singlefotonilähteitä

Single-photon sources are devices or physical systems that emit exactly one photon at a time upon excitation. This ability to deterministically emit single photons is crucial for various quantum technologies, including quantum communication, quantum computing, and quantum metrology. Unlike conventional light sources that emit photons in random bursts, single-photon sources provide a well-defined quantum state.

Several physical systems can act as single-photon sources. Quantum dots, which are semiconductor nanocrystals, exhibit quantum confinement, leading to discrete energy levels. When excited, they can emit a single photon as they transition from an excited state to a lower energy state. Defects in diamond, such as the nitrogen-vacancy (NV) center, are another prominent example. These defects can be optically manipulated to emit single photons. Trapped ions and neutral atoms, when cooled and precisely controlled, can also serve as reliable single-photon emitters through controlled excitation and decay processes. Superconducting circuits, utilizing the properties of superconducting qubits, offer another avenue for generating single photons, particularly in the microwave regime.

The performance of a single-photon source is typically characterized by several key parameters. Indistinguishability, the degree to which emitted photons are identical in all properties, is vital for interference-based quantum protocols. Purity refers to the spectral and temporal purity of the emitted photon. Efficiency measures the probability of generating a photon when triggered. Finally, the g(2)(0) value, which quantifies photon bunching, should ideally be close to zero for a perfect single-photon source, indicating that no two photons are emitted simultaneously.