Segregation of H as a surfactant during the formation of an Ag cluster on H-terminated Si(111): First-principles total-energy calculations

Abstract

The initial stages of Ag nanocluster formation on the H-terminated Si͑111͒ surface are investigated using first-principles total-energy calculations. The surface remains structurally unchanged by the adsorption of a single Ag adatom that slides nearly freely with a diffusion barrier of 0.14 eV on the H / Si͑111͒ surface ͓Phys. Rev. B 71, 035310 ͑2005͔͒. When the Ag adatoms aggregate on this surface, however, the H atoms segregate from the substrate with extremely small energy barriers of ϳ0.2 eV. The Ag n clusters ͑n ജ 2͒ with H segregation, where n is a number of Ag atoms in a cluster, are more tightly bound to the Si substrate than the clusters without H segregation since they make strong Ag-Si bonds, suggesting that such clusters can serve as seeds for island growth. The present findings are consistent with the depth-resolved measurement of H and real-space observations of the Ag islands on the H / Si͑111͒ surface.

Complete Distributed Hyper-Entangled-Bell-State Analysis and Quantum Super Dense Coding

“…In a real situation, decoherence is inevitable due to photon losses both in probe modes and signal modes. The photons losses in signal mode can be considerably suppressed by shortening the interaction time t ( t=θ/κ), however the losses of photons in probe beam is relatively large and hence the final states of signal modes will degrade to mixed states [37,44]. As described above, the small cross-Kerr nonlinearity θ can be compensated by introducing coherent state with larger amplitude.…”

“…It is demonstrated in Ref. [44] that the decoherence (photon losses), as a function of the interaction time t and the travel path αθ , will increase simultaneously with the increases of the amplitude of coherent state when homodyne measurement is used, but fortunately, the decoherence can be made arbitrarily small under the same conditions if photon-number-resolving detection is used. In addition, the distributed HBSA does not need minus phase shift, which is impractical with current technology.…”

Generation of Multiple-Atom Entangled States with Weak Cross-Kerr Nonlinearity

“…However, as the increasing of the amplitude of the coherent states, the fidelity of these schemes will decrease simultaneously due to the decoherence (photon loss). Fortunately, the decoherence can be made arbitrarily small simply by an arbitrary strong coherent state associated with a displacement D(−α) performed on the coherent state and the quantum nondemolition photon-number-resolving detection [36]. Additionally, the photon loss also causes de-phasing, corresponding to phase flip errors, in the original two-qubit state [35].…”

“…In the real situation, decoherence is inevitable, the photon loss may occur when the coherent state transmits through an optical fiber. When photon loss occurs, the qubit states will evolve to the mixed states after the homodyne detection [35][36][37], after which the fidelity of the proposed schemes will degrade. As described above, the amplitude of the coherent state α may be large enough to satisfy the requirement αθ > 1 when the cross-Kerr nonlinearity is small.…”

Nearly Deterministic Generation of Atomic Entangled State with Weak Cross-Kerr Nonlinearities

“…But the strong probe coherent field with a large amplitude will make the fidelity of the scheme decrease simultaneously because of the decoherence (photon loss) during nonlinear interaction and transmission in optical fibre. Then an arbitrary strong coherent state associated with a displacement D(−α) was required to performed on the coherent state and the QND photon-number-resolving detection [34,35], which can make the decoherence arbitrarily small. In addition, the entanglement of the degraded entangled states after transmission can be enhanced by entanglement purification [21,22,36].…”