Single-Photon Emission from Semiconductor Quantum Dots

Semiconductor quantum dots are nanoscale crystals that confine charge carriers in all three spatial dimensions, yielding discrete energy levels akin to artificial atoms. When optically or electrically excited, a single exciton within a quantum dot can recombine to emit a solitary photon on demand. Such sources combine high brightness, low multiphoton probability and the capacity for integration into photonic circuits, rendering them prime candidates for applications in quantum communication, quantum computing and quantum metrology. Key challenges have included controlling the local solid-state environment to suppress spectral diffusion and charge noise, engineering photonic structures to enhance emission rates and collection efficiencies, and extending operation into the technologically important telecom wavelengths. Advances in microcavities, strain tuning and heterogeneous integration have enabled Purcell-enhanced emission, near-transform-limited linewidths and sub-percent multiphoton contributions. At the same time, frequency conversion techniques have bridged quantum-dot emission to fibre-optic networks, facilitating long-distance quantum key distribution and on-chip quantum networks. Together, these developments underscore the global significance of quantum-dot single-photon sources as scalable building blocks for next-generation quantum technologies.

Research from Nature Portfolio

Recent studies have demonstrated fibre-based quantum key distribution over record distances by employing frequency-converted quantum-dot single photons at telecom wavelengths. By optimising finite-key analysis and using a high-rate solid-state source, secure key rates were realised over spans exceeding 175 km, with sub-5% multiphoton contributions and megahertz-level detection counts. Foundational work on deterministic fabrication of three-dimensional microlenses positioned above pre-selected quantum dots has achieved photon-extraction efficiencies approaching 25% and single-photon purity with second-order coherence values below 0.03. These microlenses preserve high indistinguishability even under pulsed excitation beyond saturation, thereby laying the groundwork for scalable, high-flux non-classical light sources in integrated photonic platforms.

Research from all publishers

A recent design of a cavity-enhanced and strain-tuned GaAs quantum dot embedded in a circular Bragg resonator has achieved simultaneous high brightness and entanglement fidelity. Mechanical strain provided by a piezoelectric actuator fine-tunes the quantum dot emission, yielding extraction efficiencies near 70% and entangled-photon fidelities above 0.95. In parallel, an intercity quantum key distribution experiment using a bright, deterministic quantum-dot source in a circular Bragg grating has demonstrated record-high secret key rates over 79 km of deployed fibre, corresponding to losses equivalent to 130 km of standard telecom fibre. The approach attained asymptotic secret key rates with low quantum bit error ratios, highlighting the potential of on-demand solid-state emitters to augment measurement-device-independent protocols and future quantum repeater infrastructures.

Single-Photon Emission from Semiconductor Quantum Dots publication trend

The graph below shows the total number of articles in single-photon emission from semiconductor quantum dots across all publications each year (not limited to Nature Index journals).

Technical terms

Semiconductor quantum dot: A nanocrystal confining electrons and holes in three dimensions, producing discrete energy levels for controlled photon emission.

Single-photon emission: Generation of exactly one photon per excitation cycle, with negligible probability of multi-photon events.

Second-order coherence (g²(0)): A statistical measure of photon correlations at zero time delay; values below 0.5 indicate predominantly single-photon emission.

Photon extraction efficiency: The proportion of emitted photons successfully collected by an external optical system.

Quantum key distribution (QKD): A secure communication protocol that uses quantum states of light to establish encryption keys immune to eavesdropping.

Indistinguishability: The degree to which photons are identical in all quantum degrees of freedom, enabling two-photon interference and entanglement protocols.

References

1. Progress in quantum-dot single photon sources for quantum information technologies: A broad spectrum overview. Applied Physics Reviews (2020).
2. Single-emitter quantum key distribution over 175 km of fibre with optimised finite key rates. Nature Communications (2023).
3. Highly indistinguishable photons from deterministic quantum-dot microlenses utilizing three-dimensional in situ electron-beam lithography. Nature Communications (2015).
4. A source of entangled photons based on a cavity-enhanced and strain-tuned GaAs quantum dot. eLight (2024).
5. High-rate intercity quantum key distribution with a semiconductor single-photon source. Light: Science & Applications (2024).