A team of physicists from BGU’s Atom Chip Lab has put a single atom in two places at the same time by utilizing a static magnetic field. This “impossible” situation is made possible in the strange world described by quantum theory. In order to enter the realm of the quantum world, the team cooled the atom to a temperature of about 100 nano-Kelvin (one part in ten million above the “absolute zero”), the coldest temperature known to mankind in a laboratory or in nature.
Known as a superposition state, the successful creation of this strange state allows a rare glimpse into the quantum world and its principles, one of the physics revolutions of the 20th Century. Furthermore, such a state also enables technological applications such as ultra-accurate inertial navigation systems, or sensors for the measurement of the gravitational field (e.g. for water and oil exploration) with unprecedented sensitivity.
The paper describing this complex experiment, authored by PhD student Shimon Machluf, researcher Dr. Yonathan Japha and Prof. Ron Folman, was recently published in Nature Communications.
In more detail: A spatial superposition is the state of a single quantum particle when it exists in several “copies” in different locations at the same time. In this unique state, these copies maintain a specific relation between them known as the “phase.” This phase determines the features of the particle once all copies are brought back together again. The value of the phase is extremely sensitive to forces acting in the vicinity of the copies, and as such is an ultra-sensitive tool for the measurement of these forces. It is this sensitivity which allows the development of new technological applications as well as new experimental insights into the foundations of quantum theory as well as the search for new physics and new forces.
The team cooled a cloud of individual atoms in a gaseous phase and forced the whole cloud into a superposition state, so that every atom in the cloud was itself in a superposition state. In total, about 10,000 atoms were cooled into a Bose-Einstein condensation state. Such extreme cooling garnered the scientists who first managed it the Nobel Prize (2001). Putting atoms in a state of superposition has also been achieved before. The novelty in the present work is the use of static magnetic fields. In 1921 scientists found that the electron, and similarly the atom in which it resides, are in fact small magnets, and as such static magnetic fields can exert a force on them (Stern-Gerlach effect).
Following the discovery of this phenomenon, it was immediately clear that it may be used to create a state of superposition, but after further calculations it was quickly made evident to the scientists that the task would be extremely hard to perform. Indeed, almost a hundred years later, it had not been achieved – until now. With the help of several alterations to the original idea, the BGU team has now successfully implemented the idea.
Above: A real picture of a group of atoms (in gas phase), where each atom exists in both the upper group and lower group, at the same time. The color is false and represents the density of the atoms.
(Picture taken by Shimon Machluf)