Counting the state of a qubit Operation of a quantum computer will be reliant on the ability to correct errors. This will typically require the fast, high-fidelity quantum nondemolition measurement of a large number of qubits. Opremcak et al. describe a method that uses a photon counter to determine the state of a superconducting qubit. Being able to simply read out the qubit state as a photon number removes the need for bulky components and large experimental overhead that characterizes present approaches. Science, this issue p. 1239 A microwave photon counter is used to determine the state of a superconducting qubit. Fast, high-fidelity measurement is a key ingredient for quantum error correction. Conventional approaches to the measurement of superconducting qubits, involving linear amplification of a microwave probe tone followed by heterodyne detection at room temperature, do not scale well to large system sizes. We introduce an approach to measurement based on a microwave photon counter demonstrating raw single-shot measurement fidelity of 92%. Moreover, the intrinsic damping of the photon counter is used to extract the energy released by the measurement process, allowing repeated high-fidelity quantum nondemolition measurements. Our scheme provides access to the classical outcome of projective quantum measurement at the millikelvin stage and could form the basis for a scalable quantum-to-classical interface.

中文翻译：

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用微波光子计数器测量超导量子位

计算量子位的状态 量子计算机的操作将依赖于纠正错误的能力。这通常需要对大量量子位进行快速、高保真量子非破坏测量。Opremcak 等人。描述一种使用光子计数器来确定超导量子位状态的方法。能够简单地将量子位状态读出为光子数，消除了现有方法对庞大组件和大量实验开销的需求。科学，这个问题 p。1239 微波光子计数器用于确定超导量子位的状态。快速、高保真测量是量子纠错的关键因素。测量超导量子位的传统方法，涉及微波探测音的线性放大，然后在室温下进行外差检测，不能很好地扩展到大型系统尺寸。我们介绍了一种基于微波光子计数器的测量方法，展示了 92% 的原始单次测量保真度。此外，光子计数器的固有阻尼用于提取测量过程释放的能量，允许重复高保真量子非爆破测量。我们的方案提供了对毫开尔文阶段投影量子测量的经典结果的访问，并且可以形成可扩展的量子到经典界面的基础。我们介绍了一种基于微波光子计数器的测量方法，展示了 92% 的原始单次测量保真度。此外，光子计数器的固有阻尼用于提取测量过程释放的能量，允许重复高保真量子非爆破测量。我们的方案提供了对毫开尔文阶段投影量子测量的经典结果的访问，并且可以形成可扩展的量子到经典界面的基础。我们介绍了一种基于微波光子计数器的测量方法，展示了 92% 的原始单次测量保真度。此外，光子计数器的固有阻尼用于提取测量过程释放的能量，允许重复高保真量子非爆破测量。我们的方案提供了对毫开尔文阶段投影量子测量的经典结果的访问，并且可以形成可扩展的量子到经典界面的基础。