Johannes Skaar

• Gulla, Jan & Skaar, Johannes (2021). Tunneling times of single photons. Journal of the Optical Society of America. B, Optical physics. ISSN 0740-3224. 38(11), p. 3457–3465. doi: 10.1364/JOSAB.437386. Full text in Research Archive Show summary

  Although the group delay of classical pulses through a barrier may suggest superluminality, the information transfer is limited by the precursor, which propagates at the vacuum light speed. Single photons, however, have infinite tails, and the question of causality becomes meaningless. We solve this problem by introducing strictly localized states close to single photons, which are examples of optical states produced by on-demand single-photon sources. These states can be arbitrarily close to single photons while demonstrating causality for their leading edge.

• Gulla, Jan & Skaar, Johannes (2021). Approaching Single-Photon Pulses. Physical Review Letters. ISSN 0031-9007. 126(7). doi: 10.1103/PhysRevLett.126.073601. Full text in Research Archive Show summary

  Single-photon pulses cannot be generated on demand, due to incompatible requirements of positive frequencies and positive times. Resulting states therefore contain small probabilities for multiphotons. We derive upper and lower bounds for the maximum fidelity of realizable states that approximate single-photon pulses. The bounds have implications for ultrafast optics; the maximum fidelity is low for pulses with few cycles or close to the onset, but increases rapidly as the pulse envelope varies more slowly. We also demonstrate strictly localized states that are close to single photons.

