Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2202.00903 · Quantum

Time-Optimal Two- and Three-Qubit Gates for Rydberg Atoms

Sven Jandura, Guido Pupillo

Published May 13, 2022• 151 citations
arXivHTMLPDF

Abstract

We identify time-optimal laser pulses to implement the controlled-Z gate and its three qubit generalization, the C 2 Z gate, for Rydberg atoms in the blockade regime. Pulses are optimized using a combination of numerical and semi-analytical quantum optimal control techniques that result in smooth Ansätze with just a few variational parameters. For the CZ gate, the time-optimal implementation corresponds to a global laser pulse that does not require single site addressability of the atoms, simplifying experimental implementation of the gate. We employ quantum optimal control techniques to mitigate errors arising due to the finite lifetime of Rydberg states and finite blockade strengths, while several other types of errors affecting the gates are directly mitigated by the short gate duration. For the considered error sources, we achieve theoretical gate fidelities compatible with error correction using reasonable experimental parameters for CZ and C 2 Z gates.

DOI
10.22331/q-2022-05-13-712

Related papers

High-fidelity Rydberg controlled-Z gates with optimized pulses

T H Chang, Tzyy-Ing Wang, H. H. Jen +1 more

Abstract High-fidelity controlled-Z (CZ ) gates are essential and mandatory to build a large-scale quantum computer. In neutral atoms, the strong dipole–dipole interactions between their Rydberg states make them one of the pioneering platforms to implement CZ gates. Here we numerically investigate the optimized pulses to generate a high-fidelity Rydberg C Z gate in a three-level ladder-type atomic system. By tuning the temporal shapes of Gaussian or segmented pulses, the populations on the intermediate excited states are shown to be suppressed within the symmetric gate operation protocol, which leads to a C Z gate with a high Bell fidelity up to 99.92 % . These optimized pulses are robust to thermal fluctuations and the excitation field variations. Our results promise a high-fidelity and fast gate operation under amenable and controllable experimental parameters, which goes beyond the adiabatic operation regime under a finite blockade strength.

arXiv:2303.16395•New Journal of Physics•Nov 24, 2023•15 citations

Robust control and optimal Rydberg states for neutral atom two-qubit gates

Madhav Mohan, Robert de Keijzer, S. J. J. M. F. Kokkelmans

We investigate the robustness of two-qubit gates to deviations of experimental controls on a neutral atom platform utilizing Rydberg states. We construct robust controlled-Z gates---employing techniques from quantum optimal control---that retain high Bell-state fidelity $F>0.999$ in the presence of significant deviations of the coupling strength to the Rydberg state. Such deviations can arise from laser intensity noise and atomic motion in an inhomogeneous coupling field. We also discuss methods to mitigate errors due to deviations of the laser detuning. The designed pulses operate on timescales that are short compared to the fundamental decay timescale set by spontaneous emission and blackbody radiation. We account for the finite lifetime of the Rydberg state in both the optimization and fidelity calculations---this makes the gates conducive to noisy intermediate-scale quantum experiments, meaning that our protocols can reduce infidelity on near-term quantum computing devices. We calculate physical properties associated with infidelity for strontium-88 atoms---including lifetimes, polarizabilities, and blockade strengths---and use these calculations to identify optimal Rydberg states for our protocols, which allows for further minimization of infidelity.

arXiv:2212.10159•Physical Review Research•Jul 25, 2023•40 citations

Quantum gates for neutral atoms with three-photon excitation of Rydberg states

Ksenia Kozenko

We have numerically simulated a two-qubit CZ gate for ultracold neutral atoms based on Rydberg blockade, utilizing three-photon excitation to Rydberg states. The three-photon laser excitation overcomes lack of individual addressability for entangling gates in atomic arrays, which is a key limitation of conventional schemes of quantum information processing with neutral atoms. This is achieved by mitigating sensitivity to laser intensity fluctuations caused by spatial motion of atoms in optical tweezers. Our goal is to investigate the gate performance when three-photon laser excitation is used. We considered Levine-Pichler gate which applies an abrupt phase jump at the center of the control laser pulse. Our simulation accounts for the influence of spontaneous decay of intermediate and Rydberg states and finite Rydberg excitation energies. We obtained the maximum fidelity of the CZ gate around 99.7% for the model based on probability amplitudes and 99.72% for the model based on density matrices. This value exceeds the threshold required for the application of quantum error correction protocols, demonstrating the promise of this gate for experimental realization. This work was supported by BASIS foundation Grant No. № 25-1-1-57-5

LaserPhys Youth School-Conference•Jan 1, 2025•0 citations

Numerically optimized amplitude-robust controlled-Z gate for ultracold neutral atoms with individual addressing capability

