1. More projects have been created, and will continously get posted here as soon as the copyright allows.

    Hope to see you soon again!

    /Krantz NanoArt

  2. Chalmers scientists create light from vacuum
    PRESS RELEASE | Scientists at Chalmers have succeeded in creating light from vacuum – observing an effect first predicted over 40 years ago. The results have been published in the journal Nature. In an innovative experiment, the scientists have managed to capture some of the photons that are constantly appearing and disappearing in the vacuum.

    The experiment is based on one of the most counterintuitive, yet, one of the most important principles in quantum mechanics: that vacuum is by no means empty nothingness.  In fact, the vacuum is full of various particles that are continuously fluctuating in and out of existence. They appear, exist for a brief moment and then disappear again. Since their existence is so fleeting, they are usually referred to as virtual particles.

    ​“Since it’s not possible to get a mirror to move fast enough, we’ve developed another method for achieving the same effect,” explains Per Delsing, Professor of Experimental Physics at Chalmers. “Instead of varying the physical distance to a mirror, we've varied the electrical distance to an electrical short circuit that acts as a mirror for microwaves.”

    C. M. Wilson, G. Johansson, A. Pourkabirian, M. Simoen, J. R. Johansson, T. Duty, F. Nori, P. Delsing, Nature 479, 376-379 (2011)
    “Instead of varying the physical distance to a mirror, we've varied the electrical distance to an electrical short circuit that acts as a mirror for microwaves.”
    - Prof. Per Delsing, Chalmers University of Technology
    Read article
  3. Quantum microphone captures extremely weak sound
    PRESS RELEASE | Scientists from Chalmers have demonstrated a new kind of detector for sound at the level of quietness of quantum mechanics. The result offers prospects of a new class of quantum hybrid circuits that mix acoustic elements with electrical ones, and may help illuminate new phenomena of quantum physics. The results have been published in Nature Physics.
    ​The “quantum microphone” is based on a single electron transistor, that is, a transistor where the current passes one electron at a time. The acoustic waves studied by the research team propagate over the surface of a crystalline microchip, and resemble the ripples formed on a pond when a pebble is thrown into it. The wavelength of the sound is a mere 3 micrometers, but the detector is even smaller, and capable of rapidly sensing the acoustic waves as they pass by.
    On the chip surface, the researchers have fabricated a three-millimeter-long echo chamber, and even though the speed of sound on the crystal is ten times higher than in air, the detector shows how sound pulses reflect back and forth between the walls of the chamber, thereby verifying the acoustic nature of the wave. 

    "The experiment is done on classical acoustic waves, but it shows that we have everything in place to begin studies of proper quantum-acoustics, and nobody has attempted that before", says Martin Gustafsson, PhD student and first author of the article.

    M. V. Gustafsson, P. V. Santos, G. Johansson, P. Delsing, Nature Physics 8338–343, (2012)
    Read article
    "The experiment is done on classical acoustic waves, but it shows that we have everything in place to begin studies of proper quantum-acoustics, and nobody has attempted that before"
    - Dr. Martin Gustafsson, Chalmers University of Technology
  4. Further Improvement of Qubit Lifetime for Quantum Computers
    PRESS RELEASE | An international team of scientists has succeeded in making further improvements to the lifetime of superconducting quantum circuits. An important prerequisite for the realization of high-performance quantum computers is that the stored data should remain intact for as long as possible. The researchers, including Jülich physicist Dr. Gianluigi Catelani, have developed and tested a technique that removes unpaired electrons from the circuits. These are known to shorten the qubit lifetime.

    When superconducting materials are cooled below a material-specific critical temperature, electrons come together to form pairs; then current can flow without resistance. However, so far it has not been possible to build superconducting circuits in which all electrons bundle together. Single electrons remain unpaired and are unable to flow without resistance. Due to these so-called quasiparticles, energy is lost and this limits the length of time that the circuits can store data.

    Researchers have now developed and tested a technique that can temporarily remove unpaired electrons away from the circuit; with the help of microwave pulses, they are in effect "pumped out". This results in a three-fold improvement in the lifespan of the qubits.

    S. Gustavsson, F. Yan, G. Catelani, J. Bylander, A. Kamal, J. Birenbaum, D. Hover, D. Rosenberg, G. Samach, A. P. Sears, S. J. Weber, J. L. Yoder, J. Clarke, A. J. Kerman, F. Yoshihara, Y. Nakamura, T. P. Orlando, W. D. Oliver, Science,  354 (6319), 1573-1577 (2016)
    Read article
  5. Imaging Photon Lattice States by Scanning Defect Microscopy
    ABSTRACT | Microwave photons inside lattices of coupled resonators and superconducting qubits can exhibit surprising matterlike behavior. Realizing such open-system quantum simulators presents an experimental challenge and requires new tools and measurement techniques.

