Quantum Field Theory of Many-Body Systems

Lecture (MVSpec)

Thomas Gasenzer

Tuesday, 11:15-13:00; Thursday, 11:15-13:00; (starting on 18/10) INF 227 (KIP), SR 3.403+4. [LSF]

Exercises
Head tutor: Dr. Markus Karl

Register here.
Classes take place on Fridays, 14:15-15:45 hrs, starting on 28/10: INF 227 (KIP), SR 3.404.

Written exam on Thu, 09/02/17, 11:00-13:00 hrs, INF 227 (KIP), SR 3.403+4.

Content - Prerequisites - Script - Literature - Additional material - Exercises - Exam

The lecture course provides an introduction to field theoretic methods for systems with many degrees of freedom. A focus will be set on applications to ultracold, mostly bosonic, atomic gases, superfluids and superconductors as they are the subject of many fore-front present-day experiments. Methodologically, the lecture will introduce the basics of the operator as well as the path-integral approach to quantum field theory. In applying these techniques I will in particular concentrate on thermal and dynamical properties of the considered systems. Knowledge of the basics of quantum mechanics and statistical mechanics is presumed while the course is designed to be self-contained on the quantum-field-theory side.

Content:

1. Introduction
   
2. Quantum field theory of matter
   From classical to quantum fields - Lagrangian and Hamiltonian field theory - ^*Constrained quantisation - Quantisation of the Bose field - Mode expansion - Harmonic oscillator - One- and multiparticle operators - Fock space - Identical particles - Bosons and fermions - Coherent states - Wigner function and phase space - Free systems and Wick's theorem - Cumulant expansion
   
3. Mean-field theory of a weakly interacting Bose gas
   Non-linear Schrödinger model - Bogoliubov quasiparticles - Phase and Number fluctuations - Renormalisation of the ground-state energy - ^*Low-energy scattering theory - Ground state: Two-mode squeezing - ^*SU(1,1) coherent states - Thermal Bogoliubov quasiparticles
   
4. Path-integral approach to quantum field theory
   A quick reminder of the Feynman path integral - Functional calculus - Saddle-point expansion and free propagator - Perturbation expansion, Dyson series, and resummation - Correlation functions - Connected functions and cumulants - Feynman diagrammatics - Low-energy effective theory - Linear-response theory - Retarded and advanced Greens functions - Spectral and statistical functions - Thermal path integral - ^*The quantum effective action - ^*Spontaneous Symmetry Breaking
   
5. Low-temperature properties of dilute Bose systems
   Path-integral representation of the interacting Bose gas - Ginsburg-Landau theory of spontaneous symmetry breaking - The Luttinger-liquid description - Superfluid phase transition and spontaneous symmetry breaking - Nambu-Goldstone theorem - ^*The Lieb-Liniger model of a one-dimensional Bose gas - Superfluid phase in low dimensions - Superfluids at non-zero temperatures - Dimensionally reduced path integral - Hydrodynamic formulation and vortices - Thomas-Fermi approximation - The Berezinskii-Kosterlitz-Thouless transition - ^*Superfluid to Mott insulator transition - ^*Superfluidity and superconductivity - ^*Anderson-Higgs mechanism
   

Prerequisites:

• Quantum Mechanics (PTP 3), Statistical Mechanics (PTP 4); Quantum Field Theory I or Quantum Optics (useful but not a precondition)

Skript :

• The notes are available for download here, separately for each chapter and as complete pdf.
• The notes and (unedited) typoscript of the previous lecture in WTs 12/13 and 14/15 (with slightly different focus) can be found here.

Literature:

General texts on quantum field theory

• Brian Hatfield, Quantum Field Theory of Point Particles and Strings. Addison Wesley, Oxford, 2010. [ Google books | HEIDI ]
• Michael E. Peskin, Daniel V. Schroeder An introduction to quantum field theory. Westview, Boulder, 2006. [ Google books | HEIDI ]
• Xiao-Gang Wen, Quantum Field Theory of Many-Body Systems. OUP, Oxford, 2010. [ Google books | HEIDI ]

Quantum optics and phase-space methods

• S.M. Barnett, P.M. Radmore, Methods in Theoretical Quantum Optics. Clarendon Press, Oxford, 1997. [ HEIDI ]
• C.W. Gardiner, Quantum Noise. 2nd Ed. Springer Verlag, Berlin, 2000. [ HEIDI ]
• L. Mandel, E. Wolf, Optical Coherence and Quantum Optics. CUP, Cambridge, 2008 (ISBN 0-521-41711-2). [ HEIDI ]
• W.P. Schleich, Quantum Optics in Phase Space. Wiley-VCH, Weinheim, 2001. [ HEIDI ]
• M.O. Scully, M.S. Zubairy, Quantum Optics. CUP, Cambridge, 2008. [ HEIDI | Google Books ]

