Abstract: Method and circuit for reading a value {circumflex over (?)}z stored in a quantum information unit (qubit) memory having a qubit frequency ?a, with a resonator defined by a resonator damping rate ?, a resonator frequency ?r, a resonator electromagnetic field characterized by ↠and â, a longitudinal coupling strength gz, an output âout and a longitudinal coupling gz{circumflex over (?)}z(â†+â). At a quantum non-demolition (QND) longitudinal modulator, periodically modulating the longitudinal coupling strength gz with a signal of amplitude {tilde over (g)}z at least three (3) times greater than the resonator damping rate ? and of frequency ?m with ?m+? resonant with ?r, wherein the longitudinal coupling strength gz varies over time (t) in accordance with gz(t)=gz+{tilde over (g)}z cos(?mt) with gz representing an average value of gz and at a QND homodyne detector, measuring the value {circumflex over (?)}z of the qubit memory from a phase reading of the output {circumflex over (?)}out.

Abstract: Method and circuit for reading a value {circumflex over (?)}z stored in a quantum information unit (qubit) memory having a qubit frequency ?a, with a resonator defined by a resonator damping rate ?, a resonator frequency ?r, a resonator electromagnetic field characterized by ↠and â, a longitudinal coupling strength gz, an output âout and a longitudinal coupling gz{circumflex over (?)}z(â†+â). At a quantum non-demolition (QND) longitudinal modulator, periodically modulating the longitudinal coupling strength gz with a signal of amplitude {tilde over (g)}z at least three (3) times greater than the resonator damping rate ? and of frequency ?m with ?m+? resonant with ?r, wherein the longitudinal coupling strength gz varies over time (t) in accordance with gz(t)=gz+{tilde over (g)}z cos(?mt) with gz representing an average value of gz and at a QND homodyne detector, measuring the value {circumflex over (?)}z of the qubit memory from a phase reading of the output {circumflex over (?)}out.