Quantum mechanics has been experimentally confirmed to hold at microscopic scales, including atoms, molecules, and subatomic particles. However, its principles have not been directly observed to govern macroscopic objects on a large scale. The boundary between the quantum and classical realms is still an active area of research and debate.
That being said, there have been some experiments exploring the quantum behavior of larger systems or ensembles of particles. One notable example is the demonstration of quantum behavior in the form of "macroscopic superposition" in the case of certain types of superconducting circuits. These circuits are composed of a large number of coupled superconducting elements, and under specific conditions, they can exhibit quantum coherence on a macroscopic scale.
In 2019, researchers at Google announced an experiment known as "Quantum Supremacy" where they claimed to have achieved a computation that is beyond the capabilities of classical computers. They used a quantum processor consisting of 53 qubits to perform a specific task, demonstrating quantum supremacy in a controlled laboratory setting.
However, it's important to note that even in these cases, the quantum behavior is still limited to a relatively small number of particles or a specific experimental setup, and the objects involved do not possess the complexity or size of everyday macroscopic objects.
To date, the exact boundary where quantum mechanics transitions into classical behavior is still an area of active research, and further advancements and experiments are needed to explore the limits of quantum theory at larger scales.