摘要：Macrorealism, as defined by Leggett and Garg, posits that a macroscopic system always exists in a well-defined state and that it can be measured without disturbing it. From these assumptions follow a set of inequalities, the Leggett-Garg inequalities, which hold under macrorealism but can be violated by quantum mechanics. The degree to which quantum systems can violate these inequalities is bounded and, in particular, if the measurements on the system are genuinely dichotomic, the bound for these temporal inequalities is the same as the Tsirelson bound of the corresponding spatial Bell inequality. We realise a photonic Leggett-Garg test on a three-level system and implement measurements that admit three distinct measurement outcomes, rather than the usual two. In this way we obtain violations of a Leggett-Garg inequality significantly in excess of the Tsirelson bound. This underlines the difference between Bell and Leggett-Garg inequalities and hence spatial and temporal correlations in quantum mechanics. We also report violations of a second consequence of macrorealism, the quantum-witness equality, up to the maximum permitted for a three-outcome measurement.