user129412

general recent conversations

The h Bar

General chat for Physics SE (physics.stackexchange.com). For M...

user129412

Apr 23, 2022 08:57

I know that typically thin film aluminium will have a critical temperature for turning superconducting that is larger than the bulk value of 1.2K. Are there cases in which you expect the (still somewhat thin, ~200nm range) aluminium to go below 1.2K? Perhaps if it is strongly oxidized or something of the sort (I would expect it to go the other way then, but I am not sure..)

user129412

Dec 22, 2021 11:23

Do you need, for example, sigma_x sigma_x coupling?

user129412

Dec 22, 2021 11:20

If I have two coupled 2-level systems, what kind of coupling do they need to have/could cause them to show the SWAP (+ excitation on one, - on the other) and double (excitation on both) transitions? Can something be said about that?

user129412

Jul 2, 2021 08:32

Anyway, this is leaving the realm of physics, I suppose!

user129412

Jul 2, 2021 08:31

And apparently Tardigrades do not care about either the vacuum or the radiation

user129412

Jul 2, 2021 08:30

Oh, apparently NASA did in 1965. Not outer space, but still 0.031 psi for 30 seconds. They were fine afterwards

user129412

Jul 2, 2021 08:28

Indeed. I'm surprised they haven't tried with animals, in less ethical endeavours. The doesn't seem to be much info on it. But that's probably for the best (for the chimps)

user129412

Jul 2, 2021 08:25

There is also some air in your other organs, but maybe the tissues are firm enough to hold that back

user129412

Jul 2, 2021 08:16

Or is the swelling from decompression what you meant?

user129412

Jul 2, 2021 08:15

I'm not sure I've heard of that before. I think you would swell from decompression, and maybe your lungs would rupture, but you would also expand?

user129412

Jul 2, 2021 07:56

Do I exert 1 atm of pressure on the atmosphere?

user129412

Jun 20, 2021 11:22

Yes, sorry. I was thinking about a superconducting film on, say, a silicon substrate. Me and some colleagues were discussing the thermal conductivity of superconductors at mK temperatures, and it was stated that they do not conduct heat. But I think that's wrong; there is virtually no heat carried by electrons, but it is still carried by phonons, right?

Or maybe phrased slightly differently, if we put a purely superconducting link between a 4K stage and a mK stage, it is not a perfect thermal isolation, right? It's just a rather poor conductor

user129412

Jun 19, 2021 11:57

Thanks, that is also what I thought! Colleagues of mine said something about superconductors being poor thermal conductors, which I did not really understand because I thought phonons should just propagate through them. But maybe what they meant is that it is hard to thermalize the electrons in the superconducting material.

For the record, I don't think films are any different than bulk superconductors. Of course the boundaries will affect phonon propagation, but that is not specific to superconductivity.

user129412

Jun 18, 2021 16:55

Can phonons with an energy below the superconducting gap propagate through superconducting films? Or are they not allowed in?

user129412

Jun 7, 2021 14:23

I have two related questions/sources of confusion.. In a superconductor far below Tc, phonons with a frequency below twice the gap can just propagate freely through it, right? Above that they can break cooper pairs, but below that they are unimpeded?

Is this related to that people often say that superconductors are hard to thermalize?

user129412

Feb 25, 2021 21:01

Probably something I should write up into an actual question, but maybe I'll probe it a bit first here.. when you have a superconducting metal, far below Tc, are almost all of the electrons then paired up into cooper pairs? I find that hard to imagine, with superconducting gaps being ~meV, but Fermi levels in metals being eV

user129412

Feb 3, 2020 17:16

I suppose my actions are independent of what is meant by the statement, but should I interpret it as mostly positive or negative, would you say? To me it sounds a bit like, make the changes that were asked for, and if you can convince us or the referee (sounds hard) that it isn't too specialized we'll publish, else we will ask a third person

user129412

Feb 3, 2020 17:16

What would you make of an editor writing "we will probably send your resubmission out for further review"? I got a paper back with two referee reports, one only had minor comments and strongly recommended it, the other only wrote a summary of the paper and said it was very nice, but then said it was too specialized so find a more specialized journal.

