Fig. 1: Sequence of quantum logic gates to demonstrate entanglement in ESR-STM.
From: Protocol for certifying entanglement in surface spin systems using a scanning tunneling microscope
a shows the pulse scheme using a quantum gate notation. From left to right this scheme applies a Hadamard gate to spin A, a negative CNOT gate, a pulse delay (or phase-sweep) gate, and a disentangling gate scheme. Finally, both states can be measured to determine their respective populations. b Bloch sphere shows the time-evolution of the entangled state on the equator. c Expected measurement signal for spin A and spin B when entangled and, in contrast, (d) the same measurement for two spins that are not entangled as emphasized by the density matrix in the inset.
