Causal State Updates in Real Scalar Quantum Field Theory

• URL: http://arxiv.org/abs/2106.09027v2
• Date: Thu, 13 Jan 2022 16:42:15 GMT
• Title: Causal State Updates in Real Scalar Quantum Field Theory
• Authors: I. Jubb
• Abstract summary: In relativistic Quantum Field Theory (QFT) ideal measurements of certain observables are physically impossible without violating causality. Here we formulate a necessary and sufficient condition that any measurement must satisfy to respect causality in real scalar QFT. We show how to do this using only causal measurements of smeared fields.
• Score: 0.0
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: In relativistic Quantum Field Theory (QFT) ideal measurements of certain observables are physically impossible without violating causality. This prompts two questions: i) can a given observable be ideally measured in QFT, and ii) if not, in what sense can it be measured? Here we formulate a necessary and sufficient condition that any measurement, and more generally any state update (quantum operation), must satisfy to respect causality in real scalar QFT. We argue that for unitary `kicks' and operations involving 1-parameter families of Kraus operators, e.g. Gaussian measurements, the only causal observables are smeared fields and the identity -- the basic observables in real scalar QFT. We provide examples with more complicated operators such as products of smeared fields, and show that the associated state updates are acausal, and hence impossible. Despite this, one can still recover expectation values of such operators, and we show how to do this using only causal measurements of smeared fields.

Related papers

• Observation as Physication. A single-world unitary no-conspiracy interpretation of quantum mechanics [0.0]
  I propose that the assignment of physical meaning to operators spreads through observation, along with the values of the observables. I propose that quantum observations are nothing more than this assignment, which can be done unitarily.
  arXiv  Detail & Related papers  (2024-12-12T18:54:05Z)
• Testing trajectory-based determinism via time probability distributions [44.99833362998488]
  Bohmian mechanics (BM) has inherited more predictive power than quantum mechanics (QM) We introduce a prescription for constructing a flight-time probability distribution within generic trajectory-equipped theories. We derive probability distributions that are unreachable by QM.
  arXiv  Detail & Related papers  (2024-04-15T11:36:38Z)
• Eliminating the "impossible": Recent progress on local measurement theory for quantum field theory [0.0]
  We investigate the consequences for measurement in quantum field theory (QFT) We review three different approaches to formulating an account of measurement for QFT and analyze their responses to the "impossible measurements" problem.
  arXiv  Detail & Related papers  (2023-07-17T14:35:03Z)
• Quantum State Tomography for Matrix Product Density Operators [28.799576051288888]
  Reconstruction of quantum states from experimental measurements is crucial for the verification and benchmarking of quantum devices. Many physical quantum states, such as states generated by noisy, intermediate-scale quantum computers, are usually structured. We establish theoretical guarantees for the stable recovery of MPOs using tools from compressive sensing and the theory of empirical processes.
  arXiv  Detail & Related papers  (2023-06-15T18:23:55Z)
• Measurement and Probability in Relativistic Quantum Mechanics [0.0]
  This paper provides a relativistic model of measurement, in which the state of the universe is decomposed into decoherent histories of measurements recorded within it. The wave functions that we actually use for such experiments are local reductions of very coarse-grained superpositions of universal eigenstates.
  arXiv  Detail & Related papers  (2022-09-26T04:21:52Z)
• The Pragmatic QFT Measurement Problem and the need for a Heisenberg-like Cut in QFT [0.0]
  Despite quantum theory's success, many philosophers worry that it lacks some crucial connection between theory and experiment. Without a solution to these pragmatic worries, quantum theory would be at risk of losing both its evidential support and its physical salience. This paper briefly reviews the state of the art in the physics literature regarding the modeling of measurement processes involving quantum fields.
  arXiv  Detail & Related papers  (2022-05-19T15:01:59Z)
• Theory of Quantum Generative Learning Models with Maximum Mean Discrepancy [67.02951777522547]
  We study learnability of quantum circuit Born machines (QCBMs) and quantum generative adversarial networks (QGANs) We first analyze the generalization ability of QCBMs and identify their superiorities when the quantum devices can directly access the target distribution. Next, we prove how the generalization error bound of QGANs depends on the employed Ansatz, the number of qudits, and input states.
  arXiv  Detail & Related papers  (2022-05-10T08:05:59Z)
• Stochastic approximate state conversion for entanglement and general quantum resource theories [41.94295877935867]
  An important problem in any quantum resource theory is to determine how quantum states can be converted into each other. Very few results have been presented on the intermediate regime between probabilistic and approximate transformations. We show that these bounds imply an upper bound on the rates for various classes of states under probabilistic transformations. We also show that the deterministic version of the single copy bounds can be applied for drawing limitations on the manipulation of quantum channels.
  arXiv  Detail & Related papers  (2021-11-24T17:29:43Z)
• Limits on Relativistic Quantum Measurement [0.0]
  Requiring causality on measurements in quantum field theory seems to impose strong conditions on a self-adjoint operator to be really measurable. Recent publications attempt to deal with this issue by including the apparatus into the formalism. I present measurement theory in AQFT, modelling the apparatus as a quantum field with coupling to the measured system restricted to a region of spacetime.
  arXiv  Detail & Related papers  (2021-09-07T16:47:00Z)
• Quantum indistinguishability through exchangeable desirable gambles [69.62715388742298]
  Two particles are identical if all their intrinsic properties, such as spin and charge, are the same. Quantum mechanics is seen as a normative and algorithmic theory guiding an agent to assess her subjective beliefs represented as (coherent) sets of gambles. We show how sets of exchangeable observables (gambles) may be updated after a measurement and discuss the issue of defining entanglement for indistinguishable particle systems.
  arXiv  Detail & Related papers  (2021-05-10T13:11:59Z)
• Entropic Uncertainty Relations and the Quantum-to-Classical transition [77.34726150561087]
  We aim to shed some light on the quantum-to-classical transition as seen through the analysis of uncertainty relations. We employ entropic uncertainty relations to show that it is only by the inclusion of imprecision in our model of macroscopic measurements that we can prepare a system with two simultaneously well-defined quantities.
  arXiv  Detail & Related papers  (2020-03-04T14:01:17Z)

This list is automatically generated from the titles and abstracts of the papers in this site.

This site does not guarantee the quality of this site (including all information) and is not responsible for any consequences.