Quantum eigenstate broadcasting assisted by a coherent link

TL;DR

This paper introduces a quantum eigenstate broadcasting method that leverages limited entanglement between distributed quantum devices to efficiently prepare Hamiltonian eigenstates with reduced circuit depth and improved suppression of unwanted amplitudes.

Contribution

The authors propose a novel distributed quantum eigenstate preparation protocol that uses minimal entanglement to enhance efficiency and suppress errors more effectively than single-device methods.

Findings

Reduced circuit depth in distributed eigenstate preparation.

Improved suppression of unwanted amplitudes to approximately 0.30.

Requires only a single auxiliary qubit per device for entanglement.

Abstract

Preparing the ground state of a local Hamiltonian is a crucial problem in understanding quantum many-body systems, with applications in a variety of physics fields and connections to combinatorial optimization. While various quantum algorithms exist which can prepare the ground state with high precision and provable guarantees from an initial approximation, current devices are limited to shallow circuits. Here we consider the setting where Alice and Bob, in a distributed quantum computing architecture, want to prepare the same Hamiltonian eigenstate. We demonstrate that the circuit depth of the eigenstate preparation algorithm can be reduced when the devices can share limited entanglement. Especially so in the case where one of them has a near-perfect eigenstate, which is more efficiently broadcast to the other device. Our approach requires only a single auxiliary qubit per device to be entangled with the outside. We show that, in the near-convergent regime, the average relative suppression of unwanted amplitudes is improved to $1/(2\sqrt{e}) \approx 0.30$ per run of the protocol, outperforming the average relative suppression of $1/e\approx 0.37$ achieved with a single device alone for the same protocol.