**Office Location:** 291 Physics**Office Phone:** (919) 660-2598**Email Address:** harold.baranger@duke.edu**Web Page:** http://www.phy.duke.edu/research/cm/bg

**Specialties:**

Theoretical condensed matter physics

Nanophysics

**Education:**

Ph.D., Cornell University, 1986

M.S., Cornell University, 1983

A.B., Harvard University, 1980

**Research Categories:** *Theoretical Condensed Matter Physics, Nanoscience, Quantum Materials Physics, Quantum Computing*

**Current projects:**
Unveiling Environmental Entanglement in Strongly Dissipative Qubits, Majorana Quantum Criticality Realized by Dissipative Resonant Tunneling, Waveguide QED: Photon Correlations Generated by Many Qubits, Zigzag Quantum Phase Transition in Quantum Wires

**Research Description:**

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.

**Recent Publications**
(More Publications)

- S. Bera, A. Nazir, A. W. Chin, H. U. Baranger, S. Florens,
*Generalized Multi-Polaron Expansion for the Spin-Boson Model: Environmental Entanglement and the Biased Two-State System*, Phys. Rev. B, vol. 90 (2014), pp. 075110 [pdf], [doi] . - H. Zheng, S. Florens, H.U. Baranger,
*Transport Signatures of Majorana Quantum Criticality Realized By Dissipative Resonant Tunneling*, Phys. Rev. B, vol. 89 (2014), pp. 235135 [pdf], [doi] . - S. Bera, S. Florens, H. U. Baranger, N. Roch, A. Nazir, A. W. Chin,
*Stabilizing Spin Coherence through Environmental Entanglement in Strongly Dissipative Quantum Systems*, Phys. Rev. B, vol. 89 (March, 2014), pp. 121108(R) [pdf], [doi] . - D. E. Liu, H. Zheng, G. FInkelstein, and H. U. Baranger,
*Tunable Quantum Phase Transitions in a Resonant Level Coupled to Two Dissipative Baths*, Phys. Rev. B, vol. 89 (February, 2014), pp. 085116 [pdf], [doi] . - Y.-L. L. Fang, H. Zheng, and H. U. Baranger,
*One-Dimensional Waveguide Coupled to Multiple Qubits: Photon-Photon Correlations*, Eur. Phys. J. Quantum Technology, vol. 1 (2014), pp. 3 [pdf], [doi] .

**Current Ph.D. Students**(Former Students)

**Postdocs Mentored**- Jose Hoyos Neto (11/07 - 8)
- Devrim Guclu (8/06 - 8)
- Eduardo Novais (10/04 - 5)
- Jaebeom Yoo (10/03 - 08)
- Ji-Woo Lee (09/03 - 07)
- Hong Jiang (08/03 - 08)
- Amit Ghosal (03/03 - 08)
- Martina Hentschel (08/02 - 04)
- San-Huang Ke (04/02 - 06)
- Gonzalo Usaj (09/01 - 04)
- Evgenii Narimanov (09/98 - 09)

**Selected Invited Lectures**, September 16, 2013, Colloquium at the Center for Nonlinear Studies, Los Alamos National Lab, NM*Waveguide QED: Quantum Transport of Strongly-Correlated Photons*, July 02, 2013, 2nd French-American Workshop, Grenoble France*Quantum Mechanics and Dissipation: Connecting the Nano- and Macro- Worlds*, April 25, 2013, Linnaeus Colloquium at Chalmers University of Technology, Goteborg, Sweden*Waveguide QED: Quantum Transport of Strongly-Correlated Photons*, April 23, 2013, Seminar at the Niels Bohr Institute, Copenhagen, Denmark*Quantum Critical Behavior in a Resonant Level Coupled to a Dissipative Environment*, December 14, 2012, Workshop on Novel Quantum Phenomena in Mesoscopic Systems, National Center for Theoretical Sciences, Hsinchu Taiwan*Quantum Critical Behavior in a Resonant Level Coupled to a Dissipative Environment*, June 21, 2011, Quantum Nanoelectronics Seminar, Institut Neel, Grenoble France*Quantum Phase Transition and Emergent Symmetry in Quadruple Quantum Dot System*, September 22, 2010, Conference on "New Frontiers in the Physics of Quantum Dots", Chernogolovka, Russia.*Interaction-Induced Localization in Quantum Dots and Wires: Quantum Monte Carlo Studies*, May 05, 2010, Condensed Matter Seminar at USPI Sao Carlos, Sao Carlos, Brazil*Tunable Electron-Electron Correlations in Quantum Wires and Dots*, May 04, 2010, Colloquium at the UFABC, Sao Paolo, Brazil*Transport Through Single-Molecule Junctions: Interference, Thermopower, and the Role of Self-Interaction Effects*, March 16, 2010, APS March Meeting (invited talk), Portland, Oregon., February 12, 2010, Theoretical Physics Seminar, Grenoble, France*Does Quantum Error Correction Keep Your Quantum Information Safe?*, April 13, 2009, Colloquium at NC State University, Raleigh NC*Toward Correlation Engineering in Electronic Nanostructures*, October 13, 2008, School on Mesoscopic Physics, Cargese France*Kondo Physics in Quantum Dots (a series of 3 lectures)*