Jongbae Hong

ANALYSIS OF OPTICAL CONDUCTIVITIES IN CUPRATES

The density of states and the optical conductivity of the doped Hubbard model on a Bethe lattice with infinite connectivities have been studied using an analytic variant of the Lanczos continued fraction method. The spectral weight of the gap states and the position of the chemical potential upon hole or electron doping have been studied. We argue that the strong correlation effects such as gap states and midinfrared band shown in two dimensions also appear in infinite dimensions. 71.20.-b, 71.27.+a, 71.30.+h Typeset using REVTEX

Electron transport from a one-dimensional lead to a two-dimensional graphene sheet through a single site

The problem of electron transport through a graphene-based device is studied theoretically and numerically. The device is composed of a single central site, with a single energy level, which is connected to a one-dimensional lead, and a two-dimensional graphene sheet. The nonequilibrium Green function formalism is utilized in modeling the problem; the formulation and numerical calculations are carried out around a K-point, in the band structure of the graphene, where the Fermi energy is located. Particular importance is placed on the transmission and current–voltage (I–V) characteristics of the device under a small bias. We find that the graphene part causes the central transmission peak, originally due to the single energy level of the central site, to split into two peaks, leaving an anti-resonant, zero-transmission, dip between them; only one of these peaks contributes to the resultant current. There always appears an almost flat, practically zero-current, region on a rather large bias interval, centered around the Fermi energy of the graphene, in the I–V graphs.

Local and nonlocal entanglement for quasiparticle pairs induced by Andreev reflection

We investigate local and nonlocal entanglement of particle pairs induced by direct and crossed Andreev reflections at the interfaces between a superconductor and two normal conductors. It is shown theoretically that both local and nonlocal entanglement can be quantified by concurrence and detected from the violation of a Bell inequality of spin current correlators, which are determined only by normal reflection and Andreev reflection eigenvalues. There exists a one-to-one correspondence between the concurrence and the maximal Bell-CHSH parameter in the tunneling limit.

Coupling of Josephson current qubits using a connecting loop

We propose a coupling scheme for the three-Josephson junction qubits which uses a connecting loop, but not mutual inductance. Present scheme offers the advantages of a large and tunable level splitting in implementing the controlled-NOT (CNOT) operation. We calculate the switching probabilities of the coupled qubits in the CNOT operations and demonstrate that present CNOT gate can meet the criteria for the fault-tolerant quantum computing. We obtain the coupling strength as a function of the coupling energy of the Josephson junction and the length of the connecting loop which varies with selecting two qubits from the scalable design.

Analytical description of V2O3 by the Hubbard model in infinite dimensions

We show that the analytic single-particle density of states and the optical conductivity for the half-filled Hubbard model on the Bethe lattice in infinite dimensions describe quantitatively the behavior of the gap and the kinetic energy ratio of the correlated insulator

Quantitative Description of

V_2O_3

V_2O_3

. The form of the optical conductivity shows

by the Hubbard Model in Infinite Dimensions

\omega^{3/2}

Persistent currents in a superconductor/normal loop

rising and is quite similar to the experimental data, and the density of states shows

Current-phase relation of the SNS junction in a superconducting loop

\omega^{1/2}