Research Bits: Feb. 13

Fast phase-change memory; miniature quantum memory; light and magnets.


Fast phase-change memory

Researchers from Stanford University, TSMC, National Institute of Standards and Technology (NIST), and University of Maryland developed a new phase-change memory for future AI and data-centric systems. It is based on GST467, an alloy of four parts germanium, six parts antimony, and seven parts tellurium, which is sandwiched between several other nanometer-thin materials in a superlattice.

“The unique composition of GST467 gives it a particularly fast switching speed,” said Asir Intisar Khan, a postdoctoral scholar at the University of California Berkeley and visiting postdoctoral scholar at Stanford, in a statement. “Integrating it within the superlattice structure in nanoscale devices enables low switching energy, gives us good endurance, very good stability, and makes it nonvolatile – it can retain its state for 10 years or longer.”

Cross-sections of phase-change memory devices in the high- and low-resistance states. The diameter of the bottom electrode is ~40 nanometers. Arrows mark some of the van der Waals (vdW) interfaces, which form between layers of the superlattice materials. The superlattice is disrupted and reformed between the high- and low-resistance states. (Image courtesy of the Pop Lab)

In tests, the memory appears to avoid drift and operates at below 1 volt. “A few other types of nonvolatile memory can be a bit faster, but they operate at higher voltage or higher power,” added Eric Pop, a professor of electrical engineering at Stanford, in a release. “With all these computing technologies, there are tradeoffs between speed and energy. The fact that we’re switching at a few tens of nanoseconds while operating below one volt is a big deal.”

The superlattice can be fabricated at temperatures compatible with commercial manufacturing and could be stacked in vertical layers to increase density. [1]

Miniature quantum memory

Researchers at the University of Basel built a quantum memory element based on rubidium atoms in a tiny glass cell.  The memory could be mass-produced on a wafer to support quantum networks, which require memory elements to temporarily store and route information.

Initially, the rubidium atoms were contained in a handmade glass cell of several centimeters. To shrink this to smaller one measuring only a few millimeters, they had to heat up the cell to 100 degrees centigrade to increase the vapor pressure and have a sufficient number of rubidium atoms for quantum storage.

They also exposed the atoms to a magnetic field of 1 tesla, more than ten thousand times stronger than Earth’s magnetic field. This shifted the atomic energy levels in a way that facilitated the quantum storage of photons using an additional laser beam. This method allowed the researchers to store photons for around 100 nanoseconds.

“In this way, we have built, for the first time, a miniature quantum memory for photons of which around 1000 copies can be produced in parallel on a single wafer,” said Philipp Treutlein, a professor at the University of Basel, in a statement. In further work, the researchers plan to store single photons in the miniature cells and optimize the glass cells. [2]

Light and magnets

Researchers from the Hebrew University of Jerusalem discovered a connection between light and magnetism such that an optical laser beam can control the magnetic state in solids.

Specifically, the magnetic component of a rapidly oscillating light wave possesses the capability to control magnets. The team identified a mathematical relation that describes the strength of the interaction and links the amplitude of the magnetic field of light, its frequency, and the energy absorption of the magnetic material.

“It paves the way for light-controlled, high-speed memory technology, notably Magneto resistive Random Access Memory (MRAM), and innovative optical sensor development. In fact, this discovery signals a major leap in our understanding of light-magnetism dynamics,” said Amir Capua, a professor and head of the Spintronics Lab within the Institute of Applied Physics and Electrical Engineering at Hebrew University of Jerusalem, in a statement. “Our findings can explain a variety of experimental results that have been reported in the last 2-3 decades.”

The team also built a specialized sensor capable of detecting the magnetic part of light. [3]


[1] Wu, X., Khan, A.I., Lee, H. et al. Novel nanocomposite-superlattices for low energy and high stability nanoscale phase-change memory. Nat Commun 15, 13 (2024).

[2] Roberto Mottola et al, Optical Memory in a Microfabricated Rubidium Vapor Cell, Physical Review Letters (2023).

[3] Benjamin Assouline et al, Helicity-dependent optical control of the magnetization state emerging from the Landau-Lifshitz-Gilbert equation, Physical Review Research (2024).

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