4pm - 5pm GMT

Wednesday 26 October - Wednesday 7 December 2022

Introduction to decoherence theory

This short course of six lectures by Jim Al-Khalili will provide an introduction to quantum decoherence and density matrix theory and will be of relevance to PhD students starting to work in open quantum systems, quantum optics, quantum information and quantum computing – or indeed for anyone interested in the foundations of quantum mechanics and the famous measurement problem.


Lecture Theatre F
University of Surrey

Places are now full for this event.


For generations we have taught quantum mechanics to students in terms of isolated systems (Schrödinger equation and unitary dynamics). However, isolated systems have long been an obstacle in understanding the quantum-to-classical transition. The reasons for this are clear: classical physics has led us to the strategy of dealing with idealised isolated systems and has been hugely successful. This then became incorporated into quantum mechanics without much scrutiny.

For the past few decades there has been a growing realisation that we can do better than the arbitrary Born postulates that sit on top of the Schrödinger picture. The development of decoherence theory, building on the work of von Neumann and others, has shown that the vagueness of the quantum measurement problem and the Copenhagen mantra of irreducible acts of amplification can be improved upon and replaced with the well-founded physical processes of entanglement and decoherence.

This short course will introduce some of the ideas developed by the likes of Zurek, Zeh, Paz and Joos since the 1970s, but which still find no place in undergraduate courses on quantum mechanics despite their obvious relevance in many areas of physics today, such as quantum optics, quantum information, quantum computing and new theoretical fields such as open quantum systems, quantum thermodynamics and quantum biology.

Who is this course for?

This course is appropriate for anyone with a basic (undergraduate) knowledge of quantum theory (plus familiarity with Dirac notation).

Topics to be covered

  • Introducing decoherence
  • Quantum entanglement
  • The Density matrix
  • Pure and mixed states
  • Quantifying ‘mixedness’
  • Reduced density matrices
  • The measurement problem
  • The double-slit experiment revisited
  • Environment-induced decoherence
  • Pointer states
  • Decoherent-free subspaces
  • Decoherence versus dissipation
  • Quantum erasure
  • Master equations.

Lecture dates

All lecture dates are on a Wednesday and will run 4pm to 5pm:

  • Lecture 1: 26 October 2022
  • Lecture 2: 2 November 2022
  • Lecture 3: 9 November 2022
  • Lecture 4: 23 November 2022
  • Lecture 5: 30 November 2022
  • Lecture 6: 7 December 2022.

Have an enquiry?

If you have any questions then please email Jim Al-Khalili at j.al-khalili@surrey.ac.uk.