Characterizing MPS and PEPS Preparable via Measurement and Feedback

TL;DR

This paper characterizes the class of long-range entangled states, specifically MPS and PEPS, that can be prepared with constant-depth local circuits combined with measurement and feedback, revealing their structural properties.

Contribution

It provides a systematic tensor network framework for understanding which MPS and PEPS states are preparable via measurement and feedback, including their symmetries and topological features.

Findings

MF-preparable states exhibit tensor symmetries.

Abelian SPT order states are a restricted class in 1D.

A subset of 2D topologically ordered states are MF-preparable.

Abstract

Preparing long-range entangled states poses significant challenges for near-term quantum devices. It is known that measurement and feedback (MF) can aid this task by allowing the preparation of certain paradigmatic long-range entangled states with only constant circuit depth. Here we systematically explore the structure of states that can be prepared using constant-depth local circuits and a single MF round. Using the framework of tensor networks, the preparability under MF translates to tensor symmetries. We detail the structure of matrix-product states (MPS) and projected entangled-pair states (PEPS) that can be prepared using MF, revealing the coexistence of Clifford-like properties and magic. In one dimension, we show that states with abelian symmetry protected topological order are a restricted class of MF-preparable states. In two dimensions, we parameterize a subset of states with abelian topological order that are MF-preparable. Finally, we discuss the analogous implementation of operators via MF, providing a structural theorem that connects to the well-known Clifford teleportation.