Bulletin of the American Physical Society
APS April Meeting 2023
Volume 68, Number 6
Minneapolis, Minnesota (Apr 15-18)
Virtual (Apr 24-26); Time Zone: Central Time
Session Q06: The Stern-Gerlach Experiment: Past and FutureInvited Undergrad Friendly
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Sponsoring Units: FHP Chair: Alberto Martinez, University of Texas at Austin Room: MG Salon F - 3rd Floor |
Monday, April 17, 2023 3:45PM - 4:21PM |
Q06.00001: A century ago the Stern-Gerlach experiment ruled unequivocally in favor of Quantum Mechanics Invited Speaker: Bretislav Friedrich In 1921, Otto Stern conceived the idea for an experiment that would decide between a classical and a quantum description of atomic behavior, as epitomized by the Bohr-Sommerfeld-Debye model of the atom. This model entailed not only the quantization of the magnitude of the orbital electronic angular momentum but also of the projection of the angular momentum on an external magnetic field – the so-called space quantization. Stern recognized that space quantization would have observable consequences: the magnetic dipole moment due to the orbital angular momentum would be space quantized as well, taking two opposite values for atoms whose only unpaired electron has just one quantum of angular momentum. When subjected to a suitable inhomogeneous magnetic field, a beam of such atoms would be split into two beams consisting of deflected atoms with opposite projections of the angular momentum on the magnetic field. In contradistinction, if atoms behaved classically, the atomic beam would only broaden along the field gradient and have maximum intensity at zero deflection, i.e., where there would be a minimum or no intensity for the beam split due to space quantization. Stern anticipated that, although simple in principle, the experiment would be difficult to carry out in the laboratory – and invited Walther Gerlach to team up with him. Gerlach’s realism and experimental skills together with his sometimes stubborn determination to make things work proved invaluable for the success of the Stern-Gerlach experiment (SGE). After a long struggle, Gerlach finally saw, on 8 February 1922, the splitting of a beam of silver atoms in a magnetic field. The absence of the concept of electron spin confused and confounded the interpretation of the SGE, as the silver atoms were, in fact, in a 2S state, with zero orbital and ½ spin angular momentum. However, a key quantum feature whose existence the SGE was designed to test – namely space quantization of electronic angular momentum – was robust enough to transpire independent of whether the electronic angular momentum was orbital or due to spin. The SGE revealed other key aspects of quantum mechanics such as the collapse of the wave function and entanglement. Confronted with the outcome of the SGE, Stern noted: “I still have objections against the idea of beauty of quantum mechanics. But she is correct.” |
Monday, April 17, 2023 4:21PM - 4:57PM |
Q06.00002: The Stern-Gerlach Experiment, 1921–1940: From the Old Quantum Theory to Spin Invited Speaker: Clayton A Gearhart Beginning in 1921, Otto Stern and Walther Gerlach collimated a beam of silver atoms (magnetic moments), and sent them through an inhomogeneous magnetic field. Their experiment, which showed a splitting of their atomic beam into two components and permitted a calculation of the Bohr magneton, was initially interpreted in the context of the “old quantum theory” — essentially, the Bohr-Sommerfeld picture of the atom in which electrons were in circular or elliptical orbits around the nucleus. In 1916, Arnold Sommerfeld augmented this picture when he developed a theory of space quantization, in which magnetic moments took discreet, quantized orientations with respect to an arbitrary direction in space—here, an external magnetic field. Stern and Gerlach adopted Sommerfeld’s theory, and saw their beam splitting as an example of space quantization. The magnetic moment was thought to be due to the orbital angular momentum of the silver atoms in the beam. |
Monday, April 17, 2023 4:57PM - 5:33PM |
Q06.00003: Realization of a Complete Stern-Gerlach Interferometer: An historical overview Invited Speaker: Ron Folman I will review the last decade of Stern-Gerlach interferometery experiments, and explain why it took almost 100 years until this was achieved. |
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