When irradiated with infrared light, certain molecules, such as metal phthalocyanines, vibrate and generate small, local magnetic fields. Researchers have calculated these effects and want to experimentally prove and manipulate these fields for possible applications in quantum computing. Credit: SciTechDaily.com
Physicists at TU Graz have determined that certain molecules can be stimulated by pulses of infrared light to generate small magnetic fields. If experimental tests are also successful, this technique could potentially be applied in quantum computer circuits.
When molecules absorb infrared light, they begin to vibrate as they receive energy. Andreas Hauser from the Institute for Experimental Physics at the Technical University of Graz (TU Graz) used this well-understood process as a basis to investigate whether these vibrations could be exploited to produce magnetic fields. Since atomic nuclei have a positive charge, the movement of these charged particles results in the creation of a magnetic field.
Using the example of metal phthalocyanines – ring-shaped, planar dye molecules – Andreas Hauser and his team have now calculated that these molecules, due to their high symmetry, actually generate small magnetic fields in the nanometer range when infrared pulses act on them.
According to the calculations, it should be possible to measure the rather low, but very accurately localized field strength using nuclear magnetic resonance spectroscopy. The researchers have published their results in the Journal of the American Chemical Society.
Circular Dance of the Molecules
For the calculations, the team used preliminary work from the early days of laser spectroscopy, some of which was decades old. They also used modern electron structure theory on supercomputers at the Vienna Scientific Cluster and TU Graz to calculate how phthalocyanine molecules behave when irradiated with circularly polarized infrared light. What happened was that the circularly polarized, that is, spirally twisted, light waves simultaneously generate two molecular vibrations that are perpendicular to each other.
Andreas Hauser from the Institute for Experimental Physics at TU Graz. Credit: Lunghammer – TU Graz
“As any rumba dance couple knows, the right combination of forward-backward and left-right creates a small, closed loop. And this circular motion of each affected atomic nucleus actually creates a magnetic field, but only very locally, with dimensions in the range of a few nanometers,” says Andreas Hauser.
Molecules as circuits in quantum computers
By selectively manipulating the infrared light, it is even possible to control the strength and direction of the magnetic field, explains Andreas Hauser. This would turn the molecules into highly precise optical switches, which could perhaps also be used to build circuits for a quantum computer.
Schematic representation of a metal phthalocyanine molecule that is set into two vibrations (red and blue), creating a rotating electric dipole moment (green) in the molecular plane and thus a magnetic field. Credit: Wilhelmer/Diez/Krondorfer/Hauser – TU Graz
Experiments as the next step
Together with colleagues from the Institute of Solid State Physics at TU Graz and a team from the University of Graz, Andreas Hauser now wants to experimentally prove that molecular magnetic fields can be generated in a controlled manner.
“For proof, but also for future applications, the phthalocyanine molecule must be placed on a surface. However, this changes the physical conditions, which in turn influence the light-induced excitation and the characteristics of the magnetic field,” explains Andreas Hauser. “We therefore want to find a support material that has minimal impact on the desired mechanism.”
In the next step, the physicist and his colleagues want to calculate the interactions between the deposited phthalocyanines, the carrier material and the infrared light before testing the most promising variants in experiments.
Reference: “Molecular pseudorotation in phthalocyanines as a tool for nanoscale magnetic field control” by Raphael Wilhelmer, Matthias Diez, Johannes K. Krondorfer and Andreas W. Hauser, May 14, 2024, Journal of the American Chemical Society.
DOI: 10.1021/jacs.4c01915
The study was funded by the Austrian Science Fund.