Single-photon limit of dispersive readout of a qubit with a photodetector

Single-photon switch controlled by a qubit embedded in an engineered electromagnetic environment

“…As it was pointed out in Ref. [66], the use of the single-photon probe allows one to avoid the readout errors arising from the nonorthog-onality of the probe state, which is always the case for the coherent-state readout pulses. The high-efficient ondemand sources of microwave single-photon pulses are readily available [70,71].…”

“…The high-efficient ondemand sources of microwave single-photon pulses are readily available [70,71]. Moreover, one can employ a detector of itinerant photons [72] attached to the output waveguide of the switch to provide a "click" for a particular state of the qubit [66]. When one prepares the qubit in the ground state, the probe photon is transmitted through the switch to the output waveguide and the photodetector clicks.…”

“…which is referred to as a switching contrast by analogy with a measurement contrast employed for the characterization of the accuracy of qubit measurement [65,66]. In Eq.…”

Signatures and characterization of dominating Kerr nonlinearity between two driven systems with application to a suspended magnetic beam

“…[8] and references therein). Dispersive interaction of a superconducting qubit and resonator photons, which is of a cross-Kerr form in the effective Hamiltonian [9][10][11], is routinely used for fast high-fidelity quantum nondemolition readout of a qubit [12,13] and can be used for the quantum nondemolition measurement of the radiation state [14].…”

“…Usually, that means that the system has to be cooled down close to the ground state of mechanical vibrations, in practice to the temperature of a few millikelvin [24,25]. Theory wise, even linear interactions are not trivial to study in quantum systems [11,26]. Study of a nonlinear quantum coupling is even more challenging technically-for example, see Ref.…”