IBM demonstrates 99% quantum state-transfer fidelity between processors, advancing modular FTQC

【Article Title】 IBM demonstrates 99% quantum state-transfer fidelity between processors, advancing modular FTQC 【Article Body】 AI TRANSLATION This article is an AI-generated translation of the original Japanese article. For the authoritative version, please refer to the original. Read the original Japanese article → (https://quantumindex.jp/ibm-nighthawk-l-coupler-state-transfer/) IBM has published results showing two IBM Quantum Nighthawk R1 processors connected inside a dilutiondilutionDilution / Dilution / Shareholder Dilution / Equity DilutionAn increase in the number of shares—such as through the issuance of new shares—that causes existing shareholders' ownership percentage and the value per share to be relatively reduced.QI NoteCan occur through issuance of new shares for fundraising or through stock options, among other mechanisms. You should check not only the amount raised but also the number of shares after issuance and the resulting change in existing shareholders' ownership. refrigerator by four l-couplers. Quantum stateQuantum stateQuantum State / Quantum StateRepresents the state of a quantum system and determines quantities such as the probabilities of outcomes obtained when the system is measured.QI NoteA quantum state is not the simple "0 or 1" value of a qubit. It includes superpositions and mixed states, and how the state was prepared and measured is also important.-transfer fidelity reached up to 99.3% and averaged 99%, demonstrating a component for modular quantum computers that combine multiple processors. ✍️ Quantum Index Analysis The background technical and business implications of this announcement, and evaluation points that are not obvious from the numbers or headlines alone. Read our analysis ↓ Overview In the experiment, two Nighthawk R1 processors were connected using four l-couplers each with 80-centimeter aluminum coaxial cables. An l-coupler consists of the cable plus a simplified l-qubitqubitQubit / Quantum Bit / QubitThe basic unit of information in a quantum computer. It can represent not only 0 or 1 but also a quantum state that is a superposition of them.QI NoteHaving more qubits does not necessarily mean higher performance. Error rates, connectivity, coherence time, and the number of logical qubits are also important., a tunable coupler, and associated controllers. Although some qubits were wired out for development purposes, the chips used were full Nighthawk processors. The internal quality factor of the l-coupler mode was 940,000. Quantum state-transfer fidelity reached a maximum of 99.3% and averaged 99%; a remote CZ gate based on state transfer achieved a two-qubit gate fidelitygate fidelityGate Fidelity / Gate Fidelity / Quantum Gate FidelityA measure of accuracy that indicates how closely a quantum gate operation was performed compared to the ideal operation.QI NoteHigher is generally better, but values depend on the measurement method and differ between single-qubit and two-qubit gates. When comparing, also check the evaluation conditions. averaging 94.75% across four links. The team also ran an experiment using two l-couplers simultaneously to generate independent entangled states between modules. Key points • Two IBM Quantum Nighthawk R1 processors were connected by four l-couplers, each using 80 cm of cable. • Quantum state-transfer fidelity peaked at 99.3% and averaged 99% across the four links. • Remote CZ two-qubit-gate fidelity averaged 94.75% across four links. • Two l-couplers were used simultaneously to generate independent entangled states between modules. • IBM plans to improve yield and reproducibility, reduce error rates, and increase the number of connections and ease of attachment/detachment. Technical and business implications Technically, the result is significant because it demonstrates the feasibility of a modular architecture that moves quantum information between multiple superconducting quantum processors rather than relying solely on scaling up a single chip. Achieving an average 99% state-transfer fidelity across multiple long links provides a foundation for cross-chip quantum algorithms and error-correction codes. That said, the remote CZ gate fidelity of 94.75% should be evaluated separately from the state-transfer numbers. On the business side, the connection approach is compatible with Nighthawk and is intended to be extendable to systems beyond IBM Quantum Starling, so this result can be seen as concretizing IBM’s modular system vision. However, IBM did not specify the number of links or target error rates needed for fault-tolerant computation, nor a timeline for commercial deployment. What to watch next Going forward, the key questions are how much l-coupler yield and reproducibility can improve and how much state-transfer and remote-gate error rates can be reduced. Results when many links operate simultaneously between larger processors, and integration into advanced processing including error correction, will be important. It will also be worth watching whether Starling-scale deployment details—such as module size, system specifications, and timelines—become concrete. ✍️ Quantum Index Analysis This result shows that IBM is making the connection technology needed to link multiple real processors tangible as part of its effort to build a modular quantum computer. Connecting multiple chips at high fidelity, not just increasing qubitqubitQubit / Quantum Bit / QubitThe basic unit of information in a quantum computer. It can represent not only 0 or 1 but also a quantum state that is a superposition of them.QI NoteHaving more qubits does not necessarily mean higher performance. Error rates, connectivity, coherence time, and the number of logical qubits are also important. counts on a single chip, is a core technical challenge on the path to large-scale fault-tolerant quantum computers (FTQCFTQCFault-Tolerant Quantum Computing / FTQCA method for future large-scale quantum computing that uses quantum error correction to allow correct computation to continue even when physical errors occur.QI NoteA demonstration of quantum error correction is not the same as realizing FTQC. Logical error rates, the number of