Add bloq for Measurement in the X basis #1683
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- MeasX measures a qubit in the X basis. - If simulated classically, this returns a classical distribution of 0 and 1 with a possible phase if 1 is measured. Original work done by mpharrigan in quantumlib#1678
mpharrigan
reviewed
Aug 11, 2025
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| with pytest.raises(ValueError, match='MeasX imparts a phase'): | ||
| _ = bloq.call_classically(q=0) |
| _ = bloq.on_classical_vals(q=2) | ||
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| results = [ | ||
| do_phased_classical_simulation(bloq, {'q': 0}, rng=np.random.default_rng()) |
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what do you think about seeding our random generator in tests? usually we do; and theoretically line 151 or 152 could fail
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| # Zero -> Zero | ||
| bb = BloqBuilder() | ||
| q = bb.add(ZeroState()) | ||
| c = bb.add(MeasX(), q=q) | ||
| cbloq = bb.finalize(c=c) | ||
| rho = cbloq.tensor_contract(superoperator=True) | ||
| should_be = np.asarray([[0.5, 0], [0, 0.5]]) | ||
| np.testing.assert_allclose(rho, should_be, atol=1e-8) | ||
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| # One -> One | ||
| bb = BloqBuilder() | ||
| q = bb.add(OneState()) | ||
| c = bb.add(MeasX(), q=q) | ||
| cbloq = bb.finalize(c=c) | ||
| rho = cbloq.tensor_contract(superoperator=True) | ||
| should_be = np.asarray([[0.5, 0], [0, 0.5]]) | ||
| np.testing.assert_allclose(rho, should_be, atol=1e-8) | ||
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| # Plus -> mixture | ||
| bb = BloqBuilder() | ||
| q = bb.add(PlusState()) | ||
| c = bb.add(MeasX(), q=q) | ||
| cbloq = bb.finalize(c=c) | ||
| rho = cbloq.tensor_contract(superoperator=True) | ||
| should_be = np.asarray([[1, 0], [0, 0]]) | ||
| np.testing.assert_allclose(rho, should_be, atol=1e-8) |
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I think these tests are correct, but the comments are not
Measuring the zero ket in the x basis gives fully-mixed state (the identity matrix); as does measuring the one ket.
Measuring the plus state in the x basis gives you a deterministic "0" result |0><0| = [[1,0],[0,0]]
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Ha, yeah, copied from Z-basis test and fixed the operators but not the comments. Fixed now.
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phase if 1 is measured.
Original work done by mpharrigan in #1678