Enhanced non-macrorealism: Extreme violations of Leggett-Garg inequalities for a system evolving under superposition of unitaries

TL;DR

This paper demonstrates that superpositions of unitary operations can significantly enhance violations of Leggett-Garg inequalities, indicating stronger non-macrorealistic behavior and increased robustness against decoherence, confirmed through NMR experiments.

Contribution

It introduces a method to achieve extreme violations of LGI via superpositions of unitaries and experimentally verifies these effects using NMR technology.

Findings

Superposition of unitaries leads to violations beyond the Tsirelson bound.

Enhanced non-macrorealism persists longer due to robustness against decoherence.

Experimental validation confirms theoretical predictions.

Abstract

Quantum theory contravenes classical macrorealism by allowing a system to be in a superposition of two or more physically distinct states, producing physical consequences radically different from that of classical physics. We show that a system, upon subjecting to transform under superposition of unitary operators, exhibits enhanced non-macrorealistic feature - as quantified by violation of the Leggett-Garg inequality (LGI) beyond the temporal Tsirelson bound. Moreover, this superposition of unitaries also provides robustness against decoherence by allowing the system to violate LGI and thereby retain its non-macrorealistic behavior for a strikingly longer duration. Using an NMR register, we experimentally demonstrate the superposition of unitaries with the help of an ancillary qubit and verify these theoretical predictions.