4-to-2 Quantum Code Achieves Supremacy Over Classical Methods

Researchers Rajdeep Paul, Prabuddha Roy, and A. Pan report a specific instance of quantum supremacy using a 4-to-1 code, in which four input bits are compressed into either one or two qubits, with performance exceeding both classical random-access codes and existing quantum methods. This achievement concerns more than faster communication; the team’s approach, detailed in a recent preprint, relies on pre-shared entanglement between communicating parties, a departure from standard quantum communication protocols. The researchers extended their analysis to demonstrate potential advantages in n-to-n-2 codes, suggesting scalability beyond the initial demonstration.

This work isn’t simply a quantum code outperforming classical methods; it’s a demonstration with a well-defined size, reducing four input bits to either one or two output bits, with the advantage definitively proven. This research builds on the random-access code framework, where Alice encodes inputs and sends qubits to Bob, but introduces the critical element of prior entanglement, enabling a new level of control and certification within the quantum communication channel and opening possibilities for more secure and reliable quantum networks.

Researchers focused on the 4-to-1 entanglement-assisted PMRAC, with l taking values 1 and 2, deriving optimal quantum success probabilities analytically. The researchers also exhibit the addition of a verification layer to the quantum process. Their analysis extends to the 5-to-1 PMRAC, establishing upper bounds on success probabilities for l = 1, 2, and 3, and further demonstrating an advantage in the n-to-n-2 case for arbitrary n. This work, submitted for publication, highlights a semi-device-independent approach to quantum communication, where prior entanglement is key to achieving and verifying quantum capabilities, potentially influencing future secure communication designs.