tag:blogger.com,1999:blog-78495072701649670362024-03-14T19:49:21.918+01:00the dilfridge blogAndreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.comBlogger191125tag:blogger.com,1999:blog-7849507270164967036.post-7948143249182162812023-10-30T16:46:00.001+01:002023-10-30T16:46:43.602+01:00Lab::Measurement 3.900 released - also dropping support for legacy scripts<p>Following a lot of smaller and larger <a href="https://www.labmeasurement.de/gitweb/?p=labmeasurement;a=blob;f=Changes;hb=HEAD" target="_blank">improvements and additions</a>, we have finally released <a href="https://metacpan.org/dist/Lab-Measurement">Lab::Measurement</a> 3.900 on CPAN. Highlights compared to the last "round version" include support for the <a href="https://www.specs-group.com/nanonis/products/tramea/" target="_blank">Nanonis Tramea</a> quantum transport measurement, the <a href="https://www.zhinst.com/europe/en/products/hdawg-arbitrary-waveform-generator" target="_blank">Zurich Instruments HDAWG</a> arbitrary waveform generator, the <a href="https://www.synktek.com/synktek-mcl1-540/">Synktek MCL1-540</a> lock-in amplifier, the <a href="https://bluefors.com/" target="_blank">Bluefors</a> dilution refrigerator temperature control, the <a href="http://www.americanmagnetics.com/magpower.php" target="_blank">American Magnetics AMI430</a> magnet power supply, as well as many improvements for <a href="https://www.lakeshore.com/products/categories/temperature-products/cryogenic-temperature-controllers" target="_blank">Lakeshore temperature controllers</a>.</p><p>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 <a href="https://metacpan.org/dist/Moose" target="_blank">Moose</a>-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 <a href="https://metacpan.org/dist/Lab-Measurement-Legacy" target="_blank">Lab::Measurement::Legacy</a>, where the deprecated modules are archived.<br /></p>Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-71775025212697277462023-01-10T12:41:00.002+01:002023-01-17T22:18:51.520+01:00Advanced Materials published: "Non-destructive low-temperature contacts to MoS2 nanoribbon and nanotube quantum dots"<div class="separator" style="clear: both; text-align: center;"><a href="https://www.akhuettel.de/publications/nondestructive.pdf" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="182" data-original-width="200" height="182" src="https://www.akhuettel.de/publications/nondestructive-fig.png" width="200" /></a></div><p>Molybdenum disulfide MoS<sub>2</sub> 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.</p><p>So how about using MoS<sub>2</sub> 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 MoS<sub>2</sub> flakes on a chip surface, and so far no research group has managed to do this in a controlled way.</p><p>That's exactly why we are interested in MoS<sub>2</sub> 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 MoS<sub>2</sub> 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 MoS<sub>2</sub> is hard - either your metals form a Schottky barrier, or they react with the MoS<sub>2</sub> and destroy its crystal structure. </p><p>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 MoS<sub>2</sub> below and next to them intact. This makes transport spectroscopy measurements on a MoS<sub>2</sub> 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 <i>T</i>=100mK. </p><p>With this, we have made a big step towards controllable charge, spin, or even valley quantum states in MoS<sub>2</sub>. 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.<br /></p><span data-seleniumid="article-doi-text"></span><p><b>"Non-destructive low-temperature contacts to MoS<sub>2</sub> nanoribbon and nanotube quantum dots"</b><br />
R. T. K. Schock, J. Neuwald, W. Möckel, M. Kronseder, L. Pirker, M. Remskar, and A. K. Hüttel<br />
accepted for publication by <a href="https://onlinelibrary.wiley.com/journal/15214095" target="_blank">Advanced Materials</a> (doi:<a aria-label="Digital Object Identifier" class="epub-doi" href="https://doi.org/10.1002/adma.202209333">10.1002/adma.202209333</a>); arXiv:2209.15515
(<a href="http://www.akhuettel.de/publications/nondestructive.pdf">PDF</a>,
<a href="http://www.akhuettel.de/publications/nondestructive-supplement.pdf">supplementary
information</a>)</p>Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-87524430330611714052022-10-24T21:18:00.002+02:002022-10-24T21:18:10.237+02:00Video from Walter Schottky Prize award ceremony now online<p> The video recording of the Walter Schottky Prize award ceremony in June is finally online. Enjoy :)<br /></p><p><br /></p><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="311" src="https://www.youtube.com/embed/cJgu_Kk9WBk" width="507" youtube-src-id="cJgu_Kk9WBk"></iframe></div><br /><p><br /></p>Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-35467837561801070702022-07-05T09:15:00.001+02:002022-07-07T03:38:17.865+02:00Airport taxis via booking.com -- nice if it works!<p>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.</p><p>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.</p><p>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.</p><p>So I take a regular cab to my hotel. Works fine. </p><p>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.</p><p>Nothing happens for over a week.</p><p>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...</p><p>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.</p><p><b>Update, 7/July/2022:</b> 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. :)<br /></p>Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-26571664678459903902022-04-13T01:06:00.000+02:002022-04-13T01:06:17.718+02:00Testing the Gentoo LiveGUI with QEmu<p>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:</p><p style="background-color: white; color: black; margin-left: 40px; text-align: left;"><span style="font-family: monospace;"><span style="background-color: white; color: #18b2b2;">#!/bin/bash</span><span style="background-color: white; color: black;">
</span></span><br /><span style="font-family: monospace;">
</span><br /><span style="font-family: monospace;">qemu-system-x86_64 <span style="background-color: white; color: #ff54ff; font-weight: bold;"> -m</span><span style="background-color: white; color: black;"> 4G </span><span style="background-color: white; color: #18b218;">\</span><span style="background-color: white; color: black;">
</span></span><br /><span style="font-family: monospace;"> -enable-kvm <span style="background-color: white; color: #18b218;">\</span><span style="background-color: white; color: black;">
</span></span><br /><span style="font-family: monospace;"> -cpu host <span style="background-color: white; color: #18b218;">\</span><span style="background-color: white; color: black;">
</span></span><br /><span style="font-family: monospace;"> -smp 4 <span style="background-color: white; color: #18b218;">\</span><span style="background-color: white; color: black;">
</span></span><br /><span style="font-family: monospace;"> -name <span style="background-color: white; color: #ffff54; font-weight: bold;">"Gentoo amd64 LiveGUI"</span><span style="background-color: white; color: black;"> </span><span style="background-color: white; color: #18b218;">\</span><span style="background-color: white; color: black;">
</span></span><br /><span style="font-family: monospace;"> <span style="background-color: white; color: #ff54ff; font-weight: bold;"> --netdev</span><span style="background-color: white; color: black;"> user,id</span><span style="background-color: white; color: #18b218;">=</span><span style="background-color: white; color: black;">vmnic,hostname</span><span style="background-color: white; color: #18b218;">=</span><span style="background-color: white; color: black;">gentoovm </span><span style="background-color: white; color: #18b218;">\</span><span style="background-color: white; color: black;">
