Quantum computing and quantum simulation can be implemented by concatenation of one-and twoqubit gates and interactions.For most physical implementations, however, it may be advantageous to explore state components and interactions that depart from this universal paradigm and offer faster or more robust access to more advanced operations on the system.In this article, we show that adiabatic passage along the dark eigenstate of excitation exchange interactions can be used to implement fast multiqubit Toffoli (C k -NOT) and fan-out (C-NOT k ) gates.This mechanism can be realized by simultaneous excitation of atoms to Rydberg levels, featuring resonant exchange interaction.Our theoretical estimates and numerical simulations show that these multiqubit Rydberg gates are possible with errors below 1% for up to 20 qubits.The excitation exchange mechanism is ubiquitous across experimental platforms, and we show that similar multiqubit gates can be implemented in superconducting circuits.
Quantum computing and quantum simulation can be implemented by concatenation of one-and twoqubit gates and interactions.For most physical implementations, however, it may be advantageous to explore state components and interactions that depart from this universal paradigm and offer faster or more robust access to more advanced operations on the system.In this article, we show that adiabatic passage along the dark eigenstate of excitation exchange interactions can be used to implement fast multiqubit Toffoli (C k -NOT) and fan-out (C-NOT k ) gates.This mechanism can be realized by simultaneous excitation of atoms to Rydberg levels, featuring resonant exchange interaction.Our theoretical estimates and numerical simulations show that these multiqubit Rydberg gates are possible with errors below 1% for up to 20 qubits.The excitation exchange mechanism is ubiquitous across experimental platforms, and we show that similar multiqubit gates can be implemented in superconducting circuits.
Practical quantum computation requires highly efficient implementation of quantum logic gates. The fan-out gate represents such a type of multiqubit controlled gate with one qubit controlling a number of target qubits. Recent efforts for fan-out gates using Rydberg atoms include adiabatic operations along with the dark-state dynamics of Rydberg states [M. Khazali and K. M\o{}lmer, Phys. Rev. X 10, 021054 (2020)] and implementation based on the asymmetric Rydberg-Rydberg interaction [J. T. Young et al., Phys. Rev. Lett. 127, 120501 (2021)]. Inspired by these advances, we propose a fast-operation scheme for geometric multiqubit fan-out gates, in which the target qubits can be executed with arbitrary operations based on the asymmetric Rydberg-Rydberg interaction and time-optimal control technology. One of the main favorable features of our scheme is its performance in a nonadiabatic way and with the time-optimal control technology, by which the shortest smooth geometric path is found. Another feature, that the target qubits could be executed with arbitrary geometric quantum operations, makes our scheme general and useful. Therefore, our scheme provides a promising alternative route toward scalable fault-tolerant quantum information processing based on Rydberg atoms.
Abstract We present a robust protocol for implementing high-fidelity multiqubit controlled phase gates (C k Z) on neutral atom qubits coupled to highly excited Rydberg states. Our approach is based on extending adiabatic rapid passage to two-photon excitation via a short-lived intermediate excited state common to alkali-atom Rydberg experiments, accounting for the full impact of spontaneous decay and differential AC Stark shifts from the complete manifold of hyperfine excited states. We evaluate and optimise gate performance, concluding that for Cs and currently available laser frequencies and powers, a CCZ gate with fidelity F > 0.995 for three qubits and CCCZ with F > 0.99 for four qubits is attainable in ∼ 1.8 μs via this protocol. Higher fidelities are accessible with future technologies, and our results highlight the utility of neutral atom arrays for the native implementation of multiqubit unitaries.
