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arXiv:2203.12535 · Physical Review A

Laser-atom interaction simulator derived from quantum electrodynamics

Manish Patel, Matthew Harvey, Andrew James Murray

Published May 23, 2022• 2 citations
arXivHTMLPDF

Abstract

A laser-atom interaction simulator derived from quantum electrodynamics (LASED) is presented, which has been developed in the python programming language. LASED allows a user to calculate the time evolution of a laser-excited atomic system. The model allows for any laser polarization, a Gaussian laser beam profile, a rotation of the reference frame chosen to define the states, and an averaging over the Doppler profile of an atomic beam. Examples of simulations using LASED are presented for excitation of calcium from the $4^{1}S_{0}$ state to the $4^{1}P_{1}$ state, for excitation from the helium $3^{1}D_{2}$ state excited by electron impact to the $10^{1}P_{1}$ state, and for laser excitation of caesium via the ${D}_{2}$ line.

DOI
10.1103/physreva.105.053117

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A laser-atom interaction simulator derived from quantum electrodynamics (LASED) is presented, which has been developed in the python programming language. LASED allows a user to calculate the time evolution of a laser-excited atomic system. The model allows for any laser polarization, a Gaussian laser beam profile, a rotation of the reference frame chosen to define the states, and an averaging over the Doppler profile of an atomic beam. Examples of simulations using LASED are presented for excitation of calcium from the 41S04^{1}S_{0}41S0​ state to the 41P14^{1}P_{1}41P1​ state, for excitation from the helium 31D23^{1}D_{2}31D2​ state excited by electron impact to the 101P110^{1}P_{1}101P1​ state, and for laser excitation of caesium via the D2{D}_{2}D2​ line.
The observation of radiation trapping effects in time-resolved, stepwise-excited, electron-photon coincidence signals is reported. Hg atoms were excited by electron impact to the 6 1^{1}1P1{\mathit{P}}_{1}P1​ state and then by laser excitation to the 6 1^{1}1D2{\mathit{D}}_{2}D2​ state. Coincidence signals were observed from the 6 1^{1}1D2{\mathit{D}}_{2}D2​--6 3^{3}3P1{\mathit{P}}_{1}P1​ (313-nm) transition. The decay time of these signals was found to depend upon radiation trapping of the electron-impact-excited 6 1^{1}1P1{\mathit{P}}_{1}P1​--6 1^{1}1S0{\mathit{S}}_{0}S0​ (185-nm) resonance line. An explanation of this effect is given in terms of the laser excitation coupling the 313- and 185-nm transitions.
We have developed computer programs for numerical experiments on laser-atom interactions. First, subroutines have been written that build a software atom with an arbitrary level scheme from elementary specifications, such as angular momenta and energies of the atomic levels. Second, the key operations of the semiclassical theory of laser spectroscopy have been implemented as transformations acting on the software atom. The software atom was initially used in investigations of the motion of an atom in three-dimensional optical molasses,1 Here we discuss two new applications, saturation and resonance fluorescence of a multistate atom.
Laser excitation of the 4s4p3P2−−4s3d1D24s4p {}^{3}{P}_{2} -- 4s3d {}^{1}{D}_{2}4s4p3P2​−−4s3d1D2​ transition in atomic calcium has been observed and the wavelength determined to 1530.5298(6) nm. The metastable 4s4p3P24s4p {}^{3}{P}_{2}4s4p3P2​ atoms were magnetically trapped in the quadrupole magnetic field of a magneto-optical trap. This state represents the only ``loss'' channel for the calcium atoms when laser cooled on the 4s21S0−−4s4p1P14{s}^{2} {}^{1}{S}_{0} -- 4s4p {}^{1}{P}_{1}4s21S0​−−4s4p1P1​ transition. A rate equation model shows that an order of magnitude more atoms are trapped in this state compared with those taking part in the main cooling cycle. Excitation of the 3P2{}^{3}{P}_{2}3P2​ atoms back up to the 4s3d1D24s3d {}^{1}{D}_{2}4s3d1D2​ state provides a means of accessing these atoms. Efficient repumping is achieved if the 1530-nm laser is used in conjunction with a 672-nm laser driving the 4s3d1D2−−4s5p1P14s3d {}^{1}{D}_{2} -- 4s5p {}^{1}{P}_{1}4s3d1D2​−−4s5p1P1​ transition. In the present experiment, we detected about $4.5\ifmmode\times\else\texttimes\fi{}{10}^{4}$ trapped 3P2{}^{3}{P}_{2}3P2​ atoms, a relatively low atom density, and measured a lifetime of approximately 1 s, which is limited by background collisions.
We propose a quantum dynamics simulator for light-irradiated matter. As the coherent control of the quantum states of matter is an intriguing problem in realizing quantum technology, the quantum properties of light-matter complexes have attracted much attention. Theoretical calculations corresponding to individual experimental configurations are required to understand these properties, and simulation methods that flexibly adapt to various experimental configurations are required. In this paper, we propose a quantum dynamics simulation method that encompasses program modules corresponding to light sources, optical components, material systems, and the evaluation of physical properties. We demonstrate the entanglement generation dynamics between two spin-chains via irradiated photons and show that a flexible and expandable quantum dynamics simulator can be constructed.
The resonant excitation of the sodium D2 transition by laser radiation was investigated experimentally in this thesis. Line polarization measurement of the resonance fluorescence was employed to investigate the excitation process. The sodium atoms, which were collimated in a very narrow beam, were excited by a monochromatic laser beam with the frequency tuned to resonance with the 32S 112(F=2) - 32P312 hyperfine transition. The direction of the laser beam was perpendicular to the atomic beam and the fluorescence photons were detected along a direction perpendicular to both the laser and atomic beams. The experimental measurements were performed to determine the effect due to the variation of the laser intensity and frequency on the line polarization. A theoretical expression of the line polarization as a function of density matrix elements of the upper excited hyperfine sub -states was derived. A full quantum electrodynamic theory was used to derive an atomic operator equation of motion which was needed to calculate atomic operator elements. These elements then yielded the corresponding density matrix elements. The experimental results and the theoretical modelling were in a good agreement. The first experimental results for the line polarization of the highly excited states, 42D512 and 42D312, are also presented. The use of two lasers enabled these highly excited states to be excited. The line polarization of the fluorescence for transitions from the 4D level down to lower states is derived in terms of the density matrix elements of the upper excited states. Two limiting cases for the theoretical predictions of the line polarization are considered.