Nascent quantum metamaterials

Fig. 1: Schematic of a new polaritonic approach to metamaterials design. The metamaterial is made of a collection of linear and nonlinear polaritonic meta-blocks. Meta-blocks rigorously incorporate multiphysics of light–matter interactions by considering internal degrees of freedom (quasiparticles) of condensed matter constituents.

Despite unprecedented success in design capabilities and realization of artificial electromagnetic media, the photonics community faces challenges in overcoming many critical limitations. Such limits of light-matter interactions and nonlinear effects remain a major obstacle towards application of metamaterials in many practical applications and lead to the saturation in the field.

This saturation can be largely attributed to the failure of the phenomenological approach prevailing today in describing light-matter interactions. In this approach, matter is considered only phenomenologically by its effective response, which is described, for instance, by its electric and magnetic polarizabilities.

The goal of this project is to develop a fundamentally different approach in designing artificial optical materials by rigorously treating the matter-response component of the light-matter interactions. To achieve this goal, we introduce a concept of polaritonic building blocks and apply it to engineer desirable linear and nonlinear responses of the hybrid quantum optical materials. The use of polaritonic building blocks described by effective solid-state Hamiltonians and Green-functions, rather than effective linear and nonlinear polarizabilities, will allow to precisely include multiphysics of light-matter interactions and to revise the current traditional views on physics of metamaterials.

As the first step in our approach we determine material-specific effective Hamiltonian of meta-blocks and we will include interactions with optical fields (shown by vector potentials in Fig. 1). Spatial symmetry of the meta-blocks will be deliberately analyzed to maximize interaction with external electromagnetic fields. This step will yield a “maximally dressed” photonic propagator which rigorously considers optimized polaritonic response of the meta-block (Fig. 1, middle panels). Next, the blocks will be arranged into a metamaterials and the electromagnetic interactions been the blocks will be considered by including multiple scattering effects. At this stage the role of geometry of the arrangement and especially its symmetry will play crucial role. The response of meta-blocks strongly depends on the characteristics of the electromagnetic field, its intensity, polarization state, and chirality, due to the internal symmetries of polaritonic states. By controlling the symmetry at the two levels (meta-block and metamaterial) we have the possibility to translate unique characteristic of internal degrees of freedom of materials to the level of effective photonic response.

As part of this project we investigate theoretically and experimentally how such responses as nonreciprocity and nonlinear effects can be enhanced and optimized by coupling photons to electronic subsystem of meta-blocks. We investigate how polaritonic meta-blocks respond in the presence of magnetic bias and optimize design of metamaterials to achieve regimes of one-way propagation.

In addition, we will apply a novel approach to nonreciprocity by breaking time-reversal symmetry via modulation of polaritonic characteristics in time. In two-dimensional materials short relaxation times allow modulating their properties at very high rates by optical pumping, which is a promising approach to nonreciprocity, and also envisions a new approach to topological photonics by designing polaritonic Floquet topological insulators.

Metamaterials for Bio-Sensing Applications

Fig.2: Schematics of proteins deposited on top of high-Q resonant metasurface.

The bio-oriented research program in our lab is aiming to facilitate in-depth characterization of bio-molecules and/or bio-molecular kinetics with the use of plasmonic and all-dielectric nanostructures and metamaterials supporting engineered high-quality resonances[1]. The main advantage of the nanostructures bring to bio-sensing and bio-monitoring stems from their two unique properties. First, they exhibit spectrally narrow high-quality electromagnetic resonances accompanied by the strong near-field enhancement, which enhances response to the analyte. Secondly, the spectral positions of the resonances and their quality factors are highly tunable by scaling dimensions and geometry of the nanoelements constituting the structure. These features enabled a novel approach to infrared spectroscopy of single and compound bio-molecules that we have recently demonstrated [1], resolving IR fingerprints of biomolecules to an unprecedented degree and extracting information about the secondary structure of the proteins.

Currently, we are pushing research beyond of what we have previously achieved. In particular, we are investigating interactions between proteins and artificial electromagnetic resonances when bio-molecules are affected by an external stimuli (dc bias to induce proton transfer, heat and photo-induced denaturation, etc) and establishing tools to resolve dynamics of the system when proteins experience structural changes induced by such external stimuli. To perform studies of proteins under such external stimulae, we have recently developed novel designs of electrically connected high-Q Fano resonant metasurfaces, which can be used to bias bio-molecules by applying external DC electric field, or pass currents to cause rapid increase of temperature. Proteins are known to exhibit conformational changes in the external field and this is the first priority subject of our bio-oriented program. These changes are investigated by conducting the time-resolved spectroscopy with the use of pulsed quantum cascade laser producing pulses down to 20ns and fast MCT detector (300KHz), which allows resolving change in the structure of proteins on a nanosecond time scale.

