Coefficient-Decoupled Matrix Product Operators as an Interface to Linear-Combination-of-Unitaries Circuits

TL;DR

This paper presents a novel coefficient-decoupled MPO representation for Pauli operators that enables efficient, reusable classical-to-quantum compilation by separating symbolic structure from tunable coefficients, facilitating dynamic updates in quantum circuits.

Contribution

The paper introduces a coefficient-decoupled MPO framework that interfaces seamlessly with LCU circuits, allowing static symbolic support to be reused while only coefficients are updated.

Findings

Constructed compact, state-adapted Pauli pools from pretrained MPS.

Enabled efficient coefficient updates without recompiling the symbolic operator structure.

Demonstrated a reusable classical-to-quantum compilation workflow.

Abstract

We introduce a coefficient-decoupled matrix product operator (MPO) representation for Pauli-sum operators that separates reusable symbolic operator support from a tunable coefficient bridge across a fixed bipartition. This representation provides a direct interface to linear-combination-of-unitaries (LCU) circuits: the symbolic left/right dictionaries define a static \textsc{Select} oracle that is compiled once, while coefficient updates modify only a dynamic \textsc{Prep} oracle. As a proof of concept, we construct compact state-adapted Pauli pools by sampling Pauli strings from a pretrained matrix product state (MPS), pruning them to a fixed symbolic pool, optimizing only their coefficients, and transferring the resulting weights directly to the LCU interface. The resulting workflow provides a reusable classical-to-quantum compilation strategy in which the symbolic operator structure is compiled once, and subsequent updates are confined to a low-dimensional coefficient object.