Quantum superdense coding protocols enhance channel capacity by using shared quantum entanglement between two users. The channel capacity can be as high as 2 when one uses entangled qubits. However, this limit can be surpassed by using high-dimensional entanglement. We report an experiment that exceeds the limit using high-quality entangled ququarts with fidelities up to 0.98, demonstrating a channel capacity of 2.09 ± 0.01. The measured channel capacity is also higher than that obtained when transmitting only one ququart. We use the setup to transmit a five-color image with a fidelity of 0.952. Our experiment shows the great advantage of high-dimensional entanglement and will stimulate research on high-dimensional quantum information processes.

中文翻译：

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纠缠四方超出了超强编码的信道容量限制。

量子超密集编码协议通过使用两个用户之间共享的量子纠缠来增强信道容量。当使用纠缠的量子比特时，信道容量可以高达2。但是，使用高维缠结可以超越此限制。我们报告了一个实验，该实验使用保真度高达0.98的高质量纠缠quaquart超出了限制，表明通道容量为2.09±0.01。测得的信道容量也高于仅发送一个四方时获得的信道容量。我们使用该设置来传输保真度为0.952的五色图像。我们的实验显示了高维纠缠的巨大优势，并将激发对高维量子信息过程的研究。