physical qubits required, logical gate performance, and so on are important.). Connecting multiple quantum processors is an area also pursued by groups such as IonQ (https://en.quantumindex.jp/ionq-afrl-quantum-networking-phase-2-funding/), but the goals and approaches differ. IonQ uses photons to connect distant quantum systems, aiming for distributed quantum computing and quantum communication networks, while IBM connects processors inside a dilutiondilutionDilution / Dilution / Shareholder Dilution / Equity DilutionAn increase in the number of shares—such as through the issuance of new shares—that causes existing shareholders' ownership percentage and the value per share to be relatively reduced.QI NoteCan occur through issuance of new shares for fundraising or through stock options, among other mechanisms. You should check not only the amount raised but also the number of shares after issuance and the resulting change in existing shareholders' ownership. refrigerator via microwaves to make multiple chips operate as a single quantum computer. ComparisonIBM (this work)IonQ (AFRL-related)Qubit modalitySuperconductingTrapped ionsConnection methodMicrowave / coaxial cablePhotons / optical linksConnection distance80 cmBetween distant systems, potentially city-scaleMain objectiveScaling modular FTQCDistributed quantum computing and quantum communicationsCommunication infrastructureDedicated in-refrigerator connectionsOptical fiber and free-space optical linksResult reportedState-transfer fidelity 99%, remote CZ fidelity 94.75%Continued funding of $7.5M from AFRLKey technical challengesReducing remote-gate error rates, increasing connection countOptical loss, entanglement rates, long-distance stability Comparison of IBM and IonQ approaches to connecting quantum processors IBM’s short-range approach is well suited to scaling FTQC, which requires high-frequency, low-latency quantum operations. IonQ’s optical approach can link distant systems and is suited to future distributed quantum computing or a quantum internet. The two approaches are not necessarily competing but address different architectural layers: within-system modularization versus networking across systems. It is important to distinguish the reported average 99% state-transfer fidelity from the average 94.75% remote CZ fidelity. Real quantum algorithms and error correction require not only state transfer but repeated, high-fidelity quantum gates between processors. The current remote-gate error rate of about 5.25% remains large and is not yet sufficient for large-scale fault-tolerant computation. This demonstration is a validation of a connection technology that would be a component of a modular quantum computer, not a finished modular machine. Future milestones to watch include improvements in remote-gate fidelitygate fidelityGate Fidelity / Gate Fidelity / Quantum Gate FidelityA measure of accuracy that indicates how closely a quantum gate operation was performed compared to the ideal operation.QI NoteHigher is generally better, but values depend on the measurement method and differ between single-qubit and two-qubit gates. When comparing, also check the evaluation conditions., performance with many simultaneous links, and demonstrations of quantum error correctionquantum error correction量子誤り訂正 / Quantum Error Correction / QECA technique that distributes information across multiple physical qubits and detects and corrects errors without directly disturbing the quantum state.QI NoteSimply implementing it does not automatically provide practical fault tolerance. What matters is whether the logical error rate is improved relative to the physical error rate. across multiple chips—metrics that will be crucial for evaluating IBM Quantum Starling and later systems. NETWORKSee the industry network around IBM Quantum → (/qi-network/) Related articles • IonQ secures $7.5M in continued AFRL funding to field-test quantum networking (https://en.quantumindex.jp/ionq-afrl-quantum-networking-phase-2-funding/) • QuEra survey: evaluation metrics shifting from qubit counts to QEC and logical performance—an industry-wide shift including IBM (https://en.quantumindex.jp/quera-quantum-readiness-survey-fault-tolerance-2026/) • Quantinuum achieves logical fidelity 99.9995%—part of the Helios/Sol performance roadmap (https://en.quantumindex.jp/quantinuum-helios-logical-fidelity-999995/) Sources Read the original announcement (https://www.ibm.com/quantum/blog/connecting-quantum-processors-with-l-couplers) If you found this article useful, please consider sharing it. ──────────────────── 【AI Evaluation Request】 Evaluate the following article critically, not based on the quality of its writing, but on its **original informational value as a specialist publication**. Do not give a high rating to summaries, paraphrases, explanations of technical terms, or generic observations such as "this will be worth watching" or "the timeline remains uncertain" if they could easily be produced by a general-purpose generative AI, even if they are well written. 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IBM has published results showing two IBM Quantum Nighthawk R1 processors connected inside a dilutiondilutionDilution / Dilution / Shareholder Dilution / Equity DilutionAn increase in the number of shares—such as through the issuance of new shares—that causes existing shareholders' ownership percentage and the value per share to be relatively reduced.QI NoteCan occur through issuance of new shares for fundraising or through stock options, among other mechanisms. You should check not only the amount raised but also the number of shares after issuance and the resulting change in existing shareholders' ownership. refrigerator by four l-couplers. Quantum stateQuantum stateQuantum State / Quantum StateRepresents the state of a quantum system and determines quantities such as the probabilities of outcomes obtained when the system is measured.QI NoteA quantum state is not the simple "0 or 1" value of a qubit. It includes superpositions and mixed states, and how the state was prepared and measured is also important.-transfer fidelity reached up to 99.3% and averaged 99%, demonstrating a component for modular quantum computers that combine multiple processors.