</span></span><br /><span style="font-family: monospace;"> -device e1000,netdev<span style="background-color: white; color: #18b218;">=</span><span style="background-color: white; color: black;">vmnic </span><span style="background-color: white; color: #18b218;">\</span><span style="background-color: white; color: black;">
</span></span><br /><span style="font-family: monospace;"> -bios /usr/share/edk2-ovmf/OVMF_CODE.fd <span style="background-color: white; color: #18b218;">\</span><span style="background-color: white; color: black;">
</span></span><br /><span style="font-family: monospace;"> -device intel-hda -device hda-duplex <span style="background-color: white; color: #18b218;">\</span><span style="background-color: white; color: black;">
</span></span><br /><span style="font-family: monospace;"> -usbdevice tablet <span style="background-color: white; color: #18b218;">\</span><span style="background-color: white; color: black;">
</span></span><br /><span style="font-family: monospace;"> -vga vmware <span style="background-color: white; color: #18b218;">\</span><span style="background-color: white; color: black;">
</span></span><br /><span style="font-family: monospace;"> -cdrom <span style="background-color: white; color: #ff5454; font-weight: bold;">$1</span></span><br /></p><p>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</p><p style="background-color: white; color: black; margin-left: 40px; text-align: left;"><span style="background-color: white; font-family: monospace;"><span style="background-color: white; color: #5454ff; font-weight: bold;"> ~ $</span><span style="background-color: white; color: black;"> ./qemu-livegui livegui-amd64-20220412T191925Z.iso &</span></span><br /></p><p> Cheers!<span style="font-family: monospace;"><br /></span></p>Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-1006803058575163042022-04-04T11:57:00.000+02:002022-04-04T11:57:26.874+02:00New Gentoo LiveGUI ISO and artwork / branding contest!<p><a href="https://www.gentoo.org/downloads/" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;">
<img alt="Artist Larry" src="https://www.gentoo.org/assets/img/news/2022/inked-larry.png" width="150" />
</a></p>
<p>After a long break, we now have again a <a href="https://www.gentoo.org/downloads/">weekly LiveGUI ISO image</a> for amd64 available! The 4.7 GB download, suitable for DVD burning or an USB stick, boots directly into <a href="https://kde.org/plasma-desktop/">KDE Plasma</a> and comes with a ton of up-to-date software. This ranges from office applicactions such as LibreOffice, Inkscape, and Gimp all the way to many system administrator tools.</p>
<p>Now, we need your help! Let’s make this the coolest and most beautiful Linux live image ever. <a href="https://www.gentoo.org/news/2022/04/03/livegui-artwork-contest.html">We’re calling for submissions</a> of artwork, themes, actually anything from a desktop background to a boot manager animation, on the topic of Gentoo! The winning entry will be added as default setting to the official LiveGUI images, and also be available for download and installation.</p>
<h2 id="the-artwork-contest">The artwork contest</h2>
<h3 id="what-are-we-looking-for">What are we looking for?</h3>
<p>Gentoo-themed artwork and branding material to make our Gentoo LiveGUI the coolest Linux live medium ever.</p>
<ul>
<li>Incorporates the <a href="https://www.gentoo.org/inside-gentoo/artwork/gentoo-logo.html">Gentoo logo</a> and maybe <a href="https://wiki.gentoo.org/wiki/Project:Artwork/Artwork">other Gentoo design elements</a> (like Larry the Cow)</li>
<li>Works for a wide range of screen resolutions etc.</li>
<li>Is packaged more or less ready-to-use for our LiveGUI image</li>
<li>Provides a coherent experience to the user, i.e., if it consists of different parts, these fit togehter</li>
<li>Can be distributed in its entirety under the <a href="https://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA 4.0 license</a></li>
</ul>
<p>We could for example imagine screen backgrounds, Plasma theming, maybe even a GRUB boot menu animation or a LibreOffice splash screen… Feel free to come up with more ideas.</p>
<p>If you base your work on freely available source material created by others, please keep track of the sources and their licenses in an accompanying readme file.</p>
<h3 id="what-are-we-not-looking-for">What are we <i>not</i> looking for?</h3>
<ul>
<li>Do not submit anything that infringes on third-party copyrights or trademarks. While a <i>Star Trek</i>-themed Gentoo desktop would be cool, Paramount might object and we wouldn’t be able to distribute it. Same for <i>My Little Pony</i> or the <i>Simpsons</i>.</li>
<li>Do not submit artwork falling under the not-safe-for-work (NSFW) category. We will recognize it when we see it, and we won’t be able to distribute it.</li>
<li>Do not submit artwork with political or religious statements. No matter how universally acceptable you think that these are, someone will be offended by them.</li>
</ul>
<p>The artwork should be such that kids or colleagues can walk into your office and you don’t have to quickly cover it up. :) Also, please think of your contribution <a href="https://wiki.gentoo.org/wiki/Project:Council/Code_of_conduct">in terms of the Gentoo Code of Conduct</a>.</p>
<h3 id="how-to-submit-an-entry">How to submit an entry</h3>
<div id="package-it-up" style="text-align: left;"><b>Package it up</b></div>
<ul>
<li>Package all the relevant files into a single tar archive and upload it to a webserver of your choice, <i>or</i> publish the files (e.g. on github) as a single git repository.</li>
<li>Add a readme file with your name and contact e-mail address, the license of the files, sources and licenses for third-party material, and detailed installation instructions</li>
<li><a href="https://bugs.gentoo.org/enter_bug.cgi?product=Gentoo%20Release%20Media">File a bug</a> for the release engineering team, component “LiveCD/DVD”, with the summary starting with “Artwork 2022 contest entry”, and add a link to your file.</li>
<li>If you link to a git repository, please mention a tag or commit which we should use.</li>
<li>By submitting your entry, you allow Gentoo to download, re-publish, and distribute your files (see also above remark about the license).</li>
</ul>
<div id="deadline" style="text-align: left;"><b>Deadline</b></div>
<ul>
<li>The contest ends 31/May/2022 at 23:59 UTC.</li>
<li>Please keep your files online for at least one more month after that date, so we can review and copy them.</li>
</ul>
<h3 id="selection-and-announcement-of-the-winner">Selection and announcement of the winner</h3>
<ul>
<li>The jury consists of the Gentoo Council, the Release Engineering team, the Artwork team, and the Public Relations team (as of beginning of April 2022).</li>
<li>The winner will be chosen by vote; depending on the amount and quality of the submissions, we may also pick a runner-up or more.</li>
<li>The announcement of the winner or the winners will be made in June.</li>
</ul>
<h2 id="the-livegui-image">The LiveGUI image</h2>
<p>The LiveGUI image is first and foremost provided to show off Gentoo and give everyone a chance to test a full-fledged Gentoo installation. As such, we have a lot of typical “desktop applications” installed. Additionally, we tried to integrate as many system administration tools as possible, so you can also use it for everything from repartitioning your hard drives to repairing an installation.</p>
