IBM researchers have successfully linked two 120-qubit Nighthawk R1 quantum processors, achieving a 99% average fidelity in quantum state transfer. This experiment validates a modular approach to scaling quantum computing by connecting individual superconducting chips rather than increasing qubit density on a single processor.
The connection system utilizes four L-couplers, each featuring an 80 cm superconducting aluminum coaxial cable and RF-SQUID-based coupling elements. These cables are mounted perpendicularly to the processor surface to facilitate higher connection density between modules.
The team performed two-qubit controlled-Z (CZ) operations across the processors to establish quantum entanglement. While the average fidelity for these inter-processor operations reached 94.75%, the researchers noted that this remains lower than intra-chip operation standards, posing a challenge for complex algorithm execution.
The experiment also demonstrated the creation of four- and six-qubit GHZ entangled states distributed across the two chips. However, the researchers emphasized that they have not yet built a universal system capable of utilizing the combined 240-qubit capacity for arbitrary computations.
Future development will focus on improving inter-chip operation fidelity, increasing the number of connections, and integrating error correction mechanisms. IBM’s roadmap includes linking up to three Nighthawk modules to create 360-qubit systems as part of its long-term modular architecture strategy.
