Atomic beam collimators are mostly found in physics labs, where they shoot a beam of atoms that produces exotic quantum phenomena and have properties that may be useful in precision technologies. By shrinking collimators from the size of a small appliance to fit on a fingertip, researchers at the Georgia Institute of Technology want to make the technology available to engineers developing next-generation atomic clocks, accelerometers, and components found in smartphones.
“Collimated atomic beams have been around for decades,” says Chandra Raman, an associate physics professor at Georgia Tech. “But currently, they must be large to be precise.”
The atomic beam starts in a box full of rubidium atoms heated to a vapor so they zing about chaotically. A tube taps into the box and random atoms with the right trajectory shoot through the tube.
Like pellets leaving a shotgun, the atoms exit the tube flying reasonably straight, but also with a random spray of atoms going at skewed angles. In an atomic beam, the spray is signal noise, and Georgia Tech’s collimator-on-a-chip eliminates most of it for a more precise, nearly perfectly parallel beam of atoms.
The beam is much more focused and pure than beams from current collimators. The researchers would also like their collimator to enable experimental physicists to more conveniently create complex quantum states. But more immediately, the collimator sets up Newtonian mechanics that could be adapted for practical use.
The improved beams are streams of unwavering "inertia" because, unlike a laser beam made of massless photons, atoms have mass and thus momentum and inertia. This makes their beams potentially ideal reference points in beam-driven gyroscopes that track motion and changes in location for navigational aids.
Current gyroscopes in GPS-free navigation devices are precise in the short run but not over the long run, which means they must be recalibrated or replaced ever so often. That makes them less convenient on the moon or Mars.
“Conventional chip-scale instruments based on MEMs technology suffer from drift over time from various stresses,” said co-principal investigator Farrokh Ayazi, a Georgia Tech professor. “To eliminate that drift, you need an absolutely stable mechanism. This atomic beam creates that kind of reference on a chip.”
Heat-excited atoms in a beam can also be converted into Rydberg atoms, which provide a wealth of quantum properties.
When an atom is energized enough, its outermost orbiting electron bumps out so far that the atom balloons in size. Orbiting so far out with so much energy, that outermost electron behaves like the lone electron of a hydrogen atom, and the Rydberg atom acts as if it has only a single proton.
“You can engineer certain kinds of multi-atom quantum entanglement using Rydberg states because the atoms interact with each other much more strongly than two atoms in the ground state,” Raman says.
“Rydberg atoms could also advance future sensor technologies because they’re sensitive to fluxes in force and in electronic fields smaller than an electron in scale,” Ayazi says. “They could also be used in quantum information processing.”
The researchers devised a surprisingly convenient way to make the new collimator, which could encourage manufacturers to adopt it: They cut long, extremely narrow channels through a silicon wafer running parallel to its flat surface. The channels are like shotgun barrels lined up side-by-side to shoot out an array of atomic beams.
Silicon is an exceptionally slick material for the atoms to fly through and also is used in many microelectronic and computing technologies. That opens up the possibility for combining these technologies on a chip with the new miniature collimator. Lithography, which is used to etch chips, was used to precisely cut the collimator's channels.
The researchers’ biggest innovation greatly reduced the shotgun-like spray (i.e., the signal noise). They sliced two gaps in the channels, forming an aligned cascade of three sets of parallel arrays of barrels.
Atoms flying at skewed angles jump out of the channels at the gaps, while those flying reasonably parallel in the first array of channels continue on to the next one; then the process repeats going from the second into the third array of channels. This gives the new collimator’s atomic beams exceptional straightness.
