Quantum Light Spectroscopy

Photosynthetic complexes have near unit quantum efficiencies. To study these highly efficient systems and the fundamental properties of light-matter interactions, we are implementing a new single photon spectroscopic technique. Some questions to be investigated include: is a single photon absorbed whole i.e. as a "quantum jump" or are interactions with multiple photons necessary for an absorption event to take place? By studying single photon absorption statistics, we can generate a distribution of photons absorbed per fluorescence event wherein a high frequency of occurrence for low photons absorbed per fluorescence event would be seen as evidence of quantum jumps. 

For quantum light spectroscopy (QLS) we generate entangled photons from a non-linear crystal via spontaneous parametric down conversion (SPDC).These photons have (1) entangled polarizations, (2) correlated times, and (3) anti-correlated frequencies. These properties allow us to use the entangled photon pairs in a heralded single photon set up, ensuring that we are only observing the system dynamics in response to interaction with a single photon, rather than the billions from a conventional laser set up. Collaboration with K. Birgitta Whaley at UC Berkeley. 

Contact: Cheng Li, Lam Lam

Helpful Background Reading:

1. Frequency- and time-resolved second order quantum coherence function of IDTBT single-molecule fluorescence. Quanwei Li, Yuping Shi, Lam Lam, K. Birgitta Whaley, and Graham Fleming. (2026)

2. Quantum Light Spectroscopy.  Gregory D. Scholes, Quanwei Li,  K. Birgitta Whaley, and Graham R. Fleming ACS Centra

3. Single-photon absorption by single photosynthetic light-harvesting complexes. H.C.H Chan, O.E. Gamel,  G.R. Fleming, and K.B. Whaley, J. Phys. B: At. Mol. Opt. Phys., 51 (2018). 

4. Entangled Two-Photon Absorption Spectroscopy. F. Schlawin, K.E. Dorfman, and S. Mukamel, Acc. Chem. Res., 51 (2018).

5. Entangled Photon Excited Fluorescence in Organic Materials: An Ultrafast Coincidence Detector. O. Varnavski, B. Pinsky, and T.J. Goodson III, Phys. Chem. Lett., 8 (2017).

6. Measurement of the spectral properties of the two-photon state generated via type II spontaneous parametric downconversion. Y.-H. Kim, and W.P. Grice, Opt. Lett., 30 (2005).