Fig. 3: Memory qubit coherence and readout.
From: Qubit teleportation between non-neighbouring nodes in a quantum network
a, Gate sequence on Bob for entanglement generation with the communication qubit while preserving states stored on the memory qubit. Entanglement generation attempts are repeated until success or a predetermined timeout. On success in the nth attempt, a phase feed-forward is applied to maintain the correct reference frame of the memory qubit18, followed by a decoupling pulse on the memory qubit. The decoupling πM pulse causes a Z rotation on the communication qubit. Afterwards, we rephase the memory qubit for the same amount of time as it took to herald entanglement (by applying q blocks of XY8 decoupling sequences on the communication qubit, in which q depends on the number of entanglement attempts needed n) and we end with another phase feed-forward on the memory qubit, to compensate for any phase picked up during this decoupling. b, Bloch vector length of a superposition state stored on the memory qubit for different number of entanglement attempts or a time-equivalent wait element. In the case of no decoupling (no πM) on the memory qubit, the gates in the yellow shaded box in a are left out. The grey dashed line indicates the chosen timeout of 1,000 entanglement attempts. c, Gate sequence for the basis-alternating repetitive readout of the memory qubit. d, Readout fidelity for each readout repetition, for states \(|0\rangle \) and \(|1\rangle \) e, Readout fidelity of the basis-alternating repetitive readout scheme for different number of readout repetitions. f, Fraction of inconsistent readout patterns for different number of readout repetitions. In d–f, the dashed lines show a numerical model using measured parameters. All error bars represent one standard deviation.
