Back-Action Evasion as an Alternative to Impedance Matching

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Science  26 Apr 1991:
Vol. 252, Issue 5005, pp. 528-532
DOI: 10.1126/science.252.5005.528


Back-action evasion is a measurement technique originally devised to overcome certain limits imposed by quantum mechanics on the sensitivity of gravitational radiation detectors. The technique is, however, more generally applicable and can be used to improve the sensitivity of instrumentation with noise floors much greater than the quantum noise floor. The principle of back-action evasion is described here by means of a simple example. A comparison of back-action evasion with impedance matching is made to clarify when back-action evasion may be useful. Back-action evasion allows one to achieve a sensitivity comparable to that achieved by impedance matching.