• Skaar, Johannes (2019). Fresnel's equations in statics and quasistatics. European Journal of Physics. ISSN 0143-0807. 40(4). doi: 10.1088/1361-6404/ab166b. Full text in Research Archive
• Hågenvik, Hans Olaf & Skaar, Johannes (2019). Magnetic permeability in Fresnel’s equation . Journal of the Optical Society of America. B, Optical physics. ISSN 0740-3224. 36(5), p. 1386–1395. doi: 10.1364/JOSAB.36.001386. Full text in Research Archive
• Skaar, Johannes; Hågenvik, Hans Olaf & Dirdal, Christopher Andrew (2019). Four definitions of magnetic permeability for periodic metamaterials. Physical review B (PRB). ISSN 2469-9950. 99(6). doi: 10.1103/PhysRevB.99.064407. Full text in Research Archive
• Joshi, Siddarth Koduru; Pienaar, Jacques; Ralph, Timothy C.; Cacciapuoti, Luigi; McCutcheon, Will & Rarity, John [Show all 45 contributors for this article] (2018). Space QUEST mission proposal: experimentally testing decoherence due to gravity. New Journal of Physics. ISSN 1367-2630. 20:063016(6), p. 1–22. doi: 10.1088/1367-2630/aac58b. Full text in Research Archive
• Dirdal, Christopher Andrew; Hågenvik, Hans Olaf; Haave, Haakon Aamodt & Skaar, Johannes (2018). Higher order multipoles in metamaterial homogenization . IEEE Transactions on Antennas and Propagation. ISSN 0018-926X. 66(11), p. 6403–6407. doi: 10.1109/TAP.2018.2863742. Full text in Research Archive
• Dirdal, Christopher Andrew & Skaar, Johannes (2018). Diamagnetism and the dispersion of the magnetic permeability. European Physical Journal B : Condensed Matter Physics. ISSN 1434-6028. 91(6). doi: 10.1140/epjb/e2018-80515-1. Full text in Research Archive
• Marøy, Øystein; Makarov, Vadim & Skaar, Johannes (2017). Secure detection in quantum key distribution by real-time calibration of receiver. Quantum Science and Technology. ISSN 2058-9565. 2(4). doi: 10.1088/2058-9565/aa83c9. Full text in Research Archive
• Hågenvik, Hans Olaf; Bløtekjær, Kjell & Skaar, Johannes (2017). Dielectric media considered as vacuum with sources. American Journal of Physics (AJP). ISSN 0002-9505. 85(11), p. 830–833. doi: 10.1119/1.5003810. Full text in Research Archive
• Svendsen, Guro Kristin; Skaar, Johannes; Weman, Helge & Dupertuis, Marc-André (2015). Symmetries and optical transitions of hexagonal quantum dots in GaAs/AlGaAs nanowires. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 92(20). doi: 10.1103/PhysRevB.92.205303.
• Hågenvik, Hans Olaf & Skaar, Johannes (2015). Fourier-Laplace analysis and instabilities of a gainy slab. Journal of the Optical Society of America. B, Optical physics. ISSN 0740-3224. 32(9), p. 1947–1953. doi: 10.1364/JOSAB.32.001947.
• Hågenvik, Hans Olaf; Malema, Markus Edward & Skaar, Johannes (2015). Fourier theory of linear gain media. Physical Review A. Atomic, Molecular, and Optical Physics (PRA). ISSN 1050-2947. 91(4). doi: 10.1103/PhysRevA.91.043826.
• Dirdal, Christopher Andrew; Bondevik, Tarjei & Skaar, Johannes (2015). Relaxed dispersion constraints and metamaterial effective parameters with physical meaning for all frequencies. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 91(13). doi: 10.1103/PhysRevB.91.134102.
• Dirdal, Christopher Andrew & Skaar, Johannes (2015). Superposing Lorentzian resonance functions towards engineering target responses. In Zouhdi, Said; Zheludev, Nikolay & Teng, Jing Hua (Ed.), Meta'14 Singapore Proceedings. META conference. ISSN 978-2-9545460-4-9. p. 53–58.
• Bugge, Audun Nystad; Sauge, Sebastien; Ghazali, Aina Mardhiyah M.; Skaar, Johannes; Lydersen, Lars Vincent Van de Wiel & Makarov, Vadim (2014). Laser damage helps the eavesdropper in quantum cryptography. Physical Review Letters. ISSN 0031-9007. 112(7:070503). doi: 10.1103/PhysRevLett.112.070503.
• Marøy, Øystein; Gudmundsen, Magne; Lydersen, Lars Vincent Van de Wiel & Skaar, Johannes (2014). Error estimation, error correction and verification in quantum key distribution. IET Information Security. ISSN 1751-8709. 8(5), p. 277–282. doi: 10.1049/iet-ifs.2012.0333.
• Liu, Qin; Lamas-Linares, Antia; Kurtsiefer, Christian; Skaar, Johannes; Makarov, Vadim & Gerhardt, Ilja (2014). A universal setup for active control of a single-photon detector. Review of Scientific Instruments. ISSN 0034-6748. 85(1). doi: 10.1063/1.4854615.
• Dirdal, Christopher Andrew & Skaar, Johannes (2013). Superpositions of Lorentzians as the class of causal functions. Physical Review A. Atomic, Molecular, and Optical Physics (PRA). ISSN 1050-2947. 88(3). doi: 10.1103/PhysRevA.88.033834.
• Dirdal, Christopher Andrew & Skaar, Johannes (2013). Negative refraction in causal media by evaluating polar paths for rational functions. Journal of the Optical Society of America. B, Optical physics. ISSN 0740-3224. 30(2), p. 370–376. doi: 10.1364/JOSAB.30.000370.
• Svendsen, Guro Kristin; Haakestad, Magnus Willum & Skaar, Johannes (2013). Reciprocity and the scattering matrix of waveguide modes. Physical Review A. Atomic, Molecular, and Optical Physics (PRA). ISSN 1050-2947. 87(1). doi: 10.1103/PhysRevA.87.013838.
• Skaar, Johannes & Haakestad, Magnus Willum (2012). Inverse scattering of dispersive stratified structures. Journal of the Optical Society of America. B, Optical physics. ISSN 0740-3224. 29(9), p. 2438–2445. doi: 10.1364/JOSAB.29.002438. Show summary

  We consider the inverse-scattering problem of retrieving the structural parameters of a stratified medium consisting of dispersive materials, given knowledge of the complex reflection coefficient in a finite frequency range. It is shown that the inverse-scattering problem does not have a unique solution in general. When the dispersion is sufficiently small, such that the time-domain Fresnel reflections have durations less than the round-trip time in the layers, the solution is unique and can be found by layer peeling. Numerical examples with dispersive and lossy media are given, demonstrating the usefulness of the method for, e.g., terahertz technology.

