Single-Spin Devices and the Foundations of Quantum Mechanics

It is well known that electron spin is quantized, and is measured to be either spin up or spin down in a magnetic field, as was first demonstrated in the classic Stern-Gerlach experiment almost 100 years ago. However, it is also believed that a quantum spin may be indeterminate until it is measured, being in a quantum superposition of the two quantum states. On the contrary, I propose (based on a locally realistic spin-quantized picture of quantum waves) that an electron quantum state is always either spin up or spin down, but is never in a superposition of the two. This concept should be directly testable using a two-stage Stern-Gerlach experiment, similar to that presented in standard quantum textbooks, but apparently never carried out experimentally. This experiment should be straightforward using modern atomic beam laboratory equipment. If successful, this could lead to a serious review of quantum foundations, as well as a new set of practical applications. In particular, a binary storage or logic element based on quantum spin should continue to work down to the atomic scale. This should enable computer memories with orders of magnitude greater density than those based on conventional magnetic memories.