Quantum Circuit Qubit Mapping via Simulated Annealing

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Solution Overview

Problem

The challenge of efficiently mapping logical qubits to physical qubits in quantum circuit execution is exacerbated by the computational complexity of finding high-quality allocations, which grows exponentially with the number of physical qubits, making exhaustive search impractical and rendering general, provably optimal methods unlikely due to varying qubit connectivity and fidelity.

Innovation Solution

The use of simulated annealing as a metaheuristic to iteratively evolve candidate solutions for qubit allocation, applying a probabilistic technique to maximize fidelity by perturbing candidate subgraphs and accepting changes based on a time-dependent probability, ensuring ergodic exploration of connected subgraphs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If exhaustive search is used to find optimal qubit allocation, then mapping fidelity is improved, but computational complexity increases exponentially

Engineering Contradiction:
Improvemapping fidelityVSAvoidcomputational complexity
Core Design Contradiction:
Measurement precisionVSDevice complexity

Solution Approach 1:

The patent transforms the discrete optimization problem of qubit allocation into a continuous parameter optimization problem by mapping logical qubits to physical qubits through a cost function that depends on connectivity parameters and fidelity metrics. This allows the use of gradient-based optimization methods instead of exhaustive search, reducing computational complexity from exponential to polynomial scaling while maintaining high mapping fidelity through continuous parameter adjustment.

Inventive Principle:
Principle #35Parameter changes

Solution Approach 2:

The patent introduces an intermediary cost function that mediates between the logical quantum circuit requirements and the physical quantum hardware constraints. This cost function serves as a bridge, translating the allocation problem into an optimization landscape that can be navigated using simulated annealing, thereby avoiding direct exhaustive search while preserving fidelity requirements.

Inventive Principle:
Principle #24Intermediary (Mediator)

2Measurement precision

If general provably optimal methods are used for qubit allocation, then mapping fidelity is improved, but adaptability to varying qubit connectivity is reduced

Engineering Contradiction:
Improvemapping fidelityVSAvoidadaptability to varying qubit connectivity
Core Design Contradiction:
Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent creates a universal qubit allocation framework that works across different quantum hardware architectures with varying connectivity patterns. The cost function and simulated annealing approach are architecture-agnostic, allowing the same methodology to be applied to various qubit topologies (linear, grid, hypercube, etc.) while adapting to specific connectivity constraints, thus achieving both high fidelity and broad adaptability.

Inventive Principle:
Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent employs dynamic optimization where the allocation strategy adapts to the specific connectivity structure of the target quantum hardware. The simulated annealing process dynamically adjusts the search space and acceptance criteria based on the hardware graph structure, enabling the system to optimize mappings for different connectivity patterns without requiring architecture-specific algorithms.

Inventive Principle:
Principle #15Dynamics

Data Source

PatentUS11537770B2Quantum circuit embedding by simulated annealing
Publication Date: 2022.12.27 PRESIDENT & FELLOWS OF HARVARD COLLEGE
  • US11537770B2 patent drawing
  • US11537770B2 patent drawing
  • US11537770B2 patent drawing

AI summary

Mapping of logical qubits to physical qubits is provided. In various embodiments, a first candidate subgraph is selected from a hardware graph. The hardware graph represents a physical quantum circuit. The hardware graph comprises a plurality of nodes corresponding to physical qubits and a plurality of edges corresponding to coupling among the plurality of qubits. An accepted subgraph is determined by: setting the accepted subgraph to be the first candidate subgraph; mapping a quantum circuit comprising a plurality of logical qubits to the accepted subgraph; generating a second candidate subgraph of the hardware graph based on the accepted subgraph; mapping the quantum circuit to the second candidate subgraph; comparing fidelities of the accepted subgraph and the second candidate subgraph for the quantum circuit; if the fidelity of the second candidate subgraph is greater than the fidelity of the accepted subgraph, setting the accepted subgraph to be the second candidate subgraph; if the fidelity of the second candidate subgraph is less than or equal to the fidelity of the accepted subgraph, setting the accepted subgraph to be the second candidate subgraph with a time-dependent probability.