Fig. 4: Different ququart readout schemes.
From: An architecture for two-qubit encoding in neutral ytterbium-171 atoms
a Two-round deterministic readout of ququart states. Two stretched transitions 1S0 ↔ 3P1 are simultaneously driven, and the resultant photons are detected in an indistinguishable manner, effectively measuring the “o”-qubit. Note that the cyclicity of the transitions ensures that the population in 1S0 substates remains in the same state after measurement. Afterward, an intra-ququart SWAP is applied, swapping the populations in \(\left\vert 01\right\rangle\) and \(\left\vert 10\right\rangle\) states. Finally, the same two stretched transitions are used to effectively measure the “n”-qubit before the swap operation. The four combinations of two readout results can thus be mapped to the four ququart states. b Single-state QND readout of \(\left\vert 00\right\rangle\), within the 1S0 ground state manifold. c The two-qubit analogue of the single-state QND measurement via an ancilla qubit and a Toffoli gate.
