Caltech Theoretical Physicist Receives the 2015 Dirac Medal and Prize

Alexei Kitaev, the Ronald and Maxine Linde Professor of Theoretical Physics and Mathematics, has been awarded the 2015 Dirac Medal and Prize from the Abdus Salam International Centre for Theoretical Physics (ICTP). The prize, named after the esteemed theoretical physicist and Nobel Laureate Paul Dirac, is one of the most prestigious honors in theoretical physics. This year it was awarded jointly to Kitaev, Gregory W. Moore of Rutgers University, and Nicholas Read of Yale University for their work on condensed matter research.

The work of Kitaev, Moore, and Read has "played a fundamental role in recent advances in our understanding of the quantum states of matter and quantum entanglement theory," according to the ICTP's press release.

Kitaev is cited for proposing an innovative method of computation, called topological quantum computation, which builds upon Moore and Read's theory of non-Abelian anyons. Anyons are special quasiparticles that exist under the conditions of the fractional quantum Hall effect (FQHE). The FQHE is observed in semiconductor structures that contain a thin layer of mobile electrons. When such systems are cooled to very low temperatures and immersed in a strong magnetic field, the electrons form a collective state analogous to a liquid.

"Anyons are like bubbles and lumps in that liquid, which can move around, fuse, or annihilate," Kitaev explains. "However, these quasiparticles have very strange properties: they carry a fractional electron charge and defy the textbook classification into bosons and fermions. For bosons, such as photons, switching the places of two identical particles has no effect, while for fermions like electrons or protons, the particle exchange introduces a minus sign into the calculation. Switching the places of two identical anyons results in an extra factor other than 1 or -1."

"Non-Abelian anyons are even weirder because their state is not determined by where they are spatially; there is also some hidden state in the liquid between them. Exchanging two particles or moving one around the other alters that state."

As part of his proposed method of topological quantum computation, Kitaev suggested that using this hidden state as a quantum computer memory could make such computation more stable and error proof.

"Kitaev's work on fault-tolerant quantum computation using topological quantum phases with non-Abelian quasiparticles has had profound implications in quantum information theory," the award citation notes.

Caltech faculty who have previously been awarded the Dirac Medal are John H. Schwarz, the Harold Brown Professor of Theoretical Physics, Emeritus, in 1989; and John Hopfield, the Roscoe G. Dickinson Professor of Chemistry and Biology, Emeritus, in 2001.