First Quantum Gate carried out with a Gigantic Atomic Ion

The ion trapping group at Stockholm University led by Markus Hennrich has implemented the first quantum gate on a trapped Rydberg ion. The result has been published in Physical Review Letters and has been highlighted as an editors’ suggestion.

“We have put our gigantic ions under some serious quantum tests. They behaved very well. In particular, they showed that they are fit for quantum technologies,” jokes Gerard Higgins, PhD student in the ion trapping group.

Strontium ions (blue point in the centre) confined in a Paul trap.

Quantum computers could revolutionize our way of solving problems. We know that a large-scale quantum computer could solve many problems significantly faster than a classical computer. In a quantum computer, information is encoded in quantum bits, and quantum calculations are composed of sequences of logical operations, so-called quantum gates, operating on these quantum bits. This works in a similar way to the NAND gates of a classical computer.
Trapped ions are the leading technology for building a quantum computer. The Ion trapping group at Stockholm University is adding a new twist to trapped ions by combining them with coherent Rydberg excitation. By bringing the outermost electron into a highly excited state close to the double-ionization limit, the ion becomes million times bigger and obtains properties which would allow for faster, scalable two-qubit gate operations.

Principle of the Rydberg quantum gate. State |1> is unchanged, while state |0> is transferred to the Rydberg state and back, and accumulates geometric phase π.

The team around Markus Hennrich has performed coherent excitation of the Rydberg states by sending carefully-tailored laser pulses onto the ion. “This is an essential step towards realizing a quantum computer with trapped Rydberg ions”, states Gerard Higgins. “Coherence is essential in quantum calculations. Without coherence the encoded quantum information is lost and only classical information remains. In our case the coherence and the quantum properties are very well preserved. This has allowed us to implement the first trapped Rydberg ion quantum gate. This result shows that trapped Rydberg ions are fit for quantum calculations.”

– Contact: Markus Hennrich (

For more information see: G. Higgins, et al., Physical Review Letters 119, 220501 (2017).

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