Fair Queue

To run quantum programs on systems and emulators, users must submit execute jobs using qnexus. A Nexus execute job targeting Quantinuum systems can consist of many circuit, with each circuit mapping to a result. Circuits contain the instructions for running a program on the quantum computer and are submitted to a user-specified emulator or hardware target. Once the execute job completes, a result is available to retrieve and view by the end user. All jobs submitted to Nexus for execution on Quantinuum systems are routed through Nexus to the Fair queue. Compilation jobs and Nexus-hosted execution jobs only use a First-in First-out queue that is global across all organizations.

Quantinuum-hosted execution jobs enter a fair queue. Jobs will wait in the queue until they run on the target device. A fair queuing process is used to ensure each organization’s queue is equally represented for machine access. The jobs submitted by users in the same organization are ordered by user and group priorities, and then submission date. If users submit a job to a specific machine that is not available, the jobs will remain at the top of an organization’s queue until that machine is available. Machines do not need to be online when submitting jobs. Users are encouraged to submit jobs at their convenience. The quantum computers are periodically taken down for upgrades. If a job is submitted whilst the machine is in an upgrade cycle, it will remain in the queue and run when the machine is back online. Users are able and encouraged to submit jobs to the queue.

The Nexus portal displays all jobs submitted to the queue for a specific user. qnexus can be used programmatically for job management and monitoring.

Queues

First-in First-out Queue

Nexus operates a First-In First-Out (FIFO) queue for all compilation jobs and execution jobs targeting Nexus-hosted emulators. Compilation jobs have a 5 minute window before termination and job failure. Jobs that use the FIFO queue are not impacted by user and group priorities.

Fair Queue on Quantinuum Systems

The fair queue fairly distributes access opportunities to quantum computers and emulators across users from all organizations. The fair queue is an important step in the software stack for scheduling jobs and maximizing compute on the hardware.

Job Selection

Job selection with the fair queue is determined by Hardware Quantum Credits (HQCs) accumulation per organization, group priority within an organization, user priority within a group and submission date for all jobs of a selected user.

1. HQCs accumulation

   • An organization from all organizations submitting to a target is selected based on the HQC accumulation, how many HQCs have been consumed by the organization, within the Fair Queue Time Window (FQTW).

   • The FQTW is defined to be 2-4 hours.

2. Group Priority

   • Within the selected organization, jobs from User Groups are ranked and chosen according to group priority.

   • If multiple groups have the same priority, HQC accumulation is used as a secondary criterion to select jobs. Jobs will run first for groups with lower HQC accumulation.

3. User Priority

   • Once a group is selected, the highest priority user is selected.

4. Submission Date

   • The job with the oldest submission date of the selected user begins execution.

5. Job Execution

   • The selected job is chunked into slices based on the number of shots requested by the user and the complexity of the job. Job complexity is determined by the number of 2-qubit gates and measurement gates.

   • A slice of a job is a small number of shots that can be executed between calibration runs.

6. Update organization HQC accumulation within FQTW.

Fairness is dictated by the HQC accumulation for each organization. Organizations with premium subscriptions will benefit from slower HQC accumulation and therefore will receive higher priority in the fair queue.

Organizations

Users from the same organization submitting jobs to a system compete for access through their organization’s queue. Organizations consist of users and groups. Multiple users can be in a group. Organizations can have multiple users. Organization administrators assign user and group priorities. If a user has no association with an existing group, they are assigned the DEFAULT group of the organization.

• Organization priority (default: 5) is defined between 1 (highest) and 10 (lowest).

• Higher priority jobs run before lower priority jobs.

• Jobs not associated with any group are assigned to the DEFAULT group with the default group priority (5).

Long queue times can arise if there are several jobs submitted from the same organization.

Organization administrators cannot modify how the Fair Queue selects organizations.

Job Chunking and Time to Solution

For jobs submitted with large shot counts, jobs are chunked with smaller shot counts. The number of shots in a chunk is dynamically chosen by the system compiler and will vary with the complexity of the circuit. A series of system checks are performed before and after each slice. If an error is detected, any suspect results are rejected and the failed chunk shots are rerun at no additional cost.

Once a job is selected and starts running, it is assigned a start date. Once the job finishes running, it is assigned a result date. For jobs consisting of multiple chunks, the time between the start date and result date will include all of the system checks and calibrations that happened in the middle of that job and possibly slices from other jobs in the queue. Users should not expect that result date less start date be the true system execution time of the job as this is more than likely not the case. The time to solution, the difference between the result-date and the start-date, also includes chunk execution from other organizations. The difference between the result-date and the start-date does not reflect the true execution time on the system.

Note

Batch jobs ensure chunks from other organizations do not execute during your jobs. Jobs in a batch will run consecutively after each other, after the batch starts.

Minimize Queue Time

The fair queue distributes access to systems and emulators across multiple organizations. Within an organization, users can improve the likelihood of their job being selected for execution via communication with the organization administrator. The organization administrator can control user and group priorities to ensure a specific user’s jobs start running first within the organization. Group and user priorities can be set by an organization administrator with Nexus. The schedule for operations hours on the system is displayed on the Nexus portal. Emulator targets are readily available to use 24 hours a day. Below are a list of steps a user should follow:

1. Keep jobs in the organization queue.

2. Utilise batching when submitting a large number of jobs.

3. Use User and Group priorities to increase job priority within the organizational queue.

4. Plan QPU and emulator usage around the calendar month.

5. Plan usage around published calendar.

6. Submit to the correct system for the job.