Digital-Analog-Digital Quantum Supremacy

TL;DR

This paper introduces a hybrid digital-analog-digital quantum computing framework that demonstrates quantum supremacy by approximating IQP circuits, applicable to current quantum annealers and hybrid devices, under certain complexity assumptions.

Contribution

It develops a new quantum-supremacy framework for hybrid digital-analog-digital models, linking analog blocks to IQP circuits and establishing complexity-theoretic hardness results.

Findings

Output distribution within constant TV distance of IQP circuits

Quantum supremacy tests feasible on current quantum annealers

Proved anticoncentration for all-to-all hardware graphs

Abstract

Quantum supremacy has been explored extensively in gate-model settings. Here, we introduce a quantum-supremacy framework for a hybrid digital-analog-digital quantum computing (DADQC) model. We consider a device that applies an initial layer of single-qubit gates, a single transverse-field Ising analog block, and a final single-qubit layer before $Z$-basis readout. The analog block approximates $Z$-diagonal Ising evolution, and we prove that the resulting output distribution is within constant total-variation (TV) distance of an Instantaneous Quantum Polynomial-time (IQP) circuit. Our bounds and constructions are established for fully connected as well as bounded-degree hardware graphs, matching a variety of architectures, including trapped-ion, neutral atom, and superconducting platforms. Assuming anticoncentration (which we prove for all-to-all hardware graphs and conjecture for bounded-degree hardware graphs) and an average-case hardness conjecture for the associated complex-temperature Ising partition functions, standard reductions imply that any efficient classical sampler achieving constant TV error collapses the polynomial hierarchy. Our results imply that quantum-supremacy tests are possible on today's quantum annealers, as well as other devices capable of hybrid digital-analog quantum evolution.