Project title: Implementation of a logical qubit using trapped ions
Supervisor: Professor Winfried Hensinger and Dr Florian Mintert
Fault tolerance is a key step toward the construction of a large-scale quantum computer. Without fault tolerance, small infidelities in quantum gates accumulate over the course of an algorithm, limiting the size of computations that could be performed. While the no-cloning Theorem ruled out the naive implementation of classical correction schemes, new ones such as the Steane code were developed. An important notion associated with quantum error correction codes is the logical qubit. Detecting and correcting errors is achieved by using multiple physical qubits to form
a smaller number of robust logical qubits. The physical implementation of a logical qubit requires multiple qubit and the ability to perform high fidelity gates on them.
The project aims to realize a logical qubit based on ions confined on a microfabricated surface trap and use the system to correct for multiple errors. This project will make use of concepts that have already been demonstrated and currently are under development at the Ion Quantum Technology Group at Sussex. Each physical qubit will be a microwave dressed state qubit based on ytterbium ions, trapped on a microfabricated surface trap. The surface trap will consist of an X-junction geometry. Gates will be realized through RF and microwave radiation in combination with magnetic field gradients . The implementation of a logical qubit forms an integral part of the group’s long term effort to construct a large scale quantum computer as laid out in the blueprint published early 2017 .
 S. Weidt, J. Randall, S. C. Webster, K. Lake, A. E. Webb, I. Cohen, T. Navickas, B. Lekitsch, A. Retzker, and W.
K. Hensinger. Trapped-ion quantum logic with global radiation elds. Phys. Rev. Lett., 117:220501, Nov 2016.
 Bjoern Lekitsch, Sebastian Weidt, Austin G. Fowler, Klaus Mlmer, Simon J. Devitt, Christof Wunderlich, and
Winfried K. Hensinger. Blueprint for a microwave trapped ion quantum computer. Science Advances, 3(2), 2017.