Single-photon source

Definition:
A single-photon source, also known as a single-photon emitter, is a light source that emits one photon at a time, rather than continuous streams or pulses of light. This distinguishes it fundamentally from classical light sources, such as lasers, which emit coherent light made up of many indistinguishable photons.

Scientific context:
Single-photon sources are essential for applications in quantum communication, quantum computing, and quantum metrology, where the precise control and detection of individual photons are required.

Example in practice:
In a QKD system based on the BB84 protocol, a single-photon source can be used to encode quantum bits (qubits) onto individual photons, enhancing security by ensuring that no more than one photon carries the key information. This prevents vulnerabilities such as photon number splitting attacks.

Did you know?
True deterministic single-photon sources are still a major area of research. Many systems today use probabilistic schemes to approximate single-photon emission under controlled conditions.