A new study published in the journal Science details how researchers from MIT brought two layers of ultracold magnetic atoms at 50 nanometers -the closest distance ever achieved- and its importance in the development of quantum technology. When ultracold atoms are squeezed together at a such distance, they start to occupy their lowest possible energy state unfolding some unusual quantum effects. Studying interactions between those short-distanced atoms is crucial for understanding phenomena such as superconductivity and superradiance. Before then it was only possible to control the distance in the order of 500 nanometers or greater. 

Beating previous limitations

When it comes to controlling the atoms at the ultra-cold temperature, laser light is usually employed for the experiment. The first author of the study, Li Du explained that trapping atoms with light was previously limited by the diffraction limit of 500 nm. Or it is equivalent to saying that the limitation occurs due to the wavelength of the laser light. 

In this study, Du’s team chose a dysprosium atom - as a study object. Dysprosium (Dy) is the 66th element in the periodic table and is found in various minerals in nature. To overcome limitations, they used the quantum property of dysprosium atoms: spin. The term ‘spin’ here does not imply what we think in mind – the spinning or rotating motion of atoms; they don’t! It is closer to the truth to say that they just behave like they are spinning. What we should be aware of is there are two spin states: up and down, subsequently resembling the clockwise and anticlockwise spinning. Atoms in those two states can have slightly different energies. Therefore, researchers were able to use two different laser beams at slightly different frequencies to trap the spin-up and spin-down versions of dysprosium atoms. 

Trapping atoms with lights

Once a laser beam is focused through a lens, scientists can create an energy well within the laser beam that traps individual atoms in a particular position. This is also known as an optical tweezer. The previously mentioned term, diffraction limit is the minimum with of the energy well or the optical tweezer. Since two different laser beams are utilized in the experiment, there will be two optical tweezers. By carefully controlling them, the team has finally brought the spin-up and spin-down Dy atoms to each other within 50 nanometers which is 100 times closer than previous measurements of 50 nm. In terms of the interaction strength between the atoms: the closer they are, the greater the strength; and according to this study, the increase in the strength of the interaction is 1000 times greater than what it was at 500-nanometer levels. 

Incredible observation

After establishing the bilayer of the atom, Du’s team conducted a series of experiments to study quantum effects. They heated one layer, and completely separated them away from the other by a vacuum gap. Even though, they observed heat transfer to the second layer across the gap. “Typically, you need contact or radiation for heat transfer, which we don’t have here,” Du said, “But we still see heat transfer, and this must be due to long-range dipole-dipole interactions (weak attractive forces between partial charges on neighboring atoms)”. 

Further explorations

The group is already beginning to explore how these bilayers interact with light. Also, Du is interested in another quantum effect called Bardeen-Cooper-Schrieffer (BCS) pairing which is a quantum-bound state experienced by fermions (subatomic particles) at low temperatures. As Du described BCS pairing between layers is so important to superconductivity and there is a theoretical paper predicted that this kind of bilayer system helps to form a BCS pair. 

Conclusion

In essence, this study marks a significant achievement in manipulating atoms with light. By bringing atoms closer than ever before and witnessing an exceptional quantum effect a research team at MIT provides new opportunities for further projects aimed at studying quantum phenomena at the atomic scale, such as understanding superconductivity more deeply will contribute enormously to the development of quantum computers. 

Full article:

https://www.science.org/doi/10.1126/science.adh3023

Source: 

https://www.livescience.com/physics-mathematics/quantum-physics/atoms-squished-closer-together-than-ever-before-revealing-seemingly-impossible-quantum-effects