Usage Calculation

The VTT QX system tracks two primary types of usage metrics to provide accurate resource accounting and transparent billing for quantum computing resources.

QPU Second Usage

QPU (Quantum Processing Unit) seconds measure the actual computational time your quantum jobs consume on the quantum hardware.

How QPU Seconds Are Calculated

QPU seconds are calculated when your job reaches the Ready status, indicating successful completion. The system uses metadata from the job execution to determine the precise timing. However, the calculation method differs between circuit jobs and pulse jobs:

Circuit Jobs

For circuit-level jobs, timestamps generated by the quantum control stack are used to calculate the usage:

qpu_seconds = execution_end - execution_start

The system extracts the execution_start and execution_end timestamps from the job results metadata (results['metadata']['timestamps']) and computes the difference. This represents the pure quantum processing time consumed on the hardware, excluding queue waiting time and compilation overhead.

Pulse Jobs

For pulse-level jobs, QPU usage is extracted from the sweep_parameters field using timestamps:

qpu_seconds = end_timestamp - begin_timestamp

QPU Usage During Bookings

During an active booking, jobs are executed immediately for dedicated access to the device. You can submit jobs when the device is booked by others and they will remain in the pending state until the device is free.

For jobs submitted during your own booking period, we don’t count the entire 1 hour period towards QPU usage, we count it towards the booking minutes. This approach accounts for the opportunity cost of reserving quantum resources while preventing double-counting of usage metrics.

Booking Usage Calculation

Booking usage tracks dedicated time slots when projects reserve exclusive or priority access to quantum devices. Bookings are allocated per project, and all users within the project can access and utilize the reserved time.

How Booking Time Is Calculated

Booking usage is calculated based on the reserved time duration rather than actual hardware utilization during the booking period. When you create a confirmed booking, the system calculates the total duration as end_time - start_time and records this as booking minutes for your project.

The booking time represents guaranteed access to the quantum device during your allocated window. This reserved time is counted regardless of whether you submit jobs during the entire period, similar to reserving laboratory equipment.

Integration with QPU Usage

Jobs submitted during your own booking period are excluded from QPU seconds usage to prevent double-counting, since the booking time itself is already counted as QPU usage.