Physicists at the University of California, Santa Barbara became the first scientist to observe a strange behavior in the quantum world through experiments: when particles in a disordered system are kicked out of their positions, the "quantum dart" effect will occur. Instead of landing in other places as expected, they turned around and stopped there.
"This is actually a basic quantum mechanical effect," said David Wilder, an atomic physicist whose laboratory produced this effect and made a physical comment on it in a paper published in 2006. "There is no classical explanation for this phenomenon."
The boomerang effect originated from a phenomenon predicted by physicist philip anderson about 60 years ago. A disorder called Anderson localization inhibits the transmission of electrons. Roshansajjad, the main author of this paper, believes that this disorder phenomenon may be caused by defects in the atomic lattice of materials, whether it is impurities, defects, dislocations or other disturbances.
Sajjad said: "This type of disorder will make them basically not spread anywhere." . Therefore, electrons will be localized instead of moving rapidly along the lattice, turning the originally conductive material into an insulator. Judging from this rather tricky quantum condition, the quantum dart effect was predicted several years ago.
It is extremely difficult, if not impossible, to track electrons leaving their local positions, but there are some hints in the welding laboratory. Researchers use a gas consisting of 654.38+ million ultra-cold lithium atoms suspended in a standing wave to "kick" them, simulating the so-called quantum kicking rotor (both Weld and Sajjad say it is similar to a pendulum that kicks periodically). Researchers can create lattice and disorder, and observe the launch and return of boomerang. They work in momentum space, which is a way to avoid some experimental difficulties without changing the basic physical principle of boomerang effect.
Sajjad explained: "In normal position space, if you are looking for boomerang effect, you will give your electron a limited speed and then see if it returns to the same position." . "Because we are in momentum space, we start with a system with zero average momentum, we look for some deviations, and then return to zero average momentum."
Using their quantum rotors, they made dozens of lattices and noticed the initial change of average momentum. However, over time, despite repeated kicking, the average momentum returned to zero.
Wilder said: "This is just a very fundamentally different behavior. He explained that in the classical system, the rotor kicked out in this way will constantly absorb the kicked energy to react. Take the quantum version of the same thing as an example. What you see is that it starts to gain energy in a short time, but stops at a certain moment and no longer absorbs any energy. It becomes a so-called dynamic positioning state.
He said that this behavior is due to the fluctuation of the quantum system.
Wilder explained: "What you push away is not only particles, but also waves, which is the core concept of quantum mechanics." . "Because of this wave-like nature, it will be disturbed. The interference of this system will eventually stabilize the regression and stay at the origin." In their experiments, researchers found that periodic kicking shows that time reversal symmetry will produce boomerang effect, but random kicking will destroy symmetry, so boomerang effect will occur.
Then there is the welding lab: if a single dart effect is cool, will several interactive dart effects be a party?
"There are many theories and problems. What if interaction destroys the boomerang? Are there many interesting physical effects? " Sajjad said. "Another exciting thing is that we can use this system to study darts in higher dimensions."
Jeremy L.Tanlimco, Hector Mas, Eber Nolasco Martinez and Ethan Q.Simmons of UCSB also studied this project; Tommaso Macrì of the Federal University of Rio Grande do Norte and Patrizia Vignolo of the Blue University.