IBM has introduced a new version of its Nighthawk quantum processor that it says can execute more than 100,000 quantum circuits per second, a 25-fold increase in circuit throughput compared with the company’s predecessor, the Heron processor.
The Nighthawk r2 has 120 programmable qubits, the same as the first-generation Nighthawk yet the company says Nighthawk r2 can deliver more than 100,000 maximum circuits per second, compared with roughly 4,000 for the current Heron line, while maintaining comparable gate fidelity.
That’s because Nighthawk r2 focuses on eliminating a major bottleneck in quantum computing: the time required to reset qubits between calculations. The distinction is important. The 25X figure represents circuit throughput, rather than a 25X increase in raw quantum computing power. IBM is effectively allowing the same 120-qubit processor to perform substantially more circuit executions in a given amount of time.
Quantum algorithms generally have to be executed many times to produce statistically reliable results. After each execution, the qubits must be returned to their initial states before the next circuit can run.
On previous chip iterations, that reset process could introduce significant idle time. Heron systems, for example, use conditional reset based on measuring a qubit and applying a corrective pulse when necessary.
Nighthawk r2 instead gives each programmable qubit an independent high-speed reset mechanism. IBM’s architecture can actively draw energy out of a qubit, rapidly returning it to its ground state without requiring the processor to wait for the qubit to naturally relax.
Because of the reduced reset time, IBM says it can reduce the default repetition delay from approximately 250 microseconds to just 1 microsecond, allowing the processor to move much more quickly from one circuit execution to the next.
The approach also addresses another problem: leakage, in which a qubit leaves the two energy states normally used to represent quantum information. IBM says its reset architecture reduces initialization errors by approximately 25 times across the device while avoiding measurable degradation of neighboring qubits.
The company also reports that some large, repetitive workloads can run as much as 10 times faster without sacrificing accuracy.
In one materials-science experiment involving neutron-scattering spectra, IBM says Nighthawk r2 reduced the runtime to approximately 60 seconds, representing a 12X improvement over the previous approach.
Those results illustrate why throughput can be as important as adding qubits. A processor that can execute substantially more circuits per second can perform larger parameter sweeps and repeat experiments more frequently, potentially making workloads that were previously impractical feasible.
IBM has made the processor available through its IBM Quantum Platform as the ibm_phoenix quantum processing unit.
