Full classification of Pauli Lie algebras

TL;DR

This paper classifies all Lie algebras generated by Pauli operators on qubits, providing a framework to understand their structure, equivalence classes, and implications for quantum control and simulation.

Contribution

It offers a comprehensive classification of Pauli-generated Lie algebras, including canonical forms and physical interpretations, with implications for quantum computing and control.

Findings

Identifies key equivalence classes of Pauli Lie algebras

Provides canonical operators for each class

Shows no small Lie algebras beyond free-fermionic case exist

Abstract

Lie groups, and therefore Lie algebras, are fundamental structures in quantum physics that determine the space of possible trajectories of evolving systems. However, classification and characterization methods for these structures are often impractical for larger systems. In this work, we provide a comprehensive classification of Lie algebras generated by an arbitrary set of Pauli operators, from which an efficient method to characterize them follows. By mapping the problem to a graph setting, we identify a reduced set of equivalence classes: the free-fermionic Lie algebra, the set of all anti-symmetric Paulis on n qubits, the Lie algebra of symplectic Paulis on n qubits, and the space of all Pauli operators on n qubits, as well as controlled versions thereof. Moreover, out of these, we distinguish 6 Clifford inequivalent cases and find a simple set of canonical operators for each, which allow us to give a physical interpretation of the dynamics of each class. Our findings reveal a no-go result for the existence of small Lie algebras beyond the free-fermionic case in the Pauli setting and offer efficiently computable criteria for universality and extendibility of gate sets. These results bear significant impact in ideas in a number of fields like quantum control, quantum machine learning, or classical simulation of quantum circuits.