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Quantum Lower Bounds for Fanout

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arxiv quant-ph/0312208 v1 pith:XBNJIE67 submitted 2003-12-28 quant-ph

classification quant-ph
keywords circuitsdepthfanoutlowerwhenboundboundsquantum
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abstract

We prove several new lower bounds for constant depth quantum circuits. The main result is that parity (and hence fanout) requires log depth circuits, when the circuits are composed of single qubit and arbitrary size Toffoli gates, and when they use only constantly many ancill\ae. Under this constraint, this bound is close to optimal. In the case of a non-constant number $a$ of ancillae, we give a tradeoff between $a$ and the required depth, that results in a non-trivial lower bound for fanout when $a = n^{1-o(1)}$.

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Cited by 2 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Quantum State Readout via Overlap-Based Feature Extraction

    quant-ph 2025-05 conditional novelty 6.0 of 10

    A quantum state is read out by measuring overlaps against Lorentzian basis states and fitting the coefficients classically, reducing the number of measurements for localized, continuous states.

  2. Quantum circuit lower bounds in the magic hierarchy

    quant-ph 2025-04 conditional novelty 6.0 of 10

    A Clifford circuit followed by a shallow two-qubit circuit cannot prepare several explicit entangled states, including some topological ground states and quantum codes.

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