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arXiv:2511.04893

Programmable Rapid Adiabatic Passage laser pulses for Ultra-fast Gates on trapped ions

En-Teng An, Hao-Qing Zhang, Yun-Feng Huang, Chuan-Feng Li, Jin-Ming Cui

quant-phSubmitted Nov 7, 2025• Announced Nov 10, 2025• 0 citations• Revised Jun 21, 2026 (v2)
v1 · Nov 7, 2025v2 · Jun 21, 2026
arXivHTMLPDF

Abstract

Scalable quantum gates remain a central challenge for trapped-ion quantum computing. Ultrafast gates driven by spin-dependent kicks (SDKs) provide a promising approach. However, current protocols rely on mode-locked lasers, suffering from inflexible timing control and limited single-SDK fidelity. To overcome this, we propose a scheme using rapid adiabatic passage (RAP) pulses modulated from a continuous-wave laser. We demonstrate that this RAP-based approach suppresses the sensitivity of SDKs to fluctuations in optical intensity, thereby enabling the construction of robust entangling gates. Furthermore, the programmable nature of these modulated pulses allows for precise control over pulse sequences, further optimizing gate performance.

Comments
11 pages, 5 figures

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Scalable quantum gates remain a central challenge for trapped-ion quantum computing. Ultrafast gates driven by spin-dependent kicks (SDKs) provide a promising approach. However, current protocols rely on mode-locked lasers, suffering from inflexible timing control and limited single-SDK fidelity. To overcome this, we propose a scheme using rapid adiabatic passage (RAP) pulses modulated from a continuous-wave laser. We demonstrate that this RAP-based approach suppresses the sensitivity of SDKs to fluctuations in optical intensity, thereby enabling the construction of robust entangling gates. Furthermore, the programmable nature of these modulated pulses allows for precise control over pulse sequences, further optimizing gate performance.
Ultrafast spin-phonon entanglement based on spin-dependent momentum kicks (SDKs) provides an approach to realize fast entangling gates with intrinsic robustness and scalability for trapped ion quantum computing. Such SDKs so far have been implemented on a nanosecond timescale by off-resonant Raman transitions where each laser pulse is split into a sequence of perturbation pulses with carefully designed temporal patterns. Here we report an experimental realization of ultrafast qubit manipulation and spin-phonon entanglement in picoseconds using SDKs from single resonant laser pulses on the magnetic-field-insensitive hyperfine qubit states. This experiment demonstrates a convenient approach to ultrafast SDKs on noise-insensitive ion-spin qubits, with improvement in its speed by more than an order of magnitude. It removes the need to engineer the pattern of a sequence of perturbation pulses and is less vulnerable to noise, simplifying the approach to large-scale trapped-ion quantum computing based on fast quantum gates with SDKs.
Trapped atomic ions are a promising medium for quantum computing, due to their long coherence times and potential for scalability. Current methods of en-tangling ions rely on addressing individual modes of motion within the trap and applying qubit state dependent forces with external fields. This approach can limit the speed of entangling gates and make them vulnerable to decoherence due to coupling to unwanted modes or ion heating. This thesis is directed towards demon-strating novel entanglement schemes which are not limited by the trap frequency, and can be made almost arbitrarily fast. Towards this goal, I report here on the first experiments using ultrafast laser pulses to control the internal and external states of a single trapped ion. I begin with experiments in ultrafast spin control, showing how a single laser pulse can be used to completely control both spin degrees of freedom of the ion qubit in tens of picoseconds. I also show how a train of weak pulses can be used to drive Raman transitions based on a frequency comb. I then discuss exper-iments using pulses to rapidly entangle the spin with the motion, and how careful spectral redistribution allows a single pulse to execute a spin-dependent momentum kick. Finally, I explain how these spin-dependent momentum kicks can be used in the future to create an ultrafast entangling gate. I go over how such a gate would work, and present experimentally realizable timing sequences which would create a maximally entangled state of two ions in a time faster than the period of motion in the trap.
