Quantum Zeno effect

The suppression of a quantum system’s evolution by sufficiently frequent measurements. In the ideal limit, repeated measurements can keep a system in its initial state.

Quantum measurement: A physical interaction that produces an outcome associated with an observable of a quantum system. The effect depends on how repeated measurements alter the system’s state.
Misra–Sudarshan theorem: A mathematical result showing that continuous observation can inhibit transitions in suitable quantum systems. It gave the effect a rigorous formulation beyond the original paradox.
Quantum Zeno dynamics: Constrained evolution within a subspace enforced by frequent measurements or strong coupling. It generalizes freezing a state to controlling motion within a measured subspace.
Quantum anti-Zeno effect: Acceleration of quantum transitions caused by repeated measurements or monitoring at particular intervals. Unlike Zeno suppression, some measurement schedules increase the transition rate.
Quantum state: A mathematical description encoding the possible outcomes of measurements on a quantum system. Repeated measurements constrain the state’s evolution.
Baidyanath Misra: A mathematical physicist who co-formulated the quantum Zeno effect with George Sudarshan. Misra helped establish the theorem that formalized the effect.
Quantum Zeno subspace: A subspace in which a quantum system can evolve while frequent measurements suppress transitions out of it. The effect can confine dynamics rather than halt it entirely.
Continuous quantum measurement: Monitoring a quantum system continuously through a measurement interaction with finite strength and resolution. It can yield Zeno-like suppression without ideal instantaneous measurements.
Quantum projection postulate: A rule that assigns a measured quantum system to an eigenstate of the measured observable. The idealized effect follows from repeatedly projecting onto the initial state.
George Sudarshan: A theoretical physicist whose work spanned quantum theory, particle physics, and mathematical physics. His collaboration with Misra gave the effect its foundational mathematical treatment.

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