Fig. 3: Simulations of two-qubit entanglement in ESR-STM showing expected measurement outcomes, where we compare the expectation values 〈Sz〉 of each spin (inaccessible in the experiment) as well as the indirect read-out \({{\mathcal{W}}}_{R}\) of these values through the sensor spin. | npj Quantum Information

Fig. 3: Simulations of two-qubit entanglement in ESR-STM showing expected measurement outcomes, where we compare the expectation values 〈Sz〉 of each spin (inaccessible in the experiment) as well as the indirect read-out \({{\mathcal{W}}}_{R}\) of these values through the sensor spin.

From: Protocol for certifying entanglement in surface spin systems using a scanning tunneling microscope

Fig. 3

From top to bottom (a, c, e) we compare the entangled subspace for different initial states (\(\left\vert\! \uparrow \uparrow \right\rangle ,\left\vert\! \uparrow \downarrow \right\rangle\)). The (b, d, f) on the right side shows simulations for the same system but for not entangled states (achieved by removing the Hadamard gate), which could serve as empty cycle for the lock-in detection in the ESR-STM experiment. The system parameters are as shown in Fig. 2a, T = 10 mK, no relaxation for spins A, B, and T1 = 20 ns for the sensor spin during read-out.

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