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.

**Keywords:**- condensed matter, solid state, nanoscience, nanoscale, mesoscopic, quantum interference, electron transport, spintronics, molecular electronics, electron correlations, novel materials, materials physics, emergent phenomena, quantum optics, non-classical light, circuit QED, waveguide QED, superconductivity, quantum networks, quantum interference, 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

**Recent 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]

- S. Bera, A. Nazir, A. W. Chin, H. U. Baranger, S. Florens,