Exploiting Entangled two-photon absorption – E2TPA

Entangled two-photon absorption (ETPA) is a rapidly emerging technique for studying atoms and molecules, especially in low photon flux regimes. It has similarities to both classical single- and two-photon absorption techniques, which are cornerstones of modern optical imaging, but the quantum correlations, or photon-pair entanglement, also brings novel characteristics to investigate other physical regimes, e.g., in studying intermediate and virtual level transitions and dynamics. There is a long-standing theoretical basis and an increasing number of experimental demonstrations, although gaps remain between them. This project aims to fill these missing links. On the theory side we plan to develop a fully quantum description of the light matter interaction for ETPA, allowing for better system design and application targeting. A limiting factor for current experiments is the signal-to-noise levels. We address this on the theory level, not only through a more complete model bridging conceptual approaches from quantum optics and physical chemistry where ETPA has been explored, but also designing nanoparticles for optimising excitation and collection efficiencies. On the experimental side, we will design and fabricate periodically poled lithium niobate sources for efficient broadband photon pair generation, as well as developing custom lasers, to improve ETPA rates. Experimentally, we have already demonstrated ETPA via fluorescence measurements and will further advance this, as well as develop a transmission-based correlation measurement scheme for complementary measurements. We will survey potential end-users and develop a toolkit to facilitate system design and describe the application potential for quantum-enhanced microscopy and quantum spectroscopy.



  • Coordinator: Rob Thew (University of Geneva, CH)
  • Christine Silberhorn (Paderborn University, DE)
  • Andreas Bülter (PicoQuant, DE)
  • Karolina Słowik (Nicolaus Copernicus University, PL)
  • Alexandra Olaya-Castro (University College London, UK)


PROJECT WEBSITE: https://www.unige.ch/etpa/

Call year

Call 2021

Call topic

Applied Quantum Science

Area of research

Quantum metrology sensing and imaging

Start date

May 2022


36 months

Funding support

€ 889 329

Project status

In Progress