photonnumbersplit

Photon number splitting is a phenomenon that can occur in certain quantum optical experiments, particularly those involving photon sources that are not ideal single-photon sources. When a non-ideal source emits a photon, there is a possibility that the emission process actually produces more than one photon, often a pair of photons. This deviation from the intended single-photon emission is referred to as photon number splitting.

This effect is problematic because many quantum information protocols, such as quantum key distribution or linear optical quantum computing, rely on the precise generation and manipulation of single photons. If a source is intended to emit one photon but instead emits two or more, the subsequent operations will be performed on an incorrect number of photons, leading to errors and reduced performance.

Photon number splitting can arise from various physical mechanisms depending on the specific type of photon source. For instance, in spontaneous parametric down-conversion (SPDC), which is commonly used to generate entangled photon pairs, there is a non-zero probability of generating two pairs of photons, or higher-order multi-photon states. Similarly, in attenuated laser sources, which are often used as practical approximations of single-photon sources, the Poissonian distribution of photon numbers means that even after attenuation, there is a chance of emitting more than one photon.

Mitigating photon number splitting is crucial for the successful implementation of many quantum technologies. Techniques to reduce its impact include improving source design and using post-selection methods to identify and discard events where multiple photons were detected. Understanding and controlling photon number splitting is an active area of research in quantum optics and quantum information science.