Quantum Computer Architecture Based on Optically Controlled Spins
Quantum computing as an engineering discipline is still in its infancy. Although the physics is well understood, developing devices which compute with quantum mechanics is technologically daunting. While experiments to date manipulate only a handful of quantum bits we consider what effort is required to build a large-scale quantum computer. This objective demands more than a cursory estimate of the number of qubits and gates required for a given algorithm. One must consider the faulty quantum hardware, with errors caused by both the environment and deliberate control operations; when error correction is invoked, classical processing is required; constructing arbitrary gate sequences from a limited fault-tolerant set requires special treatment, and so on.
An architecture decomposes complex system behaviours into a manageable set of operations. A layered architecture does this through layers of abstraction where each embodies a critical set of related functions. For our purposes, each ascending layer brings the system closer to an ideal quantum computing environment
Layered Control Stack Architecture
Layered architectures are a conventional approach to solving such engineering problems in many fields of information technology, and presents a layered architecture for quantum computer design software. This architecture, which describes the physical design of the quantum computer, consists of five layers, where each layer has a prescribed set of duties to accomplish. The interface between two layers is defined by the services a lower layer provides to the one above it. To execute an operation, a layer must issue commands to the layer below and process the results.
Primary Control Cycle of Quantum Architecture
The primary control cycle defines the dynamic behaviour of the quantum computer in this architecture since all operations must interact with this loop. The principal purpose of the control cycle is to successfully implement quantum error correction. The quantum computer must operate fast enough to correct errors; still, some control operations necessarily incur delays, so this cycle does not simply issue a single command and wait for the result before proceeding — pipelining is essential. Layers 1 to 4 interacts in the loop, whereas the Application layer interfaces only with the Logical layer since it is agnostic about the underlying design of the quantum computer.
Optically Controller Spin and The QuDOS hardware platform
The layered framework for quantum computing was developed in tandem with a specific hardware platform, known as QuDOS (quantum dots with optically controlled spins). The QuDOS platform uses electron spins within quantum dots for qubits. The quantum dots are arranged in a two-dimensional array
The QuDOS design is a promising candidate for large-scale quantum computing, beginning with an analysis of the hardware
Hardware performance summary
These are the quantum processes which are the building blocks of quantum information operations in Layers 2 and above. For a complete quantum processor, however, one would also have to consider the classical control hardware and the engineering concerns, such as delays, which may occur in a large system
Designing a quantum computer requires viewing the system as a whole, such that tradeoffs and compatibility between component choices must be addressed. A holistic picture is equally important for comparing different quantum computing technologies, such as ion traps or superconducting circuits. This work illustrates how to approach the complete challenge of designing a quantum computer so that one can adapt these techniques to develop architectures