Efficient Stabilized Two-Qubit Gates on a Trapped-Ion Quantum Computer

Detecting Qubit-coupling Faults in Ion-trap Quantum Computers

“…The quality of these approximate methods can be tested directly by comparing theoretical predictions to experimental results. Results reported in the literature [2,3,42] show that the experimental results are in excellent agreement with the theoretical prediction. The agreement indicates the failure modes of MS gates on today's ion-trap QCs are well understood, justifying our focus on the specific error models we discuss next.…”

“…All-pairs qubit connectivity provides a decisive advantage in harnessing the computational power of an ion-trap QC [12], and often the feasibility of a given computation on a given QC [21]. Applying fast gates to a remote qubit pair requires substantially more power in the driving signals than for a nearby pair [3]. Therefore, just like in VLSI layouts, shorter connections are preferred.…”

“…With the power to couple arbitrary pairs of qubits, comes the responsibility to ensure that qubit couplings are properly calibrated and can perform accurate gate operations [22]. Therefore, the lifecycle 3 of an ion-trap QC interchanges operational periods and rounds of recalibration. Figure 2 outlines the lifecycle of a commercial iontrap QC.…”

“…|00⟩ − 𝑖 |11⟩), so that the lack of |01⟩ and |10⟩ and the balance between |00⟩ and |11⟩ are indicative of perfect gate fidelity.As a more detailed example, consider evaluating the MS-gate fidelity in the case where XX(𝜋/2) induces a perfect balance between |00⟩ and |11⟩. When the gate is applied to, say, ions 𝑖 and 𝑗, the average fidelity (over arbitrary two-qubit input states) may be computed as[2,3,42] …”

“…Since the dominant failure modes of contemporary MS gates on ion-trap QCs are known, it is common to use approximate methods, which we illustrate next.On an ion-trap QC, MS gates tend to have smaller gate fidelities than single-qubit gates. In the literature[2,3], MS gate fidelities are typically approximated by first applying XX(𝜋/2) to |00⟩ and measuring (𝑖) the populations of |01⟩ and |10⟩ and (𝑖𝑖) the balance between the populations of |00⟩ and |11⟩. Note that in the absence of inaccuracies the generated state should be 1…”