Scientists Freeze Atoms to Near Absolute Zero

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We usually think of microwaves as waves that heat things up, usually leftover food, but did you know that they can also cool things down? For example, physicists recently decided to use them to freeze atoms, and attempts have been very successful: They managed to cool them down to within a millionth of a degree of absolute zero (–273.15°C or –459.67°F).

The University of Sussex team, led by Winifried Hensinger, had their results published in Physical Review Letters.

"The use of long-wavelength radiation instead of laser technology to cool ions can tremendously simplify the construction of practical quantum technology devices enabling us to build real devices much faster," said Professor Hensinger.

Cooling down atoms can be done with lasers, like Hensinger describes, in a process known as laser cooling. It takes advantage of a property of atoms called "bandgap": this is the amount of energy it takes to excite an electron sitting in an electron shell up to a higher shell. The bandgap value has a corresponding wavelength of light that exactly matches the energy it takes to make the electron jump up a level. 

But what if you shine a laser light with less energy than the bandgap onto the atom? The atom doesn't want to lose this opportunity to excite an electron, so it uses a bit of its own heat to push the electron up to the next electron level. When the electron falls down from this higher level to the lower electron shell, it releases all its extra energy: the energy from the incoming light and the energy the atom gave it. Now, the atom has less energy than when it started. This effectively cools down the atom using only laser light. 

What Hensinger has done is to take the idea behind laser cooling and use microwaves instead. By doing this, the team made the cooling technique much simpler. This isn't the first time that microwaves have been used to cool down objects instead of heating them, but this is the coldest that microwaves have ever cooled. This is a step closer to creating quantum computing technology. Quantum computing is inherently complicated and fiddly, so any advancement is great news.

Quantum physics demands that quantum computers be at the coolest temperature possible because it is individual molecules that contain processing data. These molecules have to be perfectly still, which only happens at absolute zero, meaning that they have no energy, otherwise all of the data is lost. Usually, computers run using binary code – ones and zeros. Yes or no. However, a quantum computer takes advantage of the wave-like properties of particles: they can be one and zero at the same time. 

Not all computers need this capability, but it could be extremely useful to solve problems that computers currently can't. 

This is why it's so important to try to make freezing atoms to absolute zero a simple process. "Besides finding an easy way to create atoms with zero-point energy, we have also managed to put the atom into a highly counter-intuitive state: where it is both moving and not moving at the same time," said Professor Hensinger.

Central Image: Winfried Hensinger (right) and Dr. Seb Weidt (left) are freezing individual atoms using microwaves. University of Sussex.

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