Ultrafast Variational Simulation of Non-trivial Quantum States with Long Range Interactions

TL;DR

This paper demonstrates that variational quantum algorithms leveraging long-range interactions can efficiently prepare complex quantum states and explore phase diagrams, significantly reducing the number of operations needed in near-term quantum devices.

Contribution

It introduces a highly efficient variational protocol for state preparation and phase exploration in systems with long-range interactions, achieving high fidelity with minimal iterations.

Findings

GHZ states prepared with O(1) iterations

Quantum critical point prepared with > 99% fidelity on 100 qubits

VQCS with LRIs enables ultrafast quantum state preparation

Abstract

State preparation protocols ideally require as minimal operations as possible, in order to be implemented in near-term, potentially noisy quantum devices. Motivated by long range interactions (LRIs) intrinsic to many present-day experimental platforms (trapped ions, Rydberg atom arrays, etc.), we investigate the efficacy of variationally simulating non-trivial quantum states using the Variational Quantum-Classical Simulation (VQCS) protocol explored recently in [SciPost Phys. 6, 029 (2019)], in the presence of LRIs. We show that this approach leads to extremely efficient state preparation: for example, Greene-Horne-Zeilinger (GHZ) states can be prepared with O(1) iterations of the protocol, and a quantum critical point of the long range transverse field Ising model (TFIM) can be prepared with > 99% fidelity on a 100 qubit system with only one iteration. Furthermore, we show that VQCS with LRIs is a promising route for exploring generic points in the phase diagram of the long-range TFIM. Our approach thus provides concrete, ultrafast protocols for quantum simulators equipped with long range interactions.