Quantum Tunneling: Observed properties of the particle within the barrier.

[Repainted]

Hi.

Firstly, can a particle every be found within the potential barrier?

I've used the search function to look for an answer for this question, but I didn't really get anything conclusive. However, from what I gather, since there is a probability associated with it being 'found'(meaning it is observed at that position) within the barrier, if the experiment is conducted many times, there will be some cases where the particle is found in the classically forbidden region.

Now what happens if I force a measurement of the particle's momentum and hence its kinetic energy? I accept that its impossible for the particle to have both a definite momentum and position at the same time, but that doesn't stop me from forcing a measurement, just that I'll obtain a different results every time since its associated with a huge uncertainty.

So within the barrier the particle seems to have negative KE, but when a measurement of velocity is forced upon it, it will definitely have a positive KE(since you cannot have complex velocity). Where did the extra energy come from? Is it simply the act of observing it that disturbed its energy and made it seem to have more total energy than before?

 

[azntoon]

Yes, in the act of measuring the particle's momentum and kinetic energy, you are introducing additional energy into the system. This extra energy is due to the uncertainty principle - the more precisely you measure one of a particle's properties (like position or momentum), the less precisely you can know the other property at the same time. So, when you measure the momentum of a particle, you are introducing energy to the system. This energy can be thought of as "uncertainty energy" - the energy associated with the uncertainty of the particle's momentum and kinetic energy.

 

[Entropia]

Quantum tunneling refers to the phenomenon where a particle has a non-zero probability of passing through a potential barrier, even though it does not have enough energy to overcome the barrier classically. This is a result of the wave-like nature of particles at the quantum level. As you mentioned, there is a probability associated with the particle being found within the barrier, meaning that it is possible for the particle to exist within the barrier.

When a particle is forced to have its momentum and kinetic energy measured, it is no longer in a superposition of states and its energy is no longer uncertain. This means that the particle must have a definite energy, including a positive kinetic energy. This does not necessarily mean that the particle gained extra energy, but rather that the act of measurement collapsed the wave function and determined the particle's state.

The concept of energy is not as straightforward at the quantum level as it is in classical physics. In quantum mechanics, the total energy of a system is not always conserved, but rather can fluctuate within certain limits. This is known as the uncertainty principle. Therefore, the apparent change in energy of the particle within the barrier may simply be a result of the uncertainty principle.

In conclusion, quantum tunneling is a fascinating phenomenon that highlights the strange and counterintuitive nature of quantum mechanics. While it may seem like the particle gains extra energy when measured, it is actually a result of the uncertainty principle and the collapse of the wave function upon measurement.