Dynamic properties of high-Tc superconducting nano-junctions made with a focused helium ion beam

Abstract

the Josephson junction (JJ) is the corner stone of superconducting electronics and quantum information processing. While the technology for fabricating low T c JJ is mature and delivers quantum circuits able to reach the "quantum supremacy", the fabrication of reproducible and low-noise high-T c JJ is still a challenge to be taken up. Here we report on noise properties at Rf frequencies of recently introduced high-T c Josephson nano-junctions fabricated by mean of a Helium ion beam focused at sub-nanometer scale on a YBa 2 cu 3 o 7 thin film. We show that their current-voltage characteristics follow the standard Resistively-Shunted-Junction (RSJ) circuit model, and that their characteristic frequency f c = (2e/h)I c R n reaches ~300 GHz at low temperature. Using the "detector response" method, we evidence that the Josephson oscillation linewidth is only limited by the thermal noise in the RSJ model for temperature ranging from T ~ 20 K to 75 K. At lower temperature and for the highest He irradiation dose, the shot noise contribution must also be taken into account when approaching the tunneling regime. We conclude that these Josephson nano-junctions present the lowest noise level possible, which makes them very promising for future applications in the microwave and terahertz regimes. The astonishing recent evolution of Information and Communication Technologies (ICTs) is based on an accurate control of quantum properties of semiconductors at sub-micron scales. As some limitations appear, new paradigms emerge to further improve the performances of ICT devices, based on coherent quantum states and nano-scale engineering. Superconductivity is a very interesting platform which provides robust quantum states that can be entangled and controlled to realize quantum computation and simulation 1 , or classical computation at very high speed using the so called SFQ (Single Flux Quantum) logic 2. This platform can also be used to make detectors of electromagnetic fields and photons operating at the quantum limit, i.e. with unsurpassed sensitivity and resolution. These quantum sensors can be used for classical or quantum communications 3 , THz waves detection and imaging 4 , sensitive high frequency magnetic fields measurements 5,6. Impressive results have been achieved in the recent years with devices based on Low critical Temperature (T c) Superconductors (LTS) working at liquid helium temperature, and well below for Quantum Computing. The main building block of this superconducting electronics is the Josephson Junction (JJ), a weak link between two superconducting reservoirs. While the technology for LTS JJ of typically 1 μm in size required for complex systems is mature 2 , other ways are explored to downsize the JJ using Carbon Nano-Tubes 7 , Copper nanowires 8 or LaAlO 3 /SrTiO 3 interfaces 9 for examples. The complexity and the cost of the needed cryogenic systems are clearly obstacles for large scale applications of such devices. High-T c superconductors (HTS) operating at moderate cryogenic temperature (≤40 K) appea...

A review of defect engineering, ion implantation, and nanofabrication using the helium ion microscope

“…Similar multi-step irradiation routines have been used to fabricate SQUID micromagnetometers entirely using helium ion irradiation [40][41][42][43], nano-SQUIDbased transimpedance amplifiers [44], and Josephson junctions in the superconducting bridge of spiral terahertz antenna structures [45]. The performance of Josephson junctions in YBCO thin films fabricated using the HIM has been further evaluated in [46].…”

3‐D Nanofabrication of Silicon and Nanostructure Fine‐Tuning via Helium Ion Implantation

“…Helium ion microscopy (HIM), with its unique properties, such as a super small beam spot as small as 0.5 nm and capability of fabricating sub‐10 and even sub‐5 nm features, has found a plethora of exciting applications [ 5 ] in fabricating nanodevices, such as nanopores of solid‐state materials, [ 6 ] nanoribbons of 2D materials, [ 7 ] nanogaps, [ 8 ] superconducting nanojunctions, [ 9 ] suspended nanomechanical graphene resonators, [ 10 ] quantum devices, [ 11 ] molecular devices, [ 12 ] plasmonic nanoantennas, [ 13 ] and photonic crystal biosensors. [ 14 ] Current nanofabrication using HIM generally falls into two categories.…”

Standard measurement method for normal state resistance and critical current of resistively shunted Josephson junctions

“…HTS SIS junctions with β C ≪ 1 were obtained by using a focused He ion beam [32][33][34]. The He nanobeam produced a weak link with a thickness of ∼nm directly; JJs [32,34] and DC SQUID [33] were fabricated.…”

“…HTS SIS junctions with β C ≪ 1 were obtained by using a focused He ion beam [32][33][34]. The He nanobeam produced a weak link with a thickness of ∼nm directly; JJs [32,34] and DC SQUID [33] were fabricated. By increasing ion dose, the irradiated region of YBCO was transformed from a normal metal to an insulator.…”