Monday, December 8, 2008
Recent CMU PhD Graduate Vladimir Stojanovic's Paper Selected as Editors' SuggestionA recent paper entitled "Quantum-entanglement aspects of polaron systems", by Vladimir Stojanovic and Mihajlo Vanevic, in Physical Review B 78, 214301 (2008), has been selected as an Editors' Suggestion. Vladimir Stojanovic, a recent Ph.D. graduate in the CMU Physics Department, is now a postdoc at Georgia Tech. His co-author is a graduate student at the University of Basel in Switzerland. As a service to both readers and authors, Editors' Suggestions are a small number of papers published in Physical Review B that the editors and referees find of particular interest, importance, or clarity.
Summary of the paper:
The polaron concept, a particle (electron, hole) surrounded by the quanta of the host-lattice vibrations (phonons), had been conceived by Landau as far back as 1933, and remains squarely among the central notions in condensed-matter physics. As the interaction between the particle and phonons becomes stronger, leading to an increased "phonon-dressing" of the particle, its motion invariably changes from being rather delocalized to being restricted to a single unit cell of the host crystal. This change is not accompanied by a breaking of symmetry; that is, a phase transition. In this paper, the authors show that quantitative measures of entanglement, describing correlations between parts of a quantum system, provide us with the means to better understand the inner workings of polaron physics. This appears possible for the so-called Peierls-type particle-phonon interaction, of importance in molecular crystals, whereby phonons directly affect particle's hopping amplitude. They demonstrate that the entanglement measures change abruptly in the physical regime where such interaction leads to the spatially-distant particle-phonon correlations. As an interesting sidetrack, their results exemplify that such behavior does not necessarily coincide with the onset of (zero-temperature) quantum phase transitions, a point of contention in the current literature.