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Active control of quantum materials is highly desirable for a wide range of applications. Metastable hidden states, such as the one discovered a few years ago by researchers at the Department of complex matter at the Jožef Stefan Institute, offer completely new functionalities. However, the underlying mechanisms that lead to hidden states remains a largely open scientific topic. In a new study published on November 24 in [[ https://www.science.org/doi/10.1126/sciadv.adi4661 | Science Advances ]], prof. dr. Dragan Mihailović in collaboration with a group of researchers from Germany and USA, investigated coherent control of the transition to a metastable hidden quantum state in the quantum material 1T-!TaS₂. Using time- and angle-resolved photoemission spectroscopy (trARPES), electronic and collective excitations during the transition to the hidden state were investigated in real time. Using laser excitation with time-controlled pulses, they managed to coherently control the transition to the hidden phase, thus revealing the importance of collective excitations which helped elucidate the mechanism for this interesting phenomenon.