In a race to build quantum computer hardware, silicon is starting to shine

In a race to build quantum computer hardware, silicon is starting to shine

Silicon-based device in development for use in quantum computers. Gate electrodes shown in blue, red, and green are used to define the quantum point potentials while the micromagnet above provides a magnetic field gradient. The image was taken using scanning electron microscopy and the colors were applied for clarity. Credit: Adam Mills, Princeton University

Research by Princeton University physicists paves the way for the use of silicon-based technologies in quantum computing, especially as quantum bits – the basic units of quantum computers. This research promises to accelerate the use of silicon technology as a viable alternative to other quantum computing technologies, such as superconductors or captured ions.

In research published in the journal Scientific AdvancesPrinceton physicists used twoqubit silicon quantum device to achieve an unprecedented level of fidelity. At over 99 percent, this is the highest fidelity ever achieved for a two-kbite gate in a semiconductor and equals the best results achieved by competing technologies. Fidelity, which is a measure of the ability of quantity to perform error-free operations, is a key feature in the quest to develop practical and efficient quantum computing.

Researchers around the world are trying to figure out which technologies — such as superconducting quitstrapped ions or silicon spin liquids, for example – can best be used as the basic units of quantum computing. And, equally significant, researchers are exploring which technologies will have the ability to expand most effectively for commercial use.

“Silicon spin bits are gaining momentum [in the field]”said Adam Mills, a graduate student in the Department of Physics at Princeton University and the lead author of the recently published study.” It looks like a big year for silicon overall. “

By using a silicon device called a double quantum dot, Princeton researchers were able to capture two electrons and force them to interact. The spin state of each electron can be used as a quit and the interaction between the electrons can involve those quits. This operation is crucial for quantum computing, and the research team, led by Jason Petta, Professor of Physics Eugene Higgins at Princeton, was able to perform this involving operation at a fidelity exceeding 99.8 percent.

Qubit, in its simplest terms, is a quantum version of a computer bit, which is the smallest unit of data in a computer. Like its classic equivalent, the cubit is encrypted with information that can have the value of either one or zero. But unlike the piece, the cubit is capable of exploiting the concepts of quantum mechanics so that it can perform tasks that classical bits cannot.

“In cubit you can encode zeros and ones, but you can also have overlays of these zeros and ones,” Mills said. This means that each kbit can be zero and one at a time. This concept, called superposition, is a fundamental quality of quantum mechanics and one that allows quits to perform operations that seem amazing and otherworldly. In practical terms, it allows the quantum computer to have a greater advantage over conventional computers in, for example, factoring very large numbers or isolating the most optimal solution to a problem.

The “spin” in spinquots is the angular momentum of the electron. It is a quantum property that manifests as a tiny magnetic dipole that can be used to encode information. A classic analog is a compass pin that has north and south poles, and rotates to align with the Earth’s magnetic field. Quantum mechanically, the spin of the electron can match the field generated in the laboratory (spin-up), or be oriented counter-parallel to the field (spin-down), or be in a quantum superposition of spin-up and spin-down . Spin is the property of the electron controlled in silicon-based quantum devices; Conventional computers, by contrast, operate by manipulating a negative charge of an electron.

Mills claimed that in general, silicon spin cubits have advantages over other quit types. “The idea is that every system will have to scale up to many kbit,” he said. “And now, the other qubit systems have real physical limitations to scalability. Size could be a real problem with these systems. There’s just so much space in which you can stuff these things.”

In comparison, silicon spinners are made of single electrons and are extremely small.

“Our devices are only about 100 nanometers across, while a conventional superconducting qubit is more like 300 microns across, so if you want to do a lot on a chip, it will be difficult to use a superconducting approach,” Petta said.

Petta added, the other advantage of silicon spinners is that conventional electronics today are based on silicon technology. “Our feeling is that if you really want to make a million or ten million quits that will be required to do something practical, that will only happen in a solid-state system that can be scaled by the standard semiconductor manufacturing industry.”

However, operating spin quits – like other types of quits – with high fidelity has been a challenge for researchers.

“One of the issues for spin-chip technology is that the two-kbit gate fidelity has not been that high until recently,” Petta said. “It was well below 90 percent in most experiments.”

But there was a challenge that Petta and Mills and the research team believed could be achieved.

To perform the experiment, the researchers first had to capture a single electron – not a small task.

“We capture a single electron, a very small particle, and we have to insert it into a specific region of space and then dance it,” Petta said.

To do that, Mills, Petta, and their colleagues needed to build a “cage.” This took the form of a thin semiconductor made primarily of silicon. On top of that, the team did little electrodes, which creates the electrostatic potential used to enclose the electron. Two of these cages put together, separated by a barrier, or gate, constituted the double quantum point.

“We have two turns sitting in adjacent places next to each other,” Petta said. “By adjusting the voltage on these gates, we can momentarily push the electrons together and cause them to interact. This is called a two-kbit gate.”

The interaction causes each spinbits to evolve according to the state of their neighboring spinbits, which leads to involvement in quantum systems. The researchers were able to perform this two-bit interaction with a fidelity exceeding 99 percent. So far, this is the highest fidelity for a two-kbit gate that has so far been achieved in spinning.

Petta said the results of this experiment place this technology—silicon spinning chips – on an equal footing with the best results achieved by the other major competing technologies. “This technology is on a steep slope,” he said, “and I think it’s only a matter of time before it overtakes superconducting systems.”

“Another important aspect of this article,” Petta added, “is that it’s not just a demonstration of high fidelity two-kbit gate, but this device does everything. This is the first demonstration of a semiconductor spin quit system where we have integrated the performance of the entire system — state preparation, reading, single-kbp control, two-kb control — all with performance metrics that exceed the threshold you need. to make a larger-scale system work. “

In addition to Mills and Petta, the work also included the efforts of Princeton graduate students Charles Guinn and Mayer Feldman, as well as University of Pennsylvania associate professor of electrical engineering Anthony Sigillito. Also contributing to the article and research were Michael Gullans, Department of Physics, Princeton University and the Center for Quantum Information and Computing at NIST / University of Maryland, and Erik Nielsen of the Sandia National Laboratories, Albuquerque, New Mexico.

A three-kbit involved state was realized in a fully controllable set of silicon spindles

More information:
Adam R. Mills et al, A two-kb silicon quantum processor with an operating fidelity exceeding 99%, Scientific Advances (2022). DOI: 10.1126 / sciadv.abn5130

Quote: In a race to build quantum computer hardware, silicon begins to shine (2022, April 6) taken on May 28, 2022 from

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