Quantum scrambling of observable algebras

Paolo Zanardi

doi:10.22331/q-2022-03-11-666

Abstract

In this paper we describe an algebraic/geometrical approach to quantum scrambling. Generalized quantum subsystems are described by an hermitian-closed unital subalgebra A of operators evolving through a unitary channel. Qualitatively, quantum scrambling is defined by how the associated physical degrees of freedom get mixed up with others by the dynamics. Quantitatively, this is accomplished by introducing a measure, the geometric algebra anti-correlator (GAAC), of the self-orthogonalization of the commutant of A induced by the dynamics. This approach extends and unifies averaged bipartite OTOC, operator entanglement, coherence generating power and Loschmidt echo. Each of these concepts is indeed recovered by a special choice of A. We compute typical values of GAAC for random unitaries, we prove upper bounds and characterize their saturation. For generic energy spectrum we find explicit expressions for the infinite-time average of the GAAC which encode the relation between A and the full system of Hamiltonian eigenstates. Finally, a notion of A-chaoticity is suggested.

Highlights

In this paper we describe an algebraic/geometrical approach to quantum scrambling
The goal of this paper is to lay down a novel formalism for quantum scrambling
The underlying philosophy of this paper is an extension of the observable-algebra approach to quantum subsystems originally advocated in [8, 9]

Summary

Paolo Zanardi

Quantum scrambling is defined by how the associated physical degrees of freedom get mixed up with others by the dynamics This is accomplished by introducing a measure, the geometric algebra anti-correlator (GAAC), of the self-orthogonalization of the commutant of A induced by the dynamics. This approach extends and unifies averaged bipartite OTOC, operator entanglement, coherence generating power and Loschmidt echo. We will show that specific instances of our construction allow one to recover apparently different concepts including operator entanglement [13, 14], averaged bipartite OTOCs [15, 16], coherence generating power [17–19] and Loschmidt echo [20, 21] This conceptual unification provides one of the main motivations for this work.

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