Unlimited quantum correlation advantage from bound entanglement (2504.06395v1)

Abstract: Entangled states that cannot be distilled to maximal entanglement are called bound entangled and they are often viewed as too weak to break the limitations of classical models. Here, we show a strongly contrasting result: that bound entangled states, when deployed as resources between two senders who communicate with a receiver, can generate correlation advantages of unlimited magnitude. The proof is based on using many copies of a bound entangled state to assist quantum communication. We show that in order to simulate the correlations predicted by bound entanglement, one requires in the many-copy limit either an entanglement visibility that tends to zero or a diverging amount of overhead communication. This capability of bound entanglement is unlocked by only using elementary single-qubit operations. The result shows that bound entanglement can be a scalable resource for breaking the limitations of physical models without access to entanglement.

Unlimited Quantum Correlation Advantage from Bound Entanglement

The concept of entanglement, a cornerstone of quantum information theory, often involves the distillation process, where non-maximally entangled states are transformed into maximally entangled ones. However, some entangled states, known as bound entangled states, resist this transformation even when an infinite number of copies are available. These bound entangled states do not surpass the potential of classical models in most conventional quantum information tasks, such as quantum communication and quantum teleportation. Despite their prevalence in high-dimensional Hilbert spaces, their utility has been largely underestimated due to these limitations. Yet, the paper at hand offers compelling evidence that bound entanglement can hold a surprising quantum advantage with unlimited potential.

Key Contributions

The authors establish that bound entangled states can generate correlation advantages of an unlimited magnitude in specific quantum communication scenarios. This phenomenon occurs when bound entangled states are utilized as resources in communication tasks involving two senders and one receiver. By employing many copies of a bound entangled state to assist quantum communication, they demonstrate that either the visibility of entanglement approaches zero, or there is a divergence in the needed overhead communication to simulate predicted correlations in the classical field.

A critical finding is that the binding power of entanglement is unlocked using only elementary single-qubit operations. Previously, bound entangled states were thought unsuitable for major tasks such as violating any Bell inequalities—long considered the litmus test for non-classicality. While this belief was challenged in 2014, the violations were marginal. This paper presents a stark contrast by revealing substantial and scalable correlations without the usual overhead, bridging the gap for quantum technologies that cannot access entanglement otherwise.

Implications and Future Directions

The implications of this research are multifaceted. Theoretically, it challenges our understanding of quantum resource theories and calls for a reevaluation of paradigms regarding the utility and classification of entangled states. Practically, leveraging bound entanglement may significantly enhance quantum communication strategies, providing new avenues for resource-efficient quantum networks, even suggesting future explorations into proving the first significant Bell test violations with bound entangled states.

Moreover, this research emphasizes simplicity in protocols. All encoding and decoding operations can be performed using single-qubit Pauli observables—no multi-partite entangling operations are necessary, showcasing the remarkable power of bound entanglement with simpler resources.

Conclusion

Overall, this paper elucidates bound entanglement as a previously underestimated quantum resource with the capacity to outperform classical models without entanglement. Its insights open new territories for exploration within quantum computing and quantum communication and exemplify the dynamism of entangled states when viewed through the lens of atypical quantum environments. Future research could zoom into optimizing these setups in practical implementations and leveraging them for new quantum communication protocols, further cementing the unexpected potency of bound entanglement.