<p>Some of the software on the image:</p>
<ul>
<li><a href="https://kde.org/plasma-desktop/">KDE Plasma</a> as desktop environment</li>
<li>Office productivity: <a href="https://www.libreoffice.org/">LibreOffice</a>, LyX, TeXstudio, XournalPP, kile</li>
<li>Web browsers: <a href="https://www.mozilla.org/en-US/firefox/new/">Firefox</a>, <a href="https://www.chromium.org/Home/">Chromium</a></li>
<li>IRC and similar: irssi, weechat</li>
<li>Editors: Emacs, vim, kate, nano, joe</li>
<li>Development and source control: git, subversion, gcc, Python, Perl</li>
<li>Graphics: <a href="https://inkscape.org/">Inkscape</a>, <a href="https://www.gimp.org/">Gimp</a>, <a href="http://www.povray.org/">Povray</a>, Luminance HDR, <a href="https://www.digikam.org/">Digikam</a></li>
<li>Video: <a href="https://kdenlive.org/en/">KDEnlive</a></li>
<li>Disk management: hddtemp, testdisk, hdparm, nvme-cli, gparted, partimage, btrfs-progs, ddrescue, dosfstools, e2fsprogs, zfs</li>
<li>Network tools and daemons: nmap, tcpdump, traceroute, minicom, pptpclient, bind-tools, cifs-utils, nfs-utils, ftp, chrony, ntp, openssh, rdesktop, openfortivpn, openvpn, tor</li>
<li>Backup: mt-st, fsarchiver</li>
<li>Benchmarks: bonnie, bonnie++, dbench, iozone, stress, tiobench</li>
<li>…</li>
</ul>
<p>The list of targeted packages (corresponding to a world file) can be found in the <a href="https://gitweb.gentoo.org/proj/releng.git/tree/releases/specs/amd64/livegui/livegui-stage1.spec">catalyst specification file</a>; we install the newest stable version in the Gentoo repository.</p>
<p>In addition, since - as in a normal Gentoo installation - compiler and development tools are available, you can temporarily install more software. Just run <code class="language-plaintext highlighter-rouge">emerge --sync</code> and then install whatever you need (though it will be kept in memory and be gone after the next reboot).</p>
<p>Feedback and of course <a href="https://bugs.gentoo.org/enter_bug.cgi?product=Gentoo%20Release%20Media">bug reports</a> are welcome! Enjoy!</p>Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com1tag:blogger.com,1999:blog-7849507270164967036.post-79136868488501788992022-04-03T21:18:00.001+02:002022-04-03T21:41:09.761+02:00Gentoo MIPS stages are back!<div class="separator" style="clear: both; text-align: center;"><a href="https://www.mips.com/products/" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img alt="MIPS logo" border="0" data-original-height="60" data-original-width="250" src="https://dev.gentoo.org/~dilfridge/mips-logo-blue.png" /></a></div>After a long break, we finally have up-to-date Gentoo stages for the MIPS architecture <a href="https://www.gentoo.org/downloads/">available for download</a> again!<p></p><p>The weekly builds cover at the moment for 32-bit mips2 and mips32, for 64-bit mips3 and mips64 in o32, n32, and n64 ABI - and all that for both big and little endian. Should be good as a start for just about every hardware out there.</p><p>For more information on MIPS, see the <a href="https://wiki.gentoo.org/wiki/Project:MIPS">Gentoo MIPS project page</a> (which is as of writing of this blog post still somewhat outdated), the <a href="https://en.wikipedia.org/wiki/MIPS_architecture">MIPS architecture page on Wikipedia</a>, or the <a href="https://www.mips.com/products/">MIPS corporate products page</a>.<br /></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://www.qemu.org/" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="100" data-original-width="100" height="100" src="https://dev.gentoo.org/~dilfridge/qemu-logo.png" width="100" /></a></div>The weekly stage builds are possible to a large part due to the excellent work of the <a href="https://www.qemu.org/">qemu</a> developers, which allows us to run all the builds on a single (x86-64, AMD RYZEN) server with a ton of parallel processes. Thank you!<br /><p></p>Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-52989669227545864862022-02-04T19:51:00.003+01:002022-02-04T19:52:17.360+01:00Gentoo "desktop profile" Stage 3 downloads<p>You may have noticed additional Stage 3 links marked with "desktop profile" on the <a href="https://www.gentoo.org/downloads/" target="_blank">Gentoo downloads page</a> recently. So what's this about?</p><p>The only difference between a "normal" Stage 3 file and a "desktop profile" Stage 3 file is that the latter has a desktop profile selected (surprise!). As example, if a "normal" amd64 (x86-64) systemd stage uses as profile setting <span style="font-family: courier;">default/linux/amd64/17.1/systemd</span>, then the "desktop profile" stage uses<br /><span style="font-family: courier;">default/linux/amd64/17.1/desktop/systemd</span><span style="font-family: monospace;"><span style="font-family: monospace;">.</span></span> The packages in the @system set are exactly the same, however, in the desktop profile more use-flags are enabled, which means many additional dependencies are merged.</p><p>This leads us to the point of the "desktop profile" stages: if you do a desktop installation (for anything from KDE to Gnome or XFCE), these files give you less initial rebuilds and compiles, at the cost of a larger download. And that's all. <span style="font-family: monospace;"><span style="font-family: monospace;"><br /></span></span></p>Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-41521773640859767472021-09-21T18:34:00.006+02:002024-01-02T12:00:36.076+01:00Experimental binary Gentoo package hosting (amd64)<div><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://gentoo.osuosl.org/experimental/amd64/binpkg/default/linux/17.1/x86-64/" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" data-original-height="480" data-original-width="500" height="192" src="https://dev.gentoo.org/~dilfridge/moving.png" width="200" /></a></div><b><span style="color: red;">IMPORTANT</span>: This blog post is outdated!</b> As direct result of this experiment, we now have <a href="https://www.gentoo.org/news/2023/12/29/Gentoo-binary.html"><b>official Gentoo binary packages available</b></a>. See <a href="https://www.gentoo.org/news/2023/12/29/Gentoo-binary.html">the announcement</a> for more information and further links! The old blog text follows...</div><div><hr /></div><div>As an experiment, I've started assembling a simple binary package hosting mechanism for Gentoo. Right now this comes with some serious limitations and <b>should not be used for security or mission critical applications</b> (more on this below). The main purpose of this experiment is to find out how well it works and where we need improvements in Portage's binary package handling.<p></p><p>So what do we have, and how can you use it?</p><ul style="text-align: left;"><li>The server builds an assortment of stable amd64 packages, with the use-flags as present in an unmodified 17.1/desktop/plasma/systemd profile (the only necessary change is USE=bindist).</li><li>The packages can be used on all amd64 profiles that differ from desktop/plasma/systemd only by use-flag settings. This includes 17.1, 17.1/desktop/*, 17.1/no-multilib, 17.1/systemd, but <b>not</b> anything containing selinx, hardened, developer, musl, or a different profile version such as 17.0.<br /></li><li>Right now, the package set includes kde-plasma/plasma-meta, kde-apps/kde-apps-meta, app-office/libreoffice, media-gfx/gimp, media-gfx/inkscape, and of course all their dependencies. More will possibly be added.