We demonstrate that under imperfect preshared entanglement-distribution, entanglement-assisted (EA) communication can be inferior compared to classical communication. When both signal and idler channels are used for classical transmission then classical capacity is always higher than EA-capacity.
Entanglement assisted communication is advocated by numerous authors as an alternative to classical communication offering significant improvement in channel capacity, in particular in noisy regime. In all those papers it is always assumed that entanglement can be distributed without any imperfections, except for attenuation. We demonstrate that under imperfect pre-shared entanglement distribution, assuming that entanglement distribution channel is modeled as a noisy and lossy Bosonic channel, the entanglement assisted communication can be inferior compared to the classical communication, depending on the parameters of the distribution channel. We identify the conditions under which entanglement assistance can still provide an advantage over the classical case. In particular, when both communication and entanglement distribution channels are not used for entanglement assisted communication but rather for classical transmission instead then the classical capacity is always higher than the entanglement assisted capacity. We also study the entanglement assisted communication under the strong atmospheric turbulence effects.
Entanglement underpins a variety of quantum-enhanced communication, sensing, and computing capabilities. Entanglement-assisted communication (EACOMM) leverages entanglement preshared by communicating parties to boost the rate of classical information transmission. Pioneering theory works showed that EACOMM can enable a communication rate well beyond the ultimate classical capacity of optical communications, but an experimental demonstration of any EACOMM advantage remains elusive. In this Letter we report the implementation of EACOMM surpassing the classical capacity over lossy and noisy bosonic channels. We construct a high-efficiency entanglement source and a phase-conjugate quantum receiver to reap the benefit of preshared entanglement, despite entanglement being broken by channel loss and noise. We show that EACOMM beats the Holevo-Schumacher-Westmoreland capacity of classical communication by up to 16.3%, when both protocols are subject to the same power constraint at the transmitter. As a practical performance benchmark, we implement a classical communication protocol with the identical characteristics for the encoded signal, showing that EACOMM can reduce the bit-error rate by up to 69% over the same bosonic channel. Our work opens a route to provable quantum advantages in a wide range of quantum information processing tasks.
Entanglement assisted (EA) communication represents an interesting alternative to classical communication, in particular in low-brightness and highly noisy regime when it outperforms significantly corresponding classical counterpart in terms of the channel capacity. Even though that the EA capacity is known for decades the optimum quantum receiver has not been determined yet. In this paper, we propose several low-complexity quantum receivers outperforming recently proposed receivers employing the optical parametric amplifier as a basic building block. We demonstrate by simulations that the capacity of the proposed EA schemes, employing Gaussian modulation and the proposed low-complexity joint receivers, can significantly outperform both the Holevo capacity and classical homodyne and heterodyne channel capacities.
Entanglement assisted (EA) communication has been advocated by numerous authors as a potential alternative to classical communications, in particular in noisy and low-brightness regime. In this paper, we propose an EA scheme employing the optical phase-conjugation (OPC) on transmitter side. We show that the proposed EA communication system, with the transmitter side OPC, significantly outperforms its classical counterpart in low-brightness and highly noisy regime, while employing a classical coherent detection scheme for two-dimensional demodulation. Moreover, the capacity of the proposed EA scheme is significantly higher than EA repetition-BPSK, homodyne, heterodyne, and Holevo capacities. Finally, the proposed EA scheme outperforms the corresponding EA scheme with OPC placed on a receiver side.