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"---\n",
"title: Qubit initialization\n",
"description: Explanatory content about dynamic repetition rate execution\n",
"---\n",
"\n",
"# Qubit initialization\n",
"\n"
]
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"{/*\n",
" DO NOT EDIT THIS CELL!!!\n",
" This cell's content is generated automatically by a script. Anything you add\n",
" here will be removed next time the notebook is run. To add new content, create\n",
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"\n",
"\n",
" \n",
" The code on this page was developed using the following requirements.\n",
" We recommend using these versions or newer.\n",
"\n",
" ```\n",
" qiskit-ibm-runtime~=0.46.1\n",
" ```\n",
" \n",
"\n",
"\n"
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"When a circuit is executed on an IBM® quantum processing unit (QPU), an implicit reset is typically inserted at the beginning of the circuit to ensure the qubits are initialized to zero. This is controlled by the `init_qubits` flag, set as a [primitive execution option](/docs/api/qiskit-ibm-runtime/options-execution-options-v2).\n",
"\n",
"However, imperfections in the reset process can introduce state-preparation errors. To alleviate the error, the QPU also inserts repetition delay time (or `rep_delay`) between circuits. Each backend has a different default `rep_delay`, but it's usually set to balance reset fidelity against total execution time. Run `backend.default_rep_delay` to find the default `rep_delay` for a specific QPU.\n",
"\n",
"Because all IBM QPUs use dynamic repetition rate execution, you can change the `rep_delay` for each job. Circuits you submit in a primitive job are batched together for execution on the QPU. These circuits are executed by iterating over the circuits for each shot requested; the execution is column-wise over a matrix of circuits and shots, as illustrated in the following figure.\n",
"\n",
"![The first column represents shot 0. The circuits are run in order from 0 through 3. The second column represents shot 1. The circuits are run in order from 0 through 3. The remaining columns follow the same pattern. ](https://quantum.cloud.ibm.com/docs/images/guides/repetition-rate-execution/circuits_shots_matrix1.avif \"Column-wise execution matrix\")\n",
"\n",
"Because `rep_delay` is inserted between circuits, each shot of the execution encounters this delay. Therefore, as you lower the `rep_delay`, the total QPU execution time decreases, at the expense of increasing the state preparation error rate, as the following image illustrates:\n",
"\n",
"![This image shows that as the rep\\_delay value is lowered, the state preparation error rate increases.](https://quantum.cloud.ibm.com/docs/images/guides/repetition-rate-execution/rep_delay.avif \"Repetition delay versus error rate\")\n",
"\n",
"If you set both `rep_delay=0` and `init_qubits=False`, the circuits \"merge\" together, since the qubits will begin in the final state from the previous shot.\n",
"\n",
"Note that while circuits in a primitive job are batched together for QPU execution, there is no guarantee on the order the circuits from PUBs are executed. For example, if you submit `pubs=[pub1, pub2]`, circuits from `pub1` might not run before those from `pub2`. There is also no guarantee that circuits from the same job would run as a single batch on the QPU.\n",
"\n",
"## Specify `rep_delay` for a primitive job\n",
"\n",
"\n",
" Always verify the supported `rep_delay` range for the specific QPU you are using. These values are not the same for every QPU and can also change over time.\n",
"\n",
" Please note that an increase in `rep_delay` will have a direct impact on your execution time and capacity consumption.\n",
"\n",
"\n"
]
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"from qiskit_ibm_runtime import QiskitRuntimeService, SamplerV2 as Sampler\n",
"\n",
"service = QiskitRuntimeService()\n",
"\n",
"# Make sure your backend supports it\n",
"backend = service.least_busy(\n",
" operational=True, min_num_qubits=100, dynamic_reprate_enabled=True\n",
")\n",
"\n",
"# Determine the allowable range\n",
"backend.rep_delay_range\n",
"sampler = Sampler(mode=backend)\n",
"\n",
"# Specify a value in the supported range\n",
"sampler.options.execution.rep_delay = 0.0005"
]
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"## Next steps\n",
"\n",
"\n",
" * Try an example in the [Quantum approximate optimization algorithm (QAOA)](/docs/tutorials/quantum-approximate-optimization-algorithm) tutorial.\n",
" * Review how to [get started with Estimator](/docs/guides/get-started-with-estimator).\n",
" * Review how to [get started with Sampler](/docs/guides/get-started-with-sampler).\n",
"\n",
"\n"
]
},
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"metadata": {},
"id": "a1b8767d",
"source": "© IBM Corp., 2017-2026"
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