A Quantum measurement induced ground-state transition*

The act of measurement is necessarily invasive as the observer and the system become entangled. We show that already weak (non-projective) measurements with a sensor dot can drive a ground-state transition in the adjacent double quantum dot [arXiv:2010.04635]. The experiment operates close to the (1,0)-(0,1) charge degeneracy line where an electron resides in the left and right dot with equal probabilities. With increasing measurement strength (sensor bias), the line deforms into an S-shaped curve. The area enclosed between S-shape and line hosts a new measurement induced ground-state. Here, the system prepared in the (1,0) ground state with an electron in the left dot, occupies the (0,1) state while being measured. We have developed a model that quantitatively accounts for the experiment. Each electron passing the sensor induces a capacitive shift in the adjacent quantum dot level. The resulting level-broadening enhances charge transfer with the reservoir, allowing the system to populate an energetically unfavorable state. Changing the nature of a many-body state simply by observing it is a major shift in how we understand the act of measurement and poses new challenges for quantum technologies.