Quantum protocols based on adiabatic evolution are remarkably robust against imperfections of control pulses and system uncertainties. While adiabatic protocols have been successfully implemented for quantum operations such as quantum state transfer and single-qubit gates, their use for geometric two-qubit gates remains a challenge. In this paper, we propose a general scheme to realize robust geometric two-qubit gates in multilevel qubit systems where the interaction between the qubits is mediated by an auxiliary system (such as a bus or coupler). While our scheme utilizes stimulated Raman adiabatic passage (STIRAP), it is substantially simpler than STIRAP-based gates that have been proposed for atomic platforms, requiring fewer control tones and ancillary states, as well as utilizing only a generic dispersive interaction. We also show how our gate can be accelerated using a shortcuts-to-adiabaticity approach, allowing one to achieve a gate that is both fast and relatively robust. We present a comprehensive theoretical analysis of the performance of our two-qubit gate in parametrically modulated superconducting circuits comprising two fluxonium qubits coupled to an auxiliary system.
We report the implementation of universal two- and three-qubit entangling gates on neutral-atom qubits encoded in long-lived hyperfine ground states. The gates are mediated by excitation to strongly interacting Rydberg states and are implemented in parallel on several clusters of atoms in a one-dimensional array of optical tweezers. Specifically, we realize the controlled-phase gate, enacted by a novel, fast protocol involving only global coupling of two qubits to Rydberg states. We benchmark this operation by preparing Bell states with fidelity F≥95.0(2)%, and extract gate fidelity ≥97.4(3)%, averaged across five atom pairs. In addition, we report a proof-of-principle implementation of the three-qubit Toffoli gate, in which two control atoms simultaneously constrain the behavior of one target atom. These experiments demonstrate key ingredients for high-fidelity quantum information processing in a scalable neutral-atom platform.
Abstract Multi-qubit quantum gates are the most important building blocks for quantum computation. In this article, we propose a scheme for realizing the Toffoli gate in a linear neutral atom array. Two ground-state hyperfine levels of the atoms are considered as qubit states. Our method relies on the strong and long-range interactions between atoms due to Rydberg excitations and the occurrence of dark states in the target qubit, with both control and target qubits being individually addressed with laser pulses. Our gate protocol enables precise control over the quantum states of individual qubits, effectively suppressing undesirable transitions to ensure high-fidelity gate performance. We also implement two-atom Rydberg antiblockade mechanism to avoid any unwanted population blockage in the control atoms to get the best fidelity. At zero temperature, the gate fidelity is estimated to be about 99.16% for realistic laser power omitting the motional state of the atoms when the interatomic distance ( l ) 6.55 μ m. We construct a C n NOT gate with n > 2 in a 2D atomic array by exploiting the n -atom Rydberg antiblockade (RAB) mechanism, which allows n atoms within the blockade radius to be simultaneously excited to the Rydberg states. In particular, we simulate C 3 NOT gate with about 98.37 % fidelity. We further analyze the gate error by decreasing the interatomic distance and find that gate fidelity improves more rapidly for larger n with increased interaction potential. We find that more than 99 % fidelity can be achieved for C 3 NOT gate for l < 6.2 μ m, implying that our proposed scheme promising and reliable for multi-qubit controlled NOT gates. For a finite temperature ( ∼ 30 μ K), including the Doppler dephasing, we simulate our gates to achieve 98.90% and 98.54 % fidelity for the Toffoli gate and C 3
Abstract Due to the limitation of quantum resources, direct synthesis of a multiqubit logic gate can significantly improve the efficiency of practical quantum information processing. In this article, an enhanced‐robustness gate scheme is proposed to implement three‐qubit controlled gates, i.e., and , by using resonant dipole–dipole exchange interaction‐induced adiabatic evolutions along with the dark state dynamics and super‐robust pulse sequences in Rydberg atoms. Such a gate scheme can execute arbitrary single‐qubit operations on the target qubit with pure geometric phase and is especially suitable for the case where the decoherence is not very obvious. Taking and as typical examples, various experimental imperfections are studied, including the Doppler effect, spontaneous emission of the intermediate state, laser phase noise, and fluctuations of interaction and external fields. Therefore, with the increasing demand for multiqubit gates, the proposal provides a more promising alternative for future fault‐tolerant and scalable quantum computation.