• Svendsen, Guro Kristin; Weman, Helge & Skaar, Johannes (2012). Investigations of Bragg reflectors in nanowire lasers. Journal of Applied Physics. ISSN 0021-8979. 111(12). doi: 10.1063/1.4729529.
• Grepstad, Jon Olav & Skaar, Johannes (2011). Does evanescent gain exist? In Stone, W. Ross (Eds.), Proceedings of the XXXth URSI General Assembly in Istanbul (August 2011). IEEE conference proceedings. ISSN 978-1-4244-5117-3. doi: 10.1109/ursigass.2011.6123712.
• Grepstad, Jon Olav & Skaar, Johannes (2011). Total internal reflection and evanescent gain. Optics Express. ISSN 1094-4087. 19(22), p. 21404–21418. doi: 10.1364/OE.19.021404. Full text in Research Archive
• Lydersen, Lars Vincent Van de Wiel; Akhlaghi, Mohsen K.; Majedi, A. Hamed; Skaar, Johannes & Makarov, Vadim (2011). Controlling a superconducting nanowire single-photon detector using tailored bright illumination. New Journal of Physics. ISSN 1367-2630. 13. doi: 10.1088/1367-2630/13/11/113042. Full text in Research Archive
• Sauge, Sebastien; Lydersen, Lars Vincent Van de Wiel; Anisimov, Andrey; Skaar, Johannes & Makarov, Vadim (2011). Controlling an actively-quenched single photon detector with bright light. Optics Express. ISSN 1094-4087. 19, p. 23590–23600. doi: 10.1364/OE.19.023590. Full text in Research Archive

