Fabrication of high-quality Josephson junctions for quantum computation using a self-aligned process (original) (raw)

Feasibility studies of ultra-small Josephson junctions for qubits

IEEE Transactions on Appiled Superconductivity, 2003

Most proposed realizations of a high temperature superconductor (HTS) qubit (e.g., [1]) require the use of very small Josephson junctions. The properties of bicrystal junctions are especially interesting since they make it possible to implement several types of flux qubits in a relatively simple way. We have developed a technique that allows us to produce high quality sub-micrometer junctions in a reproducible way using bicrystal technology. We have successfully fabricated and characterized a large number of YBCO junctions and SQUIDs with bridge width as small as 0.2 micrometer on 0-3 , 0-40 and 0-45 bicrystal STO substrates. The properties of these junctions have been extensively examined at temperatures down to 20 mK. The effects of external magnetic fields on these structures have been investigated. Figures of merit for the proposed qubits were also extracted from these measurements.

Sub-micrometer epitaxial Josephson junctions for quantum circuits

Superconductor Science and Technology, 2012

We present a fabrication scheme and testing results for epitaxial submicrometer Josephson junctions. The junctions are made using a high-temperature (1170 K) "via process" yielding junctions as small as 0.8 µm in diameter by use of optical lithography. Sapphire (Al 2 O 3 ) tunnel-barriers are grown on an epitaxial Re/Ti multilayer base-electrode. We have fabricated devices with both Re and Al top electrodes. While room-temperature (295 K) resistance versus area data are favorable for both types of top electrodes, the low-temperature (50 mK) data show that junctions with the Al top electrode have a much higher subgap resistance. The microwave loss properties of the junctions have been measured by use of superconducting Josephson junction qubits. The results show that high subgap resistance correlates to improved qubit performance.

In-situ bandaged Josephson junctions for superconducting quantum processors

arXiv: Quantum Physics, 2021

Shadow evaporation is commonly used to micro-fabricate the key element of superconducting qubits-the Josephson junction. However, in conventional two-angle deposition circuit topology, unwanted stray Josephson junctions are created which contribute to dielectric loss. So far, this could be avoided by shorting the stray junctions with a so-called bandage layer deposited in an additional lithography step, which may further contaminate the chip surface. Here, we present an improved shadow evaporation technique allowing one to fabricate sub-micrometer-sized Josephson junctions together with bandage layers in a single lithography step. We also show that junction aging is significantly reduced when junction electrodes are oxidized in an oxygen atmosphere directly after deposition.

Characteristics of Nb-based Josephson junctions at a temperature below 1 K

IEEE Transactions on Magnetics, 1989

In nuclear r a d i a t i o n detection, superconductors have t h e inherent advantage of b e t t e r energy resolut i o n than t h a t of semiconductors. The ultimate energy r e s o l u t i o n has never been accomplished by t h e conventional method of f a b r i c a t i n g t h e tunnel junctions. In t h i s study, lithographic technique f o r Josephson LSI c i r c u i t s is applied t o t h e production of a superconducting tunnel junction f o r r a d i a t i o n detection. Nb-AUaluminum oxide/Nb tunnel junctions with d i f f e r e n t junction s i z e s and b a r r i e r oxidation times have been fabricated t o study t h e i r c h a r a c t e r i stics. The current-voltage curves were measured i n t h e temperature range from 4.2 t o 0.45 K. The junctions

Overdamped Josephson junctions for digital applications

Physica C: Superconductivity, 2013

An interesting feature of Superconductor-Normal metal-Superconductor Josephson junctions for digital applications is due to their non-hysteretic current-voltage characteristics in a broad temperature range below T c . This allows to design Single-Flux-Quantum (SFQ) cells without the need of external shunts. Two advantages can be drawn from this property: first the SFQ cells can be more compact which leads to a more integrated solution towards nano-devices and more complex circuits; second the absence of electrical parasitic elements associated with the wiring of resistors external to the Josephson junctions increases the performance of SFQ circuits, in particular regarding the ultimate speed of operation. For this purpose Superconductor-Normal metal-Insulator-Superconductor Nb/Al-AlO x /Nb Josephson junctions have been recently developed at INRiM with aluminum layer thicknesses between 30 and 100 nm. They exhibit non-hysteretic current-voltage characteristics with I c R n values higher than 0.5 mV in a broad temperature range and optimal Stewart McCumber parameters at 4.2 K for RSFQ applications. The main features of obtained SNIS junctions regarding digital applications are presented.

APPLICATIONS OF THE MAIN DEVICES BASED ON JOSEPHSON JUNCTION: A REVIEW

International Journal of Advances in Engineering & Technology, 2020

In this paper we present a review of the main applications of Josephson Junction (JJ). This device bases its properties on the Josephson Effect, based on the relationship between Tunnel Effect and Superconducting Theory. The properties of JJ allow to realize Superconducting Quantum Interference Devices (SQUIDs), used in medical field, or industrial level electronic circuits such as Superconducting Qubits. We also describe the hybrid technology named RSFQ-CMOS, which is not realized yet for general purposes because it requires cryogenic cooling system. Although, if this problem will be bypassed, the devices based on Josephson Junction will be ready to substitute the current electronic and its limitations.

Undergraduate Research with Josephson Qubits: From Fabrication to Spectroscopy

Bulletin of the American …, 2009

Josephson junctions are scalable solid state devices that can be used as qubits in quantum computing. In this talk we will describe the different stages involved in the fabrication, characterization and state measurement of a particular superconducting qubit known as the Josephson ...

Quantum Manipulations of Small Josephson Junctions

Physical Review Letters, 1997

Low-capacitance Josephson junction arrays in the parameter range where single charges can be controlled are suggested as possible physical realizations of the elements which have been considered in the context of quantum computers. We discuss single and multiple quantum bit systems. The systems are controlled by applied gate voltages, which also allow the necessary manipulation of the quantum states. We estimate that the phase coherence time is sufficiently long for experimental demonstration of the principles of quantum computation.

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

npj Quantum Information

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 tenfold 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 qubit frequency precision. We find that, without post-fabrication tuning, the probability of finding a workable lattice quickly approaches 0. However, with the demonstrated precisions it is possible to find collision-free lattices with favorable yield. These techniques and models are currently employed in available quantum systems and will be indispensable as systems continue to scale to larger ...

Application of High-Tc Superconducting Josephson Junction Devices

2019

Abstract: The application of superconducting devices based on Josephson junction has been investigated for many years. Josephson junction is based on quantum mechanical tunneling of electrons between weakly coupled two superconducting regions. Its unique properties make it a building block for future superconducting electronic circuits. In this paper, attempt has been made to highlight the wide range of application of Josephson junction including Josephson voltage standard, SQUIDs, Quantum Computer, analog to digital converter, RSFQ digital electronics, terahertz emitter and detector etc.