Since $\rm C_{60}$ is a molecule made up of numerous subatomic particles, no matter how separated from the environment, the interaction between $\rm C_{60}$'s subatomic particles inevitably causes quantum decoherence, right? But how did quantum tunneling happen?
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Decoherence is a relative term. If the many particle system is in a pure state (which it will be in the absence of an environment) you can do one of two things. You can perform experiments on the system as a whole and see all predictions of quantum mechanics reproduced. Or you can limit yourself to only one carbon atom. The other 59 would then become "the environment". Since interactions with them are significant, the state being measured would appear to be classical even though it's part of the exact same many particle quantum pure state as before. The latter is entangled so tracing out part of the Hilbert space (a practical choice by the experimenter, not part of the dynamics) is what makes it mixed.
This is what decoherence is. A gradual increase in the power and sensitivity your experiment needs in order to still see quantum behaviour. It is not some spontaneous removal of quantum behvaiour which happens in any system that "knows" it's not free. According to every experiment so far, quantum mechanics is unitary and therefore does not contain the seeds of its own destruction.
answered Oct 25, 2022 at 9:08
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$\begingroup$ So, how did the buckyball perform quantum tunneling? $\endgroup$– NunesCommented Oct 25, 2022 at 16:04
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1$\begingroup$ The same way everything performs quantum tunneling. Its multi-particle wavefunction (x, y, z co-ordinates of 60 atoms) evaluates to something non-zero when you plug in values for the 180 variables that correspond to a classically forbidden place. $\endgroup$ Commented Oct 25, 2022 at 20:16
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$\begingroup$ So it was possible because all 60 atoms didn't interact? (Very low probability) And in the buckyball double slit experiment, don't the internal electric and nuclear forces that hold atoms and molecules together cause coherence? $\endgroup$– NunesCommented Oct 26, 2022 at 2:13
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1$\begingroup$ The 60 atoms interact but that doesn't matter. When subsystems interact, they decohere with respect to each other and still leave the full system coherent. $\endgroup$ Commented Oct 26, 2022 at 12:56
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1$\begingroup$ You are talking about decoherence as if it's one thing, but it's not. Decoherence of the full system is what's important for suppressing tunneling. And that's the type that never happens when the system is isolated. $\endgroup$ Commented Oct 27, 2022 at 9:28