End-to-End Efficient Quantum Thermal and Ground State Preparation Made Simple

TL;DR

This paper introduces efficient quantum algorithms for thermal and ground state preparation that utilize simple system-bath interactions, requiring only forward evolution and a single ancilla qubit, suitable for early fault-tolerant quantum devices.

Contribution

It presents novel algorithms based on system-bath interactions with theoretical guarantees, simplifying quantum state preparation for practical quantum computing.

Findings

Algorithms accurately approximate target states

Proven bounds on mixing times

Suitable for early fault-tolerant quantum devices

Abstract

We propose new quantum algorithms for thermal and ground state preparation based on system-bath interactions. These algorithms require only forward evolution under a system-bath Hamiltonian in which the bath is a single reusable ancilla qubit, making them especially well-suited for early fault-tolerant quantum devices. By carefully designing the bath and interaction Hamiltonians, we prove that the fixed point of the dynamics accurately approximates the desired quantum state. Furthermore, we establish theoretical guarantees on the mixing time, and thereby providing a rigorous justification for the end-to-end efficiency of system-bath interaction models in thermal and ground state preparation, for several physically relevant systems.