Johannes Skaar

• Rukan, Isak Cecil Onsager; Gulla, Jan & Skaar, Johannes (2026). Truncated Photon. Physical Review Letters. ISSN 0031-9007. 137(3). doi: 10.1103/94pm-hp34. Full text in Research Archive Show summary

  An elementary particle such as a photon cannot be cut in two pieces. Still it must be possible to truncate a photon with an optical shutter. The result is neither another photon nor a mix of a photon and a vacuum. Instead it is a superposition and mix of photon numbers up to infinity. This state is rather complicated, but nevertheless locally equivalent to a single photon or vacuum to the left and right, respectively, of a narrow transition region.

• Dirdal, Christopher Andrew; Jose, Jesil; Dullo, Firehun Tsige; Bouquet, Gregory; Thrane, Paul Conrad Vaagen & Skokic, Zeljko [Show all 7 contributors for this article] (2025). Reversal Asymmetry of Reciprocal Metasurface Enables Ultra-Compact Varifocal Reflective Lens. Laser & Photonics reviews. ISSN 1863-8880. 20(1). doi: 10.1002/lpor.202501196. Full text in Research Archive Show summary

  Reversing a ray through a conventional lens will bring it back to its starting point. Although such reversal symmetry is characteristic of reciprocal systems, such symmetry can be broken without violating reciprocity. This is demonstrated in the case when utilizing circular polarization states and chiral structures: Geometric phase metasurface lenses (metalenses) can be shown to act as positive (converging) or negative (diverging) lenses depending on transmission through the front or rear of the lens, respectively, for a given circular polarization state. Ray-tracing for such a metalens placed in front of a mirror reveals that reversal symmetry is broken: The reversed ray after the mirror does not end at the starting point. In this paper, such an arrangement is used to realize a varifocal reflective doublet that is equivalent to a transmissive doublet with a consecutive positive and negative lens. Such a reflective arrangement is not possible using a reversal symmetric lens, and allows for realizing an ultra-compact varifocal lens component. A proof-of-concept implementation using a 1550 nm NIR metalens is demonstrated, attaining a diopter change on the order of 1052 m-1 for a focal length shift of 240 µm, caused by a 53 µm thin-film piezoelectric micromirror displacement.

• Gulla, Jan; Ryen, Kai & Skaar, Johannes (2023). Limits for realizing single photons. Physical Review A (PRA). ISSN 2469-9926. 108(6), p. 063708–063708. doi: 10.1103/PhysRevA.108.063708. Full text in Research Archive Show summary

  Exact single photons cannot be generated on demand due to their infinite tails. To quantify how close realizable optical states can be to some target single photon in one dimension, we argue that there are two natural but incompatible ways to specify the target state. Either it can be expressed as a photon with a chosen positive-frequency spectrum, or it can be described as an (unphysical) photon in a chosen positive-time pulse. The results show that for sufficiently short target pulses, the closest realizable states contain substantial multiphoton components. Upper and lower bounds for the maximum fidelity are derived and are expressed as functions of the size of the target state's tail, for negative time or negative frequency, respectively. We also generalize the bounds to arbitrary photon-number states.

• Ryen, Kai; Gulla, Jan & Skaar, Johannes (2022). Strictly Localized Three-Dimensional States Close to Single Photons. International journal of theoretical physics. ISSN 0020-7748. 61(5). doi: 10.1007/s10773-022-05133-7. Full text in Research Archive Show summary

  Abstract A class of strictly localized states which can be made arbitrarily close to single photons is constructed, and expressions for central properties are provided. It is demonstrated that single photon states can be well approximated by these states down to localization scales on the order of a few pulse cycles. The results readily generalize to states close to n -photons. We also provide upper and lower bounds for the fidelity between a given single photon and any state strictly localized to a given volume. These results constitute the limit of photon localization, complementary to the weak-localization limit (Bialynicki-Birula, Phys. Rev. Lett. 80 , 5247, (1998)).

• 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), p. 073601–073601. 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.

• 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 Show summary

  Magnetic permeabilities derived for infinite, periodic media are used in the Fresnel equation to calculate the reflection from corresponding semi-infinite media. By comparison to finite-difference time-domain (FDTD) simulations, we find that the Fresnel equation gives accurate results for 2D metamaterials which mimic natural magnetism, in a frequency range where the magnetic moment density dominates the 𝒪(𝑘2) part of the total Landau–Lifshitz permittivity. For a 1D layered structure, or for large frequencies, the correspondence is poor. We also demonstrate that even if a medium is described accurately by a local permittivity and permeability, the Fresnel equation is not necessarily valid.

