Researchers from Rice University, in collaboration with Durham University and other partners, have developed a "magic trap" that prolongs quantum coherence in ultracold molecules, as detailed in their study published in Nature Physics.
Zewen Zhang (from left), Jonathan Stepp and Kaden Hazzard. Image Credit: Gustavo Raskosky/Rice University'
The promise of quantum technologies includes improved drug development, quicker computing, and new sensing applications. However, because most systems can only sustain quantum effects for a limited amount of time, studying quantum behaviors experimentally is challenging.
The reason why quantum physics’ mysterious features tend to vanish so quickly is a process called decoherence. It occurs when a quantum system interacts with its surroundings and this changes the physics. The bigger the system and the larger the couplings to the surroundings, the more the system will behave in a classical, non-quantum fashion ⎯ and you lose your ability to investigate things at the quantum level.
Kaden R.A. Hazzard, Corresponding Author and Associate Professor, Physics and Astronomy, Rice University
By employing extremely low temperatures and specific laser wavelengths to create a “magic trap” that helped postpone the onset of decoherence, researchers at Rice University and their partners were able to nearly triple the duration of quantum behavior in an experimental system. This research offers a new platform for studying quantum interactions and is the first experimental demonstration of its kind.
Hazzard and the team at Rice University worked with Simon Cornish’s group in the Department of Physics at Durham University in the United Kingdom to cool molecules to a billion times below room temperature to create a novel quantum mechanical system. Then, using microwave radiation, they caused those molecules to rotate quantum mechanically, comparable to molecules aligning and rotating simultaneously in clockwise and counterclockwise directions.
Cornish says, “When you cool atoms or molecules to these extremely low temperatures, you can control them with light. You can actually use lasers to push on the atoms and make them go where you want them to go. You can also use lasers to trap or hold them, and that gives you a level of precision and control that you wouldn’t have normally.”
In the ultracold molecules, the coherence of this rotating behavior typically decays over a very short time. The longest known quantum state of rotating molecules was measured at 1/20 of a second prior to now.
Cornish's team drew inspiration from theoretical research conducted by Svetlana Kotochigova at Temple University. This work proposed the existence of a specific "magic" wavelength of light that could extend the preservation of quantum coherence over a longer duration.
Quantum behavior becomes more prominent the colder the system is and brings the quantum behavior to larger length scales. And having lasers at the right wavelength can ‘trap’ the molecules, so they can rotate in lockstep, which preserves the quantum coherence for a longer time.
Jonathan Stepp, Graduate Student, Department of Physics and Astronomy, Rice University
Using this theory as a basis for a novel experimental method, the group produced a “magic trap” that allowed the molecules to continue rotating quantum mechanically for a noticeably longer period. Hazzard was surprised to discover that the “magic” laser trap maintained the molecules’ uniform rotation for almost 1.5 seconds - a 30-fold increase - instead of the expected two- or three-fold increase in quantum coherence.
Hazzard says, “While I’m not surprised it worked, I’m definitely surprised at how well it worked.”
Zewen Zhang, another graduate student in Hazzard’s group, said that improved coherence times will allow scientists to study fundamental questions about interacting quantum matter.
As coherence times become longer, new effects are unveiled. We can begin exploring by comparing the experimental measurements to our calculations. Improved coherence is also a step to using ultracold molecules as a platform for various quantum technologies.
Zewen Zhang, Graduate Student, Department of Physics and Astronomy, Rice University
Hazzard says, “Even though quantum behavior sounds like a very exotic thing, it’s actually responsible for things we see every day, from how metals conduct electricity to how fusion is produced by the sun. If you want to make new materials, new sensors, or other quantum technologies, you need to understand what is happening at the quantum level, and this research is a step toward achieving new insights.”
The research was supported by the UK Engineering and Physical Sciences Research Council, the UK Research and Innovation Frontier Research Grant, the Royal Society, Durham University, the Robert A. Welch Foundation, the National Science Foundation, the Office of Naval Research, the W.F. Keck Foundation and the US Air Force Office of Scientific Research.
Journal Reference:
Gregory, D. P., et al. (2024).Second-scale rotational coherence and dipolar interactions in a gas of ultracold polar molecules. Nature Physics. doi.org/10.1038/s41567-023-02328-5.