mirror of https://github.com/Qiskit/qiskit.git
34 lines
1.6 KiB
YAML
34 lines
1.6 KiB
YAML
---
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fixes:
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- |
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The control-flow builder interface (the context-manager forms of
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:meth:`.QuantumCircuit.if_test`, :meth:`~.QuantumCircuit.while_loop`,
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:meth:`~.QuantumCircuit.for_loop` and :meth:`~.QuantumCircuit.switch`) will now correctly track
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a separate global-phase advancement within that block. You can add a global-phase advancement
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to an inner block by assigning to :attr:`.QuantumCircuit.global_phase` within a builder scope::
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from math import pi
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from qiskit import QuantumCircuit
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qc = QuantumCircuit(3, 3)
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qc.global_phase = pi / 2 # Set the outer circuit's global phase.
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with qc.if_test((qc.clbits[0], False)) as else_:
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# The global phase advancement in a control-flow block begins at 0,
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# because it represents how much the phase will be advanced by an
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# execution of the block. The defined phase of the outer scope is not
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# affected by this set.
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qc.global_phase = pi
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with else_:
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# Similarly, the `else` block may induce a different global-phase
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# advancement to the `if`, so it can also be set separately.
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qc.global_phase = 1.5 * pi
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# The phase advancement caused directly by the outer scope is independent
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# of the phase advancement conditionally caused by each control-flow path.
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assert qc.global_phase == pi / 2
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The meaning of :attr:`.QuantumCircuit.global_phase` is taken to be the global-phase advancement
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that is inherent to a single execution of the block. It is still a *global* phase advancement,
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in that if the block is entered, the phase of all qubits in the entire program will be advanced.
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