Back action (quantum)

(Quantum) back action refers (in the regime of Quantum systems) to the effect of a detector on the measurement itself, as if the detector is not just making the measurement but also affecting the measured or observed system under a perturbing effect. Back action has important consequences on the measurement process and is a significant factor in measurements near the quantum limit, such as measurements approaching the Standard Quantum Limit (SQL).

Back action is an actively sought-after area of interest in present times. There have been experiments in recent times, with nanomechanical systems, where back action was evaded in making measurements, such as in.