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• Nilsen, Fabian Skalleberg & Skaar, Johannes (2020). Østlandssendingen - er det mulig å forsyne seg selv med strøm ved hjelp av spinningsykler og tredemøller? [Radio]. NRK P1.
• Skaar, Johannes (2019). Intervju av TV2 Nyhetskanalen, kl 0710, om kvantedatamaskiner. [TV]. TV2 Nyhetskanalen.
• Jemterud, Torkild; Skaar, Johannes; Eidsvoll, David & Iqbal, Yasmin Sofia (2019). Abels tårn. [Radio]. NRK P2 .
• Risan, Lars & Skaar, Johannes (2019). SENT-kveld på Teknisk museum: Foredrag om kvantedatamaskiner.
• Skaar, Johannes (2019). Musikk og matematikk.
• Fedorov, Aleksey; Gerhardt, Ilja; Huang, Anqi; Jogenfors, Jonathan; Kurochkin, Yury & Lamas-Linares, Antia [Show all 11 contributors for this article] (2019). Comment on 'Inherent security of phase coding quantum key distribution systems against detector blinding attacks' (2018 Laser Phys. Lett. 15 095203). Laser Physics Letters. ISSN 1612-2011. 16. doi: 10.1088/1612-202X/aaf22d.
• Dirdal, Christopher Andrew; Hågenvik, Hans Olaf; Haave, Haakon Aamodt & Skaar, Johannes (2018). Higher order multipoles in metamaterial homogenization.
• Skaar, Johannes (2018). Fysikk og musikk.
• Skaar, Johannes (2018). Energi - uten en tråd.
• Skaar, Johannes (2018). Matematikk i musikk.
• Andersen, Elise Rønnevig; Bratberg, Øivind; Hellum, Mari Kjos; Hjelle, Ole Petter; Hussein, Bassam & Lie, Anne Helene Kveim [Show all 11 contributors for this article] (2017). Landets beste forelesere svarer: Slik studerer du mest effektivt. [Newspaper]. Aftenposten.
• Stensvold, Tore & Skaar, Johannes (2017). Norwegian Tech Awards 2017 - WÄRTSILÄ. De lader ferge med 1,2 megawatt effekt - uten fysisk kontakt med fartøyet. [Business/trade/industry journal]. Teknisk ukeblad.
• Skaar, Johannes (2017). Musikkens fysikk.
• Sund, Steinar & Skaar, Johannes (2017). Snart kan du lade med klærne. [Journal]. Aftenposten Vitenskap.
• Mauren, Arnfinn & Skaar, Johannes (2017). Magisk teknologi kan bety farvel til hacking. [Business/trade/industry journal]. Aftenposten Vitenskap.
• Sævik, Bjørnar Torvholm; Folven, Erik; Jahre, Magnus & Skaar, Johannes (2017). Ein æra er omm. [Internet]. nrk.no.
• Klingenberg, Mathias & Skaar, Johannes (2017). 100 milliarder bilder i sekundet fanger lys som går raskere enn seg selv. [Business/trade/industry journal]. Teknisk ukeblad.
• Sande, Anniken & Skaar, Johannes (2017). Her og nå: Dagens gjest. [Radio]. NRK P1.
• Skaar, Johannes & Tollersrud, Emma (2017). Med lønnsøkning skal underviserne skinne. [Newspaper]. Morgenbladet.
• Opheim, Aagot & Skaar, Johannes (2017). Vil gi ære, status og høyere lønn til de beste underviserne. [Newspaper]. Adresseavisen.
• Skaar, Johannes (2016). Magneter, metallrør og usynlighetskapper.
• Indregard, Sigve & Skaar, Johannes (2016). Til Mars med mikrobølgeovn. [Newspaper]. Morgenbladet.
• Bakken, Kjersti & Skaar, Johannes (2016). Norgesglasset: "Lærer man egentlig noe av forelesninger, eller trenger studentene noe helt annet for å bli flinke?". [Radio]. NRK P1.
• Skaar, Johannes (2016). Kortforedrag om musikk og fysikk.
• Tollersrud, Emma & Skaar, Johannes (2016). «Hvis vi ikke underviser, er det lett å ta elementære ting for gitt.». [Newspaper]. Morgenbladet.
• Kleiven, David; Skjønsfjell, Eirik Torbjørn Bakken; Zontone, Federico; Chushkin, Yuriy; Skaar, Johannes & Breiby, Dag Werner (2016). Experimental and Numerical Studies for Improved Coherent Diffraction Phase Retrieval.
• Dirdal, Christopher Andrew; Hågenvik, Hans Olaf & Skaar, Johannes (2016). Higher order terms and origin dependence in metamaterial homogenization.
• Dirdal, Christopher Andrew; Hågenvik, Hans Olaf & Skaar, Johannes (2016). Permittivity, permeability, and the significance of the electrical quadrupole in metamaterials.
• Hågenvik, Hans Olaf; Dirdal, Christopher Andrew & Skaar, Johannes (2016). Homogenization of metamaterials: comparison and analysis.
