We explore quantum correlations, in particular, quantum entanglement, among vibrational phonon modes as well as between electronic and vibrational degrees of freedom in molecular systems,described by Jahn-Teller mechanism. Specifically, to isolate and simplify the phonon-electron interactions in a complex molecular system, the basis of our discussions is taken to be the proposal of simulating two-frequency Jahn-Teller systems using superconducting circuit quantum electrodynamics systems (circuit QED) by Tekin Dereli and co-workers in 2012. We evaluate the quantum correlations, in particular entanglement between the vibrational phonon modes, and present analytical explanations using a single privileged Jahn-Teller mode picture. Furthermore, spin-orbit entanglement or quantum correlations between electronic and vibrational degrees of freedom are examined, too. We conclude by discussing experimental feasibility to detect such quantum correlations, considering the dephasing and decoherence in state-of-the-art superconducting two-level systems (qubits).
We propose a quantum heat engine composed of two superconducting transmission line resonators interacting with each other via an optomechanical-like coupling. One resonator is periodicallyexcited by a thermal pump. The incoherently driven resonator induces coherent oscillations in the other one due to the coupling. A limit cycle, indicating finite power output, emerges in the thermodynamical phase space. The system implements an all-electrical analog of a photonic piston. Instead of mechanical motion, the power output is obtained as a coherent electrical charging in our case. We explore the differences between the quantum and classical descriptions of our system by solving the quantum master equation and classical Langevin equations. Specifically, we calculate the mean number of excitations, second-order coherence, as well as the entropy, temperature, power and mean energy to reveal the signatures of quantum behavior in the statistical and thermodynamic properties of the system. We find evidence of a quantum enhancement in the power output of the engine at low temperatures.
We propose a quantum-electrodynamics scheme for implementing the
discrete-time, coined quantum walk with the walker corresponding to the phase
degree of freedom for a quasi-magnon fieldrealized in an ensemble of
nitrogen-vacancy centres in diamond. The coin is realized as a superconducting
flux qubit. Our scheme improves on an existing proposal for implementing
quantum walks in cavity quantum electrodynamics by removing the cumbersome
requirement of varying drive-pulse durations according to mean quasiparticle
number. Our improvement is relevant to all indirect-coin-flip cavity
quantum-electrodynamics realizations of quantum walks. Our numerical analysis
shows that this scheme can realize a discrete quantum walk under realistic
conditions.