scnc
/
qiskit-documentation
mirror of https://github.com/Qiskit/documentation.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity
qiskit-documentation/docs/api/qiskit/1.2/providers.mdx

523 lines
51 KiB
Plaintext
Raw Permalink Blame History

This file contains invisible Unicode characters

This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

---
title: providers (v1.2)
description: API reference for qiskit.providers in qiskit v1.2
in_page_toc_min_heading_level: 2
python_api_type: module
python_api_name: qiskit.providers
---
<span id="module-qiskit.providers" />
<span id="qiskit-providers" />
<span id="providers-interface-qiskit-providers" />
# Providers Interface
`qiskit.providers`
This module contains the classes used to build external providers for Qiskit. A provider is anything that provides an external service to Qiskit. The typical example of this is a Backend provider which provides [`Backend`](qiskit.providers.Backend "qiskit.providers.Backend") objects which can be used for executing [`QuantumCircuit`](qiskit.circuit.QuantumCircuit "qiskit.circuit.QuantumCircuit") and/or [`Schedule`](qiskit.pulse.Schedule "qiskit.pulse.Schedule") objects. This module contains the abstract classes which are used to define the interface between a provider and Qiskit.
## Version Support
Each providers interface abstract class is individually versioned. When we need to make a change to an interface a new abstract class will be created to define the new interface. These interface changes are not guaranteed to be backwards compatible between versions.
### Version Changes
Each minor version release of `qiskit` **may** increment the version of any backend interface a single version number. It will be an aggregate of all the interface changes for that release on that interface.
### Version Support Policy
To enable providers to have time to adjust to changes in this interface Qiskit will support multiple versions of each class at once. Given the nature of one version per release the version deprecation policy is a bit more conservative than the standard deprecation policy. Qiskit will support a provider interface version for a minimum of 3 minor releases or the first release after 6 months from the release that introduced a version, whichever is longer, prior to a potential deprecation. After that the standard deprecation policy will apply to that interface version. This will give providers and users sufficient time to adapt to potential breaking changes in the interface. So for example lets say in 0.19.0 `BackendV2` is introduced and in the 3 months after the release of 0.19.0 we release 0.20.0, 0.21.0, and 0.22.0, then 7 months after 0.19.0 we release 0.23.0. In 0.23.0 we can deprecate BackendV2, and it needs to still be supported and can’t be removed until the deprecation policy completes.
It’s worth pointing out that Qiskit’s version support policy doesn’t mean providers themselves will have the same support story, they can (and arguably should) update to newer versions as soon as they can, the support window is just for Qiskit’s supported versions. Part of this lengthy window prior to deprecation is to give providers enough time to do their own deprecation of a potential end user impacting change in a user facing part of the interface prior to bumping their version. For example, let’s say we changed the signature to `Backend.run()` in `BackendV34` in a backwards incompatible way. Before Aer could update its [`AerSimulator`](https://qiskit.github.io/qiskit-aer/stubs/qiskit_aer.AerSimulator.html#qiskit_aer.AerSimulator "(in Qiskit Aer v0.15.0)") class to be based on version 34 they’d need to deprecate the old signature prior to switching over. The changeover for Aer is not guaranteed to be lockstep with Qiskit, so we need to ensure there is a sufficient amount of time for Aer to complete its deprecation cycle prior to removing version 33 (ie making version 34 mandatory/the minimum version).
