An international team of engineers and physicists has made a groundbreaking advancement that could revolutionize the field of time-domain spectroscopy. By incorporating quantum light into the process, the team has significantly enhanced the technique’s sensitivity, potentially opening doors to new applications in security, medical diagnostics, and beyond.
The development focuses on improving the way infrared electric fields are measured, making the process up to twice as sensitive as previous methods. This improvement holds immense promise for precision measurements of molecular compositions that are essential in a wide range of scientific and practical fields.
What is Time-Domain Spectroscopy?
Time-domain spectroscopy is a powerful technique that measures the properties of materials by analyzing how ultra-short laser pulses interact with them over time. These laser pulses pass through or reflect off samples, allowing researchers to observe molecular structures, their behavior, and composition. Time-domain spectroscopy is particularly valuable for investigating materials at the molecular level and provides a detailed look at their properties in a way other spectroscopy methods cannot.
Recent work, including that of 2023 Nobel Prize winner Ferenc Krausz and his team, has shown that time-domain spectroscopy can even be used to detect early signs of diseases, such as cancer, in blood samples. This makes the technique an invaluable tool in medical diagnostics, offering the potential for non-invasive and highly sensitive early detection of health conditions.
The Challenge of Classical Light in Time-Domain Spectroscopy
While time-domain spectroscopy is a promising technique, its reliance on classical light sources, such as lasers, has its limitations. One key limitation is the shot noise inherent in classical light. Shot noise is a type of random fluctuation in the intensity of light, which can interfere with the ability to measure subtle signals. Essentially, beyond a certain point, the noise overwhelms the signal, making it impossible to extract more information from the sample. This creates a ceiling for how sensitive the technique can be when using traditional light sources.
For time-domain spectroscopy to reach its full potential, overcoming the shot noise limitation is crucial. This is where the new approach introduced by the research team comes in.
The Quantum Light Solution
The team’s innovative solution involves quantum light, a form of light that behaves according to the principles of quantum mechanics. Quantum light allows for greater control over the noise properties of light, offering a way to bypass the limitations of classical light.
In their new approach, the researchers used pairs of laser pulses that are twinned through quantum mechanics. These paired pulses are correlated in a way that allows them to work together to measure an infrared field with significantly higher sensitivity than before.
While both of the paired beams are still affected by shot noise, the key advantage lies in the fact that the noise is equally mirrored in both beams. This symmetry allows for a novel technique where the measurements from one beam are subtracted from those of the other. By doing this, the shot noise that would normally mask subtle signals becomes effectively canceled out, revealing much clearer and more sensitive measurements.
As a result, the new quantum-enhanced method makes time-domain spectroscopy twice as sensitive as the classical methods, as it reduces the noise by approximately half. This allows researchers to detect even finer details in material properties and molecular structures that were previously hidden.
Potential Applications in Security and Medicine
The implications of this advancement are vast. Professor Matteo Clerici, the corresponding author of the paper and a professor at both the University of Glasgow’s James Watt School of Engineering and the University of Insubria, highlighted several potential applications for the new technique. In the near future, time-domain spectroscopy enhanced by quantum light could become a critical tool in various fields, including:
- Security: The ability to detect dangerous materials, such as explosives, in the air or on surfaces with unprecedented sensitivity could significantly improve security protocols, especially in high-risk environments.
- Medical Diagnostics: By enhancing the ability to detect and analyze biological samples, this quantum-enhanced technique could improve early disease detection, helping to identify serious conditions such as cancer at much earlier stages when treatment is most effective. It could also be used to analyze blood samples for specific molecular markers associated with disease.
- Material Science: The technique could provide deeper insights into the composition of materials, helping to identify contaminants or impurities at levels that were previously undetectable. This could have significant applications in chemistry, pharmaceuticals, and materials engineering.
Professor Clerici notes that this is just the beginning of what could be a major breakthrough in the field. “Although the technology is still developing,” he said, “time-domain spectroscopy could, in the future, help us better understand what materials are made of, detect contaminants or dangerous materials like explosives, or probe the concentration of molecules of serious diseases in patients’ blood samples.”
Next Steps: Enhancing Sensitivity Further
While the team’s quantum-enhanced technique already shows a remarkable increase in sensitivity, there’s more work to be done. Ph.D. students Dionysis Adamou and Lennart Hirsch from the University of Glasgow played a key role in developing the technique, and they are now focusing on the next steps: enhancing the sensitivity further.
To improve the technique beyond what has already been achieved, the team is likely to incorporate advanced interferometry techniques. Interferometry has been a cornerstone of gravitational wave detection, and applying similar techniques to time-domain spectroscopy could help push the sensitivity even further.
Researchers from Loughborough University and the University of Strathclyde also contributed to the development of the new technique, demonstrating the collaborative nature of this groundbreaking work. The team’s findings were published in the journal Science Advances under the paper title “Quantum-enhanced time-domain spectroscopy.”
Conclusion
The integration of quantum light into time-domain spectroscopy marks a pivotal moment in the evolution of this field. The team’s quantum-enhanced method has effectively doubled the sensitivity of the technique, enabling more precise measurements of molecular compositions and electrical fields in infrared light. This has the potential to advance multiple industries, from security to medicine, offering greater diagnostic capabilities and new insights into the properties of materials and biological samples.
As the technology continues to evolve, future breakthroughs in quantum measurement techniques could lead to even more sensitive instruments, pushing the boundaries of what can be measured and analyzed. With its wide-ranging applications and transformative potential, quantum-enhanced time-domain spectroscopy represents an exciting new frontier in both fundamental science and practical technologies.
Reference: Dionysis Adamou et al, Quantum-enhanced time-domain spectroscopy, Science Advances (2025). DOI: 10.1126/sciadv.adt2187