Salil Bedkihal, Exeter
Understanding the interplay of non-equilibrium effects, dissipation and many body interactions is a fundamental challenge in condensed matter physics. In this work, as a case study, we focus on the transient dynamics and the steady state characteristics of the double-dot Aharonov-Bohm (AB) interferometer subjected to a voltage and/or temperature bias. We first consider an exactly solvable case, the noninteracting double-dot AB interferometer. The transient dynamics of this model is studied using an exact fermionic trace formula, and the analytic expressions in the long time limit are obtained using a non-equilibrium Green's function technique. We also study the effects of elastic dephasing on the occupation-flux behaviour in this noninteracting limit. Several nontrivial magnetic flux control effects are exposed, potentially useful for the design of nanoscale devices. The real time dynamics of the coherences and the charge current in an interacting interferometer is simulated using the numerically exact influence functional path integral (INFPI) technique. The temporal characteristics of the coherence in the weak-intermediate Coulomb repulsion case are qualitatively similar to those found in the noninteracting limit. In contrast, in the large Coulomb repulsion and the large bias limit, master equation simulations reveal notably different dynamics and steady state characteristics. We study the effects of many body interactions on magneto-asymmetries of nonlinear transport coefficients using phenomenological models, Buttiker's probes. Sufficient conditions for the diode functionality in Aharonov-Bohm interferometers are obtained analytically within the framework of Landauer-Buttiker scattering theory. Predictions of the phenomenological probes models are verified by studying a microscopic model with a genuine many body interaction, a double-dot interferometer capacitively coupled to a fermionic environment. These simulations are carried out using the INFPI technique. Some general comments about the suitability of INFPI to study nonlinear transport are presented [1-4]. Our technique may be extended to study the quantum coherence dynamics in the interacting flux-qubit systems.
In the second part, I focus on the dynamics of integrating spin systems relevant to the spin chemistry and quantum biology, and propose the design of a chemical compass based on the long-range dipole-dipole interactions and the exchange interactions. We find that the interplay of discrete symmetries and the energy level crossings that leads to the pronounced magneto-sensitive reactions, even at fields weaker than the geomagnetic field. These results may have far reaching consequences on quantum magneto-reception theories of avian migration, and also to evaluate the effects of weak-magnetic fields on biological processes. Unlike the conventional model of magneto-sensitive reactions, our model does not require the hyperfine-interaction for the coherent-singlet-triplet mixing and may be relevant to explain the effects of weak-magnetic fields on bio-molecular systems devoid of hyperfine interactions [5]
In the third part, we present the quantum-dynamics of exciton-phonon interactions in the quantum-dot systems. We propose novel quantum-dot spin heat engines operating under thermal and spin-baths. The dynamics of heat engines is simulated using effective-mode master equations to capture the non-Markovian dynamics of exciton-phonon dynamics at picosecond-time scales. In particular, we theoretically demonstrate the conversion of thermal phonon energy into a coherent optical work at the cost of the spin-angular momentum in the nuclear spin-bath.
Such heat engines are beyond the traditional paradigms of thermodynamics and offer promising applications such as spin-based batteries [6,7]. I further formalize the observations and present the overview of concepts in quantum thermodynamics of multiple conserved quantities.
References:
[1] Salil Bedkihal and Dvira Segal, Phys. Rev. B 85, 155324, (2012)
[2] Salil Bedkihal, Malay Bandyopadhyay, and Dvira Segal, Phys. Rev. B 87, 045418, (2013)
[3] Salil Bedkihal, Malay Bandyopadhyay, and Dvira Segal, Phys. Rev. B 88, 155407, (2013)
[4] Salil Bedkihal and Dvira Segal, Phys. Rev. B 90, 235411, (2014)
[5] Robert H. Keens, Salil Bedkihal, and Daniel R. Kattnig, Phys. Rev. Lett. 121, (2018)
[6] Toshio Croucher, Salil Bedkihal, and Joan A. Vaccaro, Phys. Rev. Lett. 118, 060602, (2017)
[7] Jackson S. S. T. Wright, Tim Gould, André R. R. Carvalho, Salil Bedkihal, and Joan A. Vaccaro, Phys. Rev. A 97, 052104, (2018)