282 lines
14 KiB
Plaintext
282 lines
14 KiB
Plaintext
---
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title: qasm3
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description: API reference for qiskit.qasm3
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in_page_toc_min_heading_level: 2
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python_api_type: module
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python_api_name: qiskit.qasm3
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---
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<span id="module-qiskit.qasm3" />
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<span id="qiskit-qasm3" />
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<span id="openqasm-3-qiskit-qasm3" />
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# OpenQASM 3
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<span id="module-qiskit.qasm3" />
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`qiskit.qasm3`
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Qiskit provides some tools for converting between [OpenQASM 3](https://openqasm.com) representations of quantum programs, and the [`QuantumCircuit`](qiskit.circuit.QuantumCircuit "qiskit.circuit.QuantumCircuit") class. These will continue to evolve as Qiskit’s support for the dynamic-circuit capabilities expressed by OpenQASM 3 increases.
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## Exporting to OpenQASM 3
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The high-level functions are simply [`dump()`](#qiskit.qasm3.dump "qiskit.qasm3.dump") and [`dumps()`](#qiskit.qasm3.dumps "qiskit.qasm3.dumps"), which respectively export to a file (given as a filename) and to a Python string.
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### dump
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<Function id="qiskit.qasm3.dump" github="https://github.com/qiskit/qiskit/tree/stable/0.25/qiskit/qasm3/__init__.py" signature="qiskit.qasm3.dump(circuit, stream, **kwargs)">
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Serialize a [`QuantumCircuit`](qiskit.circuit.QuantumCircuit "qiskit.circuit.QuantumCircuit") object as an OpenQASM 3 stream to file-like object.
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**Parameters**
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* **circuit** ([*QuantumCircuit*](qiskit.circuit.QuantumCircuit "qiskit.circuit.QuantumCircuit")) – Circuit to serialize.
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* **stream** (*TextIOBase*) – stream-like object to dump the OpenQASM 3 serialization
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* **\*\*kwargs** – Arguments for the [`Exporter`](#qiskit.qasm3.Exporter "qiskit.qasm3.Exporter") constructor.
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</Function>
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### dumps
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<Function id="qiskit.qasm3.dumps" github="https://github.com/qiskit/qiskit/tree/stable/0.25/qiskit/qasm3/__init__.py" signature="qiskit.qasm3.dumps(circuit, **kwargs)">
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Serialize a [`QuantumCircuit`](qiskit.circuit.QuantumCircuit "qiskit.circuit.QuantumCircuit") object in an OpenQASM 3 string.
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**Parameters**
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* **circuit** ([*QuantumCircuit*](qiskit.circuit.QuantumCircuit "qiskit.circuit.QuantumCircuit")) – Circuit to serialize.
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* **\*\*kwargs** – Arguments for the [`Exporter`](#qiskit.qasm3.Exporter "qiskit.qasm3.Exporter") constructor.
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**Returns**
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The OpenQASM 3 serialization
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**Return type**
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[str](https://docs.python.org/3/library/stdtypes.html#str "(in Python v3.12)")
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</Function>
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Both of these exporter functions are single-use wrappers around the main [`Exporter`](#qiskit.qasm3.Exporter "qiskit.qasm3.Exporter") class. For more complex exporting needs, including dumping multiple circuits in a single session, it may be more convenient or faster to use the complete interface.
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### Exporter
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<Class id="qiskit.qasm3.Exporter" github="https://github.com/qiskit/qiskit/tree/stable/0.25/qiskit/qasm3/exporter.py" signature="qiskit.qasm3.Exporter(includes=('stdgates.inc', ), basis_gates=('U', ), disable_constants=False, alias_classical_registers=None, allow_aliasing=None, indent=' ', experimental=ExperimentalFeatures.None)" modifiers="class">
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QASM3 exporter main class.
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**Parameters**
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* **includes** ([*Sequence*](https://docs.python.org/3/library/typing.html#typing.Sequence "(in Python v3.12)")*\[*[*str*](https://docs.python.org/3/library/stdtypes.html#str "(in Python v3.12)")*]*) – the filenames that should be emitted as includes. These files will be parsed for gates, and any objects dumped from this exporter will use those definitions where possible.
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* **basis\_gates** ([*Sequence*](https://docs.python.org/3/library/typing.html#typing.Sequence "(in Python v3.12)")*\[*[*str*](https://docs.python.org/3/library/stdtypes.html#str "(in Python v3.12)")*]*) – the basic defined gate set of the backend.
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* **disable\_constants** ([*bool*](https://docs.python.org/3/library/functions.html#bool "(in Python v3.12)")) – if `True`, always emit floating-point constants for numeric parameter values. If `False` (the default), then values close to multiples of OpenQASM 3 constants (`pi`, `euler`, and `tau`) will be emitted in terms of those constants instead, potentially improving accuracy in the output.
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* **alias\_classical\_registers** ([*bool*](https://docs.python.org/3/library/functions.html#bool "(in Python v3.12)")) –
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If `True`, then bits may be contained in more than one register. If so, the registers will be emitted using “alias” definitions, which might not be well supported by consumers of OpenQASM 3.
