Quantum Fan-out: Circuit Optimizations and Technology Modeling¶
Gokhale, P., Koretsky, S., Huang, S., Majumder, S., Drucker, A., Brown, K. R., & Chong, F. T.. (2021). Quantum Fan-out: Circuit Optimizations and Technology Modeling. https://doi.org/10.1109/qce52317.2021.00045
SIMD:
preserve a program’s logical correctness by respecting constraints known as hazards.
In Quantum Circuit, the structural hazard is:
exclusive activation: a qubit can be involved in at most one operation per timestep
In Quantum circuit, the parallelism is enabled by:
simultaneously executing instructions on disjoint qubits.
Idea¶
Observation:
the structural hazard of exclusive activation is not actually enforced by most quantum hardware.
In fact, it can be more natural for a quantum processor to simultaneously execute multiple operations on shared qubits through global interactions.
e.g.
Actually these four CNOT can be performed together.
Controlled-U¶
decomposing U into a form amenable to ‘alignment’ of CNOTs
Into two parts:
Shared-Control Single Qubit Gates¶
we only have access to the fan-out SIMD primitive
This pattern extends ad infinitum to more qubits—the total depth will always consist of five layers: two fan-out layers and three single-qubit gate layers.
Shared-Control Toffoli’s¶
dependency between the right-most red CNOT and the subsequent blue CNOT is in fact a false dependency.
Application¶
SWAP Test¶
inner product
Hadamard Test¶
