It’s cool to be small. Scientists on the National Institute of Standards and Technology (NIST) have miniaturized the optical parts required to chill atoms down to some thousandths of a level Celsius above absolute zero, step one in using them on microchips to drive a brand new technology of super-accurate atomic clocks, allow navigation with out GPS, and simulate quantum techniques.
Cooling atoms is equal to slowing them down, which makes them so much simpler to check. At room temperature, atoms whiz via the air at almost the velocity of sound, some 343 meters per second. The fast, randomly shifting atoms have solely fleeting interactions with different particles, and their movement could make it troublesome to measure transitions between atomic vitality ranges. When atoms gradual to a crawl — about 0.1 meters per second — researchers can measure the particles’ vitality transitions and different quantum properties precisely sufficient to make use of as reference requirements in a myriad of navigation and different gadgets.
For greater than 20 years, scientists have cooled atoms by bombarding them with laser gentle, a feat for which NIST physicist Invoice Phillips shared the 1997 Nobel Prize in physics. Though laser gentle would ordinarily energize atoms, inflicting them to maneuver quicker, if the frequency and different properties of the sunshine are chosen fastidiously, the alternative occurs. Upon hanging the atoms, the laser photons scale back the atoms’ momentum till they’re shifting slowly sufficient to be trapped by a magnetic area.
However to organize the laser gentle in order that it has the properties to chill atoms usually requires an optical meeting as huge as a dining-room desk. That’s an issue as a result of it limits using these ultracold atoms outdoors the laboratory, the place they may develop into a key factor of extremely correct navigation sensors, magnetometers and quantum simulations.
Now NIST researcher William McGehee and his colleagues have devised a compact optical platform, solely about 15 centimeters (5.9 inches) lengthy, that cools and traps gaseous atoms in a 1-centimeter-wide area. Though different miniature cooling techniques have been constructed, that is the primary one which depends solely on flat, or planar, optics, that are simple to mass produce.
“That is essential because it demonstrates a pathway for making actual gadgets and never simply small variations of laboratory experiments,” mentioned McGehee. The brand new optical system, whereas nonetheless about 10 instances too huge to suit on a microchip, is a key step towards using ultracold atoms in a number of compact, chip-based navigation and quantum gadgets outdoors a laboratory setting. Researchers from the Joint Quantum Institute, a collaboration between NIST and the University of Maryland in School Park, together with scientists from the College of Maryland’s Institute for Analysis in Electronics and Utilized Physics, additionally contributed to the research.
The equipment, described on-line within the New Journal of Physics, consists of three optical parts. First, gentle is launched from an optical built-in circuit utilizing a tool known as an excessive mode converter. The converter enlarges the slim laser beam, initially about 500 nanometers (nm) in diameter (about 5 thousandths the thickness of a human hair), to 280 instances that width. The enlarged beam then strikes a fastidiously engineered, ultrathin movie often known as a “metasurface” that’s studded with tiny pillars, about 600 nm in size and 100 nm extensive.
The nanopillars act to additional widen the laser beam by one other issue of 100. The dramatic widening is critical for the beam to effectively work together with and funky a big assortment of atoms. Furthermore, by undertaking that feat inside a small area of house, the metasurface miniaturizes the cooling course of.
The metasurface reshapes the sunshine in two different essential methods, concurrently altering the depth and polarization (route of vibration) of the sunshine waves. Ordinarily, the depth follows a bell-shaped curve, through which the sunshine is brightest on the middle of the beam, with a gradual falloff on both aspect. The NIST researchers designed the nanopillars in order that the tiny constructions modify the depth, making a beam that has a uniform brightness throughout its whole width. The uniform brightness permits extra environment friendly use of the accessible gentle. Polarization of the sunshine can also be crucial for laser cooling.
The increasing, reshaped beam then strikes a diffraction grating that splits the only beam into three pairs of equal and oppositely directed beams. Mixed with an utilized magnetic area, the 4 beams, pushing on the atoms in opposing instructions, serve to entice the cooled atoms.
Every element of the optical system — the converter, the metasurface and the grating — had been developed at NIST however was in operation at separate laboratories on the 2 NIST campuses, in Gaithersburg, Maryland and Boulder, Colorado. McGehee and his workforce introduced the disparate parts collectively to construct the brand new system.
“That’s the enjoyable a part of this story,” he mentioned. “I knew all of the NIST scientists who had independently labored on these totally different parts, and I spotted the weather may very well be put collectively to create a miniaturized laser cooling system.”
Though the optical system must be 10 instances smaller to laser-cool atoms on a chip, the experiment “is proof of precept that it may be executed,” McGehee added.
“In the end, making the sunshine preparation smaller and simpler will allow laser-cooling primarily based applied sciences to exist outdoors of laboratories,” he mentioned.