Single-Molecule Quantum Photonics

Single-molecule quantum photonics explores how individual molecular emitters interact with and control light at the quantum level. Organic dye molecules or polycyclic aromatic hydrocarbons cooled to cryogenic temperatures can behave as Fourier-limited two-level systems, emitting single photons on demand with high purity, stability and coherence. By coupling these molecules to optical resonators, waveguides or plasmonic nanocavities, researchers achieve strong light–matter interactions manifested as vacuum Rabi splitting, large extinction of incident fields and nonlinear optical effects at the single-photon level. Advances in positioning, tuning and coherent control of these emitters underpin the development of integrated quantum photonic circuits, secure communication channels and quantum sensing devices. Key challenges include spectral inhomogeneity, dipole alignment, and fabrication of low-loss nanoscale photonic components. Recent work has demonstrated collective and interference phenomena among a few coupled molecules, selective excitation of entangled states and generation of indistinguishable photons, laying the groundwork for scalable quantum information processing and on-chip quantum light sources.

Research from Nature Portfolio

Recent studies have achieved controlled coupling of molecular emitters and precise spatial arrangement necessary for complex photonic architectures. One team demonstrated hyperspectral imaging of coherently coupled dibenzanthanthrene molecules, revealing superradiant and subradiant entangled states by tuning optical resonances with a Stark field. Far-field selective excitation of the long-lived subradiant mode and optical nanoscopy mapped individual emitters, showcasing the ability to tailor quantum interferences for quantum information schemes. Another advance introduced electrohydrodynamic nanoprinting to deposit and orient single organic molecules with sub-wavelength positioning accuracy in a crystalline host. Arbitrary patterns were written to couple molecules to the near fields of nanostructures, achieving high yield and photostability. This method provides a scalable route to integrate single-molecule sources into hybrid photonic devices and on-chip circuitry.

Single-Molecule Quantum Photonics publication trend

The graph below shows the total number of articles in single-molecule quantum photonics across all publications each year (not limited to Nature Index journals).

Technical terms

Superradiant state: A collective excited state of coupled emitters that decays faster than isolated emitters due to constructive interference of their dipole emissions.

Subradiant state: A collective excited state of coupled emitters that decays more slowly than isolated emitters due to destructive interference of their dipole emissions.

Dipole–dipole interaction: The coupling between two quantum emitters arising from the electromagnetic field of one acting on the transition dipole of the other.

Electrohydrodynamic nanoprinting: A non-contact technique using electric fields to deposit charged droplets containing single molecules with sub-wavelength positional control.

Vacuum Rabi splitting: The energy level splitting observed when a single quantum emitter strongly couples to a resonant cavity mode, indicating coherent exchange of quanta.

Sum-frequency generation (SFG): A nonlinear optical process in which two input photons at different frequencies combine within a medium to produce a photon at the sum of those frequencies.

Photon antibunching: A signature of single-photon emission where the probability of detecting two photons simultaneously is suppressed, often quantified by the second-order coherence g⁽²⁾(0) < 1.

References

1. Tailoring the superradiant and subradiant nature of two coherently coupled quantum emitters. Nature Communications (2022).
2. Nanoprinting organic molecules at the quantum level. Nature Communications (2019).
3. On-chip interference of scattering from two individual molecules. Optica (2023).
4. Photon antibunching in single-molecule vibrational sum-frequency generation. Nanophotonics (2025).
5. Single-Molecule Vacuum Rabi Splitting: Four-Wave Mixing and Optical Switching at the Single-Photon Level. Physical Review Letters (2021).