## Abstract Classes
### Provider
| | |
| --------------------------------------------------------------------------- | ------------------------------------------------------------- |
| [`Provider`](qiskit.providers.Provider "qiskit.providers.Provider")() | Base common type for all versioned Provider abstract classes. |
| [`ProviderV1`](qiskit.providers.ProviderV1 "qiskit.providers.ProviderV1")() | Base class for a Backend Provider. |
### Backend
| | |
| --------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| [`Backend`](qiskit.providers.Backend "qiskit.providers.Backend")() | Base common type for all versioned Backend abstract classes. |
| [`BackendV1`](qiskit.providers.BackendV1 "qiskit.providers.BackendV1")(configuration\[, provider]) | Abstract class for Backends |
| [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2")(\[provider, name, description, ...]) | Abstract class for Backends |
| [`QubitProperties`](qiskit.providers.QubitProperties "qiskit.providers.QubitProperties")(\[t1, t2, frequency]) | A representation of the properties of a qubit on a backend. |
| [`BackendV2Converter`](qiskit.providers.BackendV2Converter "qiskit.providers.BackendV2Converter")(backend\[, name\_mapping, ...]) | A converter class that takes a [`BackendV1`](qiskit.providers.BackendV1 "qiskit.providers.BackendV1") instance and wraps it in a [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2") interface. |
| [`convert_to_target`](qiskit.providers.convert_to_target "qiskit.providers.convert_to_target")(configuration\[, ...]) | Decode transpiler target from backend data set. |
### Options
| | |
| ---------------------------------------------------------------------------- | ------------------- |
| [`Options`](qiskit.providers.Options "qiskit.providers.Options")(\*\*kwargs) | Base options object |
### Job
| | |
| ---------------------------------------------------------------------------------------- | -------------------------------------------------------- |
| [`Job`](qiskit.providers.Job "qiskit.providers.Job")() | Base common type for all versioned Job abstract classes. |
| [`JobV1`](qiskit.providers.JobV1 "qiskit.providers.JobV1")(backend, job\_id, \*\*kwargs) | Class to handle jobs |
### Job Status
| | |
| ----------------------------------------------------------------------------- | ------------------------------------- |
| [`JobStatus`](qiskit.providers.JobStatus "qiskit.providers.JobStatus")(value) | Class for job status enumerated type. |
### Exceptions
#### QiskitBackendNotFoundError
<Class id="qiskit.providers.QiskitBackendNotFoundError" github="https://github.com/Qiskit/qiskit/tree/stable/1.2/qiskit/providers/exceptions.py#L30-L33" signature="qiskit.providers.QiskitBackendNotFoundError(*message)" modifiers="exception">
Base class for errors raised while looking for a backend.
Set the error message.
</Class>
#### BackendPropertyError
<Class id="qiskit.providers.BackendPropertyError" github="https://github.com/Qiskit/qiskit/tree/stable/1.2/qiskit/providers/exceptions.py#L36-L39" signature="qiskit.providers.BackendPropertyError(*message)" modifiers="exception">
Base class for errors raised while looking for a backend property.
Set the error message.
</Class>
#### JobError
<Class id="qiskit.providers.JobError" github="https://github.com/Qiskit/qiskit/tree/stable/1.2/qiskit/providers/exceptions.py#L18-L21" signature="qiskit.providers.JobError(*message)" modifiers="exception">
Base class for errors raised by Jobs.
Set the error message.
</Class>
#### JobTimeoutError
<Class id="qiskit.providers.JobTimeoutError" github="https://github.com/Qiskit/qiskit/tree/stable/1.2/qiskit/providers/exceptions.py#L24-L27" signature="qiskit.providers.JobTimeoutError(*message)" modifiers="exception">
Base class for timeout errors raised by jobs.
Set the error message.
</Class>
#### BackendConfigurationError
<Class id="qiskit.providers.BackendConfigurationError" github="https://github.com/Qiskit/qiskit/tree/stable/1.2/qiskit/providers/exceptions.py#L42-L45" signature="qiskit.providers.BackendConfigurationError(*message)" modifiers="exception">
Base class for errors raised by the BackendConfiguration.
Set the error message.
</Class>
## Writing a New Backend
If you have a quantum device or simulator that you would like to integrate with Qiskit you will need to write a backend. A provider is a collection of backends and will provide Qiskit with a method to get available [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2") objects. The [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2") object provides both information describing a backend and its operation for the [`transpiler`](transpiler#module-qiskit.transpiler "qiskit.transpiler") so that circuits can be compiled to something that is optimized and can execute on the backend. It also provides the [`run()`](qiskit.providers.BackendV2#run "qiskit.providers.BackendV2.run") method which can run the [`QuantumCircuit`](qiskit.circuit.QuantumCircuit "qiskit.circuit.QuantumCircuit") objects and/or [`Schedule`](qiskit.pulse.Schedule "qiskit.pulse.Schedule") objects. This enables users and other Qiskit APIs to get results from executing circuits on devices in a standard fashion regardless of how the backend is implemented. At a high level the basic steps for writing a provider are:
> * Implement a `Provider` class that handles access to the backend(s).
>
> * Implement a [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2") subclass and its [`run()`](qiskit.providers.BackendV2#run "qiskit.providers.BackendV2.run") method.
>
> * Add any custom gates for the backend’s basis to the session [`EquivalenceLibrary`](qiskit.circuit.EquivalenceLibrary "qiskit.circuit.EquivalenceLibrary") instance.
>
> * Implement a [`JobV1`](qiskit.providers.JobV1 "qiskit.providers.JobV1") subclass that handles interacting with a running job.
