Strengthening weak measurements of qubit out-of-time-order correlators

TL;DR

This paper introduces a method to experimentally measure multitime correlators in qubit systems through sequential generalized measurements, enabling precise out-of-time-order correlator measurements using standard quantum gates.

Contribution

It presents a novel approach for measuring a class of multitime correlators exactly via sequential measurements, applicable to superconducting qubits.

Findings

Exact measurement of correlators from measurement sequences

Quantum circuits for out-of-time-order correlators using common gates

Applicable to superconducting transmon qubit systems

Abstract

For systems of controllable qubits, we provide a method for experimentally obtaining a useful class of multitime correlators using sequential generalized measurements of arbitrary strength. Specifically, if a correlator can be expressed as an average of nested (anti)commutators of operators that square to the identity, then that correlator can be determined exactly from the average of a measurement sequence. As a relevant example, we provide quantum circuits for measuring multiqubit out-of-time-order correlators using optimized control-Z or ZX-90 two-qubit gates common in superconducting transmon implementations.