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<Admonition title="See also" type="note">
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**Parameter `allow_aliasing`**
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A value for `allow_aliasing` overrides any value given here, and supersedes this parameter.
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</Admonition>
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* **allow\_aliasing** ([*bool*](https://docs.python.org/3/library/functions.html#bool "(in Python v3.12)")) –
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If `True`, then bits may be contained in more than one register. If so, the registers will be emitted using “alias” definitions, which might not be well supported by consumers of OpenQASM 3. Defaults to `False` or the value of `alias_classical_registers`.
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New in version 0.25.0.
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* **indent** ([*str*](https://docs.python.org/3/library/stdtypes.html#str "(in Python v3.12)")) – the indentation string to use for each level within an indented block. Can be set to the empty string to disable indentation.
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* **experimental** ([*ExperimentalFeatures*](#qiskit.qasm3.ExperimentalFeatures "qiskit.qasm3.experimental.ExperimentalFeatures")) – any experimental features to enable during the export. See [`ExperimentalFeatures`](#qiskit.qasm3.ExperimentalFeatures "qiskit.qasm3.ExperimentalFeatures") for more details.
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#### dump
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<Function id="qiskit.qasm3.Exporter.dump" signature="dump(circuit, stream)">
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Convert the circuit to OpenQASM 3, dumping the result to a file or text stream.
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</Function>
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#### dumps
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<Function id="qiskit.qasm3.Exporter.dumps" signature="dumps(circuit)">
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Convert the circuit to OpenQASM 3, returning the result as a string.
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</Function>
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</Class>
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All of these interfaces will raise [`QASM3ExporterError`](#qiskit.qasm3.QASM3ExporterError "qiskit.qasm3.QASM3ExporterError") on failure.
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### QASM3ExporterError
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<Class id="qiskit.qasm3.QASM3ExporterError" github="https://github.com/qiskit/qiskit/tree/stable/0.25/qiskit/qasm3/exceptions.py" signature="qiskit.qasm3.QASM3ExporterError(*message)" modifiers="exception">
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An error raised during running the OpenQASM 3 exporter.
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Set the error message.
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</Class>
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### Experimental features
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The OpenQASM 3 language is still evolving as hardware capabilities improve, so there is no final syntax that Qiskit can reliably target. In order to represent the evolving language, we will sometimes release features before formal standardization, which may need to change as the review process in the OpenQASM 3 design committees progresses. By default, the exporters will only support standardised features of the language. To enable these early-release features, use the `experimental` keyword argument of [`dump()`](#qiskit.qasm3.dump "qiskit.qasm3.dump") and [`dumps()`](#qiskit.qasm3.dumps "qiskit.qasm3.dumps"). The available feature flags are:
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#### ExperimentalFeatures
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<Class id="qiskit.qasm3.ExperimentalFeatures" github="https://github.com/qiskit/qiskit/tree/stable/0.25/qiskit/qasm3/experimental.py" signature="qiskit.qasm3.ExperimentalFeatures(value)" modifiers="class">
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Flags for experimental features that the OpenQASM 3 exporter supports.
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These are experimental and are more liable to change, because the OpenQASM 3 specification has not formally accepted them yet, so the syntax may not be finalized.
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##### SWITCH\_CASE\_V1
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<Attribute id="qiskit.qasm3.ExperimentalFeatures.SWITCH_CASE_V1" attributeValue="1">
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Support exporting switch-case statements as proposed by [https://github.com/openqasm/openqasm/pull/463](https://github.com/openqasm/openqasm/pull/463) at [commit bfa787aa3078](https://github.com/openqasm/openqasm/pull/463/commits/bfa787aa3078).
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</Attribute>
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</Class>
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If you want to enable multiple experimental features, you should combine the flags using the `|` operator, such as `flag1 | flag2`.
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For example, to perform an export using the early semantics of `switch` support:
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```python
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from qiskit import qasm3, QuantumCircuit, QuantumRegister, ClassicalRegister
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# Build the circuit
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qreg = QuantumRegister(3)
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creg = ClassicalRegister(3)
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qc = QuantumCircuit(qreg, creg)
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with qc.switch(creg) as case:
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with case(0):
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qc.x(0)
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with case(1, 2):
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qc.x(1)
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with case(case.DEFAULT):
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qc.x(2)
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# Export to an OpenQASM 3 string.
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qasm_string = qasm3.dumps(qc, experimental=qasm3.ExperimentalFeatures.SWITCH_CASE_V1)
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```
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<Admonition title="Note" type="note">
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All features enabled by the experimental flags are naturally transient. If it becomes necessary to remove flags, they will be subject to [the standard Qiskit deprecation policy](https://qiskit.org/documentation/deprecation_policy.html). We will leave these experimental flags in place for as long as is reasonable.
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However, we cannot guarantee any support windows for *consumers* of OpenQASM 3 code generated using these experimental flags, if the OpenQASM 3 language specification changes the proposal that the flag is based on. It is possible that any tool you are using to consume OpenQASM 3 code created using these flags may update or remove their support while Qiskit continues to offer the flag. You should not rely on the resultant experimental OpenQASM 3 code for long-term storage of programs.
