Phase engineering of anomalous Josephson effect derived from Andreev molecules.

A Josephson junction (JJ) is a key device for developing superconducting circuits, wherein a supercurrent in the JJ is controlled by the phase difference between the two superconducting electrodes. When two JJs sharing one superconducting electrode are coherently coupled and form the Andreev molecules, a supercurrent of one JJ is expected to be nonlocally controlled by the phase difference of another JJ. Here, we evaluate the supercurrent in one of the coupled two JJs as a function of local and nonlocal phase differences. Consequently, the results exhibit that the nonlocal phase control generates a finite supercurrent even when the local phase difference is zero. In addition, an offset of the local phase difference giving the JJ ground state depends on the nonlocal phase difference. These features demonstrate the anomalous Josephson effect realized by the nonlocal phase control. Our results provide a useful concept for engineering superconducting devices such as phase batteries and dissipationless rectifiers.

Phase-dependent Andreev molecules and superconducting gap closing in coherently-coupled Josephson junctions.

The Josephson junction (JJ) is an essential element of superconducting (SC) devices for both fundamental and applied physics. The short-range coherent coupling of two adjacent JJs forms Andreev molecule states (AMSs), which provide a new ingredient to engineer exotic SC phenomena such as topological SC states and Andreev qubits. Here we provide tunneling spectroscopy measurements on a device consisting of two electrically controllable planar JJs sharing a single SC electrode. We discover that Andreev spectra in the coupled JJ are highly modulated from those in the single JJs and possess phase-dependent AMS features reproduced in our numerical calculation. Notably, the SC gap closing due to the AMS formation is experimentally observed. Our results help in understanding SC transport derived from the AMS and promoting the use of AMS physics to engineer topological SC states and quantum information devices.

InAs/InGaAs quantum dot lasers on multi-functional metamorphic buffer layers: erratum.

We present an erratum to correct inadvertent errors in our paper [Opt. Express29, 29378 (2021)10.1364/OE.433030]. The corrections do not affect the main conclusion.

InAs/InGaAs Quantum Dot Lasers on Multi-Functional Metamorphic Buffer Layers.

With the development of dry fiber over the past two decades, the E-band has become a new telecommunication wavelength. However, owing to material constraints, an effective high-performance semiconductor light source has not yet been realized. InAs quantum dot (QD) lasers on GaAs substrates are in the spotlight as O-band light sources because of their excellent thermal properties and high efficiency. The introduction of a very thick InGaAs metamorphic buffer layer is essential for realizing an E-band InAs QD laser, but it can cause degradation in laser performance. In this study, we fabricate an E-band InAs/GaAs QD laser on a GaAs substrate with an AlInGaAs multifunctional metamorphic buffer layer that realizes the function of the bottom cladding layer of normal thickness in addition to the functions of a metamorphic buffer layer and a dislocation filter layer. The lasing oscillation at a wavelength of 1428 nm is demonstrated at room temperature under continuous-wave operation. This result paves the way toward the realization of highly efficient light sources suitable for E-band telecommunications.