of loss and background.

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6 pages, 3 figures

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The study of dynamic systems at the nanometer scale can benefit from the loss and background resilience offered by quantum two-photon interference. However, fast measurements with the required resolution are difficult to realize. As a solution, we introduce extreme energy entanglement between the photons undergoing interference. Using a flux probing analysis technique, we recover vibrational signals with frequencies as high as 21 kHz. Along with validating nanometer-scale precision and accuracy, we observe a significant quantum advantage when measuring in the presence of loss and background.
The resilience of quantum two-photon interference against optical loss and background sets it apart from classical single-photon interference for the purpose of sensing. However, achieving fast measurements at the nanometer scale with two-photon interference is challenging, as attaining high resolution typically requires either ultrabroadband photons or many probe photons. To realize nanometer-scale measurements in a matter of seconds or less, we greatly increase the per-photon information content via highly non-degenerate energy entanglement. Our fast measurements thereby enable us to probe time-varying signals at the nanometer scale. To further develop our capabilities, we have drawn on single-photon imaging techniques to implement a robust protocol for reconstructing periodic signals from our relatively sparse detection data, complete with amplitude and frequency information. With this analysis regimen, we have successfully extracted complex multi-frequency signals as well as kHz-range acoustic vibrations. We review our method and present the results of an example measurement to illustrate our capabilities.
We present progress toward measuring nanometer-scale vibrations via a frequency-entangled two-photon interferometer. Unlike classical interference, two-photon – or Hong-Ou-Mandel – interference allows for optical metrology with resilience against imbalanced loss, dispersion, and optical background. However, the resolution of traditional degenerate frequency two-photon interference is limited by the photons’ bandwidths, requiring large bandwidths or long integration times to achieve nanometer-scale resolution. We have implemented a twophoton interferometer utilizing highly non-degenerate frequency-entangled photon pairs at 810 nm and 1550 nm, drastically increasing measurement sensitivity while retaining the advantages of two-photon interference. This enhancement comes via a beat note with frequency proportional to the photon detuning of 177 THz. The resulting measurement saturates the quantum Cram´er-Rao bound, maximizing the information extracted per photon. We have demonstrated a measurement resolution of 2.3 nm with fewer than 18,000 detected photon pairs, orders of magnitude better than previous results. By reflecting one photon from the pair off a target surface, we may use our system to study small-scale vibrations.
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 nondegenerate 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 nondestructive thickness measurement of a metallic thin film agrees with atomic force microscopy, which often achieves better resolution via destructive means. With contactless, nondestructive measurements in seconds or faster, our instrument enables metrological studies in optically challenging contexts where background, loss, or photosensitivity are factors.
Nonclassical states are essential for optics-based quantum information processing, but their fragility limits their utility for practical scenarios in which loss and noise inevitably degrade, if not destroy, nonclassicality. Exploiting nonclassical states in quantum metrology yields sensitivity advantages over all classical schemes delivering the same energy per measurement interval to the sample being probed. These enhancements, almost without exception, are severely diminished by quantum decoherence. Here, we experimentally demonstrate an entanglement-enhanced sensing system that is resilient to quantum decoherence. We employ entanglement to realize a 20% signal-to-noise ratio improvement over the optimum classical scheme in an entanglement-breaking environment plagued by 14 dB of loss and a noise background 75 dB stronger than the returned probe light. Our result suggests that advantageous quantum-sensing technology could be developed for practical situations.