2025/01/30 by Michelle Wynne Sze, Yao Tang, Sze, Michelle Wynne +9 · 1 voice · 2 citations
Computer Science · #Quantum Computing Algorithms and Architecture #quant-ph
paper · pdf · doi:10.48550/arxiv.2501.18515
openalex publication_date 2025/01/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The linear combination of unitaries (LCU) method has proven to scale better than existing product formulas in simulating long time Hamiltonian dynamics. However, given the number of multi-control gate operations in the standard prepare-select-unprepare architecture of LCU, it is still resource-intensive to implement on the current quantum computers. In this work, we demonstrate LCU implementations on an ion trap quantum computer for calculating squared overlaps |⟨ ψ(t=0)|ψ(t>0)⟩|2 of time-evolved states. This is achieved by an optimized LCU method, based on pre-selecting relevant unitaries, coupled with a compilation strategy which makes use of quantum multiplexor gates, leading to a significant reduction in the depth and number of two-qubit gates in circuits. For L Pauli strings in a Taylor series expanded n-qubit-mapped time evolution operator, we find a two-qubit gate count of 2\lceil log2(L)\rceil(2n+1)-n-2. We test this approach by simulating a Rabi-Hubbard Hamiltonian.