Researchers develop a tool for characterizing frequency-entangled photon pairs

Frequency-entangled photon pairs, an easily accessible type of entanglement, have been widely applied in fields like quantum-enhanced positioning and clock synchronization, and quantum spectroscopy.

Recently, a research group led by Profs. Dong Ruifang and Zhang Shougang from the National Time Service Center (NTSC) of the Chinese Academy of Sciences has made a series of progress in nonlocal dispersion cancelation (NDC) and wavelength-to-time mapping with frequency-entangled photon pairs.

The researchers provided a full theoretical analysis and experimental examinations of the NDC characteristics for photon pairs with finite frequency entanglement. This offered an easily accessible tool for assessing and optimizing the NDC in various quantum information applications.

They also developed a hybrid frequency-time spectrograph combining a tunable optical filter and a dispersive element, which could be used for spectral measurement of the two-photon state.

Compared with the previous single-photon spectrograph utilizing the dispersive Fourier transformation technique, this method avoids the need of additional wavelength calibration and the electronic laser trigger for coincidence measurement. Its application would be extended to continuous wave pumped two-photon sources.

Furthermore, the researchers explored the resolution limit on nonlocal wavelength-to-time mapping with entangled photon pairs.

The results showed that the spectral bandwidth of the pump laser would become the dominated factor preventing the improvement of the spectral resolution when the involved group velocity dispersion (GVD) was large enough.

This provides an excellent tool for characterizing the resolution of a nonlocal wavelength-to-time mapping for further quantum information applications.

Results were published in Optics Express (Vol. 28, Issue 12), Optics Letters (Vol. 45, Issue 11), and Optics Express (Vol. 28, Issue 5), respectively.