Creating quantum states on demand and controlling them is a critical component to developing practical quantum-based devices. Subsequent measurement of such states is also a challenge, because by definition, quantum superpositions collapse upon interaction, whether through intentional measurement or due to outside disturbances. Notably, the instability of a quantum state can also be used advantageously to create sensors. Quantum systems can be calibrated such that exposure to certain changing environmental conditions will force a switch from one quantum state to another. In some cases, a quantum phase of matter can abruptly change to a non-quantum phase of matter. Alterations to a quantum system can be monitored and detected, giving physicists information on the environment itself. JQI physicists are researching the many facets of quantum measurement and control, which has applications in areas such as precision spectroscopy and sensing.