National Institute Of Materials Physics - Romania

Nanoscale Condensed Matter Laboratory

Theoretical Physics Group

Aim: We carry out theoretical studies of low-dimensional materials in order to identify new topological and transport properties. Open hybrid quantum systems in different operating regimes are investigated in view of their implementation as solid-state qubits. These two research directions of the group were simultaneously initiated in 2014 and follow naturally from one more general direction of the NIMP’s present and future strategy (i.e. frontier research in condensed matter physics and advanced materials).

            Research team: 7 permanent positions.

Dr. V. Moldoveanu – Head of the group

Dr. M. Tolea

Dr. M. Nita

Dr. I. V. Dinu

Dr. R. Dragomir

Dr. B. Ostahie

Drd. S. Stanciu

Dr. P. Gartner (Emeritus Prof)

            Research topics: 

            A. Topological features of 2D materials and transport properties of 2D lattices.

Brief description and motivation: The discovery of 2D materials (e.g. graphene and phosphorene) and of the symmetry-protected surface states in topological insulators triggered tremendous progress in condensed matter physics. The substantial amount of experimental and theoretical studies is expected to deliver high-quality spintronic or magnetoelectric devices. Moreover, combining the topological insulators with superconductors can lead to the production of a topological quantum computer in the near future. In this context, appropriate analytical and numerical methods are needed to predict the existence of non-trivial states or topological quantum phase-transitions in such systems and related 2D lattices. The latter exhibit chiral edge states and anomalous quantum Hall effect. Recent topological classifications of non-Hermitian systems motivate extensive investigations of their transport properties and corresponding finite-size effects.

            B. Open quantum emitters and nano-electromechanical systems.

Brief description and motivation: As systematically revealed in corner-stone experiments, the coupling of electronic/spin degrees of freedom to quantized optical or vibrational modes is both studied and successfully manipulated/engineered in cavity-coupled mesoscopic conductors or nano-electromechanical systems (NEMS). At very-low temperature these couplings lie behind most promising applications in cavity-QED, microwave photonics and superconducting quantum circuits. Since most qubit-based devices must perform read-and-write operations which emerge from entangled quantum dynamics and are submitted to decoherence and dissipation, a time-dependent many-body description of open systems is required. On the other hand, recent experiments with hybrid quantum systems pushed the electron-photon coupling to ultra-strong and deep ultra-strong regimes for which the well-known effective models from quantum optics (e.g Jaynes-Cumming and Tavis-Cummnings Hamiltonians) are no longer appropriate.

            Funding (2017-2019):

– PCE 3/2017 “Electron-vibron coupling effects in nano-electromechanical systems” (PI V. Moldoveanu).

– PCE 201/2017 “Spontaneous symmetry breaking and dissipative processes in single quantum dot lasers. Lasing as a phase transition” (PI P. Gartner).

            Selected results (2015-2019):

i) Quantum transport and lasing in optically active systems. Scientific output: 4 Phys. Rev. B, 2 Phys. Rev. A, 1 Phys. Rev. Applied, 1 Beilstein Journal of Nanotechnology).

ii)  Graphene-physics, Quantum Spin Hall effect, non-Hermitian physics of 2D materials. Scientific output: 4 Phys. Rev. B, 2 Rapid Research Letters).

iii) Correlation effects in 2D lattices, circular molecules and single-molecule magnets. Scientific output:(1 Scientific Reports, 3 PRB, 1 New J. Phys.)

iv) Extension of the density-matrix operator method and the mathematical justification of the

non-equilibrium Greens’ functions formalism. Scientific output: (2 papers – Entropy and Annales Henri Poicare).

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