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We propose a model for studying the ionization, photoelectron spectra, and spin polarization of xenon atoms under intense circularly polarized (CP) pulses by solving the time-dependent Schrödinger equation (TDSE) with an effective potential for Xe. The ionization mechanism is mainly due to multiphoton absorption in these strong CP fields. The effective potential of a single active electron for Xe consists of asymptotic Coulomb and parametric screening parts and yields low-lying levels that are comparable to those by other models for the total angular momentum J = 3 / 2 of X e + and new for J = 1 / 2 . We show in detail the absorption pathways, above-threshold ionization (ATI) spectra, and spin polarization mechanisms of photoelectrons originated from the initial state 5 p m l of Xe with the magnetic quantum number m l being − 1 , 0, or 1. There exists a substructure with sub-peaks in each of multiple ATI peaks from 5 p − 1 due to pulse effects on the valence electron passing through the absorption pathways. ATI and spin polarization results agree qualitatively with experimental data at the focal volume average to include the spatial effect of CP pulses. We also present the spin polarization results of the widely used strong-field approximation model (SFA), which are inconsistent with those of TDSE and experiments. This shows that TDSE is more accurate with more details than SFA for studying spin polarization in strong CP fields.

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We point out the possibility of occurring instabilities in Laughlin liquids of rotating dipolar fermions with zero thickness. Previously such a system was predicted to be the Laughlin liquid for filling factors ν ≥ 1/7. However, from intra-Landau-level excitations of the liquid in the single-mode approximation, the roton minima become negative and Laughlin liquids are unstable for ν ≤ 1/7. We then conclude that there are correlated Wigner crystals for ν ≤ 1/7.PACS numbers: 03.75. Ss, 73.43.Lp, 73.43.Nq The cold quantum gas with the dipole-dipole interaction (DDI) was first realized in Cr atoms [1]. The quantum gases with the DDI are qualitatively different from non-dipolar ones [2]. The novel anisotropic and long-range nature of the DDI offers a broad range of strong correlated many-body physics [3,4]. New quantum phases were predicted for the dipolar Bose-Einstein condensate (BEC) [5,6]. The influence of the trapping geometry on the stability of the BEC and the effect of the DDI on the excitation spectrum were studied [7]. The vortex lattice of the rotating dipolar BEC exhibits novel bubble, stripe, and square structures [8]. For the dipolar Fermi gases, the s-wave scattering is prohibited due to the Pauli Exclusion Principle and the Fermi surface is distorted by dipolar effects [9]. Bond pairs of fermions with resonant interaction are formed and the system of a Fermi gas behaves as a bosonic gas of molecules [10,11]. The observed pairing of fermions provides the crossover between the weakly-paired, strongly overlapping BardeenCooper-Schrieffer regime, and the tightly bound, weaklyinteracting diatomic molecular BEC regime [12]. The strong correlations of fermions induced by the DDI can then be explored, such as the dipolar-induced superfluidity [13,14] and fractional-quantum-Hall-effect (FQHE) states in rotating dipolar Fermi gases [15,16].Rotating gases feel the Coriolis force in the rotating frame. The Coriolis force on rotating gases is identical to the Lorentz force of a charged particle in a magnetic field. Quantum-mechanically, energy levels of a charged particle in a uniform magnetic field show discrete Landau levels. In the lowest Landau level (LLL), the kinetic energy of rotating dipolar gases is frozen and the DDI create strong correlations on particles. Therefore, in the lowest Landau level, the potential energy from DDI dominates the kinetic energy and rotating dipolar fermions will crystallize into a Wigner crystal (WC) or become the FQHE liquid. Baranov et al. [16] have shown that the FQHE states have lower energies than the WCs as filling fac- * Electronic address: sccheng@faculty.pccu.edu.tw; FAX: +886-2-28610577 tors ν ≥ 1/7 and in the zero-extension limit along the rotating axial direction, where ν = 2πρℓ 2 . Here ρ and ℓ are the average density and the magnetic length, respectively. Although they also investigated the stability of the WC and found that the WC states were stable in the regime ν < 1/7, but there was no test on the stability of the FQHE liquid. It is still a question whether...

A ring dark soliton is a dark soltion occurring in higher dimensions. It is still unknown in microcavity-polariton condensates due to its instability. We find that a stable RDS cannot exist in a MPC without a defect. We then propose a way to create a stable RDS in a MPC by adding a defect with a ring structure to the system. A RDS pinned by the defect potential becomes stable. For various pump powers, we also investigate the stable regime of the RDS by tuning the strength and width of the defect potential. We conclude that the stable RDSs can be obtained.