Benchmarking Quantum Controllers

Quantum Real-Time (QRT) Benchmarks

Feedback latency is defined as the time from the acquisition of the last sample needed for computation to the first sample of the subsequent pulse sequence. These operations are dependent on the computed measurement results; thus, processing time builds up latency, and different computations will result in different latencies. If the computation and response are performed within the coherence time of the quantum processing unit (QPU), then they are said to happen in quantum real-time (QRT). Requiring QRT processing to be time-deterministic (takes a known amount of time) allows the controller to completely determine the timing of procedures, e.g., tracking the evolution of the system and phase changes.

At Quantum Machines, we developed one QRT benchmark for each feedback type, and we here show one example.

System Real-Time (SRT) Benchmarks

Every QPU has drifting parameters (e.g., qubit frequency, laser intensity, DC voltage bias, etc.). One effective method for compensating and mitigating their detrimental effects is to monitor these changes in real-time and update these parameters during quantum circuits. Such calculations and parametric updates need to occur at a rate significantly faster than the drift time, and as a result, they are described as taking place in system real-time (SRT).

In our ongoing work on benchmarking quantum controllers we developed a system real-time measurable metric that incorporates multi-shot and potentially multi-qubit subprograms that can run together with an application subprogram, ensuring high operational fidelities.

Near Real-Time (NRT) Benchmarks

Some classical calculations may be employed in quantum algorithms, such as variational algorithms and other hybrid quantum-classical applications, without directly impacting circuit accuracy. Instead, they influence circuit runtime, which is evaluated in near real-time (NRT) benchmarks. Current NRT benchmarks, like IBM’s CLOPS, often do not differentiate the controller’s role. Presently, NRT quantum computing is constrained by the sluggishness of quantum control – classical communication, which takes milliseconds to seconds, significantly contributing to latency. At Quantum Machines, we are developing NRT benchmarks for individual assessment of quantum controller quality. Simultaneously, in collaboration with NVIDIA, we are working on hardware and software technologies to reduce quantum control and GPU communication latency to as low as 50 milliseconds.”