  We have realized a new interaction between superconducting qubits and a
readout cavity that results in the displacement of a coherent state in the
cavity, conditioned on the state of the qubit. This conditional state, when it
reaches the cavity-following, phase-sensitive amplifier, matches its measured
observable, namely the in-phase quadrature. In a setup where several qubits are
coupled to the same readout resonator, we show it is possible to measure the
state of a target qubit with minimal dephasing of the other qubits. Our results
suggest novel directions for faster readout of superconducting qubits and
implementations of bosonic quantum error-correcting codes.
