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Can antisymmetry become an operational resource?

Treat measurements within fixed blocks as free and charge for measurements between blocks. Can an average monotone of singlet correlations or multiplicity information bound state-conversion cost?

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Working mathematical formulation

As one concrete restricted model, divide labeled qubits into fixed blocks of at most bb qubits. Allow adaptive STP inside a block, fresh maximally mixed local ancillas, and local discarding at zero cost; charge one unit for a measurement joining different blocks. Is there a nonnegative state functional RR, vanishing on the chosen free initial states, that is nonincreasing on average under free instruments and increases by at most a constant per charged measurement? Seek a lower bound on the expected number of cross-block measurements needed for a specified state-conversion task.

Scope & assumptions

The block-restricted model is one possible resource-theory convention. State explicitly whether a bound is averaged over measurement outcomes or required for every outcome. A useful measure should depend on more than the globally conserved spin label.

Why this is interesting

A count of singlet pairs can miss overlapping constraints and delocalized correlations. Declaring all adaptive STP free would also make many intended resources freely generatable.

Explicit variants

  1. Alternative restrictions

    Repeat the question with geometry, bounded adaptive depth, or a restricted preparation library as the charged resource. Each choice defines a different resource theory and must have its own free states and operations.

  2. Monotones of the actual STP process

    On a fixed closed register, characterize functions MM satisfying ∑opoM(ρo)≤M(ρ)\sum_o p_o M(\rho_o)\le M(\rho) for every allowed pair measurement. Separate conserved sector weights from quantities sensitive to the multiplicity state, and ask whether any such quantity bounds a stated conversion cost. An average monotone need not decrease in each selected branch.

  3. Information encoded in antisymmetry

    At fixed total spin, compare states with the same total singlet weight but different pair probabilities, multiplicity correlations, or coherence. Which distinctions predict advantage for a stated conversion or inference task? Determine which candidate information is operationally accessible under the chosen real invariant instruments.

  4. Subsystem-spin martingales and constraints

    For outcome history hth_t on a fixed register, let pt(S,j)=Tr⁡(ΠS,jρht)p_t(S,j)=\operatorname{Tr}(\Pi_{S,j}\rho_{h_t}). Which functions of the overlapping distributions pt(S,j)p_t(S,j) are conserved, martingales, or supermartingales under every allowed next pair measurement? Include functions of multiplicity data when the marginal distributions are insufficient. A bound on a stopped protocol must state its stopping and integrability assumptions.

A place to start

Test candidate measures on two singlets, their recoupled branches, and a fully symmetric state; reject candidates that merely reproduce global total spin.

Related work

These works provide context and established results. They need not be the origin of this exact formulation.

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