Improved Quantum Communication Complexity Bounds for Disjointness and Equality
Abstract
We prove new bounds on the quantum communication complexity of the disjointness and equality problems. For the case of exact and nondeterministic protocols we show that these complexities are all equal to n+1, the previous best lower bound being n/2. We show this by improving a general bound for nondeterministic protocols of de Wolf. We also give an O(sqrt{n}c^{log^* n})qubit boundederror protocol for disjointness, modifying and improving the earlier O(sqrt{n}log n) protocol of Buhrman, Cleve, and Wigderson, and prove an Omega(sqrt{n}) lower bound for a large class of protocols that includes the BCWprotocol as well as our new protocol.
 Publication:

arXiv eprints
 Pub Date:
 September 2001
 arXiv:
 arXiv:quantph/0109068
 Bibcode:
 2001quant.ph..9068H
 Keywords:

 Quantum Physics;
 Computer Science  Computational Complexity
 EPrint:
 11 pages LaTeX