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Quantum Lower Bound for the Collision Problem

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arxiv quant-ph/0111102 v1 pith:TNAM24I3 submitted 2001-11-20 quant-ph cs.CC

classification quant-phcs.CC
keywords boundproblemlowerquantumthetacollisiongivewhether
verification ladder T0 review T1 audit T2 compute T3 formal
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The collision problem is to decide whether a function X:{1,..,n}->{1,..,n} is one-to-one or two-to-one, given that one of these is the case. We show a lower bound of Theta(n^{1/5}) on the number of queries needed by a quantum computer to solve this problem with bounded error probability. The best known upper bound is O(n^{1/3}), but obtaining any lower bound better than Theta(1) was an open problem since 1997. Our proof uses the polynomial method augmented by some new ideas. We also give a lower bound of Theta(n^{1/7}) for the problem of deciding whether two sets are equal or disjoint on a constant fraction of elements. Finally we give implications of these results for quantum complexity theory.

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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 Communication Lower Bounds for Search Problems via Matrix Discrepancy

    quant-ph 2026-07 accept novelty 7.5 of 10

    A matrix-discrepancy argument proves tight one-way quantum lower bounds for collision finding (Ω(N^{1/4})) and for streaming triangle finding (Ω(√Δ_V)) where Boolean-Hidden-Matching reductions fail.

  2. Ancilla-Efficient QSAMPLE Preparation for Reversible Markov Chains

    quant-ph 2026-05 unverdicted novelty 7.0 of 10

    A one-ancilla framework for QSAMPLE preparation via GQSP-based selective phase compilation embedded in fixed-point amplitude amplification, improving overlap dependence to inverse square-root minimum overlap.

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