Developments over the last two decades have opened the path towards quantum technologies in many quantum systems, such as cold atoms, trapped ions, cavity-quantum electrodynamics (QED), and circuit-QED. However, the fragility of quantum states to the effects of measurement and decoherence still poses one of the greatest challenges in quantum technology. An imperative capability in this path is quantum feedback, as it enhances the control possibilities and allows for prolonging coherence times through quantum error correction. While changing parameters from shot to shot of an experiment or procedure can be considered feedback, quantum mechanics also allows for the intriguing possibility of performing feedback operations during the measurement process itself. This broader approach to measurements leads to the concepts of weak measurement, quantum trajectories, and numerous types of feedback with no classical analogs. These types of processes are the primary focus of this review. We introduce the concept of quantum feedback in the context of circuit-QED, an experimental platform with significant potential in quantum feedback and technology. We then discuss several experiments and see how they elucidate the concepts of continuous measurements and feedback. We conclude with an overview of coherent feedback, with application to fault-tolerant error correction.

过去二十年来的发展为许多量子系统中的量子技术开辟了道路，例如冷原子，捕获离子，腔量子电动力学（QED）和电路QED。然而，量子态对测量和退相干效应的脆弱性仍然构成了量子技术中的最大挑战之一。在这条路径上，当务之急是量子反馈，因为它增强了控制的可能性，并通过量子误差校正延长了相干时间。虽然可以将实验或过程的各次射击之间的参数更改视为反馈，但量子力学还允许在测量过程本身中执行反馈操作的有趣可能性。这种更广泛的测量方法导致了弱测量的概念，量子轨迹和无经典类似物的众多类型的反馈。这些类型的过程是此审查的主要重点。我们在电路QED的背景下介绍量子反馈的概念，QED是在量子反馈和技术方面具有巨大潜力的实验平台。然后，我们讨论几个实验，看看它们如何阐明连续测量和反馈的概念。最后，我们对相干反馈进行了概述，并将其应用于容错错误纠正。然后，我们讨论几个实验，看看它们如何阐明连续测量和反馈的概念。最后，我们对相干反馈进行了概述，并将其应用于容错错误纠正。然后，我们讨论几个实验，看看它们如何阐明连续测量和反馈的概念。最后，我们对相干反馈进行了概述，并将其应用于容错错误纠正。