Source-linked AI summary
Process tomography of ion trap quantum gates
M. Riebe, K. Kim, P. Schindler, T. Monz, P. O. Schmidt, T. K. Koerber, W. Haensel, H. Haeffner, C. F. Roos, R. Blatt
TL;DR
Because CNOT gates are central to trapped-ion processing, the paper uses process tomography to compare two pulse sequences and asks whether single-gate data predict concatenated behavior. Fidelity improved from 71% to almost 93%, while measured two-gate results differed from single-gate-based predictions.
Problem
The paper asks whether experimental performance of successive quantum gates can be inferred from single-gate performance, a question relevant to algorithms that apply multiple gates.
Source: pp. 3–4Method
The authors use quantum process tomography to compare two CNOT pulse sequences and test whether single-gate results predict concatenated-gate performance.
Source: pp. 1, 2, 4Results
CNOT fidelity rose from 71% to almost 93%, while measured two-gate performance differed from predictions based on single-gate tomography.
Source: pp. 1, 4Takeaways & Limitations
Process tomography supports comparisons across pulse sequences and experimental parameters, and concatenated-gate tomography demonstrates the importance of assessing gates within larger sequences.
Source: p. 4Imperfect addressing affects neighboring ions at a 2–3% Rabi-frequency ratio, and decoherence arises mainly from laser-frequency and ambient magnetic-field fluctuations.
Source: p. 2
Abstract
from arXiv · showhide
A crucial building block for quantum information processing with trapped ions is a controlled-NOT quantum gate. In this paper, two different sequences of laser pulses implementing such a gate operation are analyzed using quantum process tomography. Fidelities of up to 92.6(6)% are achieved for single gate operations and up to 83.4(8)% for two concatenated gate operations. By process tomography we assess the performance of the gates for different experimental realizations and demonstrate the advantage of amplitude--shaped laser pulses over simple square pulses. We also investigate whether the performance of concatenated gates can be inferred from the analysis of the single gates.