Physicists solved a decade-long puzzle by describing how fast a particle can pass through a barrier.
Particles can fly through seemingly insurmountable barriers like ghosts.
For decades, physicists have wondered how long this so-called quantum tunneling takes. After a three-year investigation, an international team of theoretical physicists now has an answer. According to a new study, they measured a tunneling electron from a hydrogen atom and found that the passage is virtually instantaneous. [1
Particles can pass solid objects, not because they are very small (though they are), but because the rules of physics are different at the quantum level.
Imagine a ball rolling down a valley to a slope as high as Mount Everest; Without a jetpack, the ball would never have enough energy to clear the hill. However, a subatomic particle does not have to go over the hill to get to the other side.
Particles are also waves that expand infinitely in space. According to the so-called wave equation, this means that a particle can be located anywhere in the wave.
Now imagine the wave that hits a barrier; it continues to run but loses energy and its amplitude (the peak height) falls sharply down. However, if the obstacle is thin enough, the amplitude of the wave will not drop to zero. As long as some energy remains in the flattened wave, there is a chance that a particle will fly through the hill and the other side, if only a small one.
Experiments that capture this elusive activity at the quantum level To say the least, Robert Sang, an experimental quantum physicist and professor at Griffith University in Australia, was "very challenging" in an e-mail.
"You have to combine very complicated laser systems, a reaction microscope and a hydrogen-atom beam system, all of which work simultaneously," Sang said.
Their lineup identified three important clues: the beginning of their interaction with the atom; the time when a released electron should be expected behind a barrier; and the time when it actually appeared, Sang said in a video.
Keeping Time with Light
Researchers used an optical timepiece called Attoclock – ultrashort, polarized light pulses that can measure the motion of electrons down to attosecond or to a billionth of a billionth of a second. Their attack bathed hydrogen atoms in light at a rate of 1000 pulses per second, ionizing the atoms so that their electrons could escape through the barrier, the researchers reported.
A reaction microscope on the other side of a barrier measured the electrons momentum as it emerged. The reaction microscope detects the energy levels in a charged particle after it interacts with the light pulse of the attack, "and from it we can read the time it took to go through the barrier," Sang told Live Science.
"The precision that we were able to measure this to 1.8 attoseconds," Sang said, "We concluded that tunneling should be less than 1.8 attoseconds," he added shortly.
Although the measurement system was complex, it was the atom of the researchers' experiments simple – atomic hydrogen containing only one electron Previous experiments carried out by other researchers used atoms that contained two or more electrons, such as helium, argon and krypton, according to the study.
Since released electrons can interact with each other, these interactions can affect the tunneling time of particles explain why earlier studies were longer than in the new study, by several tens of attoseconds, Sang said. The simplicity of the atomic structure of hydrogen enabled researchers to calibrate their experiments with an accuracy unattainable in previous experiments. This was an important benchmark against which further tunneling particles can now be measured, the researchers reported.
The results were published online March 18 in the journal Nature.
Originally published on Live Science .