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University Quantum Mechanics I

University Quantum Mechanics I · The Infinite Square Well · 6.08

Time evolution: each eigenstate carries its own phase

Substituting the expansion into the time-dependent equation decouples it into one ODE per coefficient: Ψ(x, t) = sum cₙ ψₙ(x) exp(−i Eₙ t/ℏ).

Course-map guide · not a complete lesson or simulation

Scope & orientation

What this subsection covers

Substituting the expansion into the time-dependent equation decouples it into one ODE per coefficient: Ψ(x, t) = sum cₙ ψₙ(x) exp(−i Eₙ t/ℏ).

A strong response uses snapshots of |ψ(x, t)|² across one beat 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

Does a two-term superposition oscillate at angular frequency (E₂ - E₁)/ℏ, and does a many-term packet return at the revival time 4mL²/(π ℏ)?

Read the complete note

Does a two-term superposition oscillate at angular frequency (E₂ - E₁)/ℏ, and does a many-term packet return at the revival time 4mL²/(π ℏ)? Useful evidence includes snapshots of |Ψ(x, t)|², ⟨x⟩(t) with its fitted period set against 2 pi ℏ/(E₂ - E₁), |cₙ|² and ⟨H⟩ shown numerically constant, and the revival traced to level gaps that are integer multiples of E₁.

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 claimTime evolution: each eigenstate carries its own phase

Substituting the expansion into the time-dependent equation decouples it into one ODE per coefficient: Ψ(x, t) = sum cₙ ψₙ(x) exp(−i Eₙ t/ℏ).

Read the complete note

Substituting the expansion into the time-dependent equation decouples it into one ODE per coefficient: Ψ(x, t) = sum cₙ ψₙ(x) exp(−i Eₙ t/ℏ). Each term turns at its own rate, so the phase factors out front only when a single term is present, and every |cₙ| is frozen. This needs V time-independent and no measurement in between.

02 · RepresentationThe subsection's claim

Model, evidence, and boundary

03 · TestPrediction before measurement

What is the strongest test of a claim about Time evolution: each eigenstate carries its own phase?

04 · Evidence & boundaryDecide, then qualify

Does a two-term superposition oscillate at angular frequency (E₂ - E₁)/ℏ, and does a many-term packet return at the revival time 4mL²/(π ℏ)?

Read the complete note

Does a two-term superposition oscillate at angular frequency (E₂ - E₁)/ℏ, and does a many-term packet return at the revival time 4mL²/(π ℏ)? Useful evidence includes snapshots of |Ψ(x, t)|², ⟨x⟩(t) with its fitted period set against 2 pi ℏ/(E₂ - E₁), |cₙ|² and ⟨H⟩ shown numerically constant, and the revival traced to level gaps that are integer multiples of E₁.

Interactive diagram for Time evolution: each eigenstate carries its own phase: 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

What is the strongest test of a claim about Time evolution: each eigenstate carries its own phase?

Quick check

Test the reasoning, not recall

What is the strongest test of a claim about Time evolution: each eigenstate carries its own phase?

Choose an answer to test the model.