Quasikoherente

Quasikoherente is a term used primarily in quantum optics and quantum mechanics to describe quantum states that are nearly coherent but do not strictly satisfy all the mathematical properties of true coherent states. In the formalism of quantum electrodynamics, a coherent state is an eigenstate of the annihilation operator with a complex amplitude, and it exhibits minimal quantum uncertainty. Quasikoherente states approximate these conditions while introducing slight deviations such as phase diffusion or amplitude modulation.

The defining characteristic of a quasikoherente state is its close resemblance to a coherent state in terms of its photon-number distribution and temporal coherence. However, the variance in photon number may be slightly larger than that of a coherent state, and the phase may fluctuate more rapidly. These deviations are often quantified using parameters such as the Mandel Q‑parameter or the second‑order correlation function g^(2)(0). When Q≈0 and g^(2)(0)=1, the state is effectively coherent; small positive Q or g^(2)(0) slightly larger than 1 indicates quasikoherente behavior.

Quasikoherente states appear in many practical optical systems. For instance, lasers operating near threshold or under the influence of technical noise can generate light that is quasikoherente rather than perfectly coherent. Similarly, atomic ensembles in cavity QED experiments can produce squeezed or partially coherent photon states that fall within this intermediate regime. In quantum information processing, quasikoherente light sources are used when perfect coherence is unattainable but high degrees of phase stability are required for protocols such as continuous‑variable quantum key distribution.

The study of quasikoherente states bridges the gap between idealized coherent light and more complex quantum states. It enables a refined understanding of noise processes, decoherence mechanisms, and the transition between classical and quantum behavior in optical systems. By characterizing these near‑coherent states, researchers can better design photonic devices, improve laser stability, and develop robust quantum communication technologies.