The world’s smallest magnetic data storage unit is made of just 12 atoms, squeezing an entire byte into just 96 atoms, a significant shrinkage in the world of information storage. It’s not a quantum computer, but it’s a computer storage unit at the quantum scale. By contrast, modern hard disk drives use about a million atoms to store a single bit, and a half billion atoms per byte.
Smallest Storage Unit Spin-polarized imaging with a scanning tunneling microscope reveals the structure of the world’s smallest magnetic data storage unit. It consists of just 12 iron atoms ordered in an antiferromagnetic structure.
Until now, it was unclear how many (or how few) atoms would be needed to build a reliable, lasting memory bit, the basic piece of information that a computer understands. Researchers at IBM and the German Center for Free-Electron Laser Science decided to start from the ground up, building a magnetic memory bit atom-by-atom. They used a scanning tunneling microscope to create regular patterns of iron atoms aligned in rows of six each. They found two rows was enough to securely store one bit, and eight pairs of rows was enough to store a byte.
Data was written into and read out of the bits using the STM — so it’s not like this type of bit will be integrated into hard disks anytime soon. But it answers some fundamental questions about the nature of classical mechanical systems, said Andreas Heinrich, the lead investigator into atomic storage at IBM Research
If you take a single atom, you have to look at quantum mechanics when you describe its behavior,” he said in an interview. “As you make the (system) bigger and bigger, several iron atoms start talking to each other, and at some point you can ignore all of this quantum behavior and just think of them as a classical magnetic structure.” It turns out that point is around 12 atoms big.
“Many people would anticipate you would have to use quantum mechanical systems to describe these structures,” Heinrich said. “That was the most surprising thing to me
At the smallest scales, quantum effects blur stored information. A bit using six atoms would switch magnetic states — switching from “0” to “1” — about 1,000 times per second, for instance, which is much too frequently to be useful for data storage, Heinrich said. Eight atoms switch states once per second. But 12 atoms switched their states infrequently enough to be usable for storage — instead, an outside magnetic influence (in this case, the STM) changes their states. The nano magnets are only stable at a chilly 5 degrees Kelvin, or -450 degrees F.
Today’s hard drives store data in what’s known as a ferromagnetic structure. This is how a compass needle or a refrigerator magnet work: They have lots of atoms lumped together, all pointing in the same magnetic directions.
IBM’s 12-atom bit-keeper uses an antiferromagnetic structure, however, meaning that the atoms point in opposite directions. This keeps the atoms from interfering with each other, an important feature when you’re storing data just 12 atoms at a time. “In a ferromagnet all of these atoms add together to make a big spin and that big spin interacts with the neighboring big spin. And so you cannot control these independently anymore,” Heinrich says. “But in an antiferromagnet there is no big spin, and so you can put these guys very close together”
12-atom storage devices would be much, much smaller than today’s disks. Heinrich’s friends at hard-drive maker Hitachi estimate that their storage drives require about 800,000 atoms per bit.So what’s keeping the atom-scale flash drive from showing up at your local Best Buy? Well, first off, they operate at 1 degree kelvin. That’s about -458 Fahrenheit. Bump things up to room temperature and Heinrich thinks it would take about 150 atoms per bit.
And there’s an even bigger problem. Nobody has a clue how to build something this small outside of the lab. And certainly, nobody can do it cheaply, Heinrich says. “That is something that many people are working on, but nobody has solved it yet.”Still, when Heinrich got his first glimpse at the 12 atoms holding a charge in his STM last spring, he was mesmerized. He sat at his Almaden lab for four hours straight, switching the tiny clump of atoms back and forth between magnetic states. “I was basically just blown away,” he says. The researchers switched the bit’s magnetic state five times to store the ASCII code for each letter of the word “think,” one of Big Blue’s slogans.
Tiny Think: A white signal on the right edge corresponds to logic 0 and a blue signal to logic 1. Between two successive images, the magnetic states of the bits were switched to encode the binary representation of the ASCII characters “THINK.” IBM Research