For the study, the scientists, based at the National Institute of Standards and Technology, ‘flash-froze’ a flat crystal of 150 beryllium ions (electrically charged atoms). Beryllium is a relatively rare element, usually occurring as a product of the spallation of larger atomic nuclei that have collided with cosmic rays. Notable gemstones which contain beryllium include aquamarine, and emerald. Beryllium has one of the highest melting points of the light metals.
The study follows on from many years of research into techniques to chill vibrating objects, which are large enough to be visible to the naked eye, to the point where they have the minimum motion governed by the rules of quantum mechanics.
For this, the colder temperature then the more stable and less distorted the structure. Until recently scientists have only been able to reduce a few types of atomic vibrations. With the new research, the scientists were able to cool magnetic and electric fields and trap the ions so that they formed a disc less than 250 micrometers (millionths of a meter) in diameter. The resultant disc-like structure has the properties of a crystal because the ions are arranged in a regularly repeating pattern.
The chilling process was achieved very rapidly, taking just 200 microseconds (that is millionths of a second). The temperature achieved was minus 459.67 °F or minus 273.15 °C. This was achieved through the use of two special lasers, operating at defined frequencies.
This led to each ion having around one-third of the energy carried by a single phonon (which refers to a packet of motional energy in the crystal). Phonons are units of vibrational energy that arises from oscillating atoms within a crystal.
This state was considered almost at the level of the amount of energy required for the lowest-possible quantum “ground” state for a crystal, that is almost free of any vibrations.
The objective of this type of research is to help develop sensors that can detect electric fields at a level that enables scientists to hunt for certain types of dark matter. These are: axions (hypothetical subatomic particles) and hidden photons (as-yet-unseen force carriers), assuming that these aspects of theoretical physics exist.
The study has been published in the journal Physical Review Letters, with the research paper titled “Near Ground-State Cooling of Two-Dimensional Trapped-Ion Crystals with More than 100 Ions.”
