arXiv subjects

Tsampikos Kottos

Publications and source records attributed to Tsampikos Kottos.

At least 55 records · Page 3Linked to original sources

arXiv2020

Orientation-sensed Optomechanical Accelerometers based on Exceptional Points

We propose an optomechanical design, consisting of a parity-time symmetric multilayer structure tuned at exceptional-point degeneracy (EPD), with an adjustable layer that is coupled to micromechanical springs. The deflections of this layer in response to accelerations $α$, lead to square-root resonance detuning $Δω\equivω-ω_{EPD}\propto \sqrtα$ - thus dramatically enhancing the probe of ultra-small accelerations $α\ll1$. Our design is scalable and can, in principle, support higher $N$ order EPDs with sensitivity $Δω\propto\sqrt[n]α$. It also provides a pathway towards a new generation of on-chip hypersensitive accelerometers and vibrometers.

physics.app-ph↗

arXiv2019

Optical Phase Transitions in Photonic Networks: A Spin System Formulation

We investigate the collective dynamics of nonlinearly interacting modes in multimode photonic settings with long-range couplings. To this end, we have established a connection with the theory of spin networks. The emerging "photonic spins" are complex, soft (their size is not fixed) and their dynamics has two constants of motion. Our analysis shed light on the nature of the thermal equilibrium states and reveals the existence of optical phase-transitions which resemble a paramagnetic to a ferromagnetic and to a spin-glass phase transitions occurring in spin networks. We show that, for fixed average optical power, these transitions are driven by the type (constant or random couplings) of the network connectivity and by the total energy of the optical signal.

cond-mat.dis-nn↗

arXiv2019

Microwave limiters implemented by coupled dielectric resonators based on a topological defect mode and CT-symmetry breaking

We present a microwave realization of a reflective topological limiter based on an explicit self-induced violation of a charge-conjugation (CT) symmetry. The starting point is a bipartite structure created by coupled dielectric resonators with a topological defect placed at the center and two lossy resonators placed on the neighboring sites of the defect. This defect supports a resonant mode if the CT-symmetry is present, while it is suppressed once the symmetry is violated due to permittivity changes of the defect resonator associated with high irradiances of the incident radiation. This destruction leads to a suppression of transmittance and a subsequent increase of the reflectance while the absorption is also suppressed.

physics.app-ph↗

arXiv2019

Adiabatic Thermal Radiation Pumps for Thermal Photonics

We control the direction and magnitude of thermal radiation, between two bodies at equal temperature (in thermal equilibrium), by invoking the concept of adiabatic pumping. Specifically, within a resonant near-field electromagnetic heat transfer framework, we utilize an {\it instantaneous} scattering matrix approach to unveil the critical role of wave interference in radiative heat transfer. We find that appropriately designed adiabatic pumping cycling near diabolic singularities can dramatically enhance the efficiency of the directional energy transfer. We confirm our results using a realistic electronic circuit set-up.

physics.optics↗

arXiv2018

Coherent Wave Propagation in Multi-Mode systems with Correlated Noise

Imperfections in multimode systems lead to mode-mixing and interferences between propagating modes. Such disorder is typically characterized by a finite correlation time (in quantum evolution) or correlation length (in paraxial evolution). We show that the long-scale dynamics of an initial excitation that spread in mode space can be tailored by the coherent dynamics on short-scale. In particular we unveil a universal crossover from exponential to power-law ballistic-like decay of the initial mode. Our results have applications to various wave physics frameworks, ranging from multimode fiber optics to quantum dots and quantum biology.

