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Optical and Quantum Sensing and Precision Metrology II

Simulation of atomic trajectories in the original Stern–Gerlach experiment

Faraz Mostafaeipour, S. Suleyman Kahraman, Kelvin Titimbo, Yixuan Tan, Lihong V. Wang

Published Mar 13, 2024• 0 citations
Publisher

Abstract

Following an analysis of the historical literature, we model the geometry of the original Stern–Gerlach experiment to numerically calculate the magnetic field using the finite-element method. Using the calculated field and a semi-classical model of spin, the propagation of the atoms in the beam is simulated to produce the well-known quantized end-pattern. Modeling the geometry of the magnets and the slits as faithfully as possible yields a two-dimensional pattern resembling the well-known postcard image sent by Gerlach to Bohr. The experimental parameters not reported in the original publications are ‘reversed engineered’ to adjust the length of the pattern.

DOI
10.1117/12.3001062

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Simulation of atom trajectories in the original Stern–Gerlach experiment

Faraz Mostafaeipour, S. Suleyman Kahraman, Kelvin Titimbo +2 more

Abstract Following a comprehensive analysis of the historical literature, we model the geometry of the Stern–Gerlach experiment to numerically calculate the magnetic field using the finite-element method. Using this calculated field and Monte Carlo methods, the semiclassical atomic translational dynamics are simulated to produce the well-known quantized end-pattern with matching dimensions. The finite-element method used provides the most accurate description of the Stern–Gerlach magnetic field and end-pattern in the literature, matching the historically reported values and figures.

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A Quantum Description of the Stern–Gerlach Experiment

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A detailed analysis of the classic Stern–Gerlach experiment is presented. An analytical simple solution is presented for the quantum description of the translational and spin dynamics of a silver atom in a magnetic field with a gradient along a single z-direction. This description is then used to obtain an approximate quantum description of the more realistic case with a magnetic field gradient also in a second y-direction. An explicit relation is derived for how an initial off center deviation in the y-direction affects the final result observed at the detector. This shows that the “mouth shape” pattern at the detector observed in the original Stern–Gerlach experiment is a generic consequence of the gradient in the y-direction. This is followed by a discussion of the spin dynamics during the entry of the silver atom into the magnet. An analytical relation is derived for a simplified case of a field only along the z-direction. A central question for the conceptual understanding of the Stern–Gerlach experiment has been how an initially unpolarized spin ends up in a polarized state at the detector. It is argued that this can be understood with the use of the adiabatic approximation. When the atoms first experience the magnetic field outside the magnet, there is in general a change in the spin state, which transforms from a degenerate eigenstate in the absence of a field into one of two possible non-degenerate states in the field. If the direction of the field changes during the passage through the device, there is a corresponding adiabatic change of the spin state. It is shown that an application of the adiabatic approximation in this way is consistent with the previously derived exact relations.

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Direct demonstration of the transverse Stern–Gerlach effect

J. L. Porter, R. F. Pettifer, David R Leadley

A Stern–Gerlach experiment constructed in the spirit of the original experiment is reported that demonstrates spatial quantization for a beam of silver atoms directly to the unaided eye. Splitting of the atomic beam is seen both parallel to the magnetic field direction, as in the “usual” experiment, and in a direction mutually perpendicular to the field and atomic trajectory, which is a new transverse Stern–Gerlach effect. Splitting of up to 4 mm can be recorded visually. Calculations based on the force components acting on the atomic beams reproduce the experimental results within the experimental accuracy of ±0.3 mm.

American Journal of Physics•Oct 13, 2003•3 citations

A Numerical Experiment with the Stern-Gerlach Geometry

Riadh Al Rabeh

The Stern-Gerlach (SG) experiment reported in 1922 was an important milestone in the history of physics. The passing of a collimated neutral beam of silver atoms through a long, strong and asymmetrical magnet caused the atoms of silver out of a horizontal slit to split roughly into two separate beams forming a hollow lip figure (as seen on a plate held normal to the beam) instead of being a filled-in lip figure as suggested by some theoretical calculations. The SG results were thought to indicate that the observed phenomenon can not be explained using classical physics. Following a classical numerical approach by the author using a double-slit geometry, results are given for a 3D numerical SG type experiment showing clearly that a binary beam splitting is possible for certain conditions using an inverse square relation as the only source of forces- thus giving the possibility of a classical interpretation to the problem. For simplicity, we use what is mathematically equivalent- a dipole of charges to represent the magnetic dipole of the atom, and sets of fixed charges or potential surfaces around the path of the beam to represent the poles of a magnet. Although not exactly following the SG setup, the present results, nonetheless, are useful in showing the clear discrete behavior that can be caused by the combination of a fixed boundary, a strong field asymmetry and the highly nonlinear mapping of the inverse square law of forces coupled with the spin direction of a particle.

