Junction Arrays Research Articles

Minimizing the Discrimination Time for Quantum States of an Artificial Atom

Fast discrimination between quantum states of superconducting artificial atoms is an important ingredient for quantum information processing. In circuit quantum electrodynamics, increasing the signal field amplitude in the readout resonator, dispersively coupled to the artificial atom, improves the signal-to-noise ratio and increases the measurement strength. Here we employ this effect over two orders of magnitude in readout power, made possible by the unique combination of a dimer Josephson junction array amplifier with a large dynamic range, and the fact that the readout of our granular aluminum fluxonium artificial atom remained quantum-non-demolition (QND) at relatively large photon numbers in the readout resonator, up to $\overline{n} = 110$. Using Bayesian inference, this allows us to detect quantum jumps faster than the readout resonator response time $2/\kappa$, where $\kappa$ is the bandwidth of the readout resonator.

Local atomic structure analysis around Mg atom doped in GaN by X-ray absorption spectroscopy and spectrum simulations.

The identification of the incorporated site of magnesium (Mg) and hydrogen (H) required for p-type formation in gallium nitride (GaN) power devices has been demonstrated by X-ray absorption spectroscopy (XAS). In this study, the fluorescence line of Mg with 3 × 1019 atoms cm-3 was successfully separated from that of Ga using a superconducting tunnel junction array detector with high sensitivity and high energy resolution, and consequently the Mg K-edge XAS spectra of such dilute samples were obtained. The site of Mg atoms incorporated into the GaN lattice was identified as the Ga substitutional site bycomparing the experimental XAS spectrum with the simulated spectra calculated by density functional theory. In addition, the presence or absence of H around Mg can be determined through distinctive characteristics expected from the spectrum simulations.

Evaluation of Effective Thermal Stability Factor for Patterned Magnetic Tunnel Junction Array

Accurate and early estimation of the thermal stability factor of a memory array is essential for the development of modern non-volatile magnetic storage devices. We propose an evaluation method for effective array-level thermal stability factors ( $\Delta _{\mathrm {eff}}$ ) via magnetic characterization of patterned magnetic tunnel junction (MTJ) arrays. These patterned arrays do not require traditional electrical contacts and circuitry that are usually needed for $\Delta _{\mathrm {eff}}$ evaluation. Using vibrating sample magnetometer (VSM) at elevated temperatures and under applied fields, we demonstrate that these MTJ arrays exhibit a moment change trend that fits the Neel–Brown model and are able to extract the respective $\Delta _{\mathrm {eff}}$ . The domain-wall-mediated reversal model is used to obtain zero-field $\Delta _{\mathrm {eff}}$ . Using this method, we have optimized MTJ film stacks based on fast array-level feedback and validated high data retention of $\Delta _{\mathrm {eff}} \sim 46$ at 260 °C from fully integrated MTJ bit arrays.

Comparison of Magnetic Field Detectors Based On SQUID And/Or Josephson Junction Arrays With HTSc

We compare the potential of SQUID arrays and Josephson junction arrays as magnetic field detectors in an open-loop configuration, accounting for such limitations as technological parameter fluctuations, current density distribution and self-field effects originating from the bias current. Because of the simplicity of its single layer process, the ion-damaged barrier technology is used to fabricate the Josephson junctions (JJ) and to make the evaluations by extrapolation to larger area detectors. From preliminary experimental results on series arrays of Josephson junctions, we expect a less detrimental effect of self-flux and parameter dispersion, which is particularly important with high critical temperature technologies.

