Expanding the Neutral Atom Gate Set: A native exchange interaction
September 9, 2026
Innsbruck / Hamburg, 09.09.2026 – A group of researchers at ParityQC and the University of Innsbruck has demonstrated a native, high-fidelity realization of iSWAP and parameterized exchange gates for neutral atom quantum processors, expanding the gate set beyond the conventional Rydberg-blockade-based entangling gates.
The challenge: a limited native gate set
Neutral atom quantum processing units have become a leading platform for quantum computing, offering high qubit numbers, flexible connectivity, and long coherence times. Entanglement between atoms is usually generated through the Rydberg blockade effect, which relies on the strong van der Waals interaction between two atoms simultaneously excited to Rydberg states. This mechanism natively realizes diagonal gates such as CZ. However, the van der Waals interaction is not the only, nor even the most fundamental, interaction available between Rydberg states, and a gate set restricted to diagonal entangling gates leaves useful operations on the table.
A dipolar route to iSWAP and exchange gates
In the latest publication “Expanding the Neutral Atom Gate Set: Native iSWAP and Exchange Gates from Dipolar Rydberg Interactions”, a group of researchers at ParityQC and the University of Innsbruck, Pedro Ildefonso, Andrew Byun, Aleksei Konovalov, Javad Kazemi, Michael Schuler, and Wolfgang Lechner, present a native realization of iSWAP and parameterized exchange gates that leverages the dipole-dipole interaction between two distinct Rydberg states.
Key features of the proposed approach include:
- A native exchange interaction: Instead of a single Rydberg state, the protocol uses two distinct, directly dipole-coupled Rydberg states. This gives access to a dipolar exchange interaction that coherently swaps the two states between atoms, without fine-tuning electric or magnetic fields. The exchange interaction also decays more slowly with distance than the van der Waals interaction, offering the potential for faster operations at larger distances and increased qubit connectivity.
- Global driving and smooth pulses: To minimize experimental complexity, the driving fields act identically on all atoms, and quantum optimal control combined with pulse-smoothing techniques is used to design high-fidelity, time-efficient gate pulses that are compatible with limited control bandwidth.
- High fidelity under realistic conditions: While detrimental van der Waals interactions pose a significant challenge, the authors show that they can be absorbed into the pulse design through van der Waals-inclusive optimization. For both caesium-133, a representative alkali atom, and strontium-88, an alkaline-earth species, the protocols reach iSWAP gate fidelities of 99.9% under realistic experimental conditions, accounting for atomic motion, Rydberg decay, as well as laser frequency and intensity noise.
Why non-diagonal gates matter
Adding non-diagonal iSWAP and exchange gates to the neutral-atom gate set on a single platform can reduce gate count and circuit depth. Arbitrary-angle exchange gates enable particle-number-conserving driver terms in variational algorithms and allow optimization sum-constraints to be encoded directly within the ParityQC Architecture. The Parity Twine method, which provides the currently most efficient implementation of the Quantum Fourier Transform, benefits further from iSWAP gates. Beyond these, iSWAP gates are relevant for novel quantum error correction approaches.
Read the paper
The paper “Expanding the Neutral Atom Gate Set: Native iSWAP and Exchange Gates from Dipolar Rydberg Interactions”, authored by Pedro Ildefonso, Andrew Byun, Aleksei Konovalov, Javad Kazemi, Michael Schuler, and Wolfgang Lechner was published on Physical Review Research and is available for download here.
FAQ
Entangling gates on neutral atom quantum processors are usually built from the Rydberg blockade effect, which naturally produces diagonal gates such as CZ. This work shows how to natively realize a different, non-diagonal class of gates, the iSWAP and parameterized exchange gates, on the same platform. Broadening the native gate set can reduce gate count and circuit depth and unlocks operations useful for optimization and quantum error correction.
An exchange gate is a parameterized gate generated by XX+YY spin exchange. the iSWAP gate is the maximally entangling member of this family, exchanging the state of the two qubits and imprinting an imaginary phase. It is non-diagonal, in contrast to the CZ gate that current neutral atom platforms typically implement, which makes it a useful complement to the existing gate set.
Rather than using a single Rydberg state, the protocol uses two distinct Rydberg states that are directly coupled by the dipole-dipole interaction. This interaction coherently exchanges the two states between neighbouring atoms. Using tailored laser and microwave pulses, designed with quantum optimal control, this exchange is transferred into the qubit states to realize the gate. The driving fields act globally on all atoms, which keeps the experimental requirements low.
The dipole-dipole exchange interaction decays more slowly with distance than the van der Waals interaction. This offers the potential for faster gates and for entangling atoms at larger separations, which can increase qubit connectivity. Working with two distinct, directly coupled Rydberg states also avoids the need to fine-tune electric or magnetic fields, which is a source of susceptibility to fluctuations in other approaches.
The work analyzes two representative species: caesium-133, an alkali metal, and the alkaline-earth metal strontium-88. Through van der Waals-inclusive and noise-aware pulse optimization, the protocols achieve iSWAP gate fidelities of 99.9% for both species under realistic experimental conditions. Caesium-133 offers a considerably wider window of experimental parameters over which this threshold holds, while the corresponding range for strontium-88 is more restricted, mainly due to stronger van der Waals interactions.
The protocols are subjected to extensive noise modeling covering atomic motion (which affects both the interaction strength and introduces Doppler shifts), Rydberg state decay, as well as laser frequency and intensity noise. Van der Waals interactions, despite their severity, are shown to be amenable to compensation through pulse shaping, since their effect is coherent. For strontium-88, a noise-aware optimization that penalizes the time atoms spend in interacting Rydberg states further reduces sensitivity to atomic position fluctuations.
Arbitrary-angle exchange gates allow optimization sum-constraints to be encoded directly within the ParityQC Architecture, and the Parity Twine method, which provides the currently most efficient implementation of the Quantum Fourier Transform, benefits from iSWAP gates through further reduced gate count and circuit depth. The broader gate set therefore ties into ongoing work on efficient compilation and quantum optimization.
Visual credits: ParityQC