For a simple example of a provider, see the [qiskit-aqt-provider](https://github.com/Qiskit-Partners/qiskit-aqt-provider)
<span id="id1" />
### Provider
A provider class serves a single purpose: to get backend objects that enable executing circuits on a device or simulator. The expectation is that any required credentials and/or authentication will be handled in the initialization of a provider object. The provider object will then provide a list of backends, and methods to filter and acquire backends (using the provided credentials if required). An example provider class looks like:
```python
from qiskit.providers.providerutils import filter_backends
from .backend import MyBackend
class MyProvider:
def __init__(self, token=None):
super().__init__()
self.token = token
self.backends = [MyBackend(provider=self)]
def backends(self, name=None, **kwargs):
if name:
backends = [
backend for backend in backends if backend.name() == name]
return filter_backends(backends, filters=filters, **kwargs)
```
Ensure that any necessary information for authentication (if required) are present in the class and that the backends method matches the required interface. The rest is up to the specific provider on how to implement.
<span id="id2" />
### Backend
The backend classes are the core to the provider. These classes are what provide the interface between Qiskit and the hardware or simulator that will execute circuits. This includes providing the necessary information to describe a backend to the compiler so that it can embed and optimize any circuit for the backend. There are 4 required things in every backend object: a [`target`](qiskit.providers.BackendV2#target "qiskit.providers.BackendV2.target") property to define the model of the backend for the compiler, a [`max_circuits`](qiskit.providers.BackendV2#max_circuits "qiskit.providers.BackendV2.max_circuits") property to define a limit on the number of circuits the backend can execute in a single batch job (if there is no limit `None` can be used), a [`run()`](qiskit.providers.BackendV2#run "qiskit.providers.BackendV2.run") method to accept job submissions, and a [`_default_options`](qiskit.providers.BackendV2#_default_options "qiskit.providers.BackendV2._default_options") method to define the user configurable options and their default values. For example, a minimum working example would be something like:
```python
from qiskit.providers import BackendV2 as Backend
from qiskit.transpiler import Target
from qiskit.providers import Options
from qiskit.circuit import Parameter, Measure
from qiskit.circuit.library import PhaseGate, SXGate, UGate, CXGate, IGate
class Mybackend(Backend):
def __init__(self):
super().__init__()
# Create Target
self._target = Target("Target for My Backend")
# Instead of None for this and below instructions you can define
# a qiskit.transpiler.InstructionProperties object to define properties
# for an instruction.
lam = Parameter("λ")
p_props = {(qubit,): None for qubit in range(5)}
self._target.add_instruction(PhaseGate(lam), p_props)
sx_props = {(qubit,): None for qubit in range(5)}
self._target.add_instruction(SXGate(), sx_props)
phi = Parameter("φ")
theta = Parameter("ϴ")
u_props = {(qubit,): None for qubit in range(5)}
self._target.add_instruction(UGate(theta, phi, lam), u_props)
cx_props = {edge: None for edge in [(0, 1), (1, 2), (2, 3), (3, 4)]}
self._target.add_instruction(CXGate(), cx_props)
meas_props = {(qubit,): None for qubit in range(5)}
self._target.add_instruction(Measure(), meas_props)
id_props = {(qubit,): None for qubit in range(5)}
self._target.add_instruction(IGate(), id_props)
# Set option validators
self.options.set_validator("shots", (1, 4096))
self.options.set_validator("memory", bool)
@property
def target(self):
return self._target
@property
def max_circuits(self):
return 1024
@classmethod
def _default_options(cls):
return Options(shots=1024, memory=False)
def run(circuits, **kwargs):
# serialize circuits submit to backend and create a job
for kwarg in kwargs:
if not hasattr(kwarg, self.options):
warnings.warn(
"Option %s is not used by this backend" % kwarg,
UserWarning, stacklevel=2)
options = {
'shots': kwargs.get('shots', self.options.shots),
'memory': kwargs.get('memory', self.options.shots),
}
job_json = convert_to_wire_format(circuit, options)
job_handle = submit_to_backend(job_jsonb)
return MyJob(self. job_handle, job_json, circuit)
```
<span id="backend-s-transpiler-interface" />
### Backend’s Transpiler Interface
The key piece of the [`Backend`](qiskit.providers.Backend "qiskit.providers.Backend") object is how it describes itself to the compiler. This is handled with the [`Target`](qiskit.transpiler.Target "qiskit.transpiler.Target") class which defines a model of a backend for the transpiler. A backend object will need to return a [`Target`](qiskit.transpiler.Target "qiskit.transpiler.Target") object from the [`target`](qiskit.providers.BackendV2#target "qiskit.providers.BackendV2.target") attribute which the [`transpile()`](compiler#qiskit.compiler.transpile "qiskit.compiler.transpile") function will use as its model of a backend target for compilation.
