Scientists Split Atom, Then Put It Back Together
Jun 15, 2012 5:00 AM PT
Mention the words, "splitting the atom," and most people will automatically think of nuclear fission, bombs and radioactivity.
Recently, however, physicists at Germany's University of Bonn not only managed to "split" an atom in a different way -- using quantum mechanics -- but also put it back together again.
"The fact that atoms, photons and molecules can be split at different locations is something already known," Andrea Alberti, team lead for the Bonn experiment and Alexander von Humboldt fellow at the Institut für Angewandte Physik, told TechNewsWorld. "What is really exciting is the level of quantum control and precision to which we pushed our system."
The results of the experiment -- which has potential ramifications for quantum computing and beyond -- were published recently in the journal Proceedings of the National Academy of Sciences.
Two Places at Once
As part of this new experiment, which amounts to what's known as an "atom interferometer," scientists managed to keep a single atom simultaneously in two places at once separated by more than 10 micrometers, or one hundredth of a millimeter. Then, they were able to put it back together undamaged.
"We are capable of trapping a single atom in a tiny box -- a box which is 0.020 micrometers in size and created by laser fields -- and subsequently split the atom into two boxes to reach separations up to 10 micrometers," Alberti explained.
For an atom, 10 micrometers is an enormous distance. To put it in perspective, if the box were a glass of about 5 centimeters in diameter, say, then the atom's two parts would have been separated in two glasses 25 meters apart, he pointed out.
The split was not directly visible, however. If you tried to take a picture, the atom would be seen in several images -- sometimes on the left, sometimes on the right, but never in both places.
Nevertheless, it can be proven by putting the atom back together, the scientists noted. In addition, differences between the magnetic fields of the two positions or accelerations of the atom are discernible, since they become imprinted in the atom's quantum mechanical state.
'A Split Personality'
Such quantum effects can only take place at the lowest temperatures and with careful handling. Specifically, the scientists involved used lasers to cool a cesium atom to a temperature of a tenth of a million degrees above absolute zero and then held it using another laser.
Next, they took advantage of the fact that atoms have a spin that can go in two directions simultaneously. Essentially, if the atom is moved by the second laser to the right and the left at the same time, it will split.
"The atom has kind of a split personality: half of it is to the right, and half to the left, and yet, it is still whole," explained Andreas Steffen, lead author on the publication describing the experiment.
'More Like a Cloud Than a Marble'
Brain hurting yet? You're not alone.
"If you think of an atom as being like a very small, very hard, very tough version of a marble or a ball bearing, then your thinking is trapped in a pre-1925 misconception," Daniel Styer, Schiffer Professor of physics at Oberlin College, told TechNewsWorld. "An atom can behave more like a cloud than a marble, although it doesn't behave exactly like either."
Many people are familiar with the famous Schrödinger's cat thought experiment, in which a hypothetical cat exists both "alive" and "dead" at the same time. That experiment illustrates the difficulty of applying quantum mechanics to everyday objects.
"In quantum mechanics, an atom doesn't have to have a position," Styer explained. "So if there are two routes to go from A to B, it is entirely possible for the atom to take both."
What's known as the classic "double slit experiment" in physics gets at much the same notion.
"Imagine a wall containing two small slits that are separated by a short distance," explained Jeanie Lau, an associate professor in the department of physics at the University of California at Riverside.
"A particle in our everyday experience can go through only one of the slits, or bounce back," Lau told TechNewsWorld.
A wave hitting the wall, however, will go through both slits, she pointed out.
"In quantum mechanics, if the particle is small enough -- i.e., as small as an atom -- it can go through both slits and form interference patterns on the other side, just like a wave," Lau added. "Atoms, like waves, can interfere with each other, due to the particle-wave duality, a fundamental property of matter and a consequence of quantum mechanics."
So, the Bonn experiment doesn't so much "split" the atom as it "uses the quantum mechanical nature of the particle -- that it can also behave like a wave -- to create interference by directing it to go through both slits," she explained.
'A Big Step Forward'
It should be noted that atom interferometry -- or the process of "splitting" atoms and reassembling them -- "has been an active field of research since the 1930s, when it was first demonstrated," Andrew Cleland, professor of physics at the University of California at Santa Barbara, told TechNewsWorld.
Indeed, "the ability to split a system into separate states and then bring them back together has long been one of the key aspects of quantum mechanics, and it has been shown experimentally in many circumstances," agreed Gary Felder, associate professor of physics at Smith College.
"However, larger objects are harder to split and recombine in this way than smaller ones, and larger distances are harder than short ones," Felder told TechNewsWorld. "To split and recombine something as large as an atom over distances as great as tens of micrometers is a big step forward."
Indeed, "only now, with this work from Bonn, have we had precise control over a single atom starting at one place with a position, then spreading out so as not to have a position, and finally ending with a single position again," Styer said.
So where is all this leading?
The Bonn scientists hope eventually it could help simulate complex quantum systems. Plant photosynthesis, for example, is a phenomenon that's hard to capture with modern supercomputers, but small quantum systems based on technology like this could be just what's needed.
Then, too, there are the possibilities for quantum computing.
"Now that we have gained control of single neutral atoms trapped in laser fields, we would like to use atoms to perform a novel kind of information processing -- namely, the so-called quantum information processing," Alberti explained.
"In essence, our atoms behave as a quantum bit, a qubit," he noted. "Each atom can encode information in its spin state, up and down, but all possible superpositions of these two states are possible, exactly as we could split the atom at far apart locations."
Computational speeds could be increased enormously as a result, Alberti added.
An Exciting Era
In some ways, however, the experiment's practical applications are almost less important, Styer opined.
"Perhaps it can be used for precision measurements, perhaps it can be used to help build a quantal computer, or perhaps it will prove useful for nothing," he concluded. "But regardless of potential applications, it is great to be alive during an era when our understanding and control of nature is becoming so subtle and nuanced."