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Atoms
Volume 12
Issue 9
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Atoms, Volume 12, Issue 9 (September 2024) – 4 articles

Cover Story (view full-size image): Determining cause-and-effect within wave–wave coupling helps us to further understand number, momentum, or energy transport. To explain our look-up table of the parent and daughter modes, we analyzed lab plasma fluctuation data where the velocity-shear-driven (IEDD) waves exhibited much stronger wave–wave coupling to the lower-frequency drift waves, with nearly 100% coherency, compared to the case of the related, single-eigenmode, current-driven (CDEIC) waves. In the figures, both high- and low-frequency pairs of the spectral components for the real part of the IEDD–drift bispectrum exhibited negative peaks that were separated by 3 kHz. No such signature appeared in the CDEIC–drift case. These findings imply that coupling is facilitated by broadband IEDD waves. In contrast, the background turbulence is characterized by random, noncoherent interactions. View this paper
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11 pages, 1230 KiB  
Article
Solving Time-Dependent Schödinger Equation for Some PT-Symmetric Quantum Mechanical Problems
by Tsin-Fu Jiang
Atoms 2024, 12(9), 46; https://doi.org/10.3390/atoms12090046 - 11 Sep 2024
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Abstract
Using a high-precision code, we generate the eigenstates of a PT-symmetric Hamiltonian. We solve the time-dependent Schrödinger equation (TDSE) of the non-Hermitian system based on the eigenset. Since the formulation is relatively new and the observables are calculated differently than conventional quantum mechanics, [...] Read more.
Using a high-precision code, we generate the eigenstates of a PT-symmetric Hamiltonian. We solve the time-dependent Schrödinger equation (TDSE) of the non-Hermitian system based on the eigenset. Since the formulation is relatively new and the observables are calculated differently than conventional quantum mechanics, we justify it with a paradigmatic case in Hermitian quantum mechanics. We present the harmonic generation spectra on some model PT-Hamiltonians driven by an electric pulse. We discuss the physical differences with the harmonic spectra of a pulse-driven atom. Full article
(This article belongs to the Section Atom Based Quantum Technology)
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1 pages, 152 KiB  
Correction
Correction: Stambulchik, E. Stark Broadening of Lyman-α in the Presence of a Strong Magnetic Field. Atoms 2023, 11, 120
by Evgeny Stambulchik
Atoms 2024, 12(9), 45; https://doi.org/10.3390/atoms12090045 - 9 Sep 2024
Viewed by 647
Abstract
In the original publication [...] Full article
14 pages, 7071 KiB  
Article
Applicability of Bispectral Analysis to Causality Determination within and between Ensembles of Unstable Plasma Waves
by Renaud Stauber and Mark Koepke
Atoms 2024, 12(9), 44; https://doi.org/10.3390/atoms12090044 - 5 Sep 2024
Viewed by 833
Abstract
Turbulence implies nonlinear wave–wave coupling, and determining cause and effect of either is important to understand mixing responsible for enhanced number, momentum, or energy (NME) transport. To explain the identification of parent and daughter modes via a look-up table, we sketch the framework [...] Read more.
Turbulence implies nonlinear wave–wave coupling, and determining cause and effect of either is important to understand mixing responsible for enhanced number, momentum, or energy (NME) transport. To explain the identification of parent and daughter modes via a look-up table, we sketch the framework of bispectral analysis without repeating the mathematical formalism of earlier bispectrum researchers. We then apply this technique to a test signal and plasma fluctuation data from the WVU-Q machine, where the inhomogeneous energy density-driven spectrum exhibited a degree of coupling to lower frequencies that was absent in the case of the related, single-eigenmode, current-driven spectrum. Full article
(This article belongs to the Special Issue Plasma Physics Highlights: Non-equilibrium Dynamics, Interfaces and Mixing)
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13 pages, 414 KiB  
Article
Cooperative Decay of an Ensemble of Atoms in a One-Dimensional Chain with a Single Excitation
by Nicola Piovella
Atoms 2024, 12(9), 43; https://doi.org/10.3390/atoms12090043 - 28 Aug 2024
Cited by 1 | Viewed by 1001
Abstract
We propose a new expression of the cooperative decay rate of a one-dimensional chain of N two-level atoms in the single-excitation configuration. From it, the interference nature of superradiance and subradiance arises naturally, without the need to solve the eigenvalue problem of the [...] Read more.
We propose a new expression of the cooperative decay rate of a one-dimensional chain of N two-level atoms in the single-excitation configuration. From it, the interference nature of superradiance and subradiance arises naturally, without the need to solve the eigenvalue problem of the atom–atom interaction Green function. The cooperative decay rate can be interpreted as the imaginary part of the expectation value of the effective non-Hermitian Hamiltonian of the system, evaluated over a generalized Dicke state of N atoms in the single-excitation manifold. Whereas the subradiant decay rate is zero for an infinite chain, it decreases as 1/N for a finite chain. A simple approximated expression for the cooperative decay rate is obtained as a function of the lattice constant d and the atomic number N. The results are obtained first for the scalar model and then extended to the vectorial light model, assuming all the dipoles aligned. Full article
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