Overview

In the experiment, two Nighthawk R1 processors were connected using four l-couplers each with 80-centimeter aluminum coaxial cables. An l-coupler consists of the cable plus a simplified l-qubitqubitQubit / Quantum Bit / QubitThe basic unit of information in a quantum computer. It can represent not only 0 or 1 but also a quantum state that is a superposition of them.QI NoteHaving more qubits does not necessarily mean higher performance. Error rates, connectivity, coherence time, and the number of logical qubits are also important., a tunable coupler, and associated controllers. Although some qubits were wired out for development purposes, the chips used were full Nighthawk processors.

The internal quality factor of the l-coupler mode was 940,000. Quantum state-transfer fidelity reached a maximum of 99.3% and averaged 99%; a remote CZ gate based on state transfer achieved a two-qubit gate fidelitygate fidelityGate Fidelity / Gate Fidelity / Quantum Gate FidelityA measure of accuracy that indicates how closely a quantum gate operation was performed compared to the ideal operation.QI NoteHigher is generally better, but values depend on the measurement method and differ between single-qubit and two-qubit gates. When comparing, also check the evaluation conditions. averaging 94.75% across four links. The team also ran an experiment using two l-couplers simultaneously to generate independent entangled states between modules.

Key points

• Two IBM Quantum Nighthawk R1 processors were connected by four l-couplers, each using 80 cm of cable.
• Quantum state-transfer fidelity peaked at 99.3% and averaged 99% across the four links.
• Remote CZ two-qubit-gate fidelity averaged 94.75% across four links.
• Two l-couplers were used simultaneously to generate independent entangled states between modules.
• IBM plans to improve yield and reproducibility, reduce error rates, and increase the number of connections and ease of attachment/detachment.

Technical and business implications

Technically, the result is significant because it demonstrates the feasibility of a modular architecture that moves quantum information between multiple superconducting quantum processors rather than relying solely on scaling up a single chip. Achieving an average 99% state-transfer fidelity across multiple long links provides a foundation for cross-chip quantum algorithms and error-correction codes. That said, the remote CZ gate fidelity of 94.75% should be evaluated separately from the state-transfer numbers.

On the business side, the connection approach is compatible with Nighthawk and is intended to be extendable to systems beyond IBM Quantum Starling, so this result can be seen as concretizing IBM’s modular system vision. However, IBM did not specify the number of links or target error rates needed for fault-tolerant computation, nor a timeline for commercial deployment.

What to watch next

Going forward, the key questions are how much l-coupler yield and reproducibility can improve and how much state-transfer and remote-gate error rates can be reduced. Results when many links operate simultaneously between larger processors, and integration into advanced processing including error correction, will be important. It will also be worth watching whether Starling-scale deployment details—such as module size, system specifications, and timelines—become concrete.

