Quantum optics
Can a laser write single-atom-scale light sources?
Open access · cc by · source: Europe PMC
Firing laser pulses just above a carefully measured damage threshold made defects smaller than 5 nm in boron nitride, and nearly every spot became a single, bright, stable source of individual photons.
Study at a glance
- Design
- Other — Femtosecond laser writing of defects in exfoliated hBN flakes near a multi-shot-extrapolated threshold, followed by annealing and single-photon characterisation
- N
- No single N: 16-site array for single-emitter yield, 150 emitters for g2(0) statistics, 200 emitters for stability, roughly ten thousand centres for the wavelength histogram
- Population
- Laser-written colour centres in mechanically exfoliated hexagonal boron nitride flakes
- Outcome
- Feature size (TEM), number of emission peaks, single-photon purity g2(0), brightness, and photostability
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Key findings
The extrapolated intrinsic threshold was 4.65 nJ, and single pulses near it produced features below 5 nm, consistent with a statistical-uncertainty estimate of about 3 nm. Lowering pulse energy reduced the number of emission peaks per site from more than ten to one, and g2(0) fell from 0.48 to 0.09. In the single-emitter array 15 of 16 sites were single-colour emitters, most emitters were brighter than 5 million counts per second, and 94% of 200 tested emitters showed negligible spectral diffusion or blinking.
Methodology
The authors varied the number of femtosecond pulses and pulse energy on hBN flakes to find the energy at which damage first appears if infinitely many shots were used (threshold tracking and lock-in). They then wrote defects with single pulses just above that threshold, annealed the flakes at high temperature, and imaged the sites by TEM and photoluminescence. They measured photon antibunching (g2), saturation brightness, polarisation and emission stability, and built a demo device with an hBN flake on a blue laser diode.
Limitations
The emission wavelength could not be controlled: centres were spread broadly across roughly 560 to 750 nm, and the defect structures behind them were not identified. The g2 values were not background-corrected and vary between emitters, so not every site is a high-purity single-photon source. The link between the 3 nm uncertainty estimate and the observed sub-5 nm features is a rough scaling argument, and TEM morphology varied from spot to spot. Annealing was essential for any emission, so the laser step alone does not create active emitters.
How this study connects
Role on claims
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Emitters can be made on demand and tuned electrically.
Single-photon emitters can be engineered and controlled: laser-written hBN defects near threshold gave single emitters with g2(0) down to 0.09 and 94% of 200 emitters with negligible spectral diffusion, and charging CdSe/CdS dots electrochemically sped emission up to 140-fold while keeping single-photon emission above -1.8 V.
Evidence for the claim as stated.
Emitters can be made on demand and tuned electrically.
Single-photon emitters can be engineered and controlled: laser-written hBN defects near threshold gave single emitters with g2(0) down to 0.09 and 94% of 200 emitters with negligible spectral diffusion, and charging CdSe/CdS dots electrochemically sped emission up to 140-fold while keeping single-photon emission above -1.8 V.
Scope note — Emission wavelength not controlled.
Limits the claim's scope: a different population, assay, or outcome.
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