K. V. Kozenko, V. V. Gromyko, I. I. Beterov +1 more

We numerically optimized a scheme for a symmetric controlled-Z (CZ) gate based on the Rydberg blockade in neutral atoms, with the aim of increasing its robustness to variations in the Rabi frequency. The scheme exploits analytically defined phase profiles of the laser pulse and proves almost an order of magnitude more robust to Rabi-frequency variations than previously proposed protocols. We designed this amplitude-robust protocol with a smooth pulse shape and optimized it for a finite Rydberg blockade strength, which makes it suitable for experimental implementation in both single-photon and two-photon configurations. We further show that the protocol can be applied to individually addressed Rydberg excitation, accounting for the asymmetry of the Rabi frequencies of two atoms excited by tightly focused laser beams. This allows the effects of residual thermal motion of the trapped atoms to be reduced. Finally, we examined the performance of the protocol for single-photon and two-photon Rydberg excitation schemes at finite blockade strength, and demonstrated its advantages for individual addressing at finite temperatures of the trapped atoms.

quant-pharXiv:2604.12279•Apr 15, 2026•0 citations

Optimal quantum gates \nfor Rydberg atoms quantum computer

Pagano, Alice

Arrays of identical neutral atoms trapped in optical tweezers are a promising candidate for use in quantum computing. These platforms are highly scalable to large numbers of qubits and neutral atoms boost several attractive features as long coherence times and the possibility to be entangled via strong dipole-dipole interactions by driving them to highly excited Rydberg states. \nThe Thesis work is developed inside the framework of the QRydDemo project, whose aim in the next few years is to realize a neutral atom quantum processor with several hundred qubits. The smallest building blocks for the quantum computer are one and two-qubit gates: to entangle two atoms in the quantum register, a controlled-phase (CZ) gate will be implemented by shining fine-tuned laser pulses onto them. In this work, after giving a theoretical description of the Hamiltonian of two neutral atoms in the quantum register, a numerical simulation of this system is exploited to reproduce the behavior of the two-qubit CZ gate. Realistic effects are taken into account as finite temperature, imperfect Rydberg blockade, or decay out of the Rydberg state. A protocol with constant pulses is analyzed and its optimal parameters are found through classical optimizers. Then, time-dependent pulses are introduced and the optimal pulses are found through the optimal control algorithm dCRAB in an open-loop optimization. For the experimental realization of the gate, this analysis is of pivotal importance to know in which aspect more effort has to be put to maximize the experimental precision of the operation and thus improving the performance of the whole device \n

•Sep 1, 2021•0 citations

Optimized ancillary drive for fast Rydberg entangling gates

Rui Li, Min-Hua Zhang, Jing Qian

Reaching fast and robust two-qubit gates with low infidelities has been an outstanding challenge for the long-term goal of useful quantum computers. Typically, optimizing the pulse shapes can minimize the gate infidelity and improve its robustness to certain types of errors; yet it remains incapable of speeding up the gate execution time which is fundamentally restricted by the attainable Rabi frequency in a realistic setup. In this work, we develop a fast implementation of two-qubit CZ gates using optimized ancillary drive to enhance the two-photon Rabi frequency between the ground and Rydberg states.This ancillary drive can work in an error-robustness framework without increasing the original gate infidelity in the absence of the drive. Considering the experimentally feasible parameters for $^{87}$Rb atoms, we demonstrate that the execution time required for such CZ gates can be shortened by more than 30$\%$ as compared to standard two-photon protocols arising the gate fidelity above 0.9954 by taking account of all relevant error sources. Our results reduce the high-power laser requirement and unlock the potential toward fast, high-fidelity quantum operations for large-scale quantum computation with neutral atoms.

