QuEra
On Tuesday, the quantum computing startup Quera laid out a road map that will bring error correction to quantum computing in only two years and enable useful computations using it by 2026, years ahead of when IBM plans to offer the equivalent. Normally, this sort of thing should be dismissed as hype. Except the company is Quera, which is a spinoff of the Harvard Universeity lab that demonstrated the ability to identify and manage errors using hardware that’s similar in design to what Quera is building.
Also notable: Quera uses the same type of qubit that a rival startup, Atom Computing, has already scaled up to over 1,000 qubits. So, while the announcement should be viewed cautiously—several companies have promised rapid scaling and then failed to deliver—there are some reasons it should be viewed seriously as well.
It’s a trap!
Current qubits, regardless of their design, are prone to errors during measurements, operations, or even when simply sitting there. While it’s possible to improve these error rates so that simple calculations can be done, most people in the field are skeptical it will ever be possible to drop these rates enough to do the elaborate calculations that would fulfill the promise of quantum computing. The consensus seems to be that, outside of a few edge cases, useful computation will require error-corrected qubits.
Error-corrected qubits spread individual bits of quantum information across several hardware qubits and connect these with additional qubits that allow identification and correction of errors. As a result, these “logical qubits” may require a dozen or more hardware qubits to function well enough to be useful. So, enabling that means generating hardware with thousands or tens of thousands of qubits, each with a sufficiently low error rate to ensure we can catch and correct any glitches before they ruin calculations.
IBM and several of its competitors are using electronic devices called transmons as their hardware qubits. Transmons are relatively simple to control, and their quality has been improving iteratively as companies get experience with fabricating devices. But they require bulky wiring to control and are large enough that any useful quantum processor will require integrating multiple transmon-containing chips.
Quera and some other companies have opted for qubits based on neutral atoms, with individual atoms held in traps formed by laser beams. These have several advantages. Unlike transmons, atoms do not suffer from device-to-device variations, and they’re incredibly compact—many thousands can potentially be held in a square centimeter. Qubits based on the spin of an atomic nucleus also hold its information for a relatively long time before suffering an error (with “long time” meaning more than a second here). Operations and readouts can also be performed using lasers, eliminating any wiring challenges.
Finally, the atoms can be moved around, potentially allowing any atom to be entangled with any other. This provides a degree of flexibility that’s impossible with the permanent wiring used to connect transmons.
Source link
