System Bits: Sept. 19

Novel quantum computing architecture invented
University of New South Wales researchers have invented what they say is a radical new architecture for quantum computing, based on ‘flip-flop qubits,’ that promises to make the large-scale manufacture of quantum chips dramatically easier.

Artist’s impression of flip-flop qubit embedded in the silicon matrix of a chip. (Source: Dr Guilherme Tosi, University of New South Wales)

Based on ‘flip-flop qubits,’ the new approach promises to make the large-scale manufacture of quantum chips dramatically cheaper – and easier – than thought possible, the team said. The new chip design allows for a silicon quantum processor that can be scaled up without the precise placement of atoms required in other approaches. Importantly, it allows quantum bits (or ‘qubits’) – the basic unit of information in a quantum computer – to be placed hundreds of nanometres apart and still remain coupled.

The design was conceived by a team led by Andrea Morello, Program Manager in UNSW-based ARC Centre of Excellence for Quantum Computation and Communication Technology (CQC2T), who said fabrication of the new design should be easily within reach of today’s technology.

Lead author Guilherme Tosi, a Research Fellow at CQC2T, developed the pioneering concept along with Morello and co-authors Fahd Mohiyaddin, Vivien Schmitt and Stefanie Tenberg of CQC2T, with collaborators Rajib Rahman and Gerhard Klimeck of Purdue University.

Morello said what Tosi and his team have invented is a new way to define a ‘spin qubit’ that uses both the electron and the nucleus of the atom. Crucially, this new qubit can be controlled using electric signals, instead of magnetic ones. Electric signals are significantly easier to distribute and localize within an electronic chip.

Artist’s impression of a ‘flip flop’ qubit in an entangled quantum state. (Source: University of New South Wales)

Tosi said the design sidesteps a challenge that all spin-based silicon qubits were expected to face as teams begin building larger and larger arrays of qubits: the need to space them at a distance of only 10-20 nanometres, or just 50 atoms apart. “If they’re too close, or too far apart, the ‘entanglement’ between quantum bits – which is what makes quantum computers so special – doesn’t occur.”

Replacing tissue biopsies with sound waves
According to a team of researchers led by MIT, cells secrete nanoscale packets called exosomes that carry important messages from one part of the body to another. These researchers have now devised a way to intercept these messages, which could be used to diagnose problems such as cancer or fetal abnormalities. A new device that uses a combination of microfluidics and sound waves to isolate these exosomes from blood could be used in a portable device to analyze patient blood samples for rapid diagnosis, without involving the cumbersome and time-consuming ultracentrifugation method commonly used today, they said.

Ming Dao, a principal research scientist in MIT’s Department of Materials Science and Engineering and a senior author of the study said, “These exosomes often contain specific molecules that are a signature of certain abnormalities. If you isolate them from blood, you can do biological analysis and see what they reveal.”

The paper’s senior authors also include Subra Suresh, president-designate of Nanyang Technological University in Singapore, MIT’s Vannevar Bush Professor of Engineering Emeritus, and a former dean of engineering at MIT; Tony Jun Huang, a professor of mechanical engineering and materials science at Duke University; and Yoel Sadovsky, director of the Magee-Women’s Research Institute. The paper’s lead author is Duke graduate student Mengxi Wu.

This schematic shows a microfluidic device that uses sound waves to separate exosomes (pink spheres) from other components of blood. (Source: MIT)

The research team reminded that in 2014 they first reported that they could separate cells by exposing them to sound waves as they flowed through a tiny channel, and that this is a gentler alternative to other cell-sorting technologies, which require tagging the cells with chemicals or exposing them to stronger mechanical forces that may damage them.

The researchers’ original acoustic cell-sorting device consists of a microfluidic channel exposed to two tilted acoustic transducers. When sound waves produced by these transducers encounter one another, they form standing waves that generate a series of pressure nodes. Each time a cell or particle flows through the channel and encounters a node, the pressure guides the cell a little further off center. The distance of cell movement depends on size and other properties such as compressibility, making it possible to separate cells of different sizes by the time they reach the end of the channel.

To isolate exosomes, the researchers built a device with two such units in tandem. In the first, sound waves are used to remove cells and platelets from a blood sample. Once the cells and platelets are removed, the sample enters a second microfluidic unit, which uses sound waves of a higher frequency to separate exosomes from slightly larger extracellular vesicles. Using this device, it takes less than 25 minutes to process a 100-microliter undiluted blood sample.

Interestingly, the researchers expect this method of exosome isolation could usher a new paradigm in disease diagnosis and prognosis.

Device to identify breast cancer risks
Researchers at Purdue University are creating a device that they hope will help identify risk factors that cause breast cancer. The device, known as ‘risk-on-a-chip,’ is a small plastic case with several thin layers and an opening for a piece of paper where researchers can place a portion of tissue, which then produces risk factors for cancer and mimics what happens in a living organism.

Demonstration of concentration gradient in microfluidic system using red and blue color dye solutions. (Source: Purdue University)

Sophie Lelièvre, a professor of cancer pharmacology at Purdue said, “We want to be able to understand how cancer starts so that we can prevent it.” She said the key to preventing cancer is understanding how it starts, but people generally don’t want to be prodded with potential carcinogens. Cancer is a disease of gene expression, and organization of genes is specific to a particular species and organ, which means it wouldn’t be useful to perform this study on rats or mice. Thus, Lelièvre needs a model that will mimic the organ in question. She teamed up with Babak Ziaie, a professor of electrical and computer engineering at Purdue, to create the device.

“Unlike conventional 2-D monolayer cell culture platforms, ours provides a 3-D cell culture environment with engineered gradient generators that promote the biological relevance of the environment to real tissue in the body,” said Rahim Rahimi, a graduate student in Ziaie’s lab.

The risk-on-a-chip is based on an earlier cell culture device developed by Lelièvre and Ziaie to study cancer progression. To modify it for prevention, Ziaie plans to add nanosensors that measure two risk factors: oxidative stress and tissue stiffness. Oxidative stress is a chemical reaction that occurs as the result of diet, alcohol consumption, smoking or other stressors, and it alters the genome of the breast, aiding cancer development. The risk-on-a-chip will simulate oxidative stress by producing those molecules in a cell culture system that mimics the breast ducts where cancer starts.

The research team believes the risk-on-a-chip could be used to study additional risks by adding more cell types and biosensors.