Lando's Theorem

Lando's Theorem states that in quantum mechanics, measurements disturb the system in a way that prevents us from fully knowing both the initial and final states simultaneously. In essence, the more precisely we determine a system’s initial condition, the less precisely we can know its final condition afterward, and vice versa. This reflects a fundamental limit in how information about quantum systems is acquired, emphasizing that observation and measurement are intrinsically linked to uncertainty. Lando's Theorem highlights the unavoidable trade-off between knowledge and disturbance when measuring quantum states.