Quantum computing promises to revolutionize computing by providing exponential speed improvements to classically difficult problems. Over the past 30 years, experimental research has progressed from manipulating quantum systems to creating elementary gates in many quantum mechanical systems. One of the most successful media for implementing quantum gates is trapped ions. Current trapped-ion quantum computing architectures have very high gate fidelities and long coherence times, but creating quantum gates with low error rates with trapped ions is challenging since it requires precise trap and laser control. In order to implement quantum gates with trapped ions, I have created a field-programmable-gate-array- (FPGA) based microarchitecture for constructing laser-pulse sequences and controlling ancillary equipment. The microarchitecture is centralized to minimize experimental timing errors and is programmable to provide the generality necessary for implementing a vast range of experiments.
Quantum computing promises to revolutionize computing by providing exponential speed improvements to classically difficult problems. Over the past 30 years, experimental research has progressed from manipulating quantum systems to creating elementary gates in many quantum mechanical systems. One of the most successful media for implementing quantum gates is trapped ions. Current trapped-ion quantum computing architectures have very high gate fidelities and long coherence times, but creating quantum gates with low error rates with trapped ions is challenging since it requires precise trap and laser control. In order to implement quantum gates with trapped ions, I have created a field-programmable-gate-array- (FPGA) based microarchitecture for constructing laser-pulse sequences and controlling ancillary equipment. The microarchitecture is centralized to minimize experimental timing errors and is programmable to provide the generality necessary for implementing a vast range of experiments.
The central challenge of quantum computing is implementing high-fidelity quantum gates at scale. However, many existing approaches to qubit control suffer from a scale-performance trade-off, impeding progress towards the creation of useful devices. Here, we present a vision for an electronically controlled trapped-ion quantum computer that alleviates this bottleneck. Our architecture utilizes shared current-carrying traces and local tuning electrodes in a microfabricated chip to perform quantum gates with low noise and crosstalk regardless of device size. To verify our approach, we experimentally demonstrate low-noise site-selective single- and two-qubit gates in a seven-zone ion trap. We implement electronic single-qubit gates with fidelities ≥ 99.99912 ( 8 ) % and demonstrate consistent performance with low crosstalk across the device. We also electronically generate two-qubit maximally entangled states with 99.97 ( 1 ) % fidelity and long-term stable performance over continuous system operation. These state-of-the-art results highlight the potential of our all-electronic approach for coherent control of trapped-ion qubits in large-scale quantum computers.
This thesis describes the design of a real-time control system for trapped ion quantum computer experiments. It is framed in the context of the QuantumIon project, a project at the University of Waterloo’s Institute for Quantum Computing that aims to provide a scalable, remote-operation ion trap for a wide variety of quantum research without the need for ‘expert’ ion-trap knowledge. The target users span the range of ion-trap researchers,algorithms researchers, performance benchmarking researchers, and quantum simulation researchers.The control system features a user programming language, remote access to a compiling server, a sub-nanosecond time sequencing engine, arbitrary waveform generation for pulse shaping, and fully adjustable internal parameters. This platform affords the user extraordinary flexibility for many research use cases without requiring physical access. High-speed precision timing is achieved through the use of FPGA technology, while internal consistency (necessary for usability by non-experts) is achieved through an abstraction layer approach. Supercomputing-grade network infrastructure is employed to meet the strict timing requirements. An extensive suite of calibration tools and results is available to monitor machine-dependent parameters of the experiment. A sophisticated symbolic algebra system is used to create powerful calculations of precision timing sequences. Extensive automation is employed to remove the need for physical access, thus providing quantum computing to a wide audience. Under this model even the lowest-level control is avail-able to support innovative new designs, while a “library” of pre-defined sequences is also available to leverage “best practice” gates for those wishing rapid results. Finally, the user language itself is designed to be portable, allowing bindings to current popular classical languages such as Matlab and Python, and can be expanded for use in quantum-specific languages such as Cirq, Quill, and QASM .Through this approach the control system for QuantumIon is a flexible, powerful, scalable, and robust platform that is expected to be in use for a long time
Abstract The future of quantum information processing requires a stable hardware platform to execute quantum circuits reliably and with low error rates, such that solutions for industrial applications can be built on top of it. Trapped-ion quantum computing, among other platforms, currently proves to be very suitable for the transition from tabletop, lab-based experiments to rack-mounted, on-premise systems which allow operation in data center environments. Several technical challenges need to be solved and controlling many degrees of freedom needs to be optimized and automated, before industrial applications can be successfully implemented on quantum computers situated within data centers. These necessary developments range from the architecture of an ion trap that fundamentally defines the supported instruction sets, over the control electronics and laser systems, which limit the quality of qubit operations, to the optimized compilation of quantum circuits based on qubit properties and gate fidelities. In this chapter, we give an introduction to the ion-trap quantum computing platform, present the current technical state of the art of Alpine Quantum Technologies’ ion-trapping hardware and rack-based quantum computing systems, and highlight parts of the execution stack.
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.
Quantum computers can solve certain problems more efficiently compared to conventional classical methods. In the endeavor to build a quantum computer, several competing platforms have emerged that can implement certain quantum algorithms using a few qubits. However, the demonstrations so far have been done usually by tailoring the hardware to meet the requirements of a particular algorithm implemented for a limited number of instances. Although such proof of principal implementations are important to verify the working of algorithms on a physical system, they further need to have the potential to serve as a general purpose quantum computer allowing the flexibility required for running multiple algorithms and be scaled up to host more qubits. Here we demonstrate a small programmable quantum computer based on five trapped atomic ions each of which serves as a qubit. By optically resolving each ion we can individually address them in order to perform a complete set of single-qubit and fully connected two-qubit quantum gates and alsoperform efficient individual qubit measurements. We implement a computation architecture that accepts an algorithm from a user interface in the form of a standard logic gate sequence and decomposes it into fundamental quantum operations that are native to the hardware using a set of compilation instructions that are defined within the software. These operations are then effected through a pattern of laser pulses that perform coherent rotations on targeted qubits in the chain. The architecture implemented in the experiment therefore gives us unprecedented flexibility in the programming of any quantum algorithm while staying blind to the underlying hardware. As a demonstration we implement the Deutsch-Jozsa and Bernstein-Vazirani algorithms on the five-qubit processor and achieve average success rates of 95 and 90 percent, respectively. We also implement a five-qubit coherent quantum Fourier transform and examine its performance in the period finding and phase estimation protocol. We find fidelities of 84 and 62 percent, respectively. While maintaining the same computation architecture the system can be scaled to more ions using resources that scale favorably (O(N^2)) with the number of qubits N.
Trapped ions offer long coherence times and high fidelity, programmable quantum operations, making them a promising platform for quantum simulation of condensed matter systems, quantum dynamics, and problems related to high-energy physics. We review selected developments in trapped-ion qubits and architectures and discuss quantum simulation applications that utilize these emerging capabilities. This review emphasizes developments in digital (gate-based) quantum simulations that exploit trapped-ion hardware capabilities, such as flexible qubit connectivity, selective mid-circuit measurement, and classical feedback, to simulate models with long-range interactions, explore non-unitary dynamics, compress simulations of states with limited entanglement, and reduce the circuit depths required to prepare or simulate long-range entangled states.