Scientists have proposed a new type of data storage device that harnesses the powerful properties of quantum mechanics.
The ultra-high-density optical memory device would consist of numerous memory cells, each containing rare earth elements embedded within a solid material — in this case, magnesium oxide (MgO) crystals. The rare earth elements emit photons, or particles of light, which are absorbed by nearby "quantum defects" — vacancies in the crystal lattice containing unbonded electrons, which become excited by light absorption.
Current optical memory storage methods such as CDs and DVDs are constrained by the diffraction limit of light, meaning a single piece of data stored on the device cannot be smaller than the wavelength of the laser reading and writing the data. However, scientists hypothesized that optical disks could hold more data within the same area by using a technique called "wavelength multiplexing," in which slightly different wavelengths of light are used in combination.
Now, researchers propose that MgO could be interspersed with narrow-band rare earth emitters. These elements emit light at specific wavelengths, which could be densely packed together. The scientists published their findings Aug. 14 in the journal Physical Review Research.
"We worked out the basic physics behind how the transfer of energy between defects could underlie an incredibly efficient optical storage method," study co-author Giulia Galli, a professor at the University of Chicago's Pritzker School of Molecular Engineering, said in a statement.
The study modeled how light spreads at the nanometer scale to understand how energy moves between the rare earth emitters and the quantum defects within the material, as well as how the quantum defects store the captured energy, Galli added.
Scientists already understood how quantum defects in solid materials interact with light. But they had not studied how the quantum defects' behavior changes when the light source is incredibly close, such as narrow-band rare earth emitters embedded a few nanometers (a millionth of a millimeter) away.
The photons are much smaller than conventional laser photons. By way of comparison, the photons from a conventional optical or near-infra-red laser emitter tend to be 500 nm to 1 micrometer (a thousandth of a millimeter). Hence, this new research could lead to data storage devices 1,000 times more dense than previously possible.
The scientists discovered that when the quantum defects absorbed the narrow band of energy emitted from the nearby rare earth elements, they became excited from their ground state and flipped into a spin state. As the spin state transition is hard to reverse, these defects could potentially store data for a useful period — although further work would be required to measure this, the scientist said. Furthermore, narrow-band rare earth emitters generate smaller wavelengths of light, which enables a denser data storage method than other optical approaches.
Most quantum-based technologies operate at near absolute zero, which suppresses decoherence and dephasing — the corruption and loss of information in a quantum system. For technology based on this research to be viable, it would need to operate at room temperature.
"To start applying this to developing optical memory, we still need to answer additional basic questions about how long this excited state remains and how we read out the data," co-author Swarnabha Chattaraj, a postdoctoral researcher at Argonne National Laboratory, said in the statement. "But understanding this near-field energy transfer process is a huge first step."
