2024/06/04 by Matthew DeCross, Reza Haghshenas, Minzhao Liu +74 · 4 voices · 15 citations
Computer Science · Physics and Astronomy · #Computational Physics and Python Applications #Parallel Computing and Optimization Techniques #Quantum Computing Algorithms and Architecture #quant-ph
paper · pdf · doi:10.1103/physrevx.15.021052
arxiv published 2024/06/04 · arxiv updated 2024/06/21 · openalex publication_date 2025/05/13 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
Empirical evidence for a gap between the computational powers of classical and quantum computers has been provided by experiments that sample the output distributions of two-dimensional quantum circuits. Many attempts to close this gap have utilized classical simulations based on tensor network techniques, and their limitations shed light on the improvements to quantum hardware required to frustrate classical simulability. In particular, quantum computers having in excess of approximately 50 qubits are primarily vulnerable to classical simulation due to restrictions on their gate fidelity and their connectivity, the latter determining how many gates are required (and, therefore, how much infidelity is suffered) in generating highly entangled states. Here, we describe recent hardware upgrades to Quantinuum’s H2 quantum computer, enabling it to operate on up to 56 qubits with arbitrary connectivity and 99.843(5)% two-qubit gate fidelity. We define a class of circuits with random geometries that become hard to classically simulate in very low depth and implement them utilizing the flexible connectivity of H2. A careful analysis demonstrating the fast saturation of classical simulation complexity with depth indicates that H2 can yield data well beyond the reach of state-of-the art classical simulation methods at unprecedented fidelities. We find that the considerable difficulty of classically simulating H2 is likely limited only by qubit number, demonstrating the promise and scalability of the quantum charge-coupled device architecture as continued progress is made toward building larger machines.