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Journal of Experimental and Theoretical Physics Letters

Reduction of the Systematic Error in the Readout of 171Yb+-Ion Optical Qubits Using Microwave Pumping

Yury P. Anosov, A. S. Borisenko, Ilia V. Zalivako, Nikita V. Semenin, Ilya A. Semerikov, Ksenia Yu. Khabarova, N. Kolachevsky

Published Apr 1, 2026• 0 citations
Publisher

Abstract

An increase in the readout fidelity of an optical qubit in a 171Yb+ ion by adding a microwave pumping stage before the measurement has been experimentally demonstrated. The introduction of a microwave $$\pi $$ -pulse between the hyperfine components of the ion ground state before the readout makes it possible to avoid the optical pumping stage at the beginning of the measurement, which leads to a systematic error in the state determination. The conclusions of the theoretical model of the readout process have been experimentally confirmed and an increase in the readout accuracy from (98.98 ± 0.10)% to (99.48 ± 0.07)% has been demonstrated.

DOI
10.1134/s0021364026600540

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An increase in the readout fidelity of an optical qubit in a 171Yb+ ion by adding a microwave pumping stage before the measurement has been experimentally demonstrated. The introduction of a microwave π\pi π -pulse between the hyperfine components of the ion ground state before the readout makes it possible to avoid the optical pumping stage at the beginning of the measurement, which leads to a systematic error in the state determination. The conclusions of the theoretical model of the readout process have been experimentally confirmed and an increase in the readout accuracy from (98.98 ± 0.10)% to (99.48 ± 0.07)% has been demonstrated.
A scheme based on a laser cooling system has been proposed to detect the state of an optical qubit in the 171Yb+ ion. Analytical expressions have been derived for the readout fidelity including the dark photon counts and background. The parameters of the experiment have been numerically optimized to minimize the readout infidelity. The upper bound on the fidelity associated with a transient process at the beginning of the measurement procedure has been determined as 99.4%. The characteristic parameters of detection ensuring a sufficient proximity to the upper bound have been found.
We propose and demonstrate a protocol for high-fidelity indirect readout of trapped ion hyperfine qubits, where the state of a 9Be+^{9}{\mathrm{Be}}^{+}9Be+ qubit ion is mapped to a 25Mg+^{25}{\mathrm{Mg}}^{+}25Mg+ readout ion using laser-driven Raman transitions. By partitioning the 9Be+^{9}{\mathrm{Be}}^{+}9Be+ ground-state hyperfine manifold into two subspaces representing the two qubit states and choosing appropriate laser parameters, the protocol can be made robust to spontaneous photon scattering errors on the Raman transitions, enabling repetition for increased readout fidelity. We demonstrate combined readout and back-action errors for the two subspaces of ${1.2}_{\ensuremath{-}0.6}^{+1.1}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ and ${0}_{\ensuremath{-}0}^{+1.9}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ with 68% confidence while avoiding decoherence of spectator qubits due to stray resonant light that is inherent to direct fluorescence detection.
We demonstrate single-shot qubit readout with a fidelity sufficient for fault-tolerant quantum computation. For an optical qubit stored in 40Ca+ we achieve 99.991(1)% average readout fidelity in 10(6) trials, using time-resolved photon counting. An adaptive measurement technique allows 99.99% fidelity to be reached in 145 micros average detection time. For 43Ca+, we propose and implement an optical pumping scheme to transfer a long-lived hyperfine qubit to the optical qubit, capable of a theoretical fidelity of 99.95% in 10 micros. We achieve 99.87(4)% transfer fidelity and 99.77(3)% net readout fidelity.
Ultracold ions provide one of the most promising platforms for quantum computing and make it possible to reach record coherence times, the fidelity of preparation and readout operations, and single- and two-qubit operations. Encoding quantum information in an optical qubit based on the 2S1/2(F=0,mF=0)^{2}{{S}_{{1/2}}}(F = 0,{{m}_{F}} = 0)2S1/2​(F=0,mF​=0) → 2D3/2(F=2,mF=0)^{2}{{D}_{{3/2}}}(F = 2,{{m}_{F}} = 0)2D3/2​(F=2,mF​=0) quadrupole transition in the 171Yb+ ion at a wavelength of 435.5 nm, which has potential advantages over similar systems in the scaling of the number of qubits and their sensitivity to fluctuations of the magnetic field, is proposed and experimentally studied. The proposed optical qubit in ytterbium is compared to other most widespread types of ion qubits. Experimental results on the implementation of the Pauli-X single-qubit operation are given. The fidelity of the operation is 96% after correction to the error of preparation and readout and is limited by the temperature of the ion.
We are developing a highly miniaturized171Yb+ion clock that operates in a continuous microwave-optical double-resonance mode by continuously probing the 12.6 GHz hyperfine transition in the171Yb+ion. In the continuous mode, the clock will not require optical shutters and electrical switches, minimizing the components of the clock. Here, we demonstrate operating the ion clock with ions trapped in a permanently sealed, passively pumped vacuum package 3 cm3in volume. With resonant 369-nm light continuously illuminating the ions, the light shift is a substantial systematic shift of the hyperfine ground state that must to be well characterized and controlled. We present measurements of the liaht shift and demonstrate clock frequency instabilities below 1×10-12at 100 s of averaging.
We report high-fidelity state readout of a trapped ion qubit using a trap-integrated photon detector. We determine the hyperfine qubit state of a single ^{9}Be^{+} ion held in a surface-electrode rf ion trap by counting state-dependent ion fluorescence photons with a superconducting nanowire single-photon detector fabricated into the trap structure. The average readout fidelity is 0.9991(1), with a mean readout duration of 46 μs, and is limited by the polarization impurity of the readout laser beam and by off-resonant optical pumping. Because there are no intervening optical elements between the ion and the detector, we can use the ion fluorescence as a self-calibrated photon source to determine the detector quantum efficiency and its dependence on photon incidence angle and polarization.