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24 juillet 2023 - 13:42
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The Quantum Bomb-Tester!
Elitzur-Vaidman bomb tester. You have a bunch of bombs, but some of them are duds. Can quantum physics help us find the live ones without detonating any of them?
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Imagine you have a bunch of photon-sensitive bombs, so if you shine a single photon at any of them they will detonate and explode. But the problem is that some of these bombs are duds. Is there a way to test which bombs are live and which bombs are duds without detonating any of them? Quantum physics says there is!
A thought experiment called the Elitzure-Vaidman bomb tester uses the principles of quantum superposition to perform an interaction-free measurement. In short, this means they can test if a bomb is live without and explosion.
An Elitzur-Vaidman bomb-tester uses a Mach-Zehnder interferometer, with the light source emitting only single photons at a time. Classically, we would expect that 50% of the time the photon showed up on detector A and 50% of the time it showed up on detector B. However, the results showed that 100% of the time the photon showed up on detector A. So what was going on? Well a photon is a quantum object so it no longer obeys the laws of classical physics. The photon undergoes quantum superposition, takes both paths and interferes with itself.
So how can we use this weird phenomena of quantum superposition to test bombs? Well if we place a dud bomb in the Mach-Zehnder interferometer, from the perspective of the photon, nothing has changed. It still undergoes quantum superposition and there is a 50/50 chance it will show up on either detector. Now if we place a live bomb in the Mach-Zehnder interferometer, if the photon takes the path of the bomb nothing will show up on either detector. If the photon takes the other path there is a 50/50 chance it will show up on either detector. This asymmetry means the photon can no longer undergo quantum superposition and is forced to choose a path.
So if a photon is detected on detector B, we know it is a live bomb without the photon having to interact with it.
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