Robust Modular Quantum Processor Achieves Redundancy Against Failure Via Double-Star Configuration

The vulnerability of quantum computers to disruption from external events, such as cosmic rays, presents a significant challenge to building reliable machines. Ramesh Bhandari, from the Laboratory for Physical Sciences, and colleagues demonstrate a novel approach to address this issue by introducing redundancy into the core architecture of a quantum processor. Their work centres on a modular design, resembling a star-like configuration with a central router enabling qubit interactions, and expands this to a ‘double-star’ system, effectively providing a backup router in case of failure. This innovative configuration not only safeguards against disruptions but also enhances the processor’s capabilities, allowing for complex operations like simultaneous two-qubit interactions and the implementation of multiqubit gates, representing a substantial step towards robust and scalable quantum computing.

The research centres on a modular quantum processor design featuring a central router that enables interactions between superconducting qubits across multiple modules. Recognizing the router as a critical component, the team proposes a double-star configuration, where a secondary router provides redundancy should the primary router fail. This double-star configuration also proves useful under normal operating conditions, assuming the quantum hardware is protected against cosmic rays through shielding or relocation. This architecture readily facilitates simultaneous two-qubit-pair interactions, such as two simultaneous CZ gates, and supports multiqubit gates like CCZS.

Modular Router Architecture Mitigates Cosmic Ray Errors

The success of quantum computation relies on controlling external factors that can introduce errors into qubits. To mitigate these errors, quantum error correcting codes have been developed, and researchers are now addressing the emerging concern of cosmic rays impacting superconducting qubit devices. Shielding and underground placement reduce cosmic ray effects, but this work explores an alternative approach: building redundancy into the quantum hardware. The team investigates a star-like architecture for superconducting modular quantum computing, featuring a central router connected to individual qubits.

To address the disruption caused by a single connection failure, the researchers propose a double-star configuration with a backup router. If the primary router fails, the backup takes over, ensuring continuous operation. The current star configuration connects qubits to a central router, allowing for pairwise interactions one pair at a time, controlled by on-off switches. The proposed double-star configuration adds a second router and corresponding switches, initially set to the off position. In the event of a primary router failure, a fast signaling mechanism activates the backup router, preserving ongoing quantum computations.

When the risk of failure is negligible, both routers can remain active, enabling simultaneous quantum operations. This allows for two CZ gates to occur concurrently, one between qubit pairs Q1-Q4 and another between Q2-Q3, without interference. Furthermore, this configuration facilitates multiqubit gates, such as the CCZS gate, which requires fewer gate decompositions than using only single and two-qubit gates. The researchers demonstrate that extending this concept to a multi-star configuration could enable even more complex multiqubit gates. In summary, this work illustrates how redundancy in critical hardware elements can maintain quantum operations despite failures, offering a means to achieve simultaneous two-qubit operations and multiqubit entanglement, potentially speeding up quantum computations and reducing hardware requirements.

Double-Star Architecture Maintains Quantum Processor Continuity

This work demonstrates a novel double-star configuration for superconducting modular quantum processors, designed to maintain operational continuity even with the failure of a critical router component, such as from a cosmic ray event. The team proposes backing up a central router with a second, identical unit, enabling uninterrupted qubit interactions. Importantly, this configuration also facilitates simultaneous quantum operations under normal conditions, even when hardware is shielded from cosmic rays. Experiments reveal that the double-star architecture allows for the simultaneous execution of two CZ gates, each achieving a fidelity of 96%, comparable to single CZ gate performance.

The system enables coupling of qubits Q1 and Q4 through one router, while simultaneously coupling qubits Q2 and Q3 through the second router. Analysis shows a total of 15 possible double-pairs of qubits can be engaged simultaneously, including configurations allowing for two simultaneous CZ gates. Furthermore, the team demonstrates the formation of three-qubit gates, specifically the CCZS gate, through the simultaneous application of two CZ gates. This is achieved by leveraging the double-star configuration and utilizing a common control qubit, effectively bypassing the need to decompose the operation into a universal set of single and two-qubit gates.

Implementing a three-qubit Fredkin gate, for example, typically requires five two-qubit gates, but the double-star configuration streamlines this process. Extending this concept to a multi-star configuration promises even more complex multiqubit gate formations. The research confirms that this redundancy not only safeguards against failures but also accelerates quantum computations and reduces hardware requirements, representing a significant advancement in the development of scalable and robust quantum computing platforms.

Double-Star Architecture Boosts Quantum Resilience and Speed

This research introduces a novel architecture for superconducting quantum computing designed to enhance system resilience and operational capability. The team proposes a ‘double-star’ configuration, augmenting a standard star-like modular architecture with a redundant router. This secondary router provides a crucial backup, ensuring continued operation even if the primary router fails due to disruptive events such as cosmic ray interference. Beyond providing a safeguard against failure, the double-star configuration offers performance benefits under normal operating conditions. With two active routers, the system facilitates simultaneous two-qubit operations, such as CZ gates, and more complex multiqubit gates like CCZS, significantly increasing computational speed and flexibility.

The researchers demonstrate how this architecture enables parallel processing of quantum information, a key step towards building more powerful quantum computers. The authors acknowledge that this configuration introduces additional hardware complexity, and future work will focus on optimizing the design and minimizing the overhead associated with the redundant router, as well as exploring the scalability of this approach to larger quantum systems. This work represents a significant advance in the development of fault-tolerant and high-performance quantum computing architectures.