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"... But now ... researchers have explored a technique to make ones and zeroes out of crystal defects, each the size of an individual atom, for classical computer memory applications. ...
“Now you can pack terabytes of bits within a small cube of material that's only a millimeter in size.” ...
To create the new memory storage technique, the team added ions of “rare earth,” a group of elements also known as lanthanides, to a crystal.
Specifically, they used a rare-earth element called Praseodymium and an Yttrium oxide crystal, but the process they reported could be used with a variety of materials, taking advantage of rare earths’ powerful, flexible optical properties.
“It’s well known that rare earths present specific electronic transitions that allows you to choose specific laser excitation wavelengths for optical control, from UV up to near-infrared regimes,” ...
Unlike with dosimeters, which are typically activated by X-rays or gamma rays, here the storage device is activated by a simple ultraviolet laser. The laser stimulates the lanthanides, which in turn release electrons. The electrons are trapped by some of the oxide crystal’s defects, for instance the individual gaps in the structure where a single oxygen atom should be, but isn’t. ..."
From the abstract:
"Charge-trapping defects in crystalline solids play important roles in applications ranging from microelectronics, optical storage, sensing and quantum technologies. On one hand, depleting trapped charges in the host matrix reduces charge noise and enhances coherence of solid-state quantum emitters.
On the other hand, stable charge traps can enable high-density optical storage systems.
Here we report all-optical control of charge-trapping defects via optical charge trapping (OCT) spectroscopy of a rare-earth ion doped oxide (Y2O3).
Charge trapping is realized by low intensity optical excitation in the 200–375 nm range.
Charge detrapping or depletion is carried out by optically stimulated luminescence (OSL) under 532 nm stimulation.
Using a Pr-doped Y2O3 polycrystalline ceramic host matrix, we observe charging pathways via the inter-band optical absorption of Y2O3 and via the 4f-5d transitions of Pr3+.
We demonstrate effective control of the density of trapped charges within the Y2O3 matrix at ambient environment. These results point to a viable method for controlling the local charge environment in rare-earth doped crystals via all-optical means, and pave the way for further development of efficient optical storage technologies with ultrahigh storage capacity, as well as for the localized control of quantum coherence in rare-earth doped solids."
Figure 1: Schematic setup for the PL/PLE spectroscopy and TL/OSL emission readout, as well as the time sequence of the OCT measurement.
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