  An important desired ingredient of superconducting quantum circuits is a
readout scheme whose complexity does not increase with the number of qubits
involved in the measurement. Here, we present a readout scheme employing a
single microwave line, which enables simultaneous readout of multiple qubits.
Consequently, scaling up superconducting qubit circuits is no longer limited by
the readout apparatus. Parallel readout of 6 flux qubits using a frequency
division multiplexing technique is demonstrated, as well as simultaneous
manipulation and time resolved measurement of 3 qubits. We discuss how this
technique can be scaled up to read out hundreds of qubits on a chip.
