What changed
IBM researchers announced they have connected two IBM Quantum Nighthawk processors using four meter-scale l-couplers. This connection achieved quantum state transfer fidelities of 99%, demonstrating reliable transmission of quantum information between processors. The new inter-chip connection design is compatible with IBM Quantum Nighthawk and can scale to IBM Quantum Starling and beyond.
What this means in practice
The successful demonstration of high-fidelity l-couplers provides a key building block for modular quantum computers. This advancement allows for the reliable transfer of quantum information between processors, which is essential for running more powerful error correction codes and larger quantum algorithms across higher numbers of entangled qubits. The l-couplers are part of a modular cryogenic platform designed for scaling quantum computers, with the processors sitting inside dilution fridges that share a cryogenic environment.
Limitations and availability
The experiment specifically demonstrated the connection between two IBM Quantum Nighthawk R1 processors with four l-couplers, each with an 80-centimeter cable. The work reports l-coupler modes with internal quality factors of 940,000 and quantum state transfer fidelities of up to 99.3%, with an average fidelity of 99%. The system includes four l-couplers and custom hardware designed to enable l-coupler installation after processor payloads are mounted inside a cryostat. IBM plans to improve the yield and reproducibility of l-couplers, reduce their error rates, and scale to more l-couplers that can be easily plugged and unplugged between larger and more complex processors as they build connected Nighthawks and work toward IBM Quantum Starling.