cond-mat.dis-nn↗

arXiv2018

Asymmetric Acoustic Energy Transport in Non-Hermitian Metamaterials

The ability to control and direct acoustic energy is essential for many engineering applications such as vibration and noise control, invisibility cloaking, acoustic sensing, energy harvesting, and phononic switching and rectification. The realization of acoustic regulators requires overcoming fundamental challenges inherent to the time-reversal nature of wave equations. Typically, this is achieved by utilizing either a parameter that is odd-symmetric under time-reversal or by introducing passive nonlinearities. The former approach is power consuming while the latter has two major deficiencies: it has high insertion losses and the outgoing signal is harvested in a different frequency than that of the incident wave due to harmonic generation. Here, we adopt a unique approach that exploits spatially distributed linear and nonlinear losses in a fork-shaped resonant metamaterial. Our compact design demonstrates asymmetric acoustic reflectance and transmittance, and acoustic switching. In contrast to previous studies, our non-Hermitian metamaterial exhibits asymmetric transport with high frequency purity of the outgoing signal.

physics.app-ph↗

arXiv2018

Design algorithms of driving-induced nonreciprocal components

We utilize an effective Hamiltonian formalism, within the Floquet scattering framework, to design a class of driving-induced non-reciprocal components with {\it minimal} complexity. In the high driving-frequency limit, where our scheme is formally applicable, these designs demonstrate a leading order non-reciprocal performance which is inverse proportional to the driving frequency. Surprisingly, the optimal non-reciprocal behavior persists also in the slow driving regime. Our approach highlights the importance of physical loops in the design of these driven non-reciprocal components.

physics.app-ph↗

arXiv2018

Unidirectional Photonic Circuit with Phase-Change Fano Resonator

We demonstrate that the integration of a phase-change material (PCM) in one of the two microresonators of a photonic metamolecule, coupled to a bus waveguide, can lead to unidirectional Fano resonances and to the emergence of a unidirectional transmission window. The phase change is caused by light-induced heating and is accompanied by an abrupt increase in the extinction coefficient of the PCM resonator. Due to the photonic circuit asymmetry, the critical value of the input light intensity triggering the phase change is strongly dependent on the input light direction. The latter determines the unidirectional nature of the emerging transmission window. This effect can be utilized in on-chip magnetic-free isolators and Q-switches.

physics.optics↗

arXiv2018

Floquet Scattering Theory based on Effective Hamiltonians of Driven Systems

The design of time-independent effective Hamiltonians that describe periodically modulated systems, provides a promising approach to realize new forms of matter. This, so-called, Floquet engineering approach is currently limited to the description of wavepacket dynamics. Here, we utilize the notion of effective Hamiltonians and develop a Floquet engineering scattering formalism that relies on a systematic high-frequency expansion of the scattering matrix. The method unveils the critical role of micromotion. An application to the case of non-reciprocal transport is presented.

cond-mat.mes-hall↗

arXiv2018

Floquet Perfect Absorbers based on Periodically Driven Targets

We introduce the concept of multichannel Floquet Perfect Absorbers (FPAs) which are periodically modulated lossy interferometric traps that completely absorb incident monochromatic waves. The proposed FPA protocols utilize a Floquet engineering approach which inflicts a variety of emerging phenomena and features: reconfigurability of perfect absorption (PA) for a broad range of frequencies of the incident wave; PA for infinitesimal local losses, and PA via critical coupling with high-Q modes by inducing back-reflection dynamical mirrors.

physics.optics↗

arXiv2018

Driving-induced metamorphosis of transport in arrays of coupled resonators

We propose a new driving scheme, when different parts of a system are driven with different, generally incommensurate, frequencies. Such driving provides a flexible handle to control various properties of the system and to obtain new types of effective (static) Hamiltonians with arbitrary static on-site potential, be it deterministic or random. This allows us to obtain reconfigurable changes in transport, from ballistic to localized (including sub- and super-diffusion), depending on the driving protocol. The versatile reconfigurability extends also to scattering from (locally) driven extended targets. We demonstrate our scheme using, an analytically solvable example, of an one-dimensional tight-binding chain with appropriately driven couplings between nearby sites.

