Quantum Computer Microarchitecture

Abstract

Nowadays, the need for better and faster computing searches for solutions in the field of quantum computing. It is believed that quantum computing can and will surpass conventional, classical computing. When quantum computing surpasses classical computing, it is called quantum supremacy. There are many different projects that use different quantum technologies aim to achieve quantum supremacy, such as projects from Google and Intel. In this thesis, the reader is introduced to a new project: the Fujitsu Project. The project is a collaboration between TU Delft and Fujitsu and has the goal of fabricating a new distributed quantum quantum computer based on color centers in diamond. The focus of the thesis is the definition of the microarchitecture.

The quantum computer stack is explained in detail. Precise and robust definitions for each of the seven layers of the quantum computer stack are given, where the definition of the microarchitecure is most important. A microarchitecture is defined as the list of instructions of the lowest level before entering control electronics. To define the diamond microarchitecture, a set of goals have to be completed. Other architectures such as QuTech's QuMA and QuTech's Central Controller were identified and analyzed. Combined with the requirements of the overall diamond system architecture as defined by the project, a list of requirements for the microarchitecture is created. Using these requirements, a Quantum Instruction Set Architecture (QISA) and a microarchitecture are defined.

Based on the defined QISA and microarchitecture, a compiler is designed. The compiler is made in OpenQL. OpenQL is a framework for high-level quantum programming that targets different quantum computing platforms. The main task of the compiler is to translate high-level quantum algorithms, expressed in a high-level quantum programming language (C++/Python APIs), to quantum microcode. The quantum microcode consists of instructions that are defined in the microarchitecture.

The QISA, microarchitecture and compiler are verified against the requirements that are set at the beginning of their respective definition phases. The microarchitecture supports for all gates that are part of cQASM 1.0. In addition, it supports all diamond color center specific protocols and rules. The compiler supports all instructions from cQASM as well. Moreover, the compiler supports all standard (gate) instructions and diamond specific instructions through OpenQL's Python API.

The work is intended to be a solid baseline, where the future of the project can rely and improve upon. Possible improvements could be the adaption of the microarchitecture to the growth of the number of controlled qubits per controller, the parallelization of the microarchitecture instructions to improve instruction throughput, and alignment with the quantum network group. The compiler can also be improved with for example enhanced scheduling, differentiation between qubit types and an entanglement library. The next step in the design of the microarchitecture will be the design of a microarchitecture simulator, which takes the microcode as input and simulates the hardware architecture.