<span id="id3" />
#### Custom Basis Gates
1. If your backend doesn’t use gates in the Qiskit circuit library ([`qiskit.circuit.library`](circuit_library#module-qiskit.circuit.library "qiskit.circuit.library")) you can integrate support for this into your provider. The basic method for doing this is first to define a [`Gate`](qiskit.circuit.Gate "qiskit.circuit.Gate") subclass for each custom gate in the basis set. For example:
```python
import numpy as np
from qiskit.circuit import Gate
from qiskit.circuit import QuantumCircuit
class SYGate(Gate):
def __init__(self, label=None):
super().__init__("sy", 1, [], label=label)
def _define(self):
qc = QuantumCircuit(1)
q.ry(np.pi / 2, 0)
self.definition = qc
```
The key thing to ensure is that for any custom gates in your Backend’s basis set your custom gate’s name attribute (the first param on `super().__init__()` in the `__init__` definition above) does not conflict with the name of any other gates. The name attribute is what is used to identify the gate in the basis set for the transpiler. If there is a conflict the transpiler will not know which gate to use.
2. Add the custom gate to the target for your backend. This can be done with the [`Target.add_instruction()`](qiskit.transpiler.Target#add_instruction "qiskit.transpiler.Target.add_instruction") method. You’ll need to add an instance of `SYGate` and its parameters to the target so the transpiler knows it exists. For example, assuming this is part of your [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2") implementation for your backend:
```python
from qiskit.transpiler import InstructionProperties
sy_props = {
(0,): InstructionProperties(duration=2.3e-6, error=0.0002)
(1,): InstructionProperties(duration=2.1e-6, error=0.0001)
(2,): InstructionProperties(duration=2.5e-6, error=0.0003)
(3,): InstructionProperties(duration=2.2e-6, error=0.0004)
}
self.target.add_instruction(SYGate(), sy_props)
```
The keys in `sy_props` define the qubits where the backend `SYGate` can be used on, and the values define the properties of `SYGate` on that qubit. For multiqubit gates the tuple keys contain all qubit combinations the gate works on (order is significant, i.e. `(0, 1)` is different from `(1, 0)`).
3. After you’ve defined the custom gates to use for the backend’s basis set then you need to add equivalence rules to the standard equivalence library so that the [`transpile()`](compiler#qiskit.compiler.transpile "qiskit.compiler.transpile") function and [`transpiler`](transpiler#module-qiskit.transpiler "qiskit.transpiler") module can convert an arbitrary circuit using the custom basis set. This can be done by defining equivalent circuits, in terms of the custom gate, for standard gates. Typically if you can convert from a [`CXGate`](qiskit.circuit.library.CXGate "qiskit.circuit.library.CXGate") (if your basis doesn’t include a standard 2 qubit gate) and some commonly used single qubit rotation gates like the [`HGate`](qiskit.circuit.library.HGate "qiskit.circuit.library.HGate") and [`UGate`](qiskit.circuit.library.UGate "qiskit.circuit.library.UGate") that should be sufficient for the transpiler to translate any circuit into the custom basis gates. But, the more equivalence rules that are defined from standard gates to your basis the more efficient translation from an arbitrary circuit to the target basis will be (although not always, and there is a diminishing margin of return).
For example, if you were to add some rules for the above custom `SYGate` we could define the [`U2Gate`](qiskit.circuit.library.U2Gate "qiskit.circuit.library.U2Gate") and [`HGate`](qiskit.circuit.library.HGate "qiskit.circuit.library.HGate"):
```python
from qiskit.circuit.equivalence_library import SessionEquivalenceLibrary
from qiskit.circuit.library import HGate
from qiskit.circuit.library import ZGate
from qiskit.circuit.library import RZGate
from qiskit.circuit.library import U2Gate
# H => Z SY
q = qiskit.QuantumRegister(1, "q")
def_sy_h = qiskit.QuantumCircuit(q)
def_sy_h.append(ZGate(), [q[0]], [])
def_sy_h.append(SYGate(), [q[0]], [])
SessionEquivalenceLibrary.add_equivalence(
HGate(), def_sy_h)
# u2 => Z SY Z
phi = qiskit.circuit.Parameter('phi')
lam = qiskit.circuit.Parameter('lambda')
q = qiskit.QuantumRegister(1, "q")
def_sy_u2 = qiskit.QuantumCircuit(q)
def_sy_u2.append(RZGate(lam), [q[0]], [])
def_sy_u2.append(SYGate(), [q[0]], [])
def_sy_u2.append(RZGate(phi), [q[0]], [])
SessionEquivalenceLibrary.add_equivalence(
U2Gate(phi, lam), def_sy_u2)
```
You will want this to be run on import so that as soon as the provider’s package is imported it will be run. This will ensure that any time the [`BasisTranslator`](qiskit.transpiler.passes.BasisTranslator "qiskit.transpiler.passes.BasisTranslator") pass is run with the custom gates the equivalence rules are defined.