AJAP1 Silencing in Epithelial Cells Alters Markers of Biologic Function

Introduction The epicardium and coronary vessels of the embryonic mammalian heart are derived from epithelial-like progenitor cells of the proepicardium (PE). These epithelial cells migrate from the PE during development to envelop and adhere to the myocardium to form the epicardium. Epithelial cells maintain their cellular integrity through adherens and tight junctions before undergoing epithelial-mesenchymal transition (EMT) to become epicardial-derived cells that invade the myocardium and transform into the vascular smooth muscle cells and vascular endothelial cells of the coronary vessels. Adherens junction-associated protein 1 (AJAP1) is a cell adhesion molecule that is expressed in the epicardium and coronary vessels, and it regulates epithelial cell behaviors. Study Objective Our goal was to identify and assess the molecular target(s) of AJAP1-modifiable epithelial cell behaviors that are important for formation of the epicardium and coronary vessels during cardiovascular development. We speculate that AJAP1 regulates epithelial cell behaviors by altering the expression of transcripts of adherens junctions, tight junctions and EMT markers. Methods Primary human mammary epithelial cells (HMEpiCs) retain characteristics of epithelial cells in vivo. We examined the in vitro contributions of AJAP1 to epithelial cell behaviors necessary for epicardium formation using HMEpiCs. We silenced AJAP1 mRNA expression in HMEpiCS with small interfering RNAs (siRNAs) and this produced changes in HMEpiC behavior. We obtained qPCR array plates to assay AJAP1-gene-silenced versus control HMEpiCs for differential expression of transcripts classified as markers of adherens junctions, tight junctions and EMT. This array expression data was subjected to gene ontology (GO) analysis to query the targeted genes and classify them by distinct biologic functions. Results A reduction in AJAP1 mRNA expression produced discernible changes in epithelial cell morphology and functions. A comparison of adherens junction, tight junction and EMT qPCR arrays revealed transcripts with altered expression in AJAP1-silenced versus control HMEpiCs. GO analysis showed these transcripts are involved in several biological processes including blood vessel development, cell migration, cell-cell adhesion, cytoskeleton organization and cell junction organization. This analysis correlates with our previous cell behavioral data. Conclusion Our results indicate that AJAP1 plays an important role in epithelial cells to enable expression of genes involved in an array of biological processes such as cell migration, cell-cell adhesion, cytoskeleton organization and cell junction organization. These biological processes are important for formation of the epicardium and coronary vessels during cardiovascular development.

Description of zero field steps on the potential energy surface of a Frenkel-Kontorova model for annular Josephson junction arrays

We explain the emergence of zero field steps (ZFS) in a Frenkel-Kontorova (FK) model for a 1D annular chain being a model for an annular Josephson junction array. We demonstrate such steps for a case with a chain of 10 phase differences. We necessarily need the periodic boundary conditions. We propose a mechanism for the jump from M fluxons to M+1 in the chain.Graphic abstract

Charge quantization and detector resolution

Charge quantization, or the absence thereof, is a central theme in quantum circuit theory, with dramatic consequences for the predicted circuit dynamics. Very recently, the question of whether or not charge should actually be described as quantized has enjoyed renewed widespread interest, with however seemingly contradictory propositions. Here, we intend to reconcile these different approaches, by arguing that ultimately, charge quantization is not an intrinsic system property, but instead depends on the spatial resolution of the charge detector. We show that the latter can be directly probed by unique geometric signatures in the correlations of the supercurrent. We illustrate these findings at the example of Josephson junction arrays in the superinductor regime, where the transported charge appears to be continuous. Finally, we comment on potential consequences of charge quantization beyond superconducting circuits.

Fabrication of pn junction arrays with highly successful grown n-Si microneedles by using low temperature VLS method

Arrays of pn junctions have been fabricated with n-Si microneedles. In situ doping vapor–liquid–solid (VLS) growth has been carried out with p-Si substrate having metallic catalyst (Au) dots on its surface, using Si2H6 and PH3 for supplying Si and phosphorus to fabricate n-Si microneedles on the surface of p-Si substrate in vertical direction; thus, pn junctions have been fabricated at microneedle-substrate interface. These n-Si microneedles have been grown at the temperature of 680 °C, which is about 420 °C less than the temperature (at least 1100 °C) required by conventional diffusion method of doping. In this work, n-Si microneedles have been successfully fabricated with 100% yield, the highest success ever for n-type VLS growth in micro range. The position and size of these n-Si microneedles are controllable. These n-Si microneedles are highly conductive. Physical and electrical characteristics of n-Si microneedles have been investigated by varying Au dot size and the level of phosphorus doping. The properties of interface pn junction have been investigated and compared with standard diode characteristics and theoretical results. Highly conductive n-Si microneedle arrays, embedded with interface pn junctions, might be used for collecting and processing bio-signals, profiling temperature/pressure inside living cells and many other sensor applications.