• Skaar, Johannes (2015). Maxwells teori og Hertz' eksperiment – grunnlaget for moderne telekommunikasjon ble skapt for 150 år siden.
• Skaar, Johannes (2015). Hva er lys?
• Dirdal, Christopher Andrew & Skaar, Johannes (2015). Giving Freedom and Physical Meaning to the Effective Parameters of Metamaterials for all Frequencies.
• Hågenvik, Hans Olaf & Skaar, Johannes (2015). Laplace-Fourier analysis and instabilities of an active slab.
• Jegtvik, Karin & Skaar, Johannes (2015). Er du vinneren av påskefjellet? [Internet]. nrk.no.
• Ramsdal, Roar & Skaar, Johannes (2015). Her sendes 10 kilowatt trådløst. [Internet]. Teknisk ukeblad.
• Dirdal, Christopher Andrew & Skaar, Johannes (2014). Superposing Lorentzian functions towards engineering target responses. The 5th International Conference on Metamaterials, Photonic Crystals and Plasmonics Book of Abstracts.
• Dirdal, Christopher Andrew & Skaar, Johannes (2014). Superposing Lorentzian functions towards engineering target responses.
• Dirdal, Christopher Andrew & Skaar, Johannes (2014). Metamaterial responses beyond the Kramers-Kronig relations.
• Børringbo, Klaus & Skaar, Johannes (2014). Trådløs strøm – snart er den her. [Newspaper]. Aftenposten.
• Dalløkken, Per Erlien; Skaar, Johannes & Samset, Bjørn Hallvard (2014). «Metamaterialer» skal beskytte piloter mot laserangrep fra bakken. [Internet]. Teknisk ukeblad.
• Svendsen, Guro Kristin; Skaar, Johannes; Weman, Helge & Dupertuis, M.-A. (2014). Symmetries and optical transitions of hexagonal quantum dots in GaAs/AlGaAs nanowires.
• Iversen, Marita Løvmo; Jansrud, Line & Skaar, Johannes (2014). Går det an å gjøre noe usynlig? NRK Newton. [TV]. NRK 1.
• Schirber, Michael; Bugge, Audun Nystad; Sauge, Sebastien; Ghazali, Aina; Skaar, Johannes & Lydersen, Lars Vincent Van de Wiel [Show all 7 contributors for this article] (2014). Synopsis: Cyberattack by Breaking and Entering. [Internet]. APS Physics.
• Andreassen, Katrine; Skaar, Johannes; Løland, Anders & Rolén, Tage (2014). Finn ut om du er en sinke på ski. [Internet]. klikk.no.
• Brandslet, Steinar; Skaar, Johannes; Løland, Anders & Rolén, Tage (2014). Hvor fort går du på ski? Aftenposten (morgenutg. : trykt utg.). ISSN 0804-3116.
• Lydersen, Lars Vincent Van de Wiel & Skaar, Johannes (2013). Kvantekryptografi. Fra Fysikkens Verden. ISSN 0015-9247. 75(1).
• Skaar, Johannes; Løland, Anders; Rolén, Tage & Kokkegård, Hanne (2013). Vild med tal? Tæl dig frem til, om du er hurtigst. [Internet]. dr.dk.
• Flæten, Sigurd Øygarden & Skaar, Johannes (2013). Laser kan bli fremtidens spionkamera. [Internet]. Teknisk ukeblad.
• Brandslet, Steinar; Skaar, Johannes; Løland, Anders & Rolén, Tage (2013). Hvor fort går du på ski? [Internet]. forsking.no.
• Brandslet, Steinar; Skaar, Johannes; Løland, Anders & Rolén, Tage (2013). Hvor fort går du på ski? Gemini. ISSN 0802-085X. p. 6–7.
• Moe, Enok & Skaar, Johannes (2013). Rockheim forstyrrer flytrafikken på Værnes. Adresseavisen. ISSN 0805-3804.
• Haugen, Vegard & Skaar, Johannes (2013). Døde av elektrosjokk med iPhone 5 i hånden. VG : Verdens gang. ISSN 0805-5203.
• Haugen, Vegard & Skaar, Johannes (2013). Døde av elektrosjokk med iPhone 5 i hånden. [Internet]. amobil.no.
• Grepstad, Jon Olav; Kaspar, Peter; Johansen, Ib-Rune; Skaar, Johannes; Sudbø, Aasmund & Solgaard, Olav (2012). Optical detection of single biomolecules using photonic-crystal membranes.
• Time, Jon Kåre & Skaar, Johannes (2012). Trollmannen fra Tyrifjord. [Newspaper]. Morgenbladet.
• Time, Jon Kåre & Skaar, Johannes (2012). I bakvendtland der alt går an. [Newspaper]. Morgenbladet.
• Bugge, Audun Nystad; Sauge, Sebastien; Ghazali, Aina; Skaar, Johannes; Lydersen, Lars Vincent Van de Wiel & Makarov, Vadim (2012). Laser damage of photodiodes helps the eavesdropper.
• Miller, Johanna; Makarov, Vadim; Kurtsiefer, Christian; Liu, Qin & Skaar, Johannes (2011). "Faked states" mimic quantum entanglement. [Internet]. Physics Today. Show summary

