Vivien M. Kendon,* Karol Życzkowski, and William J. Munro Optics Section, Blackett Laboratory, Imperial College, London SW7 2BW, United Kingdom Center for Theoretical Physics, Polish Academy of Sciences, Al. Lotników 32/44, 02-668 Warszawa, Poland Hewlett-Packard Laboratories, Filton Road, Stoke Gifford, Bristol BS34 8QZ, United Kingdom ~Received 18 March 2002; revised manuscript received 31 Ma...
