Abstract
We develop a layered quantum-computer architecture, which is a systematic framework for tackling the individual challenges of developing a quantum computer while constructing a cohesive device design. We discuss many of the prominent techniques for implementing circuit-model quantum computing and introduce several new methods, with an emphasis on employing surface-code quantum error correction. In doing so, we propose a new quantum-computer architecture based on optical control of quantum dots. The time scales of physical-hardware operations and logical, error-corrected quantum gates differ by several orders of magnitude. By dividing functionality into layers, we can design and analyze subsystems independently, demonstrating the value of our layered architectural approach. Using this concrete hardware platform, we provide resource analysis for executing fault-tolerant quantum algorithms for integer factoring and quantum simulation, finding that the quantum-dot architecture we study could solve such problems on the time scale of days.
- Received 1 September 2011
DOI:https://doi.org/10.1103/PhysRevX.2.031007
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Published by the American Physical Society
Popular Summary
A quantum computer is a machine that would utilize the unique and complex properties of quantum mechanical systems to solve problems thought to be intractable on classical computers, such as factoring large integers or simulating quantum physics. Many technologies for the basic hardware information-processing units (qubits) are under development; these may be photons, trapped ions, or semiconductor quantum dots, to name a few. However, construction of a practical quantum computer will be more technologically and conceptually demanding than the engineering of the qubits alone. How might this technology develop in the future? In this paper, we address this question by proposing a general, constructive framework of layered architecture for quantum computers, as well as a specific hardware platform based on quantum dots.
For a quantum computer to function, a number of components must interact as a synchronized system. These components include the qubits and their associated “write” and “read-out” operations, quantum error correction that protects information from the damaging effects of noise, and programs to execute logical algorithms. The guiding principle of our layered architecture is to group related components or operations together in an intuitive manner. The architecture consists of five ascending layers, going from the physical qubits through quantum error correction up to algorithms. This complete framework allows us to answer concretely many practical questions about the size and complexity of quantum computers. For example, we are able to estimate how many quantum-dot qubits are required in a quantum error-correcting code for the practical task of factoring a 1024-bit number. We are also able to calculate the total resources required for two interesting problems: Shor’s factoring algorithm and simulating quantum chemistry.
This conceptual framework of layered architecture will serve as a concrete basis for further explorations of quantum-computer engineering.
