Contents 7.4 Exchange interaction 7.5 Two recent applications Summary 257 Problem Further reading 派 8 Symmetries and conservation laws 259 81 Quantum transformations and symmetries 8.2 Continuous symmetries 83 Discrete symmetries 8.4 A brief introduction to group theory 267 Summary Problems Further reading 276 9 The measurement problem in quantum mechanics 27 9.1 Statement of the problem 9.2 A brief history of the problem 284 93 Schrodinger cats 9.4 Decoherence 9.5 Reversibility/irreversibility 9.6 Interaction-free measurement 315 97 Delayed-choice experim 98 Quantum Zeno effect 9. Conditional measurements or postselection 02 9.10 Positive operator valued measure 9.11 Quantum non-demolition measurements 9.12 Decision and estimation theory Summary 349 Problems 351 Further reading 353 Part Ill Matter and light 10 Perturbations and approximation methods 10.1 Stationary perturbation theory 357 10.2 Time-dependent perturbation theory 36 10.3 Adiabatic theorem 10.4 The variational methoc 10.5 Classical limit 372 106 Semiclassical limit and WKB approximation 10.7 Scattering theory 10.8 Path integrals Summary 398vii Contents 7.4 Exchange interaction 254 7.5 Two recent applications 255 Summary 257 Problems 257 Further reading 258 8 Symmetries and conservation laws 259 8.1 Quantum transformations and symmetries 259 8.2 Continuous symmetries 264 8.3 Discrete symmetries 266 8.4 A brief introduction to group theory 267 Summary 275 Problems 275 Further reading 276 9 The measurement problem in quantum mechanics 277 9.1 Statement of the problem 278 9.2 A brief history of the problem 284 9.3 Schrödinger cats 291 9.4 Decoherence 297 9.5 Reversibility/irreversibility 308 9.6 Interaction-free measurement 315 9.7 Delayed-choice experiments 320 9.8 Quantum Zeno effect 322 9.9 Conditional measurements or postselection 325 9.10 Positive operator valued measure 327 9.11 Quantum non-demolition measurements 335 9.12 Decision and estimation theory 341 Summary 349 Problems 351 Further reading 353 Part III Matter and light 10 Perturbations and approximation methods 357 10.1 Stationary perturbation theory 357 10.2 Time-dependent perturbation theory 366 10.3 Adiabatic theorem 369 10.4 The variational method 371 10.5 Classical limit 372 10.6 Semiclassical limit and WKB approximation 378 10.7 Scattering theory 384 10.8 Path integrals 389 Summary 398