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arXiv:2506.15487

Can the gate time of Rydberg two-qubit gate be shorten by increasing the strength of Rydberg interaction?

Yan-Xiong Du

Published Jun 18, 2025• 0 citations
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Abstract

In this manuscript we discuss the relationship between the gate time of Rydberg two-qubit gate and the Rydberg interaction strength. Different from the two-qbuit gates that directly depend on the interactions between the spins (or pseudo spins), the ones in atomic arrays are realized by driving the atoms to the Rydberg states. As a consequence, competition happens between shortening the gate time and decreasing the excitation probability of Rydberg states. For the case of Rydberg blockade, it is found that the gate time is irrelevant of the Rydberg interaction strength. In contrast, for the case of weak Rydberg interactions, the interactions will help to accelerate the two-qubit gates. This implies that the scheme of weak Rydberg interactions will be faster than the Rydberg blockade one to realize the two-qbuit gates under the same Rabi frequencies of Rydberg excitation. Through using the geometric control under the region of weak Rydberg interaction, fast and robust two-qubit gates can be achieved in atomic arrays, of which detailed discussion can be referred to the manuscript \textsl{arXiv:2412. 19193 (2024)}.

DOI
10.48550/arxiv.2506.15487

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In this manuscript we discuss the relationship between the gate time of Rydberg two-qubit gate and the Rydberg interaction strength. Different from the two-qbuit gates that directly depend on the interactions between the spins (or pseudo spins), the ones in atomic arrays are realized by driving the atoms to the Rydberg states. As a consequence, competition happens between shortening the gate time and decreasing the excitation probability of Rydberg states. For the case of Rydberg blockade, it is found that the gate time is irrelevant of the Rydberg interaction strength. In contrast, for the case of weak Rydberg interactions, the interactions will help to accelerate the two-qubit gates. This implies that the scheme of weak Rydberg interactions will be faster than the Rydberg blockade one to realize the two-qbuit gates under the same Rabi frequencies of Rydberg excitation. Through using the geometric control under the region of weak Rydberg interaction, fast and robust two-qubit gates can be achieved in atomic arrays, of which detailed discussion can be referred to the manuscript \textsl{arXiv:2412. 19193 (2024)}.
We propose several schemes for implementing a two-qubit quantum phase gate between two Rydberg atoms. The schemes could be realized in one step without adiabatic passage which depends on the specifical shapes and tailored pulse sequences of the laser fields. When the Rydberg-Rydberg-interaction (RRI) strength and the parameters of the driving fields satisfy some certain conditions, the effective Rabi oscillation between the two-excitation Rydberg state and the ground state would be generated, which is out of the Rydberg blockade regime and essential for our scheme. In addition, the individual addressing of the atoms is not required. And the schemes can work under strong or weak RRI strength. The imperfections induced by the variation of RRI strength and spontaneous emission are discussed through solving the master equation numerically.
Arrays of qubits encoded in the ground-state manifold of neutral atoms trapped in optical (or magnetic) lattices appear to be a promising platform for the realization of a scalable quantum computer. Two-qubit conditional gates between nearest-neighbor qubits in the array can be implemented by exploiting the Rydberg blockade mechanism, as was shown by D. Jaksch et al. [Phys. Rev. Lett. 85, 2208 (2000)]. However, the energy shift due to dipole-dipole interactions causing the blockade falls off rapidly with the interatomic distance, and protocols based on direct Rydberg blockade typically fail to operate between atoms separated by more than one lattice site. In this work, we propose an extension of the protocol of Jaksch et al. for controlled-ZZZ and controlled-not gates which works in the general case where the qubits are not nearest neighbors in the array. Our proposal relies on the Rydberg excitation hopping along a chain of ancilla noncoding atoms connecting the qubits on which the gate is to be applied. The dependence of the gate fidelity on the number of ancilla atoms, the blockade strength, and the decay rates of the Rydberg states is investigated. A comparison between our implementation of a distant controlled-not gate and one based on a sequence of nearest-neighbor two-qubit gates is also provided.
Abstract Connectivity between qubits plays an irreplaceable role in quantum computation. An urgent task of quantum computation based on atomic arrays is to generate effective coupling between two distant qubits, thereby enhancing connectivity. In this paper, we investigate the realization of two-qubit gates utilizing buffer-atomic configuration, where the non-coding atoms serve as quantum buses to connect the computational qubits. Geometric control is achieved through globally-shined laser pulses in the Rydberg blockade region. It is found that acceleration based on shortcut to adiabaticity can be realized by reshaping the original control waveforms. The proposed distant two-qubit gate demonstrates robustness against systematic errors and random noise. Further numerical simulations indicate that high-fidelity control is maintained even when considering next-nearest-neighbor coupling among the atoms. Thus, our proposal provides a fast and experimentally feasible method for realizing distant two-qubit gates in atomic arrays, which may contribute to improving the scalability of quantum computations.
Accurate quantum gates are basic elements for building quantum computers. There has been great interest in designing quantum gates by using blockade effect of Rydberg atoms recently. The fidelity and operation speed of these gates, however, are fundamentally limited by the blockade error. Here we propose another type of quantum gates, which are based on Rydberg blockade effect, yet free from any blockade error. In contrast to the `blocking' method in previous schemes, we use Rydberg energy shift to realise a rational generalised Rabi frequency so that a novel π\piπ phase for one input state of the gate emerges. This leads to an accurate Rydberg-blockade based two-qubit quantum gate that can operate in a 0.1μs0.1\mu s0.1μs timescale or faster thanks to that it operates by a Rabi frequency which is comparable to the blockade shift.
The Rydberg blockade effect plays an important role in realizing two-qubit gates in atomic arrays. Meanwhile, such mechanics will increase the crosstalk between atoms and enhance the decoherence. In this paper, we propose a new scheme to realize the controlled-phase gate without Rydberg blockade. The scheme works effectively with large atomic spacings and is insensitive to the thermal motions of atoms. The proposal is robust against random noises due to the geometric characteristic and operates fast based on the non-adiabatic evolution. The proposed gate is actually a new-type geometric gate that consolidates the non-adiabatic holonomic control and the unconventional geometric control simultaneously. The interference between two different types of geometric phases can be investigated. Furthermore, we show that the scheme with weak Rydberg interaction requires much less physical resources than the present Rydberg blockade scheme. Therefore, our proposal provides a fast and robust way to realize geometric quantum control, and it may trigger the discoveries of new geometric gates in high-dimensional Hilbert space.
Unlike the Rydberg blockade regime, the Rydberg antiblockade regime (RABR) allows more than one Rydberg atom to be excited, which can bring other interesting phenomena and applications. We propose an alternative scheme to quickly achieve the RABR. The proposed RABR can be implemented by adjusting the detuning of the classical driving field, which is, in turn, based on the former numbers of the excited Rydberg atoms. In contrast to the former schemes, the current one enables more than two atoms to be excited to Rydberg states in a short period of time and thus is useful for large-scale quantum information processing. The proposed RABR can be used to construct two- and multiqubit quantum logic gates. In addition, a Rydberg excitation superatom, which can decrease the blockade error and enlarge the blockade radius for Rydberg blockade-based schemes, is constructed based on the suggested RABR and used to realize a more robust quantum logic gate. The mechanical effect and the ionization are discussed, and the performance is investigated using the master-equation method. Finally, other possible applications of the present RABR are also given.