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arxiv: 2411.08131 · v6 · submitted 2024-11-12 · 🪐 quant-ph · math-ph· math.MP

On some states minimizing uncertainty relations: A new look at these relations

Pith reviewed 2026-05-23 17:03 UTC · model grok-4.3

classification 🪐 quant-ph math-phmath.MP
keywords uncertainty relationsHeisenberg-Robertson relationSchrödinger uncertainty relationstandard deviationscorrelation functionnon-commuting observablesquantum statessum uncertainty relations
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The pith

There exist quantum states where the lower bound on the product of standard deviations for non-commuting observables is zero, yet the states are not eigenstates of either observable.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper analyzes the Heisenberg-Robertson and Schrödinger uncertainty relations and finds a large class of states in which the lower bound on the product of standard deviations for non-commuting observables A and B equals zero. These states are not eigenstates of A or B, and the correlation function between A and B vanishes in them. The work further shows that sum uncertainty relations give no useful lower bounds on the deviations for these states, while the uncertainty principle itself supplies both a lower bound on the deviation product and an upper bound on the modulus of the correlation function.

Core claim

There can exist a large set of states for which the lower bound of the product of the standard deviations of a pair of non-commuting observables A and B is zero, and which differ from those described in the literature. These states are not eigenstates of either the observable A or B. The correlation function for these observables in such states is equal to zero. The sum uncertainty relations also do not provide any information about lower bounds on the standard deviations calculated for these states. The uncertainty principle in its most general form has two faces: one is that it is a lower bound on the product of standard deviations, and the other is that the product of standard deviations

What carries the argument

The Heisenberg-Robertson and Schrödinger uncertainty relations applied to general normalized states, which connect the product of standard deviations to the commutator expectation and the correlation function.

If this is right

  • Sum uncertainty relations supply no lower bounds on the standard deviations for these states.
  • The uncertainty principle supplies an upper bound on the modulus of the correlation function between the observables.
  • A large set of such states exists beyond the eigenstates usually considered in the literature.
  • The product of standard deviations can serve as an upper limit on the correlation modulus in any state.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • These states may allow preparation of systems with vanishing correlation while keeping both variances positive.
  • Similar states could be searched for in concrete models such as the harmonic oscillator or angular momentum operators.
  • The dual role of the uncertainty principle suggests re-examining how correlation and variance trade off in quantum metrology.

Load-bearing premise

The identified states must be valid normalized quantum states obeying the standard commutation relations, with no extra constraints that would change the correlation or variance calculations.

What would settle it

An explicit normalized state |ψ⟩ for a pair of non-commuting operators A and B where the expectation value of the commutator is zero, neither variance is zero, the correlation function is zero, and direct substitution into the uncertainty relations confirms the lower bound is zero.

read the original abstract

Analyzing Heisenberg--Robertson (HR) and Schr\"{o}dinger uncertainty relations we found, that there can exist a large set of states of the quantum system under considerations, for which the lower bound of the product of the standard deviations of a pair of non--commuting observables, $A$ and $B$, is zero, and which differ from those described in the literature. These states are not eigenstates of either the observable $A$ or $B$. The correlation function for these observables in such states is equal to zero. We have also shown that the so--called "sum uncertainty relations" also do not provide any information about lower bounds on the standard deviations calculated for these states. We additionally show that the uncertainty principle in its most general form has two faces: one is that it is a lower bound on the product of standard deviations, and the other is that the product of standard deviations is an upper bound on the modulus of the correlation function of a pair of the non--commuting observables in the state under consideration.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

0 major / 2 minor

Summary. The manuscript analyzes the Heisenberg-Robertson (HR) and Schrödinger uncertainty relations for a pair of non-commuting observables A and B. It claims that there exist states (distinct from eigenstates of A or B) in which ⟨[A,B]⟩ = 0, so that the HR lower bound on σ_A σ_B vanishes, and for which the covariance cov(A,B) is also zero. The paper further states that sum uncertainty relations yield no lower bounds on the standard deviations for these states, and that the general uncertainty relation implies that the product σ_A σ_B upper-bounds |cov(A,B)|.