•Jan 1, 2011•0 citations

Моделирование движения частиц в аппарате Штерна-Герлаха

Трунев Александр Петрович

The model of the motion of particles in the Stern-Gerlach apparatus in the classical and quantum mechanics was developed. The data simulation of particle trajectories and distribution of silver atoms on the surface of the plate in their deposition are discussed. It was found that for the experimentally observed distribution of two-dimensional shapes of the atoms must be assumed that the atoms are not involved in the precession motion in a magnetic field, while maintaining the direction of the magnetic moment, for example, parallel to the induction vector of the magnetic field during the time of motion in the apparatus. To obtain a realistic picture of the figure of the scattering of atoms used a classical model of movement and expression of forces compatible with the quantum picture of the motion of particles with spin ½. The magnetic field is simulated based on the original Stern-Gerlach data describing the distribution of the gradient of the induction components related to the splitting of the beam. Quantum model of particle motion is based on the Pauli equation in the boundary layer approximation. It is found that in this model, depending on the initial polarization of the particle, beam is split into either two or is deflected towards the magnet blade or in the opposite direction. It is shown that if the initial conditions for the task are reproducing the geometric dimensions and the magnetic field in the Stern-Gerlach apparatus, the figure of the scattering particles in the shape of the outline is similar to the experimentally observed shape

Политематический сетевой электронный научный журнал Кубанского государственного аграрного университета•Jan 1, 2016•0 citations

Quantum Dynamical Simulation of a Transversal Stern–Gerlach Interferometer

Mikołaj M. Paraniak, Berthold‐Georg Englert

Originally conceived as a thought experiment, an apparatus consisting of two Stern–Gerlach apparatuses joined in an inverted manner touched on the fundamental question of the reversibility of evolution in quantum mechanics. Theoretical analysis showed that uniting the two partial beams requires an extreme level of experimental control, making the proposal in its original form unrealizable in practice. In this work, we revisit the above question in a numerical study concerning the possibility of partial-beam recombination in a spin-coherent manner. Using the Suzuki–Trotter numerical method of wave propagation and a configurable, approximation-free magnetic field, a simulation of a transversal Stern–Gerlach interferometer under ideal conditions is performed. The result confirms what has long been hinted at by theoretical analyses: the transversal Stern–Gerlach interferometer quantum dynamics is fundamentally irreversible even when perfect control of the associated magnetic fields and beams is assumed.

