Breakthroughs in Microwave Quantum Photonics in Superconducting Circuit;]. The three-level artificial atom can also be pumped to create population inversion and demonstrate microwave amplification by stimulated emission of radiation (MASER) [10], a single-atom analog of fiber amplifiers in optics. Further progress has been accelerated by development of novel techniques for characterizing itinerant microwave fields. In optics experiments, in order to characterize an itinerant light field, single-photon detection and counting are commonly used. In the microwave domain, however, because of the smallness of the single-photon energy, single-photon detectors had been elusive until very recently. Nevertheless, it has been shown that it is still possible to measure the field correlations by using linear detectors [11]–[13]. Simultaneous homodyne measurements at two output ports of a Bbeam splitter[ (a hybrid coupler in microwave engineering) allow full characterization of the correlation functions of the input field [Fig. 1(a)]. This has been applied in a series of experiments performing quantum state tomography of nonclassical microwave fields [14], [15]. In parallel, a single-photon detector using a current-biased Josephson junction has been proposed and demonstrated recently [16]–[18]. The Josephson junction works as an effective three- level system with a -type configuration. Placed at the end of a transmission line, the -system absorbs an incoming photon most efficiently when the excited state has equal relaxation rates for the two decay channels. A pair of such detectors has been used in a Hanbury–Brown–Twiss experiment, revealing photon bunching in a microwave thermal field [Fig. 1(b)] [17]. Microwave photon counting with number resolutio would be the next challenge. The itinerant quantum states of microwave are expected to be exploited in various quantum technologies. Entangled states between two modes can be used in quantum teleportation. ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=06476623
Posted on: Sun, 29 Jun 2014 04:30:39 +0000
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