The new quantum clock, built from a few dozen strontium atoms arranged in a lattice, uses a form of quantum entanglement to combine multiple clocks into one. This technique, which links the behavior of atoms, enables the clock to surpass a key precision benchmark known as the "standard quantum limit."

"What we're able to do is divide the same length of time into smaller and smaller units," explained Adam Kaufman, senior author of the study and a fellow at JILA, a joint research institute between CU Boulder and NIST. "That acceleration could allow us to track time more precisely."

The team's innovation could lead to future quantum technologies, including sensors that detect subtle environmental changes such as variations in Earth's gravity. The results were published on October 9 in the journal 'Nature'.

Building atomic clocks
Optical atomic clocks are not just precise timekeepers - they are also important tools in quantum research. Typically, scientists trap a cloud of atoms and cool them to extremely low temperatures before exposing them to a laser. This causes the electrons in the atoms to oscillate between energy levels, similar to the swinging pendulum of a clock, but ticking trillions of times per second.

These clocks are highly sensitive: the latest models at JILA can even detect changes in gravity if they are lifted by a tiny fraction of a millimeter.

"Optical clocks have become an important platform in many areas of quantum physics," said Kaufman. "They allow you to control individual atoms with great precision - both where the atoms are, and what state they're in." However, uncertainty at the atomic scale has long posed a limit on the precision of these devices.

Quantum entanglement offers a solution. By entangling groups of atoms, the researchers made them behave more like a single entity, reducing uncertainty and improving accuracy.

Quantum entanglement
Kaufman explained that entangling atoms helps synchronize their behavior. In the study, the team nudged the atoms so that their electrons orbited far from their nuclei, increasing the interaction between atoms. The resulting pairs of entangled atoms ticked faster than unentangled atoms.

The researchers created clocks that included combinations of individual atoms and entangled groups of two, four, and eight atoms. The results showed that, under certain conditions, the entangled atoms exhibited much less uncertainty than traditional atomic clocks.

"That means it takes us less time to reach the same level of precision," Kaufman said.

Challenges and future potential
The new clock is still a work in progress, as it only functions effectively for about 3 milliseconds before the entanglement breaks down. However, Kaufman sees great potential for the technique, particularly for creating multi-qubit gates - the fundamental operations in quantum computers.

"The question is: Can we create new kinds of clocks with tailored properties, enabled by the exquisite control that we have in these systems?" Kaufman asked.

Research Report:'Multi-qubit gates and Schrodinger cat states in an optical clock'

Related Links
University of Colorado at Boulder
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