Entangled Two-Photon Spectroscopy (eTPA)
Two-photon spectroscopy is powerful, but inefficient. The large optical power required is sometimes too much for delicate organic compounds. Using entangled photon pairs has long been rumored to improve the efficiency of the process, but as it turns out, things aren’t as straight forward.
The idea of supplying exactly two photons at a time for a process that requires two photons seems great. As it turns out, there is an improvement compared to classical, non-entangled light from a laser, but in most cases it’s not useful and only present at a flux so low, there isn’t a signal to measure. This makes eTPA impossible to harness in most situations. In this project - carried out primarily by graduate student Tiemo Landes - we had to confront this fact and convince the spectroscopy community of our findings, contradicting a 20-year legacy of literature saying otherwise. Now we’ve moved on to finding new ways of how quantum states of light can be used to enhance spectroscopy based on TPA.
My role in the project
With Tiemo doing most of the heavy lifting in the lab, and Tiemo and Mike Raymer taking care of the theory work, my main role was in the beginning. When we first discovered that eTPA wasn’t as straight-forward and useful as we thought, I designed an experiment that would test the limits and put limits on the enhancement achieved by entangled photon pair.
After helping that experiment and publications along, I still assist in designing new experiments and writing papers that hopefully end in a practical application.
With my focus on new sensing techniques based on light and quantum optical techniques in particular, this is still one of my favorite projects to ever work on as it relies on all of the quantum optics tools in our arsenal - photon counting, pair sources, nonlinear processes, ultrafast optics.
Publications:
Tiemo Landes, Markus Allgaier, Sofiane Merkouche, Brian J. Smith, Andrew H. Marcus, and Michael G. Raymer, “Experimental feasibility of molecular two-photon absorption with isolated time-frequency-entangled photon pairs”, Phys. Rev. Research 3, 033154 (2021)
Tiemo Landes, Michael G. Raymer, Markus Allgaier, Sofiane Merkouche, Brian J. Smith, and Andrew H. Marcus, "Quantifying the enhancement of two-photon absorption due to spectral-temporal entanglement," Opt. Express 29, 20022-20033 (2021)
Michael G. Raymer, Tiemo Landes, Markus Allgaier, Sofiane Merkouche, Brian J. Smith, and Andrew H. Marcus, "How large is the quantum enhancement of two-photon absorption by time-frequency entanglement of photon pairs?," Optica 8, 757-758 (2021)