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MIT's chip fires frikkin' laser at qubits

Another step towards miniaturising quantum computing

MIT boffins reckon they've cracked one of the more difficult challenges of practical quantum computing – the miniaturisation of components.

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.

Trapped ions are a popular qubit carrier, but the laboratory equipment to address them is bulky, with what the group calls “an entire laboratory of external optics” to guide the lasers.

The MIT work integrates two systems on-chip: a surface ion trap (the qubits), and nanophotonic waveguides to route lasers to individual ions.

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.

Trapped ions are a popular approach to creating qubits: they have long “coherence times” (in lay terms, the qubits hold their quantum states long enough to be usable); and many quantum primitives (the qubit analogue to gates in classical computers) have already been built using trapped ions.

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”.

That would speed up programming the qubits, which in turn means more quantum operations could be performed within the qubits' coherence time. ®

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