quantum mechanics Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, ...

, back action refers to the effect of a

detector A sensor is a device that produces an output signal for the purpose of sensing a physical phenomenon. In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends ...

on a measurement. Ideally, a detector should have no influence on the quantity it is measuring. However, in quantum systems it is sometimes the case that back action by the detector is an inherent feature of the system, and not just a result of the detector being imperfect. Back action has important consequences for the measurement process, and is a significant factor in measurements near quantum limits, such as measurements approaching the

Standard Quantum Limit A quantum limit in physics is a limit on measurement accuracy at quantum scales. Depending on the context, the limit may be absolute (such as the Heisenberg limit), or it may only apply when the experiment is conducted with naturally occurring qua ...

(SQL). Back action is an area of active research. Recent experiments with nanomechanical systems have attempted to evade back action while making measurements.

References

Quantum mechanics {{quantum-stub