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Quantum EngineeringYear 2: Advanced Quantum ScienceMonth 35Day 972

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Year 2·Month 35·Week 3

Day 972: Expressibility & Trainability

Day 972 of 2,016~19 min read

Learning Objectives

  • •**Quantify expressibility** of parameterized quantum circuits
  • •**Explain the barren plateau phenomenon** and its mathematical origin
  • •**Identify conditions** that lead to barren plateaus
  • •**Apply mitigation strategies** for vanishing gradients
  • •**Design circuits** balancing expressibility and trainability
  • •**Analyze gradient landscapes** numerically and theoretically

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Year 2 Semester 2B Fault Tolerance HardwareMonth 35 Advanced Algorithms - Week 139 QML FoundationsSchedule OverviewLearning ObjectivesMorning Session Theory 3 hours1 Expressibility Covering Hilbert SpaceMotivationFormal DefinitionComputing Expressibility2 Entangling CapabilityDefinitionMeyer-Wallach Measure3 The Barren Plateau PhenomenonDiscovery McClean et al 2018Mathematical OriginIntuition Why Barren Plateaus Occur4 Types of Barren Plateaus41 Depth-Induced Barren Plateaus42 Cost-Function-Induced Barren Plateaus43 Noise-Induced Barren Plateaus44 Entanglement-Induced Barren Plateaus5 Detecting Barren PlateausVariance of GradientsPractical Detection Algorithm6 Mitigation Strategies61 Parameter Initialization62 Layer-wise Training63 Local Cost Functions64 Shallow Circuits65 Problem-Inspired Anstze66 Correlated Parameters7 The Expressibility-Trainability Trade-offThe Fundamental DilemmaOptimal Design PrinciplesAfternoon Session Problem Solving 2 hoursWorked Example 1 Computing ExpressibilityWorked Example 2 Gradient Variance ScalingWorked Example 3 Local vs Global Cost FunctionsPractice ProblemsProblem 1 Expressibility Calculation Direct ApplicationProblem 2 Barren Plateau Onset IntermediateProblem 3 Cost Function Design ChallengingEvening Session Computational Lab 2 hoursLab Analyzing and Mitigating Barren PlateausSummaryKey FormulasThe Expressibility-Trainability Trade-offKey TakeawaysMitigation Strategies SummaryDaily ChecklistPreview Day 973
Day 971Day 972 of 2,016Day 973