Quantum computing systems have the potential to outperform classical computers on some tasks, helping to solve complex real-world problems in shorter times. Research teams worldwide have thus been trying to realize this quantum advantage over traditional computers, by creating and testing different quantum systems.
Researchers at Tsinghua University recently developed a new programmable quantum phononic processor with trapped ions. This processor, introduced in a paper in Nature Physics, could be easier to scale up in size than other previously proposed photonic quantum processors, which could ultimately enable better performances on complex problems.
"Originally, we were interested in the proposal of Scott Aaronson and others about Boson sampling, which might show the quantum advantages of simple linear optics and photons," Kihwan Kim, one of the researchers who carried out the study, told Phys.org. "We were wondering if it is possible to realize it with the phonons in a trapped ion system."
The use of phonons (i.e., sound waves or elementary vibrations) to create quantum computing systems was theoretically explored for some time. In recent years, however, physicists created trapped-ion systems created the technology necessary to use phonons as a quantum information processing resource, rather than mere mediators for entangling qubits.
"It has been shown that phonons at a harmonic potential can coherently transfer to the other harmonic potential and these phonons can interfere with each other," Kihwan Kim explained. "When we learned that a modified boson sampling (Gaussian boson sampling) can also be applied to a chemical problem (i.e., vibrational sampling) we demonstrated the sampling of SO2 molecules and developed a method to create a highly entangled phononic state; yet this was limited to a single ion. In this work, we finally implemented the phononic network in a scalable way, overcoming the limits of single ions."
The system created by Kihwan Kim and his colleagues is a programmable bosonic network, a network consisting of a set of bosonic modes, connected to each other via controllable beam splitters. They realized this network using phonons, excitations of collective vibrational modes that are also bosons. READ MORE...
There’s been no greater act of magic in technology than the sleight of hand performed by Moore’s Law. Electronic components that once fit in your palm have long gone atomic, vanishing from our world to take up residence in the quantum realm.
But we’re now brushing the bitter limits of this trend. In a paper published in Nature this week, scientists at Tsinghua University in Shanghai wrote that they’ve built a graphene transistor gate with a length of 0.34 nanometers (nm)—or roughly the size of a single carbon atom.
The gate, a chip component that switches transistors on and off, is a critical measure of transistor size. Previous research had already pushed gate lengths to one nanometer and below. By scaling gate lengths down to the size of single atoms, the latest work sets a new mark that’ll be hard to beat. “In the future, it will be almost impossible for people to make a gate length smaller than 0.34 nm,” the paper’s senior author Tian-Ling Ren told IEEE Spectrum. “This could be the last node for Moore’s Law.”
Etching a 2D Sandwich
Transistors have a few core components: the source, the drain, the channel, and the gate. Electrical current flows from the source, through the channel, past the gate, and into the drain. The gate switches this current on or off depending on the voltage applied to it.
Recent advances in extreme transistor gate miniaturization rely on some fascinating materials. In 2016, for example, researchers used carbon nanotubes—which are single-atom-thick sheets of carbon rolled into cylinders—and a 2D material called molybdenum disulfide to achieve a gate length of one nanometer. Silicon is a better semiconductor, as electrical currents encounter more resistance in molybdenum disulfide, but when gate lengths dip below five nanometers, electrons leak across the gates in silicon transistors. Molybdenum disulfide’s natural resistance prevents this leakage at the tiniest scales.
Building on this prior work, the researchers in the most recent study also chose molybdenum disulfide for their channel material and a carbon-based gate. But instead of carbon nanotubes, which are a nanometer across, they looked to go smaller. Unroll a nanotube and you get a sheet made of carbon atoms called graphene. Graphene has all kinds of interesting properties, one of which is excellent conductivity. The width and length of a graphene sheet are, of course, bigger than a nanotube—but the edge is a single carbon atom thick. The team cleverly exploited this property. READ MORE...
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China, the world’s largest carbon emitter, is on the cusp of a clean energy transition as new solar power becomes cheaper than coal throughout most of the country, according to a new study.
By 2023, China will have the capacity to deploy solar power nationwide at the same price as coal, and currently has that ability in three-quarters of the country, according to a joint study from Harvard, Tsinghua, Nankai and Renmin universities.
“Today subsidy-free solar power has become cheaper than coal power in most parts of China” in a trajectory spreading across the country, study coauthor Xi Lu said in a statement.
While the country is a long way from tapping that theoretical potential, the new research highlights “a crucial energy transition point” at which solar becomes a “cheaper alternative to coal-fired electricity and a more grid-compatible option,” said co-author Michael McElroy.
By 2060, the study found, China will have the capacity to meet 43 percent of its power needs with solar energy that costs less than 2.5 cents per kilowatt hour — less than half of China’s 2019 price for coal energy, and less than a quarter the current average U.S. energy cost.
That projection is much faster than previous studies, which researchers say failed to account for the way that China’s growing solar sector — which now represents a third of total global solar production — has benefited from technical advances and economies of scale.
The report comes ahead of the global climate summit in Scotland next month, where China’s plans to transition away from coal will be a major factor in the world’s ability to limit the rise in global temperatures to 1.5 degrees Celsius.
One key accelerant of China’s solar growth is the “cost of capital:” how much solar developers have to pay in interest or dividends to secure funding for new projects.
This number plummeted 63 percent in China between 2011 and 2018, even as government subsidies fell away, researchers said. READ MORE...
