# Harold U. Baranger

### **Professor of Physics**

### Overview

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.

### Selected Grants

Quantum Phases in Nanosystems: Non-Equilibrium Phenomena Near Quantum Critical Points awarded by Department of Energy (Principal Investigator). 2010 to 2020

Quantum machine learning for dissipative dynamics of NISQ devices awarded by (Principal Investigator). 2020

Waveguide QED: Photon Correlations in Strongly Coupled Open Systems awarded by National Science Foundation (Principal Investigator). 2011 to 2017

Enhancing Light-Matter Interfaces via Collective Self-Organization awarded by National Science Foundation (Co-Principal Investigator). 2012 to 2016

Development of dissipative resonant levels to study Majorana physics in nanotube quantum dots awarded by Army Research Office (Co-Principal Investigator). 2014 to 2015

Coherence and Correlations in Electronic Nanostructures awarded by National Science Foundation (Principal Investigator). 2005 to 2009

Collaborative Research: Is Resilient Quantum Computing in Solid State Systems Possible? awarded by National Science Foundation (Principal Investigator). 2005 to 2008

Coherence and Correlation in Electronic Nanostructures awarded by National Science Foundation (Principal Investigator). 2001 to 2006

Robustness of Quantum Computing in Quantum Dots awarded by Army Research Office (Principal Investigator). 2002 to 2005

Electronic Properties of Nanostructures awarded by National Science Foundation (Principal Investigator). 2002 to 2005

Novais, E., et al. “Hamiltonian methods in quantum error correction and fault tolerance.” *Quantum Error Correction*, vol. 9780521897877, 2012, pp. 585–611. *Scopus*, doi:10.1017/CBO9781139034807.027.
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Zhang, Gu, and Harold U. Baranger. “Stabilization of a Majorana Zero Mode through Quantum Frustration.” *Arxiv*, Dec. 2019.

Zhao, Lingfei, et al. “Interference of chiral Andreev edge states.” *Arxiv*, July 2019.

Zhang, Xin H. H., and Harold U. Baranger. “Heralded Bell State of Dissipative Qubits Using Classical Light in a Waveguide.” *Phys Rev Lett*, vol. 122, no. 14, Apr. 2019, pp. 140502–140502. *Manual*, doi:10.1103/PhysRevLett.122.140502.
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Calajó, Giuseppe, et al. “Exciting a Bound State in the Continuum through Multiphoton Scattering Plus Delayed Quantum Feedback.” *Physical Review Letters*, vol. 122, no. 7, Feb. 2019, p. 073601. *Epmc*, doi:10.1103/physrevlett.122.073601.
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Gheeraert, N., et al. “Particle production in ultrastrong-coupling waveguide QED.” *Physical Review A*, vol. 98, no. 4, Oct. 2018. *Scopus*, doi:10.1103/PhysRevA.98.043816.
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Fang, Y. L. L., et al. “Non-Markovian dynamics of a qubit due to single-photon scattering in a waveguide.” *New Journal of Physics*, vol. 20, no. 4, Apr. 2018. *Scopus*, doi:10.1088/1367-2630/aaba5d.
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Zhang, X. H. H., and H. U. Baranger. “Quantum interference and complex photon statistics in waveguide QED.” *Physical Review A*, vol. 97, no. 2, Feb. 2018. *Scopus*, doi:10.1103/PhysRevA.97.023813.
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Fang, Y. L. L., and H. U. Baranger. “Multiple emitters in a waveguide: Nonreciprocity and correlated photons at perfect elastic transmission.” *Physical Review A*, vol. 96, no. 1, July 2017. *Scopus*, doi:10.1103/PhysRevA.96.013842.
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Zhang, G., et al. “Universal Nonequilibrium I-V Curve at an Interacting Impurity Quantum Critical Point.” *Arxiv*, vol. 1609, Sept. 2016.
Open Access Copy

Fang, Yao-Lung L., and Harold U. Baranger. “Photon correlations generated by inelastic scattering in a one-dimensional waveguide coupled to three-level systems.” *Physica E: Low Dimensional Systems and Nanostructures*, vol. 78, Elsevier BV, Apr. 2016, pp. 92–99. *Crossref*, doi:10.1016/j.physe.2015.11.004.
Full Text Open Access Copy

## Pages

Usaj, G., and H. U. Baranger. “TMR in nanoscale F-N-F systems: Mesoscopic fluctuations.” *Electronic Correlations: From Meso to Nano Physics*, edited by T. Martin et al., E D P SCIENCES, 2001, pp. 493–96.

BARANGER, H. U. “TRANSPORT IN ELECTRON WAVE-GUIDES - FILTERING AND BEND RESISTANCES.” *Computational Electronics*, edited by K. HESS et al., KLUWER ACADEMIC PUBLISHERS, 1991, pp. 201–06.

Davies, John H., et al. *Potential Fluctuations in Heterostructure Devices*. Springer US, 1991, pp. 387–97. *Crossref*, doi:10.1007/978-1-4684-1348-9_30.
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BARANGER, H. U., and A. D. STONE. “SELECTIVE-POPULATION OF MODES IN ELECTRON WAVE-GUIDES - BEND RESISTANCES AND QUENCHING OF THE HALL RESISTANCE.” *Science and Engineering of One and Zero Dimensional Semiconductors*, edited by S. P. BEAUMONT and C. M. SOTOMAYORTORRES, vol. 214, PLENUM PRESS DIV PLENUM PUBLISHING CORP, 1990, pp. 121–32.