Non-Markovian disentanglement dynamics of two-qubit system

We investigated the disentanglement dynamics of two-qubit system in Non-Markovian approach. We showed that only the couple strength with the environment near to or less than fine-structure constant 1/137, entanglement appear exponential decay for a certain class of two-qubit entangled state. While the coupling between qubit and the environment is much larger, system always appears the sudden-death of entanglement even in the vacuum environment.Comment: 17 pages, 3 figure

Non-Markovian coherence dynamics of driven spin boson model: damped quantum beat or large amplitude coherence oscillation

The dynamics of driven spin boson model is studied analytically by means of the perturbation approach based on a unitary transformation. We gave the analytical expression for the population difference and coherence of the two level system. The results show that in the weak driven case, the population difference present damped coherent oscillation (single or double frequency) and the frequencies depend on the initial state. The coherence exhibit damped oscillation with Rabi frequency. When driven field is strong enough, the population difference exhibit undamped large-amplitude coherent oscillation. The results easily return to the two extreme cases without dissipation or without periodic driven.Comment: 15 pages,5 figure

Barrier RF Stacking

A novel wideband RF system, nicknamed the barrier RF, has been designed, fabricated and installed in the Fermilab Main Injector. The cavity is made of seven Finemet cores, and the modulator made of two bipolar high-voltage fast solid-state switches. The system can deliver ±7 kV square pulses at 90 kHz. The main application is to stack two proton batches injected from the Booster and squeeze them into the size of one so that the bunch intensity can be doubled. High intensity beams have been successfully stacked and accelerated to 120 GeV with small losses. The problem of large longitudinal emittance growth is the focus of the present study. An upgraded system with two barrier RF cavities for continuous stacking is under construction. This work is part of the US-Japan collaborative agreement

Quantum dynamics of a qubit coupled with structured bath

The dynamics of an unbiased spin-boson model with Lorentzian spectral density is investigated theoretically in terms of the perturbation theory based on a unitary transformation. The non-equilibrium correlation function $P(t)$ and susceptibility $\chi^{\prime\prime}(\omega)$ are calculated for both the off-resonance case $\Delta\lesssim 0.5\Omega$ and the on-resonance case $\Delta\sim \Omega$. The approach is checked by the Shiba's relation and the sum rule. Besides, the coherent-incoherent transition point $\alpha_c$ can be determined, which has not been demonstrated for the structured bath by previous authors up to our knowledge.Comment: 25 pages, 11 figure