Heat is the enemy of quantum uncertainty. By arranging light-absorbing molecules in an ordered fashion, physicists in Japan have maintained the critical, yet-to-be-determined state of electron spins for 100 nanoseconds near room temperature.
The innovation could have a profound impact on progress in developing quantum technology that doesn’t rely on the bulky and expensive cooling equipment currently needed to keep particles in a so-called ‘coherent’ form.
Unlike the way we describe objects in our day-to-day living, which have qualities like color, position, speed, and rotation, quantum descriptions of objects involve something less settled. Until their characteristics are locked in place with a quick look, we have to treat objects as if they are smeared over a wide space, spinning in different directions, yet to adopt a simple measurement.
The rules governing this multitude of possibilities, called superpositions, present engineers with a whole box of mathematical tricks to play with. These can be used as special kinds of computers to crunch numbers, or to exploit in security measures for communication, and even used in ultra-sensitive measurement and imaging devices.
Yet every interaction with their environment changes this haze of possibility in some fashion. On one level, this is useful. Quantum computers rely on the entanglement of particles with one another to fine-tune their superpositions. Quantum sensors rely on precise interactions between a superposition and the environment to measure their surroundings.
Turn up the temperature, the bump-and-grind of jiggling atoms and blinding shine of electromagnetism will easily turn a coherent hum of particle possibility into a useless lump of boring old electron.
This isn’t a huge problem if you’ve got the resources to pump super-cold liquids through your equipment to keep that noise down. But what every quantum physicist really dreams of is a way to keep down costs by running their devices at temperatures well over freezing.
The feat has been accomplished before in specially-designed complexes made of metals that preserve quantum states in superposition form just long enough for them to be relatively useful.
In this new breakthrough, researchers made use of a different kind of material called a metal-organic framework (MOF) for the first time. Into this structure they embedded molecules called chromophores, which absorb and emit light at particular wavelengths.
“The MOF in this work is a unique system that can densely accumulate chromophores. Additionally, the nanopores inside the crystal enable the chromophore to rotate, but at a very restrained angle,” says Nobuhiro Yanai, a physicist from Kyushu University.
As they do, pairs of electrons in these chromophores with a matching spin are kicked into a new arrangement that operate in a superposition. Though the phenomenon has been scrutinized closely in solar cell technology, it had yet been tinkered with for purposes of quantum sensing.
In an experiment led by Yanai, a team of researchers used microwaves to probe the electrons in their transformed states to demonstrate they could remain coherent in a superposition form for around 100 billionths of a second while at room temperature – a respectable duration that could be expanded upon with some fine-tuning.
This research was published in Science Advances.