The readout of a microwave qubit state occurs using an amplification chain that enlarges the quantum state to a signal detectable with a classical measurement apparatus. However, at what point in this process is the quantum state really “measured”? To investigate whether the “measurement” takes place in the amplification chain, in which a parametric amplifier is often chosen as the first amplifier, it is proposed to construct a microwave interferometer that has such an amplifier added to each of its arms. Feeding the interferometer with single photons, the interference visibility depends on the gain of the amplifiers and whether a measurement collapse has taken place during the amplification process. The visibility as given by standard quantum mechanics is calculated as a function of gain, insertion loss, and temperature. A visibility of $1/3$ is found in the limit of large gain without considering losses, which is reduced to $0.26$ in case the insertion loss of the amplifiers is $2.2\text{dB}$ at a temperature of $50\text{mK}$. It is shown that if the wave function collapses within the interferometer, the measured visibility is reduced compared with its magnitude predicted by standard quantum mechanics once this collapse process sets in.

中文翻译：

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研究行波参数放大器中波函数崩溃的实验建议

微波量子位状态的读取是使用放大链发生的，该放大链将量子状态扩大到可以用传统测量设备检测到的信号。但是，在这个过程中的什么时候真正地“测量”了量子态？为了研究“测量”是否发生在通常选择参量放大器作为第一个放大器的放大链中，建议构造一种微波干涉仪，在其每个臂上都添加这样的放大器。向干涉仪馈入单光子，干涉可见度取决于放大器的增益以及在放大过程中是否发生了测量崩溃。由标准量子力学给出的可见度根据增益，插入损耗和温度的函数进行计算。能见度$\mathrm{1个}/3$ 可以在不考虑损失的情况下在大收益的极限中找到，减少到 $0.26$ 如果放大器的插入损耗为 $2.2\text{D b}$ 在...的温度下 $50\text{千卡}$。结果表明，如果波函数在干涉仪内塌陷，则一旦崩溃过程开始，与标准量子力学所预测的幅度相比，所测得的可见度就会降低。