  Also in print edition: Physics Today Vol. 64, Issue 12, pages 20-23.

• Voss, David; Makarov, Vadim; Kurtsiefer, Christian; Liu, Qin & Skaar, Johannes (2011). Synopsis: Eve Fools Alice and Bob. [Internet]. Physics.
• Merali, Zeeya; Makarov, Vadim; Liu, Qin & Skaar, Johannes (2011). Lasers illuminate quantum security loophole. [Internet]. Nature News.
• Zyga, Lisa; Makarov, Vadim; Liu, Qin & Skaar, Johannes (2011). Fake violations of Bell tests reinforce importance of closing loopholes. [Internet]. PhysOrg.com.
• Lee, Chris; Makarov, Vadim; Liu, Qin & Skaar, Johannes (2011). Researchers show how to break quantum cryptography by faking quantum entanglement. [Internet]. Ars Technica.
• Makarov, Vadim; Liu, Qin; Skaar, Johannes & Goodin, Dan (2011). Uncrackable quantum crypto undermined by new attack. [Internet]. The Register.
• Scharf, Rainer; Makarov, Vadim; Liu, Qin & Skaar, Johannes (2011). Quantenkryptographie: Bell-Ungleichung ausgetrickst. [Internet]. pro-physik.de.
• Makarov, Vadim; Skaar, Johannes; Lydersen, Lars Vincent Van de Wiel; Knight, Helen & Liu, Qin (2011). Quantum hackers: Cracking the uncrackable code. [Internet]. New Scientist. Show summary

  Also in print edition of the magazine: vol. 2835, pages 44-47 (2011)

• Grepstad, Jon Olav; Kaspar, Peter; Due-Hansen, Jon; Johansen, Ib-Rune; Borch, Morten & Furuberg, Liv [Show all 9 contributors for this article] (2011). System for optical characterization of photonic crystal membranes - designed for biological sensing with single molecule sensitivity.
• Grepstad, Jon Olav; Due-Hansen, Jon; Johansen, Ib-Rune; Borch, Morten; Kaspar, Peter & Furuberg, Liv [Show all 9 contributors for this article] (2011). Umiddelbar diagnose i 2020.
• Grepstad, Jon Olav & Skaar, Johannes (2011). Does evanescent gain exist?
• Lydersen, Lars Vincent Van de Wiel; Makarov, Vadim & Skaar, Johannes (2011). Comment on "Resilience of gated avalanche photodiodes against bright illumination attacks in quantum cryptography" [Appl. Phys. Lett. 98, 231104 (2011)]. Applied Physics Letters. ISSN 0003-6951. 99(19). doi: 10.1063/1.3658806.
• Lydersen, Lars Vincent Van de Wiel; Makarov, Vadim & Skaar, Johannes (2011). SNSPD's in quantum cryptography.
• Lydersen, Lars Vincent Van de Wiel; Skaar, Johannes; Makarov, Vadim & Liu, Qin (2011). Quantum cryptography and quantum hacking.
• Hågenvik, Hans Olaf & Skaar, Johannes (2019). Analysis of active and passive metamaterials. NTNU Grafisk senter. ISSN 978-82-326-3915-1.
• Skaar, Johannes (2011). Elektromagnetisme. Tapir Akademisk Forlag.

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