POVMs for Infinite Dimensional Hilbert Spaces

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Discussion Overview

The discussion revolves around the construction and understanding of Positive Operator-Valued Measures (POVMs) in the context of infinite dimensional Hilbert spaces, particularly focusing on simultaneous measurements of position and momentum. Participants explore theoretical frameworks, relevant literature, and the implications of finite versus infinite dimensional settings.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses interest in modeling a POVM for simultaneous measurement of position and momentum, noting a lack of examples in the infinite dimensional setting.
  • Another participant suggests reviewing specific sections of a paper for relevant information on POVMs.
  • References to Arthurs-Kelly measurements are made, with links to related research articles that discuss joint measurements with correlated probes.
  • Concerns are raised about the appropriateness of finite dimensions for POVMs, with a participant arguing that while measurements yield discrete results, the formalism of POVMs can extend to infinite dimensions through continuum limits.
  • A distinction is made between finite valued POVMs and those acting on finite dimensional Hilbert spaces, with a request for clarification on the definition of discrete position measurements.
  • Another participant emphasizes the need to define "discrete position" and references their own work for further context.

Areas of Agreement / Disagreement

Participants exhibit a mix of agreement and disagreement regarding the applicability of finite versus infinite dimensional POVMs, with some asserting that finite dimensions are suitable in practice while others challenge this view by discussing the implications of infinite dimensions.

Contextual Notes

Participants note that the discussion is influenced by the definitions and assumptions surrounding measurements and POVMs, particularly in the context of quantum mechanics and quantum tomography.

jbergman
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TL;DR
Most discussion of POVM focus on examples on finite-dimensional Hilbert Spaces. How do we construct a POVM for multiple observables with continuous spectrum?
After reading up on some of the discussion in the Quantum Interpretations forums, I became interested in learning more about POVMs.

However, most of the examples are from the finite dimensional setting. If I wanted to model a POVM that approximately measures position and momentum simultaneously, how would I construct such a POVM?
 
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See Part IV https://journals.aps.org/pra/pdf/10.1103/PhysRevA.87.062112.
 
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Since measurements always produce discrete results, finite dimensions are quite appropriate for POVMs in practice; see the paper accompanying my Insight article Quantum Physics via Quantum Tomography.

Many examples of POVMs in infinite dimensional Hilbert spaces arise from them by taking a continuum limit.
 
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A. Neumaier said:
Since measurements always produce discrete results, finite dimensions are quite appropriate for POVMs in practice; see the paper accompanying my Insight article Quantum Physics via Quantum Tomography.
A finite valued POVM isn't the same as a POVM that acts on state vectors in finite dimensional Hilbert space is it?

For instance, if I want to measure a discrete position value.
 
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jbergman said:
A finite valued POVM isn't the same as a POVM that acts on state vectors in finite dimensional Hilbert space is it?
Yes, there is a difference. But for finite valued POVMs, the (finite or infinite) dimension of the Hilbert spaces does not really figure in the formalism.
jbergman said:
For instance, if I want to measure a discrete position value.
In this case you first need to define what you mean by discrete position. Maybe you find the setting in Sections 3.3-4 of my quantum tomography paper
  • A. Neumaier, Quantum mechanics via quantum tomography, Manuscript (2022). arXiv:2110.05294v3
convincing.
 

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