Back action (quantum)

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(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.[1][2] 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. There have been experiments in recent times, with nanomechanical systems, where back action was evaded in making measurements, such as by inches.[3]


  1. ^ Braginsky, V .B.; Khalili, F. Ya. (1992). Quantum Measurement. Cambridge University Press. ISBN 978-0521484138
  2. ^ Hartridge, M. et al., Quantum Back-Action of an Individual Variable-Strength Measurement, Science 339, 178 (2013),
  3. ^ Hertzberg, J. B. et al., arXiv/0906.0967,