</li><li>CFLAGS are chosen such that the packages will be usable on all amd64 (i.e., x86-64) machines. <br /></li></ul><p>To use the packages, I recommend the following steps: First, <b>create a file</b> /etc/portage/<b>binrepos.conf</b> with the following content:</p><p style="margin-left: 40px; text-align: left;">[binhost]<br />priority = 9999<br />sync-uri = https://gentoo.osuosl.org/experimental/amd64/binpkg/default/linux/17.1/x86-64/</p><p style="text-align: left;">You can pick a different mirror according to your preferences (but also see the remarks below). Then, edit /etc/portage/make.conf, and add the following EMERGE_DEFAULT_OPTS (in addition to flags that you might already have there):</p><p style="margin-left: 40px; text-align: left;">EMERGE_DEFAULT_OPTS="--binpkg-respect-use=y --getbinpkg=y"</p><p style="text-align: left;">And that's it. Your next update should download the package index and use binary packages whenever the versions and use-flag settings match. Everything else is compiled as usual.</p><p style="text-align: left;">What is still missing, and what are the limitations and caveats?</p><ul style="text-align: left;"><li>Obviously, the packages are not optimized for your processor.</li><li>Right now, the server only carries packages for the use-flag settings in an unmodified 17.1/desktop/plasma/systemd profile. If you use other settings, you will end up compiling part of your packages (which is not really a probem, you just lose the benefit of the binary download). It is technically possible to provide binary packages for different use-flag settings at the same URL, and eventually it will be implemented if this experiment succeeds.<br /></li><li>At the moment, <b>no cryptographic signing of the binary packages is in place yet</b>. This is the main reason why I'm talking about an experiment. Effectively you trust our mirror admins and the https protocol. Package signing and verification is in preparation, and before the binary package hosting "moves into production", it will be enforced.</li></ul></div>That's it. Enjoy! And don't forget to leave feedback in the comments.<br />Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com12tag:blogger.com,1999:blog-7849507270164967036.post-10174100998207792722021-03-14T10:55:00.001+01:002021-03-14T10:55:36.639+01:00Gentoo AMD64 Handbook "Preparing the disks" section reworked<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://wiki.gentoo.org/wiki/Handbook:AMD64/Installation/Disks" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;" target="_blank"><img border="0" data-original-height="176" data-original-width="169" src="https://wiki.gentoo.org/images/b/b3/Larry-hi.png" /></a></div>Since the text was becoming more and more outdated and also more and more convoluted, I have completely reworked the <a href="https://wiki.gentoo.org/wiki/Handbook:AMD64/Installation/Disks" target="_blank">"Preparing the disks" section of the Gentoo AMD64 handbook</a>. <p></p><ul style="text-align: left;"><li>Since fdisk supports GUID partition tables (GPT) for a long time now, references to parted have been dropped.</li><li>The text restricts itself now to the combinations 1) UEFI boot and GPT and 2) BIOS / legacy boot and MBR. While mixing and matching is here certainly possible, we should treat it out of the scope of the manual.<br /></li><li>Hopefully the terminology regarding the boot partition, UEFI system partition, and BIOS boot partition is more clear now (it was horribly mixed up before).</li></ul><p>Please proofread and check for mistakes! I'll drop the "work in progress" label in a few days if nothing comes up. <br /></p>Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com5tag:blogger.com,1999:blog-7849507270164967036.post-15163594527550568182021-01-31T22:31:00.000+01:002021-01-31T22:31:02.137+01:00New Gentoo riscv (and arm) stages<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://bouncer.gentoo.org/fetch/root/all/releases/riscv/autobuilds/" target="_blank"><img border="0" data-original-height="91" data-original-width="192" src="https://dev.gentoo.org/~dilfridge/stages.png" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;" /></a></div>With the help of our infrastructure team, I've finally managed to integrate the riscv stage builds with our signing and mirroring system. So now we have a riscv tab on the <a href="https://www.gentoo.org/downloads/" target="_blank">installation media download page</a>, and the mirrors carry weekly <a href="https://bouncer.gentoo.org/fetch/root/all/releases/riscv/autobuilds/" target="_blank">signed stage3 archives for riscv64-lp64d and riscv64-lp64</a>, in both openrc and systemd variants.<p></p><p>Using the same build infrastructure based on <a href="https://www.qemu.org/" target="_blank">qemu</a>, there are now also slowly <a href="https://bouncer.gentoo.org/fetch/root/all/releases/arm/autobuilds/" target="_blank">updated stages for all arm variants</a> coming to the mirrors. Please test them, and if anything does not work as expected, <a href="https://bugs.gentoo.org/enter_bug.cgi?product=Gentoo%20Release%20Media&format=guided" target="_blank">file bugs</a>! The qemu-based builds are here a temporary measure; Matt Turner
(mattst88) is preparing a fast multi-core arm64 machine, where this task will move to soon.<br /></p>Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com1tag:blogger.com,1999:blog-7849507270164967036.post-10559800431827604262020-11-26T17:14:00.000+01:002020-11-26T17:14:09.767+01:00Walter Schottky prize; return to Regensburg with DFG Heisenberg grant<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://www.dfg.de/en/research_funding/programmes/individual/heisenberg/index.html" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;" target="_blank"><img border="0" data-original-height="88" data-original-width="150" src="https://www.akhuettel.de/images/logo_heisenberg.png" /></a></div>The last weeks have brought excellent news in more than one way. First of all, it's now official that I'll return to University of Regensburg starting 1 March 2021 with a <a href="https://www.dfg.de/en/research_funding/programmes/individual/heisenberg/index.html" target="_blank">Heisenberg grant</a> of the <a href="https://www.dfg.de/en/index.jsp" target="_blank">Deutsche Forschungsgemeinschaft (DFG)</a>. Named for the physics Nobel laureate and co-founder of quantum mechanics (and <a href="https://www.stiftung-maximilianeum.com/stipendiaten-der-stiftung-maximilianeum-2/ber%C3%BChmte-maximer/">Maximilianeum scholarship recipient</a>) <a href="https://en.wikipedia.org/wiki/Werner_Heisenberg">Werner Heisenberg</a>, this is the most renowned DFG grant line for researchers of all subjects who already fulfill the requirements for a tenured professorship. The grant with official title "Quantum transport in nanotubes: Single electron optomechanics and novel materials" has a duration of five years, with funding of approximately € 750.000 within the first three years. It is essentially a research fellowship, combined with money for equipment and employing students. <p></p><p>As an important consequence, I am looking for PhD students. Two positions and projects are available:</p><ul style="text-align: left;"><li>"<a href="http://www.physik.uni-r.de/forschung/huettel/heisenberg-phd-1.pdf">Microwave optomechanics of the transversal carbon nanotube vibration</a>"</li><li>"<a href="http://www.physik.uni-r.de/forschung/huettel/heisenberg-phd-2.pdf">Transport spectroscopy and hybrid devices of transition metal dichalcogenide nanotubes</a>" </li></ul><p>In case you are interested, please have a look at the announcements, see the links above or our <a href="http://www.physik.uni-r.de/forschung/huettel/jobs.php">jobs page</a>, and send me an e-mail!