Power-optimal, stabilized entangling gate between trapped-ion qubits

Abstract

To achieve scalable quantum computing, improving entangling-gate fidelity and its implementation-efficiency are of utmost importance. We present here a linear method to construct provably power-optimal entangling gates on an arbitrary pair of qubits on a trapped-ion quantum computer. This method leverages simultaneous modulation of amplitude, frequency, and phase of the beams that illuminate the ions and, unlike the state of the art, does not require any search in the parameter space. The linear method is extensible, enabling stabilization against external parameter fluctuations to an arbitrary order at a cost linear in the order.

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.…”

“…More complicated dynamics and modulation [2,11,19,43] are used to realize the canonical Mølmer-Sørensen (MS) two-qubit gate [38,39], which implements an XX(𝜃 ) = exp(−𝑖𝜃𝜎 𝑥 ⊗ 𝜎 𝑥 /2). This gate uses vibrational modes of the ion chain as the medium of information exchange, akin to a memory bus.…”

“…This architecture limits sources of noise that may disturb quantum information, and leading implementations report a stability window (coherence time) of 10 11 sec for amplitudes (𝑇 1 time) and 90 min for phases (𝑇 2 time) [40]. 2 1 Here commercial means "supporting paying customers. " 2 Long 𝑇 1 and 𝑇 2 coherence times are crucial metrics for reliable quantum computation.…”

“…2 1 Here commercial means "supporting paying customers. " 2 Long 𝑇 1 and 𝑇 2 coherence times are crucial metrics for reliable quantum computation. Short coherence times limit the depth of quantum computations before the information is lost to decoherence.…”

“…|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] …”