Quantum-Computing Startup Rigetti To Offer Modular Processors

An anonymous reader quotes a report from Ars Technica: A quantum-computing startup announced Tuesday that it will make a significant departure in its designs for future quantum processors. Rather than building a monolithic processor as everyone else has, Rigetti Computing will build smaller collections of qubits on chips that can be physically linked together into a single functional processor. This isn't multiprocessing so much as a modular chip design. The decision has several consequences, both for Rigetti processors and quantum computing more generally. We'll discuss them below. Rigetti's computers rely on a technology called a "transmon," based on a superconducting wire loop linked to a resonator. That's the same qubit technology used by larger competitors like Google and IBM. Transmons are set up so that the state of one can influence that of its neighbors during calculations, an essential feature of quantum computing. To an extent, the topology of connections among transmon qubits is a key contributor to the machine's computational power. Two other factors that currently hold back performance are the error rate of individual qubits and the qubit count. Scaling up the qubit count can boost the computational power of a processor -- but only if all the added qubits are of sufficiently high quality that the error rate doesn't limit the ability to perform accurate computations. Once qubit counts reach the thousands, error correction becomes possible, which changes the process significantly. At the moment, though, we're stuck with less than 100 qubits. So this is change is still in the indefinite future. For Rigetti, the ability to merge several smaller processors -- which it has already shown it can produce -- into a single larger one should let it run up its qubit count relatively rapidly. In today's announcement, the company expects that an 80-qubit processor will be available within the next few months. (For context, IBM's roadmap includes plans for a 127-qubit processor sometime this year.) The other advantage of moving away from a monolithic design is that most chips tend to have one or more qubits that are either defective or have an unacceptably high error rate. By going with a modular design, the consequences of that are reduced. Rigetti can manufacture a large collection of modules and assemble chips from those with the fewest defects. Alternately, the company can potentially select for the modules that have qubits with low error rates and build the equivalent of an all-star processor. The reduced error rate could possibly offset the impact of a lower qubit count.

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