arXiv subjects

S. Y. Zhu

Publications and source records attributed to S. Y. Zhu.

4 recordsLinked to original sources

arXiv2015

Application of the weak-measurement technique to study atom-vacuum interactions

Quantum weak measurement has attracted much interest recently [J. Dressel et al., Rev. Mod. Phys. 86, 307 (2014)] because it could amplify some weak signals and provide a technique to observe nonclassical phenomena. Here, we apply this technique to study the interaction between the free atoms and the vacuum in a cavity. Due to the gradient field in the vacuum cavity, the external orbital motions and the internal electronic states of atoms can be weakly coupled via the atom-field electric-dipole interaction. We show that, within the properly postselected internal states, the weak atom-vacuum interaction could generate a large change to the external motions of atoms due to the postselection-induced weak values.

quant-ph↗

arXiv2012

Evolution of band structure from optimally doped to heavily overdoped Co-substituted NaFeAs

Using angle-resolved photoemission spectroscopy, we studied the electronic structure of NaFe$_{1-x}$Co$_x$As from an optimally doped superconducting compound ($x=0.028$) to a heavily overdoped non-superconducting one ($x=0.109$). Similar to the case of "122" type iron pnictides, our data suggest that Co dopant in NaFe$_{1-x}$Co$_x$As supplies extra charge carriers and shifts the Fermi level accordingly. In the $x=0.109$ compound, the hole-like bands around the zone center $Γ$ move to deeper binding energies and an electron pocket appears instead. The overall band renormalization remains basically the same throughout the doping range we studied, suggesting that the local magnetic/electronic correlations are not affected by carrier doping. We speculate that a balance between itinerant properties of mobile carriers and local interactions may play an important role for the superconductivity.

cond-mat.supr-con↗

arXiv2011

Quasiparticle interference on the surface of 3D topological insulator Bi$_{2}$Se$_{3}$ induced by cobalt adatom in the absence of ferromagnetic ordering

Quasiparticle interference induced by cobalt adatoms on the surface of the topological insulator Bi$_{2}$Se$_{3}$ is studied by scanning tunneling microscopy, angle-resolved photoemission spectroscopy and X-ray magnetic circular dichroism. It is found that Co atoms are selectively adsorbed on top of Se sites and act as strong scatterers at the surface, generating anisotropic standing waves. A long-range magnetic order is found to be absent, and the surface state Dirac cone remains gapless. The anisotropy of the standing wave is ascribed to the heavily warped iso-energy contour of unoccupied states, where the scattering is allowed due to a non-zero out-of-plane spin.

cond-mat.mtrl-sci↗

arXiv2008

Quantum Zeno and Anti-Zeno Effect without Rotating Wave Approximation

The effect of the anti-rotating terms on the short-time evolution and the quantum Zeno (QZE) and anti-Zeno (AQZE) effects is studied for a two-level system coupled to a bosonic environment. A unitary transformation and perturbation theory are used to obtain the electron self-energy, energy shift and the enhanced QZE or the AQZE, simultaneously. The calculated Zeno time depends on the atomic transition frequency sensitively. When the atomic transition frequency is smaller than the central frequency of the spectrum of boson environment, the Zeno time is prolonged and the anti-rotating terms enhance the QZE; when it is larger than that the Zeno time is reduced and the anti-rotating terms enhance the AQZE.

quant-ph↗