A first look at laser-cooled ions

Tuesday, August 27, 2019

Eight individual ions levitating in a near-perfect vacuumThe atomic ions here are laser-cooled close to the absolute zero temperature (at a few milliKelvin above the absolute zero temperature of -273.15 deg C or 0 Kelvin).

Pictured left: eight individual Ytterbium ions levitating less than 10 microns apart from each other in a nearly perfect vacuum

At such low temperatures, the ions do not have enough energy to overcome the trapping forces created by the ‘ion trap’ (electrodes carrying static and radio-frequency voltages). In the interplay between Coulomb repulsion between these positively charged ions and the trapping forces, the ions find themselves trapped in a linear chain, spaced by several microns apart from each other. Due to their near-zero temperature, the ions are almost motionless, hence we can image them with a long exposure (~300 ms here)! A laser beam is used to electronically excite the ions. The photons (particles of light) emitted by these excited ions are imaged using a standard optical miscroscope onto a CCD camera. As the atoms are several microns apart, the miscrocope can optically resolve between individual atoms - each blob of light in the image above is from a single atom! Further, the ion trapping apparatus is housed inside an ultra-vacuum environment (pressure of approx. 10-10 mbar, or about one tenth of a millionth of a millionth of the normal atmospheric pressure), so there are practically no atoms or molecules to knock them out of their place for a long time (many minutes or even hours)!

Atoms close to the absolute zero temperature behave according to the laws of quantum mechanics as opposed to the laws of classical physics observed in the macroscopic world. The quantum world is bizzare - here a particle can be at two places or states at once, and the distinction between waves and particles get blurry! The strange properties of quantum objects may be harnessed to build new kinds of computing machines, such as a quantum simulator or a quantum computer that can potentially perform tasks beyond the capability of the fastest supercomputer. At Waterloo, Prof. Islam and his co-workers are building a trapped ion quantum simulator, a purpose-built quantum computer, to solve complex problems in many-particle physics. Fundamental research in such problems can shed light into a range of hard problems relevant in many areas of science and technology - such as condensed matter physics and material science, high energy physics, quantum chemistry, and optimization problems encountered in logistics.

QITI research teamThe QITI research team lead by Prof. Islam is building the first trapped ion quantum simulator for exploring many-particle physics in Canada. There are a handful of such laboratories worldwide. Ion trapping apparatuses suited for quantum information processing are complex and require expertise in a range of areas such as electronics, vacuum technology, optics and laser physics, mechanical engineering, and atomic and quantum physics. The ion trap apparatus and the ultra-high vacuum chamber as well as the optics used in laser-cooling and trapping these ions have been built and assembled by Waterloo researchers, including postdocs, PhD and MSc students and undergraduate researchers, in Prof. Islam’s laboratory at IQC over the past couple of years. Due to the multidisciplinary nature of the work, the entire team works in close collaboration with each other, and especially offers valuable educational and training opportunities to undergraduate students.

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