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arXiv:2512.07656 · npj Quantum Information

Single-Operation Rydberg Phase Gates via Dynamic Population Suppression

Sebastian C. Carrasco, Jabir Chathanathil, Svetlana A. Malinovskaya, Ignacio Sola, Vladimir S. Malinovsky

quant-phSubmitted Dec 8, 2025• Announced Dec 9, 2025• 2 citations
v1 · Dec 8, 2025v2 · Dec 23, 2025
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Abstract

We propose a versatile control protocol based on modulated zero-pulse-area fields that dynamically suppresses Rydberg excitation while retaining Rydberg-Rydberg interactions as an entangling phase resource. This mechanism enables single-step, perfectly entangling phase gates for arbitrary blockade strengths, eliminating finite-blockade errors even when the Rabi frequency approaches or exceeds the interaction energy. The approach defines a new operational regime for Rydberg-blockade quantum logic in which speed, fidelity, and robustness are achieved simultaneously within a simple dynamical framework. Owing to its simplicity and generality, the technique is compatible with a wide range of neutral-atom architectures and offers a promising route toward scalable, high-fidelity quantum computation and simulation.

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quant-pharXiv:2608.13090•Aug 14, 2026•0 citations
We propose a versatile control protocol based on modulated zero-pulse-area fields that dynamically suppresses Rydberg excitation while retaining Rydberg-Rydberg interactions as an entangling phase resource. This mechanism enables single-step, perfectly entangling phase gates for arbitrary blockade strengths, eliminating finite-blockade errors even when the Rabi frequency approaches or exceeds the interaction energy. The approach defines a new operational regime for Rydberg-blockade quantum logic in which speed, fidelity, and robustness are achieved simultaneously within a simple dynamical framework. Owing to its simplicity and generality, the technique is compatible with a wide range of neutral-atom architectures and offers a promising route toward scalable, high-fidelity quantum computation and simulation.
We analyze a new Rydberg gate design based on the original π−2π−ππ-2π-ππ−2π−π protocol [Jaksch, et. al. Phys. Rev. Lett. {\bf 85}, 2208 (2000)] that is modified to enable high fidelity operation without requiring a strong Rydberg interaction. The gate retains the π−2π−ππ-2π-ππ−2π−π structure with an additional detuning added to the 2π2π2π pulse on the target qubit. The protocol reaches within a factor of 2.39 (1.68) of the fundamental fidelity limit set by Rydberg lifetime for equal (asymmetric) Rabi frequencies on the control and target qubits. We generalize the gate protocol to arbitrary controlled phases. We design optimal target-qubit phase waveforms to generalize the gate across a range of interaction strengths and we find that, within this family of gates, the constant-phase protocol is time-optimal for a fixed laser Rabi frequency and tunable interaction strength. Quantum control techniques are used to design gates that are robust against variations in Rydberg Rabi frequency or interaction strength.
Neutral-atom arrays serve as an ideal platform to study quantum simulation and quantum logic gates, where intense efforts have been devoted to improving the fidelity of two-qubit gates. We report our recent findings in constructing a different type of two-qubit controlled phase gate protocol with neutral atoms enabled by the Rydberg blockade, which aims at both robustness and high fidelity. It relies upon a modulated driving pulse with a specially tailored smooth waveform to gain appropriate phase accumulations for quantum gates. The major features include finishing a gate operation within a single pulse, not necessarily requiring individual site addressing, not being sensitive to the exact value of the blockade shift, and suppressing the population leakage error and rotation error. Building upon this progress, we further develop an upgrade in the form of dual-pulse off-resonant modulated driving with the major distinct feature of Doppler insensitivity, in order to address the challenge to the fidelity of two-qubit gates caused by residual thermal motion of the cold atoms. In principle, the gate fidelity remains reasonably high over a relatively significant velocity range of the qubit atoms. Moreover, we anticipate that this will inspire future improvements in gate protocols for other types of qubit platforms, and the strategies used here may find applications in the area of quantum optimal control.