High-fidelity and robust quantum gates are essential for quantum information processing, with neutral Rydberg atoms trapped in optical tweezer arrays serving as a versatile platform for the implementation. We propose a rapid adiabatic passage (RAP) scheme for achieving a high-fidelity controlled-ZZZ (CZ) gate on a neutral-atom Rydberg platform. Utilizing only global laser dressing, our scheme involves echoing two identical RAP pulses within the Rydberg blockade regime to realize a CZ gate and can be readily extended to a CkZ{\mathrm{C}}^{k}\mathrm{Z}CkZ gate with additional qubits. We predict a CZ gate with fidelity over 0.9995 using alkali-metal atom parameters, and a CCZ gate with fidelity exceeding 0.999. Moreover, the direct utilization of echoing RAP pulses enables the implementation of a four-bit CCCZ gate at fidelity over 0.996 without further optimization. The proposed scheme, remarkably robust to variations in driving fields and realistic decoherence effects, holds promise for future quantum information processing applications.
Excitation of trapped-ion hyperfine qubits with fast optical Raman pulses enables faster-than-trap-period entangling gates with qubits of long coherence time for practical quantum computation. Achieving high-fidelity fast two-qubit gates requires high-quality spin-dependent kicks (SDKs), which form their fundamental building blocks. Here, we characterize the control parameters (including Raman frequency difference, pulse arrival times, Lamb--Dicke parameter, temperature, pulse width, and SDK time) that maximize the performance of single-ion SDKs for protocols compatible with performed experiments involving a small number of fast pulses. We demonstrate through analytical methods and numerical simulations that, within the model commonly used for infidelity optimization, finite pulse duration is the dominant source of error, exceeding the contribution of secular motion by orders of magnitude for nanosecond-scale SDKs. Low infidelities -- below 10−310^{-3}10−3 for schemes with ≳10\gtrsim10≳10 fixed-amplitude, equispaced, picosecond pulses -- are achievable in SDK times on the order of nanoseconds. These results provide quantitative design rules for achieving competitive SDK fidelities with current pulsed-laser technology, laying the foundation for sub-microsecond trapped-ion quantum entangling operations.
Trapped atomic ions are a promising medium for quantum computing, due to their long coherence times and potential for scalability. Current methods of entangling ions rely on addressing individual modes of motion within the trap and applying qubit state dependent forces with external fields. This approach can limit the speed of entangling gates and make them vulnerable to decoherence due to coupling to unwanted modes or ion heating. This thesis is directed towards demonstrating novel entanglement schemes which are not limited by the trap frequency, and can be made almost arbitrarily fast. Towards this goal, I report here on the first experiments using ultrafast laser pulses to control the internal and external states of a single trapped ion. I begin with experiments in ultrafast spin control, showing how a single laser pulse can be used to completely control both spin degrees of freedom of the ion qubit in tens of picoseconds. I also show how a train of weak pulses can be used to drive Raman transitions based on a frequency comb. I then discuss experiments using pulses to rapidly entangle the spin with the motion, and how careful spectral redistribution allows a single pulse to execute a spin-dependent momentum kick. Finally, I explain how these spin-dependent momentum kicks can be used in the future to create an ultrafast entangling gate. I go over how such a gate would work, and present experimentally realizable timing sequences which would create a maximally entangled state of two ions in a time faster than the period of motion in the trap.
One of the major problems in building a quantum computer is the development of scalable and robust methods to entangle many qubits. Quantum computers based on trapped atomic ions are one of the most mature and promising platforms for quantum information processing, exhibiting excellent coherence properties, near-perfect qubit detection efficiency, and high-fidelity entangling gates. Entangling operations between multiple ions in a chain typically rely on qubit state-dependent forces that modulate their Coulomb-coupled normal modes of motion. However, scaling these operations to large qubit numbers in a single chain must account for the increasing complexity of the normal mode spectrum, and can result in a gate time slowdown or added complexity of the control forces. In this thesis, I present an alternative route to the scalability problem using optical interactions faster than any state evolution. The experiments shown here represent a proof of principle for quantum manipulation of atoms in the strong coupling regime. This work relies on spin dependent forces (SDK) with short laser pulses and use it as our fundamental building block for thermometry and non-trivial motional state preparation. Together with a robust stabilization of the ion trap and high light collection efficiency, we demonstrate two-ion entanglement with ten ultrafast pulses. Due to the nature of the interaction, the demonstrated entangling operation can be made arbitrarily fast only limited by laser engineering.