Why can information not be transmitted via phase velocity?

[San K]

why can information not be transmitted via phase velocity (of a matter wave)?

can we not change the phase at will?

 

[Bill_K]

Yes, but the change won't keep up with the phase!

 

[mfb]

A uniform wave would not transmit any information - just energy and momentum. To transfer information, you have to modify it in some way which can be read by the receiver. And this modification travels with the signal speed (which is equivalent to the group velocity without losses).

 

[San K]

Yes, but the change won't keep up with the phase!

thanks Bill and mfb, well put