Analog-Digital Quantum Computing with Quantum Annealing Processors

TL;DR

This paper demonstrates how to perform analog-digital quantum computing on superconducting quantum annealing processors, enabling a broader set of quantum operations beyond traditional annealing.

Contribution

It introduces a method to implement single-qubit gates during analog evolution, expanding the computational capabilities of quantum annealing hardware.

Findings

Successfully demonstrated single-qubit and two-qubit coherent oscillations.

Realized a multi-qubit quantum walk consistent with theoretical fermionic dispersion.

Observed Anderson localization in a disordered chain.

Abstract

Quantum annealing processors typically control qubits in unison, attenuating quantum fluctuations uniformly until the applied system Hamiltonian is diagonal in the computational basis. This simplifies control requirements, allowing annealing QPUs to scale to much larger sizes than gate-based systems, but constraining the class of available operations. Here we expand the class by performing analog-digital quantum computing in a highly-multiplexed, superconducting quantum annealing processor. This involves evolution under a fixed many-body Hamiltonian that, in the weak-coupling regime, is well-described by an effective XY model, together with arbitrary-basis initialization and measurement via auxiliary qubits. Operationally, this is equivalent to implementing single-qubit gates at the beginning and end of an analog quantum evolution. We demonstrate this capability with several foundational applications: single-qubit and two-qubit coherent oscillations with varying initialization and measurement bases, a multi-qubit quantum walk with fermionic dispersion in line with theory, and Anderson localization in a disordered chain. These experiments open the door to a wide range of new possibilities in quantum computation and simulation, greatly expanding the applications of commercially available quantum annealing processors.