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Atomic tweezers — levitated optomechanics

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I’ve been following articles for awhile about micron, nanometer, and atomic level confinement and manipulation.

The development of “optical tweezers” facilitated exploration of biological particles with sizes in the micrometer and nanometer range such as viruses and bacteria and subcellular components.

Optical traps also facilitated exploring properties of trapped individual molecules and atoms.

Related techniques have been used to better understand the physics of exotic condensed matter such as the quantum properties of 1d and 2d collections of atoms. Research in manipulating quantum properties of individual atoms is particularly fascinating.

So, to start this topic, here’s an APS article on cooling nanoparticles: “Viewpoint: Nanoparticles Get Cool by Light Scattering” (March 27, 2019).

Researchers performed 3D cavity cooling of levitated nanoparticles, reaching record low temperatures by utilizing light that scatters off the particles.

Arthur Ashkin pioneered the optical manipulation of small particles with the development of optical tweezers, for which he was awarded the 2018 Nobel Prize in Physics. (See 4 October 2018 Focus story.) The ability to control small particles with tweezers and other optical tools has enabled many breakthroughs in biology, physical chemistry, and atomic, molecular, and optical physics. As part of this trend, researchers have developed ways to “cool” trapped nanoparticles by reducing the amplitude of their motion within the trap. However, effort is still needed to reach the quantum limit where the motion is dominated by quantum fluctuations. A new method … is promising to reduce the motion of a levitated nanoparticle to its quantum-mechanical ground state.

Key factors in levitated optomechanics:

• Isolation from the thermal environment (air molecules, vibration)
• Position stability of optical tweezer
• Cavity cooling vs. feedback cooling
• Coherent light scattering
• Optical cavity tuning
• Particle position monitoring


I’ve already encountered articles which discuss sorting and assembly of individual atoms and fabrication of macroscopic layers only a single atom in thickness.

Ultracold atom []

Ultracold atoms are atoms that are maintained at temperatures close to 0 kelvins (absolute zero), typically below temperatures of some tenths of microkelvins (µK). At these temperatures the atom’s quantum-mechanical properties become important.

To reach such low temperatures, a combination of several techniques has to be used. First, atoms are usually trapped and pre-cooled via laser cooling in a magneto-optical trap. To reach the lowest possible temperature, further cooling is performed using evaporative cooling in a magnetic or optical trap.

Fermi–Dirac statistics[–Dirac_statistics]

In quantum statistics, a branch of physics, Fermi–Dirac statistics describe a distribution of particles over energy states in systems consisting of many identical particles that obey the Pauli exclusion principle.

Bose–Einstein statistics [–Einstein_statistics]

In quantum statistics, Bose–Einstein statistics (or colloquially B–E statistics) is one of two possible ways in which a collection of non-interacting indistinguishable particles may occupy a set of available discrete energy states, at thermodynamic equilibrium. The aggregation of particles in the same state, … a collection of identical and indistinguishable particles

Pauli exclusion principle []

The Pauli exclusion principle is the quantum mechanical principle which states that two or more identical fermions (particles with half-integer spin) cannot occupy the same quantum state within a quantum system simultaneously.

A more rigorous statement is that with respect to exchange of two identical particles the total wave function is antisymmetric for fermions, and symmetric for bosons. This means that if the space and spin co-ordinates of two identical particles are interchanged, then the wave function changes its sign for fermions and does not change for bosons.

2 thoughts on “Atomic tweezers — levitated optomechanics

  1. Here’s a article about putting “one atom inside each of two laser beams before moving them together” — which I assume uses optomechanics: “Atom interaction discovery valuable for future quantum technologies” by University of Otago published on April 24, 2019.

    In a study, just published in Nature Communications, researchers put one atom inside each of two laser beams before moving them together until they started to interact with each other.

    Co-author Associate Professor Mikkel F. Andersen, of the Department of Physics, says this allows the atoms to exchange properties in a way which could be “very useful” for future quantum technologies.

    As atoms are like magnets, when the pair start interacting, they start changing each other’s direction, counterbalancing each other.

    “Assembling small physical systems atom by atom, in a controlled way, opens up a wealth of research directions and opportunities that are not otherwise possible. It also leads to the atoms displaying different behaviours than if they were one of many in the system,” Dr. Andersen says.

    This includes a finite-temperature quantum entanglement resource. This is significant because entangled particles remain connected, even over great distances, and actions performed on one affect the other.

  2. Here’s another article on research based on use of optical cavities.

    Caltech > News > “Tiny Optical Cavity Could Make Quantum Networks Possible” by Robert Perkins (March 30, 2020) – Engineers at Caltech have shown that atoms in optical cavities – tiny boxes for light – could be foundational to the creation of a quantum internet. Their work was published on March 30 by the journal Nature [“Control and single-shot readout of an ion embedded in a nanophotonic cavity”].

    In order to work, a quantum network needs to be able to transmit information between two points without altering the quantum properties of the information being transmitted. One current model works like this: a single atom or ion acts as a quantum bit (or “qubit”) storing information via one if its quantum properties, such as spin. To read that information and transmit it elsewhere, the atom is excited with a pulse of light, causing it to emit a photon whose spin is entangled with the spin of the atom. The photon can then transmit the information entangled with the atom over a long distance via fiber optic cable.

    … researchers led by Caltech’s Andrei Faraon, professor of applied physics and electrical engineering, constructed a nanophotonic cavity, a beam that is about 10 microns in length with periodic nano-patterning, sculpted from a piece of crystal. They then identified a rare-earth ytterbium ion in the center of the beam. The optical cavity allows them to bounce light back and forth down the beam multiple times until it is finally absorbed by the ion.

    … the ytterbium ions are able to store information in their spin for 30 milliseconds. In this time, light could transmit information to travel across the continental United States.

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