When irradiated with infrared light, certain molecules such as metal phthalocyanines vibrate and generate small, localized magnetic fields. The researchers have calculated these effects and aim to experimentally demonstrate and manipulate these fields for potential applications in quantum computers. Credit: SciTechDaily.com
Physicists from TU Graz discovered that certain molecules can be stimulated by pulses of infrared light to generate small magnetic fields. If the experimental trials are also successful, this technique could potentially be used in quantum computer circuits.
When molecules absorb infrared light, they begin to vibrate because they are receiving energy. Andreas Hauser of the Institute of Experimental Physics at the Graz University of Technology (TU Graz) used this well-understood process as a basis for investigating whether these vibrations could be used to create magnetic fields. Because atomic nuclei carry a positive charge, the movement of these charged particles results in the creation of a magnetic field.
Using the example of metallic phthalocyanines – ring-shaped, planar dye molecules – Andreas Hauser and his team have now calculated that, due to their high symmetry, these molecules actually generate small magnetic fields in the nanometer range when they are subjected to infrared pulses.
According to calculations, it should be possible to measure a relatively low but very precisely localized field strength using nuclear magnetic resonance spectroscopy. The researchers published their results in Journal of the American Chemical Society.
Circular dance of molecules
For the calculations, the team drew on preliminary work from the early days of laser spectroscopy, some of which was decades old. They also used modern electronic structure theory on supercomputers at the Vienna Science Cluster and TU Graz to calculate how phthalocyanine molecules behave when irradiated with circularly polarized infrared light. It happened that circularly polarized, i.e. spirally twisted, light waves excite two molecular vibrations at the same time, which are at right angles to each other.
Andreas Hauser from the Institute of Experimental Physics at TU Graz. Credit: Lunghammer – TU Graz
“As every rumba dancing 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 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 that could hopefully also be used to build circuits for a quantum computer.
Schematic representation of the metal phthalocyanine molecule, which is set into two vibrations (red and blue), creating a rotational electric dipole moment (green) and thus a magnetic field in the molecular plane. 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 needs to be placed on the surface. However, this changes the physical conditions, which subsequently affect the light-induced excitation and the characteristics of the magnetic field,” explains Andreas Hauser. “We therefore want to find a support material that will have minimal impact on the desired mechanism.”
In the next step, the physicist and his colleagues want to calculate the interactions between the stored phthalocyanines, the carrier material and infrared light before putting the most promising variants to the experiments.
Reference: “Molecular Pseudorotation in Phthalocyanines as a Tool for Magnetic Field Control at the Nanoscale” by Raphael Wilhelmer, Matthias Diez, Johannes K. Krondorfer, and Andreas W. Hauser, 14 May 2024, Journal of the American Chemical Society.
DOI: 10.1021/jacs.4c01915
The study was financed by the Austrian Science Fund.