Tuesday, May 28, 2024

German bureaucracy, or: things going downhill, part 1 of n

[Update at end]

I've been working in university research now for quite some time, and one of the great things about it is international cooperation. The sciences live and breathe via cooperation visits, seminar invitations, ... One of the fixtures at probably nearly every university is the faculty colloquium, where each week, covering a wide range of topics, a renowned expert is invited to speak. Then there are locally organized conferences, regular seminars connected to research programs...  And "invited" is the real word here; while typically no remuneration is paid to the speakers, the travel expenses from tickets to hotel costs are reimbursed (within reasonable limits given by guidelines and rules), and of course we strive to make the visit as easy and pleasant for the guest as possible.

Enter Germany, or in this case more precisely Bavaria. Starting 1 January 2024, travel expenses can only be reimbursed to persons with a German tax id number ("Steueridentifikationsnummer"). How about international guests, not German citizens, not living in Germany, you may ask? Well, obviously, they most likely don't have one. So they need to get one! This involves sending a filled-out form with personal data and passport copies by paper mail to our local tax office well in advance, after all processing and assigning this life-long id (and adding them to the German tax register) can take up to 4 weeks. Seriously, I am ashamed to ask this of our international guests who don't intend to stay here long or take up employment here, just so they can get their plane tickets reimbursed, and can fully understand if someone is not happy about it.

And then, once you got over that, you realize that you can't even pre-book some arrangements since the university still has no credit card and thus can't do online bookings.

It's getting worse year by year. Blargh.

Update. So I've been informed in the meantime that here the faculty administration can take care of it (during the visit of the guest? unclear), that it is a matter of 10min and no problem, and that I should not worry about it. (?) Also, it's apparently due to some EU regulation (?) and Berlin is apparently already doing the same as Bavaria. ?!?

Monday, April 1, 2024

The interpersonal side of the xz-utils compromise

While everyone is busy analyzing the highly complex technical details of the recently discovered xz-utils compromise that is currently rocking the internet, it is worth looking at the underlying non-technical problems that make such a compromise possible. A very good write-up can be found on the blog of Rob Mensching...

"A Microcosm of the interactions in Open Source projects"

Monday, October 30, 2023

Lab::Measurement 3.900 released - also dropping support for legacy scripts

Following a lot of smaller and larger improvements and additions, we have finally released Lab::Measurement 3.900 on CPAN. Highlights compared to the last "round version" include support for the Nanonis Tramea quantum transport measurement, the Zurich Instruments HDAWG arbitrary waveform generator, the Synktek MCL1-540 lock-in amplifier, the Bluefors dilution refrigerator temperature control, the American Magnetics AMI430 magnet power supply, as well as many improvements for Lakeshore temperature controllers.

In addition, version 3.900 now finally drops the unmaintained legacy code layers (Lab::Bus, Lab::Connection, Lab::Instrument, Lab::XPRESS) and focuses on the Moose-based Modern Perl interface alone. This should make maintenance easier in the future. Anyone who still needs the old interfaces for measurement scripts should install the distribution Lab::Measurement::Legacy, where the deprecated modules are archived.

Tuesday, January 10, 2023

Advanced Materials published: "Non-destructive low-temperature contacts to MoS2 nanoribbon and nanotube quantum dots"

Molybdenum disulfide MoS2 is often discussed as a groundbreaking material for electronics applications. As bulk crystal or as 2D layer material similar to graphene, it is an excellent semiconductor with strong spin-orbit interaction. At strong doping it even becomes intrinsically superconducting, with possibly interesting topological properties.

So how about using MoS2 for quantum electronics, single electron devices, or (charge, spin, or valley) qubits? There's already enough science fiction literature out there mentioning "molycircuits"... Well, a small problem stands in the way.  It turns out that the electronic band structure of the material makes reaching quantum confinement, i.e., discrete, addressable electronic quantum states, quite hard. The chip structures need to be built at very small scale, difficult to reach with MoS2 flakes on a chip surface, and so far no research group has managed to do this in a controlled way.

That's exactly why we are interested in MoS2 nanotubes. They can be grown clean and straight, with diameters down to 20nm - which automatically confines charge carriers in one more direction compared to a two-dimensional MoS2 flake. What remains is to restrict motion of the charge carriers along the nanotube axis and to make good metallic contacts. However, it turns out that making good contacts to MoS2 is hard - either your metals form a Schottky barrier, or they react with the MoS2 and destroy its crystal structure.

