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 the near term.

Imaginary Time Evolution for Ground State Preparation

The team constructed circuits approximating imaginary time evolution, a technique that suppresses higher-energy states, and demonstrated polynomial-in-depth convergence. This improvement signifies a potential pathway toward more efficient quantum computation and simulation by refining how initial quantum states are established. The circuits developed rely on real-time evolution applied to each copy of the system alongside controlled-SWAP operations that mediate interactions between them; this combination allows for deterministic, unitary protocols that approximate the effects of imaginary time evolution.