“When we do this, we don’t have any errors left,” Lemyre said. “And this builds confidence into this approach, meaning that if we build the next generation of codes that is now able to correct these errors that were detected in this two-mode approach, we should have that flat line of no errors occurring over a long period of time.”
Several other companies have already performed experiments in which errors were detected—and corrected. In a few instances, companies have even performed operations with logical qubits, although these were not sophisticated calculations. Nord Quantique, in contrast, is only showing the operation of a single logical qubit, so it’s not even possible to test a two-qubit gate operation using the hardware it has described so far.
So simply being able to identify the occurrence of errors is not on the cutting edge. Why is this notable?
All the other companies require multiple hardware qubits to host a single logical qubit. Since building many hardware qubits has been an ongoing challenge, most researchers have plans to minimize the number of hardware qubits needed to support a logical qubit—some combination of high-quality hardware, a clever error correction scheme, and/or a hardware-specific feature that catches the most common errors. You can view Nord Quantique’s approach as being at the extreme end of the spectrum of solutions, where the number of hardware qubits required is simply one.
From Nord Quantique’s perspective, that’s significant because it means that its hardware will ultimately occupy less space and have lower power and cooling requirements than some of its competitors. (Other hardware, like neutral atoms, requires lots of lasers and a high vacuum, so the needs are difficult to compare.) But it also means that, should it become technically difficult to get large numbers of qubits to operate as a coherent whole, Nord Quantique’s approach may ultimately help us overcome some of these limits.
