查看更多>>摘要：The recent stochastic signal observed jointly by NANOGrav,parkes pulsar timing array,European pulsar timing array,and Chinese pulsar timing array can be accounted for by scalar-induced gravitational waves(SIGWs).The source of the SIGWs is from the primordial curvature perturbations,and the main contribution to the SIGWs is from the peak of the primordial curvature power spectrum.To effectively model this peak,we apply the Taylor expansion to parameterize it.With the Taylor expansion parameterization,we apply Bayesian methods to constrain the primordial curvature power spectrum based on the NANOGrav 15 year data set.The constraint on the primordial curvature power spectrum possesses a degree of generality,as the Taylor expansion can effectively approximate a wide range of function profiles.
查看更多>>摘要：Multiple quantum coherences are often employed to describe quantum many-body dynamics in nuclear spin systems and recently,to characterize quantum phase transitions in trapped ions.Here we investigate the multiple-quantum-coherence dynamics of a spin-1 Bose-Einstein condensate.By adjusting the quadratic Zeeman shift,the condensate exhibits three quantum phases.Our numerical results show that the spectrum of multiple quantum coherence does indeed catch the quantum critical points.More importantly,with only a few low-order multiple quantum coherences,the spin-1 condensate exhibits rich signals of the many-body dynamics,beyond conventional observables.The experimental implementation of such multiple quantum coherence protocol is also discussed.
查看更多>>摘要：By numerically solving the time-dependent Schrödinger equation and employing the analytical perturbative model,we investigated the chirp-induced electron vortex in the photoionization of hydrogen atoms by a pair of counter-rotating circularly polarized chirped attosecond extremely ultraviolet pulses.We demonstrated that single-photon ionization of hydrogen atoms generates photoelectron momentum distributions(PMDs)with distinct helical vortex structures either with or without a time delay between two counter-rotating circularly polarized laser pulses.These structures are highly sensitive to both the time delay between the pulses and their chirp parameters.Our analytical model reveals that the splitting of vortex spirals is caused by the sign changing of the chirp-induced frequency-dependent time delay.We showed that to obtain the counterpart of the PMD under a pair of counter-rotating circularly polarized chirped pulses,both chirp parameters and ordering of pulses need to be reversed.
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