Computer Memory Takes a Spin

Photo: Data core

"The length of spin memory we observed is more than adequate to create memories for computers," says Doctor Christoph Boehme, an associate professor of physics. "It's a completely new way of storing and reading information."

However, some big technical hurdles remain: the nuclear spin storage-and-read-out apparatus works only at 3.2 degrees Kelvin, or slightly above absolute zero – the temperature at which atoms almost freeze to a standstill, and only can jiggle a little bit. And the apparatus must be surrounded by powerful magnetic fields roughly 200,000 times stronger than Earth's.

"Yes, you could immediately build a memory chip this way, but do you want a computer that has to be operated at 454 degrees below zero Fahrenheit and in a big national magnetic laboratory environment?" Boehme says. "First we want to learn how to do it at higher temperatures, which are more practical for a device, and without these strong magnetic fields to align the spins." As for obtaining an electrical readout of data held within atomic nuclei, "nobody has done this before," he adds.

The new study puts together nuclear storage of data with an electrical readout of that data, and "that's what's new," Boehme says. The study was led by Boehme and first author Doctor Dane McCamey.

Modern computers are electronic, meaning that information is processed and stored by flowing electricity in the form of electrons, which are negatively charged subatomic particles that orbit the nucleus of each atom. Transistors in computers are electrical switches that store data as "bits" in which "off" (no electrical charge) and "on" (charge is present) represent one bit of information: either 0 or 1.

Quantum computers would run on the odd principles of quantum mechanics, in which the smallest particles of light and matter can be in different places at the same time. In a quantum computer, one quantum bit or "qubit" could be both 0 and 1 at the same time. That means quantum computers theoretically could be billions of times faster than conventional computers.

McCamey says a memory made of silicon "doped" with phosphorus atoms could be used in both conventional electronic computers and in quantum computers in which data is stored not by "on" or "off" electrical charges, but by "up" or "down" magnetic spins in the nuclei of phosphorus atoms.

Externally applied electric fields would be used to read and process the data stored as "spins" – what McCamey, Boehme and colleagues did in their latest study. By demonstrating an ability to read data stored in nuclear spins, the physicists took a key step in linking spin to conventional electronics – a field called spintronics.
Boehme says the spins of atoms' nuclei are better for storing information than the spin of electrons. That's because electron spin orientations have short lifetimes because spins are easily changed by nearby electrons and the temperature within atoms.

In contrast, "the nucleus sits in the middle of an atom and its spin isn't messed with by what's going on in the clouds of electrons around the nucleus," McCamey says. "Nuclei experience nearly perfect solitude. That's why nuclei are a good place to store information magnetically. Nuclear spins where we store information have extremely long storage times before the information decays."
The average 112 second storage time in the study may not seem long, but Boehme says the dynamic random access memory (DRAM) in a modern PC or laptop stores information for just milliseconds (thousandths of a second). The information must be repeatedly refreshed, which is how computer memory is maintained, he adds.

COMPAMED.de; Source: University of Utah