Chaotic behavior of a stack of intrinsic Josephson junctions at the transition to branching for overcritical currents

Phase dynamics of a stack of coupled intrinsic Josephson junctions was investigated in the framework of capacitively coupled Josephson junctions with diffusion current model. We study the transition from the current-voltage characteristic specific to Josephson junctions arrays with small dissipation and weak coupling between the junctions to the arrays with strong coupling between the junctions and high dissipation. Low dissipative arrays of Josephson junctions are characterized by the absence of branching for overcritical currents which appears for highly dissipative arrays. Described branching appears due to charging on the superconducting layers and charge traveling waves generation. Arrays of Josephson junctions with intermediate values of coupling and dissipation parameters are characterized by the chaotic behavior, confirmed by positive Lyapunov exponent, and branching on the current voltage characteristic for both sub- and overcritical currents.

A four-terminal-pair Josephson impedance bridge combined with a graphene-quantized Hall resistance

This paper introduces a four-terminal-pair impedance bridge based on pulse-driven Josephson junctions arrays which is designed to link any kind of impedance to the quantized Hall resistance. The unique features of the quantized Hall resistance in a multiple series connection allows to dispense a combining network and leads to a compact and simple design of the whole setup. Moreover, the low noise of a quantized Hall resistance reduces the measurement time compared to resistance standards at room temperature which is essential for the characterization of quantum Hall devices in the AC regime. A first measurement campaign confirmed the expected low noise of 1.82 for a link to a 10 nF capacitance standard. The repeatability of the bridge was found to be few parts in 108. Capacitance and resistance standards were measured at 1233.15 Hz against graphene based quantum Hall resistance devices.

Cluster formation and non-metal-to-metal transition in a diamond-shaped graphene-like lattice

This work is a numerical simulation of the bond percolation in an array of junctions and bifurcations mimicking a section of a graphene slab. We calculate the size distribution of graphene clusters as a filler of a polymer aiming to obtain the percolation threshold. We obtained the sigmoidal distribution of graphene clusters as a function of concentration of persistent conducting bonds creating these clusters. The probability density of this distribution shows a universal complementary Fermi–Dirac behavior as a signature of a topological response. Using a tight-binding model for the transmission from the source to the drain, we obtain a smooth transition from an insulator to a conductor through a dirty metal as the concentration of conductive bonds increases for small arrays. As the array size increases, the simulation shows a sharp non-metal-to-metal transition from a pure polymer into a pristine suspended graphene layer.

Thermoelectric Sensor Coupled Yagi–Uda Nanoantenna for Infrared Detection

We present an experimental demonstration of a thermoelectric sensor coupled with a nanoantenna as an alternative option for detecting infrared energy. Two nanoantenna design (single element and an array) variations based on Yagi-Uda technology and one separate nano-thermoelectric junction array were fabricated and tested. The nanoantennas were tuned to operate and respond at a center wavelength of 1550 nm (193.5 THz) optical C-band window, but they also exhibited a resonance response when excited by lasers of various wavelengths (650 nm and 940 nm). The radiation-induced electric currents in the nanoantennas, coupled with a nano-thermoelectric sensor, produced a potential difference as per the Seebeck effect. With respect to the uniform thermal measurements of the reference nanoantenna, the experiments confirmed the detection properties of the proposed nanoantennas; the single element detected a peak percentage voltage hike of 28%, whereas the array detected a peak percentage voltage hike of 80% at the center wavelength. Compared to state-of-the-art thermoelectric designs, this was the first time that such peak percentage voltages were experimentally reported following a planar design based on the Seebeck principle.

Microwave functionality of spintronic devices implemented in a hybrid complementary metal oxide semiconductor and magnetic tunnel junction technology

This letter presents magnetic tunnel junction based spintronic devices completely implemented in a hybrid semiconductor process that comprises a complementary metal oxide semiconductor and a magnetic tunnel junction technology. To demonstrate the coexistence of both complementary metal oxide semiconductor circuits and magnetic tunnel junction based spintronic devices, a proof-of-concept circuit prototype comprising 40 spintronic devices and a digital complementary metal oxide semiconductor serial peripheral interface is fabricated. According to measurement results, a selected spintronic device from the magnetic tunnel junction array, when surrounded by an external out-ofplane magnetic field of 1 kOe, emitted microwave signals from 2.235 to 2.464 GHz with an output power from 0.88 to 0.72 nW, when the DC current was increased from 0.6 to 1.0 mA. To the authors' best knowledge, this is the first work demonstrating the functionality of spintronic oscillators fully integrated in complementary metal oxide semiconductor circuit implemented in a hybrid complementary metal oxide semiconductor and magnetic tunnel junction process.