It’s also worth noting that depending on the basis you’re using, some optimization passes in the transpiler, such as [`Optimize1qGatesDecomposition`](qiskit.transpiler.passes.Optimize1qGatesDecomposition "qiskit.transpiler.passes.Optimize1qGatesDecomposition"), may not be able to operate with your custom basis. For our `SYGate` example, the [`Optimize1qGatesDecomposition`](qiskit.transpiler.passes.Optimize1qGatesDecomposition "qiskit.transpiler.passes.Optimize1qGatesDecomposition") will not be able to simplify runs of single qubit gates into the SY basis. This is because the `OneQubitEulerDecomposer` class does not know how to work in the SY basis. To solve this the `SYGate` class would need to be added to Qiskit and `OneQubitEulerDecomposer` updated to support decomposing to the `SYGate`. Longer term that is likely a better direction for custom basis gates and contributing the definitions and support in the transpiler will ensure that it continues to be well supported by Qiskit moving forward.
<span id="custom-transpiler-backend" />
#### Custom Transpiler Passes
The transpiler supports the ability for backends to provide custom transpiler stage implementations to facilitate hardware specific optimizations and circuit transformations. Currently there are two stages supported, `get_translation_stage_plugin()` and `get_scheduling_stage_plugin()` which allow a backend to specify string plugin names to be used as the default translation and scheduling stages, respectively. These hook points in a [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2") class can be used if your backend has requirements for compilation that are not met by the current backend/[`Target`](qiskit.transpiler.Target "qiskit.transpiler.Target") interface. Please also consider submitting a Github issue describing your use case as there is interest in improving these interfaces to be able to describe more hardware architectures in greater depth.
To leverage these hook points you just need to add the methods to your [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2") implementation and have them return a string plugin name. For example:
```python
class Mybackend(BackendV2):
def get_scheduling_stage_plugin(self):
return "SpecialDD"
def get_translation_stage_plugin(self):
return "BasisTranslatorWithCustom1qOptimization"
```
This snippet of a backend implementation will now have the [`transpile()`](compiler#qiskit.compiler.transpile "qiskit.compiler.transpile") function use the `SpecialDD` plugin for the scheduling stage and the `BasisTranslatorWithCustom1qOptimization` plugin for the translation stage by default when the target is set to `Mybackend`. Note that users may override these choices by explicitly selecting a different plugin name. For this interface to work though transpiler stage plugins must be implemented for the returned plugin name. You can refer to [`qiskit.transpiler.preset_passmanagers.plugin`](transpiler_plugins#module-qiskit.transpiler.preset_passmanagers.plugin "qiskit.transpiler.preset_passmanagers.plugin") module documentation for details on how to implement plugins. The typical expectation is that if your backend requires custom passes as part of a compilation stage the provider package will include the transpiler stage plugins that use those passes. However, this is not required and any valid method (from a built-in method or external plugin) can be used.
This way if these two compilation steps are **required** for running or providing efficient output on `Mybackend` the transpiler will be able to perform these custom steps without any manual user input.
<span id="providers-guide-real-time-variables" />
#### Real-time variables
The transpiler will automatically handle real-time typed classical variables (see [`qiskit.circuit.classical`](circuit_classical#module-qiskit.circuit.classical "qiskit.circuit.classical")) and treat the [`Store`](circuit#qiskit.circuit.Store "qiskit.circuit.Store") instruction as a built-in “directive”, similar to [`Barrier`](circuit#qiskit.circuit.Barrier "qiskit.circuit.Barrier"). No special handling from backends is necessary to permit this.
If your backend is *unable* to handle classical variables and storage, we recommend that you comment on this in your documentation, and insert a check into your [`run()`](qiskit.providers.BackendV2#run "qiskit.providers.BackendV2.run") method (see [Backend.run Method](#providers-guide-backend-run)) to eagerly reject circuits containing them. You can examine [`QuantumCircuit.num_vars`](qiskit.circuit.QuantumCircuit#num_vars "qiskit.circuit.QuantumCircuit.num_vars") for the presence of variables at the top level. If you accept [control-flow operations](circuit#circuit-control-flow-repr), you might need to recursively search the internal [`blocks`](qiskit.circuit.ControlFlowOp#blocks "qiskit.circuit.ControlFlowOp.blocks") of each for scope-local variables with [`QuantumCircuit.num_declared_vars`](qiskit.circuit.QuantumCircuit#num_declared_vars "qiskit.circuit.QuantumCircuit.num_declared_vars").
