Harold U. Baranger
Professor of Physics
The broad focus of Prof. Baranger's group is quantum open systems at the nanoscale, particularly the generation of correlation between particles in such systems. Fundamental interest in nanophysics-- the physics of small, nanometer scale, bits of solid-- stems from the ability to control and probe systems on length scales larger than atoms but small enough that the averaging inherent in bulk properties has not yet occurred. Using this ability, entirely unanticipated phenomena can be uncovered on the one hand, and the microscopic basis of bulk phenomena can be probed on the other. Additional interest comes from the many links between nanophysics and nanotechnology. Within this thematic area, our work ranges from projects trying to nail down realistic behavior in well-characterized systems, to more speculative projects reaching beyond regimes investigated experimentally to date.
Correlations between particles are a central issue in many areas of condensed matter physics, from emergent many-body phenomena in complex materials, to strong matter-light interactions in quantum information contexts, to transport properties of single molecules. Such correlations, for either electrons or bosons (photons, plasmons, phonons,…), underlie key phenomena in nanostructures. Using the exquisite control of nanostructures now possible, experimentalists will be able to engineer correlations in nanosystems in the near future. Of particular interest are cases in which one can tune the competition between different types of correlation, or in which correlation can be tunably enhanced or suppressed by other effects (such as confinement or interference), potentially causing a quantum phase transition-- a sudden, qualitative change in the correlations in the system.
My recent work has addressed correlations in both electronic systems (quantum wires and dots) and photonic systems (photon waveguides). We have focused on 3 different systems: (1) qubits coupled to a photonic waveguide, (2) quantum dots in a dissipative environment, and (3) low-density electron gas in a quantum wire. The methods used are both analytical and numerical, and are closely linked to experiments.
Yoo, J., et al. “On the sign problem in the Hirsch-Fye algorithm for impurity problems.” Journal of Physics A: Mathematical and General, vol. 38, no. 48, Dec. 2005, pp. 10307–10. Scopus, doi:10.1088/0305-4470/38/48/004. Full Text
Vorojtsov, S., et al. “Phonon decoherence of a double quantum dot charge qubit.” Physical Review B Condensed Matter and Materials Physics, vol. 71, no. 20, Dec. 2005. Scopus, doi:10.1103/PhysRevB.71.205322. Full Text
Usaj, G., and H. U. Baranger. “Erratum: Mesoscopic tunneling magnetoresistance (Physical Review B- Condensed Matter and Materials Physics (2001) 63 (184418)).” Physical Review B Condensed Matter and Materials Physics, vol. 71, no. 17, Dec. 2005. Scopus, doi:10.1103/PhysRevB.71.179903. Full Text
Mucciolo, E. R., et al. “Phonon decoherence in quantum dot qubits.” Proceedings of Spie the International Society for Optical Engineering, vol. 5815, Nov. 2005, pp. 53–61. Scopus, doi:10.1117/12.603649. Full Text
Vorojtsov, S., and H. U. Baranger. “Coulomb blockade peak spacings: Interplay of spin and dot-lead coupling.” Physical Review B Condensed Matter and Materials Physics, vol. 72, no. 16, Oct. 2005. Scopus, doi:10.1103/PhysRevB.72.165349. Full Text
Usaj, G., and H. U. Baranger. “Anisotropy in ferromagnetic nanoparticles: Level-to-level fluctuations of a collective effect.” Europhysics Letters, vol. 72, no. 1, Oct. 2005, pp. 110–16. Scopus, doi:10.1209/epl/i2005-10210-4. Full Text
Ke, San-Huang, et al. “Models of electrodes and contacts in molecular electronics..” The Journal of Chemical Physics, vol. 123, no. 11, Sept. 2005. Epmc, doi:10.1063/1.1993558. Full Text