Skip to main content

Defects in diamond nanomaterial speeding up the quantum computers

Quantum computers are experimental devices that offer large speedups on some computational problems. One promising approach to building them involves harnessing nanometer-scale atomic defects in diamond materials.
But practical, diamond-based quantum computing devices will require the ability to position those defects at precise locations in complex diamond structures, where the defects can function as qubits, the basic units of information in quantum computing. In Nature Communications, a team of researchers from MIT, Harvard University, and Sandia National Laboratories reports a new technique for creating targeted defects, which is simpler and more precise than its predecessors.
In experiments, the defects produced by the technique were, on average, within 50 nanometers of their ideal locations.
Appealing defects
Quantum computers, which are still largely hypothetical, exploit the phenomenon of quantum "superposition," or the counterintuitive ability of small particles to inhabit contradictory physical states at the same time. An electron, for instance, can be said to be in more than one location simultaneously, or to have both of two opposed magnetic orientations.
Where a bit in a conventional computer can represent zero or one, a "qubit," or quantum bit, can represent zero, one, or both at the same time. It's the ability of strings of qubits to, in some sense, simultaneously explore multiple solutions to a problem that promises computational speedups.
Diamond-defect qubits result from the combination of "vacancies," which are locations in the diamond's crystal lattice where there should be a carbon atom but there isn't one, and "dopants," which are atoms of materials other than carbon that have found their way into the lattice. Together, the dopant and the vacancy create a dopant-vacancy "center," which has free electrons associated with it. The electrons' magnetic orientation, or "spin," which can be in superposition, constitutes the qubit.
A perennial problem in the design of quantum computers is how to read information out of qubits. Diamond defects present a simple solution, because they are natural light emitters. In fact, the light particles emitted by diamond defects can preserve the superposition of the qubits, so they could move quantum information between quantum computing devices.
Silicon switch
The most-studied diamond defect is the nitrogen-vacancy center, which can maintain superposition longer than any other candidate qubit. But it emits light in a relatively broad spectrum of frequencies, which can lead to inaccuracies in the measurements on which quantum computing relies.
In their new paper, the MIT, Harvard, and Sandia researchers instead use silicon-vacancy centers, which emit light in a very narrow band of frequencies. They don't naturally maintain superposition as well, but theory suggests that cooling them down to temperatures in the millikelvin range -- fractions of a degree above absolute zero -- could solve that problem. (Nitrogen-vacancy-center qubits require cooling to a relatively balmy 4 kelvins.)
To be readable, however, the signals from light-emitting qubits have to be amplified, and it has to be possible to direct them and recombine them to perform computations. That's why the ability to precisely locate defects is important: It's easier to etch optical circuits into a diamond and then insert the defects in the right places than to create defects at random and then try to construct optical circuits around them.
In the process described in the new paper, the MIT and Harvard researchers first planed a synthetic diamond down until it was only 200 nanometers thick. Then they etched optical cavities into the diamond's surface. These increase the brightness of the light emitted by the defects (while shortening the emission times).
Then they sent the diamond to the Sandia team, who have customized a commercial device called the Nano-Implanter to eject streams of silicon ions. The Sandia researchers fired 20 to 30 silicon ions into each of the optical cavities in the diamond and sent it back to Cambridge.
Mobile vacancies
At this point, only about 2 percent of the cavities had associated silicon-vacancy centers. But the MIT and Harvard researchers have also developed processes for blasting the diamond with beams of electrons to produce more vacancies, and then heating the diamond to about 1,000 degrees Celsius, which causes the vacancies to move around the crystal lattice so they can bond with silicon atoms.
After the researchers had subjected the diamond to these two processes, the yield had increased tenfold, to 20 percent. In principle, repetitions of the processes should increase the yield of silicon vacancy centers still further.
When the researchers analyzed the locations of the silicon-vacancy centers, they found that they were within about 50 nanometers of their optimal positions at the edge of the cavity. That translated to emitted light that was about 85 to 90 percent as bright as it could be, which is still very good.



  1. Tim Schröder, Matthew E. Trusheim, Michael Walsh, Luozhou Li, Jiabao Zheng, Marco Schukraft, Alp Sipahigil, Ruffin E. Evans, Denis D. Sukachev, Christian T. Nguyen, Jose L. Pacheco, Ryan M. Camacho, Edward S. Bielejec, Mikhail D. Lukin, Dirk Englund. Scalable focused ion beam creation of nearly lifetime-limited single quantum emitters in diamond nanostructuresNature Communications, 2017; 8: 15376 DOI: 10.1038/ncomms15376

Story Source:
Materials provided by Massachusetts Institute of Technology. Original written by Larry Hardesty. Note: Content may be edited for style and length.
Journal Reference:

Comments

Popular posts from this blog

Intel's upcoming 10-nanometer chip manufacturing technology

At long last, chip giant  Intel  (NASDAQ: INTC) opened up about its upcoming 10-nanometer chip manufacturing technology, at its first-ever Technology and Manufacturing Day. The company has -- frustratingly -- kept key details of this technology under wraps for years now, but Intel is now putting them out there for all to see.  Without further ado, let's look at what Intel had to tell us about this new tech. A large jump in density Let's talk performance Competitive comparison and no yield information Image source: Intel. Chipmakers generally like to reduce the area of its transistors with major new technology shifts. This area reduction is important in reducing transistor costs on a yield-normalized basis, a really important factor for product cost. Chipmakers are ultimately able to cram more features and functionality into a chip while maintaining reasonable cost structures. Intel says that in moving from 14 nanometers to 10, it's delivering an incre...

2D FET from polymorphic material molbdenum telluride

In simple terms, FETs can be thought as high-speed switches, composed of two metal electrodes and a semiconducting channel in between. Electrons (or holes) move from the source electrode to the drain electrode, flowing through the channel. While 3D FETs have been scaled down to nanoscale dimensions successfully, their physical limitations are starting to emerge. Short semiconductor channel lengths lead to a decrease in performance: some electrons (or holes) are able to flow between the electrodes even when they should not, causing heat and efficiency reduction. To overcome this performance degradation, transistor channels have to be made with nanometer-scale thin materials. However, even thin 3D materials are not good enough, as unpaired electrons, part of the so-called "dangling bonds" at the surface interfere with the flowing electrons, leading to scattering. Passing from thin 3D FETs to 2D FETs can overcome these problems and bring in new attractive properties. ...

Spintronics in place of electronics : Future of IoT

Information technologies of the future will likely use electron spin -- rather than electron charge -- to carry information. But first, scientists need to better understand how to control spin and learn to build the spin equivalent of electronic components, from spin transistors, to spin gates and circuits. Now, researchers have developed a technique to control and measure spin voltage, known as spin chemical potential. The technique, which uses atomic-sized defects in diamonds to measure chemical potential, is essentially a nanoscale spin multimeter that allows measurements in chip-scale devices. The research is published in  Science . "There is growing interest in insulating materials that can conduct spin," said Amir Yacoby, Professor of Physics in the Department of Physics and of Applied Physics at Harvard John A. Paulson School of Engineering and Applied Sciences and senior author of the paper. "Our work develops a new way to look at these spins in material...