• 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 Show summary

  We state and compare four different definitions of magnetic permeability for periodic, artificial media, or metamaterials. The connections among them, and properties in general, are discussed in detail, including causality, passivity, symmetry, asymptotic behavior, and origin dependence. The analysis is limited to metamaterials made from linear and nonmagnetic constituents

• 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 Show summary

  Fresnel's equations describe the reflection and transmission of electromagnetic waves at an interface between two media. It turns out that these equations can be used in quasistatics and even statics, for example to straightforwardly calculate magnetic forces between a permanent magnet and a bulk medium. This leads to a generalization of the classical image method.

• 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 Show summary

  The higher order multipoles above the electric quadrupole are commonly neglected in metamaterial homogenization. We show that they nevertheless can be significant when the second-order spatial dispersive effects, such as the magnetic response, are considered. In this respect, they can be equally important as the magnetization and quadrupole terms, and should not be automatically neglected.

• 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. 20:063016(6), p. 1–22. doi: 10.1088/1367-2630/aac58b. Full text in Research Archive Show summary

  Models of quantum systems on curved space-times lack sufficient experimental verification. Some speculative theories suggest that quantum correlations, such as entanglement, may exhibit different behavior to purely classical correlations in curved space. By measuring this effect or lack thereof, we can test the hypotheses behind several such models. For instance, as predicted by Ralph et al [5] and Ralph and Pienaar [1], a bipartite entangled system could decohere if each particle traversed through a different gravitational field gradient. We propose to study this effect in a ground to space uplink scenario. We extend the above theoretical predictions of Ralph and coworkers and discuss the scientific consequences of detecting/failing to detect the predicted gravitational decoherence. We present a detailed mission design of the European Space Agency's Space QUEST (Space—Quantum Entanglement Space Test) mission, and study the feasibility of the mission scheme.

• 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 Show summary

  It is well known that the usual Kramers–Kronig relations for the relative permeability function μ(ω) are not compatible with diamagnetism (μ(0) < 1) and a positive imaginary part (Im μ(ω) > 0 for ω > 0). We demonstrate that a certain physical meaning can be attributed to μ for all frequencies, and that in the presence of spatial dispersion, μ does not necessarily tend to 1 for high frequencies ω and fixed wavenumber k. Taking the asymptotic behavior into account, diamagnetism can be compatible with Kramers–Kronig relations even if the imaginary part of the permeability is positive. We provide several examples of diamagnetic media and metamaterials for which μ(ω, k) ↛ 1 as ω →∞.

• 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 Show summary

  Conventional textbook treatments on electromagnetic wave propagation consider the induced charge and current densities as “bound” and therefore absorb them into a refractive index. In principle, it must also be possible to treat the medium as vacuum but with explicit charge and current densities, thus giving a more direct, physical description. However, since the induced waves propagate in vacuum in this picture, it is not straightforward to reconcile that the wavelength becomes different compared to that in vacuum. We provide an explanation for this phenomenon, including associated time-domain simulations. As an extra bonus, the results turn out to illuminate the behavior of metamaterials.

• Marøy, Øystein; Makarov, Vadim & Skaar, Johannes (2017). Secure detection in quantum key distribution by real-time calibration of receiver. Quantum Science and Technology. 2(4). doi: 10.1088/2058-9565/aa83c9. Full text in Research Archive Show summary

  The single-photon detectionefficiency of the detector unit is crucial for the security of common quantum key distribution protocols like Bennett-Brassard 1984 (BB84). A low value for the efficiency indicates a possible eavesdropping attack that exploits the photon receiver's imperfections. We present a method for estimating the detection efficiency, and calculate the corresponding secure key generation rate. The estimation is done by testing gated detectors using a randomly activated photon source inside the receiver unit. This estimate gives a secure rate for any detector with non-unity single-photon detection efficiency, both inherit or due to blinding. By adding extra optical components to the receiver, we make sure that the key is extracted from photon states for which our estimate is valid. The result is a quantum key distribution scheme that is secure against any attack that exploits detector imperfections.

