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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.

  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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