We show experimentally that a dc-biased Josephson junction in series with two microwave resonators emits entangled beams of microwaves leaking out of the resonators. In the absence of a stationary phase reference for characterizing the entanglement of the outgoing beams, we measure second-order coherence functions to prove the entanglement. The experimental results are found in quantitative agreement with theory, proving that the low-frequency noise of the dc bias is the main limitation for the coherence time of the entangled beams. This agreement allows us to evaluate the entropy of entanglement of the resonators, estimate the entanglement flux at their output, and to identify the improvements that could bring this device closer to a useful bright source of entangled microwaves for quantum-technological applications.

中文翻译：

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使用直流偏置约瑟夫森结产生两个连续纠缠微波束

我们通过实验表明，与两个微波谐振器串联的直流偏置约瑟夫森结会发射从谐振器泄漏的纠缠微波束。在没有用于表征出射光束纠缠的固定相位参考的情况下，我们测量二阶相干函数以证明纠缠。实验结果与理论定量一致，证明直流偏置的低频噪声是纠缠光束相干时间的主要限制因素。该协议使我们能够评估谐振器的纠缠熵，估计其输出处的纠缠通量，并确定可以使该设备更接近用于量子技术应用的有用的纠缠微波明亮源的改进。