Superconducting neural networks with disordered Josephson junction array synaptic networks and leaky integrate-and-fire loop neurons

Fully coupled randomly disordered recurrent superconducting networks with additional open-ended channels for inputs and outputs are considered the basis to introduce a new architecture to neuromorphic computing in this work. Various building blocks of such a network are designed around disordered array synaptic networks using superconducting devices and circuits as an example, while emphasizing that a similar architectural approach may be compatible with several other materials and devices. A multiply coupled (interconnected) disordered array of superconducting loops containing Josephson junctions [equivalent to superconducting quantum interference devices (SQUIDs)] forms the aforementioned collective synaptic network that forms a fully recurrent network together with compatible neuron-like elements and feedback loops, enabling unsupervised learning. This approach aims to take advantage of superior power efficiency, propagation speed, and synchronizability of a small world or a random network over an ordered/regular network. Additionally, it offers a significant factor of increase in scalability. A compatible leaky integrate-and-fire neuron made of superconducting loops with Josephson junctions is presented, along with circuit components for feedback loops as needed to complete the recurrent network. Several of these individual disordered array neural networks can further be coupled together in a similarly disordered way to form a hierarchical architecture of recurrent neural networks that is often suggested as similar to a biological brain.

Investigation of Broadband Wilkinson Power Dividers for Pulse-Driven Josephson Voltage Standards

This paper describes recent developments for increasing the output voltage of the Josephson Arbitrary Waveform Synthesizer (JAWS) at PTB. For this purpose, we developed modified broadband Wilkinson power dividers, which enable the operation of two or four Josephson junction series arrays per RF channel of the pulse pattern generator and thus the generation of increased output voltages. In detail, we designed and investigated two different Wilkinson power dividers: the one-stage three-section Wilkinson power divider with extended bandwidth and the two-stage single-section Wilkinson divider with more outputs to combine four parallel series arrays. They were both integrated with triple-stacked Josephson junction series arrays. Additionally, a new modulator pulse amplifier was introduced into the JAWS set-up to provide sufficient power for all the junction arrays. Our measurement results show that spectrally pure sinusoidal waveforms were successfully generated with both types of power dividers. With the one-stage three-section Wilkinson power divider, we obtained RMS voltages of nearly 53 mV at a clock-frequency of 15 GHz combined with a test array of 3000 Josephson junctions. As for the two-stage single-section Wilkinson power divider combined with a test array of 6000 Josephson junctions, we synthesized RMS output voltages of about 105 mV. These test results show a promising prospect for quantum voltage standard applications.

Topological Josephson plasmon modes on honeycomb lattice [Invited

Topological protection is a promising way to deal with the decoherence issue in quantum systems. To induce topological excitations in Josephson junction arrays (JJA), we propose a scheme where only Josephson critical currents are tuned in JJA on honeycomb lattice, which is easily achieved by changing potential barriers or lengths of insulators between superconducting islands. In the present system, a hexagonal cluster with six superconducting islands forms a unit cell, and the difference between intra- and inter-hexagon Josephson critical currents yields a topologically nontrivial state accompanied by a band inversion. Topological Josephson plasmon modes appear at the interface between topological and trivial domains, carrying pseudospin dominant energy flows, which mimics the spin-momentum locking in the renowned quantum spin Hall effect.

