Entanglement Boosts Spectroscopy
From atomic clocks to environmental sensors, many technologies rely on light sources called optical frequency combs. These devices produce spectra of equally spaced lines—akin to a hair comb’s teeth—that can be used for spectroscopic measurements. For a typical comb, the speed and precision of these measurements are limited by noise, which is caused by the light’s inherent quantum fluctuations. Now Zheshen Zhang at the University of Michigan and his colleagues have demonstrated how entanglement can be used to suppress this noise for faster, more precise measurements [1].
The researchers combined the light from an ordinary optical frequency comb with that from a specially engineered one in which many pairs of frequency lines were entangled. They then sent the resulting bright, entangled light through a gas sample, where the light picked up the gas’s absorption signature. Lastly, they compared the light leaving the sample with that from a reference comb to measure the gas’s absorption spectrum. This measurement process exploited the correlations between the entangled frequency lines to make the quantum noise partly cancel out.
To verify the effectiveness of their technique, Zhang and his colleagues repeated their experiment but started with two ordinary combs. They found that their entanglement-based approach increased the signal-to-noise ratio by 80% and cut the time needed to measure the absorption spectrum by 40%. They say that their technique could have uses in metrology and timekeeping and is well suited for dynamic chemical and biological sensing, which often need fast, precise measurements under strong power constraints.
–Ryan Wilkinson
Ryan Wilkinson is a Corresponding Editor for Physics Magazine based in Durham, UK.
References
- A. Hariri et al., “Entangled dual-comb spectroscopy,” Phys. Rev. X 15, 041009 (2025).