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Quantum EngineeringYear 0: Mathematical FoundationsMonth 11Day 305

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Year 0·Month 11·Week 4

Day 305: Addition of Angular Momenta

Day 305 of 2,016~12 min read

Learning Objectives

  • •Understand the tensor product structure of composite systems
  • •Master the uncoupled and coupled bases
  • •Derive the range of total angular momentum
  • •Apply to physical examples: singlet/triplet, spin-orbit coupling
  • •Prepare for Clebsch-Gordan coefficients

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OverviewLearning Objectives1 The Physical ProblemWhy Add Angular MomentaThe Question2 Tensor Product SpaceThe Combined Hilbert SpaceOperators on Composite SystemCommutation Relations3 The Uncoupled BasisProduct StatesExample Two Spin-12 ParticlesTotal m in Uncoupled Basis4 The Coupled BasisA Different Set of Quantum NumbersThe Key Question5 Range of Total Angular MomentumThe Triangle RuleDerivation via CountingDimension Check6 The Basis ChangeRelation Between BasesNotationSelection Rule7 Example Two Spin-12 ParticlesThe SetupFinding the StatesSummary Singlet and Triplet8 Physical ApplicationsSpin-Orbit CouplingHelium AtomNuclear Physics9 Representation Theory PerspectiveTensor Product of RepresentationsDimension FormulaGroup Theory Interpretation10 Computational Lab11 Practice ProblemsProblem 1 Dimension CountingProblem 2 Three Spin-12Problem 3 Singlet ProjectionProblem 4 Exchange OperatorProblem 5 Spin-Orbit SplittingSummaryAngular Momentum Addition RuleTwo Spin-12 Singlet and TripletKey RelationsPreview Day 306
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