A Brief Introduction to Quantum Superposition
Imagine you're the holder of a special passport that has many possible nationalities at once until authorities check it, at which point it is forced to randomly resolve into one citizenship.
That's how quantum superposition works. You are the electron. The electron has a dual nature and exists in both wave and particle forms, which is technically impossible. This is until it is observed and interacts with its surroundings, forcing it to “choose” one nature. Even though Austrian physicist Erwin Schrödinger developed the mathematical equation behind quantum mechanics in late 1925, he mocked the interpretation of his own wave equation using the thought experiment titled “Schrödinger's Cat.” The experiment is as follows: imagine you have a cat in a box, along with a poison that has a 50/50 chance of killing the cat after the box is closed for an hour. After an hour, before you open the box, the cat is both dead and alive, just as an electron remains both wave and particle until it is observed or measured. It is only when you open the box that the cat “chooses” one state: life or death (Schrödinger, 1935). Nowadays, this experiment is used as a simple way to explain superposition. Of course, this is just a thought experiment, and in reality, quantum superposition only applies to quantum-scale entities such as photons or electrons.
The strongest evidence for superposition we have now is the single-electron double-slit experiment of 1974. This experiment was performed by the Italian physicists Pier Giorgio Merli, Gian Franco Missiroli, and Giulio Pozzi. In this experiment, an electron gun was used to fire electrons one at a time at an electron biprism, which is a thin charged wire that splits the electron’s wave into two paths and makes them interfere (Rosa, 2012). The wave then hits a detector screen, allowing scientists to observe the interference. On the screen, each electron appeared as a single dot, like a particle. However, after many electrons were fired, the dots formed a pattern of bright and dark bands, showing wave-like interference. This interference pattern proves that each electron must have behaved like a wave traveling along both paths at the same time before hitting the screen. This clearly shows that superposition is real. In later experiments, where physicists placed detectors or sensors in positions that could reveal which path an electron took, these detectors interacted with the electron and provided path information. Once this information existed, the interference pattern disappeared, showing that attempting to measure results in the electron “choosing” one nature (Jaroszkiewicz, 2017).
Overall, as the American physicist and Nobel laureate Richard Feynman said, “I think I can safely say that nobody understands quantum mechanics,” quantum superposition is one of the most bizarre concepts in quantum mechanics that has, ironically, been proven real by experiments like the single-electron double-slit (Feynman, 1965). It reminds us that our world behaves very differently—and in ways we do not expect—at the quantum level. I hope this has helped and motivated you to learn more about the quantum world. Keep searching!
Writer:Blen Dagnachew
Editor:Menna
Bibliography
Feynman, R. (1965). The character of physical law. MIT Press.
Jaroszkiewicz, G. (2017). Quantum eraser experiments. In Cambridge University Press eBooks (pp. 179–197). https://doi.org/10.1017/9781316477182.015
Rosa, R. (2012). The Merli–Missiroli–Pozzi two-slit electron-interference experiment. Physics in Perspective, 14(2), 178–195. https://doi.org/10.1007/s00016-011-0079-0�https://doi.org/10.1007/s00016-011-0079-0
Schrödinger, E. (1935). Die gegenwärtige Situation in der Quantenmechanik [The present situation in quantum mechanics]. Naturwissenschaften, 23(48–50), 807–849. https://doi.org/10.1007/BF01491891
Comments