• 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. Full text in Research Archive
• 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 9782954546049. p. 53–58. 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. Full text in Research Archive
• 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. Full text in Research Archive
• 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. Full text in Research Archive
• 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. Full text in Research Archive
• 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. Full text in Research Archive
• 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. Full text in Research Archive
• 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. Full text in Research Archive
• 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. Full text in Research Archive
• 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. doi: 10.1103/PhysRevA.87.013838. Full text in Research Archive Show summary

  The implications of the Lorentz reciprocity theorem for a scatterer connected to waveguides with arbitrary modes, including degenerate, evanescent, and complex modes, are discussed. In general it turns out that a matrix CSis symmetric, where Cis the matrix of generalized orthogonality coefficients and Sis the scattering matrix. Examples are given, including a scatterer surrounded by waveguides or free space, and discontinuities of waveguides.

• 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. Full text in Research Archive

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• Rukan, Isak Cecil Onsager; Gulla, Jan & Skaar, Johannes (2026). Truncating a photon. Full text in Research Archive
• Gupta, Chaitanya; Skaar, Johannes; Rukan, Isak Cecil Onsager & Gulla, Jan (2026). What can cutting a photon in half tell us about causality and local equivalence? – Physics World. [Internet]. Physics World. Full text in Research Archive Show summary

  Calculations identify complicated consequences of removing a mirror

• Skaar, Johannes; Thorsteinsen, Pål Henrik; Rukan, Isak Cecil Onsager & Gulla, Jan (2026). Kan et foton deles i to? Ny studie fra UiO gir et oppsiktsvekkende svar. [Internet]. Instagram. Full text in Research Archive Show summary

  166 likes, 6 comments - unioslo_mn on September 4, 2026: "Kan et foton deles i to? Ny studie fra UiO gir et oppsiktsvekkende svar.   Alt lys og all stråling består av fotoner. Elementærpartikler som man tidligere har tenkt ikke kan deles i to. Men forskere ved Universitetet i Oslo stilte seg et ganske grunnleggende spørsmål: Hva skjer om vi prøver å kutte av enden til et foton? Forskerne eksperimenterte med å sende et foton mot et speil i vakuum. Ettersom fotoner oppfører seg både bølger og partikler, går det an å se dem for seg som bølger med en viss lengde.  Så fjerner de speilet midt i bølgen. Det blir som å prøve å kutte det i to. Men i stedet for å få to fotoner får du en blanding av mange ulike tilstander, som for eksempel null, ett, ti eller tusen fotoner. Studien har fått stor oppmerksomhet i fagmiljøet og blitt publisert i anerkjente tidsskrifter. 🎤 Johannes Skaar 📸 Henrik Thorsteinsen ✂️ Henrik Thorsteinsen".

• Borgan, Eldrid; Skaar, Johannes; Sudbø, Asle; Rukan, Isak Cecil Onsager & Gulla, Jan (2026). Kan et foton deles i to? Svaret er ganske sprøtt, viser en ny norsk studie. [Internet]. forskning.no. Full text in Research Archive Show summary

  Dette er viktig å vite for mange som jobber med kvanteteknologi, mener forsker.

• Melteig, Elina & Skaar, Johannes (2026). Hva er tyngst: Å løpe ute eller på mølle? [Internet]. forskning.no. Full text in Research Archive Show summary

  Kanskje du har opplevd at det ene er mye tyngre enn den andre. Hva svarer ekspertene?

• Melteig, Elina & Skaar, Johannes (2026). Hvorfor er noen områder i skiløypa isete? - Titan.uio.no. [Internet]. Titan. Full text in Research Archive
• Melteig, Elina & Skaar, Johannes (2026). Spørsmål som fysikkprofessorer svarer feil på - Titan.uio.no. [Internet]. Titan. Full text in Research Archive
• Skaar, Johannes & Thorsteinsen, Pål Henrik (2026). Er det noe forskjell på å løpe ute og inne hvis du løper med samme stigning? [Internet]. Instagram. Full text in Research Archive Show summary

  640 likes, 12 comments - unioslo_mn on May 15, 2026: "Noen som blir med på noen intervaller i GS-trappa?🏃🏻‍♂️ #science #vitenskap #løping 🎤 Johannes Skaar 📸 Henrik Thorsteinsen ✂️ Henrik Thorsteinsen".

• Skaar, Johannes (2026). Enkle fysikkspørsmål som fysikkprofessorer svarer feil på. Full text in Research Archive
• Harris, Rory; Rukan, Isak Cecil Onsager; Gulla, Jan & Skaar, Johannes (2026). 'A mixture from zero to infinity': Physicists split apart a photon — and ended up with an improbable swarm of particles. [Internet]. LiveScience. Full text in Research Archive Show summary

  Physicists have found that splitting a photon would lead to a complex state that may change the way we think of particles.

