Room-temperature hundred-μm quantum states in Cu(111)

Abstract The quantum state of matter, a platform of profound quantum physics, is coherent under extreme conditions, such as ultralow temperature and two-dimensional confinement. Herein, in contrast to conventional views, the Cu(111) grain boundary (GB)-free films show quantum states greater than 400 μm at room temperature (RT). We directly observe hundred-micrometre-scale coherence and interference in the Cu(111) quantum states across four dimensions over time, frequency, and space. This RT macroscopic quantum nature is observed via tip-assisted terahertz spectroscopy, enabling access to electrons in picoseconds before losing their coherence due to impurity scattering. The quantum edge and bulk electron states exhibiting ‘quantum oscillation’ are separately visualized under cross-polarization conditions at distinct frequencies: vortical edge charges at 0.2 THz and circulating bulk charges at 0.6 THz. Our findings highlight the combination of the lengthened coherence in GB-free noble metals; here, the quantum states are sustainable for over one year due to the oxidation resistance of GB-free Cu(111), and GB-free Cu(111) is an unprecedented room-temperature quantum platform.