arXiv:2106.00205•Symmetry•Sep 8, 2021•9 citations
Following an analysis of the historical literature, we model the geometry of the original Stern–Gerlach experiment to numerically calculate the magnetic field using the finite-element method. Using the calculated field and a semi-classical model of spin, the propagation of the atoms in the beam is simulated to produce the well-known quantized end-pattern. Modeling the geometry of the magnets and the slits as faithfully as possible yields a two-dimensional pattern resembling the well-known postcard image sent by Gerlach to Bohr. The experimental parameters not reported in the original publications are ‘reversed engineered’ to adjust the length of the pattern.
Abstract Following a comprehensive analysis of the historical literature, we model the geometry of the Stern–Gerlach experiment to numerically calculate the magnetic field using the finite-element method. Using this calculated field and Monte Carlo methods, the semiclassical atomic translational dynamics are simulated to produce the well-known quantized end-pattern with matching dimensions. The finite-element method used provides the most accurate description of the Stern–Gerlach magnetic field and end-pattern in the literature, matching the historically reported values and figures.
A detailed analysis of the classic Stern–Gerlach experiment is presented. An analytical simple solution is presented for the quantum description of the translational and spin dynamics of a silver atom in a magnetic field with a gradient along a single z-direction. This description is then used to obtain an approximate quantum description of the more realistic case with a magnetic field gradient also in a second y-direction. An explicit relation is derived for how an initial off center deviation in the y-direction affects the final result observed at the detector. This shows that the “mouth shape” pattern at the detector observed in the original Stern–Gerlach experiment is a generic consequence of the gradient in the y-direction. This is followed by a discussion of the spin dynamics during the entry of the silver atom into the magnet. An analytical relation is derived for a simplified case of a field only along the z-direction. A central question for the conceptual understanding of the Stern–Gerlach experiment has been how an initially unpolarized spin ends up in a polarized state at the detector. It is argued that this can be understood with the use of the adiabatic approximation. When the atoms first experience the magnetic field outside the magnet, there is in general a change in the spin state, which transforms from a degenerate eigenstate in the absence of a field into one of two possible non-degenerate states in the field. If the direction of the field changes during the passage through the device, there is a corresponding adiabatic change of the spin state. It is shown that an application of the adiabatic approximation in this way is consistent with the previously derived exact relations.
A Stern–Gerlach experiment constructed in the spirit of the original experiment is reported that demonstrates spatial quantization for a beam of silver atoms directly to the unaided eye. Splitting of the atomic beam is seen both parallel to the magnetic field direction, as in the “usual” experiment, and in a direction mutually perpendicular to the field and atomic trajectory, which is a new transverse Stern–Gerlach effect. Splitting of up to 4 mm can be recorded visually. Calculations based on the force components acting on the atomic beams reproduce the experimental results within the experimental accuracy of ±0.3 mm.
The Stern-Gerlach (SG) experiment reported in 1922 was an important milestone in the history of physics. The passing of a collimated neutral beam of silver atoms through a long, strong and asymmetrical magnet caused the atoms of silver out of a horizontal slit to split roughly into two separate beams forming a hollow lip figure (as seen on a plate held normal to the beam) instead of being a filled-in lip figure as suggested by some theoretical calculations. The SG results were thought to indicate that the observed phenomenon can not be explained using classical physics. Following a classical numerical approach by the author using a double-slit geometry, results are given for a 3D numerical SG type experiment showing clearly that a binary beam splitting is possible for certain conditions using an inverse square relation as the only source of forces- thus giving the possibility of a classical interpretation to the problem. For simplicity, we use what is mathematically equivalent- a dipole of charges to represent the magnetic dipole of the atom, and sets of fixed charges or potential surfaces around the path of the beam to represent the poles of a magnet. Although not exactly following the SG setup, the present results, nonetheless, are useful in showing the clear discrete behavior that can be caused by the combination of a fixed boundary, a strong field asymmetry and the highly nonlinear mapping of the inverse square law of forces coupled with the spin direction of a particle.
The model of the motion of particles in the Stern-Gerlach apparatus in the classical and quantum mechanics was developed. The data simulation of particle trajectories and distribution of silver atoms on the surface of the plate in their deposition are discussed. It was found that for the experimentally observed distribution of two-dimensional shapes of the atoms must be assumed that the atoms are not involved in the precession motion in a magnetic field, while maintaining the direction of the magnetic moment, for example, parallel to the induction vector of the magnetic field during the time of motion in the apparatus. To obtain a realistic picture of the figure of the scattering of atoms used a classical model of movement and expression of forces compatible with the quantum picture of the motion of particles with spin ½. The magnetic field is simulated based on the original Stern-Gerlach data describing the distribution of the gradient of the induction components related to the splitting of the beam. Quantum model of particle motion is based on the Pauli equation in the boundary layer approximation. It is found that in this model, depending on the initial polarization of the particle, beam is split into either two or is deflected towards the magnet blade or in the opposite direction. It is shown that if the initial conditions for the task are reproducing the geometric dimensions and the magnetic field in the Stern-Gerlach apparatus, the figure of the scattering particles in the shape of the outline is similar to the experimentally observed shape
Originally conceived as a thought experiment, an apparatus consisting of two Stern–Gerlach apparatuses joined in an inverted manner touched on the fundamental question of the reversibility of evolution in quantum mechanics. Theoretical analysis showed that uniting the two partial beams requires an extreme level of experimental control, making the proposal in its original form unrealizable in practice. In this work, we revisit the above question in a numerical study concerning the possibility of partial-beam recombination in a spin-coherent manner. Using the Suzuki–Trotter numerical method of wave propagation and a configurable, approximation-free magnetic field, a simulation of a transversal Stern–Gerlach interferometer under ideal conditions is performed. The result confirms what has long been hinted at by theoretical analyses: the transversal Stern–Gerlach interferometer quantum dynamics is fundamentally irreversible even when perfect control of the associated magnetic fields and beams is assumed.