Towards microwave based ion trap quantum technology

Weidt, Sebastian (2014) Towards microwave based ion trap quantum technology. Doctoral thesis (PhD), University of Sussex.

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Scalability is a challenging yet key aspect required for large scale quantum computing and
simulation using ions trapped in radio-frequency (rf) Paul traps.

In this thesis 171Yb+ ions are used to demonstrate a magnetic field insensitive qubit
which has a measured coherence time of 1.5 s, making it an ideal candidate to use for storing quantum information. A magnetic field sensitive qubit is also characterised which can be used for the implementation of multi-qubit gates using a potentially very scalable scheme based on microwaves in conjunction with a static magnetic field gradient instead of using lasers. However, the measured coherence time is limited by magnetic field fluctuations and will prohibit high fidelity gate operations from being performed. To address this issue, the preparation of a dressed-state qubit using a microwave based stimulated rapid adiabatic passage (STIRAP) pulse sequence will be presented. This qubit is protected against the noisy environment making it less sensitive to magnetic field fluctuations. The lifetime of this qubit is measured to demonstrate its suitability for storing quantum information. A powerful method for manipulating the dressed-state qubit will be presented and is used to measure a coherence time of the qubit of 500 ms which is two orders of magnitude longer compared to the magnetic field sensitive qubit. It will also be shown that our method allows for the implementation of arbitrary rotations of the dressed-state qubit on the Bloch sphere using only a single rf field. This substantially simplifies the experimental setup for single and multi-qubit gates.

Furthermore, this thesis will present a experimental setup capable of successfully operating
microfabricated surface ion traps. This setup is then used to operate and characterise
the first two-dimensional (2D) lattice of ion traps on a microchip. A unique feature of the
microfabrication technique used for this device is the extremely large voltage that can be
applied which allows long ion lifetimes along with large secular frequencies to be measured,
demonstrating the robustness of this device. Rudimentary shuttling between neighbouring
lattice sites will be shown which could be used as part of a efficient scheme to load a large
lattice of ions. One of the many applications of a 2D lattice of ions lies in the field of
quantum simulations where many-body systems such as quantum magnetism, high temperature superconductivity, the fractional quantum hall effect and synthetic gauge fields
can be simulated. It will be shown how making only minor modifications to the microchip
the ion-ion separation can be reduced sufficiently to offer an exciting platform for the
successful implementation of 2D quantum simulations. A theoretical investigation on the
optimal 2D ion trap lattice geometry will also be presented with the aim to maximise the
ratio of ion-ion coupling strength to decoherence from motional heating of the ions and to
laser induced off-resonant coupling.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Subjects: Q Science > QC Physics > QC0501 Electricity and magnetism > QC0522 Electricity > QC0661 Electric oscillations. Electric waves > QC0676.4 Radio waves (Theory)
Q Science > QC Physics > QC0501 Electricity and magnetism > QC0522 Electricity > QC0680 Quantum electrodynamics
Depositing User: Library Cataloguing
Date Deposited: 16 Jun 2014 05:35
Last Modified: 21 Sep 2015 14:25

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