Synopsis

# Opening the gate to quantum computation

Physics 3, s9
The demonstration of entanglement between two neutral atoms would be a key step toward using them for quantum computation.

Entanglement lies at the heart of quantum computation. Entangling neutral atoms is attractive because they interact weakly with their environment, but by the same token, they are difficult to entangle compared with strongly interacting ions. Papers appearing simultaneously in Physical Review Letters demonstrate how separate groups are achieving entanglement between two neutral atoms by using a method called Rydberg blockade.

The underlying idea behind Rydberg blockade is that the state of one atom (the control) determines whether the other (the target) can be excited into a high-energy state. This effective coupling between the two atoms turns them into a collectively two-level system.

Tatjana Wilk and colleagues at the Institut d’Optique (CNRS and Université Paris-Sud) in France use the Rydberg blockade to entangle $87Rb$ atoms that are held a few microns apart by optical tweezers. In a separate paper, Larry Isenhower and colleagues at the University of Wisconsin, US, report similar methods to create a two-qubit controlled-NOT (CNOT) gate between $87Rb$ atoms. The CNOT gate then serves as a means to achieve entanglement between the atoms.

Both groups report the preparation of quantum states with an accuracy (or, fidelity) that is near the threshold needed to prove entanglement; correcting for losses associated with atoms that fell out of the optical traps suggests that the remaining pairs of atoms are entangled with a fidelity well over the threshold. Although there is still work to be done in fine tuning the methods reported by both groups, the papers collectively show important progress toward quantum processing with neutral atoms. – Jessica Thomas and Sonja Grondalski

## Related Articles

Quantum Information

### Turning a Quantum Computer into a Time Crystal

Google’s Sycamore quantum processor can simulate an elusive quantum system called a discrete time crystal. Read More »

Quantum Information

### A Scalable Code for Reducing Quantum Errors

A new scheme could offer a technologically viable solution for remedying computational errors in near-term quantum devices. Read More »

Chemical Physics

### Superpositions of Chiral Molecules

Matter-wave diffraction can put chiral molecules into superpositions of left- and right-handed forms, enabling new studies of how the two states interact with their environment. Read More »