<br /></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://www.dpg-physik.de/auszeichnungen/dpg-preise/walter-schottky-preis/preistraeger" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;" target="_blank"><img border="0" data-original-height="114" data-original-width="150" src="https://www.akhuettel.de/images/logo_schottky.png" /></a></div>The second phantastic news is that I've been awarded the <a href="https://www.dpg-physik.de/auszeichnungen/dpg-preise/walter-schottky-preis/preistraeger" target="_blank">Walter Schottky Prize 2021</a> for our results on microwave optomechanics with a carbon nanotube. This is a a scientific prize awarded annually by the <a href="https://www.dpg-physik.de/" target="_blank">German Physical Society</a> for outstanding research work of young academics in the field of solid-state physics. The prize is named after <a href="https://en.wikipedia.org/wiki/Walter_H._Schottky" target="_blank">Walter Schottky</a>, one of the pioneers of electronics and in particular semiconductor devices. Obviously this is a great honour, but also a great encouragement to build on and expand our exciting nano-electromechanics research.<br /><p></p><p>Further information: </p><ul style="text-align: left;"><li><a href="https://www.dpg-physik.de/veroeffentlichungen/aktuell/2020/deutsche-physikalische-gesellschaft-verleiht-zahlreiche-angesehene-physikpreise">press release of the German Physical Society</a> (in German)</li><li><a href="https://www.uni-regensburg.de/pressearchiv/pressemitteilung/1093589.html" target="_blank">press release of University of Regensburg regarding the Walter Schottky Prize</a> (in German)</li><li><a href="https://www.dpg-physik.de/auszeichnungen/dpg-preise/walter-schottky-preis/preistraeger" target="_blank">list of Walter Schottky Prize recipients</a> (in German)</li><li><a href="https://www.uni-regensburg.de/pressearchiv/pressemitteilung/1092352.html">press release of University of Regensburg regarding the Heisenberg grant</a> (in German)</li><li><a href="http://www.physik.uni-r.de/forschung/huettel/">home page of my research group</a></li><li><a href="https://www.akhuettel.de/">my homepage</a> <br /></li></ul>Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-52932977126235241712020-10-19T18:04:00.000+02:002020-10-19T18:04:19.388+02:00PRB published: "Magnetic field control of the Franck-Condon coupling of few-electron quantum states"<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://www.akhuettel.de/publications/franckcondon.pdf" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="227" data-original-width="200" src="https://www.akhuettel.de/publications/franckcondon-fig.png" /></a></div>The second-lowest vibration mode of carbon nanotubes is the so-called longitudinal or stretching mode; here the vibrational direction is along the axis of the carbon nanotube. The vibration frequency <i>f</i> and with it the harmonic oscillator quantum h<i>f</i> is already much higher than for the transversal motion; it scales with the length <i>L</i> of the vibrating nanotube segment as 1/<i>L</i>, and is for 100nm < <i>L</i> < 1000nm in the range 0.1meV < h<i>f</i> < 1meV.<p></p><p>With such a large frequency, the harmonic oscillator is at typical dilution refrigerator temperatures <i>T</i> < 100mK fully quantized. The mechanics now becomes visible in the transport spectrum of the quantum dot within the carbon nanotube as so-called Franck-Condon sidebands: For current to pass through the nanotube, an electron has to tunnel onto the quantum dot and then off it again. In our nanomechanical system, however, the mechanical equilibrium position depends on the electrostatic forces on the nanotube, and thus on the charge on it - the equilibrium position for <i>N</i> electrons is different from the one for <i>N</i>+1 electrons. This means that tunneling in is suppressed by a geometric factor describing this coupling, i.e., the limited overlap between the macromolecule wavefunction in both situations. If we provide enough energy to reach excited vibrational states, this suppression is partially lifted. Thus, as function of applied bias voltage, we see a series of steps in the current or lines in the differential conductance.<br /></p><p>In our article, we demonstrate for the first time Franck-Condon sidebands in a clean carbon nanotube quantum dot with known absolute number of trapped electrons. We evaluate the coupling parameter and see that it depends on a magnetic field, but also on the precise electronic state that the electrons tunnel through. The so-called valley quantum number turns out to be crucial here; it is related to the angular momentum of the electron. Comparing our evaluation results with <a href="https://dilfridge.blogspot.com/2019/02/prl-published-shaping-electron-wave.html">our previous calculations on the distribution of electrons along the nanotube axis</a>, we propose a model that describes the coupling parameter as function of magnetic field for different quantum states. While the model is a simplification, it nevertheless is clearly able to qualitatively reproduce our experimental results of a tunable electron-vibron coupling.<br /></p><p><b>"Magnetic field control of the Franck-Condon coupling of few-electron quantum states"</b><br />
P. L. Stiller, A. Dirnaichner, D. R. Schmid, and <a href="https://www.akhuettel.de/">A. K. Hüttel</a><br />
<a href="https://doi.org/10.1103/PhysRevB.102.115408" target="_blank">Physical Review B <b>102</b>, 115408 (2020)</a>;
arXiv:1812.02657
(<a href="http://www.akhuettel.de/publications/franckcondon.pdf">PDF</a>)</p>Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-72718817806410165442020-10-19T16:40:00.003+02:002020-10-19T16:40:34.638+02:00Top Alexander von Humboldt foundation ranking for Regensburg University<p>After the <a href="https://dilfridge.blogspot.com/2019/07/wheres-best-sciences-research-in.html">top position in the Nature Index 2019</a> and repeated great rankings in physics in the DFG Förderatlas (<a href="https://dilfridge.blogspot.com/2012/06/top-position-in-condensed-matter.html">2012</a>, <a href="https://www.dfg.de/sites/foerderatlas2018/download/dfg_foerderatlas_2018.pdf" target="_blank">2018</a>), there's another excellent news for Regensburg. In the so-called <a href="https://www.humboldt-foundation.de/entdecken/zahlen-und-statistiken/humboldt-ranking#c18797" target="_blank">Humboldt-Ranking</a> 2020, listing where most of the foreign scholars with an Alexander von Humbold foundation scholarship go to pursue their research in Germany, Regensburg is at position 1 of the natural sciences! The <a href="https://www.humboldt-foundation.de/en/" target="_blank">Alexander von Humboldt foundation</a> sponsors advanced career stages, from post-doc all the way to professor. Congratulations everyone!<br /></p>Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-84666020172794508052020-07-20T18:28:00.000+02:002020-07-20T18:28:27.144+02:00Updated Gentoo RISC-V stages<div class="separator" style="clear: both; text-align: center;">
<a href="https://dev.gentoo.org/~dilfridge/risc-v-logo-square.png" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" data-original-height="118" data-original-width="150" src="https://dev.gentoo.org/~dilfridge/risc-v-logo-square.png" /></a></div>
