Capacity of a simultaneous quantum secure direct communication scheme between the central party and other M parties

We analyze the capacity of a simultaneous quantum secure direct communication scheme between the central party and other $M$ parties via $M+1$-particle GHZ states and swapping quantum entanglement. It is shown that the encoding scheme should be secret if other $M$ parties wants to transmit $M+1$ bit classical messages to the center party secretly. However when the encoding scheme is announced publicly, we prove that the capacity of the scheme in transmitting the secret messages is 2 bits, no matter how big $M$ is.Comment: 3 page

{4-Bromo-2-[(2-morpholinoeth­yl)imino­meth­yl]phenolato}iodido(methanol)zinc(II)

The title compound, [Zn(C13H16BrN2O2)I(CH3OH)], is a new mononuclear zinc(II) complex synthesized by the reaction of equimolar quanti­ties of 5-bromo­salicylaldehyde, 2-morpholinoethyl­amine and ZnI2 in methanol. The Zn atom is four-coordinate in a distorted tetra­hedral geometry, binding to a phenolate O and an imine N atom of the Schiff base ligand, the O atom of a methanol mol­ecule and one I− anion. In the crystal structure, adjacent mol­ecules are linked through inter­molecular O—H⋯O hydrogen bonds, forming centrosymmetric dimers