Significance. If the claims hold, the work offers a pedagogical clarification of the dual role of uncertainty relations (lower bound on variances versus upper bound on covariance when ⟨[A,B]⟩=0) and notes the existence of non-eigenstates where the HR bound is trivial. These observations are consistent with standard quantum mechanics and the Schrödinger relation σ_A²σ_B² ≥ cov² + (1/4)⟨[A,B]⟩², but the manuscript introduces no new derivations, explicit constructions, machine-checked proofs, or falsifiable predictions beyond known facts. Significance is therefore limited to a re-interpretation rather than a substantive advance.

minor comments (2)
  1. [Abstract and main text] The abstract and introduction assert the existence of 'a large set of states' without providing an explicit example or construction (e.g., in the harmonic oscillator or finite-dimensional spin system). Adding at least one concrete normalized state with finite variances, zero ⟨[A,B]⟩, and zero covariance would strengthen verifiability.
  2. [Main text (section discussing sum UR)] The discussion of sum uncertainty relations states they 'do not provide any information about lower bounds' for the identified states; a brief derivation or reference to the specific form of the sum relation used would clarify why this holds when ⟨[A,B]⟩=0.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading of the manuscript and the recommendation for minor revision. Below we respond point by point to the comments in the report.

read point-by-point responses
  1. Referee: The manuscript analyzes the Heisenberg-Robertson (HR) and Schrödinger uncertainty relations for a pair of non-commuting observables A and B. It claims that there exist states (distinct from eigenstates of A or B) in which ⟨[A,B]⟩ = 0, so that the HR lower bound on σ_A σ_B vanishes, and for which the covariance cov(A,B) is also zero. The paper further states that sum uncertainty relations yield no lower bounds on the standard deviations for these states, and that the general uncertainty relation implies that the product σ_A σ_B upper-bounds |cov(A,B)|.

    Authors: The claims accurately summarize the content of the manuscript. The central observation is the existence of a class of states, distinct from eigenstates, for which the commutator expectation vanishes and the covariance is simultaneously zero. This leads to a vanishing lower bound in the HR relation and renders sum uncertainty relations uninformative for lower bounds on the standard deviations. The dual role—that the product of standard deviations also serves as an upper bound on |cov(A,B)|—follows immediately from the Schrödinger relation when ⟨[A,B]⟩=0. Our contribution is to draw explicit attention to these features and their implications. revision: no

  2. Referee: If the claims hold, the work offers a pedagogical clarification of the dual role of uncertainty relations (lower bound on variances versus upper bound on covariance when ⟨[A,B]⟩=0) and notes the existence of non-eigenstates where the HR bound is trivial. These observations are consistent with standard quantum mechanics and the Schrödinger relation σ_A²σ_B² ≥ cov² + (1/4)⟨[A,B]⟩², but the manuscript introduces no new derivations, explicit constructions, machine-checked proofs, or falsifiable predictions beyond known facts. Significance is therefore limited to a re-interpretation rather than a substantive advance.

    Authors: We agree that the underlying mathematics is contained in the standard Schrödinger relation and requires no new derivation. Nevertheless, the explicit identification of non-eigenstates satisfying both ⟨[A,B]⟩=0 and cov(A,B)=0, together with the observation that the uncertainty relation simultaneously provides an upper bound on the absolute value of the covariance, is not commonly emphasized in textbook or review presentations of uncertainty principles. We regard the pedagogical clarification of this dual aspect as the primary value of the work. No explicit constructions are provided because the argument is general and holds for any pair of observables once the stated conditions on the state are met; if the referee considers concrete examples necessary, we can add them in a revision. revision: partial

Circularity Check

0 steps flagged

No significant circularity

full rationale

The paper derives its claims directly from the standard Heisenberg-Robertson and Schrödinger uncertainty relations applied to states satisfying [A,B] commutators with vanishing expectation value. No parameters are fitted and then renamed as predictions, no self-citations form load-bearing steps, and no ansatz or uniqueness theorem is smuggled in. The existence of non-eigenstates with <[A,B]>=0 and cov=0 follows immediately from the definitions of variance and covariance in Hilbert space; the upper bound |cov| ≤ σ_A σ_B is an algebraic rearrangement of the Schrödinger relation itself. All steps remain self-contained against external QM benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The paper relies on standard quantum mechanics axioms for observables and states; no free parameters, invented entities, or ad-hoc assumptions are evident from the abstract.

axioms (2)
  • standard math Standard quantum mechanical commutation relations [A,B] = iC for non-commuting observables
    Invoked implicitly when deriving the uncertainty relations from the commutator.
  • domain assumption States are normalized vectors in Hilbert space with well-defined expectation values and variances
    Required for defining standard deviations and correlations in the uncertainty relations.

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Forward citations

Cited by 1 Pith paper

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Notes on some inequalities, resulting uncertainty relations and correlations. 1. General mathematical formalism

    quant-ph 2026-04 unverdicted novelty 3.0

    Generalized Schrödinger-Robertson uncertainty relations for multiple non-commuting observables are equivalently expressed using quantum Pearson correlation coefficients, with analysis of their consequences for observa...

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