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Sparse connectivity of a superconducting quantum computer results in large experimental overheads of SWAP gates. In this study, we consider employing a virtual two-qubit gate (VTQG) as an error suppression technique. The VTQG enables a non-local operation between a pair of distant qubits using only single qubit gates and projective measurements. Here, we apply the VTQG to the digital quantum simulation of the transverse-field Ising model on an IBM quantum computer to suppress the errors due to the noisy two-qubit operations. We present an effective use of VTQG, where the reduction in multiple SWAP gates results in increasing the fidelity of output states. The obtained results indicate that the VTQG can be useful for suppressing the errors due to additional SWAP gates. In our experiments, we have observed one order of magnitude improvement in accuracy for the quantum simulation of the transverse-field Ising model with 8 qubits. Finally, we have demonstrated an efficient implementation of the VTQG by utilizing dynamic circuits. This scheme reduces experimental overheads for implementing m VTQGs from O (10 m) to O (6 m). [ABSTRACT FROM AUTHOR]

Holographic gratings were formed in an optically isotropic state of polymer azobenzene liquid crystal films.

We theoretically and computationally examined carrier localization in semiconducting edge-disordered graphene nanoribbons (ED-GNRs) with sub-100nm lengths that correspond to the typical gate length for field-effect transistors. We numerically found that the localization length of ED-GNRs is proportional to the square of ribbon width and inversely proportional to the edge-disorder concentration. Furthermore, we obtained an analytical formula of the localization length in terms of the GNR width and the roughness concentration. [ABSTRACT FROM AUTHOR]

We present a theoretical study on inelastic transient electrical currents and the effects of phonon heating in a single-level quantum dot system weakly coupled to a localized vibration degree of freedom, using the nonequilibrium Green's function method under the wide-band-limit and the lowest-order-expansion approximations. The energy transfer between electron and phonon systems is evaluated using both approximations, which separately are exact in the limits of the equilibrium state (t < 0) and steady state (t→∞). The time-dependent phonon number, which determines the system temperature and heating effects on the inelastic current, is calculated using a phenomenological method employing the time-dependent power transfer. The two approximations are shown to provide qualitatively similar dynamical behaviors for the system temperature, which can be grouped under two responses: if the energy corresponding to the applied bias voltage is smaller than or equal to the phonon energy, the temperature first increases because of phonon emission, and then decreases because of phonon absorption; alternatively, if the energy corresponding to the bias voltage is larger than the phonon energy, the temperature increases monotonically until a steady state is reached. The total electrical current is suppressed by phonon heating, while heat transferring between dot and environment mitigates the effects of such heating. Furthermore, the relaxation time of the current is extended by phonon scattering and heating. [ABSTRACT FROM AUTHOR]

The transient current dynamics of multilevel nanoscale systems weakly coupled with two electrodes has been theoretically investigated by the nonequilibrium Green's function method. We have proposed a technique for decomposing the total time-dependent current into almost independent current components. This is a powerful technique for gaining insight into transient current behavior because the decomposed currents exhibit simple behaviors similar to those of single-level systems. We have clarified the transient current behaviors of a hydrogen molecule (two-level system) and an octatetraene molecule (eight-level system) connected to two electrodes as typical examples of multilevel systems. The transient current of the molecular hydrogen system is characterized by two current components with the same relaxation time and different oscillation periods, whereas the current of the octatetraene molecular system is decomposed into eight components, a few of which dominate the total current behavior during the initial stage. [ABSTRACT FROM AUTHOR]