We introduce a novel family of protocols for entangling gates for neutral atom qubits based on the Rydberg blockade mechanism.These protocols realize controlled-phase gates through a series of global laser pulses that are on resonance with the Rydberg excitation frequency.We analyze these protocols with respect to their robustness against calibration errors of the Rabi frequency or shot-to-shot laser intensity fluctuations, and show that they display robustness in various fidelity measures.In addition, we discuss adaptations of these protocols in order to make them robust to atomic-motion-induced Doppler shifts as well.
We propose an adiabatic protocol for implementing a controlled-phase gate ${\mathrm{CZ}}_{\ensuremath{\theta}}$ with continuous $\ensuremath{\theta}$ of neutral atoms through a symmetrical two-photon excitation process via the second resonance line, 6P6P6P in 87Rb{}^{87}\mathrm{Rb}87Rb, with a single-temporal-modulation-coupling of the ground state and intermediate state. Relying on different adiabatic paths, the phase factor $\ensuremath{\theta}$ of the ${\mathrm{CZ}}_{\ensuremath{\theta}}$ gate can be accumulated on the logic qubit state ∣11⟩|11⟩∣11⟩ alone by calibrating the shape of the temporal pulse where strict zero amplitudes at the start and end of the pulse are not needed. For a wide range of $\ensuremath{\theta}$, we can obtain the fidelity of the ${\mathrm{CZ}}_{\ensuremath{\theta}}$ gate over 99.7% in less than $1\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{s}$, in the presence of spontaneous emission from intermediate and Rydberg states. And in particular for $\ensuremath{\theta}=\ensuremath{\pi}$, we benchmark the performance of the CZ gate by taking into account various experimental imperfections, such as Doppler shifts, fluctuation of Rydberg-Rydberg interaction strength, inhomogeneous Rabi frequency, and noise of driving fields, etc., and show that the predicted fidelity is able to maintain at about 98.4% after correcting the measurement error. This gate protocol provides a robustness against the fluctuation of pulse amplitude and a flexible way for adjusting the entangling phase, which may contribute to the experimental implementation of near-term noisy intermediate-scale quantum computation and algorithm with neutral-atom systems.
The neutral atom platform has become an attractive choice to study the science of quantum information and quantum simulation, where intense efforts have been devoted to the entangling processes between individual atoms. A two-qubit controlled-phase gate via Rydberg blockade is one of the most essential elements. Recent theoretical studies have suggested the advantages of introducing nontrivial waveform modulation into the gate protocol, which is anticipated to improve its performance towards the next stage. We report our recent experimental results in realizing the two-qubit controlled-phase (CZ{C}_{Z}CZ​) gate via single-modulated-pulse off-resonant modulated driving embedded in a two-photon transition for Rb atoms. It relies on a global driving laser pulse with a carefully calculated smooth waveform to gain the appropriate phase accumulations required by CZ{C}_{Z}CZ​ gate. Combining this CZ{C}_{Z}CZ​ gate with global microwave pulses, two-atom entanglement is generated with the raw fidelity of 0.945(6). After accounting for state preparation and measurement errors, we extract the entanglement operation fidelity to be 0.980(7). Our work features completing the CZ{C}_{Z}CZ​ gate operation within a single pulse to avoid shelved population in the Rydberg levels, thus demonstrating another promising route for realizing a high-fidelity two-qubit gate for the neutral atom platform.
We propose a controlled-Z gate scheme for Rydberg atoms based on level-crossing-free echoing rapid adiabatic population transfer. We design antisymmetric Rabi frequency pulses and symmetric detuning pulses, enabling the system to completely avoid level-crossing points throughout the evolution, and the dynamical phase is naturally eliminated by the time-reversal symmetry of the double-pulse sequence. We incorporate dissipative effects through the Lindblad master equation. The numerical simulation yields a two-qubit CZ gate fidelity of 0.9999. When the Rabi-frequency fluctuation is within ±2%\pm 2\%±2%, and the detuning offset is within ±1%\pm 1\%±1%, the fidelity can still remain above 0.999. Under the same dissipative model, the three-qubit CCZ gate achieves a fidelity of 0.999. When a single-parameter fluctuation does not exceed ±3%\pm 3\%±3%, the fidelity is always higher than 0.997. Our scheme requires no laser phase jumps or fast switching operations. The zero-area pulse structure suppresses first-order intensity noise, and the symmetric double-pulse sequence avoids spatially resolved laser switching, making it suitable for parallel gate operations in large-scale neutral-atom arrays.