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arXiv:2504.03853

Multiqubit GHZ state preparation with $^{171}\text{Yb}^+$ ions for frequency standards

Korolkov Andrey Evgenyevich, Ilia V. Zalivako, Borisenko, A. S., Smirnov, V. N., Pavel A. Kamenskikh, Ilya A. Semerikov, Ksenia Yu. Khabarova, N. Kolachevsky

Published Apr 4, 2025• 0 citations
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Abstract

Multiqubit Greenberger-Horne-Zeilinger (GHZ) state preparation is demonstrated on two to eight qubits in the chain of ten $^{171}Yb^+$ ions in the linear Paul trap with a sequence of single-qubit and two-qubit operations and pulsed dynamical decupling. Fidelity of the 8-qubit GHZ state is estimated to be $58.9 \pm 0.6\%$. The expected enhanced sensitivity of the parity oscillations phase to the analyzing pulse phase is observed. This result is a step towards a multi-ion optical clock with ytterbium ions with frequency averaging following $1/N$ scaling law in contrast to the slower $1/\sqrt{N}$ scaling for an ensemble of independent particles in case when the decoherence is dominated by the spontaneous decay.

DOI
10.48550/arxiv.2504.03853

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Multiqubit GHZ state preparation with 171Yb+^{171}\text{Yb}^+171Yb+ ions for frequency standards
Multiqubit Greenberger-Horne-Zeilinger (GHZ) state preparation is demonstrated on two to eight qubits in the chain of ten 171Yb+^{171}Yb^+171Yb+ ions in the linear Paul trap with a sequence of single-qubit and two-qubit operations and pulsed dynamical decupling. Fidelity of the 8-qubit GHZ state is estimated to be 58.9±0.6%58.9 \pm 0.6\%58.9±0.6%. The expected enhanced sensitivity of the parity oscillations phase to the analyzing pulse phase is observed. This result is a step towards a multi-ion optical clock with ytterbium ions with frequency averaging following 1/N1/N1/N scaling law in contrast to the slower 1/N1/\sqrt{N}1/N​ scaling for an ensemble of independent particles in case when the decoherence is dominated by the spontaneous decay.
Greenberger–Horne–Zeilinger states on two to eight qubits in a chain of ten 171Yb+ ions in a linear Paul trap has been prepared by executing a sequence of one- and two-qubit operations on the corresponding ions. The obtained states have been analyzed and their fidelity for the Greenberger–Horne–Zeilinger state on eight qubits has been estimated at (58.9 ± 0.6)%. The expected increase in the sensitivity of parity oscillations as a function of the phase of the probe laser pulse has also been demonstrated. This result is an important step towards the creation of a multiparticle ytterbium ion optical clock with frequency averaging according to the law 1/N in contrast to the slower law 1/N1{\text{/}}\sqrt N 1/N​ for an ensemble of independent particles in the case where decoherence is dominated by spontaneous decay.
Abstract Generating and detecting genuine multipartite entanglement (GME) of sizeable quantum states prepared on physical devices is an important benchmark for highlighting the progress of near-term quantum computers. A common approach to certify GME is to prepare a Greenberger-Horne-Zeilinger (GHZ) state and measure a GHZ fidelity of at least 0.5. We measure the fidelities using multiple quantum coherences of GHZ states on 11 to 27 qubits prepared on the IBM Quantum ibmq_montreal device. Combinations of quantum readout error mitigation (QREM) and parity verification error detection are applied to the states. A fidelity of 0.546 ± 0.017 was recorded for a 27-qubit GHZ state when QREM was used, demonstrating GME across the full device with a confidence level of 98.6%. We benchmarked the effect of parity verification on GHZ fidelity for two GHZ state preparation embeddings on the heavy-hexagon architecture. The results show that the effect of parity verification, while relatively modest, led to a detectable improvement of GHZ fidelity.
Hybrid entangled states are essential quantum resources not only for hybrid quantum communication but also for creating robust hybrid quantum networks and processors.By considering a circuit-cavity quantum electrodynamics (QED) system composed of a superconducting (SC) qutrit (a three-level quantum system) and n microwave cavities, we here present a method to prepare hybrid Greenberger-Horne-Zeilinger (GHZ) entangled states of n+1 qubits.The use of a single SC qutrit as the coupler leads to a significant saving in circuit hardware resources.The GHZ state preparation is deterministic without measurement.The operation time for the GHZ state preparation is independent of the number of qubits.Decoherence from the highest energy level of the SC qutrit is suppressed because this level remains unoccupied during the GHZ state preparation.Our numerical simulations demonstrate that the high-fidelity generation of hybrid GHZ states of an SC qubit and three photonic qubits is achievable within current circuit-QED technology.The proposed scheme possesses universality and is suitable for preparing hybrid GHZ states of a matter qubit (e.g., atomic qubit, trapped ion, quantum dot, magnon, NV center, and SC qubit with various types) and multiple photonic qubits across a wide range of physical systems.
A multi-ion optical clock with 5×10−19\mathbf{5 \times 10^{-19}}5×10−19 uncertainty
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Important tasks in cavity quantum electrodynamics include the generation and control of quantum states of spatially separated particles distributed in different cavities. An interesting question in this context is how to prepare entanglement among particles located in different cavities, which are important for large-scale quantum information processing. We here consider a multi-cavity system where cavities are coupled to a superconducting (SC) qubit and each cavity hosts many SC qubits. We show that all intra-cavity SC qubits plus the coupler SC qubit can be prepared in an entangled Greenberger–Horne–Zeilinger (GHZ) state, by using a single operation and without the need of measurements. The GHZ state is created without exciting the cavity modes; thus greatly suppressing the decoherence caused by the cavity-photon decay and the effect of unwanted inter-cavity crosstalk on the operation. We also introduce two simple methods for entangling the intra-cavity SC qubits in a GHZ state. As an example, our numerical simulations show that it is feasible, with current circuit-QED technology, to prepare high-fidelity GHZ states, for up to nine SC qubits by using SC qubits distributed in two cavities. This proposal can in principle be used to implement a GHZ state for an arbitrary number of SC qubits distributed in multiple cavities. The proposal is quite general and can be applied to a wide range of physical systems, with the intra-cavity qubits being either atoms, NV centers, quantum dots, or various SC qubits.