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University Quantum Mechanics I

University Quantum Mechanics I · Angular Momentum · 12.05

Simultaneous eigenstates and the uncertainty they leave

Commuting operators admit a common eigenbasis, so |l, m⟩ is labelled by L² and Lz together, while [Lₓ, Ly] = i ℏ Lz forces Δ Lₓ Δ Ly ≥ (ℏ/2)|⟨Lz⟩|.

Course-map guide · not a complete lesson or simulation

Scope & orientation

What this subsection covers

Commuting operators admit a common eigenbasis, so |l, m⟩ is labelled by L² and Lz together, while [Lₓ, Ly] = i ℏ Lz forces Δ Lₓ Δ Ly ≥ (ℏ/2)|⟨Lz⟩|.

A strong response uses ladder diagrams over the 2l+1 m states and states where the model stops being reliable.

Reasoning checklist

Evidence, assumptions and limits

01

Assumptions to state

State the system, observable, approximation, and conditions held fixed before using a model.

02

Evidence to collect

Do matrices built only from the Lₚₘ matrix elements reproduce [Lₓ, Ly] = i ℏ Lz, and does L² come out as ℏ² l(l+1) times the identity for each l?

Read the complete note

Do matrices built only from the Lₚₘ matrix elements reproduce [Lₓ, Ly] = i ℏ Lz, and does L² come out as ℏ² l(l+1) times the identity for each l? Useful evidence includes matrices for l = 1, 2 and 3 built from the Lₚₘ elements, commutator residuals near machine ε, L² equal to ℏ² l(l+1) times I, Lₚₗᵤₛ annihilating m = l, and the algebra fixing the spectrum, not which l occurs..

03

Limits to state

This GioPhysics course map is an adaptable learning sequence, not academic credit, accreditation, or a universal university syllabus.

Read the complete note

This GioPhysics course map is an adaptable learning sequence, not academic credit, accreditation, or a universal university syllabus. It is a first dedicated quantum-mechanics course, distinct from University Physics V, which covers quantum mechanics alongside atomic, nuclear and particle physics in twenty units: this course is narrower, slower, and teaches the linear algebra it needs rather than assuming it. Hydrogen appears here as an introduction, with the full radial derivation belonging to a second course. A midterm examination is assumed around week 8. Follow your institution's published scope, notation, laboratory programme, and assessment rules. A result should be checked against units, signs, limiting cases, and the conditions under which its model was derived.

Diagram & examples

Work the claim before choosing an equation

Interactive concept map

Follow the model from claim to evidence.

01 · Physical claimSimultaneous eigenstates and the uncertainty they leave

Commuting operators admit a common eigenbasis, so |l, m⟩ is labelled by L² and Lz together, while [Lₓ, Ly] = i ℏ Lz forces Δ Lₓ Δ Ly ≥ (ℏ/2)|⟨Lz⟩|.

Read the complete note

Commuting operators admit a common eigenbasis, so |l, m⟩ is labelled by L² and Lz together, while [Lₓ, Ly] = i ℏ Lz forces Δ Lₓ Δ Ly ≥ (ℏ/2)|⟨Lz⟩|. That bound vanishes only at l = 0, the lone state all three components do share. Degeneracy leaves the basis non-unique, and the cone picture is bookkeeping, not motion.

02 · RepresentationThe subsection's claim

Model, evidence, and boundary

03 · TestPrediction before measurement

Which response about Simultaneous eigenstates and the uncertainty they leave is most defensible?

04 · Evidence & boundaryDecide, then qualify

Do matrices built only from the Lₚₘ matrix elements reproduce [Lₓ, Ly] = i ℏ Lz, and does L² come out as ℏ² l(l+1) times the identity for each l?

Read the complete note

Do matrices built only from the Lₚₘ matrix elements reproduce [Lₓ, Ly] = i ℏ Lz, and does L² come out as ℏ² l(l+1) times the identity for each l? Useful evidence includes matrices for l = 1, 2 and 3 built from the Lₚₘ elements, commutator residuals near machine ε, L² equal to ℏ² l(l+1) times I, Lₚₗᵤₛ annihilating m = l, and the algebra fixing the spectrum, not which l occurs..

Interactive diagram for Simultaneous eigenstates and the uncertainty they leave: follow the physical claim through its representation, proposed test, evidence, and model boundary.

modelModel, evidence, and boundary turns the stated idea into a representation that can make a prediction.

Example questions

Try the reasoning before revealing the structure.

Diagram check

Which response about Simultaneous eigenstates and the uncertainty they leave is most defensible?

Quick check

Test the reasoning, not recall

Which response about Simultaneous eigenstates and the uncertainty they leave is most defensible?

Choose an answer to test the model.