The part of the process still up for debate is the timescale involved for the particle to tunnel to freedom. There are two theories: the “simple man” model says that it happens instantly, so the escaping electron will just appear at the exit of the tunnel with no velocity. But in 1955, physicist Eugene Wigner proposed the idea that it takes a finite (albeit short) amount of time for the particle to make the journey.
To investigate, the Max Planck team induced quantum tunneling of electrons in atoms, and then measured the time (if any) it took them to do so. Since it would be happening over an incredibly tiny timescale, the scientists developed a clever little trick that would allow them to see which scenario was happening.
To induce quantum tunneling, the scientists blasted a gas mixture of krypton and argon atoms with short laser pulses. This temporarily weakens the electric field that binds the electrons in place, increasing the probability that one of them will tunnel out. The trajectory of the electron’s exit from the nucleus is guided by the laser’s electric field, and in this particular experiment, the laser beam is rotating, which causes the “energy pot” containing the electrons to rotate too.
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