[1] C. Wu, A.B. Khanikaev, N. Arju, R. Adato, A.A. Yanik, H. Altug, and G. Shvets,“Fano-resonant asymmetric metamaterials for ultra-sensitive spectroscopy and identification of molecular monolayers”, Nature Mater. 11, 69–75 (2012).

Photonic topological insulators in optical and RF domains

Recent advances in understanding of topological phases and discovery of novel materials with topological order, such as topological insulators, have overturned our views on condensed states of matter. I have recently demonstrated that artificial electromagnetic structures represent a unique platform for realization of photonic topologically nontrivial phases and excitations [1].

This can be achieved by the same key ingredients previously found necessary in their condensed matter counterparts, such as spin of photons and spin-orbital coupling engineered in a new class of artificial media – photonic metacrystals. We demonstrated that by judiciously choosing metamaterials’ parameters one can observe photonic phases analogous to those of topological insulator and characterized by a presence of a guided edge states robust to different type of disorder and structural imperfections [2,3,4].

[1] Khanikaev, A. B. et al. Nature Materials 12, 233 (2013),

[2] A. Slobozhanyuk, S. H. Mousavi, X. Ni, D. Smirnova, Y. S. Kivshar, and A. B. Khanikaev, Nature Photonics 11, 130 (2017).

[3] A. B. Khanikaev, G. Shvets, Nature Photonics 11, 763 (2017).

[4] M. A. Gorlach, …, A. B. Khanikaev, Nature Communications, 9, 909 (2018).

Ultra-compact Nonreciprocal Optical Elements

Nonreciprocity is of immense value in optics governing a key elements of photonic circuits - isolators (or “optical diodes”), which enforce one-way propagation being used to protect optical components from reflected light, and circulators, which allow the construction of unidirectional circular paths.

As photonics moves into the sub-micron regime, the techniques enabling nonreciprocal devices at this scale should be developed. Scaling down optical devices to nanoscale dimensions and their integration in photonic circuits requires novel approaches to light manipulation. One of the possible approaches, which hold the great promise for the whole field of photonics, is a concept of metamaterials - artificial structures that display properties beyond those occurring in Nature.

Development of the nonreciprocal optical devices was one of the major topics of our research leading to a number of publication (five recent publications [1-5]). Because of significant industrial needs in ultra-compact nonreciprocal optical elements in a broad variety of applications, ranging from telecommunications, to on-chip integration of the optical and electronic circuits, laser systems, magneto-optical spatial light modulators, we pursue research in this area and extending our approaches to design novel and practical nonreciprocal optical devices.

The structures we study represent arrays of subwavelength-sized optical resonators, embedded into optically active, nonlinear or magnetic environment. When electromagnetic waves interact with such a structure, optically active components act on the optical field in a way, that effective parameters perceived by the wave is different for opposite (e.g. forward and backward) directions. This enables a unique response of the structure when the guided signal couples to it and the whole structure behaves as a photonic diode, transmitting light only in one direction, while stopping (reflecting or absorbing) it in the opposite direction. The main advantage of the proposed metamaterials as compared to its contemporary photonic counterparts stems from nano-scale patterning. Thanks to the ability of nanostructures to trap light on such the scale, the devices can be rendered as compact as several wavelengths of light.

[1] A. B. Khanikaev, S. H. Mousavi, G. Shvets, and Y. S. Kivshar, “One-way extraordinary optical transmission and nonreciprocal spoof plasmons”, Phys. Rev Lett. 105, 126804 (2010),

[2] A. Khanikaev (corresponding author), A. Alù, Silicon photonics: One-way photons in silicon, Nature Photonics 8, 680 (2014).

[3] S. H. Mousavi, A.B. Khanikaev (corresponding author, equal contributor), J. Allen, M. Allen, G. Shvets, Gyromagnetically Induced Transparency of Metasurfaces, Physical Review Letters 112 , 1174021 (2014).

[4] A. Levyev, B. Stein, A. Christofi, T. Galfski, H. Chakramurti, I. Kuskovsky, V. Menon, A. B. Khanikaev, Nonreciprocity and one-way topological transitions in hyperbolic metamaterials, APL Photonics 2, 076103 (2017).

[5] A. Christofi, Y. Kawaguchi, A. Alù, A. B. Khanikaev, Giant enhancement of Faraday rotation due to electromagnetically induced transparency in all-dielectric magneto-optical metasurfaces, Optics Letters 43 (8), 1838-1841 (2018).