Combining quantum processors with real-time classical communication

Area of Science:

• Quantum Computing
• Quantum Information Science

Background:

• Current quantum hardware is limited by noisy qubits, short coherence times, and planar connectivity.
• Many quantum applications require greater qubit connectivity and more qubits than available on a single quantum processing unit (QPU).
• Connecting multiple QPUs via classical communication is a proposed solution but lacks experimental proof.

Purpose of the Study:

• To experimentally demonstrate the creation of quantum states requiring periodic connectivity using multiple QPUs.
• To validate the use of error-mitigated dynamic circuits and circuit cutting for enhanced quantum computation.
• To establish a real-time classical link between QPUs for conditional quantum gate operations.

Main Methods:

• Implemented error-mitigated dynamic circuits with mid-circuit measurement-based classical control.
• Utilized circuit cutting to construct quantum states across multiple quantum processing units (QPUs).
• Established a real-time classical link connecting two QPUs (127 qubits each) to enable inter-QPU conditional operations.

Main Results:

• Successfully created quantum states requiring periodic connectivity using up to 142 qubits across two QPUs.
• Demonstrated real-time conditional quantum gate operations between QPUs based on measurement outcomes.
• Showcased enhanced qubit connectivity and instruction sets through error-mitigated control flow.

Conclusions:

• Multiple quantum processors can be integrated and utilized as a single, more powerful quantum computer.
• Error-mitigated dynamic circuits, enabled by real-time classical links, significantly enhance quantum computing versatility and scalability.
• This experimental realization paves the way for tackling complex quantum problems previously intractable due to hardware constraints.