**Office Location:** 291 Physics Bldg, Durham, NC 27708**Email Address:** harold.baranger@duke.edu**Web Page:** https://orcid.org/0000-0002-1458-2756

**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)

- Lee, JW; Baranger, HU,
*Quantum critical region of a two-dimensional spin-half XXZ model*, Journal of the Korean Physical Society, vol. 82 no. 7 (April, 2023), pp. 688-691 [doi] [abs]. - Zhang, G; Novais, E; Baranger, HU,
*Conductance of a dissipative quantum dot: Nonequilibrium crossover near a non-Fermi-liquid quantum critical point*, Physical Review B, vol. 104 (October, 2021), pp. 165423-165423, American Physical Society (APS) (arXiv:2108.00064.) [2108.00064], [doi] [abs]. - Zhang, XHH; Baranger, HU,
*Driven-Dissipative Phase Transition in a Kerr Oscillator: From Semi-Classical PT Symmetry to Quantum Fluctuations.*, Physical Review A, vol. 103 (March, 2021), pp. 033711-033711, American Physical Society (arXiv:2007.01422.) [2007.01422], [doi] [abs]. - Zhang, G; Chung, C-H; Ke, C-T; Lin, C-Y; Mebrahtu, H; Smirnov, AI; Finkelstein, G; Baranger, HU,
*Nonequilibrium quantum critical steady state: Transport through a dissipative resonant level*, Physical Review Research, vol. 3 no. 1 (February, 2021), pp. 013136-013136, American Physical Society (APS) (arXiv:1609.04765.) [1609.04765], [doi] [abs]. - Zhang, G; Baranger, HU,
*Stabilization of a Majorana Zero Mode through Quantum Frustration.*, Physical Review B, vol. 102 (July, 2020), pp. 035103-035103 (arXiv:1912.12950.) [doi] [abs].

**Highlight:**

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) interfaces between graphene and a superconductor, particularly when graphene is in the quantum Hall state. The methods used are both analytical and numerical, and are closely linked to experiments.

**Current Ph.D. Students**(Former Students)- Gu Zhang
- Yao-Lung Fang

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