Is it possible to send multiple data bits on a single wire at once?
16-QAM transmits 4 bits simultaneously by modulating both the phase angle and the carrier amplitude: -



At the receiving end, the noise added during transmission propagation may make the bits look like this: -



But, providing there is still a gap between data received and the halfway point between symbols you can detect it.

So, if you understand the noise in your channel and your channel bandwidth is accommodating, you will be able to send more than one bit simultaneously (as suggested by the Shannon-Hartley theorum): -