quant-pharXiv:2602.21512•Feb 26, 2026•0 citations
We identify time-optimal laser pulses to implement the controlled-Z gate and its three qubit generalization, the C 2 Z gate, for Rydberg atoms in the blockade regime. Pulses are optimized using a combination of numerical and semi-analytical quantum optimal control techniques that result in smooth Ansätze with just a few variational parameters. For the CZ gate, the time-optimal implementation corresponds to a global laser pulse that does not require single site addressability of the atoms, simplifying experimental implementation of the gate. We employ quantum optimal control techniques to mitigate errors arising due to the finite lifetime of Rydberg states and finite blockade strengths, while several other types of errors affecting the gates are directly mitigated by the short gate duration. For the considered error sources, we achieve theoretical gate fidelities compatible with error correction using reasonable experimental parameters for CZ and C 2 Z gates.
Abstract High-fidelity controlled-Z (CZ ) gates are essential and mandatory to build a large-scale quantum computer. In neutral atoms, the strong dipole–dipole interactions between their Rydberg states make them one of the pioneering platforms to implement CZ gates. Here we numerically investigate the optimized pulses to generate a high-fidelity Rydberg C Z gate in a three-level ladder-type atomic system. By tuning the temporal shapes of Gaussian or segmented pulses, the populations on the intermediate excited states are shown to be suppressed within the symmetric gate operation protocol, which leads to a C Z gate with a high Bell fidelity up to 99.92 % . These optimized pulses are robust to thermal fluctuations and the excitation field variations. Our results promise a high-fidelity and fast gate operation under amenable and controllable experimental parameters, which goes beyond the adiabatic operation regime under a finite blockade strength.
We investigate the robustness of two-qubit gates to deviations of experimental controls on a neutral atom platform utilizing Rydberg states. We construct robust controlled-Z gates---employing techniques from quantum optimal control---that retain high Bell-state fidelity F>0.999F>0.999F>0.999 in the presence of significant deviations of the coupling strength to the Rydberg state. Such deviations can arise from laser intensity noise and atomic motion in an inhomogeneous coupling field. We also discuss methods to mitigate errors due to deviations of the laser detuning. The designed pulses operate on timescales that are short compared to the fundamental decay timescale set by spontaneous emission and blackbody radiation. We account for the finite lifetime of the Rydberg state in both the optimization and fidelity calculations---this makes the gates conducive to noisy intermediate-scale quantum experiments, meaning that our protocols can reduce infidelity on near-term quantum computing devices. We calculate physical properties associated with infidelity for strontium-88 atoms---including lifetimes, polarizabilities, and blockade strengths---and use these calculations to identify optimal Rydberg states for our protocols, which allows for further minimization of infidelity.
We have numerically simulated a two-qubit CZ gate for ultracold neutral atoms based on Rydberg blockade, utilizing three-photon excitation to Rydberg states. The three-photon laser excitation overcomes lack of individual addressability for entangling gates in atomic arrays, which is a key limitation of conventional schemes of quantum information processing with neutral atoms. This is achieved by mitigating sensitivity to laser intensity fluctuations caused by spatial motion of atoms in optical tweezers. Our goal is to investigate the gate performance when three-photon laser excitation is used. We considered Levine-Pichler gate which applies an abrupt phase jump at the center of the control laser pulse. Our simulation accounts for the influence of spontaneous decay of intermediate and Rydberg states and finite Rydberg excitation energies. We obtained the maximum fidelity of the CZ gate around 99.7% for the model based on probability amplitudes and 99.72% for the model based on density matrices. This value exceeds the threshold required for the application of quantum error correction protocols, demonstrating the promise of this gate for experimental realization. This work was supported by BASIS foundation Grant No. № 25-1-1-57-5
We numerically optimized a scheme for a symmetric controlled-Z (CZ) gate based on the Rydberg blockade in neutral atoms, with the aim of increasing its robustness to variations in the Rabi frequency. The scheme exploits analytically defined phase profiles of the laser pulse and proves almost an order of magnitude more robust to Rabi-frequency variations than previously proposed protocols. We designed this amplitude-robust protocol with a smooth pulse shape and optimized it for a finite Rydberg blockade strength, which makes it suitable for experimental implementation in both single-photon and two-photon configurations. We further show that the protocol can be applied to individually addressed Rydberg excitation, accounting for the asymmetry of the Rabi frequencies of two atoms excited by tightly focused laser beams. This allows the effects of residual thermal motion of the trapped atoms to be reduced. Finally, we examined the performance of the protocol for single-photon and two-photon Rydberg excitation schemes at finite blockade strength, and demonstrated its advantages for individual addressing at finite temperatures of the trapped atoms.
Arrays of identical neutral atoms trapped in optical tweezers are a promising candidate for use in quantum computing. These platforms are highly scalable to large numbers of qubits and neutral atoms boost several attractive features as long coherence times and the possibility to be entangled via strong dipole-dipole interactions by driving them to highly excited Rydberg states. \nThe Thesis work is developed inside the framework of the QRydDemo project, whose aim in the next few years is to realize a neutral atom quantum processor with several hundred qubits. The smallest building blocks for the quantum computer are one and two-qubit gates: to entangle two atoms in the quantum register, a controlled-phase (CZ) gate will be implemented by shining fine-tuned laser pulses onto them. In this work, after giving a theoretical description of the Hamiltonian of two neutral atoms in the quantum register, a numerical simulation of this system is exploited to reproduce the behavior of the two-qubit CZ gate. Realistic effects are taken into account as finite temperature, imperfect Rydberg blockade, or decay out of the Rydberg state. A protocol with constant pulses is analyzed and its optimal parameters are found through classical optimizers. Then, time-dependent pulses are introduced and the optimal pulses are found through the optimal control algorithm dCRAB in an open-loop optimization. For the experimental realization of the gate, this analysis is of pivotal importance to know in which aspect more effort has to be put to maximize the experimental precision of the operation and thus improving the performance of the whole device \n
Reaching fast and robust two-qubit gates with low infidelities has been an outstanding challenge for the long-term goal of useful quantum computers. Typically, optimizing the pulse shapes can minimize the gate infidelity and improve its robustness to certain types of errors; yet it remains incapable of speeding up the gate execution time which is fundamentally restricted by the attainable Rabi frequency in a realistic setup. In this work, we develop a fast implementation of two-qubit CZ gates using optimized ancillary drive to enhance the two-photon Rabi frequency between the ground and Rydberg states.This ancillary drive can work in an error-robustness framework without increasing the original gate infidelity in the absence of the drive. Considering the experimentally feasible parameters for 87^{87}87Rb atoms, we demonstrate that the execution time required for such CZ gates can be shortened by more than 30%\%% as compared to standard two-photon protocols arising the gate fidelity above 0.9954 by taking account of all relevant error sources. Our results reduce the high-power laser requirement and unlock the potential toward fast, high-fidelity quantum operations for large-scale quantum computation with neutral atoms.