Scientists have squeezed two layers of supercold magnetic atoms 50 nanometers apart, 10 times closer than in previous experiments, revealing strange quantum effects never seen before.
The extreme proximity of these atoms will allow researchers to study quantum interactions at this length scale for the first time and could lead to important advances in the development of superconductors and superconductors. quantum computersscientists report in a new study published on May 2 in the journal Science.
Unusual quantum behavior begins to emerge at extremely cold temperatures, as atoms are forced into their lowest energy states. “In the nanokelvin regime, there is a type of matter called Bose Einstein condenser [in which] all particles behave like waves” Li Du, MIT physicist and lead author of the study told Live Science. “Mostly those quantum mechanical things”.
Interactions between these isolated systems are particularly important for understanding quantum phenomena such as superconductivity and super bright. But the strength of these interactions usually depends on the separation distance, which can create practical problems for researchers studying these effects; their experiments are limited by how close they can get to the atoms.
“Most atoms used in cold experiments, such as the alkali metals, need to be in contact to interact,” Du said. “We are interested in dysprosium atoms, which are special [in that they] can interact with each other over long distances through dipole-dipole interactions [weak attractive forces between partial charges on adjacent atoms]. But even though there is this long-range interaction, there are still some kinds of quantum phenomena that cannot happen because this dipole interaction is so weak.”
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Bringing the cold atoms maintaining control over their quantum states is a major challenge, and until now experimental limitations have prevented researchers from fully testing theoretical predictions about the consequences of these quantum interactions.
“In conventional experiments, we trap atoms with light, and this is limited by the diffraction limit, on the order of 500 nanometers,” Du said. For comparison, the width of a human hair is 80,000-100,000 nanometers. National Nanotechnology Initiative.)
By using a laser beam focused through a lens, researchers can create a “Gaussian focal point,” which is like a well of energy inside the laser beam that locks in the position of specific atoms. This is known as optical tweezers, but the size of the tweezers (the width of the energy well) is limited by the wavelength of the laser light. This minimum width is called the diffraction limit.
Du’s team devised a clever trick to overcome the diffraction limit by exploiting another quantum property of dysprosium atoms: their spin. An atomic spin can point up or down, but it’s important that they have slightly different energies. This means the team can use two different laser beams with slightly different frequencies and polarization angles to spin the dysprosium atoms up and down separately.
“If atom A doesn’t see light B and atom B doesn’t see light A, they basically have independent control,” he explained. “Because the atoms are always in the center of the Gaussian beam, you can move [the two different trapped particles] close arbitrarily”. By carefully controlling two optical tweezers, Du’s team brought the spinning and spinning dysprosium atoms within 50 nanometers of each other, increasing the interaction strength 1,000 times from 500 nanometers.
By creating this bilayer, the team began a series of experiments to study quantum interactions at close range. They heated one of the dysprosium layers with a vacuum gap completely separated from the other. Incredibly, they observed heat transfer to the second layer across empty space.
“Usually heat transfer requires contact or radiation, which we don’t have here,” Du said. “But we still see heat transfer, and it must be due to the long-range dipole-dipole interaction.”
The seemingly impossible transfer of heat was just one of the strange effects the team studied. Now they want to further explore the potential of quantum interactions on this scale. The team is already beginning to study how these bilayers interact with light. But Du is particularly interested in another quantum effect called Bardeen-Cooper-Schrieffer (BCS) coupling, a quantum bound state experienced by certain subatomic particles called fermions at low temperatures.
“The BCS coupling between the layers is very important for superconductivity,” he said. “A theoretical paper a few years ago predicted that if we had this kind of bilayer coupled with a long-range dipole-dipole interaction, you could form a BCS pair. possible with our system.”