For example, a function to check for the presence of any manual storage locations, or manual stores to memory:
```python
from qiskit.circuit import Store, ControlFlowOp, QuantumCircuit
def has_realtime_logic(circuit: QuantumCircuit) -> bool:
if circuit.num_vars:
return True
for instruction in circuit.data:
if isinstance(instruction.operation, Store):
return True
elif isinstance(instruction.operation, ControlFlowOp):
for block in instruction.operation.blocks:
if has_realtime_logic(block):
return True
return False
```
<span id="backend-run-method" />
<span id="providers-guide-backend-run" />
### Backend.run Method
Of key importance is the [`run()`](qiskit.providers.BackendV2#run "qiskit.providers.BackendV2.run") method, which is used to actually submit circuits to a device or simulator. The run method handles submitting the circuits to the backend to be executed and returning a [`Job`](qiskit.providers.Job "qiskit.providers.Job") object. Depending on the type of backend this typically involves serializing the circuit object into the API format used by a backend. For example, on IBM backends from the `qiskit-ibm-provider` package this involves converting from a quantum circuit and options into a [`qpy`](qpy#module-qiskit.qpy "qiskit.qpy") payload embedded in JSON and submitting that to the IBM Quantum API. Since every backend interface is different (and in the case of the local simulators serialization may not be needed) it is expected that the backend’s [`run`](qiskit.providers.BackendV2#run "qiskit.providers.BackendV2.run") method will handle this conversion.
An example run method would be something like:
```python
def run(self, circuits. **kwargs):
for kwarg in kwargs:
if not hasattr(kwarg, self.options):
warnings.warn(
"Option %s is not used by this backend" % kwarg,
UserWarning, stacklevel=2)
options = {
'shots': kwargs.get('shots', self.options.shots)
'memory': kwargs.get('memory', self.options.shots),
}
job_json = convert_to_wire_format(circuit, options)
job_handle = submit_to_backend(job_jsonb)
return MyJob(self. job_handle, job_json, circuit)
```
### Backend Options
There are often several options for a backend that control how a circuit is run. The typical example of this is something like the number of `shots` which is how many times the circuit is to be executed. The options available for a backend are defined using an [`Options`](qiskit.providers.Options "qiskit.providers.Options") object. This object is initially created by the [`_default_options`](qiskit.providers.BackendV2#_default_options "qiskit.providers.BackendV2._default_options") method of a Backend class. The default options returns an initialized [`Options`](qiskit.providers.Options "qiskit.providers.Options") object with all the default values for all the options a backend supports. For example, if the backend supports only supports `shots` the [`_default_options`](qiskit.providers.BackendV2#_default_options "qiskit.providers.BackendV2._default_options") method would look like:
```python
@classmethod
def _default_options(cls):
return Options(shots=1024)
```
You can also set validators on an [`Options`](qiskit.providers.Options "qiskit.providers.Options") object to provide limits and validation on user provided values based on what’s acceptable for your backend. For example, if the `"shots"` option defined above can be set to any value between 1 and 4096 you can set the validator on the options object for you backend with:
```python
self.options.set_validator("shots", (1, 4096))
```
you can refer to the [`set_validator()`](qiskit.providers.Options#set_validator "qiskit.providers.Options.set_validator") documentation for a full list of validation options.
<span id="id4" />
### Job
The output from the [`run`](qiskit.providers.BackendV2#run "qiskit.providers.BackendV2.run") method is a [`JobV1`](qiskit.providers.JobV1 "qiskit.providers.JobV1") object. Each provider is expected to implement a custom job subclass that defines the behavior for the provider. There are 2 types of jobs depending on the backend’s execution method, either a sync or async. By default jobs are considered async and the expectation is that it represents a handle to the async execution of the circuits submitted with `Backend.run()`. An async job object provides users the ability to query the status of the execution, cancel a running job, and block until the execution is finished. The [`result`](qiskit.providers.JobV1#result "qiskit.providers.JobV1.result") is the primary user facing method which will block until the execution is complete and then will return a [`Result`](qiskit.result.Result "qiskit.result.Result") object with results of the job.
For some backends (mainly local simulators) the execution of circuits is a synchronous operation and there is no need to return a handle to a running job elsewhere. For sync jobs its expected that the [`run`](qiskit.providers.BackendV1#run "qiskit.providers.BackendV1.run") method on the backend will block until a [`Result`](qiskit.result.Result "qiskit.result.Result") object is generated and the sync job will return with that inner [`Result`](qiskit.result.Result "qiskit.result.Result") object.
