Scientists at the University of Maryland have successfully demonstrated the control of the nuclear spin of a hydrogen molecule (H2) using dry ice. This simple ability to control the quantum state of a material could unlock multiple applications, ranging from measuring comet temperatures in outer space to new approaches to quantum computing on Earth.
Quantum applications are the next frontier of technology, enabling scientists to harness the ‘spooky behavior’ of materials to perform complex calculations and measurements that were previously impossible. However, to achieve this, scientists have relied on ultra-low temperatures near absolute zero. While this is expensive, it also limits the potential number of applications that can be attained outside the laboratory.
Chemical physicists at the University of Maryland have now unlocked quantum state control using nothing but dry ice. Made by cooling carbon dioxide at standard atmospheric pressure and relatively higher temperatures of -109 Fahrenheit (-75 degrees Celsius), dry ice is widely available and can be sourced cheaply.
Quantum spin states of hydrogen
The nuclear spin of an atom also describes its angular momentum. Molecular hydrogen, or the H2 molecule, exists in two states. One where the nuclear spins of its two hydrogen atoms cancel each other out. This is known as para-H2.
While ortho-H2 naturally wants to reach its low-energy state, para-H2, when cooled, Maryland researchers found that freezing the molecule in dry ice prevents this conversion for two of the three substates of ortho-H2.
“The big finding is that depending on what ice we put an H2 molecule into, its quantum dynamics are entirely dependent on the surrounding environment,” explained Nathan McLane, a graduate student in physics who was involved in the work. According to McLane, the geometry of dry ice imposes a set of rules on H2 molecules that prevent their transition to a low-energy state.
Interestingly, the addition of nitrogen dioxide to the crystal lattice of dry ice relaxes these rules and allows all three ortho-H2 molecules to convert to their low-energy state.
Possible applications
Prior to this, scientists have turned to powerful magnetic fields and chemical catalysts to control the nuclear spins of atoms. But doing so could be much easier with dry ice. This could help researchers protect quantum states of materials, making more stable forms of quantum memory.
It is unlikely that future quantum computers will just need hydrogen molecules and dry ice, but the research is helping establish foundational rules for protecting quantum states.
Among other applications, the researchers hope that measurements of the proportions of ortho- and para-water released from comets could help estimate the temperatures at which these comets formed.
Space agencies like NASA use certain patterns to determine how nuclear spins change in comets. Some of these calculations rely on unverified assumptions. The researchers hope their research will either refute or verify these assumptions in the lab.
Hydrogen fuel releases heat when its state changes from ortho to para, and this heat has to be managed efficiently for safety. The research will also help store hydrogen more stably and efficiently by enriching certain nuclear spin states while protecting others.
The research findings were published in Physical Review Letters.