quantum optics

Exotic physics can happen when quantum particles come together and talk to each other. Understanding such processes is challenging for scientists, because the particle interactions can be hard to glimpse and even harder to control. Moreover, modern computer simulations struggle to make sense of all the intricate dynamics going on in a large group of particles. Luckily, atoms cooled to near zero temperatures can provide insight into this problem.Lasers can make cold atoms mimic the physics seen in other systems—an approach that is familiar terrain for atomic physicists. They regularly use intersecting laser beams to capture atoms in a landscape of rolling hills and valleys called an optical lattice. Atoms, when cooled, don’t have enough energy to walk up the hills, and they get stuck in the valleys. In this environment, the atoms behave similarly to the electrons in the crystal structure of many solids, so this approach provides a straightforward way to learn about interactions inside real materials. But the conventional way to make optical lattices has some limitations. The wavelength of the laser light determines the location of the hills and valleys, and so the distance between neighboring valleys—and with that the spacing between atoms—can only be shrunk to half of the light’s wavelength. Bringing atoms closer than this limit could activate much stronger interactions between them and reveal effects that otherwise remain in the dark. Now, a team of scientists from the Joint Quantum Institute (JQI), in collaboration with researchers from the Institute for Quantum Optics and Quantum Information in Innsbruck, Austria, has circumvented the wavelength limit by leveraging the atoms’ inherent quantum features, which should allow atomic lattice neighbors to get closer than ever before. The new technique manages to squeeze the gentle lattice hills into steep walls separated by only one-fiftieth of the laser’s wavelength—25 times narrower than possible with conventional methods. The work, which is based on two prior theoretical proposals, was recently published in Physical Review Letters.

If you holler at someone across your yard, the sound travels on the bustling movement of air molecules. But over long distances your voice needs help to reach its destination—help provided by a telephone or the Internet. Atoms don’t yell, but they can share information through light. And they also need help connecting over long distances.Now, researchers at the Joint Quantum Institute (JQI) have shown that nanofibers can provide a link between far-flung atoms, serving as a light bridge between them. Their research, which was conducted in collaboration with the Army Research Lab and the National Autonomous University of Mexico, was published last week in Nature Communications. The new technique could eventually provide secure communication channels between distant atoms, molecules or even quantum dots.

Experimental quantum physics often resides in the coldest regimes found in the universe, where the lack of large thermal disturbances allows quantum effects to flourish. A key ingredient to these experiments is being able to measure just how cold the system of interest is. Laboratories that produce ultracold gas clouds have a simple and reliable method to do this: take pictures! The temperature of a gas depends on the range of velocities among the particles: how large is the difference between the slowest- and the fastest-moving particles. If all the atoms evolve for the same amount of time, the velocity distribution gets imprinted in the position of the atoms. This is analogous to a marathon where all the runners start together so you cannot immediately tell whom is the fastest, but after some time you can discern by eye whom is faster or slower based on their location.
In some experiments, however, the cloud is so well-hidden that snapshots are near impossible. A new technique developed by JQI researchers and published in Physical Review A as an Editor’s Suggestion, circumvents this issue by inserting an optical nanofiber (ONF) into a cold atomic cloud.

The storage of light-encoded messages on film and compact disks and as holograms is ubiquitous -- grocery scanners, Netflix disks, credit-card images are just a few examples. And now light signals can be stored as patterns in a room-temperature vapor of atoms. Scientists at the Joint Quantum Institute (*) have stored not one but two letters of the alphabet in a tiny cell filled with rubidium (Rb) atoms which are tailored to absorb and later re-emit messages on demand. This is the first time two images have simultaneously been reliably stored in a non-solid medium and then played back.