System Bits: Nov. 23

Entanglement bonanza
Quantum computers — or other quantum information devices — powerful enough to be of practical use could be closer than thought, according to researchers at MIT and IBM’s Thomas J. Watson Research Center who have shown that simple systems of quantum particles exhibit exponentially more entanglement than previously believed.

They reminded that quantum computers promise huge speedups on some computational problems because they harness a strange physical property called entanglement, in which the physical state of one tiny particle depends on measurements made of another. In quantum computers, entanglement is a computational resource, roughly like a chip’s clock cycles — kilohertz, megahertz, gigahertz — and memory in a conventional computer. And where ordinary computers deal in bits of information, quantum computers deal in quantum bits, or qubits. It has been believed that in a certain class of simple quantum systems, the degree of entanglement was, at best, proportional to the logarithm of the number of qubits.

In this illustration, each colored line represents a different state of a “spin chain,” which can be thought of as the magnetic orientations, or spins, of a string of quantum particles. Where the line rises, the spin is up; where it falls, the spin is down; and where it’s flat, the spin is zero. MIT researchers modeled the entanglement of a quantum system as the “superposition” of such states.
(Source: MIT)

Essentially, they discovered that a 10,000-qubit quantum computer could exhibit about 10 times as much entanglement as previously thought, which only increases exponentially as more qubits are added.

Biomedical machine learning
A team of researchers from UCLA and the University of Illinois at Urbana-Champaign that originally set out to discover and design antimicrobial peptides — short chains of amino acids that can kill bacteria by punching holes in their cell membranes — also discovered that the computer program they developed started to recognize features of peptides that could alter the shape of membranes.

The program could differentiate between amino acid sequences that can kill bacteria and those that cannot. This shape-altering feature helps peptides travel through the membrane and into the cell, making it possible for the peptides to carry and deliver medicines directly into diseased cells. They found not only new peptides that had this property, but also discovered that many known human proteins, longer chains of amino acids, also had this ability, even though membrane-crossing is not their primary known function.

This discovery has a wide range of applications in biomedicine, such as combatting infections and delivering drugs directly into cells.
The UCLA researchers, led by Gerard Wong, a professor of bioengineering, spearheaded the experimental work, while the computational tools were developed in collaboration with Andrew Ferguson, a professor of materials science and engineering at Illinois.

Images show various types of curvatures on cell membranes that are conducive to permeability.
(Source: UCLA)

Wong: “Using machine learning, we developed a computer program that can differentiate between a peptide sequence that is antimicrobial and one that isn’t antimicrobial. During this process, we serendipitously discovered a way to differentiate between peptides that permeate membranes and peptides that don’t.”

Nanowire-based ‘skin-like bandage’
According to Purdue University researchers, a skin-like biomedical technology that uses a mesh of conducting nanowires and a thin layer of elastic polymer might bring new electronic bandages that monitor biosignals for medical applications and provide therapeutic stimulation through the skin.

The biomedical device mimics the human skin’s elastic properties and sensory capabilities, they said, and can intimately adhere to the skin and simultaneously provide medically useful biofeedback such as electrophysiological signals.

Interestingly, this work combines high-quality nanomaterials into a skin-like device, thereby enhancing the mechanical properties.

The conducting nanowires are around 50 nanometers in diameter and more than 150 microns long, and are embedded inside a thin layer of elastomer, or elastic polymer, about 1.5 microns thick. (Purdue University image/Min Ku Kim)

The device could be likened to an electronic bandage and might be used to treat medical conditions using thermotherapeutics, where heat is applied to promote vascular flow for enhanced healing. Traditional approaches to developing such a technology have used thin films made of ductile metals such as gold, silver and copper but the problem is that thin films are susceptible to fractures by over-stretching and cracking, so instead of thin films, the team used nanowire mesh film, which makes the device more resistive to stretching and cracking than otherwise possible. In addition, the nanowire mesh film has very high surface area compared to conventional thin films, with more than 1,000 times greater surface roughness. So once attached to the skin the adhesion is much higher, reducing the potential of inadvertent delamination.