    Here, we introduce scanning defect microscopy as one such tool and illustrate its use in mapping the normal-mode structure of microwave photons inside a 49-site kagome lattice of coplanar waveguide resonators. Scanning is accomplished by moving a probe equipped with a sapphire tip across the lattice. This locally perturbs resonator frequencies and induces shifts of the lattice resonance frequencies, which we determine by measuring the transmission spectrum.

    From the magnitude of mode shifts, we can reconstruct photon field amplitudes at each lattice site and thus create spatial images of the photon-lattice normal modes.

    D. L. Underwood, W. E. Shanks, A. C. Y. Li, L. Ateshian, J. Koch, and A. A. Houck,
    Physical Review X 6, 021044 (2016)

    Read article
  6. Optical frequency comb technology for ultra-broadband radio-frequency photonics
    ABSTRACT | The outstanding phase-noise performance of optical frequency combs has led to a revolution in optical synthesis and metrology, covering a myriad of applications, from molecular spectroscopy to laser ranging and optical communications. However, the ideal characteristics of an optical frequency comb are application dependent. In this review, the different techniques for the generation and processing of high-repetition-rate (>10 GHz) optical frequency combs with technologies compatible with optical communication equipment are covered. Particular emphasis is put on the benefits and prospects of this technology in the general field of radio-frequency photonics, including applications in high-performance microwave photonic filtering, ultra-broadband coherent communications, and radio-frequency arbitrary waveform generation.

    V. Torres-Company, A. Wiener,  Laser & Photonics Reviews 8:3, 368-393, (2014)
    Read article
  7. The sound of an atom has been captured
    PRESS RELEASE | Researchers at Chalmers are first to show the use of sound to communicate with an artificial atom. They can thereby demonstrate phenomena from quantum physics with sound taking on the role of light. The results are published by the journal Science.

    On the right, an artificial atom generates sound waves consisting of ripples on the surface of a solid. The sound, known as a surface acoustic wave (SAW) is picked up on the left by a "microphone" composed of interlaced metal fingers. According to theory, the sound consists of a stream of quantum particles, the weakest whisper physically possible. The illustration is not to scale.

    ​The interaction between atoms and light is well known and has been studied extensively in the field of quantum optics. However, to achieve the same kind of interaction with sound waves has been a more challenging undertaking. The Chalmers researchers have now succeeded in making acoustic waves couple to an artificial atom. The study was done in collaboration between experimental and theoretical physicists.

    Martin V. Gustafsson, T. Aref, A. F. Kockum, M. K. Ekström, G. Johansson, P. Delsing, Science, 1245993 (2014)

    Read article
    "We have opened a new door into the quantum world by talking and listening to atoms"
    - Prof. Per Delsing, Chalmers University of Technology
  8. Advanced brain investigations can become better and cheaper
    PRESS RELEASE | An important method for brain research and diagnosis is magnetoencephalography (MEG). But the MEG systems are so expensive that not all EU countries have one today. A group of Swedish researchers are now showing that MEG can be performed with technology that is significantly cheaper than that which is used today – technology that can furthermore provide new knowledge about the brain.​ A group of researchers at Chalmers University of Technology and the University of Gothenburg are now working on technology that can make MEG far more accessible. The vision is an MEG system that is simple and cheap enough to be available at every hospital, while furthermore providing totally new possibilities for fundamental investigations in brain research.

    At the heart of the system is a new class of sensors that, unlike today’s MEG sensors, don’t require cooling to -269 Celsius. Instead, these work at -196 Celsius. This capability provides many advantages:“One of them is the reduction of insulation between the sensors and the subject’s head,” says Dag Winkler, professor of physics at Chalmers. “The sensors can therefore get much closer to the brain so that one can take a more high-resolution picture of brain activity.”

    F. Öisjöen, J. F. Schneiderman, GA Figueras, ML Chukharkin, A Kalabukhov, A. Hedström, M. Elam, and D. Winkler, Applied Physics Letters, 100, 132601 (2012)

    Read article
    “Communication between brain cells generates magnetic fields that can be measured with SQUID sensors. Focal MEG puts the sensors closer to the head, thereby improving signal levels and enhancing focus on brain activity”
    - Prof. Dag Winkler, Chalmers University of Technology
  9. Phonon black-body radiation limit for heat dissipation in electronics
    ABSTRACT | Thermal dissipation at the active region of electronic devices is a fundamental process of considerable importance. Inadequate heat dissipation can lead to prohibitively large temperature rises that degrade performance, and intensive e orts are under way to mitigate this self-heating.

