Argonne National Lab, UChicago scientists develop theory on storing data with light, rare earths, and quantum defects.

Imagine trying to fit the contents of the entire internet into a single grain of sand - a seemingly impossible task. Yet, recent research suggests that such a thing could soon be possible in digital memory storage, using light and engineered materials to vastly increase data density beyond today's quickly shrinking limits.

The evolution of electronic storage has been marked by dramatic leaps in capacity and groundbreaking innovation, with each step building upon the last and opening new understanding for the next.

As industries expanded and data grew more complex, handwritten records could no longer keep pace, prompting the shift toward more scalable solutions. This urgent need for rapid data access and preservation laid the groundwork for early storage methods, such as punch cards, wax cylinders, and magnetic tape reels.

As the mid-20th century approached, data storage continued to evolve through mediums like vinyl records and film reels, which offered greater capacity but were limited by their physical size – often requiring entire rooms or buildings for memory banks.

From this, floppy disks emerged as a compact alternative to magnetic tape, representing the first major shift from analog to digital storage.

Unlike earlier formats that stored data as physical waves or grooves, floppy disks recorded data into binary – the language of computers written as ones and zeroes that function as on-and-off switches – enabling faster, more accurate data processing and retrieval.

While it could still be considered a half-analog process, as it required physical writing onto film, encoding information in binary allowed computers to process data more efficiently, enabling the early tech and software industries to take root.

Following the success of floppy disks, the 1980s saw the rise of music cassettes, compact discs (CDs), and video cassette tapes, otherwise known as video home system (VHS) tapes. These formats significantly increased storage capacity, with CDs offering a fully digital approach by encoding data through laser technology, while both music and video cassettes maintained analog signals for audio and video storage, respectively.

Together, these formats marked a new era of media storage, catering to both consumer entertainment and expanding data needs.

As the 1990s unfolded, digital video discs (DVDs) emerged as the next iteration in storage technology, offering even greater capacity than CDs while maintaining the same digital encoding methods.

This surge in digital storage innovations coincided with advancements in computer-based storage, as hard disk drives (HDDs), which had existed since the 1950s, became more accessible to consumers during this era, leveraging improvements in cost, speed, and capacity made possible by growing demand for data storage.

However, the turn of the century brought the true turning point into digital, with the introduction of solid-state drives (SSDs) and flash drives – forms of non-volatile memory, or memory that retains data even without power. Unlike traditional HDDs, SSDs and flash drives store data electronically without moving parts, enabling faster access, greater reliability, and compact formats.

Stably and cheaply producing these technologies at scale is what truly marked the onset of the modern digital age, enabling rapid access to vast amounts of information in more compact and reliable formats.

As electronic storage continues to evolve, the drive for even greater capacity, faster speeds, and more efficient designs remains relentless. Now, the focus is shifting beyond traditional circuits and mechanical parts toward harnessing light itself as a medium for data storage.

With researchers tapping into the properties of photons, optical memory could redefine how information is stored and accessed, marking a quantum leap in the Digital Age.

Quantum memory

Optical memory has long been explored for its potential to offer faster, more energy-efficient, and more durable data storage compared to traditional electronic methods.

Standard optical media, such as CDs and DVDs, use lasers to read and write data. However, these technologies are constrained by the diffraction limit of light – the minimum size at which data can be stored, limited by the wavelength of the laser itself.

This physical limit creates a bottleneck, restricting how much data can be densely packed onto optical storage devices. However, recent breakthroughs aim to break past this barrier using quantum physics principles and novel materials, revolutionizing the very concept of data density.

University of Chicago

Researchers at Argonne National Lab and the University of Chicago combined classical physics with quantum modeling to show how rare earths (red dots) and defects (blue dots) within solids can interact to store optically encoded data.

In a joint study, researchers from Argonne National Laboratory (ANL) and the University of Chicago Pritzker School of Molecular Engineering (PME) have proposed a cutting-edge approach to optical storage.

By integrating rare earth elements into a solid-state material and pairing them with quantum defects – tiny, engineered imperfections within the material that can trap and hold light-based energy – the researchers aim to increase the density of optically stored data exponentially.

Traditional optical media store bits of data through laser etching, but the quantum approach relies on specific wavelengths of light to transfer data to these defects, enabling information storage at a much finer scale.

"We worked out the basic physics behind how the transfer of energy between defects could underlie an incredibly efficient optical storage method," said Giulia Galli, an Argonne senior scientist and Liew Family Professor at PME.

To test the viability of this optical storage method, the research team developed theoretical models of a material embedded with narrow-band rare earth emitters – atoms that absorb light and then re-emit it at specific, narrow wavelengths.

Through this modeling, they demonstrated that the emitted light could be captured by nearby quantum defects, paving the way for ultra-high-density data storage.

"This research illustrates the importance of exploring first-principles and quantum mechanical theories to illuminate new, emerging technologies," added Galli.

Using a blend of foundational physics principles with quantum mechanical models, the researchers first mapped how energy transfer could occur between the rare earth particles and the engineered defects.

These models not only helped predict the behavior of energy movement at the nanometer scale but also clarified how defects store the absorbed energy.

"We wanted to develop the necessary theory to predict how energy transfer between emitters and defects works," said Swarnabha Chattaraj, a postdoctoral research fellow at Argonne. "That theory then allowed us to figure out the design rules for potentially developing new optical memories."

What makes this method unique is the way light transfers energy to defects that are only nanometers apart, a phenomenon called near-field energy transfer. In this experiment, the close distance between light and the defects altered how energy is absorbed and stored, resulting in a more direct and efficient exchange.

"This kind of near-field energy transfer is thought to follow different symmetry rules than more commonly known far-field processes," said Supratik Guha, Argonne senior scientist and advisor to Argonne's Physical Sciences and Engineering Directorate and PME professor.

Remarkably, the study found that quantum defects, when excited by this nearby energy, not only shift from their ground state but also experience a spin state transition – a change that is difficult to reverse.

This stability suggests that these defects could reliably retain data over long periods, and the narrow wavelengths and small defect size could enhance storage density beyond conventional optical methods.

While significant hurdles remain – such as determining the duration of the excited state and how to effectively retrieve the stored data – this research represents a promising initial exploration into the potential of quantum-enhanced optical memory.

"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," said Chattaraj. "But understanding this near-field energy transfer process is a huge first step."