Ultracold atomic gases: General texts and theory reviews

• A. Griffin, D. W. Snoke, S. Stringari (Eds.), Bose-Einstein condensation. CUP, Cambridge, 2002. [ Google books | HEIDI ]
• C.J. Pethick and H. Smith, Bose-Einstein condensation in Dilute Gases. CUP, Cambridge, 2002. [ Google books | HEIDI | Full Text ]
• A. Leggett, Bose-Einstein condensation in the alkali gases: Some fundamental concepts. Review of Modern Physics 73, 307 (2001).
• L.P. Pitaevskii and S. Stringari, Bose-Einstein condensation. Clarendon Press, Oxford, 2003. [ Google books | HEIDI ]
• F. Dalfovo, S. Giorgini, L. P. Pitaevskii, and S. Stringari, Theory of Bose-Einstein condensation in trapped gases. Review of Modern Physics 71, 463 (1999).
• A. Fetter, Theory of a dilute low-temperature trapped Bose condensate. arXiv.org:cond-mat/9811366 (1998).
• T. Gasenzer, Ultracold gases far from equilibrium. Eur. Phys. Journ. ST 168, 89 (2009); arXiv.org: 0812.0004 [cond-mat.other] .

Ultracold atomic gases: A few original experimental perspectives

• E.A. Cornell, J.R. Ensher, and C.E. Wieman, Experiments in Dilute Atomic Bose-Einstein Condensation. arXiv.org:cond-mat/9903109 (1999).
• W. Ketterle, D.S. Durfee, and D.M. Stamper-Kurn, Making, probing and understanding Bose-Einstein condensates. arXiv.org:cond-mat/9904034 (1999).

Few-body scattering theory

• K. Burnett, P.S. Julienne, P.D. Lett, E. Tiesin, and C.J. Williams, Quantum encounters of the cold kind. Nature (London) 416, 225 (2002).
• J. Dalibard, Collisional dynamics of ultra-cold atomic gases. Proc. Int. School Phys. Enrico Fermi, Course CXL: Bose-Einstein condensation in gases, Varenna 1998, M. Inguscio, S. Stringari, C. Wieman edts.
• C.J. Joachain, Quantum Collision Theory. North-Holland, Amsterdam, 1983. [ HEIDI | Scribd Full Text ]
• L.D. Landau and E. M. Lifshitz, Quantum Mechanics. Non-relativistic theory. (see Chapters XVII & XVIII.) Pergamon Press, Oxford, 1977. [ HEIDI | Online Full Text ]
• R.G. Newton, Scattering Theory of Waves and Particles. Dover publications, 2002. [ HEIDI | Google Books ]

Non-equilibrium quantum field theory and quantum kinetic theory

• L.P. Kadanoff and G. Baym, Quantum statistical mechanics. Addison-Wesley, Redwood City, 1989. [ HEIDI ]
• Jørgen Rammer, Quantum field theory of non-equilibrium states. CUP, Cambridge, 2007. [ Online edition | HEIDI ]
• J. Berges, Introduction to nonequilibrium quantum field theory, AIP Conf. Proc. 739, 3 (2005); arXiv.org: hep-ph/0409233 .
• P. Danielewicz, Quantum Theory of Nonequilibrium Processes, Annals of Physics 152, 239 (1984) .
• M. Bonitz, Quantum kinetic theory. Teubner, Stuttgart, 1998. [ Contents | HEIDI ]
• E. Calzetta and B.-L. Hu, Nonequilibrium quantum field theory. CUP, Cambridge, 2008. [ Online fulltext | HEIDI ]

Additional material

• D. Ebert and V. S. Yarunin, Functional-Integral Approach to the Quantum Dynamics of Nonrelativistic Bose and Fermi Systems in the Coherent-state Representation. Fortschr. Phys. 42, 7, 589 (1994).

Exercises:

Exercises will be held on Fridays, 14:15-15:45 hrs, in SR 3.404, INF 227 (KIP), starting on 28/10/16. Tutor: Markus Karl. (Please register here.)

Problem Sheets will be available for download here.

Exam:

Passing the written exam, which will take place on Thu, 09/02/17, 11:00-13:00 hrs, INF 227 (KIP), SR 3.403+4, will be the condition to obtain 8 CPs for the lecture.