A team led by University of Illinois Physics Professor Paul Kwiat has introduced a groundbreaking quantum interferometry tool capable of performing nanometer-scale measurements with unprecedented precision and speed, even in environments plagued by background noise and optical loss. This innovative approach harnesses the unique quantum characteristics of light—most notably, extreme color entanglement—to overcome the inherent shortcomings of classical and existing quantum measurement technologies. By exploiting these quantum phenomena, the research marks a significant leap forward in the capabilities of precision optical measurements.
At the core of this advancement lies the intertwining of quantum interference and entanglement, enabling the detection of minute differences in sample thickness and structure that have traditionally eluded classical interferometric methods. Graduate student and lead author Colin Lualdi highlights the transformative potential of this technique, explaining that it allows for measurements previously unattainable using standard approaches. This opens new horizons for fields ranging from medical diagnostics to environmental monitoring, where detecting subtle changes rapidly and accurately is crucial.
Classical optical interferometry, the prevailing standard for high-precision measurement, operates by splitting a light beam into two paths, reflecting each back, and analyzing the interference patterns that emerge based on the path differences. While powerful, these systems face significant challenges when dealing with thin or low-transmission samples, and their sensitivity is often compromised by background illumination. Such noise introduces inaccuracies that limit the efficacy of classical devices in real-world settings, particularly in outdoor or biologically sensitive environments.
Quantum two-photon interferometry offers a radical departure by treating light not as continuous waves but as discrete photons possessing entangled properties. In this setup, pairs of photons traverse separate arms of the interferometer, with one interacting with the sample and the other serving as a reference. The strength of this approach lies in how both photons are equally influenced by transmission losses, preserving the contrast of the interference signal and thereby maintaining measurement sensitivity where classical methods falter.
One of the most remarkable features of this quantum interferometer is its robustness against background light interference. By confining photon detection to an ultra-narrow temporal window on the order of 100 picoseconds, the system effectively filters out extraneous photons that do not arrive synchronously. This temporal precision ensures the high fidelity of the interference signature, allowing for reliable measurements even in brightly illuminated or noisy environments that would swamp classical instruments with irrelevant signals.
A significant hurdle that has limited quantum interferometry’s practicality until now has been the necessity for broad-spectrum photons or prolonged data collection periods to achieve nanometer-level resolution. Broad spectral bandwidth photons are technically difficult to generate and manipulate, and hours-long measurement sessions restrict the applicability of such technologies, particularly for dynamic or time-sensitive samples. Addressing these constraints is critical for transitioning quantum interferometry from the laboratory to widespread scientific and industrial use.
The innovation introduced by the Kwiat group circumvents these issues by utilizing pairs of narrow-bandwidth photons that are entangled across extreme differences in wavelength, a technique referred to as extreme color entanglement. This method amplifies the sensitivity of the interferometric measurement without resorting to unwieldy broad spectral ranges. By selecting two photons with widely separated but discrete colors, such as 810 and 1550 nanometers, the system achieves a heightened interferometric resolution in a more manageable and efficient manner.
This strategy not only simplifies experimental complexities but also yields a high rate of entangled photon pair generation, in the hundreds of thousands per second. This jump in photon flux accelerates measurement times dramatically, enabling swift and precise characterization of samples. Validation experiments measuring metallic thin films with low optical transmission demonstrated excellent agreement with independent atomic force microscopy assessments, confirming the accuracy and robustness of the quantum interferometric method.
Beyond rapid, high-precision thickness measurements, this technology’s non-invasive nature—requiring no physical contact or close proximity probes—expands its suitability for delicate biological samples, sensitive materials, and remote sensing applications. For instance, biological tissues such as retina or brain samples, which are highly vulnerable to photo-damage, could be examined more safely and comprehensively. Similarly, materials research, where precise nanoscale characterization is vital, stands to benefit enormously.
The Kwiat team envisions integrating this quantum interferometric technique with other measurement modalities, such as atomic force microscopy, to create multidimensional sensing platforms. This hybrid approach could unlock new insights into material properties and biological processes, fostering breakthroughs in both fundamental research and applied sciences. Moreover, the system’s ability to conduct rapid measurements opens the door to studying dynamic nanoscopic phenomena like surface vibrations, previously challenging to monitor in real time.
One of the more exciting possibilities arises from the method’s low light intensity, since entangled photons are generated in pairs rather than continuous beams. This feature makes it uniquely suited to investigating photosensitive organisms and tissues under conditions that avoid light-induced stress, a notable advantage over conventional imaging techniques dependent on bright illumination. Researchers foresee applications in environmental biology, neuroimaging, and even quantum-enhanced microscopy.
Ongoing research is exploring the device’s capability to detect nanometer-scale vibrations, a technically demanding task with existing tools. Here, the combination of high sensitivity and rapid data acquisition promises to resolve transient vibrational modes in mechanical and biological systems, providing deeper understanding of structural dynamics. Such advancements could impact a range of arenas including material fatigue testing, acoustics, and cellular biomechanics.
The interdisciplinary collaboration underpinning this breakthrough resulted from partnerships among physicists, electrical engineers, and materials scientists. Key contributors include graduate students, former students now working at NASA and Los Alamos National Laboratory, and faculty from various University of Illinois departments. The project also benefits from institutional support through the Illinois Quantum Information Science and Technology Center and the Holonyak Micro and Nanotechnology Laboratory, evidencing the collaborative nature of cutting-edge quantum research.
This work, supported by multiple U.S. government agencies including the Air Force and Department of Energy, embodies how fundamental quantum mechanical principles can be translated into practical, scalable technologies. The quantum limits of information extraction from physical systems, long posited in theoretical contexts, have here found concrete realization, equipping scientists and engineers with tools to push the boundaries of measurement science.
In sum, the quantum interferometer developed by the Kwiat group stands as a shining example of how exploiting entanglement and quantum interference can drive revolutionary advances in precision metrology. From probing fragile biological samples to enabling field measurements impervious to environmental noise, this technology heralds a new era in quantum-enhanced sensing with broad, transformative impacts anticipated across diverse scientific and industrial applications.
Subject of Research: Quantum-enhanced optical interferometry for precision measurement using extreme color entanglement of photons.
Article Title: Illinois physicists develop revolutionary measurement tool, exploiting quantum properties of light
News Publication Date: 21-May-2025
Web References:
- https://www.science.org/doi/10.1126/sciadv.adw4938
- https://mrl.illinois.edu/facilities
- https://iquist.illinois.edu/
- https://hmntl.illinois.edu/
References:
Paul Kwiat et al., “Illinois physicists develop revolutionary measurement tool, exploiting quantum properties of light,” Science Advances, DOI: 10.1126/sciadv.adw4938 (2025).
Image Credits: Liam Ramsey / University of Illinois
Keywords
Physical sciences, Materials science, Quantum interferometry, Precision measurement, Quantum optics, Entanglement, Optical sensing, Nanometer-scale measurement, Photonics, Quantum information science
