Fig. 2: Characterization of the nonlocal CNOT gate.

a Truth table of the CNOT gate. The diagram shows the probability P of measuring a certain output state for the four input states: \(\left\vert HH\right\rangle\), \(\left\vert HV\right\rangle\), \(\left\vert VH\right\rangle\), \(\left\vert VV\right\rangle\). The expected output states for an ideal CNOT gate are shown as light-shaded bars. b–e Density matrices of generated Bell states. The diagrams show the real parts of the density matrices of the generated states with inputs of \(\left\vert+\right\rangle \left\vert H\right\rangle\), \(\left\vert+\right\rangle \left\vert V\right\rangle\), \(\left\vert -\right\rangle \left\vert H\right\rangle\), \(\left\vert -\right\rangle \left\vert V\right\rangle\), respectively. The ideal Bell states are indicated as shaded bars in the plots. The error bars are one standard deviation.