Dephasing

Cavity loses coherence due to dephasing.

In physics, dephasing or phase damping is a loss of phase coherence between different states of a quantum system. It is a type of decoherence, and can contribute to loss of information in the system, even if no energy is exchanged.

In a quantum superposition, states have a relative phase responsible for interference effects. The phase relationship between different states stores information about the system. Dephasing can happen when a system becomes correlated to an external environment, instead of the system of interest. If a system has experienced significant dephasing, it ceases to behave like a coherent superposition with probabilities determined by quantum mechanics, and instead behaves like a classical probabilistic mixture of states. In this sense, decoherence recovers classical behaviour from a quantum system.

Dephasing is an important effect in molecular and atomic spectroscopy, in nuclear and magnetic resonance (NMR), in the condensed matter physics of mesoscopic devices, and in quantum information, specifically open quantum systems. In imaging and spectroscopy techniques such as MRI and NMR, dephasing can lead to decreased signal strength or image intensity. In quantum information, dephasing in a quantum processor can cause noise and loss of information, making quantum computation unreliable.