Readout State Preparation and Quantum Non-Demolition

  • W. G. Unruh
Part of the NATO Advanced Science Institutes Series book series (NSSB, volume 94)


The purpose of this article is to show that if one can prepare the initial state of the readout system appropriately, one can at times perform better (i.e. more accurate) measurements of a classi cal force acting on a harmonic oscillator than one can with quantum non-demolition or back action evading techniques. One can, for example; measure both phases of the classical force on one oscillator with “arbitrary” accuracy with a simple amplitude coupling to the harmonic oscillator. However, in the process the ideas behind “quantum non-demoliton” are not being abandoned but are being applied to the readout system in a more complex fashion. This paper will provide two examples of such a readout preparation, the first to demonstrate the possibility of measuring both phases of a classical force arbitrarily accurately on a “one shot” basis and the second to demonstrate a system which could perform such a measurement in a continuous manner.


Wave Packet Harmonic Oscillator Gravity Wave Dynamic Variable Fourier Amplitude 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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  1. 1.
    See the superb list of references on quantum non-demolition which have been compiled by C. Caves in his lecture notes in this volumeGoogle Scholar
  2. 2.
    See for example W. G. Unruh, Physics Review D 19 2888 (1979).Google Scholar

Copyright information

© Plenum Press, New York 1983

Authors and Affiliations

  • W. G. Unruh
    • 1
  1. 1.Department of PhysicsUniversity of British ColumbiaVancouverCanada

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