Quantum MIMO Diversity over Discrete-Variable Crosstalk Channels

TL;DR

This paper introduces a quantum MIMO diversity strategy using approximate cloning and purification to enhance communication fidelity over channels with crosstalk and depolarization, highlighting advantages and limitations of distributing quantum information across multiple channels.

Contribution

It proposes a novel quantum MIMO diversity method employing cloning and purification, analyzing its performance compared to simpler strategies under various channel conditions.

Findings

Cloning-purification strategy outperforms best-channel selection in certain scenarios.

Full channel state information improves cloning asymmetry optimization.

Distributing quantum information across channels has limitations due to cloning costs.

Abstract

Quantum communication plays a pivotal role in enabling distributed quantum computing and sensing. Diversity strategies can be used to increase the communication reliability (in the sense of output fidelity with respect to the input quantum state) when multiple communication channels are available. The current paper proposes a diversity strategy for quantum discrete variable (DV) multiple-input-multiple-output (MIMO) channels, utilizing approximate cloning to distribute information across multiple channels at the transmitter and purification to merge the noisy and entangled joint state into a single quantum state at the receiver. The proposed method is compared with simpler strategies, such as the best-channel selection, to identify the advantage regions over a quantum channel combining both crosstalk and depolarization, where the crosstalk is modeled by a controlled-SWAP operator. Our numerical results show that the cloning-purification strategy offers an advantage, especially in cases where full channel state information (CSI) can be exploited to optimize the cloning asymmetry. More importantly, and in contrast to the classic MIMO diversity, we demonstrate that the distribution of quantum information over all available channels does not always provide an advantage due to the dilution cost of the cloning operation.