In a cavity quantum electrodynamics (QED) system, where atoms coherently interact with photons in a cavity, the eigenstates of the system are the superposition states of atoms and cavity photons, the so-called dressed states of atoms. When two cavities are connected by an optical fiber with negligible loss, the coherent coupling between the cavities gives rise to photonic normal modes. One of these normal modes is the fiber-dark mode, in which photons are delocalized in the two distant cavities. Here we demonstrate the setting of coupled-cavities QED, where two nanofiber cavity-QED systems are coherently connected by a meter-long low-loss channel in an all-fiber fashion. Specifically, we observe dressed states of distant atoms with delocalized photons of the fiber-dark normal mode. Our system will provide a platform for the study of delocalized atomic and photonic states, photonic many-body physics, and distributed quantum computation.

We analytically derive the upper bound on the overall efficiency of single-photon generation based on cavity quantum electrodynamics (QED), where cavity internal loss is treated explicitly. The internal loss leads to a tradeoff relation between the internal generation efficiency and the escape efficiency, which results in a fundamental limit on the overall efficiency. The corresponding lower bound on the failure probability is expressed only with an "internal cooperativity," introduced here as the cooperativity parameter with respect to the cavity internal loss rate. The lower bound is obtained by optimizing the cavity external loss rate, which can be experimentally controlled by designing or tuning the transmissivity of the output coupler. The model used here is general enough to treat various cavity-QED effects, such as the Purcell effect, on-resonant or off-resonant cavity-enhanced Raman scattering, and vacuum-stimulated Raman adiabatic passage. A repumping process, where the atom is reused after its decay to the initial ground state, is also discussed.

A field-effect transistor (FET) with a gate length of 13 nm having a c-axis aligned crystalline In-Ga-Zn oxide (CAAC-IGZO) channel was fabricated. The CAAC-IGZO FET has an off-state leakage current of 200 yA/μm, a cutoff frequency of 60GHz, and a maximum oscillation frequency of 16GHz. A CAAC-IGZO FET, though it is a small transistor, withstands voltages up to approximately 2.5 V. It also has stable current characteristics with less temperature dependence than Si devices. We have constructed an equivalent-circuit model of the CAAC-IGZO FET and designed an RF amplifier to show CAAC-IGZO FET's applicability to the GHz-range RF circuitry.

A field-effect transistor (FET) using CAAC-IGZO, a crystalline oxide semiconductor having a c-axis alignment, is considered for application to various circuits. In particular, its extremely low off-state leakage current[1,2] enables design of non-volatile memory and analog memory devices[3], allowing AI tasks to be run in non-von-Neumann architectures. Furthermore, CAAC-IGZO FET can be applied to use cases other than memory, such as RF applications. CAAC-IGZO FET can be integrated in the back-end-of-line processes of CMOS technologies[4], and allows higher power supply voltages than conventional CMOS devices[4]. This may contribute to reduced chip area, which can create smaller packages, which are demanded for IoT endpoints. As there are not many applications that currently use scaled CAAC-IGZO FET, CAAC-IGZO FET is not yet applied to quasi-millimeter-wave applications. In addition, circuit design for high-frequency applications of CAAC-IGZO FETs will require extraction of FET characteristics that will be utilized in this application. Compact models are available for large IGZO FETs [5], but not for scaled CAAC-IGZO FETs. For this work, we have prototyped and evaluated scaled CAAC-IGZO FETs (Fig. 1(a)) that are suitable for high-frequency applications in addition to memory applications. From network measurements, it was found that the CAAC-IGZO FET exhibits a cutoff frequency of 60 GHz (Fig. 1(b)) and a maximum oscillation frequency of 16 GHz, which is promising for quasi-millimeter-wave designs. In addition, we have designed equivalent circuits of the scaled CAAC-IGZO FET using linear devices. This circuit shows not only the characteristics of the scaled CAAC-IGZO FET, but also the potential for circuit designs with the device. This work compiles the characteristics of the scaled CAAC-IGZO FET, and proposes a novel circuit application for the device. Fig. 1 (a) L-direction cross section of the scaled CAAC-IGZO FET. (b) Network measurment result of the scaled CAAC-IGZO FET References [1] N. Kimizuka and S. Yamazaki, “Physics and Technology of Crystalline Oxide Semiconductor CAAC-IGZO FUNDAMENTALS,” WILEY, 2017. [2] S. Yamazaki and M. Fujita, “Physics and Technology of Crystalline Oxide Semiconductor CAAC-IGZO Application to LSI,” WILEY, 2017. [3] Y. Kurokawa et al., JJAP, vol. 59, pp. (SGGB03-1)-(SGGB03-11), 2020. [4] H. Kunitake et al., J-EDS, vol. 7, pp.495-502, 2019. [5] L. J. Giacoletto et al., JSSC, vol. 4, issue 2, pp.80-83, 1969. Figure 1