Variational Estimation of Optimal Signal States for Quantum Channels

Abstract

This paper explores the performance of quantum communication systems in the presence of noise and focuses on finding the optimal encoding for maximizing the classical communication rate, approaching the classical capacity in some scenarios. Instead of theoretically bounding the ultimate capacity of the channel, we adopt a signal-processing perspective to estimate the achievable performance of a physically available but otherwise unknown quantum channel. By employing a variational algorithm to estimate the trace distance between quantum states, we numerically determine the optimal encoding protocol for the amplitude damping and Pauli channels. Our simulations demonstrate the convergence and accuracy of the method with a few iterations, confirming that optimal conditions for binary quantum communication systems can be variationally determined with minimal computation. Further, since the channel knowledge is not required at the transmitter or at the receiver, these results can be employed in arbitrary quantum communication systems, including satellite-based communication systems, a particularly relevant platform for the quantum Internet.

Characterizing and Utilizing the Interplay Between Quantum Technologies and Non-Terrestrial Networks

“…Furthermore, the recent progress in quantum nonlinear optics, entangled photon generation, and single-photon detection has positioned NTNs as an important driver for the advancement of robust long-range quantum communication [85]. In the context of quantum communication, the transfer of quantum states across spatial distances is achieved through quantum channels [86]. These channels are in the optical domain and include optical fiber, FSO, or Li-Fi channels, as depicted in the schematic diagram in Fig.…”