The parity of the number of elementary excitations present in a quantum system provides important insights into its physical properties. Parity measurements are used, for example, to tomographically reconstruct quantum states or to determine if the decay of an excitation has occurred, information that can be used for quantum error correction in computation or communication protocols. Here, we demonstrate a versatile parity detector for propagating microwaves, which distinguishes between radiation fields containing an even or odd number $n$ of photons, both in a single-shot measurement and without perturbing the parity of the detected field. We showcase applications of the detector for direct Wigner tomography of propagating microwaves and heralded generation of Schrödinger cat states. This parity detection scheme is applicable over a broad frequency range and may prove useful, for example, for heralded or fault-tolerant quantum communication protocols.

中文翻译：

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传播微波场的奇偶检测

量子系统中存在的基本激发数的奇偶性提供了对其物理性质的重要见解。奇偶性测量可用于例如以断层摄影的方式重建量子状态或确定是否发生了激励衰减，这些信息可用于计算或通信协议中的量子误差校正。在这里，我们演示了一种用于微波传播的通用奇偶检测器，该检测器可区分包含偶数或奇数的辐射场$ñ$在单次测量中并且不会干扰检测到的场的奇偶性的光子的数量。我们展示了该探测器在传播微波直接威格纳层析成像和先驱Schrödinger猫态上的应用。此奇偶校验检测方案可在很宽的频率范围内应用，并且可能证明对例如预告或容错量子通信协议很有用。