Making measurements is at the heart of doing science. Whether scientists are peeking at the inside of a cell or looking for habitable planets orbiting distant stars, all scientists would kill for a more sensitive detection device. In fact, scientists already spend a ton of energy trying to improve detection devices by eliminating noise or any unwanted signals which drown out the thing they are trying to measure.
But even if they could make the best detector possible by eliminating all sources of noise, scientists still wouldn't be able to get around a fundamental limit: the Heisenberg uncertainty principle. A consequence of quantum mechanics, the Heisenberg uncertainty principle states that if we measure one aspect of a system very precisely, for example, an object's position, then we lose information about a different aspect of the system, e.g., how fast the object is moving.
While this is a rule of quantum mechanics that can't be broken, quantum mechanics also provides a means of bending the rule. For example, if we really care about the position of an object, but not so much about the way it's moving, then we can put the object in a quantum state where the uncertainty of the position is reduced at the expense of greater uncertainty in the motion.
Let’s apply this concept to a pendulum: if we want to know how fast it is swinging back and forth, we could make a “quantum” pendulum that has lower uncertainty in its frequency of oscillation, or the swinging motion. As a consequence, though we would lose information about its energy, or the height of each swing.
This is what we explored in our Nature study earlier this year. A single ion, or charged atom, confined by electric fields, behaves just like this pendulum: it oscillates back and forth. By increasing the uncertainty in the ion’s energy, we were able to reduce the uncertainty in our measurement of its oscillation, thereby bending the rules of the pesky Heisenberg uncertainty principle in our favor.
Many things in our world behave just like this pendulum, and the demonstration of using quantum mechanics to enhance our measurement precision is an important step that many other fields can benefit from.