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QUASIRIO Report Summary

Project ID: 279508
Funded under: FP7-IDEAS-ERC
Country: Sweden

Final Report Summary - QUASIRIO (Quantum simulations with trapped Rydberg ions)

The project QuaSIRIO focused on the realization of trapped Rydberg ions and their application for quantum information processing and quantum simulations. Trapped Rydberg ions are a novel quantum system that combines the two existing quantum technologies trapped ions and Rydberg atoms. It can benefit from both sides, in particular, from the advanced quantum control of trapped ions and the strong dipolar interaction between Rydberg atoms. Such a system has the outmost electron of the trapped ion lifted into a highly excited electronic state, which is several hundred nanometers away from the atomic core. On an atomic scale this is a huge object with very special properties, which, for instance, allow two Rydberg ions to “sense” each other at a distance.
Nonetheless, the ions are still trapped in an oscillating electric field, which distinguishes them from neutral Rydberg atoms.

Due to these extraordinary characteristics, trapped Rydberg ions promise to speed up entangling interactions and to make such operations possible in larger ion crystals. The higher speed of entangling interactions would allow the execution of more complex quantum algorithms before decoherence destroys the stored quantum information. The quantum operations in larger crystals would make trapped Rydberg ions a powerful alternative approach for scalable quantum information processing. In particular, a string or crystal of interacting trapped Rydberg ions could be used for simulations of complex quantum systems intractable by classical computers.

In the QuaSIRIO project, we realized the first trapped Rydberg ions with strontium. The trapped Rydberg ions are stable, and can be precisiely controlled in the large electric fields of an ion trap. Using very narrowband UV lasers at 243nm and 305nm, we demonstrated full coherent control over the Rydberg excitation, in particular, we can prepare and fully control the quantum state of Rydberg and initial state. We showed that we can combine ground state qubit manipulation with coherent Rydberg excitation, which we then employed to realize a single qubit phase gate. We demonstrated microwave-dressing of trapped ion Rydberg states, one of the basic technologies for Rydberg entanglement operations. We verified that it is possible to control the polarizability of a microwave-dressed Rydberg state by controlling its S- vs P-components, which is essential to avoid unwanted entanglement and decoherence during Rydberg excitation. All achievements are novel, and have never been shown before.
In conclusion, the ERC project QuaSIRIO enabled the new technology of trapped Rydberg ions, which is a promising route to realize scalability in a trapped ion quantum computer. We are convinced that entanglement operations will be realized in the near future based on the trapped Rydberg ion technology developed within QuaSIRIO. This will open up a plethora of applications within quantum simulations and computations.

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