Quantum Cloud Brokers and API Gateway Patterns

Most organizations will not operate a single quantum target forever. They will use simulators, cloud QPUs, vendor-specific runtimes, reserved capacity, local test backends, and eventually internal hardware. A broker layer prevents every application from learning every provider API directly.

Provider platforms differ in execution modes, job objects, local development flows, reservations, billing, and target semantics. IBM Qiskit Runtime exposes execution modes such as jobs, sessions, and batches; Amazon Braket supports hybrid jobs and local debugging workflows; Azure Quantum has workspace, job, cost, and provider abstractions. A broker should hide accidental differences while preserving meaningful hardware differences. [R146]

Diagram loads as you read

Quantum Cloud Brokers and API Gateway Patterns · Figure 1

View diagram source

flowchart TB
    App[Application] --> Gateway[Quantum API gateway]
    Gateway --> Broker[Broker and policy layer]
    Broker --> IBM[IBM Runtime adapter]
    Broker --> AWS[Amazon Braket adapter]
    Broker --> Azure[Azure Quantum adapter]
    Broker --> Lab[Internal lab adapter]
    Broker --> Sim[Simulator adapter]

Do not erase physics

A broker is not a portability fantasy. It should normalize control-plane mechanics, not pretend all backends are equivalent.

Diagram loads as you read

Do not erase physics · Figure 2

View diagram source

flowchart LR
    Portable[Portable concerns] --> Auth[Auth]
    Portable --> Metadata[Metadata]
    Portable --> Cost[Cost controls]
    Portable --> Submission[Submission]
    Portable --> Results[Result retrieval]

    Specific[Target-specific concerns] --> NativeGates[Native gates]
    Specific --> Connectivity[Connectivity]
    Specific --> Noise[Noise]
    Specific --> Timing[Timing]
    Specific --> Queue[Queue semantics]

The broker should expose capabilities explicitly.

Capability negotiation

Diagram loads as you read

Capability negotiation · Figure 3

View diagram source

sequenceDiagram
    participant App as Application
    participant Broker as Broker
    participant Catalog as Capability catalog
    participant Provider as Provider adapter

    App->>Broker: Request workload constraints
    Broker->>Catalog: Find compatible targets
    Catalog-->>Broker: Candidate capabilities
    Broker->>Provider: Validate current availability
    Provider-->>Broker: Availability and constraints
    Broker-->>App: Ranked execution plan

Capability records should include:

target type;
supported circuit features;
shot limits;
dynamic-circuit support;
reservation support;
data-region constraints;
cost model;
queue behavior;
calibration metadata availability.

Routing policy

Diagram loads as you read

Routing policy · Figure 4

View diagram source

flowchart TB
    Workload[Workload] --> Classify[Classify]
    Classify --> Need{Needs hardware?}
    Need -- no --> Simulator[Simulator route]
    Need -- yes --> Constraints[Apply constraints]
    Constraints --> Rank[Rank targets]
    Rank --> Policy{Policy allow?}
    Policy -- yes --> Submit[Submit]
    Policy -- no --> Review[Review or deny]

Routing features:

Feature	Purpose
simulator-first routing	avoid unnecessary QPU runs
region-aware routing	respect data and latency constraints
cost-aware routing	stay within budget
calibration-aware routing	match workload to device state
reservation-aware routing	exploit reserved windows

Provider adapters

Adapters translate broker contracts into provider-specific calls.

Diagram loads as you read

Provider adapters · Figure 5

View diagram source

flowchart LR
    Contract[Broker contract] --> Adapter[Provider adapter]
    Adapter --> Submit[Submit job]
    Adapter --> Poll[Poll status]
    Adapter --> Results[Fetch results]
    Adapter --> Metadata[Fetch metadata]
    Adapter --> Costs[Estimate or record cost]

Adapter outputs should be normalized into a canonical job record.

Illustrative listing · yaml

canonical_job:
  broker_job_id: qb-2026-04-19-001
  provider: provider-name
  provider_job_id: provider-specific-id
  target_id: target-name
  execution_mode: batch-or-session-or-job
  status: completed
  submitted_at: 2026-04-19T00:00:00Z
  completed_at: 2026-04-19T00:12:00Z
  result_uri: warehouse://results/qb-001

Semantic versioning for the gateway

Changing the gateway contract can break downstream applications. Version it.

Diagram loads as you read

Semantic versioning for the gateway · Figure 6

View diagram source

stateDiagram-v2
    [*] --> Experimental
    Experimental --> StableV1: adoption and tests
    StableV1 --> StableV2: incompatible API change
    StableV1 --> Deprecated: replacement exists
    Deprecated --> Removed: migration window ends
    StableV2 --> Deprecated

The gateway should publish:

API version;
capability-schema version;
result-schema version;
policy-bundle version;
deprecation windows.

Cross-cloud failover

Failover is constrained by hardware semantics. The broker must distinguish equivalent fallback, degraded fallback, and no fallback.

Diagram loads as you read

Cross-cloud failover · Figure 7

View diagram source

flowchart LR
    Primary[Primary target] --> Failure{Failure}
    Failure -- transient API --> Retry[Retry same target]
    Failure -- target unavailable --> Fallback{Fallback class}
    Fallback -- equivalent --> Alternate[Alternate QPU]
    Fallback -- degraded --> Degraded[Run with changed claim]
    Fallback -- none --> Hold[Hold workload]

A degraded fallback must modify the claim label. It is invalid to route from hardware to simulator and preserve a hardware-performance claim.

Broker observability

Diagram loads as you read

Broker observability · Figure 8

View diagram source

flowchart TB
    Broker[Broker] --> Metrics[Metrics]
    Broker --> Traces[Traces]
    Broker --> Logs[Logs]
    Metrics --> MTTR[Routing MTTR]
    Metrics --> Cost[Cost per accepted job]
    Metrics --> Waste[Invalid route rate]
    Traces --> Debug[Cross-provider debugging]
    Logs --> Audit[Audit trail]

Key metrics:

route decision latency;
target rejection reasons;
provider failure rate;
fallback rate;
cost per accepted job;
policy-denial rate;
stale capability count.

Operating rule

Build a broker to standardize operational contracts, not to hide the fact that different quantum targets are scientifically different machines.

Additional technical sources: [R232].