Einstein would have been pleased

BGU scientists put the same atomic ‘clock’ in two places at the same time.

Albert Einstein (photo credit: Courtesy)
Albert Einstein
(photo credit: Courtesy)
Although logically it’s impossible to put one object in two different places at the same time, a team of Ben-Gurion University researchers have managed to put a clock in two locations simultaneously.
Led by Prof. Ron Folman, the group described recently in Science, one of the world’s most prestigious scientific journals, which is published by the American Association for the Advancement of Science, how the achievement in the future will facilitate the study of the role of time in the dynamics of the universe and could provide better understanding of the connection between Albert Einstein’s theory of general relativity and quantum mechanics.
These two theories constitute the physics revolutions of the 20th century, and many attempts have been made to unify them or – at the very least – understand how they work together.
“We demonstrate a new tool for investigating time in the overlap of these two theories – a self-interfering clock, comprising two atomic spin states,” they wrote.
The Beersheba researchers, all members of BGU’s atom chip laboratory, took an atom and turned it into an atomic clock – like those used in many technological zero applications such as global positioning systems (GPS).
At the same time, they transferred the atom through a device capable of positioning it in two places simultaneously.
This device, called an interferometer, works according to the laws of quantum mechanics, which enable an object to be in several places at once.
According to standard quantum mechanics, time “ticks” at the same speed all over the universe. In Einstein’s theory of general relativity (which he proposed in 1915, showing how light was at the center of the very structure of space and time) time depends locally on gravity and does not “tick” at the same pace everywhere because it is influenced by gravitational forces of large masses such as the Earth.
Therefore, the researchers asked what would happen to the clock after passing simultaneously through several places where time “ticks” at a different pace once it was in one place again.
They showed that in this very odd situation, a new phenomenon presents itself that may, in the future, show that the general theory of relativity plays an important role at the border between the quantum world, in which an object can be in several places simultaneously, and the classical world (as our day-today world of large objects is known), in which an object is not allowed to be in several places at once.
The research hints at the possibility that a particle, such as the electron, can move from the quantum world to the classical world with the help of general relativity.
Technically, the team used advanced technologies to cool atoms with lasers, so that the atoms enter the quantum realm where a state in which they are in several places simultaneously may survive for times long enough to conduct the experiment.
The atoms are cooled to a few nano-Kelvin, namely, very close to absolute zero (-273 degrees Celsius).
The atoms were then exposed to strong magnetic fields, which positioned each atom in two places simultaneously.
In parallel, the atoms were transferred to a state in which they could act as atomic clocks and measure time. This is done by manipulating the internal atomic states made of a variety of energies and angular momentum levels.
In scientific language, instead of saying that an object (such as a clock) is in several places simultaneously, it is typically said that the object is in a “spatial quantum superposition. This new terminology is meaningful, the BGU researchers said, because all attempts to interpret the reality of this situation with day-to-day language have led to some sort of contradiction.
The strange reality of the quantum world can be accurately described by mathematics, they said.
Using words that originate in our classical experience, they explained, always fails those who attempt to harness them for the description of the quantum world. They suggested that, in the future, one may alternatively state that the clock is in a state in which it “feels” how time “ticks” in several places at once.