Quantum metrology, which uses entangled photons to make more precise measurements, has generated enormous interest over the last few decades as a way to advance imaging, quantum information processing and quantum computing, among other applications.

In what’s called parametric scattering, a laser beam strikes an optical crystal to convert a high-energy photon into a pair of entangled lower energy photons. The challenge is resolving more than two photons in a light signal. Quantum technologies are highly susceptible to photon losses due to shot noise, or random light fluctuations, and the fragile nature of multiphoton entangled states.

You et al. show how up to 10 photons can be resolved with 80% accuracy. The researchers achieved this by combining a more efficient source of parametric scattering with a superconducting transition edge sensor (STES), a photon-number-resolving detection scheme capable of counting all the individual photons in a single signal.

Adding STES for photon identification dramatically increases the likelihood of decoding information in all the produced entangled photons with high efficiency, something that has not been previously accomplished.

“Our multiphoton method opens the possibility of estimating small physical parameters with supreme quantum sensitivity,” co-author Omar S. Magaña-Loaiza said. “The goal is utilizing all the generated photons and not discarding them.”

The researchers hope to advance the work for the development of nanoscale sensing devices and high-efficiency quantum imaging.

Source: “Scalable multiphoton quantum metrology with neither pre- nor post-selected measurements,” by Chenglong You, Mingyuan Hong, Peter Bierhorst, Adriana E. Lita, Scott Glancy, Steve Kolthammer, Emanuel Knill, Sae Woo Nam, Richard P. Mirin, Omar S. Magaña-Loaiza, and Thomas Gerrits, Applied Physics Reviews (2021). The article can be accessed at https://doi.org/10.1063/5.0063294.