Quantum computers could be one step closer to reality, as researchers have developed a laser capable of stopping molecules from tumbling. Atoms are relatively easy to control in microscopic samples, compared to molecules. Groups of atoms tumble in highly-random directions due to complex interactions of magnetically-charged particles. The energy in these rotations, and thus their rotational velocity, is partly dependent on temperature.
Northwestern University researchers have developed a means of using a single laser to cool molecules down to the same temperature as outer space.
"It's counterintuitive that the molecule gets colder, not hotter when we shine intense laser light on it. We modify the spectrum of a broadband laser, such that nearly all the rotational energy is removed from the illuminated molecules. We are the first to stop molecular tumbling in such a powerful yet simple way," Brian Odom of Weinberg College of Arts and Sciences, and leader of research, said.
Aluminum monohydride molecules, struck with the laser, which cooled the groupings down to four degrees above absolute zero. This is the average temperature of the empty space between the stars. This cooling, which took place in a small fraction of a second, froze the molecules in position.
Physicists previously believed several lasers would be required to effectively freeze small groups of molecules. While some frequencies of light excite, or heat, the molecules, others cool the families of atoms. Researchers used filters to block wavelengths of light that excited the molecules, while allowing beneficial frequencies to pass to the sample.
"In our quantum world, every type of motion has only certain allowed energies. If I want to slow down a molecule, quantum mechanics tells me that it happens in steps. And there is a very lowest step that we can get the molecule down to, which is what we've done," Odom told the press.
The laser equipment used to cool aluminum monohydride operates at room temperature, while older technology often employed cryostats filled with liquid helium. This advance alone could represent a large step forward in quantum computer technology.
Quantum computers could soon provide processing speeds far beyond today's fastest systems. Control of molecules and their rotations is essential to designing the processors required for the next generation of super-fast computers.
Aluminum monohydride was chosen for the study partly because it does not vibrate (heat) when struck by a laser. The material is also inexpensive and used in various applications.
Investigation of the role lasers can play in freezing molecular rotation in quantum computers was detailed in the journal Nature Communications.