Ions held in place by a laser

Stay in line or we’ll zap you with a laser


It’s a new record. Physicists have trapped 219 beryllium ions in strong electronic and magnetic fields and entangled their quantum properties with lasers. With some further tweaks, these charged particles could carry out quantum calculations that ordinary computers can’t handle.

Quantum entanglement is the “spooky” phenomenon that links up particles’ quantum states even across vast distances, meaning that you can’t measure one without affecting the other. Earlier experiments entangled 100,000 photons and 3000 neutral atoms. But this one has entangled ten times more ions than ever before.

It’s an important milestone, because you’d need this many entangled ions to solve quantum mechanics problems that would stump a classical computer. Each ion acts as a quantum bit, or qubit. Just 10 to 20 qubits isn’t enough for such calculations.

Ion cage

Trapping more than a handful of ions in a chamber for quantum experiments is challenging, because you need strong electromagnetic fields to wrangle them into place, says Justin Bohnet at the National Institute of Standards and Technology in Boulder, Colorado.


Rather than laboriously grab ions one at a time, Bohnet’s team used a tool called a Penning trap, invented in 1959 to catch atoms so their properties can be measured. It uses electric and magnetic fields to grab many ions at once and let them form a two-dimensional crystal on their own. “We rely on the fact that the ions bump into each other to self-assemble into an array,” Bohnet says.

Once the ions were in place, the team used a set of lasers to cool them to nearly absolute zero. Another pair of lasers zapped the outermost electrons of each ion until they all shared the same quantum property called spin, entangling all the ions’ spins.

 Metal behaviour

“This is a great first step,” said Kazi Rajibul Islam of the MIT-Harvard Center for Ultracold Atoms. He says it’s exciting that the NIST Penning trap can read out each ion’s quantum state as well as control the entangled crystal’s behaviour.

It puts the team on the right track to study the quantum behaviour of metals, Islam says. The trapped ions could be used to simulate how the ions of magnetic materials behave when they are entangled.

Such mysterious materials could represent an undiscovered phase of matter, and studying them might help scientists learn how to make superconducting materials stable at room temperature, Islam says. “One of the long-term goals of this field is to understand what gives rise to these high-temperature superconducting materials,” he says.

What the NIST team needs to do now is gain control over the individual ions rather than the whole group, says Hartmut Häffner of the University of California, Berkeley. “That would make it so you could run a quantum algorithm with 200 qubits,” he says. “That would be a big thing. It could easily outperform any classical computer.”

Journal reference: Science, DOI: 10.1126/science.aad9958

Read more: Quantum computer firm D-Wave claims massive performance boost; Ethereal quantum state stored in solid crystal

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