Non-signaling assistance can replicate quantum communication in prepare-and-measure scenarios
Researchers show that non-signaling correlations, even without adaptive measurements, can simulate the transmission of a qudit using a classical message of the same dimension, and they identify the exact cases where adaptive strategies give a genuine advantage.
A recent theoretical study examined prepare-and-measure (PM) communication protocols that use only classical messages but are assisted by non-signaling (NS) correlations. The authors distinguished between adaptive strategies, where the receiver’s measurement depends on the received message, and non-adaptive strategies, where the measurement is fixed in advance.
The analysis demonstrated that non-adaptive NS assistance is sufficient to reproduce the capabilities of quantum communication with the same message dimension; specifically, the transmission of a qudit can be simulated by a classical dit when supplemented by NS correlations. This result implies that the advantage previously attributed to quantum entanglement can be matched without requiring adaptive measurement choices.
When comparing adaptive and non-adaptive NS assistance, the researchers proved that any advantage of adaptation originates only from scenarios in which the receiver has no genuine measurement choice. Consequently, the multi-setting benefits observed in entanglement-assisted quantum protocols do not arise in NS-assisted classical settings.
The team also provided a complete classification of PM scenarios where adaptive NS strategies outperform non-adaptive ones, clarifying the limits and potential of NS assistance in communication theory.
"Non-adaptive NS assistance is already strong enough to reproduce quantum communication with the same message dimension," the authors state.
"Any adaptive NS advantage can be traced back to scenarios in which the receiver has no measurement choice," they add.