• Farkas, Ivan; Rukan, Isak Cecil Onsager; Gulla, Jan & Skaar, Johannes (2026). Physicists Find a Way to 'Split' Particles of Light in Half to Make Infinite Photons : ScienceAlert. [Internet]. ScienceAlert. Full text in Research Archive Show summary

  Photons act in freaky ways that remind us that nothing is as it seems at the smallest scales and most fundamental levels of existence.

• Stephens, Marric; Rukan, Isak Cecil Onsager; Gulla, Jan & Skaar, Johannes (2026). Cutting the tail of a photon. [Internet]. Physics Magazine. doi: https:/physics.aps.org/articles/v19/s91. Full text in Research Archive Show summary

  Removing a mirror while a single photon is in the process of reflecting creates a quantum state of countless photons, theorists say.

• Temming, Maria; Rukan, Isak Cecil Onsager; Gulla, Jan & Skaar, Johannes (2026). Here’s what would happen if you tried to break a photon in half. [Internet]. ScienceNews. Full text in Research Archive
• Padavic-Callaghan, Karmela; Rukan, Isak Cecil Onsager; Gulla, Jan & Skaar, Johannes (2026). Photons behave very strangely if you try to cut them. [Internet]. New Scientist. Full text in Research Archive Show summary

  Particles of light cannot be divided into smaller particles, but if you try to snip off the end of one, instead of shortening it multiplies

