Multiple qubit copies speed up quantum state preparation

Tal Schwartzman of ITAMP, Center for Astrophysics | Harvard & Smithsonian, and colleagues have devised new unitary protocols for preparing ground states in quantum systems by leveraging multiple copies of the system alongside controlled-SWAP operations. Their work addresses a key challenge in quantum computation: efficiently achieving low-energy state preparation, a goal crucial for both simulation and computation. The researchers detail two circuit designs, one offering provable polynomial-in-depth convergence but rapidly growing width, and a more scalable "hedge" architecture, and demonstrate that mid-circuit post-selection can accelerate the process with achievable probabilities. This approach outlines how hybrid analog-digital circuits can complement existing state-preparation methods in…