Atomic, Molecular, Optical Science

AMOS Journal Club

Photon correlations as a probe of photosynthetic light-harvesting complexes (Hadar Kaslasi)

In photosynthetic organisms, light-harvesting pigment-protein complexes capture sunlight and transfer excitation energy with remarkable efficiency. Conventional methods probe their dynamics through classical emission properties - intensity, spectra and lifetime. However, treating emitted photons as quantum objects and measuring their correlations provides access to fundamentally different information: the nature of the emitting state, whether a multi-pigment complex behaves as a single emitter, and how emitted photon statistics are affected by excitation source properties.
In this talk, recent applications of these techniques to photosynthesis, focusing on two ensemble studies, will be presented. Using a heralded single-photon source, Li et al. (Nature 2023)1 provide experimental support in LH2 complexes from purple bacteria to a long-standing assumption - that photosynthesis can be initiated by a single photon. In a follow-up study (Sci. Adv. 2025)2, the same setup was used to compare single-photon and pseudothermal excitation, finding that while fluorescence lifetime and quantum efficiency are unchanged, the photon statistics of the emitted light preserve those of the excitation.
1.    Li, Q. et al. Single-photon absorption and emission from a natural photosynthetic complex. Nature 619, 300–304 (2023).
2.    Li, Q., Ko, L., Whaley, K. B. & Fleming, G. R. Comparing photosynthetic light harvesting of single photons and pseudothermal light under ultraweak illumination. Sci. Adv. 11, eadz2616.

Trapping and Cooling of Single Nitrogen Molecular Ions (Idan Hochner)

Molecules offer a rich quantum structure, with rotational, vibrational, electronic, and isomeric degrees of freedom that are absent in atomic systems. Diatomic homonuclear molecular ions, such as N2+, combine this rich internal structure with comparatively simple spectra and long-lived states, making them promising platforms for precision molecular physics.
Many of the techniques required to probe and control such systems—state preparation, coherent manipulation, precision spectroscopy, and motional ground-state cooling—are well established in atomic and atomic-ion experiments, where they underpin advances in metrology and quantum information science. Extending these methods to molecules would open new opportunities for quantum control of molecular degrees of freedom, but remains experimentally challenging. In particular, molecular ions must be prepared in a well-defined internal state, detected with high fidelity, and cooled to the ground-state of their external motion.

I will present our experimental setup for quantum control of single molecular ions. Our approach focuses on preparing individual N2+ ions in the electronic and rovibrational ground state, trapping them alongside atomic ions, and cooling their motion to the quantum ground state. I will describe our progress toward these goals and discuss a planned detection method based on a state-dependent optical dipole force, which provides a route to nondestructive internal-state readout.

I. Hochner,1 T. Shahaf,1 D. Einav,1 O. Barnea,1 E. Kipiatkov, and Z. Meir1
1Weizmann Institute of Science, Rehovot, Israel