MIT researchers report an important step toward practical quantum computers

MIT researchers report an important step toward practical quantum computers

Quantum computers are mainly imaginary devices that may do some calculations quite faster in comparison to conventional computers. The bits of classical computation can represent 0 or 1, and quantum computers have quantum bits, or qubits, which can at times represent 0 and 1 at once.

Though quantum systems containing around 12 qubits have been exhibited in the lab, development of quantum computers sufficiently complex to carry out useful computations is going to need miniaturizing qubit technology, quite like the way the transistors’ miniaturization made modern computers possible.

Perhaps, the most broadly studied qubit technology is trapped ions, but historically they needed a huge and complex hardware apparatus. Recently in Nature Nanotechnology, researchers from MIT and MIT Lincoln Laboratory have reported a significant step in the direction of practical quantum computers, through a paper explaining a prototype chip, capable of trapping ions in an electric field and, using built-in optics, point laser light in the direction of each of them.

One of the paper’s senior authors Rajeev Ram, an MIT professor of electrical engineering, said, “If you observe traditional assembly, its barrel with vacuum inside it, and inside there are cage trapping ions. Then there’s entire laboratory of external optics guiding laser beams to assembly of ions. We want to take external laboratory and miniaturize much of it onto chip”.

Lincoln Laboratory’s Quantum Information and Integrated Nanosystems group was among the several research groups that have been working for the development of simpler, tinnier ion traps called surface traps.

A normal ion trap has a small cage like outlook, with electrodes as bars that generate an electric field. The cage’s center has ions lined up parallel to the bars. In contrast, a surface trap is a chip with electrodes fixed in the surface. The ions stay at 50 micrometers over the electrodes.

A report published in The Register informed, "In a paper at Nature, the Karan Mehta, Colin Bruzewicz, Robert McConnell, Rajeev Ram, Jeremy Sage and John Chiaverini say they've printed an ion trap and optical waveguide together in a standard lithographic process."

The silicon nitride waveguides are fabricated on a quartz substrate. A layer of glass separates this from niobium electrodes, which trap strontium ions 50 microns above the surface. The waveguides are formed into diffraction gratings that can address each individual ion.

The group's next challenge is to find a way to adjust how much light is delivered to each ion. If they can add modulators to the diffraction gratings, MIT explains, “different qubits can simultaneously receive light of different, time-varying intensities”.

According to a report in MIT by Larry Hardesty, "Although quantum systems with as many as 12 qubits have been demonstrated in the lab, building quantum computers complex enough to perform useful computations will require miniaturizing qubit technology, much the way the miniaturization of transistors enabled modern computers."

“If you look at the traditional assembly, it’s a barrel that has a vacuum inside it, and inside that is this cage that’s trapping the ions. Then there’s basically an entire laboratory of external optics that are guiding the laser beams to the assembly of ions,” says Rajeev Ram, an MIT professor of electrical engineering and one of the senior authors on the paper. “Our vision is to take that external laboratory and miniaturize much of it onto a chip.”

“We believe that surface traps are a key technology to enable these systems to scale to the very large number of ions that will be required for large-scale quantum computing,” says Jeremy Sage, who together with John Chiaverini leads Lincoln Laboratory’s trapped-ion quantum-information-processing project. “These cage traps work very well, but they really only work for maybe 10 to 20 ions, and they basically max out around there.”

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