--- title: PhaseOracle (v2.0) description: API reference for qiskit.circuit.library.PhaseOracle in qiskit v2.0 source: https://eu-de.quantum.cloud.ibm.com/docs/en/api/qiskit/2.0/qiskit.circuit.library.PhaseOracle --- # PhaseOracle *class* `qiskit.circuit.library.PhaseOracle(expression, var_order=None)` [GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.0/qiskit/circuit/library/phase_oracle.py#L22-L129) Bases: [`QuantumCircuit`](/docs/api/qiskit/2.0/qiskit.circuit.QuantumCircuit "qiskit.circuit.quantumcircuit.QuantumCircuit") Phase Oracle. The Phase Oracle object constructs circuits for any arbitrary input logical expressions. A logical expression is composed of logical operators & (logical AND), | (logical OR), \~ (logical NOT), and ^ (logical XOR). as well as symbols for literals (variables). For example, ‘a & b’, and (v0 | \~v1) & (\~v2 & v3) are both valid string representation of boolean logical expressions. A phase oracle for a boolean function f(x) performs the following quantum operation: $$ |x\rangle \mapsto (-1)^{f(x)}|x\rangle $$ For convenience, this oracle, in addition to parsing arbitrary logical expressions, also supports input strings in the [DIMACS CNF format](https://web.archive.org/web/20190325181937/https://www.satcompetition.org/2009/format-benchmarks2009.html), which is the standard format for specifying SATisfiability (SAT) problem instances in [Conjunctive Normal Form (CNF)](https://en.wikipedia.org/wiki/Conjunctive_normal_form), which is a conjunction of one or more clauses, where a clause is a disjunction of one or more literals. See `qiskit.circuit.library.phase_oracle.PhaseOracle.from_dimacs_file()`. From 16 variables on, possible performance issues should be expected when using the default synthesizer. **Parameters** - **expression** ([*str*](https://docs.python.org/3/library/stdtypes.html#str)) – A Python-like boolean expression. - **var\_order** ([*list*](https://docs.python.org/3/library/stdtypes.html#list)*\[*[*str*](https://docs.python.org/3/library/stdtypes.html#str)*] | None*) – A list with the order in which variables will be created. (default: by appearance) ## Attributes ### ancillas A list of `AncillaQubit`s in the order that they were added. You should not mutate this. ### clbits A list of `Clbit`s in the order that they were added. You should not mutate this. **Example** ```python from qiskit import QuantumRegister, ClassicalRegister, QuantumCircuit qr1 = QuantumRegister(2) qr2 = QuantumRegister(1) cr1 = ClassicalRegister(2) cr2 = ClassicalRegister(1) qc = QuantumCircuit(qr1, qr2, cr1, cr2) print("List the qubits in this circuit:", qc.qubits) print("List the classical bits in this circuit:", qc.clbits) ``` ```text List the qubits in this circuit: [Qubit(QuantumRegister(2, 'q0'), 0), Qubit(QuantumRegister(2, 'q0'), 1), Qubit(QuantumRegister(1, 'q1'), 0)] List the classical bits in this circuit: [Clbit(ClassicalRegister(2, 'c0'), 0), Clbit(ClassicalRegister(2, 'c0'), 1), Clbit(ClassicalRegister(1, 'c1'), 0)] ``` ### cregs A list of `Clbit`s in the order that they were added. You should not mutate this. ### data The circuit data (instructions and context). **Example** ```python from qiskit import QuantumCircuit qc = QuantumCircuit(2, 2) qc.measure([0], [1]) print(qc.data) ``` ```text [CircuitInstruction(operation=Instruction(name='measure', num_qubits=1, num_clbits=1, params=[]), qubits=(Qubit(QuantumRegister(2, 'q'), 0),), clbits=(Clbit(ClassicalRegister(2, 'c'), 1),))] ``` **Returns** A list-like object containing the [`CircuitInstruction`](/docs/api/qiskit/2.0/qiskit.circuit.CircuitInstruction "qiskit.circuit.CircuitInstruction") instances in the circuit. ### duration The total duration of the circuit, set by a scheduling transpiler pass. Its unit is specified by [`unit`](#qiskit.circuit.library.PhaseOracle.unit "qiskit.circuit.library.PhaseOracle.unit"). > **Deprecated since version 1.3.0** > > The property `qiskit.circuit.quantumcircuit.QuantumCircuit.duration` is deprecated as of Qiskit 1.3.0. It will be removed in Qiskit 3.0.0. ### global\_phase The global phase of the current circuit scope in radians. **Example** ```python from qiskit import QuantumCircuit circuit = QuantumCircuit(2) circuit.h(0) circuit.cx(0, 1) print(circuit.global_phase) ``` ```text 0.0 ``` ```python from