200 lines
9.8 KiB
Plaintext
200 lines
9.8 KiB
Plaintext
---
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title: Configure error mitigation
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description: How to configure error mitigation with Qiskit Runtime.
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---
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# Configure error mitigation
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Error mitigation techniques allow users to mitigate circuit errors by
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modeling the device noise at the time of execution. This typically
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results in quantum pre-processing overhead related to model training and
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classical post-processing overhead to mitigate errors in the raw results
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by using the generated model.
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The Estimator primitive supports several error mitigation techniques, including [TREX](/api/qiskit-ibm-runtime/qiskit_ibm_runtime.options.ResilienceOptionsV2#measure_mitigation), [ZNE](/api/qiskit-ibm-runtime/qiskit_ibm_runtime.options.ResilienceOptionsV2#zne), [PEC](/api/qiskit-ibm-runtime/qiskit_ibm_runtime.options.ResilienceOptionsV2#pec), and [PEA](/api/qiskit-ibm-runtime/qiskit_ibm_runtime.options.ZneOptions). See [Error mitigation and suppression techniques](error-mitigation-and-suppression-techniques) for an explanation of each. When using primitives, you can turn on or off individual methods. See the [Custom error settings](#advanced-error) section for details.
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<Admonition type="note">
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Sampler does not support error mitigation, but you can use the [mthree](https://qiskit.github.io/qiskit-addon-mthree/) (matrix-free measurement mitigation) package to perform error mitigation locally.
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</Admonition>
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Estimator also supports `resilience_level`. The resilience level specifies how much resilience to build against
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errors. Higher levels generate more accurate results, at the expense of
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longer processing times. Resilience levels can be used to configure the
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cost/accuracy trade-off when applying error mitigation to your primitive
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query. Error mitigation reduces errors (bias) in results by processing
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the outputs from a collection, or ensemble, of related circuits. The
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degree of error reduction depends on the method applied. The resilience
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level abstracts the detailed choice of error mitigation method to allow
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users to reason about the cost/accuracy trade that is appropriate to
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their application.
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Given this, each level corresponds to a method or methods with
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increasing level of quantum sampling overhead to enable you experiment
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with different time-accuracy tradeoffs. The following table shows you
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which levels and corresponding methods are available for each of the
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primitives.
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<Admonition type="info" title="Attention">
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Error mitigation is task-specific, so the techniques you can
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apply vary based whether you are sampling a distribution or generating
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expectation values.
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</Admonition>
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<span id="resilience-table"></span>
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Estimator supports the following resilience levels. Sampler does not support resilience levels.
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| Resilience Level | Definition | Technique |
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|------------------|-------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------|
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| 0 | No mitigation | None |
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| 1 [Default] | Minimal mitigation costs: Mitigate error associated with readout errors | Twirled Readout Error eXtinction (TREX) measurement twirling |
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| 2 | Medium mitigation costs. Typically reduces bias in estimators, but is not guaranteed to be zero-bias. | Level 1 + Zero Noise Extrapolation (ZNE) and gate twirling
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<Admonition type="info" title="Attention">
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Resilience levels are currently in beta so sampling overhead and
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solution quality will vary from circuit to circuit. New features,
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advanced options, and management tools will be released on a rolling
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basis. Specific error mitigation methods are not guaranteed to be
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applied at each resilience level.
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</Admonition>
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## Configure Estimator with resilience levels
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You can use resilience levels to specify error mitigation techniques, or you can set custom techniques individually as described in [Custom error settings.](#advanced-error)
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<details>
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<summary>Resilience Level 0</summary>
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No error mitigation is applied to the user program.
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</details>
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<details>
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<summary>Resilience Level 1</summary>
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Level 1 applies **readout error mitigation** and **measurement twirling** by applying a model-free technique known
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as Twirled Readout Error eXtinction (TREX). It reduces measurement error
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by diagonalizing the noise channel associated with measurement by
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randomly flipping qubits through X gates immediately before measurement. A
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rescaling term from the diagonal noise channel is learned by
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benchmarking random circuits initialized in the zero state. This allows
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the service to remove bias from expectation values that result from
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readout noise. This approach is described further in [Model-free
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readout-error mitigation for quantum expectation
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values](https://arxiv.org/abs/2012.09738).
