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The position-momentum preparation relation of the massive spin-s model
The position-momentum preparation relation of the massive spin-s particle model of the framework, for one particle of mass parameter m>0 and spin label s: for every unit state vector in D(Q_j) cap D(P_j) the product of the preparation spreads of the j-th position and j-th momentum is at least hbar/2, with no product-domain hypothesis, together with the equality characterization by linear dependence of the centered vectors and the exact imaginary part -hbar/2. The statement is a conditional consequence of P1, P2, P5, P6 and the cited mathematics; P1 assigns pure preparations to unit rays, P2 supplies the outcome laws and spread reading, and P5/P6 assign this massive spin-s model. It concerns the spreads of the two separately assigned outcome laws and asserts no joint sharp observable with the exact spectral marginals, no claim about unsharp joint measurements, no apparatus realisation, no disturbance relation and no empirical result.
Statement
Adopt the state and composition postulate P1, the observable and probability postulate P2, the kinematics and massive-particle model postulate P5, and the internal-factor assignment P6 of the framework, read for the spin- model of The massive spin-s particle model of the framework: state space, operators, units and frame readings with mass parameter , spin label and (State and composition postulate P1: Hilbert spaces, preparations and composite systems, Observable and probability postulate P2: self-adjoint observables, spectral probability and finite unsharp outcomes, Kinematics and massive-particle model postulate P5: Newtonian frames and one-particle operators, Identical-particle and spin assignments P6: permutation sectors and finite-spin representations), and assume the Axiom of Countable Choice and the Axiom of Choice (The Axiom of Countable Choice (), The Axiom of Choice). Let be the model's -th position and -th momentum operators with their maximal domains, and let and be their preparation spreads in the reading of Preparation variance and spread of an assigned sharp observable. Let be a unit vector and put Then:
(a) and are defined and
(b) if in addition , then and the bound of (a) follows from the Robertson relation for the two observables;
(c) for every unit the centered pairing has the exact imaginary part consequently equality holds if and only if and are linearly dependent and ;
(d) Scope. The statement is conditional on P1, P2, P5, P6 and the cited mathematics. It concerns the two separately assigned position and momentum outcome laws in one preparation, needs no hypothesis on the products or . The compatibility results of this page show that no joint sharp observable with the exact spectral marginals of and exists; this statement makes no claim about existence or nonexistence of unsharp joint measurements or their outcome laws. It asserts no apparatus realization, no disturbance relation, no dynamics and no empirical result. Massless, relativistic, singular-potential and boundary realizations are separate models for which no such relation is asserted.
Facts & Assumptions
Given: The postulates P1, P2, P5 and P6 read through The massive spin-s particle model of the framework: state space, operators, units and frame readings; the Axiom of Countable Choice and the Axiom of Choice; the operators of the model with their maximal domains; a unit vector ; the numbers and the centered vectors .
Model operators. and are the componentwise position and momentum operators of Componentwise position and momentum operators on the component-valued wave-function space clause (a), self-adjoint with domains and , and the model assigns to them the status of assigned sharp observables in the reading of Assigned sharp observables and the outcome law of the framework clause (a) (The massive spin-s particle model of the framework: state space, operators, units and frame readings clause (b)).
Moments and spreads. For a unit vector in the mean and variance of the position law exist with where is real, and likewise for (Mean, second moment and variance of an assigned observable in a preparation clauses (a) and (b), Preparation variance and spread of an assigned sharp observable clauses (b) and (c)).
Product domain and commutator. and on it (The position-momentum commutator identity on the product domain clauses (b) and (c)).
Approximation. For every unit there is a sequence of unit vectors in with , and in , and with , and the analogous momentum limits (Approximation of Q-P graph-domain vectors by product-domain vectors).
Robertson relation. For two assigned sharp observables and a unit vector in the intersection of the two operator domains and the two product domains, the spread product is at least half the absolute value of the commutator pairing (The Robertson relation for preparation spreads of assigned sharp observables clause (b)).
Cauchy-Schwarz and its equality case. In a complex inner product space, and , with equality in the first inequality if and only if are linearly dependent (Cauchy–Schwarz: , with equality exactly for linearly dependent vectors, Hilbert space).
Proof
Given: The data of the statement and [F1]-[F6].
[Product-domain case] Let be a unit vector in . By [F1] the operators are the model's assigned sharp observables with their maximal domains, so the preparation spreads and the Robertson relation of [F5] apply to them. By [F3], , so . By [F5] the product of the preparation spreads of the two assigned observables satisfies .
[Approximation] Let be a unit vector and let be the approximating sequence of [F4]. For every , is a unit product-domain vector, so step 1.1 gives . By [F2] and [F4], , and the analogous identity holds for with the momentum limits of [F4]; taking square roots and products gives . Hence the limit satisfies , which is (a); and on the product domain the same computation together with [F3] is the derivation of (b).
[Exact imaginary part] Keep the notation of step 2.1 and put , , , . Since lies in both product domains, symmetry of and gives . The means are real by [F2], and expanding with the inner product linear in the first argument gives ; hence . By [F3], ; hence and . By [F4], and in (each is the sum of a convergent term and a scalar multiple of a convergent term), so the inner product is continuous and . This is the first display of (c).
[Equality characterization] For a unit put , . By step 3.1, , and by [F6] Equality holds exactly when both inequalities are equalities, that is (by the equality case of [F6] and the identity ) when are linearly dependent and . This completes (c).
[Scope] Clauses (a)-(c) were obtained from the model's operators, the product-rule identity, the approximation lemma and the Robertson relation; no joint outcome law, apparatus, disturbance, dynamics or empirical input enters. This is (d).
Depends on
The Axiom of Choice
The Axiom of Countable Choice ()
Hilbert space
Dimensions, SI unit conventions and quantity types of the framework
The massive spin-s particle model of the framework: state space, operators, units and frame readings
Assigned sharp observables and the outcome law of the framework
The state space of the framework: preparations, pure rays and density operators
Preparation variance and spread of an assigned sharp observable
Componentwise position and momentum operators on the component-valued wave-function space
Approximation of Q-P graph-domain vectors by product-domain vectors
The position-momentum commutator identity on the product domain
Identical-particle and spin assignments P6: permutation sectors and finite-spin representations
Kinematics and massive-particle model postulate P5: Newtonian frames and one-particle operators
Observable and probability postulate P2: self-adjoint observables, spectral probability and finite unsharp outcomes
State and composition postulate P1: Hilbert spaces, preparations and composite systems
Mean, second moment and variance of an assigned observable in a preparation
The Robertson relation for preparation spreads of assigned sharp observables
Cauchy–Schwarz: , with equality exactly for linearly dependent vectors
Dependency tree · 2 levels
Sources
- D. Tong, Quantum Mechanics (author-hosted lecture set), Sections 3.4 and 3.4.1, printed pages 81-88 (PDF pages 84-91): canonical commutation relations, the position-momentum bound Delta x Delta p >= hbar/2 and the Gaussian saturation
- B. Zwiebach, MIT 8.05 Quantum Physics II (Fall 2013), Chapter 5 'Uncertainty Principle and Compatible Observables', Section 2, printed pages 3-6: the uncertainty inequality for position and momentum and the conditions for saturation
- G. Teschl, Mathematical Methods in Quantum Mechanics, 1st edition 2009, Section 2.1 and Section 8.1, printed pages 55-58 and 173-175 (PDF pages 67-70 and 185-187): position and momentum as self-adjoint operators and the algebraic calculus behind the canonical commutation relation