scholarly journals Persistent Josephson Phase-Slip Memory with Topological Protection

2021 ◽  
Author(s):  
Nadia Ligato ◽  
Elia Strambini ◽  
Federico Paolucci ◽  
Francesco Giazotto
Keyword(s):  
Magnetic Flux ◽  
Memory Cell ◽  
Phase Slip ◽  
Operation Speed ◽  
Typical Time ◽  
The One ◽  
Slip Transition ◽  
Phase Slips ◽  
Non Destructive ◽  
Device Miniaturization

Abstract Superconducting computing promises enhanced computational power in both classical and quantum approaches. Yet, efficient schemes for scalable and fast superconducting memories are still missing. On the one hand, the large inductance required in magnetic flux-controlled Josephson memories impedes device miniaturization and scalability. On the other hand, schemes based on the ferromagnetic order to store information often degrades superconductivity, and limits the operation speed to the magnetization switching rate of a few GHz. Here, we overcome these limitations with a fully superconducting memory cell based on the hysteretic phase-slip transition existing in long aluminum nanowire Josephson junctions. The memory logic state is codified in the topological index of the junction providing a robust protection against stocastic phase slips and magnetic flux noise. Our direct and non-destructive read-out schemes, based on local DC or AC tunneling spectroscopy, ensure reduced dissipation (≤ 40 fW) thereby yielding a very low energy per bit read-out power consumption as low as ~ 10-24 J as estimated from the typical time response of the structure (≤ 30 ps). The memory, measured over several days, showed no evidence of information degradation up to ~1.1 K, i.e., ~85% of the critical temperature of aluminum. The ease of operation combined with remarkable performance elects the Josephson phase-slip memory as an attractive storage cell to be exploited in advanced superconducting classical logic architectures or flux qubits.

scholarly journals Preliminary demonstration of a persistent Josephson phase-slip memory cell with topological protection

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Nadia Ligato ◽  
Elia Strambini ◽  
Federico Paolucci ◽  
Francesco Giazotto
Keyword(s):  
Weak Link ◽  
Memory Cell ◽  
Superconducting Gap ◽  
Phase Slip ◽  
Superconducting Ring ◽  
Flux Qubits ◽  
Memory Scheme ◽  
Promising Solution ◽  
Slip Transition ◽  
Phase Slips

AbstractSuperconducting computing promises enhanced computational power in both classical and quantum approaches. Yet, scalable and fast superconducting memories are not implemented. Here, we propose a fully superconducting memory cell based on the hysteretic phase-slip transition existing in long aluminum nanowire Josephson junctions. Embraced by a superconducting ring, the memory cell codifies the logic state in the direction of the circulating persistent current, as commonly defined in flux-based superconducting memories. But, unlike the latter, the hysteresis here is a consequence of the phase-slip occurring in the long weak link and associated to the topological transition of its superconducting gap. This disentangles our memory scheme from the large-inductance constraint, thus enabling its miniaturization. Moreover, the strong activation energy for phase-slip nucleation provides a robust topological protection against stochastic phase-slips and magnetic-flux noise. These properties make the Josephson phase-slip memory a promising solution for advanced superconducting classical logic architectures or flux qubits.

scholarly journals Solar and Interplanetary Magnetic Helicity Balance of Active Regions

2005 ◽  
Vol 13 ◽  
pp. 122-123
Author(s):  
Cristina H. Mandrini ◽  
Pascal Démoulin ◽  
Lidia van Driel-Gesztelyi ◽  
Sergio Dasso ◽  
Lucinda M. Green ◽  
...  
Keyword(s):  
Magnetic Flux ◽  
Differential Rotation ◽  
Active Regions ◽  
Magnetic Helicity ◽  
Constant Current ◽  
Flux Tubes ◽  
Combining Data ◽  
Free Model ◽  
Linear Force ◽  
The One

