Quantum-resource separation for random-function f-BB84 schemes

Determine whether the ancilla-size lower bounds known for random-function f-BB84 schemes establish a separation between the quantum resources required by honest and dishonest players, particularly when classical memory used by a physical attacker may be counted as quantum ancilla in the purified model.

Background

The paper discusses prior lower bounds for random-function f-BB84 schemes that concern the quantum ancilla size of an attacker, and notes that these bounds are obtained in a purified model. Because such a model may treat an attacker's classical memory as quantum ancilla, the authors leave unresolved whether the results demonstrate a genuine separation in the quantum resources required by honest and dishonest participants.

References

This purified model may be counting classical memory used by a physical attacker as quantum ancilla, so it is not clear if this establishes a separation in the quantum resources needed by an honest or dishonest player.

— Quantum gate lower bounds for loss-tolerant position verification  (2608.16495 - May et al., 17 Aug 2026) in Section 1, subsection “Prior work”