physics.optics↗

arXiv2018

Towards a Floquet-Network Theory of Non-Reciprocal Transport

We develop a theoretical framework that lays out the fundamental rules under which a periodic (Floquet) driving scheme can induce non-reciprocal transport. Our approach utilizes an extended Hilbert space where a Floquet network with an extra (frequency) dimension naturally arises. The properties of this network (its on-site potential and the intersite couplings) are in one-to-one correspondence with the initial driving scheme. Its proper design allows for a control of the multipath scattering processes and the associated interferences. We harness this degree of freedom to realize driving schemes with narrow or broad-band non-reciprocal transport.

physics.optics↗

arXiv2017

Statistical Design of Chaotic Waveforms with Enhanced Targeting Capabilities

We develop a statistical theory of waveform shaping of incident waves that aim to efficiently deliver energy at weakly lossy targets which are embedded inside chaotic enclosures. Our approach utilizes the universal features of chaotic scattering -- thus minimizing the use of information related to the exact characteristics of the chaotic enclosure. The proposed theory applies equally well to systems with and without time-reversal symmetry.

cond-mat.dis-nn↗

arXiv2017

Floquet Protocols of Adiabatic State-Flips and Re-Allocation of Exceptional Points

We introduce the notion of adiabatic state-flip of a Floquet Hamiltonian associated with a non-Hermitian system that it is subjected to two driving schemes with clear separation of time scales. The fast (Floquet) modulation scheme is utilized to re-allocate the exceptional points in the parameter space of the system and re-define the topological features of an adiabatic cyclic modulation associated with the slow driving scheme. Such topological re-organization can be used in order to control the adiabatic transport between two eigenmodes of the Floquet Hamiltonian. The proposed scheme provides a degree of reconfigurability of adiabatic state transfer which can find applications in system control in photonics and microwave domains.

physics.optics↗

arXiv2017

Frozen Mode Regime in Finite Periodic Structures

Periodic structures with Bloch dispersion relation supporting a stationary inflection point (SIP) can display a unique scattering feature, the frozen mode regime (FMR). The FMR is much more robust than common cavity resonances; it is much less sensitive to the boundary conditions, structural imperfections, and losses. Using perturbation theory, we analyze the FMR in the realistic case of a finite fragment of a periodic structure. We show that in close proximity of SIP frequency, the character of the FMR is qualitatively different from the known case of a semi-infinite structure.

physics.optics↗

arXiv2017

Distribution of zeros of the S-matrix of chaotic cavities with localized losses and Coherent Perfect Absorption: non-perturbative results

We employ the Random Matrix Theory framework to calculate the density of zeroes of an $M$-channel scattering matrix describing a chaotic cavity with a single localized absorber embedded in it. Our approach extends beyond the weak-coupling limit of the cavity with the channels and applies for any absorption strength. Importantly it provides an insight for the optimal amount of loss needed to realize a chaotic coherent perfect absorbing (CPA) trap. Our predictions are tested against simulations for two types of traps: a complex network of resonators and quantum graphs.

cond-mat.dis-nn↗

arXiv2017

Random Matrix Theory Approach to Chaotic Coherent Perfect Absorbers

We employ Random Matrix Theory in order to investigate coherent perfect absorption (CPA) in lossy systems with complex internal dynamics. The loss strength $γ_{\rm CPA}$ and energy $E_{\rm CPA}$, for which a CPA occurs are expressed in terms of the eigenmodes of the isolated cavity -- thus carrying over the information about the chaotic nature of the target -- and their coupling to a finite number of scattering channels. Our results are tested against numerical calculations using complex networks of resonators and chaotic graphs as CPA cavities.

cond-mat.dis-nn↗

arXiv2017

Experimental realization of Floquet PT-symmetric systems

We provide an experimental framework where periodically driven PT-symmetric systems can be investigated. The set-up, consisting of two UHF oscillators coupled by a time-dependent capacitance, demonstrates a cascade of PT-symmetric broken domains bounded by exceptional point degeneracies. These domains are analyzed and understood using an equivalent Floquet frequency lattice with local PT-symmetry. Management of these PT-phase transition domains is achieved through the amplitude and frequency of the drive.

physics.class-ph↗