user129412

Jan 24, 2020 08:48

I have a silly question... What happens if I cover a loop of area A with a thin (thicknes << penetration depth) superconducting film, and apply a perpendicular magnetic field? Will I thread a flux through that loop?

user129412

Aug 8, 2019 13:36

If we think of a standard 'charge qubit' such as the transmon or the cooper pair box, why do the excited states have higher charge sensitivity (charge dispersion, or dependence of the energy levels with offset charge) than the ground state?

user129412

Aug 6, 2019 08:12

Or maybe a shorter way of stating it, is there a term that can be used to denote that a system is very narrow in the charge basis? Say a cooper pair box versus a transmon qubit

user129412

Aug 6, 2019 08:09

If I consider some small conductor (an island), isolated from the environment, it'll well described by a single charge state. This is in contrast to an island connected to a lead by a tunnel junction with large conductance, where charge fluctuates quite heavily among multiple charge states. What kind of term could one use to describe such a system? Is it fair to say that charge is localized on the island, or does that imply more of a spatial concept rather than being in a single charge state?

user129412

Aug 2, 2019 08:50

Direct tunneling, vs ABS mediated

user129412

Aug 2, 2019 08:50

Is the ABS picture simply a more refined one of the first one, or are they separate processes?

user129412

Aug 2, 2019 08:50

I have a question of which I'm not sure it warrants opening one on the main page. It's about the Josephson effect. I've learned two interpretations of it; one is that the superconductors on either side of the junction have a finite overlap between their wavefunctions, allowing Cooper pairs to tunnel. The other is that Andreev bound states allow transferring Cooper pairs across the junction depending on the transparency of the junction and the number of channels.

user129412

Jul 27, 2019 14:18

Coulomb blockade in a normal metal island separated by a tunnel junction requires the resistance of the junction R >> hbar/e^2. Is there an equivalent condition for a superconducting island, where it is not R that matters but the Josepshson energy Ej?

user129412

Jul 18, 2019 16:08

Does anyone happen to know (a way of finding) the highest Ramsey T_2 (so T_2^*) measured in a transmon? I haven't been able to track it down myself

user129412

Jan 16, 2019 12:28

Does anyone here (from the top of their head) remember how the size of a superconducting gap depends on perpendicular magnetic field, for a type 1 superconductor? Away from the critical field lets say.

user129412

Jan 14, 2019 13:56

What I wrote above is true for parallel magnetic fields. Anyone know where (in Tinkham, probably) I can find something on the field dependence of the superconducting gap for a perpendicular magnetic field?

user129412

Jan 14, 2019 13:34

I found it, I should have looked a little harder. Its equation 4-52, somewhere in the chapter on Ginzburg Landau

user129412

Jan 14, 2019 13:30

It seems to mimic the phenomenological parabolic law discussed very early on in the book for Bc in terms of Tc, but beyond that I can't find much

user129412

Jan 14, 2019 13:28

The paper talks about Al, so it should be in type 1 part of the book, but I can't seem to locate it

The Ivory Tower

General discussion for academia.stackexchange.com

user129412

Mar 13, 2022 16:33

Thank you, that's good advice.

user129412

Mar 13, 2022 14:23

Perhaps not really worthy of a separate post, but if you get a desk rejection by the editor where they give you an explicit reason (so not just a standard template), and that reasoning does not appear to be correct, does it make sense to appeal? In this case they said that for topic A, which your paper is about, we only publish papers where they show record performance in metric X. But our paper is not about topic A (nor measures X), it is just mentioned somewhere in the introduction.