✍️ Quantum Index Analysis

This result shows that IBM is making the connection technology needed to link multiple real processors tangible as part of its effort to build a modular quantum computer. Connecting multiple chips at high fidelity, not just increasing qubitqubitQubit / Quantum Bit / QubitThe basic unit of information in a quantum computer. It can represent not only 0 or 1 but also a quantum state that is a superposition of them.QI NoteHaving more qubits does not necessarily mean higher performance. Error rates, connectivity, coherence time, and the number of logical qubits are also important. counts on a single chip, is a core technical challenge on the path to large-scale fault-tolerant quantum computers (FTQCFTQCFault-Tolerant Quantum Computing / FTQCA method for future large-scale quantum computing that uses quantum error correction to allow correct computation to continue even when physical errors occur.QI NoteA demonstration of quantum error correction is not the same as realizing FTQC. Logical error rates, the number of physical qubits required, logical gate performance, and so on are important.).

Connecting multiple quantum processors is an area also pursued by groups such as IonQ, but the goals and approaches differ. IonQ uses photons to connect distant quantum systems, aiming for distributed quantum computing and quantum communication networks, while IBM connects processors inside a dilutiondilutionDilution / Dilution / Shareholder Dilution / Equity DilutionAn increase in the number of shares—such as through the issuance of new shares—that causes existing shareholders' ownership percentage and the value per share to be relatively reduced.QI NoteCan occur through issuance of new shares for fundraising or through stock options, among other mechanisms. You should check not only the amount raised but also the number of shares after issuance and the resulting change in existing shareholders' ownership. refrigerator via microwaves to make multiple chips operate as a single quantum computer.

Comparison	IBM (this work)	IonQ (AFRL-related)
Qubit modality	Superconducting	Trapped ions
Connection method	Microwave / coaxial cable	Photons / optical links
Connection distance	80 cm	Between distant systems, potentially city-scale
Main objective	Scaling modular FTQC	Distributed quantum computing and quantum communications
Communication infrastructure	Dedicated in-refrigerator connections	Optical fiber and free-space optical links
Result reported	State-transfer fidelity 99%, remote CZ fidelity 94.75%	Continued funding of $7.5M from AFRL
Key technical challenges	Reducing remote-gate error rates, increasing connection count	Optical loss, entanglement rates, long-distance stability

IBM’s short-range approach is well suited to scaling FTQC, which requires high-frequency, low-latency quantum operations. IonQ’s optical approach can link distant systems and is suited to future distributed quantum computing or a quantum internet. The two approaches are not necessarily competing but address different architectural layers: within-system modularization versus networking across systems.

It is important to distinguish the reported average 99% state-transfer fidelity from the average 94.75% remote CZ fidelity. Real quantum algorithms and error correction require not only state transfer but repeated, high-fidelity quantum gates between processors. The current remote-gate error rate of about 5.25% remains large and is not yet sufficient for large-scale fault-tolerant computation.

This demonstration is a validation of a connection technology that would be a component of a modular quantum computer, not a finished modular machine. Future milestones to watch include improvements in remote-gate fidelitygate fidelityGate Fidelity / Gate Fidelity / Quantum Gate FidelityA measure of accuracy that indicates how closely a quantum gate operation was performed compared to the ideal operation.QI NoteHigher is generally better, but values depend on the measurement method and differ between single-qubit and two-qubit gates. When comparing, also check the evaluation conditions., performance with many simultaneous links, and demonstrations of quantum error correctionquantum error correction量子誤り訂正 / Quantum Error Correction / QECA technique that distributes information across multiple physical qubits and detects and corrects errors without directly disturbing the quantum state.QI NoteSimply implementing it does not automatically provide practical fault tolerance. What matters is whether the logical error rate is improved relative to the physical error rate. across multiple chips—metrics that will be crucial for evaluating IBM Quantum Starling and later systems.

NETWORKSee the industry network around IBM Quantum →

Related articles

• IonQ secures $7.5M in continued AFRL funding to field-test quantum networking
• QuEra survey: evaluation metrics shifting from qubit counts to QEC and logical performance—an industry-wide shift including IBM
• Quantinuum achieves logical fidelity 99.9995%—part of the Helios/Sol performance roadmap

Sources

Read the original announcement