numpy import pi circuit.global_phase = pi/4 print(circuit.global_phase) ``` ```text 0.7853981633974483 ``` ### instances Default value: `274` ### layout Return any associated layout information about the circuit. This attribute contains an optional [`TranspileLayout`](/docs/api/qiskit/2.0/qiskit.transpiler.TranspileLayout "qiskit.transpiler.TranspileLayout") object. This is typically set on the output from [`transpile()`](/docs/api/qiskit/2.0/compiler#qiskit.compiler.transpile "qiskit.compiler.transpile") or [`PassManager.run()`](/docs/api/qiskit/2.0/qiskit.transpiler.PassManager#run "qiskit.transpiler.PassManager.run") to retain information about the permutations caused on the input circuit by transpilation. There are two types of permutations caused by the [`transpile()`](/docs/api/qiskit/2.0/compiler#qiskit.compiler.transpile "qiskit.compiler.transpile") function: an initial layout that permutes the qubits based on the selected physical qubits on the [`Target`](/docs/api/qiskit/2.0/qiskit.transpiler.Target "qiskit.transpiler.Target"), and a final layout, which is an output permutation caused by [`SwapGate`](/docs/api/qiskit/2.0/qiskit.circuit.library.SwapGate "qiskit.circuit.library.SwapGate")s inserted during routing. **Example** ```python from qiskit import QuantumCircuit from qiskit.providers.fake_provider import GenericBackendV2 from qiskit.transpiler import generate_preset_pass_manager # Create circuit to test transpiler on qc = QuantumCircuit(3, 3) qc.h(0) qc.cx(0, 1) qc.swap(1, 2) qc.cx(0, 1) # Add measurements to the circuit qc.measure([0, 1, 2], [0, 1, 2]) # Specify the QPU to target backend = GenericBackendV2(3) # Transpile the circuit pass_manager = generate_preset_pass_manager( optimization_level=1, backend=backend ) transpiled = pass_manager.run(qc) # Print the layout after transpilation print(transpiled.layout.routing_permutation()) ``` ```text [0, 1, 2] ``` ### metadata Arbitrary user-defined dictionary of metadata for the circuit. Qiskit will not examine the content of this mapping, but it will pass it through the transpiler and reattach it to the output, so you can track your own metadata. **Example** ```python from qiskit import QuantumCircuit qc = QuantumCircuit(2, 2, metadata={'experiment_type': 'Bell state experiment'}) print(qc.metadata) ``` ```text {'experiment_type': 'Bell state experiment'} ``` ### num\_ancillas Return the number of ancilla qubits. **Example** ```python from qiskit import QuantumCircuit, QuantumRegister, AncillaRegister # Create a 2-qubit quantum circuit reg = QuantumRegister(2) qc = QuantumCircuit(reg) # Create an ancilla register with 1 qubit anc = AncillaRegister(1) qc.add_register(anc) # Add the ancilla register to the circuit print("Number of ancilla qubits:", qc.num_ancillas) ``` ```text Number of ancilla qubits: 1 ``` ### num\_captured\_stretches The number of stretches in the circuit marked as captured from an enclosing scope. This is the length of the `iter_captured_stretches()` iterable. If this is non-zero, [`num_input_vars`](#qiskit.circuit.library.PhaseOracle.num_input_vars "qiskit.circuit.library.PhaseOracle.num_input_vars") must be zero. ### num\_captured\_vars The number of real-time classical variables in the circuit marked as captured from an enclosing scope. This is the length of the `iter_captured_vars()` iterable. If this is non-zero, [`num_input_vars`](#qiskit.circuit.library.PhaseOracle.num_input_vars "qiskit.circuit.library.PhaseOracle.num_input_vars") must be zero. ### num\_clbits Return number of classical bits. **Example** ```python from qiskit import QuantumCircuit # Create a new circuit with two qubits and one classical bit qc = QuantumCircuit(2, 1) print("Number of classical bits:", qc.num_clbits) ``` ```text Number of classical bits: 1 ``` ### num\_declared\_stretches The number of stretches in the circuit that are declared by this circuit scope, excluding captures. This is the length of the `iter_declared_stretches()` iterable. ### num\_declared\_vars The number of real-time classical variables in the circuit that are declared by this circuit scope, excluding inputs or captures. This is the length of the `iter_declared_vars()` iterable. ### num\_identifiers The number of real-time classical variables and stretches in the circuit. This is equal to [`num_vars()`](#qiskit.circuit.library.PhaseOracle.num_vars "qiskit.circuit.library.PhaseOracle.num_vars") + [`num_stretches()`](#qiskit.circuit.library.PhaseOracle.num_stretches "qiskit.circuit.library.PhaseOracle.num_stretches"). ### num\_input\_vars The number of real-time classical variables in the circuit marked as circuit inputs. This is the length of the `iter_input_vars()` iterable. If this is non-zero, [`num_captured_vars`](#qiskit.circuit.library.PhaseOracle.num_captured_vars "qiskit.circuit.library.PhaseOracle.num_captured_vars") must be zero. ### num\_parameters The number of parameter objects in the circuit. ### num\_qubits Return number of qubits. ### num\_stretches The number of stretches in the circuit. This is the length of the `iter_stretches()` iterable. ### num\_vars The number of real-time classical variables in the circuit. This is the length of the `iter_vars()` iterable. ### op\_start\_times Return a list of operation start times. > **Note** > > This attribute computes the estimate starting time of the operations in the scheduled circuit and only works for simple circuits that have no control flow or other classical feed-forward operations. This attribute is enabled once one of scheduling analysis passes runs on the quantum circuit. **Example** ```python from qiskit import QuantumCircuit from qiskit.providers.fake_provider import GenericBackendV2 from qiskit.transpiler import generate_preset_pass_manager qc = QuantumCircuit(2) qc.h(0) qc.cx(0, 1) qc.measure_all() # Print the original circuit print("Original circuit:") print(qc) # Transpile the circuit with a specific basis gates list and print the resulting circuit backend = GenericBackendV2(2, basis_gates=['u1', 'u2', 'u3', 'cx']) pm = generate_preset_pass_manager( optimization_level=1, backend=backend, scheduling_method="alap" ) transpiled_qc = pm.run(qc) print("Transpiled circuit with basis gates ['u1', 'u2', 'u3', 'cx']:") print(transpiled_qc) # Print the start times of each instruction in the transpiled circuit print("Start times of instructions in the transpiled circuit:") for instruction, start_time in zip(transpiled_qc.data, transpiled_qc.op_start_times): print(f"{instruction.operation.name}: {start_time}") ``` ```text Original circuit: ┌───┐ ░ ┌─┐ q_0: ┤ H ├──■───░─┤M├─── └───┘┌─┴─┐ ░ └╥┘┌─┐ q_1: ─────┤ X ├─░──╫─┤M├ └───┘ ░ ║ └╥┘ meas: 2/══════════════╩══╩═ 0 1 Transpiled circuit with basis gates ['u1', 'u2', 'u3', 'cx']: ┌─────────┐ ░ ┌─────────────────┐┌─┐ q_0 -> 0 ───┤ U2(0,π) ├──────■───░─┤ Delay(1255[dt]) ├┤M├ ┌──┴─────────┴───┐┌─┴─┐ ░ └───────┬─┬───────┘└╥┘ q_1 -> 1 ┤ Delay(196[dt]) ├┤ X ├─░─────────┤M├─────────╫─ └────────────────┘└───┘ ░ └╥┘ ║ meas: 2/═══════════════════════════════════╩══════════╩═ 1 0 Start times of instructions in the transpiled circuit: u2: 0 delay: 0 cx: 196 barrier: 2098 delay: 2098 measure: 3353 measure: 2098 ``` **Returns** List of integers representing instruction estimated start times. The index corresponds to the index of instruction in `QuantumCircuit.data`. **Raises** [**AttributeError**](https://docs.python.org/3/library/exceptions.html#AttributeError) – When circuit is not scheduled. ### parameters The parameters defined in the circuit. This attribute returns the [`Parameter`](/docs/api/qiskit/2.0/qiskit.circuit.Parameter "qiskit.circuit.Parameter") objects in the circuit sorted alphabetically. Note that parameters instantiated with a [`ParameterVector`](/docs/api/qiskit/2.0/qiskit.circuit.ParameterVector "qiskit.circuit.ParameterVector") are still sorted numerically. **Examples** The snippet below shows that insertion order of parameters does not matter. ```python >>> from qiskit.circuit import QuantumCircuit, Parameter >>> a, b, elephant = Parameter("a"), Parameter("b"), Parameter("elephant") >>> circuit = QuantumCircuit(1) >>> circuit.rx(b, 0) >>> circuit.rz(elephant, 0) >>> circuit.ry(a, 0) >>> circuit.parameters # sorted alphabetically! ParameterView([Parameter(a), Parameter(b), Parameter(elephant)]) ``` Bear in mind that alphabetical sorting might be unintuitive when it comes to numbers. The literal “10” comes before “2” in strict alphabetical sorting. ```python >>> from qiskit.circuit import QuantumCircuit, Parameter >>> angles = [Parameter("angle_1"), Parameter("angle_2"), Parameter("angle_10")] >>> circuit = QuantumCircuit(1) >>> circuit.u(*angles, 0) >>> circuit.draw() ┌─────────────────────────────┐ q: ┤ U(angle_1,angle_2,angle_10) ├ └─────────────────────────────┘ >>> circuit.parameters ParameterView([Parameter(angle_1), Parameter(angle_10), Parameter(angle_2)]) ``` To respect numerical sorting, a [`ParameterVector`](/docs/api/qiskit/2.0/qiskit.circuit.ParameterVector "qiskit.circuit.ParameterVector") can be used. ```python >>> from qiskit.circuit import QuantumCircuit, Parameter, ParameterVector >>> x = ParameterVector("x", 12) >>> circuit = QuantumCircuit(1) >>> for x_i in x: ... circuit.rx(x_i, 0) >>> circuit.parameters ParameterView([ ParameterVectorElement(x[0]), ParameterVectorElement(x[1]), ParameterVectorElement(x[2]), ParameterVectorElement(x[3]), ..., ParameterVectorElement(x[11]) ]) ``` **Returns** The sorted [`Parameter`](/docs/api/qiskit/2.0/qiskit.circuit.Parameter "qiskit.circuit.Parameter") objects in the circuit. ### prefix Default value: `'circuit'` ### qregs A list of `Qubit`s in the order that they were added. You should not mutate this. ### qubits A list of `Qubit`s in the order that they were added. You should not mutate this. ### unit The unit that [`duration`](#qiskit.circuit.library.PhaseOracle.duration "qiskit.circuit.library.PhaseOracle.duration") is specified in. > **Deprecated since version 1.3.0** > > The property `qiskit.circuit.quantumcircuit.QuantumCircuit.unit` is deprecated as of Qiskit 1.3.0. It will be removed in Qiskit 3.0.0. ### name Type: `str` A human-readable name for the circuit. **Example** ```python from qiskit import QuantumCircuit qc = QuantumCircuit(2, 2, name="my_circuit") print(qc.name) ``` ```text my_circuit ``` ## Methods ### evaluate\_bitstring `evaluate_bitstring(bitstring)` [GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.0/qiskit/circuit/library/phase_oracle.py#L70-L81) Evaluate the oracle on a bitstring. This evaluation is done classically without any quantum circuit. **Parameters** **bitstring** ([*str*](https://docs.python.org/3/library/stdtypes.html#str)) – The bitstring for which to evaluate. The input bitstring is expected to be in little-endian order. **Returns** True if the bitstring is a good state, False otherwise. **Return type** [bool](https://docs.python.org/3/library/functions.html#bool) ### from\_dimacs\_file *classmethod* `from_dimacs_file(filename)` [GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.0/qiskit/circuit/library/phase_oracle.py#L83-L129) Create a PhaseOracle from the string in the DIMACS format. It is possible to build a PhaseOracle from a file in [DIMACS CNF format](https://web.archive.org/web/20190325181937/https://www.satcompetition.org/2009/format-benchmarks2009.html), which is the standard format for specifying SATisfiability (SAT) problem instances in [Conjunctive Normal Form (CNF)](https://en.wikipedia.org/wiki/Conjunctive_normal_form), which is a conjunction of one or more clauses, where a clause is a disjunction of one or more literals. The following is an example of a CNF expressed in the DIMACS format: ```text c DIMACS CNF file with 3 satisfying assignments: 1 -2 3, -1 -2 -3, 1 2 -3. p cnf 3 5 -1 -2 -3 0 1 -2 3 0 1 2 -3 0 1 -2 -3 0 -1 2 3 0 ``` The first line, following the c character, is a comment. The second line specifies that the CNF is over three boolean variables — let us call them $x_1, x_2, x_3$, and contains five clauses. The five clauses, listed afterwards, are implicitly joined by the logical AND operator, $\land$, while the variables in each clause, represented by their indices, are implicitly disjoined by the logical OR operator, $lor$. The $-$ symbol preceding a boolean variable index corresponds to the logical NOT operator, $lnot$. Character 0 (zero) marks the end of each clause. Essentially, the code above corresponds to the following CNF: $(\lnot x_1 \lor \lnot x_2 \lor \lnot x_3) \land (x_1 \lor \lnot x_2 \lor x_3) \land (x_1 \lor x_2 \lor \lnot x_3) \land (x_1 \lor \lnot x_2 \lor \lnot x_3) \land (\lnot x_1 \lor x_2 \lor x_3)$. **Parameters** **filename** ([*str*](https://docs.python.org/3/library/stdtypes.html#str)) – A file in DIMACS format. **Returns** A quantum circuit with a phase oracle. **Return type** [PhaseOracle](#qiskit.circuit.library.PhaseOracle "qiskit.circuit.library.PhaseOracle")