The Quantum Communication Complexity of the Pointer Chasing Problem: The Bit Version

  • Authors:
  • Rahul Jain;Jaikumar Radhakrishnan;Pranab Sen

  • Affiliations:
  • -;-;-

  • Venue:
  • FST TCS '02 Proceedings of the 22nd Conference Kanpur on Foundations of Software Technology and Theoretical Computer Science
  • Year:
  • 2002

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Abstract

We consider the two-party quantum communication complexity of the bit version of the pointer chasing problem when the 'wrong' player starts, originally studied by Klauck, Nayak, Ta-Shma and Zuckerman [7]. We show that in any quantum protocol for this problem, the two players must exchange 驴(n/k4) qubits. This improves the previous best lower bound of 驴(n/22O(k)) in [7], and comes significantly closer to the best upper bounds known: O(n + k log n) (classical deterministic [12]) and O(k log n + n/k (log(驴 k/2驴) n+log k)) (classical randomised [7]). Our result demonstrates a separation between the communication complexity of k and k - 1 round bounded error quantum protocols, for all k O((m/log2 m)1/5), where m is the size of the inputs to Alice and Bob. Earlier works could prove such a separation for much smaller k only. Our proof uses a round elimination argument for a class of quantum sampling protocols with correlated input generation, making better use of information-theoretic tools than previous works.