I finally got around to updating the experimental riscv stages. You can find the result <a href="https://dev.gentoo.org/~dilfridge/stages/">on our webserver</a>. All stages use the rv64gc instruction set; there is a multilib stage with both lp64 and lp64d support, and there are non-multilib stages for both lp64 and lp64d ABI. Please test, and <a href="https://bugs.gentoo.org/enter_bug.cgi?product=Gentoo%20Release%20Media&format=guided">report bugs</a> if anything doesn't work.<br />
As for the technical details, the stages are built using <a href="https://www.qemu.org/">qemu-user</a> on a big and beefy Gentoo amd64 <a href="https://aws.amazon.com/en/ec2/instance-types/m5/">AWS instance</a>. We are currently working on automating that process, such that riscv (and potentially also arm and others) get the same level of support as amd64 and friends. Thanks a lot to Amazon for the credits via their <a href="https://aws.amazon.com/de/blogs/opensource/aws-promotional-credits-open-source-projects/">open source promotial program</a>!Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-19253566631814190172020-04-29T20:08:00.002+02:002020-04-29T20:09:05.128+02:00Press release (in German) on our recent Nature Communications<div class="separator" style="clear: both; text-align: center;">
<a href="https://www.akhuettel.de/publications/optomechanics.pdf" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="200" data-original-width="200" src="https://www.akhuettel.de/publications/optomechanics-fig.png" /></a></div>
We've <a href="https://www.uni-regensburg.de/pressearchiv/pressemitteilung/1064883.html" target="_blank">published a press release (in German)</a> on our recent Nature Communications publication "<a href="https://doi.org/10.1038/s41467-020-15433-3" target="_blank">Quantum capacitance mediated carbon nanotube optomechanics</a>".<br />
<br />
<a href="https://www.uni-regensburg.de/pressearchiv/pressemitteilung/1064883.html" target="_blank">Read it on the university web page!</a><br />
<br />
(A summary in English can be found in a <a href="https://dilfridge.blogspot.com/2020/04/nature-communications-published-quantum.html" target="">previous blog post</a>.)
Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-39401253562525190682020-04-09T21:54:00.001+02:002020-04-09T21:54:33.846+02:00Nature Communications published: "Quantum capacitance mediated carbon nanotube optomechanics"<div class="separator" style="clear: both; text-align: center;">
<a href="https://www.akhuettel.de/publications/optomechanics.pdf" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="200" data-original-width="200" src="https://www.akhuettel.de/publications/optomechanics-fig.png" /></a></div>
Coupling carbon nanotube motion to microwaves is hard. Why so? Because typical electromagnetic wavelengths are in the millimeter range there, and a typical nanotube device is less than a micrometer long, with mechanical deflections of nanometers or smaller. As a result, the motion of the nanotube just does not modify the electromagnetic field much; the coupling parameters resulting from optomechanical theory are minimal. <br />
Still, achieving such a coupling and controlling it, <i>without</i> resonantly driving the nanotube to large motion amplitudes, is for many reasons an attractive idea. A nanotube is a very good beam resonator, storing energy coherently for a long time; the mechanics could be used to translate quantum information between different quantum mechanical degrees of freedom. And both single electrons trapped within semiconductors (as a carbon nanotube) and superconducting coplanar microwave circuits are hot candidates for quantum computation architectures, and the topic of much research worldwide.<br />
From this background we are excited to present a first optomechanical experiment where the motion of a suspended single carbon nanotube has been coupled to a superconducting coplanar microwave cavity; our work has been <a href="http://dx.doi.org/10.1038/s41467-020-15433-3" target="_blank">published in Nature Communications</a>. Using the quantization of electric charge, we have been able to amplify the interaction between the two systems, vibration and electromagnetic field, by a factor 10000 compared to simple geometric predictions - and this is by far not the limit yet on what is achievable with our method. In addition, the coupling is controllable, and can be switched on and off quickly.<br />
We obtain a so-called dispersively coupled optomechanical system - novel and exciting on one hand because of the miniaturization of the mechanical part and the coherent single electron effects, but well known on the other hand, since a huge body of theoretical and experimental research on larger (up to macroscopic scales) optomechanical systems exists. There, it has been shown that the coupling can be used for cooling of the vibration, for coherent amplification of signals, or even for arbitrary preparation of quantum states. Based on our results, also the quantum control of the string-like nanotube vibration will be reachable in the near future.<br />
<br />
<b>"Quantum capacitance mediated carbon nanotube optomechanics"</b><br />
S. Blien, P. Steger, N. Hüttner, R. Graaf, and <a href="https://www.akhuettel.de/" target="_blank">A. K. Hüttel</a><br />
<a href="http://dx.doi.org/10.1038/s41467-020-15433-3" target="_blank">Nature Communications <b>11</b>, 1636 (2020)</a>
Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-18469320912233673462020-03-02T18:00:00.000+01:002020-04-08T23:29:02.918+02:00Visiting professor at Aalto University, absence from Regensburg<div class="separator" style="clear: both; text-align: center;">
<a href="https://www.aalto.fi/en" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" data-original-height="164" data-original-width="200" src="https://www.akhuettel.de/images/logo_aalto.png" /></a></div>
Since 15 February 2020, I have moved to Finland, following an invitation to the <a href="https://www.aalto.fi/en/department-of-applied-physics/quantum-circuits-and-correlations-nano" target="_blank">Department of Applied Physics</a>, <a href="https://www.aalto.fi/en" target="_blank">Aalto University</a> as visiting professor. This is a great chance to make contacts and contribute to projects there, as well as to learn techniques and push our own project planning ahead.<br />
For Regensburg this means that I am currently not accepting any students for thesis projects anymore, and that it may be quite difficult to find time for oral exams (like those "Modulprüfungen").Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-69367178065471096382019-08-12T14:06:00.000+02:002019-08-12T14:07:56.841+02:00pssRRL accepted: Coulomb Blockade Spectroscopy of a MoS2 Nanotube<div class="separator" style="clear: both; text-align: center;">
<a href="https://www.akhuettel.de/publications/mos2dots.pdf" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="182" data-original-width="200" src="https://www.akhuettel.de/publications/mos2dots-fig.png" /></a></div>
We are happy to be able to announce that our manuscript "<a href="https://www.akhuettel.de/publications/mos2dots.pdf" target="_blank">Coulomb Blockade Spectroscopy of a MoS<sub>2</sub> Nanotube</a>" has been accepted for publication by <a href="https://doi.org/10.1002/pssr.201900251" target="_blank">pssRRL Rapid Research Letters</a>.<br />
<br />
Everybody is talking about novel semiconductor materials, and in particular the transition metal dichalcogenides (TMDCs), "layer materials" similar to graphene. With a chemical composition of TX<sub>2</sub>, where the transition metal T is, e.g., tungsten W or molybdenum Mo, and the chalcogenide X is, e.g., sulphur S or selenium Se, a wide range of interesting properties is expected.<br />
<br />