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</Admonition>
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## Importing from OpenQASM 3
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Currently only two high-level functions are offered, as Qiskit support for importing from OpenQASM 3 is in its infancy, and the implementation is expected to change significantly. The two functions are [`load()`](#qiskit.qasm3.load "qiskit.qasm3.load") and [`loads()`](#qiskit.qasm3.loads "qiskit.qasm3.loads"), which are direct counterparts of [`dump()`](#qiskit.qasm3.dump "qiskit.qasm3.dump") and [`dumps()`](#qiskit.qasm3.dumps "qiskit.qasm3.dumps"), respectively loading a program indirectly from a named file and directly from a given string.
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<Admonition title="Note" type="note">
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While we are still in the exploratory release period, to use either function, the package `qiskit_qasm3_import` must be installed. This can be done by installing Qiskit Terra with the `qasm3-import` extra, such as by:
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```python
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pip install qiskit-terra[qasm3-import]
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```
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We expect that this functionality will eventually be merged into core Terra, and no longer require an optional import, but we do not yet have a timeline for this.
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</Admonition>
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### load
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<Function id="qiskit.qasm3.load" github="https://github.com/qiskit/qiskit/tree/stable/0.25/qiskit/qasm3/__init__.py" signature="qiskit.qasm3.load(filename)">
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Load an OpenQASM 3 program from the file `filename`.
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**Parameters**
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**filename** ([*str*](https://docs.python.org/3/library/stdtypes.html#str "(in Python v3.12)")) – the filename to load the program from.
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**Returns**
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a circuit representation of the OpenQASM 3 program.
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**Return type**
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[QuantumCircuit](qiskit.circuit.QuantumCircuit "qiskit.circuit.QuantumCircuit")
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**Raises**
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[**QASM3ImporterError**](#qiskit.qasm3.QASM3ImporterError "qiskit.qasm3.QASM3ImporterError") – if the OpenQASM 3 file is invalid, or cannot be represented by a [`QuantumCircuit`](qiskit.circuit.QuantumCircuit "qiskit.circuit.QuantumCircuit").
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</Function>
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### loads
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<Function id="qiskit.qasm3.loads" github="https://github.com/qiskit/qiskit/tree/stable/0.25/qiskit/qasm3/__init__.py" signature="qiskit.qasm3.loads(program)">
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Load an OpenQASM 3 program from the given string.
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**Parameters**
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**program** ([*str*](https://docs.python.org/3/library/stdtypes.html#str "(in Python v3.12)")) – the OpenQASM 3 program.
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**Returns**
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a circuit representation of the OpenQASM 3 program.
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**Return type**
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[QuantumCircuit](qiskit.circuit.QuantumCircuit "qiskit.circuit.QuantumCircuit")
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**Raises**
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[**QASM3ImporterError**](#qiskit.qasm3.QASM3ImporterError "qiskit.qasm3.QASM3ImporterError") – if the OpenQASM 3 file is invalid, or cannot be represented by a [`QuantumCircuit`](qiskit.circuit.QuantumCircuit "qiskit.circuit.QuantumCircuit").
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</Function>
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Both of these two functions raise [`QASM3ImporterError`](#qiskit.qasm3.QASM3ImporterError "qiskit.qasm3.QASM3ImporterError") on failure.
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### QASM3ImporterError
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<Class id="qiskit.qasm3.QASM3ImporterError" github="https://github.com/qiskit/qiskit/tree/stable/0.25/qiskit/qasm3/exceptions.py" signature="qiskit.qasm3.QASM3ImporterError(*message)" modifiers="exception">
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An error raised during the OpenQASM 3 importer.
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Set the error message.
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</Class>
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For example, we can define a quantum program using OpenQASM 3, and use [`loads()`](#qiskit.qasm3.loads "qiskit.qasm3.loads") to directly convert it into a [`QuantumCircuit`](qiskit.circuit.QuantumCircuit "qiskit.circuit.QuantumCircuit"):
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```python
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import qiskit.qasm3
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program = """
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OPENQASM 3.0;
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include "stdgates.inc";
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input float[64] a;
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qubit[3] q;
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bit[2] mid;
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bit[3] out;
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let aliased = q[0:1];
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gate my_gate(a) c, t {
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gphase(a / 2);
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ry(a) c;
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cx c, t;
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}
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gate my_phase(a) c {
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ctrl @ inv @ gphase(a) c;
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}
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my_gate(a * 2) aliased[0], q[{1, 2}][0];
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measure q[0] -> mid[0];
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measure q[1] -> mid[1];
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while (mid == "00") {
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reset q[0];
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reset q[1];
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my_gate(a) q[0], q[1];
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my_phase(a - pi/2) q[1];
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mid[0] = measure q[0];
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mid[1] = measure q[1];
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}
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if (mid[0]) {
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let inner_alias = q[{0, 1}];
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reset inner_alias;
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}
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out = measure q;
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"""
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circuit = qiskit.qasm3.loads(program)
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circuit.draw("mpl")
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```
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