Add loss policies to NoiseConfig to express different kinds of behavior on lost qubits#3302
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orpuente-MS wants to merge 1 commit into
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Add loss policies to NoiseConfig to express different kinds of behavior on lost qubits#3302orpuente-MS wants to merge 1 commit into
NoiseConfig to express different kinds of behavior on lost qubits#3302orpuente-MS wants to merge 1 commit into
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orpuente-MS
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billti,
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minestarks and
swernli
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billti
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Jun 13, 2026
| # | ||
| # These exercise the per-gate `NoiseConfig.<gate>.on_loss` behavior. The | ||
| # `on_loss` policy is honored by the cpu (full-state) and clifford (stabilizer) | ||
| # simulators, so these tests are parametrized over just those two. |
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Is this correct? Looks like GPU is included below.
billti
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Jun 13, 2026
| @pytest.mark.parametrize("sim_type", LOSS_POLICY_SIM_TYPES) | ||
| def test_on_loss_swap_skip_keeps_state_but_swaps_loss_flag(sim_type): | ||
| # Overriding `swap.on_loss` to SKIP skips the SWAP unitary, but the loss | ||
| # flag is still exchanged. qs[0] keeps its reset |0> and qs[1] becomes lost. |
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This one is interesting. Worth discussing more. Seems odd you would skip the unitary (which swaps the state) but still swap which is lost. Not sure if that would be physically possible.
billti
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Jun 13, 2026
| // Loss policy values. These are stamped onto a gate op's `q3` field by the host | ||
| // (see `LossPolicy::as_u32` on the Rust side) and tell the shader how to handle | ||
| // the gate when one of its operands is lost. `0` means "no policy stamped", | ||
| // which the shader treats the same as SKIP. |
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When I was looking at the enum I was wondering why the default value (0) wasn't skip. Is there a reason to start at 1 and leave 0 undefined/no-policy?
billti
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Jun 13, 2026
| if (shot.qubit_state[q1].heat == -1.0) { | ||
| return true; | ||
| } | ||
| let is_2q = (op.id == OPID_CX || op.id == OPID_CY || op.id == OPID_CZ || |
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You already have is_1q_op defined (line 74). Can you just negate that? For now we only have 1q and 2q ops.
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With this change, users are able to specify how gates should behave if at least one of their qubit operands is lost. Below is a comprehensive example, showing all 5 loss policies.