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Register a new userStrong Modification of Radiative Transition Rates due to a Breit-Interaction-Induced Avoided Crossing
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We present the observations of x-rays emitted from the $1s2s^{2}2p_{1/2}2p_{3/2}$ inner shell excited state of B-like W and Bi ions. The relative transition rates are obtained for two dominant radiative transitions to $1s^{2}2s^{2}2p_{1/2}$ and $1s^{2}2s^{2}2p_{3/2}$. The experimental results and the comparison with rigorous relativistic calculations show that the rates of the strong electric dipole allowed $1s^22s^22p$ -- $1s2s^22p^2$ transitions are strongly modified due to a drastic change in the wavefunction caused by the Breit interaction.
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In 3D topological insulators, an effective closure of the bulk energy gap with increasing magnetic field expected at a critical point can yield a band crossing at a gapless Dirac node. Using high-field magnetooptical Landau level spectroscopy on the topological crystalline insulator Pb1-xSnxSe, we demonstrate that such a gap closure does not occur, and an avoided crossing is observed as the magnetic field is swept through the critical field. We attribute this anticrossing to orbital parity and spin mixing of the N=0 levels. Concurrently, we observe no gap closure at the topological phase transition versus temperature suggesting that the anticrossing is a generic property of topological phase transitions.
We consider correlated transfer ionization in relativistic collisions between a highly charged ion and a light atom. In this process two quasi-free electrons of the atom interact with each other during the short collision time that results in capture of one of them by the ion and emission of the other. We show that this process is strongly influenced by the generalized Breit interaction already at modest relativistic impact energies.
We examine structural and dynamical properties of quantum resonances associated with an avoided crossing and identify the parameter shifts where these properties attain maximal or extreme values, first at a general level, and then for a two-level system coupled to a harmonic oscillator, of the type commonly found in quantum optics. Finally the results obtained are exemplified and applied to optimize the fidelity and speed of quantum gates in trapped ions.
Second-order optical processes lead to a host of applications in classical and quantum optics. With the enhancement of parametric interactions that arise due to light confinement, on-chip implementations promise very-large-scale photonic integration. But as yet there is no route to a device that acts at the single photon level. Here we exploit the $chi^{(3)}$ nonlinear response of a Si$_{3}$N$_{4}$ microring resonator to induce a large effective $chi^{(2)}$. Effective second-order upconversion (ESUP) of a seed to an idler can be achieved with 74,000 %/W efficiency, indicating that single photon nonlinearity is within reach of current technology. Moreover, we show a nonlinear coupling rate of seed and idler larger than the energy dissipation rate in the resonator, indicating a strong coupling regime. Consequently we observe a Rabi-like splitting, for which we provide a detailed theoretical description. This yields new insight into the dynamics of ultrastrong effective nonlinear interactions in microresonators, and access to novel phenomena and applications in classical and quantum nonlinear optics.
We compute of the lowest order quantum radiative correction to the mass of the kink in $phi^4$ theory in 1+1 dimensions using an alternative renormalization procedure which has been introduced earlier. We use the standard mode number cutoff in conjunction with the above program. Our results show a small correction to the previously reported values.[The paper has been withdraw by the authors because a new version is been written to better emphasize on renormalization in problems with nontrivial background. The new version has been submitted by our new co-author (arXiv:1205.2775).]
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