What's by far not so well known is that many of these materials also form nanotubes, similar to carbon nanotubes in structure but with distinct properties inherited from the planar system. Here, we present first low temperature transport measurements on a quantum dot in a MoS<sub>2</sub> nanotube. The metallic contacts to the nanotube still require a lot of improvements, but the nanotube between them acts as clean potential well for electrons.<br />
<br />
Also, our measurements show possible traces of quantum confined behaviour. This is something that has not been achieved yet in planar, lithographically designed devices - since these have by their very geometric nature larger length scales. It means that via transport spectroscopy we can learn about the material properties and its suitability for quantum electronics devices. <br />
<br />
A lot of complex physical phenomena have been predicted for MoS<sub>2</sub>, including spin filtering and intrinsic, possibly topologic superconductivity - a topic of high interest for the quantum computing community, where larger semiconductor nanowires are used at the moment. So this is the start of an exciting project!<br />
<br />
"Coulomb Blockade Spectroscopy of a MoS<sub>2</sub> Nanotube"<br />
S. Reinhardt, L. Pirker, C. Bäuml, M. Remskar, and A. K. Hüttel<br />
<a href="https://doi.org/10.1002/pssr.201900251" target="_blank">Physica
Status Solidi RRL, doi:10.1002/pssr.201900251 (2019)</a>; arXiv:1904.05972
(<a href="http://www.akhuettel.de/publications/mos2dots.pdf">PDF</a>)Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-67212147242452992302019-07-02T13:55:00.002+02:002019-07-02T13:55:54.091+02:00Where's the best sciences research in Germany? Here in Regensburg!<div class="separator" style="clear: both; text-align: center;">
<a href="https://www.natureindex.com/annual-tables/2019/institution/academic-normalized" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="45" data-original-width="250" src="https://www.akhuettel.de/images/logo_natureindex.png" /></a></div>
The <a href="https://www.natureindex.com/annual-tables/2019" target="_blank">Nature Index 2019 Annual Tables</a> have been published, and there is a valuable new addition: the tables now include a "normalized ranking", where the quality of a university's research output, and not its quantity counts. If we look at the <a href="https://www.natureindex.com/annual-tables/2019/institution/academic-normalized" target="_blank">world-wide natural sciences ranking</a>, University of Regensburg is at spot 44, best of all universities in Germany, and in a similar ranking range as, e.g., University of Oxford, University of Tokyo, or University of California San Francisco! Cheers and congratulations!Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-64675307673067496112019-05-02T14:43:00.000+02:002019-05-02T14:43:15.441+02:00Lecture announcement: High Frequency Engineering for Physicists<div class="separator" style="clear: both; text-align: center;">
<a href="http://www.physik.uni-regensburg.de/studium/uebungen/ss19/hf/" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="283" data-original-width="200" src="https://www.akhuettel.de/teaching/hf19-thumbnail.jpg" /></a></div>
Term has already started, so this announcement is technically a bit late, however... This summer term I'm offering a lecture "<b>High Frequency Engineering for Physicists</b>". If you plan to work with signals in the frequency range 10MHz - 50GHz, this might be interesting for you...<br />
<br />
<div style="text-align: left;">
When and where? Wednesdays, 12h - 14h, seminar room PHY 9.1.10. The next lecture is on 8 May 2019</div>
<ul>
<li>Concepts and formalisms for the frequency range 10MHz - 50GHz</li>
<li>Handling equipment for this frequency range, designing devices and measurements</li>
<li>Using this frequency range in a (millikelvin) cryostat</li>
</ul>
More information can be found soon on the <a href="http://www.physik.uni-regensburg.de/studium/uebungen/ss19/hf/" target="_blank">homepage of the lecture</a>. <br />
<br />
See you next wednesday!<br />
<br />Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-84837630927884974202019-04-30T15:43:00.000+02:002019-04-30T15:43:09.603+02:00Press release (in German) on our recent PRL<div class="separator" style="clear: both; text-align: center;">
<a href="http://www.akhuettel.de/publications/high-field.pdf" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="639" data-original-width="800" height="159" src="https://www.uni-regensburg.de/aktuelles/medien/pm-im-text/bridges-final-800px.png" width="200" /></a></div>
<a href="https://www.uni-regensburg.de/" target="_blank">Regensburg University</a> has published a <a href="https://www.uni-regensburg.de/pressearchiv/pressemitteilung/976992.html" target="_blank">press release (in German)</a> on our recent Physical Review Letters "Editor's Suggestion" publication, "<a class=" " href="https://epub.uni-regensburg.de/38394/" target="_blank">Shaping Electron Wave Functions in a Carbon Nanotube with a Parallel Magnetic Field</a>". <a href="https://www.uni-regensburg.de/pressearchiv/pressemitteilung/976992.html" target="_blank">Read it on the university web page!</a><br />
<br />
(A summary in English can be found in a <a href="http://dilfridge.blogspot.com/2019/02/prl-published-shaping-electron-wave.html" target="_blank">previous blog post</a>.)Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-24230284438177892322019-02-27T10:55:00.000+01:002019-02-27T10:57:17.775+01:00PRL published: Shaping electron wave functions in a carbon nanotube with a parallel magnetic field<div class="separator" style="clear: both; text-align: center;">
<a href="https://www.akhuettel.de/publications/high-field.pdf" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="185" data-original-width="200" src="https://www.akhuettel.de/publications/high-field-fig.png" /></a></div>
We're happy to announce that our manuscript "<a href="https://www.akhuettel.de/publications/high-field.pdf">Shaping electron wave functions in a carbon nanotube with a parallel magnetic field</a>" has been published as Editor's Suggestion in <a href="https://doi.org/10.1103/PhysRevLett.122.086802" target="_blank">Physical Review Letters</a>.<br />
<br />
When a physicist thinks of an electron confined to a one-dimensional object such as a carbon nanotube, the first idea that comes to mind is the „particle in a box“ from elementary quantum mechanics. A particle can behave as a wave, and in this model it is essentially a standing wave, reflected at two infinitely high, perfect barrier walls. The mathematical solutions for the wave function describing it are the well-known half-wavelength resonator solutions, with a fundamental mode where exactly half a wavelength fits between the walls, a node of the wave function at each wall and an antinode in the center.<br />
<br />
In this publication, we show how wrong this first idea can be, and what impact that has. In a carbon nanotube as quasi one-dimensional system, an electron is not in free space, but confined to the lattice of carbon atoms which forms the nanotube walls. This hexagonal lattice, the same that also forms in planar form graphene, is called bipartite, since every elementary cell of the lattice contains two carbon atoms; one can imagine the nanotube wall as being built out of two sub-lattices, with one atom per cell each, that are shifted relative to each other. Surprisingly, the hexagonal bipartite lattice does not generally support the half-wavelength solutions mentioned above, where the electronic wave function becomes zero at the edges. In each sublattice, we can only force the wave function to zero at one end of the nanotube "box"; its value at the other end remains finite. This means that the wave function shape for each of the two sublattices is more similar to that of a quarter wavelength resonator, where one end displays a node, the other an antinode. The two sublattice wave functions are mirrored in shape to each other, with node and antinode swapping position.<br />