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</details>
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<details>
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<summary>Resilience Level 2</summary>
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Level 2 applies the **error mitigation techniques included in level 1** and also applies **gate twirling** and uses the **Zero Noise Extrapolation method (ZNE)**. ZNE computes an
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expectation value of the observable for different noise factors
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(amplification stage) and then uses the measured expectation values to
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infer the ideal expectation value at the zero-noise limit (extrapolation
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stage). This approach tends to reduce errors in expectation values, but
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is not guaranteed to produce an unbiased result.
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The overhead of this method scales with the number of noise factors. The
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default settings sample the expectation value at three noise factors,
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leading to a roughly 3x overhead when employing this resilience level.
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In Level 2, the TREX method randomly flips qubits through X gates immediately before measurement,
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and flips the corresponding measured bit if an X gate was applied. This approach is described further in [Model-free
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readout-error mitigation for quantum expectation
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values](https://arxiv.org/abs/2012.09738).
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</details>
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### Example
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The `EstimatorV2` interface lets users seamlessly work with the variety of
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error mitigation methods to reduce error in expectation values of
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observables. The following code uses Zero Noise Extrapolation and readout error mitigation by simply
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setting `resilience_level 2`.
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```python
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from qiskit_ibm_runtime import QiskitRuntimeService
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from qiskit_ibm_runtime import EstimatorV2 as Estimator
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service = QiskitRuntimeService()
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backend = service.least_busy(operational=True, simulator=False)
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# Setting options during primitive initialization
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estimator = Estimator(backend, options={"resilience_level": 2})
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```
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<span id="advanced-error"></span>
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## Custom error settings
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You can turn on and off individual error mitigation and suppression methods, including dynamical decoupling, gate and measurement twirling, measurement error mitigation, PEC, and ZNE. See [Error mitigation and suppression techniques](error-mitigation-and-suppression-techniques) for an explanation of each.
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<Admonition type = "note" title = "Notes">
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- Not all options are available for both primitives. See the [available options table](runtime-options-overview#options-table) for the list of available options.
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- Not all methods work together on all types of circuits. See the [options compatibility table](runtime-options-overview#options-compatibility-table) for details.
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</Admonition>
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<Tabs>
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<TabItem value="Estimator" label="Estimator">
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```python
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from qiskit_ibm_runtime import QiskitRuntimeService
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from qiskit_ibm_runtime import EstimatorV2 as Estimator
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service = QiskitRuntimeService()
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backend = service.least_busy(operational=True, simulator=False)
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estimator = Estimator(backend)
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options = estimator.options
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# Turn on gate twirling.
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options.twirling.enable_gates = True
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# Turn on measurement error mitigation.
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options.resilience.measure_mitigation = True
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print(f">>> gate twirling is turned on: {estimator.options.twirling.enable_gates}")
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print(f">>> measurement error mitigation is turned on: {estimator.options.resilience.measure_mitigation}")
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```
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</TabItem>
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<TabItem value="Sampler" label="Sampler">
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```python
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from qiskit_ibm_runtime import SamplerV2 as Sampler
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# Estimator and Sampler have different options
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options = sampler.options
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options.dynamical_decoupling.enable = True
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# Turn on gate twirling. Requires qiskit_ibm_runtime 0.23.0 or later.
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options.twirling.enable_gates = True
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print(f">>> dynamical decoupling is turned on: {sampler.options.dynamical_decoupling.enable}")
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print(f">>> gate twirling is turned on: {sampler.options.twirling.enable_gates}")
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```
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</TabItem>
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</Tabs>
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## Turn off all error mitigation
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For instructions to turn off all error mitigation, see the [Turn off all error suppression and mitigation](specify-runtime-options#no-error-mitigation) section.
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## Next steps
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<Admonition type="tip" title="Recommendations">
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- Walk through an example that uses error mitigation in the [Cost function lesson](https://learning.quantum.ibm.com/course/variational-algorithm-design/cost-functions#primitives) in IBM Quantum Learning.
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- Learn more about [error mitigation and error suppression techniques.](error-mitigation-and-suppression-techniques)
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- [Configure error suppression.](configure-error-suppression)
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- Explore other [options.](runtime-options-overview)
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- Decide what [execution mode](execution-modes) to run your job in.
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</Admonition> |