Dense indistinguishability conjecture for adaptive quantum query algorithms

Prove that every T-query quantum algorithm has distinguishing advantage at most C T^a delta^b between a (1-delta)-dense oracle distribution and the uniform oracle distribution, for absolute constants C, a >= 0, and b > 0.

Background

A distribution over Boolean oracles is (1-delta)-dense when every marginal has min-entropy at least (1-delta) times its dimension. The conjecture asserts that bounded-query quantum algorithms cannot substantially distinguish such distributions from uniformly random oracles.

The paper proves the conjecture for one massively parallel quantum-query layer and derives restricted extensions, but the adaptive quantum-query case remains the unresolved general target motivating the computationally hidden flipped set approach.

References

We call this the Dense Indistinguishability Conjecture.

Parallel Quantum Advantage with Limited Adaptivity Requires Structure  (2608.20297 - Liu et al., 20 Aug 2026) in Introduction, Dense Indistinguishability Conjecture; Section 3, Conjecture 3