Non-classical electromagnetic radiation created by superconducting quantum circuits.A tool for highly sensitive spectroscopy.

在这个项目中，我们计划追求以下想法：(i)使用超导量子电路作为非经典电磁辐射的来源，（ii）使用这种辐射来提高拉曼光谱的信噪比。我们建议利用类似激光的过程，在耦合到超导量子比特系综的腔中产生强亚泊松光子分布。由于约瑟夫森效应，耦合是高度非线性的。研究表明，在光谱学中使用亚泊松光子分布可以大大提高信噪比。微波光谱应经常在较高的温度下进行，例如，对于生物分子的研究，温度应不低于4K。另一方面，超导电路应在20mK左右运行。这种巨大温差的后果需要解决，并构成我们研究项目的另一个主要部分（iii）。

In this project we plan to pursue ideas (i) to use superconducting quantum circuits as a source of non-classical electromagnetic radiation, and (ii) to use this radiation to enhance the signal to noise ratio for Raman spectroscopy. We suggest to exploit a laser-like process to generate a strongly sub-Poissonian photon distribution in a cavity coupled to an ensemble of superconducting qubits. Due to the Josephson effect the coupling is highly nonlinear. It has been shown that by using sub-Poissonian photon distributions for spectroscopy one can drastically enhance the signal-to-noise ratio. Frequently microwave spectroscopy should be performed at elevated temperatures, e.g., for the study of biological molecules the temperature should be not lower than 4K. On the other hand, the superconducting circuits should be operated at around 20mK. The consequences of this large temperature difference need to be addressed and constitute another major part (iii) of our research project.