Flerfotons

Flerfotons, or flerfotoner in Swedish, is a term used in quantum optics to describe systems or states that contain multiple photons. It is a descriptive concept rather than a single fundamental particle, covering two-photon, three-photon, and generally n-photon states. Photons in these states can be prepared, detected, and manipulated using various optical techniques.

In practice, flerfoton states arise from nonlinear optical processes such as spontaneous parametric down-conversion, four-wave mixing, or cavity quantum electrodynamics setups. These processes generate correlated photons and enable control over photon number, timing, and quantum statistics. In some contexts, researchers explore bound or quasi-bound photonic states and “photon molecules” in media where effective interactions between photons are mediated by the medium’s nonlinear response or by strong atomic interactions (for example, via Rydberg blockade). In vacuum, direct photon-photon interactions are extremely weak, so truly bound states are not established, and any observed multiphoton behavior typically relies on the optical medium.

Measurement and characterization of flerfotons rely on photon counting, coincidence detection, and analysis of photon statistics, including Hanbury Brown–Twiss correlations and state tomography. Applications include quantum information processing, quantum communication, quantum imaging, and precision metrology, where precise control of multiphoton states enables protocols that surpass classical limits. Challenges remain, including losses, decoherence, and scalable generation of high-purity multis photon states.

See also: multiphoton processes, entangled photon pairs, photon statistics, quantum optics.