sf.ops.MeasureX¶
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MeasureX= <strawberryfields.ops.MeasureHomodyne object>¶ Performs a homodyne measurement, measures one quadrature of a mode.
Position basis measurement: \(\phi = 0\) (also accessible via the shortcut variable
MeasureX).Momentum basis measurement: \(\phi = \pi/2\). (also accessible via the shortcut variable
MeasureP)
The measured mode is reset to the vacuum state.
- Parameters
phi (float) – measurement angle \(\phi\)
select (None, float) – (Optional) desired values of measurement result. Allows the post-selection of specific measurement results instead of randomly sampling.
Details and Conventions
Definition
Homodyne measurement is a Gaussian projective measurement given by projecting the state onto the states
\[\ket{x_\phi}\bra{x_\phi},\]defined as eigenstates of the Hermitian operator
\[\hat{x}_\phi = \cos(\phi) \hat{x} + \sin(\phi)\hat{p}.\]In the Gaussian backend, this is done by projecting onto finitely squeezed states approximating the \(x\) and \(p\) eigenstates. Due to the finite squeezing approximation, this results in a measurement variance of \(\sigma_H^2\), where \(\sigma_H=2\times 10^{-4}\).
In the Fock backends, this is done by using Hermite polynomials to calculate the \(\x_\phi\) probability distribution over a specific range and number of bins, before taking a random sample.