Improving wafer-scale Josephson junction resistance variation in superconducting quantum coherent circuits

Quantum bits, or qubits, are an example of coherent circuits envisioned for next-generation computers and detectors. A robust superconducting qubit with a coherent lifetime of $O$(100 $\mu$s) is the transmon: a Josephson junction functioning as a non-linear inductor shunted with a capacitor to form an anharmonic oscillator. In a complex device with many such transmons, precise control over each qubit frequency is often required, and thus variations of the junction area and tunnel barrier thickness must be sufficiently minimized to achieve optimal performance while avoiding spectral overlap between neighboring circuits. Simply transplanting our recipe optimized for single, stand-alone devices to wafer-scale (producing 64, 1x1 cm dies from a 150 mm wafer) initially resulted in global drifts in room-temperature tunneling resistance of $\pm$ 30%. Inferring a critical current $I_{\rm c}$ variation from this resistance distribution, we present an optimized process developed from a systematic 38 wafer study that results in $<$ 3.5% relative standard deviation (RSD) in critical current ($\equiv \sigma_{I_{\rm c}}/\left\langle I_{\rm c} \right\rangle$) for 3000 Josephson junctions (both single-junctions and asymmetric SQUIDs) across an area of 49 cm$^2$. Looking within a 1x1 cm moving window across the substrate gives an estimate of the variation characteristic of a given qubit chip. Our best process, utilizing ultrasonically assisted development, uniform ashing, and dynamic oxidation has shown $\sigma_{I_{\rm c}}/\left\langle I_{\rm c} \right\rangle$ = 1.8% within 1x1 cm, on average, with a few 1x1 cm areas having $\sigma_{I_{\rm c}}/\left\langle I_{\rm c} \right\rangle$ $<$ 1.0% (equivalent to $\sigma_{f}/\left\langle f \right\rangle$ $<$ 0.5%). Such stability would drastically improve the yield of multi-junction chips with strict critical current requirements.Comment: 10 pages, 4 figures. Revision includes supplementary materia

Transition Metal Complexes of a-Naphthylamine Dithiocarbamate

a-Naphthylamine dithiocarbamate and its complexes with Co(II), Ni(U), Cu(II), Ru(III) , Rh(III), Pd(II), Pt(IV), Zn(II), Cd(II) and Hg(II) have been prepared and characterized by chemical analysis, IR - and reflectance spectral studies and magnetic susceptibili ty measurements. In all these complexes the dithiocarbamato moiety acts as a chelate. The Ni(II), Cu(II) and Pd(Il) complexes have been found to be square planar while those of Ru(III), Rh(III) and Pt(IV) were proposed to be octahedral in nature. The Co(II) ion seems to have a tetrahedral geometry, unlike the other known square planar dithiocarbamato complexes of Co(II). No definite structure, however, could be proposed for Zn(II), Cd(II) and Hg(II) on the basis of limited studies

Digitally Programmable Fully Differential Filter

In this paper a new digitally programmable voltage mode fully differential Kerwin-Huelsman-Newcomb(KHN) filter is realized using digitally controlled CMOS fully balanced output transconductor (DCBOTA). The realized filter uses five DCBOTAs, a single resistor and two capacitors. The filter provides low-pass, high-pass and band-pass responses simultaneously. The pole-frequency of all the responses is controlled by externally applying an 8- bit digital control word. All the responses exhibit independent digital control for pole-ω0 and pole-Q. The proposed filter also offers low passive sensitivities. Non-ideal gain and parasitic associated with the actual DCBOTA is also discussed. The CMMR results for low-pass response are also included which highlight the advantage of a fully-differential operation. Exhaustive PSPICE simulation is carried out using 0.5µ technology which may be further scaled to explore state-of-the-art applications of the proposed circuit

Dynamic priority-based efficient resource allocation and computing framework for vehicular multimedia cloud computing

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works In intelligent transportation system, smart vehicles are equipped with a variety of sensing devices those offer various multimedia applications and services related to smart driving assistance, weather forecasting, traffic congestion information, road safety alarms, and many entertainment and comfort-related applications. These smart vehicles produce a massive amount of multimedia related data that required fast and real-time processing which cannot be fully handled by the standalone onboard computing devices due to their limited computational power and storage capacities. Therefore, handling such multimedia applications and services demanded changes in the underlaying networking and computing models. Recently, the integration of vehicles with cloud computing is emerged as a challenging computing paradigm. However, there are certain challenges related to multimedia contents processing, (i.e., resource cost, fast service response time, and quality of experience) that severely affect the performance of vehicular communication. Thus, in this paper, we propose an efficient resource allocation and computation framework for vehicular multimedia cloud computing to overcome the aforementioned challenges. The performance of the proposed scheme is evaluated in terms of quality of experience, service response time, and resource cost by using the Cloudsim simulator

Resonance fluorescence from an artificial atom in squeezed vacuum

We present an experimental realization of resonance fluorescence in squeezed vacuum. We strongly couple microwave-frequency squeezed light to a superconducting artificial atom and detect the resulting fluorescence with high resolution enabled by a broadband traveling-wave parametric amplifier. We investigate the fluorescence spectra in the weak and strong driving regimes, observing up to 3.1 dB of reduction of the fluorescence linewidth below the ordinary vacuum level and a dramatic dependence of the Mollow triplet spectrum on the relative phase of the driving and squeezed vacuum fields. Our results are in excellent agreement with predictions for spectra produced by a two-level atom in squeezed vacuum [Phys. Rev. Lett. \textbf{58}, 2539-2542 (1987)], demonstrating that resonance fluorescence offers a resource-efficient means to characterize squeezing in cryogenic environments

A young boy with abdominal pain

At times, acute diffuse abdominal pain can be a diagnostic dilemma, especially when the symptoms appear to be out of proportion to the findings on physical examination. The case of a young boy with abdominal pain is presented