On some states minimizing uncertainty relations: A new look at these relations
Pith reviewed 2026-05-23 17:03 UTC · model grok-4.3
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.
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 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.
Referee Report
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)
- [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.
- [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
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
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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
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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
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
axioms (2)
- standard math Standard quantum mechanical commutation relations [A,B] = iC for non-commuting observables
- domain assumption States are normalized vectors in Hilbert space with well-defined expectation values and variances
Lean theorems connected to this paper
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IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
the uncertainty relation in its most general form (14) is in fact an upper bound on the modulus of the correlation function Cϕ(A,B) ... ΔϕA · ΔϕB ≥ |Cϕ(A,B)|
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IndisputableMonolith/Foundation/RealityFromDistinction.leanreality_from_one_distinction unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
states ... for which the lower bound of the product of the standard deviations ... is zero ... not eigenstates ... correlation function ... equal to zero
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Forward citations
Cited by 1 Pith paper
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Notes on some inequalities, resulting uncertainty relations and correlations. 1. General mathematical formalism
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...
Reference graph
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discussion (0)
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