Scalable Quantum Computing with Two-Dimensional Arrays of Trapped Ions Enabled by Fast Gates
Date
2019
Authors
Mehdi, Zain
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Abstract
Realising large-scale quantum computation in the near
future will require increasing the number of low-error two-qubit
gates that can be implemented on a quantum computer before
decoherence. One of the biggest challenges facing current trapped
ion quantum computers is implementing high-speed two-qubit
operations, whilst increasing the number of qubits. One of the
most promising proposals for overcoming current limitations is
the use of ultra-fast pulses to implement fast two-qubit gates
between nearest-neighbour pairs of ions. In this thesis, I
investigate these ‘fast gates’ in two-dimensional arrays of
microtraps, each containing a single ion. I argue that
two-dimensional architectures allow for a significant reduction
in the number of two-qubit gates required for a particular
computation, as compared to one-dimensional ion chains. I
demonstrate this reduction for a quantum simulation of a 40-mode
Fermi-Hubbard Hamiltonian. I develop an efficient scheme that
allows fast gates to be numerically optimised for two-dimensional
geometries. I find that this optimisation scheme is capable of
designing gates that are faster, higher fidelity, and require
lower laser repetition rates. Using this scheme, I find that
high-speed two-qubit gates can be optimised for two-dimensional
architectures, with fidelities well above thresholds required for
fault tolerant error correction, around 99.99%. Furthermore, I
find that fast gates in these architectures are robust to the
presence of large numbers of surrounding ions. Following previous
studies [1, 2] which have identified pulse imperfections as a
dominant source of error in fast gates, I perform a worst-case
error analysis. I find the fast gates presented in this thesis to
require very small errors in single-qubit rotations, and I
present recommendations for achieving those requirements. I also
investigate other experimental considerations, and make
recommendations for overcoming other technical challenges in
realising fast gates.
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Quantum computing, quantum information, trapped ion, fast gates, qubit, quantum computation, quantum simulation
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Thesis (Honours)
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