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.
Jin, L. J., et al. “Detecting photon-photon interactions in a superconducting circuit.” Physical Review B Condensed Matter and Materials Physics, vol. 92, no. 13, Oct. 2015. Scopus, doi:10.1103/PhysRevB.92.134503. Full Text
Fang, Y. L. L., and H. U. Baranger. “Waveguide QED: Power spectra and correlations of two photons scattered off multiple distant qubits and a mirror.” Physical Review a Atomic, Molecular, and Optical Physics, vol. 91, no. 5, May 2015. Scopus, doi:10.1103/PhysRevA.91.053845. Full Text
Fang, Yao-Lung L., et al. “One-dimensional waveguide coupled to multiple qubits: photon-photon correlations.” Epj Quantum Technology, vol. 1, no. 1, Springer Science and Business Media LLC, Dec. 2014. Crossref, doi:10.1140/epjqt3. Full Text
Bera, S., et al. “Generalized multipolaron expansion for the spin-boson model: Environmental entanglement and the biased two-state system.” Physical Review B Condensed Matter and Materials Physics, vol. 90, no. 7, Aug. 2014. Scopus, doi:10.1103/PhysRevB.90.075110. Full Text
Zheng, H., et al. “Transport signatures of Majorana quantum criticality realized by dissipative resonant tunneling.” Physical Review B Condensed Matter and Materials Physics, vol. 89, no. 23, June 2014. Scopus, doi:10.1103/PhysRevB.89.235135. Full Text
Ullmo, Denis, et al. “Mesoscopic fluctuations in the Fermi-liquid regime of the Kondo problem.” The European Physical Journal B, vol. 86, no. 8, Springer Science and Business Media LLC, Aug. 2013. Crossref, doi:10.1140/epjb/e2013-40418-3. Full Text
Zheng, Huaixiu, and Harold U. Baranger. “Persistent quantum beats and long-distance entanglement from waveguide-mediated interactions..” Physical Review Letters, vol. 110, no. 11, Mar. 2013. Epmc, doi:10.1103/physrevlett.110.113601. Full Text
Zheng, Huaixiu, et al. “Decoy-state quantum key distribution with nonclassical light generated in a one-dimensional waveguide..” Optics Letters, vol. 38, no. 5, Mar. 2013, pp. 622–24. Epmc, doi:10.1364/ol.38.000622. Full Text
Mebrahtu, H. T., et al. “Observation of majorana quantum critical behaviour in a resonant level coupled to a dissipative environment.” Nature Physics, vol. 9, no. 11, Jan. 2013, pp. 732–37. Scopus, doi:10.1038/nphys2735. Full Text
Mebrahtu, Henok T., et al. “Quantum phase transition in a resonant level coupled to interacting leads..” Nature, vol. 488, no. 7409, Aug. 2012, pp. 61–64. Epmc, doi:10.1038/nature11265. Full Text