Abstract:
The potential of quantum computers to solve tasks intractable to classical computers has boosted extraordinary progress in development of quantum computers over the past decade. Meanwhile the solution of practical tasks requires the increase of both the number of qubits and the number of fault tolerant operations. One of the perspective approaches in that respect is to move from two qubit entangling operations to multiqubit gates. The interest to such gates is driven by their role in the field of quantum metrology for quantum-mechanically enhanced sensors, the advantages for improving the performance of quantum error correction codes, for compilation of quantum Fourier transforms, Clifford unitary operators with a gate count that is independent of the qubit register size and N-qubit Toffoli gates, for the improvements in the performance of QAOA algorithms and for digital-analog algorithms. Moreover, for trapped ion systems the global entangling gates can be naturally realized thanks to the mutual coulomb interactions of the trapped ions. In addition to long range connectivity trapped ions are known for the accurate control of individual and long coherence times and as a result represent one of the leading platforms among quantum computers hardware. Therefore, the talk will focus on the global entangling gates in these systems. More specifically, we investigate N-qubit Greenberger-Horne-Zeilinger (GHZ) states as one of the important examples of global gates. The GHZ state was generated for 2, 4, 8, 12, 16 ion chains with the fidelity of 63.2(6)% for 16 ions. We compare the obtained results with the theoretical calculations. In our calculations, we account for the technical noises present in our setup such as laser intensity, laser frequency, and trap frequency fluctuations. Also, we account for the fundamental errors originating from laser-ion interaction, in particular, carrier transition, spectator phonon modes contribution and high-order Lamb-Dicke effects. We believe our analyses will help to improve global gate fidelities and pave the way for experimental demonstration of quantum algorithms with global gates.
