In quantum communication and computing, single photons are carriers of information that cannot be eavesdropped on or copied. Existing sources either require cryogenic temperatures, like epitaxial quantum dots, or suffer from instability and short lifetimes, like colloidal quantum dots. Alongside this work on the arXiv are studies of single photons from single molecules, atoms in chips, and optical cavities, all seeking a balance between brightness, stability, and ease of fabrication. This paper stands out: it takes a common, mass-produced material, C60, and shows that it can serve as a single-photon source without complex nanofabrication.
C60 molecules were dissolved in toluene with polystyrene, and a drop was spin-coated onto a gold substrate at 4000 rpm. This produced a thin film in which individual fullerene molecules were isolated from each other. Excitation was done with a 405 nm laser operating in continuous or pulsed mode with a pulse duration of 50 picoseconds. The emitted light around 620 nm was collected by an objective and directed into a Hanbury Brown and Twiss interferometer, where two detectors recorded photon coincidences. From the histogram of delays between events, the second-order correlation function g(2)(τ) was computed, which indicates whether photons are emitted one by one.
Under continuous excitation, the value of g(2)(0) was 0.304 ± 0.024, below the 0.5 threshold, confirming single-photon emission. Under pulsed excitation at 10 MHz, g(2)(0) = 0.308 ± 0.024, meaning photons are emitted on command. The exciton lifetime was about 4.5 ns, with a spread from 3 to 27 ns depending on the local environment of the molecule. The emission blinking, where the molecule switches between bright and dark states, follows a power law with exponent α = 0.369, indicating multi-level dynamics rather than a simple three-level model. The emission spectrum, peaking at 620 nm, is explained by photo-oxidation of C60: oxygen attachment breaks the symmetry and allows transitions that are forbidden in pristine fullerene.
This work differs from neighboring studies by using commercially available C60 instead of specially synthesized quantum dots or defects in diamond. This lowers the barrier to entry: no cryogenic temperatures or complex chemistry are needed. The short exciton lifetime promises high photon generation rates, important for quantum cryptography. However, the blinking and spread of lifetimes show that the molecules are sensitive to their environment, and practical applications will require control over oxidation and stabilization of the emitters.
One could investigate how the number of attached oxygen atoms affects brightness and stability. Chemical modification of fullerenes, for example by attaching functional groups, might suppress blinking and narrow the distribution of lifetimes. Embedding in optical resonators or photonic structures could accelerate emission and improve photon collection efficiency.
Quantum communication, quantum computing, quantum sensing.
Determine the exact composition of oxidized fullerenes C60On and study their photophysics in a controlled atmosphere.
The problem of stable and bright single emitters at room temperature remains open in quantum optics. Blinking and photobleaching limit the operational time of sources, and the spread of lifetimes indicates inhomogeneity in the local environment. Understanding the mechanisms of oxidation and degradation of molecules will help create sources with predictable properties.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
The study demonstrates that C60 molecules embedded in a polystyrene film emit single photons at room temperature with g(2)(0) around 0.3 under both continuous-wave and pulsed excitation. The exciton lifetime is about 4.5 ns with some spread, and blinking follows a power law with an exponent of 0.369. The emission spectrum, peaking at 620 nm, is attributed to photooxidation of the fullerene.
Where its strength is
Using commercially available C60 and a simple film fabrication method yields a cheap and scalable source of single photons at room temperature. The short exciton lifetime promises high generation rates.
Where it could go next
Worth trying
Why this may matter
If the emission can be stabilized and brightness increased, such sources could underpin affordable quantum communication devices operating at room temperature.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.54, against a usual 0.64. It looks like few have drilled nearby.
The C60 fullerene has the shape of a soccer ball: 60 carbon atoms form 12 pentagons and 20 hexagons. It was first synthesized in 1985, and the Nobel Prize in Chemistry was awarded in 1996 for this discovery.