Thermal annealing enhancement of Josephson critical currents in ferromagnetic CoFeB

Laser-annealing Josephson junctions for yielding scaled-up superconducting quantum processors

As superconducting quantum circuits scale to larger sizes, the problem of frequency crowding proves a formidable task. Here we present a solution for this problem in fixed-frequency qubit architectures. By systematically adjusting qubit frequencies post-fabrication, we show a nearly ten-fold improvement in the precision of setting qubit frequencies. To assess scalability, we identify the types of 'frequency collisions' that will impair a transmon qubit and cross-resonance gate architecture. Using statistical modeling, we compute the probability of evading all such conditions, as a function of …

Tuning the proximity effect in a superconductor-graphene-superconductor junction

We have tuned in situ the proximity effect in a single graphene layer coupled to two Pt/Ta superconducting electrodes. An annealing current through the device changed the transmission coefficient of the electrode/graphene interface, increasing the probability of multiple Andreev reflections. Repeated annealing steps improved the contact sufficiently for a Josephson current to be induced in graphene.

Josephson junction array type I-V characteristics of quench-condensed ultra thin films of Bi

In this communication we report studies of d.c current-voltage (I-V) characteristics of ultra thin films of Bi, quench condensed on single crystal sapphire substrates at T = 15K. The hysteretic I-V characteristics are explained using a resistively and capacitively shunted junction (RCSJ) model of Josephson junction arrays. The Josephson coupling energy($E_J$) and the charging energy($E_c$) are calculated for different thickness($d$) values. A low resistance state is found in the low current regime below the critical current, $I_c$. This resistance $R_0$ is found to have a minimum at a particul…

Evidence for triplet superconductivity in Josephson junctions with ferromagnetic Cu$_{2}$MnAl-Heusler barriers

We have studied Josephson junctions with barriers prepared from the Heusler compound Cu$_2$MnAl. In the as-prepared state the Cu$_2$MnAl layers are non ferromagnetic and the critical Josephson current density $j_{c}$ decreases exponentially with the thickness of the Heusler layers $d_{F}$. On annealing the junctions at 240\degree C the Heusler layers develop ferromagnetic order and we observe a dependence $j_{c}(d_{F}$) with $j_{c}$ strongly enhanced and weakly thickness dependent in the thickness range 7.0 nm < $d_{F}$ < 10.6 nm. We attribute this feature to a triplet component in the superco…

Toward Practical-Scale Quantum Annealing Machine for Prime Factoring

We propose a prime factorizer operated in a framework of quantum annealing (QA). The idea is inverse operation of a multiplier implemented with QA-based Boolean logic circuits. We designed the QA machine on an application-specific-annealing-computing architecture which efficiently increases available hardware budgets at the cost of restricted functionality. The invertible operation of QA logic gates consisting of superconducting flux qubits was confirmed by circuit simulation with classical noise sources. The circuits were implemented and fabricated by using superconducting integrated circuit …

Superconducting properties of nanocrystalline MgB$_2$ thin films made by an in situ annealing process

We have studied the structural and superconducting properties of MgB$_2$ thin films made by pulsed laser deposition followed by in situ annealing. The cross-sectional transmission electron microscopy reveals a nanocrystalline mixture of textured MgO and MgB$_2$ with very small grain sizes. A zero-resistance transition temperature ($T_{c0}$) of 34 K and a zero-field critical current density ($J_c$) of $1.3 \times 10^6$ A/cm$^2$ were obtained. The irreversibility field was $\sim$ 8 T at low temperatures, although severe pinning instability was observed. These bulk-like superconducting properties…

钽 Josephson 结构的三明治制备与结构分析：具有Ta₂O₅屏障

Fabrication and Structural Analysis of Trilayers for Tantalum Josephson Junctions with Ta$_2$O$_5$ Barriers

本文提出了一种用于制备清洁界面Josephson结的钽氧化物三明治结构，通过等离子体氧化技术实现了平滑的Ta₂O₅层，并展示了其在超导量子比特中的应用潜力。

铌-锗界面在混合超导-半导体器件中的固态反应

Solid-State Reactions at Niobium-Germanium Interfaces in Hybrid Superconductor-Semiconductor Devices

研究通过低温蒸发铌并分析其与锗界面的固态反应，揭示了锗扩散对超导电子性能的影响，强调了低温生长对减少界面混入和能带弯曲的重要性。

热激光外延法在蓝宝石上生长超导TiN及其界面工程

Growth and Interface Engineering of Superconducting TiN on Sapphire by Thermal-Laser Epitaxy

本研究采用热激光外延法在蓝宝石上生长TiN，通过低温种子层缓解界面空洞，实现了5.8 K超导转变温度和1.19微欧姆厘米的低电阻率。