In our work, we show that this problem has now been solved. Using a thin layer of the semimetal bismuth, we obtain contacts which remain transparent even at cryogenic (millikelvin) temperatures and leave the structure of MoS2 below and next to them intact. This makes transport spectroscopy measurements on a MoS2 quantum dot forming within the nanotube possible. We indeed observe quantum dot behaviour; the temperature dependence of the Coulomb oscillations of conductance indicates that we reach electronic tunneling through single, discrete quantum states below a temperature of T=100mK. 

With this, we have made a big step towards controllable charge, spin, or even valley quantum states in MoS2. Next we need to miniaturize our devices even further, and increase our measurement resolution to be able to analyze the electronic level spectrum in magnetic fields.

"Non-destructive low-temperature contacts to MoS2 nanoribbon and nanotube quantum dots"
R. T. K. Schock, J. Neuwald, W. Möckel, M. Kronseder, L. Pirker, M. Remskar, and A. K. Hüttel
accepted for publication by Advanced Materials (doi:10.1002/adma.202209333); arXiv:2209.15515 (PDF, supplementary information)

Monday, October 24, 2022

Video from Walter Schottky Prize award ceremony now online

 The video recording of the Walter Schottky Prize award ceremony in June is finally online. Enjoy :)

Tuesday, July 5, 2022

Airport taxis via booking.com -- nice if it works!

So I'm a good, and normally very happy booking.com customer (Genius Level 3 if that means anything), and have spent a lot of money over the past years via that company. This year, during this trip, I tried booking airport pick-up in advance for the first time. The first pick-up failed spectacularly, and I'm still dealing with it.

Long flight(s). Frankfurt (FRA) - Bangkok (BKK), Bangkok (BKK) - Sydney (SYD). Things didn't go exactly to plan, the flight arrived late in Sydney, but hey, booking.com says the drivers are tracking the arrival schedule and adapt to that. After immigration and luggage pick-up, I leave the security area and scan the waiting crowd. Lots of drivers waiting for lots of travellers, but unfortunately noone waiting for me.

After half an hour of waiting, I get into a conversation with a driver who works for the same company that is supposed to pick me up. He asks around, can't help me either, and recommends to phone the company office. I do that, with the number given in the reservation confirmation in the booking.com app. On the phone, I get told there is no reservation on my name.

So I take a regular cab to my hotel. Works fine. 

Except that the transfer was of course already paid (and since the date is past, it can't be cancelled anymore). Clicking through the labyrinth of the booking.com website, I find out it is really difficult to file a complaint. Anyway, I manage to arrive at the proper form, state the situation and request a refund.

Nothing happens for over a week.

So I file another report again, on Sat 2/July/2022, including this time that in case of no response within three business days I will dispute the corresponding credit card booking, with them being liable for associated fees. Clock's ticking...

I like booking.com, and am otherwise a very happy customer. Also, a second pickup later worked out just fine (SGN). Nevertheless, this is somewhat annoying.

Update, 7/July/2022: With effective date 2/July/2022 the money was refunded to my credit card by booking.com. No e-mail or status change or notification on the website, but hey, the money is back. So no need for further complaints. :)

Wednesday, April 13, 2022

Testing the Gentoo LiveGUI with QEmu

If you want to test the Gentoo LiveGUI, but don't feel like cutting short the precious uptime of your machine, here's a handy bash script for testing the iso files with qemu:


qemu-system-x86_64    -m 4G \
           -enable-kvm \
           -cpu host \
           -smp 4 \
           -name "Gentoo amd64 LiveGUI" \
           --netdev user,id=vmnic,hostname=gentoovm \
           -device e1000,netdev=vmnic \
           -bios /usr/share/edk2-ovmf/OVMF_CODE.fd \
           -device intel-hda -device hda-duplex \
           -usbdevice tablet \
           -vga vmware \
           -cdrom $1

You'll need to be in the kvm group and have kvm configured in your kernel. Also you may want to adapt the memory (now 4Gbyte) and the number of CPUs (now 4) for the virtual machine. Then you can simply start the boot process with

~ $ ./qemu-livegui livegui-amd64-20220412T191925Z.iso &