Figure 1

Experimental setup and energy levels of the atoms. (a) Light described by the annihilation operator ${\widehat{a}}_{\mathrm{i}\mathrm{n}}$ is shined onto a cavity containing two atoms. By detecting the reflected light, described by ${\widehat{a}}_{\mathrm{o}\mathrm{u}\mathrm{t}}$, we perform a QND detection of the presence of atoms interacting with the field. (b) The atoms have two ground states $|0⟩$ and $|1⟩$ and an excited state $|e⟩$ which decays to the ground state $|1⟩$ with a rate $\gamma$. The cavity field couples the state $|1⟩$ to the state $|e⟩$ with a coupling strength $g$ and a detuning $\delta$.Reuse & Permissions

Figure 2

Success probability with a Fock state as input. Full lines assume a single detection, the dashed line is for double detection. Starting from above the full lines have the fidelities $F=0.8$, $0.9$, and $0.99$. Within the present model the fidelity of the dashed line is unity. The probabilities assume a detector efficiency of unity. With nonideal detectors the full (dashed) lines should be multiplied by $\eta$ (${\eta }^2$).Reuse & Permissions

Figure 3

Success probability for $F\ge 0.9$ with coherent light as an input. Full lines assume a single detection, and dashed lines are for double detection. The upper (lower) curves are for a detector efficiency $\eta =1$ ($\eta =0.5$).Reuse & Permissions