Abstract
How can the state of a quantum system (the wave function, density matrix or Wigner function) be determined and how does it relate to the properties of the measuring system as well as the state under investigation? I will discuss the use of the concept of “propensity” in the comparison of a quantum state of interest with a reference state of some “quantum ruler”. I demonstrate how this is utilized in phase space measurements of nonclassical field states. In particular, I will show how the propensity approach may be used to determine the results of joint measurements of conjugate variables in 8-port homodyne measurements, which exhibit excess noise from the measurement process, noise derived in part from the quantum fluctuations of the ruler. I then discuss the use of squeezed ruler states and show how the propensity idea of joint measurements in phase space relates to the measurement of marginals in tomography which do not suffer from the excess noise problem and allow the Wigner function of the measured system alone to be reconstructed.
© 1996 Optical Society of America
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