    At room temperature, thermal resistance is due to scattering, often by defects and interfaces in the active region, that impedes the transport of phonons. Here, we demonstrate that heat dissipation in widely used cryogenic electronic devices instead occurs by phonon black-body radiation with the complete absence of scattering, leading to large self-heating at cryogenic temperatures and setting a key limit on the noise floor.

    Our result has important implications for the many fields that require ultralow-noise electronic devices.

    J. Schleeh, J. Mateos, I. Íñiguez-de-la-Torre, N. Wadefalk, P. A. Nilsson, J. Grahn and A. J. Minnich, Nature Materials, 14, 187-191 (2015)
    Read article
    “A cross sectional image of an ultra-low noise transistor. Electrons, accelerated in the high mobility channel under the 100 nanometer gate, collide and dissipate heat that fundamentally limits the noise performance of the transistor.”
    - Dr. Joel Schleeh, Chalmers University of Technology
  10. Extends the lifetime of atoms using a mirror
    PRESS RELEASE | Researchers at Chalmers University of Technology have succeeded in an experiment where they get an artificial atom to survive ten times longer than normal by positioning the atom in front of a mirror. The findings were recently published in the journal Nature Physics.

    The artificial atom is actually a superconducting electrical circuit that the researchers make behave as an atom. Just like a natural atom, you can charge it with energy, excite the atom, which it then emits in the form of light particles. In this case, the light has a much lower frequency than ordinary light and in reality are microwaves.

    “We have demonstrated how we can control the lifetime of an atom in a very simple way,” says Per Delsing, Professor of Physics and leader of the research team.“We can vary the lifetime of the atom by changing the distance between the atom and the mirror. If we place the atom at a certain distance from the mirror the atom’s lifetime is extended by such a length that we are not even able to observe the atom. Consequently, we can hide the atom in front of a mirror,” he continues.

    I.-C. Hoi, A. F. Kockum, L. Tornberg, A. Pourkabirian, G. Johansson, P. Delsing and C. M. Wilson, Nature Physics (2015)​​

    Read article
    “We have demonstrated how we can control the lifetime of an atom in a very simple way,”
    - Prof. Per Delsing, Chalmers University of Technology
  11. Tailoring Charge Recombination in Photoelectrodes Using Oxide Nanostructures
    ABSTRACT | Optimizing semiconductor devices for solar energy conversion requires an explicit control of the recombination of photogenerated electron–hole pairs. Here we show how the recombination of charge carriers can be controlled in semiconductor thin films by surface patterning with oxide nanodisks.

    The control mechanism relies on the formation of dipole-like electric fields at the interface that, depending on the field direction, attract or repel minority carriers from underneath the disks. The charge recombination rate can be controlled through the choice of oxide material and the surface coverage of nanodisks.

    We provide proof-of-principle demonstration of this approach by patterning the surface of Fe2O3, one of the most studied semiconductors for light-driven water splitting, with TiO2 and Cu2O nanodisks. We expect this method to be generally applicable to a range of semiconductor-based solar energy conversion devices.

    B. Iandolo, B. Wickman, E. Svensson, D. Paulsson, and A. Hellman, Nano Letters, 16 (4), 2381–2386 (2016)
    Read article
    “We expect this method to be generally applicable to a range of semiconductor-based solar energy conversion devices.”
    - Prof. Anders Hellman, Chalmers University of Technology
  12. Functionalization mediates heat transport of graphene nanoflakes
    PRESS RELEASE | Heat dissipation in electronics and optoelectronics is a severe bottleneck in the further development of systems in these fields. To come to grips with this serious issue, researchers at Chalmers University of Technology have developed an efficient way of cooling electronics by using functionalized graphene nanoflakes. The results are being published in the renowned journal, Nature Communications, on 29 April.

    “Essentially, we have found a golden key with which to achieve efficient heat transport in electronics and other power devices by using graphene nanoflake-based film. This can open up potential uses of this kind of film in broad areas, and we are getting closer to pilot-scale production based on this discovery,” says Johan Liu, Professor of Electronics Production and Head of the Electronics Materials and Systems Laboratory at the Department of Microtechnology and Nanoscience – MC2 – at Chalmers University of Technology in Sweden.

    H. Han, Y. Zhang, N. Wang, M. Kabiri Samani, Y. Ni, Z. Y. Mijbil, M. Edwards, S. Xiong, K. Sääskilahti, M. Murugesan, Y. Fu, L. Ye, H. Sadeghi, S. Bailey, Y. A. Kosevich, C. J. Lambert, J. Liu, and S. Volz, Nature Communications 7, 11281 (2016)
    “Essentially, we have found a golden key with which to achieve efficient heat transport in electronics and other power devices by using graphene nanoflake-based film.”
    - Prof. Johan Liu, Chalmers University of Technology
    Read article