More than 70 years ago, scientists in the field of physics came up with an idea to use magnetic fields and an atomic property called spin in order to put a body in two places at the same time. Now, a research group from Ben-Gurion University of the Negev has succeeded in implementing the idea and has even proposed an advanced version of the device that will provide future answers to one of the central questions in physics: Is there a connection between quantum theory and gravitation?
A sealed chip used to create a magnet-based informer: Photo: Yair Margalit
In the 20th century, two revolutions took place in the field of physics: relativity (which also deals with gravitation) and quantum theory. Both are still the pillars of modern physics. One of the open questions in modern physics is why they fail to unite these two successful theories into a single theory called quantum-gravitation?
In an article published in the journal Science Advances managed to explain a research group led by Prof. Ron Pullman From the Department of Physics at Ben-Gurion University of the Negev how to conduct an experiment that will test the relationship between the two theories.
At the core of the idea is a device based on the principles of quantum theory and capable of putting one body in two places at the same time. The device is called an interferometer. There are many types of interferometers, but the interferometer that was developed for the first time is especially important because it is suitable for working with particles with a large mass (which are exposed to a large gravitational interaction). The unique device, which the group managed to realize is a 'full loop interferometer based on the Stern-Gerlach effect' or in short a 'magnetic interferometer'.
Exactly 100 years ago, an experiment was conducted in which the 'Stern-Gerlach effect' was discovered, named after the physicists Walter Gerlach וOtto Stern. A beam of silver atoms is launched towards a screen, as it crosses a magnetic field of varying magnitude. The magnetic field split the atoms into two rays. The quantum explanation for this splitting is that the atom is actually a small magnet that can only be found in two directions with respect to the magnetic field and thus two magnetic forces act on it. The internal magnet of the atom is given the name spin.
In the 50s it was the theorist bohemian who proposed to create a complete loop of splitting and rejoining the rays: after the splitting, a magnetic field would stop the rays and direct them back towards each other, so that the rays would unite again into one ray, after making a complete loop. This is how the magnetic interferometer was created. After a body has been in two places at the same time, it again unites into one body and by measurements performed on this one body, it is possible to learn about differences in the conditions experienced by the body in the two orbits, conditions such as the gravitational interaction.
In fact, it was very difficult to implement such a loop. It was necessary that the parts of the split atom not only be returned to the same place but also at exactly the same speed. The scientists from Ben-Gurion University of the Negev did this by being able to control the magnetic field with a particularly high level of precision using a chip (such as the chips in a computer). In addition, the atomic beam they used was not of silver atoms, but of rubidium atoms that underwent a process of deep cooling to a temperature of almost minus 273 degrees, so that the control of the atom's properties was very high.
A few years ago, the group performed an experiment with a similar purpose when they used a clock consisting of a single atom that was placed in two places at the same time, one closer than the other to the Earth (according to the theory of relativity, time changes as a function of gravitational forces). However, in order to reach unequivocal results in this experiment, significant improvements in the performance of the atomic clocks will be required. Now the group proposes to put in the interferometer a body with a very large mass, such that the gravitational forces acting on it will not be negligible. In this way, one experiment will be obtained, in which the quantum theory will work, which allows to put one body in two places at the same time, alongside the theory of gravitation, the force it exerts depends on the size of the body's mass. Only by combining the two theories together will it be possible to explain the experiment.
To prove the feasibility of the ambitious experiment, the research group, called the 'Atomic Chip Group', carried out a preliminary experiment in which, on the one hand, they used individual atoms, and on the other hand, they implemented the entire process that would be required to do this with a heavy mass.
This is the first time that an experiment of this kind has been carried out in the world. To date, research groups have placed individual atoms and even molecules in various types of interferometers, but no one has yet succeeded in putting atoms in a 'magnetic interferometer'.
"This achievement has considerable significance," he explains Prof. Ron Pullman. "For it is possible that the creation of such a Stern-Gerlach interferometer with a large mass will give us new clues about the quantum nature of gravity, and thus we may be able to solve one of the great mysteries of modern physics."
Now that there seems to be a practical way to do this, the group will begin, together with other groups around the world, in the realization of the experiment.
The research team included: Dr. Yair Margalit, Mr. Or Dovkovski, Dr. Zhifan Zo, Mr. Omer Amit, Dr. Yonatan Yaffe, Dr. Samuel Mukuri, Dr. Daniel Rorlich, Prof. Anupam Mazumder, Prof. Sugato Bose, Dr. Karsten Henkel and Prof. Ron Polman.
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