• Vogt, Yngve & Skaar, Johannes (2025). Kjeltringer kan avsløre krypteringsnøklene i dagens internett - Forskningsnytt. [Journal]. Apollon. Full text in Research Archive
• Skaar, Johannes (2023). Det er ett strømspareråd som nesten aldri nevnes. Aftenposten (morgenutg. : trykt utg.). ISSN 0804-3116. Full text in Research Archive
• 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. Full text in Research Archive
• Skaar, Johannes (2019). Musikk og matematikk. Full text in Research Archive
• Jemterud, Torkild; Skaar, Johannes; Eidsvoll, David & Iqbal, Yasmin Sofia (2019). Abels tårn. [Radio]. NRK P2 . Full text in Research Archive
• Risan, Lars & Skaar, Johannes (2019). SENT-kveld på Teknisk museum: Foredrag om kvantedatamaskiner. Full text in Research Archive
• 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. Full text in Research Archive
• Skaar, Johannes (2019). Intervju av TV2 Nyhetskanalen, kl 0710, om kvantedatamaskiner. [TV]. TV2 Nyhetskanalen. Full text in Research Archive
• Dirdal, Christopher Andrew; Hågenvik, Hans Olaf; Haave, Haakon Aamodt & Skaar, Johannes (2018). Higher order multipoles in metamaterial homogenization. Full text in Research Archive
• Skaar, Johannes (2018). Matematikk i musikk. Full text in Research Archive
• Skaar, Johannes (2018). Fysikk og musikk. Full text in Research Archive
• Skaar, Johannes (2018). Energi - uten en tråd. Full text in Research Archive
• Sævik, Bjørnar Torvholm; Folven, Erik; Jahre, Magnus & Skaar, Johannes (2017). Ein æra er omm. [Internet]. nrk.no. Full text in Research Archive
• Mauren, Arnfinn & Skaar, Johannes (2017). Magisk teknologi kan bety farvel til hacking. [Journal]. Aftenposten Vitenskap. Full text in Research Archive
• 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. [Journal]. Aftenposten. Full text in Research Archive
• Opheim, Aagot & Skaar, Johannes (2017). Vil gi ære, status og høyere lønn til de beste underviserne. [Journal]. Adresseavisen. Full text in Research Archive
• Skaar, Johannes & Tollersrud, Emma (2017). Med lønnsøkning skal underviserne skinne. [Journal]. Morgenbladet. Full text in Research Archive
• Klingenberg, Mathias & Skaar, Johannes (2017). 100 milliarder bilder i sekundet fanger lys som går raskere enn seg selv. [Journal]. Teknisk ukeblad. Full text in Research Archive
• Skaar, Johannes (2017). Musikkens fysikk. Full text in Research Archive
• Sund, Steinar & Skaar, Johannes (2017). Snart kan du lade med klærne. [Journal]. Aftenposten Vitenskap. Full text in Research Archive
• Sande, Anniken & Skaar, Johannes (2017). Her og nå: Dagens gjest. [Radio]. NRK P1. Full text in Research Archive
• Stensvold, Tore & Skaar, Johannes (2017). Norwegian Tech Awards 2017 - WÄRTSILÄ. De lader ferge med 1,2 megawatt effekt - uten fysisk kontakt med fartøyet. [Journal]. Teknisk ukeblad. Full text in Research Archive
• Hågenvik, Hans Olaf; Dirdal, Christopher Andrew & Skaar, Johannes (2016). Homogenization of metamaterials: comparison and analysis. Full text in Research Archive
• Indregard, Sigve & Skaar, Johannes (2016). Til Mars med mikrobølgeovn. [Journal]. Morgenbladet. Full text in Research Archive
• Skaar, Johannes (2016). Magneter, metallrør og usynlighetskapper. Full text in Research Archive
• 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. Full text in Research Archive
• Dirdal, Christopher Andrew; Hågenvik, Hans Olaf & Skaar, Johannes (2016). Higher order terms and origin dependence in metamaterial homogenization. Full text in Research Archive
• Dirdal, Christopher Andrew; Hågenvik, Hans Olaf & Skaar, Johannes (2016). Permittivity, permeability, and the significance of the electrical quadrupole in metamaterials. Full text in Research Archive
• Skaar, Johannes (2016). Kortforedrag om musikk og fysikk. Full text in Research Archive
• Tollersrud, Emma & Skaar, Johannes (2016). «Hvis vi ikke underviser, er det lett å ta elementære ting for gitt.». [Journal]. Morgenbladet. Full text in Research Archive
• 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. Full text in Research Archive
• Hågenvik, Hans Olaf & Skaar, Johannes (2015). Laplace-Fourier analysis and instabilities of an active slab. Full text in Research Archive
• Ramsdal, Roar & Skaar, Johannes (2015). Her sendes 10 kilowatt trådløst. [Internet]. Teknisk ukeblad. Full text in Research Archive
• Skaar, Johannes (2015). Hva er lys? Full text in Research Archive
• Jegtvik, Karin & Skaar, Johannes (2015). Er du vinneren av påskefjellet? [Internet]. nrk.no. Full text in Research Archive
• Dirdal, Christopher Andrew & Skaar, Johannes (2015). Giving Freedom and Physical Meaning to the Effective Parameters of Metamaterials for all Frequencies. Full text in Research Archive
• Skaar, Johannes (2015). Maxwells teori og Hertz' eksperiment – grunnlaget for moderne telekommunikasjon ble skapt for 150 år siden. Full text in Research Archive
• Andreassen, Katrine; Skaar, Johannes; Løland, Anders & Rolén, Tage (2014). Finn ut om du er en sinke på ski. [Internet]. klikk.no. Full text in Research Archive
• Dirdal, Christopher Andrew & Skaar, Johannes (2014). Metamaterial responses beyond the Kramers-Kronig relations. Full text in Research Archive
• Dirdal, Christopher Andrew & Skaar, Johannes (2014). Superposing Lorentzian functions towards engineering target responses. Full text in Research Archive
• Dalløkken, Per Erlien; Skaar, Johannes & Samset, Bjørn Hallvard (2014). «Metamaterialer» skal beskytte piloter mot laserangrep fra bakken. [Internet]. Teknisk ukeblad. Full text in Research Archive
• 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. Full text in Research Archive
• Svendsen, Guro Kristin; Skaar, Johannes; Weman, Helge & Dupertuis, M.-A. (2014). Symmetries and optical transitions of hexagonal quantum dots in GaAs/AlGaAs nanowires. Full text in Research Archive
• Iversen, Marita Løvmo; Jansrud, Line & Skaar, Johannes (2014). Går det an å gjøre noe usynlig? NRK Newton. [TV]. NRK 1. Full text in Research Archive
• 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. Full text in Research Archive
• Brandslet, Steinar; Skaar, Johannes; Løland, Anders & Rolén, Tage (2014). Hvor fort går du på ski? [Journal]. Aftenposten (morgenutg. : trykt utg.). Full text in Research Archive
• Børringbo, Klaus & Skaar, Johannes (2014). Trådløs strøm – snart er den her. [Journal]. Aftenposten. Full text in Research Archive
• Flæten, Sigurd Øygarden & Skaar, Johannes (2013). Laser kan bli fremtidens spionkamera. [Internet]. Teknisk ukeblad. Full text in Research Archive
• Haugen, Vegard & Skaar, Johannes (2013). Døde av elektrosjokk med iPhone 5 i hånden. [Internet]. amobil.no. Full text in Research Archive
• Haugen, Vegard & Skaar, Johannes (2013). Døde av elektrosjokk med iPhone 5 i hånden. [Journal]. VG : Verdens gang. Full text in Research Archive
• Moe, Enok & Skaar, Johannes (2013). Rockheim forstyrrer flytrafikken på Værnes. [Journal]. Adresseavisen. Full text in Research Archive
• Brandslet, Steinar; Skaar, Johannes; Løland, Anders & Rolén, Tage (2013). Hvor fort går du på ski? [Internet]. forsking.no. Full text in Research Archive
• Brandslet, Steinar; Skaar, Johannes; Løland, Anders & Rolén, Tage (2013). Hvor fort går du på ski? [Journal]. Gemini. Full text in Research Archive
• Skaar, Johannes; Løland, Anders; Rolén, Tage & Kokkegård, Hanne (2013). Vild med tal? Tæl dig frem til, om du er hurtigst. [Internet]. dr.dk. Full text in Research Archive
• Lydersen, Lars Vincent Van de Wiel & Skaar, Johannes (2013). Kvantekryptografi. Fra Fysikkens Verden. ISSN 0015-9247. 75(1), p. 10–10. Full text in Research Archive
• Grepstad, Jon Olav; Kaspar, Peter; Johansen, Ib-Rune; Skaar, Johannes; Sudbø, Aasmund & Solgaard, Olav (2012). Optical detection of single biomolecules using photonic-crystal membranes. Full text in Research Archive
• 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. Full text in Research Archive
• Time, Jon Kåre & Skaar, Johannes (2012). I bakvendtland der alt går an. [Journal]. Morgenbladet. Full text in Research Archive
• Time, Jon Kåre & Skaar, Johannes (2012). Trollmannen fra Tyrifjord. [Journal]. Morgenbladet. Full text in Research Archive
• Hågenvik, Hans Olaf & Skaar, Johannes (2019). Analysis of active and passive metamaterials. Norges teknisk-naturvitenskapelige universitet. ISSN 9788232639151. Full text in Research Archive Show summary

