The European Physical Journal D最新文献

A low energy particle confined by a horizontal reflective surface and gravity settles in gravitationally bound quantum states. These gravitational quantum states (GQS) were so far only observed with neutrons. However, the existence of GQS is predicted also for atoms. The GRASIAN collaboration pursues the first observation of GQS of atoms, using a cryogenic hydrogen beam. This endeavor is motivated by the higher densities, which can be expected from hydrogen compared to neutrons, the easier access, the fact that GQS were never observed with atoms and the accessibility to hypothetical short-range interactions. In addition to enabling gravitational quantum spectroscopy, such a cryogenic hydrogen beam with very low vertical velocity components—a few cm (hbox {s}^-1), can be used for precision optical and microwave spectroscopy. In this article, we report on our methods developed to reduce background and to detect atoms with a low horizontal velocity, which are needed for such an experiment. Our recent measurement results on the collimation of the hydrogen beam to 2 mm, the reduction of background and improvement of signal-to-noise and finally our first detection of atoms with velocities (<{72},hbox {ms}{^-1}) are presented. Furthermore, we show calculations, estimating the feasibility of the planned experiment and simulations which confirm that we can select vertical velocity components in the order of cm (hbox {s}^-1).

To further reduce the confinement loss of hollow-core anti-resonant fibers (HC-ARFs), broaden the low-loss operating bandwidth, and decrease the bending losses, this paper proposes a novel double-single-layer nested HC-ARF. The influence of structural parameters on its optical performance is analyzed using the full-vector finite element method, and the relevant structural parameters are optimized accordingly. The results indicate that, after optimizing the structural parameters, the HC-ARF exhibits extremely low confinement loss (on the order of 10^–8 dB/km) at the wavelength of 1.55 μm. When the bending radius is 10 cm, the bending loss is also very low (on the order of 10^–4 dB/km), which demonstrates an excellent bend-resistant property. Moreover, the HC-ARF possesses a very flat dispersion characteristic, with a low-loss operating bandwidth of approximately 945 nm, covering all the communication bands (O + E + S + C + L band).

Graphical Abstract

Cross section of the proposed double-single-layer nested HC-ARF and its Performance under the optimized structural parameters. This paper presents a new type of hollow - core anti - resonant fiber. The optical properties of this fiber, including confinement loss, bending loss and dispersion, etc., are numerically calculated by using the full-vector finite-element method. On this basis, the structural parameters of the fiber are optimized, and excellent optical properties are finally obtained.

We propose an dimer model consisting of two coupled microwave cavities with each cavity containing a two-level atom and a YIG sphere placed in the biased magnetic field. We use the semiclassical approximation and quantum master equation to investigate the delocalization–localization transition of the system. We find the sharp transition and the great photon localization under lower excitation. We also find that increasing initial photon number and magnon excitation can facilitate the localization. We also investigate the local second-order photon correlations to reflect the localization. The work suggests a new platform for studying the delocalization–localization transition of photons in cavity optomagnonic systems, with potential applications in quantum information processing. The article also discusses the experimental relevance of the model parameters.

We conducted a study on high-harmonic generation (HHG) in mixed gases, specifically Ar–Ne or Ar–Kr, with the aim of investigating the impact of ionization rate and neutral dispersion on the HHG process. Our focus was on understanding how these factors influence the HHG process when using gases with low and high ionization potentials. Based on phase-matched high-order harmonic generation in pure Ar gas, our investigation shows that the influence of plasma dispersion and neutral dispersion can be varied independently in mixed gas while the laser intensity is kept constant. Our results reveal that the addition of low ionization potential gases, such as Kr, to the Ar gas leads to a more rapid reduction in phase matching, due to the strong effects of ionization. The observed experimental outcomes align well with our theoretical calculations. This study provides valuable insights into the interplay of ionization rate and neutral dispersion in high-harmonic generation and the special requirement of the controlling of laser intensity for phase-matched harmonic generation. The findings contribute to a deeper understanding of the underlying dynamics and offer practical considerations for optimizing HHG properties.

Graphical abstract

The Triple-Differential Cross Section (TDCS) for the Photo Double-Ionization of carbon dioxide molecule to the CO₂²⁺ X³ Σ_g⁻ ground state has been measured at 20 eV excess energy. In the experiment the coincidence angular distributions of the two photoelectrons, where the direction of one photoelectron has been fixed at 0, 30 and 60° with respect to the direction of the polarization of the incident radiation, have been measured for a condition where the two photoelectrons equally share the excess energy. Care has been taken to perform the measurements with an energy resolution which enabled to isolate the TDCS of the X³Σ⁻_g ground state of the dication. An appreciable contribution to TDCS at a relative angle θ₁₂ = 180° has been observed and attributed to a favorite symmetry of the wavefunction of the two ejected electrons.

Graphical abstract

TDCS of CO₂ measures at photon energy 57.7eV, θ₁=0, 30 and 60° and equal energy sharing of 10 eV are reported as black dots. Panels (a) and (c) report the TDCS as calculated by Alwan et al. (J Phys B: At Mol Opt Phys 48:185203, 2015) using the charge in the Sommerfeld parameters for the oxygen atom of 0.2 (black full curve) and 0.8 (ref full curve). The blue full curve in panels (d)-(f) is the fit to the experiments with the helium=like model by Reddsih and Feaging (J Phys B: At Mol Opt Phys 32:2473, 1999).