Spooky Atomic Clocks

Image by Patrick L. Barry Making a measurement on one entangled particle affects the properties of the other instantaneously.

But two entangled particles can appear to influence one another instantaneously, whether they're in the same room or at opposite ends of the Universe. Pretty spooky indeed.

Quantum entanglement occurs when two or more particles interact in a way that causes their fates to become linked: It becomes impossible to consider (or mathematically describe) each particle's condition independently of the others'. Collectively they constitute a single quantum state.

Two entangled particles often must have opposite values for a property - for example, if one is spinning in "up" direction, the other must be spinning in the "down" direction. Suppose you measure one of the entangled particles and, by doing so, you nudge it "up." This causes the entangled partner to spin "down." Making the measurement "here" affected the other particle "over there" instantaneously, even if the other particle was a million miles away.

While physicists and philosophers grapple with the implications for the nature of causation and the structure of the Universe, some physicists are busy putting entanglement to work in applications such as "teleporting" atoms and producing uncrackable encryption.

Atomic clocks also stand to benefit. "Entangling the atoms in an atomic clock reduces the inherent uncertainties in the system," Kuzmich explains.

At the heart of every atomic clock lies a cloud of atoms, usually cesium or rubidium. The natural resonance's of these atoms serve the same purpose as the pendulum in a grandfather clock. Tick-tock-tick-tock. A laser beam piercing the cloud can count the oscillations and use them to keep time. This is how an atomic clock works.