  Metamaterials are composite materials acting as effectively continuous media, which are capable of realizing entirely new phenomena such as negative refraction and transformation optics. This class of new materials may therefore in principle make available concepts such as the perfect lens and invisibility cloaks. These materials are thus promised to achieve electromagnetic properties which most certainly go beyond materials found in nature, or ever encountered before, except from perhaps in science fiction. Such media may in general be built up of both active and passive components. New physical phenomena may require new physical models. A thorough investigation should therefore be made regarding the well established mathematical models from earlier research on electromagnetic properties of continuous, as well as structured media. This thesis contributes in various ways to the development of a solid theoretical framework, which can be used in the analysis of such novel materials. Two lines of inquiry are followed. The first part of the thesis considers isotropic, possibly active media, which are described by given material parameters; a permittivity (ω) and a permeability μ(ω). A mathematical framework based on Fourier-Laplace analysis is introduced for representing the response from such media in terms of (possibly complex) frequency- and transversal wavenumber components. The idealization of monochromatic plane waves may for active systems be dangerous due to the presence of growing waves, and the possibility of approaching this limit is investigated by deforming the integration surface in complex frequency-complex wavenumber space. We also give the most general criterion for absolute instabilities. The general theory is used to analyze example media with weak or strong gain. In particular it is used to show the existence of isotropic media which in principle exhibit simultaneous refraction, meaning they refract positively and negatively at the same time. In the second part, the importance of spatial dispersion in metamaterials consisting of passive components is considered. We discuss the importance of higher order multipole terms in homogenization theories for metamaterials. While it is common to include polarization, magnetic dipole and perhaps electric quadrupole terms, it is shown that certain higher order terms are generally significant when second order spatially dispersive effects (e.g. magnetism) are concerned. Based on this notion it is not necessarily clear how the magnetic permeability should be defined. We therefore state and compare four different definitions of the permeability, and analyze their properties in general. As a further investigation of their physical relevance we compare how well the parameters predict the reflection from semi-infinite periodic metamaterial structures. The predictions are based on the Fresnel equation using these four permeabilities. It is found that the Fresnel equation gives accurate results for 2D metamaterials which mimic natural magnetism, in a frequency range where the magnetic moment dominates the O(k2) part of the total Landau-Lifshitz permittivity. For a 1D layered structure, or for large frequencies, the correspondece is poor.

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