In defense of real quantum theory
Two recent papers (Renou et al., arXiv:2101.10873, and Chen et al., arXiv:2103.08123) have indicated that complex numbers are necessary for quantum theory. This short note is a comment on their result.
quant-ph↗
arXiv subjects
J. Finkelstein
Publications and source records attributed to J. Finkelstein.
More trouble for unitary quantum theory
Single-world unitary quantum theories imply that some measurements have results whose probabilities can not be calculated by the Born rule.
quant-ph↗
A classical paradox of choice
A classical analogue of the Adlam-Kent "Quantum paradox of choice" (arXiv:1509.04226) is presented.
quant-ph↗
One-way speed of light?
This is a comment on a paper by Greaves, Rodriguez, and Ruiz-Camacho [Am. J. Phys. 77, 894 (2009)] which reports a measurement of the one-way speed of light.
physics.gen-ph↗
Has the Born rule been proven?
This note is a somewhat-lighthearted comment on a recent paper by David Wallace, arXiv:0906.2718[quant-ph] entitled "A formal proof of the Born rule from decision-theoretic assumptions".
quant-ph↗
What is paradoxical about the "Three-box paradox"?
This paper is a comment on quant-ph/0606067 by Ravon and Vaidman, in which they defend the position that the ``three-box paradox'' is indeed paradoxical.
quant-ph↗
"Quantum-states-as-information" meets Wigner's friend: A comment on Hagar and Hemmo
This is a comment on the paper by Hagar and Hemmo (quant-ph/0512095) in which they suggest that information-theoretic approaches to quantum theory are incomplete.
quant-ph↗
On relational time and energy decoherence
Students Alice and Bob take an examination in their quantum mechanics class, and thereby illustrate some aspects of energy decoherence.
quant-ph↗
On PSI-complete and PSIR-complete measurements
I construct a POVM which has 2d rank-one elements and which is informationally complete for generic pure states in d dimensions, thus confirming a conjecture made by Flammia, Silberfarb, and Caves (quant-ph/0404137). I show that if a rank-one POVM is required to be informationally complete for all pure states in d dimensions, it must have at least 3d-2 elements. I also show that, in a POVM which is informationally complete for all pure states in d dimensions, for any vector there must be at least 2d-1 POVM elements which do not annihilate that vector.
quant-ph↗
On "Bell's inequality without alternative settings"
Cabello has recently (in quant-ph/0210081) observed that ``...an EPR-experiment with a fixed POVM on each particle provides a violation of Bell's inequality without requiring local observers to choose between the alternatives.'' In this note I discuss the implications of this observation for tests of locality.
quant-ph↗
Do macroscopic properties dictate microscopic probabilities?
Aharonov and Reznik have recently (in quant-ph/0110093) argued that the form of the probabilistic predictions of quantum theory can be seen to follow from properties of macroscopic systems. An error in their argument is identified.
quant-ph↗
How much state assignments can differ
We derive necessary and sufficient conditions for a group of density matrices to characterize what different people may know about one and the same physical system.
quant-ph↗
Property Attribution and the Projection Postulate in Relativistic Quantum Theory
State-vectors resulting from collapse along the forward light cone from a measurement interaction can be used for the attribution of both local and non-local properties.
quant-ph↗
Quantum Probability from Decision Theory?
In a recent paper (quant-ph/9906015), Deutsch claims to derive the "probabilistic predictions of quantum theory" from the "non-probabilistic axioms of quantum theory" and the "non-probabilistic part of classical decision theory." We show that his derivation fails because it includes hidden probabilistic assumptions.
quant-ph↗
Quantum Probability from Decision Theory?
Deutsch has recently (in quant-ph/9906015) offered a justification, based only on the non-probabilistic axioms of quantum theory and of classical decision theory, for the use of the standard quantum probability rules. In this note, this justification is examined.
quant-ph↗
Space-time counterfactuals
A definition is proposed to give precise meaning to the counterfactual statements that often appear in discussions of the implications of quantum mechanics. Of particular interest are counterfactual statements which involve events occurring at space-like separated points, which do not have an absolute time ordering. Some consequences of this definition are discussed.
quant-ph↗
Ambiguities of arrival-time distributions in quantum theory
We consider the definition that might be given to the time at which a particle arrives at a given place, both in standard quantum theory and also in Bohmian mechanics. We discuss an ambiguity that arises in the standard theory in three, but not in one, spatial dimension.
quant-ph↗
Comment on "Consistency, amplitudes, and probabilities in quantum theory"
In a recent article [Phys. Rev. A 57, 1572 (1998)] Caticha has concluded that ``nonlinear variants of quantum mechanics are inconsistent.'' In this note we identify what it is that nonlinear quantum theories have been shown to be inconsistent with.
quant-ph↗