An example job class for an async API based backend would look something like:
```python
from qiskit.providers import JobV1 as Job
from qiskit.providers import JobError
from qiskit.providers import JobTimeoutError
from qiskit.providers.jobstatus import JobStatus
from qiskit.result import Result
class MyJob(Job):
def __init__(self, backend, job_id, job_json, circuits):
super().__init__(backend, job_id)
self._backend = backend
self.job_json = job_json
self.circuits = circuits
def _wait_for_result(self, timeout=None, wait=5):
start_time = time.time()
result = None
while True:
elapsed = time.time() - start_time
if timeout and elapsed >= timeout:
raise JobTimeoutError('Timed out waiting for result')
result = get_job_status(self._job_id)
if result['status'] == 'complete':
break
if result['status'] == 'error':
raise JobError('Job error')
time.sleep(wait)
return result
def result(self, timeout=None, wait=5):
result = self._wait_for_result(timeout, wait)
results = [{'success': True, 'shots': len(result['counts']),
'data': result['counts']}]
return Result.from_dict({
'results': results,
'backend_name': self._backend.configuration().backend_name,
'backend_version': self._backend.configuration().backend_version,
'job_id': self._job_id,
'qobj_id': ', '.join(x.name for x in self.circuits),
'success': True,
})
def status(self):
result = get_job_status(self._job_id)
if result['status'] == 'running':
status = JobStatus.RUNNING
elif result['status'] == 'complete':
status = JobStatus.DONE
else:
status = JobStatus.ERROR
return status
def submit(self):
raise NotImplementedError
```
and for a sync job:
```python
class MySyncJob(Job):
_async = False
def __init__(self, backend, job_id, result):
super().__init__(backend, job_id)
self._result = result
def submit(self):
return
def result(self):
return self._result
def status(self):
return JobStatus.DONE
```
### Primitives
While not directly part of the provider interface, the [`qiskit.primitives`](primitives#module-qiskit.primitives "qiskit.primitives") module is tightly coupled with providers. Specifically the primitive interfaces, such as [`BaseSampler`](qiskit.primitives.BaseSampler "qiskit.primitives.BaseSampler") and [`BaseEstimator`](qiskit.primitives.BaseEstimator "qiskit.primitives.BaseEstimator"), are designed to enable provider implementations to provide custom implementations which are optimized for the provider’s backends. This can include customizations like circuit transformations, additional pre- and post-processing, batching, caching, error mitigation, etc. The concept of the [`qiskit.primitives`](primitives#module-qiskit.primitives "qiskit.primitives") module is to explicitly enable this as the primitive objects are higher level abstractions to produce processed higher level outputs (such as probability distributions and expectation values) that abstract away the mechanics of getting the best result efficiently, to concentrate on higher level applications using these outputs.
For example, if your backends were well suited to leverage [mthree](https://github.com/Qiskit-Partners/mthree/) measurement mitigation to improve the quality of the results, you could implement a provider-specific [`Sampler`](qiskit.primitives.Sampler "qiskit.primitives.Sampler") implementation that leverages the `M3Mitigation` class internally to run the circuits and return quasi-probabilities directly from mthree in the result. Doing this would enable algorithms to get the best results with mitigation applied directly from your backends. You can refer to the documentation in [`qiskit.primitives`](primitives#module-qiskit.primitives "qiskit.primitives") on how to write custom implementations. Also the built-in implementations: [`Sampler`](qiskit.primitives.Sampler "qiskit.primitives.Sampler"), [`Estimator`](qiskit.primitives.Estimator "qiskit.primitives.Estimator"), [`BackendSampler`](qiskit.primitives.BackendSampler "qiskit.primitives.BackendSampler"), and [`BackendEstimator`](qiskit.primitives.BackendEstimator "qiskit.primitives.BackendEstimator") can serve as references/models on how to implement these as well.
