Fix phase for [-1, 0] Isometry.
#15470
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Signed-off-by: Kalpesh Bhatnagar <[email protected]>
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Summary
Addresses #15465
Adds a extra condition to _disentangle function in
isometry.pythat prevents the code from ignoring the pi phase of [-1, 0] Isometry.Details and comments
The problem only occurs for when the
UCGate(given as list of single-qubit gates), which is used to disentangle a qubit while encoding the Isometry, is just a single diagonal gate with real values. This only occurs when this gate is eitheridentityor-1*identity. Earlier this-1*identitywas skipped, ignoring the global phase, leading to the phase-incorrect [-1,0]. But with the new check this is fixed.