# 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.

## Appointments and Affiliations

- Professor of Physics

## Contact Information

**Office Location:**291 Physics Bldg, Durham, NC 27708**Office Phone:**(919) 660-2598**Email Address:**harold.baranger@duke.edu**Websites:**

## Education

- Ph.D. Cornell University, 1986
- M.S. Cornell University, 1983

## Research Interests

My recent work has addressed correlations in both electronic systems (quantum wires and dots) and photonic systems. The methods used are both analytical and numerical, and the work is closely linked to experiments. We have focused on 3 different systems:

- Nonlinear photonic system: Unveiled a continuous quantum phase transition in a simple nonlinear oscillator. Showed it is exactly solvable in the thermodynamic limit, and so analyzed using several theoretical approaches (e.g., mean field theory, Keldysh quantum field theory, numerics). Paradigmatic dissipative quantum phase transition. [student Xin Zhang]
- Quantum dot in a dissipative environment. [collaborators Gu Zhang, Eduardo Novais, Luiz Guessi, and Xin Zhang]
- Interface between a quantum Hall insulator and a superconductor. [student Alexey Bondarev, undergrad Will Klein, collaborate with the Finkelstein group]

## Awards, Honors, and Distinctions

- Fellow. American Physical Society. 2007

## Courses Taught

- PHYSICS 516: Quantum Materials: Introduction to Solid State Physics
- PHYSICS 764: Quantum Mechanics

## In the News

- A Quantum Critical Approach (Nov 5, 2013 | Nature Physics "News & Views")
- Particles of light overcome their lack of attraction (Dec 5, 2011 | Duke Research Blog)
- Huaixiu Zheng wins John T. Chambers Scholar Award (Sep 14, 2011 | Duke Physics News)
- Prof. Baranger, "Chaire d'Excellence" (Sep 11, 2011 | Duke Physics News)

## Representative Publications

- 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 (2021), pp. 165423-165423 [10.1103/physrevb.104.165423] [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 (2021), pp. 033711-033711 [10.1103/PhysRevA.103.033711] [abs]. - Zhang, G; Chung, C-H; Ke, CT; Lin, C-Y; Mebrahtu, H; Smirnov, AI; Finkelstein, G; Baranger, HU,
*Universal Nonequilibrium I-V Curve at an Interacting Impurity Quantum Critical Point*, Physical Review Research, vol 3 (2021), pp. 013136-013136 [10.1103/PhysRevResearch.3.013136] [abs]. - Zhang, G; Baranger, HU,
*Stabilization of a Majorana Zero Mode through Quantum Frustration.*, Physical Review B, vol 102 (2020), pp. 035103-035103 [10.1103/PhysRevB.102.035103] [abs]. - Zhao, L; Arnault, EG; Bondarev, A; Seredinski, A; Larson, T; Draelos, AW; Li, H; Watanabe, K; Taniguchi, T; Amet, F; Baranger, HU; Finkelstein, G,
*Interference of Chiral Andreev Edge States*, Nature Physics, vol 16 (2020), pp. 862-867 [10.1038/s41567-020-0898-5] [abs]. - Zhang, XHH; Baranger, HU,
*Heralded Bell State of Dissipative Qubits Using Classical Light in a Waveguide.*, Physical Review Letters, vol 122 (2019), pp. 140502-140502 [10.1103/PhysRevLett.122.140502] [abs]. - Calajó, G; Fang, Y-LL; Baranger, HU; Ciccarello, F,
*Exciting a Bound State in the Continuum through Multiphoton Scattering Plus Delayed Quantum Feedback.*, Phys Rev Lett, vol 122 no. 7 (2019) [10.1103/PhysRevLett.122.073601] [abs]. - Zhang, XHH; Baranger, HU,
*Quantum interference and complex photon statistics in waveguide QED*, Physical Review A, vol 97 (2018), pp. 023813-023813 [10.1103/PhysRevA.97.023813] [abs].