The pulling chain, assembled #
MIPRE/Background/QLD/Chain.lean and MIPRE/Background/QLD/ChainPhysical.lean prove the eleven
displays of lem:qld-pauli-selfcons's derivation one at a time. This file names the terms they run
through and reads the displays as bounds on consecutive deviations, which is the form the
chaining inequality consumes.
chainT is the chain, on the physical model: ten terms for nine steps. The four displays
eq:qld-pulling-0 to -3 are the first cut's (SimulPair.chainS), and everything from -5 on is
the physical model's own. The three terms between -3 and -5 are left out, the chain paying
nothing for them (SimulPair.chainS_three_mulVec, MirrorSimul.chainS3b_mulVec).
Three of the nine steps are free --- eq:qld-pulling-2 and -2b, then -3a to -5, then
-9a --- and the six that are not cost, in order: item 1 of lem:qld-helper, the game's
point--point consistency, item 2 of lem:qld-helper, eq:qld-pulling-10 complete, item 2 of
lem:qld-helper again at the second cut, and Schwartz--Zippel. The chain's total is nine times
their sum, not two to the ninth power, because a chain's deviation telescopes and Cauchy--Schwarz
against the constant one turns the squared norm of a sum of nine terms into nine times the sum of
their squares (StateModel.sum_snorm_sq_chain_le).
The last thing this file needs that Chain.lean did not have is the cost of eq:qld-pulling-3:
sum_uniform_xSqNorm_pt_le reads the game's point--point consistency on the physical model, which
reproduces the strategy's expectations for operators that do not see the registers.
Stated in a bipartite model #
Stated in a bipartite model (Phase 5 of planning/mipco-track.md). The chain runs in the physical
model phys (Anc F m) F m d M Mi.K of a MirrorSimul. The matrix route ran the first four terms on
a regrouping mVec of the first cut's state and carried them to the physical cut by an explicit
lift (physLift); the first cut is a reading of the physical model's state model, so here the
first four terms are the first cut's terms as they stand, and nothing is lifted. That the physical
model reproduces the strategy's expectations (bornProb_mVec_ext, xSqNorm_mVec_ext) is the
embedding of the model into its physical model with the registers inert (physInert); the steps
that read the second cut go through MirrorSimul.bornProb_physVec_bOp. The constants are the
matrix ones.
The cut the chain runs on reproduces the strategy's own expectations for operators
extended by the identity on every register: the model embeds in its physical model with the
registers inert (physInert).
And so it reproduces the strategy's cross-party deviations.
The cost of eq:qld-pulling-3: the point measurements' own cross-party deviation, read
on the physical model, is the game's point--point consistency and nothing more.
The chain, on the physical model. Ten terms: the four displays eq:qld-pulling-0 to -3
of the first cut, then -5, -7, -9a, -10, -11 and -12. The three terms between -3 and
-5 are left out, the chain paying nothing for them.
Equations
- One or more equations did not get rendered due to their size.
- Mi.chainT W v u 0 = fun (a : F) => MIPRE.QLD.SimulPair.chainS Mi.first W v u 0 a
- Mi.chainT W v u 1 = fun (a : F) => MIPRE.QLD.SimulPair.chainS Mi.first W v u 1 a
- Mi.chainT W v u 2 = fun (a : F) => MIPRE.QLD.SimulPair.chainS Mi.first W v u 2 a
- Mi.chainT W v u 3 = fun (a : F) => MIPRE.QLD.SimulPair.chainS Mi.first W v u 3 a
- Mi.chainT W v u xâ = fun (a : F) => Mi.endOp W v a
Instances For
Step 0 to 1 is eq:qld-pulling-1, at item 1 of lem:qld-helper's own constant.
Step 1 to 2 is free, being displays eq:qld-pulling-2 and -2b.
Step 2 to 3 is eq:qld-pulling-3, the insertion, at the game's point--point
consistency.
Step 3 to 4 is free, being displays eq:qld-pulling-3a, -3b, -4 and -5.
Step 4 to 5 is what eq:qld-pulling-5 to -7 bounds: the gap between Alice's pair
measurement with her own point measurement beside it and without.
And its cost is display eq:qld-pulling-9, item 2 of lem:qld-helper.
Step 5 to 6 is free, being display eq:qld-pulling-9a: left-multiplying by Bob's own
pair measurement, which is the identity.
Step 6 to 7 is eq:qld-pulling-10: what the chain drops is the pairs whose outcomes
disagree at the sampled point.
Bob's sandwiched marginal, read on the second cut: the sandwich of the second cut's pair
measurement by Bob's hatted point measurement, which is what SimulPair.sum_uniform_qform_ne_le
bounds at the second cut.
And its cost, which is display eq:qld-pulling-10 complete, read on the second cut.
Bob's lift is unital.
And additive.
Step 7 to 8 is eq:qld-pulling-11: dropping Bob's point measurement from his side.
And its cost, which is item 2 of lem:qld-helper at the second cut.
Coupled pairs agree at every point. The coupling is an identity of polynomials, so evaluating it at the sampled point gives the chain's agreement condition.
Step 8 to 9 is eq:qld-pulling-12: what the chain drops is the pairs that agree at the
sampled point without being coupled.
And its cost is md/q, by Schwartz--Zippel.
The three free steps, averaged #
Averaging a constant multiple of a chain's steps: the average goes inside.
The chain starts at Alice's exact Pauli measurement on her physical registers.
And ends at eq:qld-pulling-12.
The pulling chain, assembled. Nine steps, of which three are free; the chain's total deviation is at most nine times the sum of the steps', by Cauchy--Schwarz against the constant one.
Display eq:qld-pulling-cons for Alice: her exact Pauli measurement on her physical
registers is close, in summed squared state distance, to the chain's endpoint.