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arXiv:1902.02417

SurfBraid: A concept tool for preparing and resource estimating quantum circuits protected by the surface code

Alexandru Paler

Published Feb 6, 2019• 7 citations
arXivHTMLPDF

Abstract

The first generations of quantum computers will execute fault-tolerant quantum circuits, and it is very likely that such circuits will use surface quantum error correcting codes. To the best of our knowledge, no complete design automation tool for such circuits is currently available. This is to a large extent because such circuits have three dimensional layouts (e.g. two dimensional hardware and time axis as a third dimension) and their optimisation is still ongoing research. This work introduces SurfBraid, a tool for the automatic design of surface code protected quantum circuits -- it includes a complete workflow that compiles an arbitrary quantum circuit into an intermediary Clifford+T equivalent representation which is further synthesised and optimised to surface code protected structures (for the moment, braided defects). SurfBraid is arguably the first flexible (modular structure, extensible through user provided scripts) and interactive (automatically updating the results based on user interaction, browser based) tool for such circuits. One of the prototype's methodological novelty is its capability to automatically estimate the resources necessary for executing large fault-tolerant circuits. A prototype implementation and the corresponding source code are available at https://alexandrupaler.github.io/quantjs/.

DOI
10.48550/arxiv.1902.02417

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The first generations of quantum computers will execute fault-tolerant quantum circuits, and it is very likely that such circuits will use surface quantum error correcting codes. To the best of our knowledge, no complete design automation tool for such circuits is currently available. This is to a large extent because such circuits have three dimensional layouts (e.g. two dimensional hardware and time axis as a third dimension) and their optimisation is still ongoing research. This work introduces SurfBraid, a tool for the automatic design of surface code protected quantum circuits -- it includes a complete workflow that compiles an arbitrary quantum circuit into an intermediary Clifford+T equivalent representation which is further synthesised and optimised to surface code protected structures (for the moment, braided defects). SurfBraid is arguably the first flexible (modular structure, extensible through user provided scripts) and interactive (automatically updating the results based on user interaction, browser based) tool for such circuits. One of the prototype's methodological novelty is its capability to automatically estimate the resources necessary for executing large fault-tolerant circuits. A prototype implementation and the corresponding source code are available at https://alexandrupaler.github.io/quantjs/.
As quantum circuits grow beyond small toy examples, preparing them for execution on physical devices becomes increasingly complex. Design automation is therefore essential for scalable quantum computing: Compilation procedures optimize resource requirements and transform circuits to a format compatible with specific hardware; resource estimation evaluates execution cost; verification methods prove circuit correctness. However, these concepts present a steep learning curve for novices, particularly when quantum circuits are introduced through low-level textual representations. To address this, we present a block-based programming framework for quantum design automation, implemented as an extension to the Scratch programming platform. This system allows users to build quantum circuits as a sequence of blocks and embed them in classical control logic to perform evaluations, compare simulation results, and directly apply different design automation techniques. We evaluated the approach in a user study with computer science students, who completed guided exercises using the platform and provided structured feedback in the form of self-reports and short knowledge assessments. Results demonstrate strong understanding and confidence in quantum design automation concepts, suggesting that the block-based approach successfully lowers the entry barrier to quantum design automation. The implemented framework is open-source and available at https://github.com/munich-quantum-toolkit/scratch-quantum.
Quantum circuits are the preferred formalism for expressing quantum information processing tasks. Quantum circuit design automation methods mostly use a waterfall approach and consider that high level circuit descriptions are hardware agnostic. This assumption has lead to a static circuit perspective: the number of quantum bits and quantum gates is determined before circuit execution and everything is considered reliable with zero probability of failure. Many different schemes for achieving reliable fault-tolerant quantum computation exist, with different schemes suitable for different architectures. A number of large experimental groups are developing architectures well suited to being protected by surface quantum error correcting codes. Such circuits could include unreliable logical elements, such as state distillation, whose failure can be determined only after their actual execution. Therefore, practical logical circuits, as envisaged by many groups, are likely to have a dynamic structure. This requires an online scheduling of their execution: one knows for sure what needs to be executed only after previous elements have finished executing. This work shows that scheduling shares similarities with place and route methods. The work also introduces the first online schedulers of quantum circuits protected by surface codes. The work also highlights scheduling efficiency by comparing the new methods with state of the art static scheduling of surface code protected fault-tolerant circuits.
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The failure susceptibility of the quantum hardware will force quantum computers to execute fault-tolerant quantum circuits. These circuits are based on quantum error correcting codes, and there is increasing evidence that one of the most practical choices is the surface code. Design methodologies of surface code based quantum circuits were focused on the layout of such circuits without emphasizing the reduced availability of hardware and its effect on the execution time. Circuit layout has not been investigated for practical scenarios, and the problem presented herein was neglected until now. For achieving fault-tolerance and implementing surface code based computations, a significant amount of computing resources (hardware and time) are necessary for preparing special quantum states in a procedure called distillation. This work introduces the problem of how distilleries (circuit portions responsible for state distillation) influence the layout of surface code protected quantum circuits, and analyses the trade-offs for reducing the resources necessary for executing the circuits. A first algorithmic solution is presented, implemented and evaluated for addition quantum circuits.
The failure susceptibility of the quantum hardware will force quantum computers to execute fault-tolerant quantum circuits. These circuits are based on quantum error correcting codes, and there is increasing evidence that one of the most practical choices is the surface code. Design methodologies of surface code based quantum circuits were focused on the layout of such circuits without emphasizing the reduced availability of hardware and its effect on the execution time. Circuit layout has not been investigated for practical scenarios, and the problem presented herein was neglected until now. For achieving fault-tolerance and implementing surface code based computations, a significant amount of computing resources (hardware and time) are necessary for preparing special quantum states in a procedure called distillation. This work introduces the problem of how distilleries (circuit portions responsible for state distillation) influence the layout of surface code protected quantum circuits, and analyses the tradeoffs for reducing the resources necessary for executing the circuits. A first algorithmic solution is presented, implemented and evaluated for addition quantum circuits.
Fault-tolerant quantum computing is progressing from demonstrations of individual logical components toward the execution of useful quantum algorithms on large-scale error-corrected processors. Realizing this transition requires co-design across algorithms, fault-tolerant implementations, and hardware resources. Here we develop an algorithm-to-execution framework for low-cost surface-code quantum computing that carries the structure of a computation from hierarchical logical descriptions to circuit-specific spatial organization, non-Clifford resource planning, and physical resource evaluation. We apply the framework to twenty benchmark circuits spanning seven algorithm families and to a hierarchically reconstructed application-scale elliptic-curve discrete-logarithm workload. Under the stated error and resource-supply models, combining circuit-specific layouts with hybrid non-Clifford implementation reduces space--time volume by up to 12.70x relative to an all-synthesis Litinski fast-block baseline. Circuit-specific layouts reduce both modeled runtime and space--time volume in eighteen benchmarks, while the remaining two retain the fast layout. These results show that the physical cost of fault-tolerant computation emerges from the interaction between algorithm structure, error-corrected implementation, and hardware organization rather than from aggregate logical resource counts alone.