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Stop the atom: Researchers miniaturize laser cooling



Stagnant atoms: NIST minimizes laser cooling

An illustration of a new optical system that minimizes laser cooling of atoms, which is a key step in cooling atoms on a microchip. The light beam is emitted from the photonic integrated circuit (PIC) and greatly expanded by a component called an extreme mode converter (EMC). Then, the beam hits a carefully designed ultra-thin film called a metasurface (MS), which is covered with tiny pillars that further expand and shape the beam. The light beam is diffracted from the grating chip, forming multiple overlapping laser beams in the vacuum chamber. The combination of laser beam and magnetic field effectively cools and traps a large number of gaseous atoms in the magnetic gas trap (MOT). Credit: NIST

Very small and cool. Scientists at the National Institute of Standards and Technology (NIST) have miniaturized optical components that cool atoms to a few thousandths higher than absolute zero. This is the first application of them on microchips to drive a new generation of ultra-high precision. One-step atomic clock can navigate without GPS and simulate quantum systems.

Cooling the atoms is equivalent to slowing them down, which makes them easier to study. At room temperature, atoms sway in the air at a speed close to the speed of sound, about 343 meters per second. The interaction of fast, randomly moving atoms with other particles is only short-lived, and their motion makes it difficult to measure the transitions between atomic energy levels. When the atom is crawling slowly (about 0.1 meters per second), researchers can accurately measure the energy transitions and other quantum properties of the particles to use as a reference standard for many navigation and other devices.

For more than two decades, scientists have cooled the atoms by bombarding them with lasers. This is the 1997 Nobel Prize in Physics shared by NIST physicist Bill Phillips (Bill Phillips). Although lasers usually excite atoms and make them move faster, the opposite can happen if the frequency and other properties of the light are carefully chosen. After hitting the atoms, the laser photons reduce the momentum of the atoms until they move slowly enough to be captured by the magnetic field.

But to prepare the laser to have the properties of cooling atoms, usually an optical component as large as a restaurant table is required. This is a problem because it limits the use of these ultra-cold atoms outside the laboratory, where they may become a key element of high-precision navigation sensors, magnetometers, and quantum simulations.

Now, NIST researcher William McGehee and his colleagues have designed a compact optical platform, only about 15 cm (5.9 inches) long, that can cool and capture gaseous atoms in a 1 cm wide area. Although other micro-cooling systems have been built, this is the first system that relies entirely on flat or flat optical systems that are easy to mass produce.

McGehee said: “This is important because it shows the way to make real devices, not just small laboratory experiments.” Although this new optical system is still 10 times larger than it can be mounted on a microchip, It is a crucial step in the use of ultra-cold atoms in many compact, chip-based navigation and quantum devices outside the laboratory. Researchers from the Joint Quantum Institute between NIST and the University of Maryland in University Park, as well as scientists from the Institute of Electronics and Applied Physics at the University of Maryland, also contributed to this research.

The device, in New Journal of Physics, It consists of three optical elements. First, a device called an extreme mode converter is used to emit light from the optical integrated circuit. The converter magnifies the narrow laser beam. The initial diameter is about 500 nanometers (nm) (about one-fifth of a hair), which is 280 times the width. Then, the amplified light beam hits a carefully designed ultra-thin film called the “metasurface”, which is covered with tiny columns, about 600 nm long and 100 nm wide.

The role of the nanopillar is to further broaden the laser beam by 100 times. For the beam to effectively interact with and cool a large number of atoms, it must be broadened dramatically. In addition, by accomplishing this feat in a smaller space area, the metasurface can minimize the cooling process.

Metasurfaces shape light in two other important ways, while changing the intensity and polarization (direction of vibration) of light waves. In general, the intensity follows a bell-shaped curve, in which the light is brightest in the center of the beam, while the two sides gradually attenuate. Researchers at NIST designed the nanopillars to change the intensity of tiny structures to produce a beam of uniform brightness across the width. Uniform brightness can make more efficient use of available light. The polarization of light is also crucial for laser cooling.

Then, after expansion, the shaped beam is incident on the diffraction grating, which divides the single beam into three pairs of equal and opposite beams. Combined with the applied magnetic field, the four beams push the atoms in opposite directions to trap the cooled atoms.

Each component of the optical system—converters, metasurfaces, and gratings—are developed at NIST but performed in separate laboratories on two NIST campuses in Gaithersburg, Maryland and Boulder, Colorado. operating. McGehee and his team combined different components to build a new system.

He said: “This is the most interesting part of this story.” “I know all the NIST scientists who independently study these different components, and I realized that these elements can be put together to create a miniaturized laser cooling system.”

McGehee added that although the optical system must be 10 times smaller than the atoms on the laser cooling chip, the experiment “is a proof of principle that can be done.”

He said: “Ultimately, making the light preparation work smaller and simpler will enable laser cooling-based technology to be used outside the laboratory.”


Scientists shrink quantum technology


More information:
William McGehee et al. “Magneto-Optical Capture Using Planar Optics”, New journal of physics (2021). DOI: 10.1088 / 1367-2630 / abdce3

Provided by the National Institute of Standards and Technology



Citation: Putting the atom to a standstill: Researchers will miniaturize laser cooling (January 21, 2021) from January 22, 2021 from https://phys.org/news/2021-01-atoms-standstill-miniaturize-laser- cooling.htmlSearch

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