Physics

In atomic, molecular, and nuclear physics, the method of complex coordinate rotation is a widely used theoretical tool for studying resonant states. Here, we propose a novel implementation of this method based on the gradient optimization (CCR-GO). The main strength of the CCR-GO method is that it does not require manual adjustment of optimization parameters in the wave function; instead, a mathematically well-defined optimization path can be followed. Our method is proven to be very efficient in searching resonant positions and widths over a variety of few-body atomic systems, and can significantly improve the accuracy of the results. As a special case, the CCR-GO method is equally capable of dealing with bound-state problems with high accuracy, which is traditionally achieved through the usual extreme conditions of energy itself.

The crystal growth and the structural, transport and magnetic properties of the magnetically frustrated YbMn 2 Sb 2 single crystals are reported. The crystals show a trigonal symmetry (space group P 3 ¯ m1 ), where corrugated honeycomb layers of MnSb are separated by Yb atoms. No structural phase transition was observed down to 22~K. The resistivity measurements show a predominantly insulating behavior. The combined resistivity, dc susceptibility and heat capacity measurements confirm successive transitions at 230~K, 116~K and 27~K, being the transition at T N =116~K due to the Mn +2 lattice antiferromagnetic ordering. Muon spin rotation experiments ( μ SR) reveal a more complicated scenario, with temperature dependence of the magnetic volume fraction reflecting short range and long range magnetic order, and a strongly disordered magnetic ground state. The role of spin-lattice coupling and its relationship with exchange interactions between Mn moments are discussed as possible cause of the complex magnetic behavior observed.

Astrophysical molecular spectroscopy is an important means of searching for new physics through probing the variation of the proton-to-electron mass ratio, μ . New molecular probes could provide tighter constraints on the variation of μ and better direction for theories of new physics. Here we summarise our previous paper \citep{this http URL} for astronomers, highlighting the importance of accurate estimates of peak molecular abundance and temperature as well as spectral resolution and sensitivity of telescopes in different regions of the electromagnetic spectrum. Whilst none of the 11 astrophysical diatomic molecules we investigated showed enhanced sensitive rovibronic transitions at observable intensities for astrophysical environments, we have gained a better understanding of the factors that contribute to high sensitivities. From our results, CN, CP, SiN and SiC have shown the most promise of all astrophysical diatomic molecules for further investigation, with further work currently being done on CN.

We show that we can predict the first ionization energy of the carbon atom to within 0.872 cm −1 of the experimental value. This is an improvement of more than a factor of 6.5 over the preceding best prediction in [Phys. Rev. A 81, 022503], and opens the door to achieving sub-cm −1 accuracy for ab-initio predictions in larger elements of the periodic table.

We demonstrate a compact magneto-optical trap (MOT) of alkaline-earth atoms using a nanofabricated diffraction grating chip. A single input laser beam, resonant with the broad 1 S 0 → 1 P 1 transition of strontium, forms the MOT in combination with three diffracted beams from the grating chip and a magnetic field produced by permanent magnets. A differential pumping tube limits the effect of the heated, effusive source on the background pressure in the trapping region. The system has a total volume of around 2.4 L. With our setup, we have trapped up to 5× 10 6 88 Sr atoms, at a temperature of approximately 6 mK, and with a trap lifetime of approximately 1 s. Our results will aid the effort to miniaturize optical atomic clocks and other quantum technologies based on alkaline-earth atoms.

We investigate twisted electrons with a well defined orbital angular momentum, which have been ionised via a strong laser field. By formulating a new variant of the well-known strong field approximation, we are able to derive conservation laws for the angular momenta of twisted electrons in the cases of linear and circularly polarised fields. In the case of linear fields, we demonstrate that the orbital angular momentum of the twisted electron is determined by the magnetic quantum number of the initial bound state. The condition for the circular field can be related to the famous ATI peaks, and provides a new interpretation for this fundamental feature of photoelectron spectra. We find the length of the circular pulse to be a vital factor in this selection rule and, employing an effective frequency, we show that the photoelectron OAM emission spectra is sensitive to the parity of the number of laser cycles. This work provides the basic theoretical framework with which to understand the OAM of a photoelectron undergoing strong field ionisation.

The article presents the development of a new and innovative experimental method to fully characterize a solenoidal "spin-flip" Zeeman slower (ZS) using a Quartz Crystal μ -balance (QCM) as a kinetic energy sensor. In this experiment, we focus a 447.1 nm laser into a counter-propagating beam of gadolinium (Gd) atoms in order to drive the dipole transition between ground 9 D 0 2 state and 9 D 3 excited state. The changes in the velocity of the beam were measured using a QCM during this process, as a novel and alternative method to characterize the efficiency of a 1 m-long spin-flip Zeeman slower. The QCM, normally used in solid-state physics, is continuously and carefully monitored to determine the change in its natural frequency of oscillation. These changes reveal a direct relation with changes in the deposition rate and the momentum exchanged between the QCM and Gd atoms. Hence, in terms of ultracold atom physics, it might be used to study the time-evolution of the velocity distribution of the atoms during the cooling process. By this method, we obtain a maximum atom average velocity reduction of (43.5 ± 6.4) % produced by our apparatus. Moreover, we estimate an experimental lifetime of τ e = 8.2 ns for the used electronic transition, and then we compared it with the reported lifetime for 443.06 nm and 451.96 nm electronic transitions of Gd. These results confirm that the QCM offers an accessible and simple solution to take into account for laser cooling experiments. Therefore, a novel and innovative technique can be available for future experiments.

Scattering dynamics are examined for Gaussian and non-Gaussian wave packets with identical momentum densities. Average arrival time delays, dwell times, and phase time delays are calculated for wave packets scattering from a square barrier, and it is shown that the non-Gaussian wave packets exhibit different average arrival time delays than the Gaussian wave packets. These differences result from the non-linear terms in the momentum wave function phase of the non-Gaussian wave packets, which alters the self-interaction times of the wave packets. Control of the average arrival time delay can be achieved through adjustment of the momentum wave function phase, independent of wave packet energy and momentum density.

To first order, a strong, external field doubly-ionizes the electrons in helium such that they are ejected into the same direction (front-to-back motion). Here, using a (1+1)-dimensional model, we optimize the field with the objective that the two electrons be ejected into opposite directions (back-to-back motion). The optimization is performed using four different control procedures: (1) Local control, (2) derivative-free optimization of basis expansions of the field, (3) the Krotov method and (4) control of the classical equations of motions. Superficially, all four procedures give different fields. However, upon a more careful analysis all the fields obtained exploit essentially the same two-step mechanism leading to back-to-back motion: First, the electrons are displaced by the field into the same direction. Second, after the field turns off, the nuclear attraction and the electron-electron repulsion combine to generate the final motion into opposite directions for each electron. By performing quasi-classical calculations, we confirm that this mechanism is essentially classical.

It has long been believed that core-hole lifetime (CHL) of an atom is an intrinsic physical property, and controlling it is significant yet is very hard. Here, CHL of the 2p state of W atom is manipulated experimentally through adjusting the emission rate of a resonant fluorescence channel with the assistance of an x-ray thin-film planar cavity. The emission rate is accelerated by a factor linearly proportional to the cavity field amplitude, that can be directly controlled by choosing different cavity modes or changing the angle offset in experiment. This experimental observation is in good agreement with theoretical predictions. It is found that the manipulated resonant fluorescence channel even can dominate the CHL. The controllable CHL realized here will facilitate the nonlinear investigations and modern x-ray scattering techniques in hard x-ray region.