Testing complementarity on a transmon quantum processor

TL;DR

This paper demonstrates tests of quantum complementarity principles using interferometric circuits on a superconducting transmon processor, revealing systematic errors that limit the observation of ideal quantum behavior.

Contribution

It introduces quantum circuits for testing complementarity on a transmon processor and analyzes how gate errors affect the results.

Findings

Good agreement with theory at a coarse level

Systematic deviations prevent full observation of complementarity

Modeling of gate errors explains observed deviations

Abstract

We propose quantum circuits to test interferometric complementarity using symmetric two-way interferometers coupled to a which-path detector. First, we consider the two-qubit setup in which the controlled transfer of path information to the detector subsystem depletes interference on the probed subspace, testing the visibility-distinguishability trade-off via minimum-error state discrimination measurements. Next, we consider the quantum eraser setup, in which reading out path information in the right basis recovers an interference pattern. These experiments are then carried out in an IBM superconducting transmon processor. A detailed analysis of the results is provided. Despite finding good agreement with theory at a coarse level, we also identify small but persistent systematic deviations preventing the observation of full particle-like and wave-like statistics. We understand them by carefully modeling two-qubit gates, showing that even small coherent errors in their implementation preclude the observation of Bohr's strong formulation of complementarity.