정연욱 교수

We have developed vertically stacked superconductor normal-metal-superconductor Josephson junction technology for the next-generation quantum voltage standards. Stacked junctions provide a practical way of increasing the output voltage and operating margins. In this paper, we present fully functioning programmable voltage standard chips with double- and triple- stacked MoSi/sub 2/ barrier Josephson junctions with over 100 000 junctions operating simultaneously on a 1 cm /spl times/ 1 cm chip. Th

Dense, vertically stacked Josephson junction arrays are being developed for voltage metrology applications. We present measurements of the uniformity and reproducibility of Nb/(MoSi2/Nb)N vertically stacked junctions that clarify the superconducting properties of the middle Nb superconducting electrode. Middle electrode thicknesses down to 20 nm have shown minimal suppression of the superconducting order parameter as measured through the critical current density. Even with a middle electrode thi

Abstract Quantum computing devices are inevitably subject to errors. To leverage quantum technologies for computational benefits in practical applications, quantum algorithms and protocols must be implemented reliably under noise and imperfections. Since noise and imperfections limit the size of quantum circuits that can be realized on a quantum device, developing quantum error mitigation techniques that do not require extra qubits and gates is of critical importance. In this work, we present a

We present a detailed study of the electrical properties of planar Nb–MoSi2–Nb Josephson junctions. The Nb–MoSi2–Nb junction is an excellent system to study proximity coupling in junctions with rigid superconductor/normal metal boundaries by precisely and independently controlling the barrier thickness and the temperature. With regard to applications, the Josephson properties are very reproducible, and the characteristic voltage can be tuned easily over more than two orders of magnitude while st

Nb/MoSi 2 / Nb stacked superconductor–normal metal–superconductor (SNS) Josephson junctions has proven to be a good candidate for high-density series arrays for Josephson voltage-standard applications. As the junction density increases, self-heating becomes an issue because the high power density per junction (1 W/cm2) generates significant power dissipation under typical operating conditions. In this letter, we analyze the heating effect of these sandwich-type SNS junctions using a model to qua

Abstract When a magnetic moment is embedded in a metal, it captures nearby itinerant electrons to form a so-called Kondo cloud. When magnetic impurities are sufficiently dense that their individual clouds overlap with each other they are expected to form a correlated electronic ground state. This is known as Kondo condensation and can be considered a magnetic version of Bardeen–Cooper–Schrieffer pair formation. Here, we examine this phenomenon by performing electrical transport and high-precisio

Using a new circuit design and double-stacked junction technology we have demonstrated fully functional high-resolution programmable voltage standard chips with 67 410 junctions that operate up to a maximum output voltage of 2.6 V. The circuit uses double-stacked junctions, where two junctions are fabricated in each stack, in order to increase the output voltage. We have also improved the voltage resolution at fixed frequencies 16-fold by using a circuit optimized for three voltage states and 12

We present a detailed study of the electrical properties of Nb-based planar Josephson junctions with superconducting metal silicide barriers, TiSi2 and WSi2. While these nonhysteretic junctions are useful for voltage standard applications, they are also an excellent model system to study proximity coupling in junctions having a barrier with a finite superconducting transition temperature. These silicide-barrier junctions have excellent uniformity and controllability, but as opposed to junction b

We measured the static error rate of a high-Tc superconductor dc superconducting quantum interference device (SQUID), which, in the form as a storage loop for single flux quanta, is a basic element of rapid single flux quantum circuits. Using high-Tc multilayer bicrystal technology, we fabricated a stacked dc SQUID pair, one SQUID serving as the storage loop, the other one as the readout device. The escape rate of a stored flux quantum was measured as a function of the bias current at a temperat

We experimentally constructed an all-microwave scheme for the controlled-NOT (cNOT) gate between two superconducting transmon qubits in a three dimensional cavity. Our cNOT gate is based on the microwave-activated phase (MAP) gate, which requires an additional procedure to compensate the accumulated phases during the operation of the MAP gate. We applied Z-axis phase gates using microwave hyperbolic secant pulse on both qubits with adequate rotation angles systematically calibrated by separate m

The remarkable advances of quantum computation technology with superconducting qubits based on circuit quantum electrodynamics (QED) architecture have been achieved by improving control, protection and measurement of the quantum states at the same time. At the heart of all these quantum operations, the significant enhancement of the qubit coherence time during the last decades was the key. Even after all these advances, the coherence and relaxation time of superconducting qubits still requires f

We report our progress in the Josephson arbitrary waveform synthesis system in KRISS. The system is based on the pulse-driven Josephson junction array, and currently we routinely produce arbitrary waveforms up to 100 mVrms amplitude with distortions smaller than 100 dBc. Precision waveform synthesis results are presented. Our future works will include AC-DC thermal transfer measurement and quantum noise source for Johnson noise thermometry.

The pulse-driven ac Josephson voltage standard (ACJVS) system has been operated stably in Korea Research Institute of Standards and Science(KRISS). We have improved the system operation so that the distortion has been reduced compared to our previous report [1]. Since this system can generate arbitrary waveform with quantum-mechanically precise voltages, it can be applied to precision ac electrical measurements. We will present single-tone waveform synthesis results at different amplitudes and f