Alberto Bertoni Carlo Mereghetti Beatrice Palano Lower Bounds on the Size of Quantum Automata Accepting Unary Languages. 86-96 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2841&spage=86 2003 conf/ictcs/2003 ICTCS db/conf/ictcs/ictcs2003.html#BertoniMP03