Oriented titania nanotube biphase junction arrays on water splitting

Photocatalyst with phase junction is of great importance to achieve high charge separation and transfer efficiency on solar energy utilization. Herein, an oriented anatase/rutile biphase junction based on TiO2 nanotube arrays are facile prepared by novel oriented thermal annealing method. Its phase distribution and proportion can be tuned by adjusting heat radiation direction and time, respectively. Light absorption spectroscopy and photoelectrochemical measurements reveal that the oriented phase junction is crucial for charge transfer and separation. The sample containing with 34.4% rutile phase has the highest incident photon-to-current efficiency and charge separation efficiency, and achieves ca. 2.2 and 4.7 folds photocurrent density enhancement compared to pristine anatase and rutile phase TiO2 arrays, respectively. The photocurrent density of oriented biphase junction arrays (0.458 mA·cm−2 at 1.23 V vs RHE) is also significantly higher than random phase junction sample or previous reported result. This work demonstrates that the great potential of oriented biphase junction arrays can be applied in efficient charge separation and transfer on solar energy conversion.

Phase coherence in out-of-equilibrium supersolid states of ultracold dipolar atoms

A supersolid is a counterintuitive phase of matter that combines the global phase coherence of a superfluid with a crystal-like self-modulation in space. Recently, such states have been experimentally realized using dipolar quantum gases. Here we investigate the response of a dipolar supersolid to an interaction quench that shatters the global phase coherence. We identify a parameter regime in which this out-of-equilibrium state rephases, indicating superfluid flow across the sample as well as an efficient dissipation mechanism. We find a crossover to a regime where the tendency to rephase gradually decreases until the system relaxes into an incoherent droplet array. Although a dipolar supersolid is, by its nature, ‘soft’, we capture the essential behaviour of the de- and rephasing process within a rigid Josephson junction array model. Yet, both experiment and simulation indicate that the interaction quench causes substantial collective mode excitations that connect to phonons in solids and affect the phase dynamics. A supersolid is a phase of matter featuring both crystalline order as a solid and global phase coherence as a superfluid. Now an experiment shows how this global phase coherence can be established across the system in a non-equilibrium process.

Fabrication and Characterization of a Quantum Voltage Noise Source Chip for a Johnson Noise Thermometer

A Johnson noise thermometer (JNT) determines the thermodynamic temperature through cross-correlation measurement of the Johnson noise in a sense resistor at an unknown temperature. In the quantum voltage calibrated JNT system, a superconductive quantum voltage noise source (QVNS) is required to produce artificial pseudo-random noise to calibrate the gain of the cross-correlation electronics. In this paper, we present the design, fabrication, and characterization of the QVNS chip. Compared with our previous design, a new straightforward mirror symmetric layout is implemented. For this layout, the coplanar waveguides (CPWs) have the same lengths and transmission parameters. Equal pulse magnitudes are delivered to each Josephson junction array under the same output settings of the bipolar pattern generator. The modified QVNS chip is thereby enhanced because the quantum locking range is enlarged. A copper foil shielding package is used to eliminate crosstalk in this design. The first spectral comparison of two Josephson junction (JJ) arrays of with and without shielding is presented in this paper. The comparative results demonstrate that the shielding is effective. The abovementioned improvements enable us to synthesize both single and multitone waveforms with good spectral results, such that the chip satisfies the requirement of a QVNS-based JNT system for temperature measurements.

Study of single-electron tunneling oscillations using monte-carlo based modeling algorithms to a capacitive slanted two-dimensional array of tunnel junctions

<abstract> This work simulates and examines the circuit's operation for a single-electron nanostructure which is composed of slanted coupled two-dimensional arrays of tunnel junctions. The structure under study is modeled by combined computational simulation methods, both the Master Equation and the Monte-Carlo techniques. Throughout this process, the distribution of the time between successive random events could be computed at a reference junction. From these time distribution values, further calculations have been carried out to obtain the power spectral density trends, which reflect the corresponding properties on the frequency domain. For these homogeneous structures, the biasing conditions have been inspected for a combination of the two array's legs. It is found that, for some shorter lengths 3, 5, and up to 7 tunnel junctions could be triggered from any same or opposite side ends having different voltage polarities. For relatively longer structures of sizes 10, 15, 20, and 30 tunnel junctions, the circuit initial parameters are readjusted for obtaining remarkable results for their oscillations study. By increasing the value of the slanted coupling capacitance, the steady-state currents are in terms increased, and in this way, it is possible to realize the tunnel events correlations. It is shown that tuning the stray capacitances by slightly increasing their values will lead to a good clearer effect, especially for those longer array sets. </abstract>