Evidence for the utility of quantum computing before fault tolerance

Quantum computing promises to offer substantial speed-ups over its classical counterpart for certain problems. However, the implementation of fault-tolerant quantum circuits is out of reach for current processors. The recent paper by Yantao Wu (RIKEN iTHEMS) together with the IBM and UC Berkeley teams demonstrates the measurement of accurate expectation values on a noisy IBM-Q 127-qubit processor for circuit volumes at a scale beyond brute-force classical computation. In the regime of strong entanglement for the temporal dynamics of the transverse-field Ising model, the quantum computer provides correct results for which leading classical approximations such as the tensor network methods break down. This represents evidence for the utility of quantum computing in a pre-fault-tolerant era. At the same time, their results will motivate and help advance classical approximation methods as both approaches serve as valuable benchmarks of one another.