## Migrating from BackendV1 to BackendV2
The [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2") class re-defined user access for most properties of a backend to make them work with native Qiskit data structures and have flatter access patterns. However this means when using a provider that upgrades from [`BackendV1`](qiskit.providers.BackendV1 "qiskit.providers.BackendV1") to [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2") existing access patterns will need to be adjusted. It is expected for existing providers to deprecate the old access where possible to provide a graceful migration, but eventually users will need to adjust code. The biggest change to adapt to in [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2") is that most of the information accessible about a backend is contained in its [`Target`](qiskit.transpiler.Target "qiskit.transpiler.Target") object and the backend’s attributes often query its [`target`](qiskit.providers.BackendV2#target "qiskit.providers.BackendV2.target") attribute to return information, however in many cases the attributes only provide a subset of information the target can contain. For example, `backend.coupling_map` returns a [`CouplingMap`](qiskit.transpiler.CouplingMap "qiskit.transpiler.CouplingMap") constructed from the [`Target`](qiskit.transpiler.Target "qiskit.transpiler.Target") accessible in the [`target`](qiskit.providers.BackendV2#target "qiskit.providers.BackendV2.target") attribute, however the target may contain instructions that operate on more than two qubits (which can’t be represented in a [`CouplingMap`](qiskit.transpiler.CouplingMap "qiskit.transpiler.CouplingMap")) or has instructions that only operate on a subset of qubits (or two qubit links for a two qubit instruction) which won’t be detailed in the full coupling map returned by [`coupling_map`](qiskit.providers.BackendV2#coupling_map "qiskit.providers.BackendV2.coupling_map"). So depending on your use case it might be necessary to look deeper than just the equivalent access with [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2").
Below is a table of example access patterns in [`BackendV1`](qiskit.providers.BackendV1 "qiskit.providers.BackendV1") and the new form with [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2"):
| [`BackendV1`](qiskit.providers.BackendV1 "qiskit.providers.BackendV1") | [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2") | Notes |
| ---------------------------------------------------------------------- | ---------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `backend.configuration().n_qubits` | `backend.num_qubits` | |
| `backend.configuration().coupling_map` | `backend.coupling_map` | The return from [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2") is a [`CouplingMap`](qiskit.transpiler.CouplingMap "qiskit.transpiler.CouplingMap") object. while in [`BackendV1`](qiskit.providers.BackendV1 "qiskit.providers.BackendV1") it is an edge list. Also this is just a view of the information contained in `backend.target` which may only be a subset of the information contained in [`Target`](qiskit.transpiler.Target "qiskit.transpiler.Target") object. |
| `backend.configuration().backend_name` | `backend.name` | |
| `backend.configuration().backend_version` | `backend.backend_version` | The [`version`](qiskit.providers.BackendV2#version "qiskit.providers.BackendV2.version") attribute represents the version of the abstract [`Backend`](qiskit.providers.Backend "qiskit.providers.Backend") interface the object implements while [`backend_version`](qiskit.providers.BackendV2#backend_version "qiskit.providers.BackendV2.backend_version") is metadata about the version of the backend itself. |
| `backend.configuration().basis_gates` | `backend.operation_names` | The [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2") return is a list of operation names contained in the `backend.target` attribute. The [`Target`](qiskit.transpiler.Target "qiskit.transpiler.Target") may contain more information that can be expressed by this list of names. For example, that some operations only work on a subset of qubits or that some names implement the same gate with different parameters. |
| `backend.configuration().dt` | `backend.dt` | |
| `backend.configuration().dtm` | `backend.dtm` | |
| `backend.configuration().max_experiments` | `backend.max_circuits` | |
| `backend.configuration().online_date` | `backend.online_date` | |
| `InstructionDurations.from_backend(backend)` | `backend.instruction_durations` | |
| `backend.defaults().instruction_schedule_map` | `backend.instruction_schedule_map` | |
| `backend.properties().t1(0)` | `backend.qubit_properties(0).t1` | |
| `backend.properties().t2(0)` | `backend.qubit_properties(0).t2` | |
| `backend.properties().frequency(0)` | `backend.qubit_properties(0).frequency` | |
| `backend.properties().readout_error(0)` | `backend.target["measure"][(0,)].error` | In [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2") the error rate for the `Measure` operation on a given qubit is used to model the readout error. However a [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2") can implement multiple measurement types and list them separately in a [`Target`](qiskit.transpiler.Target "qiskit.transpiler.Target"). |
| `backend.properties().readout_length(0)` | `backend.target["measure"][(0,)].duration` | In [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2") the duration for the `Measure` operation on a given qubit is used to model the readout length. However, a [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2") can implement multiple measurement types and list them separately in a [`Target`](qiskit.transpiler.Target "qiskit.transpiler.Target"). |
There is also a [`BackendV2Converter`](qiskit.providers.BackendV2Converter "qiskit.providers.BackendV2Converter") class available that enables you to wrap a [`BackendV1`](qiskit.providers.BackendV1 "qiskit.providers.BackendV1") object with a [`BackendV2`](qiskit.providers.BackendV2 "qiskit.providers.BackendV2") interface.
Reference in New Issue View Git Blame Copy Permalink