AbstractWe analyzed the long-term evolution of two active regions (ARs), NOAA 7978 and 8100, from their emergence through their decay using observations from several instruments on board SoHO (MDI, EIT and LASCO) and Yohkoh/SXT. We computed the evolution of the relative coronal magnetic helicity from one central meridian passage to the next, combining data from MDI and SXT with linear force-free models of the coronal magnetic field. Next, we calculated the injection of helicity by photospheric differential rotation using MDI magnetic maps and a mean differential rotation profile. To estimate the depletion of magnetic helicity we counted all the CMEs of which these ARs were the source, and we evaluated their helicity assuming a one to one correspondence with magnetic clouds (MCs) with an average helicity content; this value was computed for a sample of 18 clouds using a cylindrical linear force-free model. Out of our three helicity estimates (variation of coronal magnetic helicity, injection by differential rotation and ejection via CMEs) the one with the largest uncertainty is the amount of helicity ejected via CMEs. However, we determined, by modeling a particular MC using three different approaches in cylindrical geometry (two force-free models and a non force-free model with constant current), that its magnetic helicity content was nearly independent of the model used to fit in situ field observations (Dasso et al. 2003, in preparation). This result justifies our use of the average magnetic helicity value considering only a single MC model. Comparing the three components in the helicity balance (see Table 1), we find that photospheric differential rotation is a minor contributor to the AR magnetic helicity budget. CMEs carry away at least 10 times more helicity than the one differential rotation can provide. Therefore, the magnetic helicity flux needed in the global balance should come from localized photospheric motions that, at least partially, reflect the emergence of twisted flux tubes. Taking into account the magnetic flux in the ARs and the number of turns that a uniformly twisted flux tube should have to survive its rise through the convection zone, we have found that the total helicity carried away in CMEs is approximately equal to the end-to-end helicity of the flux tubes that formed these two ARs. Therefore, we conclude that most of the helicity ejected in CMEs is generated below the photosphere and emerges with the magnetic flux. Extended versions of this work were published in Demoulin et al. (2002, Astronomy & Astrophys. 382, 650) and in Green et al. (2002, Solar Phys. 208, 43), while in Mandrini et al. (2003, Astrophys. & Space Sci., 290, 319) and van Driel-Gesztelyi et al. (2003, Adv. Space Res., 32, 1855) the helicity computations were revised to include the underestimation of magnetic flux density found in MDI data. After this revision, we confirmed our former results.

Problems of development of traction drives with brushless traction motors for passenger electric locomotives

2020 ◽  
pp. 20-25
Author(s):  
Andrey Sergeevich Kosmodamianskiy ◽  
◽  
Vladimir Ivanovich Vorobyev ◽  
Mikhail Yuryevich Kapustin ◽  
Oleg Vasilyevich Izmerov ◽  
...  
Keyword(s):  
Magnetic Flux ◽  
Rotation Frequency ◽  
Axial Direction ◽  
Traction Drive ◽  
Traction Motors ◽  
Adaptability To Manufacture ◽  
Traction Drives ◽  
Conducting Research ◽  
The One ◽  
Electric Traction

The paper considers a problem of creation of new traction drives with brushless electric traction motors (ETM) for passenger locomotives. Analysis of drive designs revealed that the increase of power of induction motors through the increase of rotation frequency leads to the contradiction between requirements for the design reliability, on the one hand, and requirements for technological simplicity, on the other hand. In order to solve the contradiction it is necessary to use ETM designs that have enhanced torque and minimal dimensions in axial direction. It is established that ETM with disk rotor (axial magnetic flux) satisfy such requirements. The authors proposed an aggregate scheme of support-frame traction drives that include ETM with disk rotor, which allows significantly increasing the adaptability to manufacture and repairability of drive at preservation of reliability. As a result, the authors made a conclusion about the reasonability of conducting research and development work on creation of locomotive ETM with axial magnetic flux. The authors have submitted an application for a patent on the proposed design of traction drive.

scholarly journals QUARKS AS TOPOLOGICAL DEFECTS — OR, WHAT IS CONFINED INSIDE A HADRON?

1993 ◽  
Vol 08 (31) ◽  
pp. 5575-5604 ◽  
Author(s):  
A. KOVNER ◽  
B. ROSENSTEIN
Keyword(s):  
Magnetic Flux ◽  
Topological Charge ◽  
Domain Walls ◽  
Topological Defects ◽  
Complex Scalar ◽  
Yang Mills ◽  
Effective Lagrangian ◽  
Local Complex ◽  
Complex Scalar Field ◽  
The One

We present a picture of confinement based on representation of constituent quarks as pointlike topological defects. The topological charge carried by quarks and confined in hadrons is explicitly constructed in terms of Yang-Mills variables. In 2+1 dimensions we are able to construct a local complex scalar field V(x), in terms of which the topological charge is [Formula: see text]. The VEV of the field V in the confining phase is nonzero and the charge is the winding number corresponding to homotopy group π1(S1). Quarks carry the charge Q and therefore are topological solitons. The phase rotation of V is generated by the operator of magnetic flux. Unlike in QED, the U(1) magnetic flux is explicitly broken by the monopoles. This results in formation of a string between a quark and an antiquark. The effective Lagrangian for V is derived in models with adjoint and fundamental quarks. This topological mechanism of confinement is basically different from the one proposed by ’t Hooft in which the elementary objects are linelike domain walls. A baryon is described as a Y-shaped configuration of strings. In 3+1 dimensions the explicit expression for V, and therefore a detailed picture, is not available. However, assuming the validity of the same mechanism we point out several interesting qualitative consequences.

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