Ke-Hui Song

Semiconducting states and transport in metallic armchair-edged graphene nanoribbons

Based on the nonequilibrium Greens function method within the tight-binding approximation scheme, through a scanning tunneling microscopy (STM) model, we study the low-energy electronic states and transport properties of carbon chains in armchair-edged graphene nanoribbons (AGNRs). We show that semiconducting AGNRs possess only semiconducting chains, while metallic ones possess not only metallic chains but also unconventional semiconducting chains located at the 3 jth (j ≠ 0) column from the edge (the first chain) due to the vanishing of the metallic component in the electron wavefunction. The two types of states for carbon chains in a metallic AGNR system are demonstrated by different density of states and STM tunneling currents. Moreover, a similar phenomenon is predicted in the edge region of very wide AGNRs. However, there is remarkable difference in the tunneling current between narrow and wide ribbons.

Entanglement dynamics of two electron-spin qubits in a strongly detuned and dissipative quantum-dot-cavity system

We investigate the entanglement dynamics of two electron-spin qubits in the quantum-dot (QD)–microcavity system in the large-detuning limit and subjected to two different noise sources: electron-spin dephasing and relaxation. We show that when one of the two dots is prepared initially in the excited state, the created entanglement exhibits oscillatory behavior at the beginning of evolution and then completely disappears over time. For two QDs that are initially in either the Einstein–Podolsky–Rosen-Bell states or the Werner states, their entanglement evolution exhibits the same behavior in the presence of pure dephasing, but is completely different under the relaxation process. We also show that the interdot interaction induced by a single-mode cavity field does not contribute to the dynamics of entanglement for these Bell states and Werner states.

Robust and controllable electronic local transports in armchair silicene nanoribbons under a perpendicular electric field

We study the electronic local distribution and transports in pristine armchair-edge silicene nanoribbons (ASiNRs) based on the tight-binding approximation. By calculating the local densities of states at different sites and the bond current between two adjacent sites, we show that comparing to the pristine armchair-edge graphene nanoribbons, a similar “3j” rule and multiple low-electron transport channels exist in the pristine (3p + 2)-ASiNRs. However, differently, they are controllable to appear and disappear by applying an electric field perpendicular to the ribbon plane. Therefore, one can manipulate the semiconducting channels and realize the current switch “on/off,” unchanging their structures. Moreover, the results are robust against the edge-passivation and a few structural defects, which ensures their stability for the practical application in the silicene-based device.

Electronic structure, chemical bonding and optical properties of the nonlinear optical crystal ZnGeP2 by first-principles calculations

Using the plane wave pseudopotential method within density-functional theory, we have theoretically investigated the structural, electronic, chemical bonding and optical properties of the chalcopyrite semiconductor ZnGeP2. It is found that ZnGeP2 has an indirect band gap of 1.222 eV. The covalent character of the bonds in ZnGeP2 crystal is verified by Mulliken population. By analyzing the optical properties including the dielectric function, refractive index, extinction coefficient, reflectivity spectrum and absorption coefficient, we indicate that ZnGeP2 is a promising mid-IR optical material, which is in good agreement with the available experimental results.

Influence of cavity decay on unconventional geometric quantum phase gates with superconducting quantum-interference-device qubits inside a cavity

We propose a potential scheme for carrying out two-qubit unconventional geometric logic gates on two identical superconducting quantum-interference-device (SQUID) qubits coupled to a single-mode microwave field. The geometric logic gate operation is performed in two lower flux states, and the excited state |2 does not participate in the procedure. The SQUIDs undergo no transitions during gate operation. Thus, the decoherence due to energy spontaneous emission based on the levels of SQUIDs is suppressed. We present the two-qubit unconventional geometric logic gates in both an ideal cavity and a real cavity with decay. Discussions about the fidelity and the success probability of the proposed scheme as well as the experimental feasibility are given in detail.