A University of Maryland team has found a way to control the nuclear spin of hydrogen molecules by simply freezing them in dry ice—a discovery with implications for energy storage, quantum computing, and astronomy.
Controlling Quantum Spins with Dry Ice
A study by University of Maryland chemical physicists demonstrates a novel method to control nuclear spin in molecular hydrogen (H₂) by confining it within crystalline dry ice. The research, published in Physical Review Letters on April 29, 2026, reveals that the dry ice crystal structure can selectively block or enable the conversion of hydrogen’s quantum spin states.
The Science of Ortho and Para Hydrogen
Molecular hydrogen exists in two forms based on nuclear spin alignment:
- Ortho-H₂: Nuclear spins are aligned. This state has three distinct substates.
- Para-H₂: Nuclear spins are opposed.
When hydrogen is cooled, ortho-H₂ naturally converts to the para state, releasing heat—a process that has been difficult to control without strong magnetic fields or chemical catalysts.
Key Findings
In dry ice crystals, the symmetry of the crystal structure prevents two of the three ortho-H₂ substates from converting to para-H₂ upon cooling.
The research, led by Leah Dodson (assistant professor, UMD Department of Chemistry and Biochemistry) and graduate student Nathan McLane, found that the crystal lattice of dry ice creates an environment that protects certain quantum states.
Adding nitrogen dioxide to the crystal lattice alters its properties, enabling all three ortho-H₂ substates to convert to para-H₂. This chemical modification effectively "unlocks" the blocked conversion pathways.
Potential Applications
The study, funded by the U.S. Department of Energy, opens several promising avenues:
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Energy Storage: By enriching specific nuclear spin states, researchers could better manage the heat released during ortho-to-para conversion, potentially improving hydrogen fuel storage systems.
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Quantum Computing: The ability to protect quantum states from conversion may enable more stable quantum memory, a critical challenge for quantum computing development.
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Astronomy: The method could test fundamental assumptions about ortho/para ratios of water in comets—ratios currently used to estimate the formation temperatures of these celestial bodies.
Significance and Next Steps
The researchers emphasize that this study provides foundational rules for quantum state protection, moving beyond previous methods that required strong magnetic fields or chemical catalysts.
Future work will involve repeating the experiment with methane, extending the technique to other molecules and potentially uncovering additional quantum control mechanisms.