<br />
When we now apply a magnetic field along the carbon nanotube, a magnetic flux enters the nanotube, and the boundary conditions for the electron wave function change via the Aharonov-Bohm effect. Astonishingly, its shape along the carbon nanotube can thereby be tuned between half-wavelength and quarter-wavelength behaviour. This means that the probability of the trapped electron to be near the contacts changes, and with it the tunnel current, leading to a very distinct behaviour of the electronic conductance. It turns out that our measurement and the corresponding calculations are agreeing very well. Thus, our work shows the impact of a non-trivial host crystal on the electronic behaviour, important for many novel types of material.<br />
<br />
"Shaping electron wave functions in a carbon nanotube with a parallel magnetic field"<br />
M. Marganska, D. R. Schmid, A. Dirnaichner, P. L. Stiller, Ch. Strunk, M. Grifoni, and A. K. Hüttel<br />
<a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.086802" target="_blank">Physical Review Letters <b>122</b>, 086802 (2019)</a>, Editor's Suggestion;
arXiv:1712.08545
(<a href="http://www.akhuettel.de/publications/high-field.pdf">PDF</a>,
<a href="http://www.akhuettel.de/publications/high-field-supplement.pdf">supplementary
information</a>)Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-65413743744889451442018-10-18T18:27:00.000+02:002018-10-18T19:59:32.097+02:00Comp. Phys. Comm. published: "Lab::Measurement - a portable and extensible framework for controlling lab equipment and conducting measurements"<div class="separator" style="clear: both; text-align: center;">
<a href="https://www.akhuettel.de/publications/labmeasurement.pdf" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="105" data-original-width="200" src="https://www.akhuettel.de/publications/labmeasurement-fig.png" /></a></div>
We're happy to announce that our article <a href="https://doi.org/10.1016/j.cpc.2018.07.024">"Lab::Measurement — a portable and extensible framework for controlling lab equipment and conducting measurements"</a>, describing our measurement software package <a href="https://www.labmeasurement.de/" target="_blank">Lab::Measurement</a>, has been published in <a href="https://www.sciencedirect.com/journal/computer-physics-communications" target="_blank">Computer Physics Communications</a>.<br />
<br />
Lab::Measurement is a collection of object-oriented Perl 5 modules for controlling lab instruments, performing measurements, and recording and plotting the resultant data. Its operating system independent driver stack makes it possible to use nearly identical measurement scripts both on Linux and Windows. Foreground operation with live plotting and background operation for, e.g., process control are supported. For more details, please <a href="https://www.labmeasurement.de/labmeasurement.pdf">read our article</a>, visit the <a href="https://www.labmeasurement.de/" target="_blank">Lab::Measurement homepage</a>, or visit <a href="https://metacpan.org/release/Lab-Measurement" target="_blank">Lab::Measurement on CPAN</a>!<br />
<br />
"Lab::Measurement - a portable and extensible framework for controlling lab equipment and conducting measurements"<br />
S. Reinhardt, C. Butschkow, S. Geissler, A. Dirnaichner, F. Olbrich, C. Lane, D. Schröer, and A. K. Hüttel<br />
<a href="https://doi.org/10.1016/j.cpc.2018.07.024" target="_blank">Comp. Phys. Comm. <b>234</b>, 216 (2019)</a>; arXiv:1804.03321
(<a href="https://www.labmeasurement.de/labmeasurement.pdf">PDF</a>) Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0tag:blogger.com,1999:blog-7849507270164967036.post-72292387989897732252018-05-18T12:23:00.000+02:002018-06-14T22:42:52.910+02:00PRL accepted: Nanomechanical characterization of the Kondo charge dynamics in a carbon nanotube<div class="separator" style="clear: both; text-align: center;">
<a href="https://www.akhuettel.de/publications/kondocharge.pdf" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="163" data-original-width="200" src="https://www.akhuettel.de/publications/kondocharge-fig.png" /></a></div>
Today's great news is that our manuscript "<a href="https://www.akhuettel.de/publications/kondocharge.pdf">Nanomechanical characterization of the Kondo charge dynamics in a carbon nanotube</a>" has been accepted for publication by <a href="https://journals.aps.org/prl/" target="_blank">Physical Review Letters</a>.<br />
<br />
The <a href="http://www.scholarpedia.org/article/Kondo_effect">Kondo effect</a> is a many-body phenomenon at low temperature that results from a quantum state degeneracy, as, e.g., the one of spin states in absence of a magnetic field. In its simplest case, it makes a quantum dot, in our case a carbon nanotube with some trapped electrons on it, behave very different for an even and an odd number of electrons. At an even number of trapped electrons, no current can flow through the nanotube, since temperature and applied bias voltage are too low to charge it with one more elementary charge; this phenomenon is called Coulomb blockade. Strikingly, at odd electron number, when two degenerate quantum states in the nanotube are available, Coulomb blockade seems not to matter, and a large current can flow. Theory explains this by assuming that a localized electron couples to electrons in the contacts, forming a combined, delocalized singlet quantum state.<br />
What carries the Kondo-enhanced current, and how does the electric charge now accumulate in the carbon nanotube? We use the vibration of the macromolecule to measure this. As also in the case of, e.g., a guitar string, the resonance frequency of a nanotube changes when you pull on it; in the case of the carbon nanotube this is sensitive enough to resolve fractions of the force caused by a single elementary charge. From the vibration frequency, as function of the electrostatic potential, we calculate the average number of electrons on the nanotube, and can then compare the odd and even number cases.<br />
A surprising result of our evaluation is that the charge trapped on the nanotube behaves the same way in the even and odd occupation case, even though the current through it is completely different. Sequential tunneling of electrons can model the charge accumulation, and with it the mechanical behaviour. The large Kondo current is carried by virtual occupation of the nanotube alone, i.e., electrons tunneling on and immediately off again so they do not contribute to the charge on it.<br />
<br />
"Nanomechanical Characterization of the Kondo Charge Dynamics in a Carbon Nanotube"<br />
K. J. G. Götz, D. R. Schmid, F. J. Schupp, P. L. Stiller, Ch. Strunk, and A. K. Hüttel<br />
<a href="https://doi.org/10.1103/PhysRevLett.120.246802" target="_blank">Physical Review Letters <b>120</b>, 246802 (2018)</a>; arXiv:1802.00522
(<a href="http://www.akhuettel.de/publications/kondocharge.pdf">PDF</a>,
<a href="http://www.akhuettel.de/publications/kondocharge.html">HTML</a>,
<a href="http://www.akhuettel.de/publications/kondocharge-supplement.pdf">supplementary information</a>)Andreashttp://www.blogger.com/profile/12314847423280010909noreply@blogger.com0