Wolfram Mathematica

Welcome! This is the main Mathematica chat room for mathematic...

user129412

Jan 18, 2022 16:14

This is probably an inappropriate question, but could someone help me understand what this piece of code does? The inputs are 2 long lists of numbers. Where I get confused is mainly that I have only ever seen functions defined in 1 statement, but here separate seems to be defined in some way that depends on itself?

separate[l1_List, l2_List] /; Length[l1] == Length[l2] :=
separate[Take[l1, 2], Take[l2, 2], Drop[l1, 2], Drop[l2, 2]];
separate[{s1___, a1_, b1_}, {s2___, a2_, b2_}, {n1_, l1___}, {n2_,

user129412

Feb 19, 2019 16:24

Yes, that fixed it!

user129412

Feb 19, 2019 16:20

@ChrisK Thanks! I see that I'm on 10, so I'll try with an actual up to date version as well. Good to know

user129412

Feb 19, 2019 14:50

Would anyone be able to check for me if they can reproduce the results of mathematica.stackexchange.com/a/191795/24936 ? Because for me I don't seem to get the same result, I just get an empty list

Electrical Engineering

A place to talk with friends from the EE community about vacuu...

user129412

Nov 11, 2021 19:26

Is there a closed form solution for how a 1st order high pass RC filter acts on a (single, but periodic is also okay) square pulse? In terms of pulse duration and RC constant?

user129412

Sep 20, 2020 10:55

But it could also be quite a bit more, I suppose. The lower limit is useful though, thanks for pointing that out.

user129412

Sep 20, 2020 10:53

@JRE Thanks, I meant to ask for the capacitance value indeed. In my setup It'll function as a type of high pass filter (as there is some resistance to ground after the DC block) and I'm wondering what the cutoff frequency will be, more or less.

user129412

Sep 20, 2020 08:24

I understand it is.... challenging to judge when the manufacturer doesn't specify anything, but would anyone have an order of magnitude estimate of the size of the capacitor in a DC block like pasternack.com/…

user129412

Sep 13, 2020 13:24

Is it relevant that I essentially break the ground of the coax coming into the microstrip? The PCB sits on a metal frame, and that in the end is on the same ground as the enclosure in which the (stainless steel) coax is clamped. Also, I wrote silly because I feel like this should be obvious, but I honestly do not really have an intuition for it.

user129412

Sep 13, 2020 13:22

I have a silly RF related question. I'm using coax lines to send GHz signals through a microstrip on a PCB. I am, however, getting Hz-kHz noise on the coax lines (the origin is a bit subtle). I was thinking that I could get rid of the noise with a DC block; essentially just a capacitor in series. But there are 3 types of capacitors: inner-only, outer-only, and inner-outer. I definitely need an inner, as the signal is carried on the inner conductor. But would it hurt to have an inner-outer?

user129412

Oct 28, 2019 14:30

@JRE Thanks! That is an interesting article.

user129412

Oct 28, 2019 08:15

Does anyone know the expression for the capacitance of a slotline? So two (lets say very thin) metallic sheets separated by a gap g on top of a (very thick) dielectric with dielectric constant eps_r? For some reason I can only find expressions for the impedance. Or for two parallel strips, but I am not sure that is exactly the same.

Root Access

For all you Super Users out there. You have backups, right?

user129412

Oct 18, 2019 08:43

Is there a way for me to say to windows, don't let a program use more than X gb of RAM?

user129412

Oct 18, 2019 08:43

I can't seem to google the right term, but I have an issue with a windows 10 computer where running a piece of software (finite element simulation) with too liberal settings (very fine mesh) takes up so much memory that the computer completely freezes. Or at least that is what I have deduced; when it starts aggressively maxing out the used RAM it hangs indefinitely. I've ran a memtest for more than 24 hours and there's no issues there, a CPU stress test is also no problem.

The Classical Channel

General chat for Quantum Computing SE. For MathJax see meta.st...

user129412

Aug 8, 2019 13:36

user129412

Jul 18, 2019 16:08

Does anyone happen to know (a way of finding) the highest Ramsey T_2 (so T_2^*) measured in a transmon? I haven't been able to track it down myself