Pavlos Savvidis’s research while affiliated with Westlake University and other places

What is this page?


This page lists works of an author who doesn't have a ResearchGate profile or hasn't added the works to their profile yet. It is automatically generated from public (personal) data to further our legitimate goal of comprehensive and accurate scientific recordkeeping. If you are this author and want this page removed, please let us know.

Publications (13)


Optically and remotely controlling localization of exciton-polariton condensates in a potential lattice
  • Article

February 2025

·

7 Reads

Physical Review Applied

Qiang Ai

·

Jan Wingenbach

·

Xinmiao Yang

·

[...]

·


High Quality–Factor All–Dielectric Metacavity for Label–Free Biosensing (Adv. Sci. 4/2025)
  • Article
  • Full-text available

January 2025

·

7 Reads

Download

Illustration of the all‐dielectric analyte medium metacavity. (A) Schematic of the metacavity. A normal plane wave was coupled to the DBR microcavity (characterized by cavity length Lcav). The square lattice dielectric metasurface (characterized by height h, diameter d, and inter‐atom distance a) was embedded at the inner surface of the bottom DBR. Sample solutions were injected into the cavity to directly serve as cavity media. Viral particles selectively adhered to the biorecognition element—a capture antibody immobilized on the silica surface via a silica‐binding protein. (B) Simulated transmission spectra of the bare DBR (grey line), the optimized metacavity ((Lcav = 3000 nm, 10 pair DBR, a = 400 nm, h = 180 nm, d = 200 nm); red line), and the optimized metacavity with intracavity RI increased by 0.01 (red‐dashed line). Experimental absorption spectrum of the SARS‐CoV‐2 pseudovirus solution is presented by the blue area. Detailed views of the three modes are displayed at the bottom part. (C) Left: electric field distribution of the 2nd mode of the optimized metacavity. Right (top): electric field distribution of the bare metasurface at the working wavelength. Right (bottom): electric field distribution of the 2nd mode of the bare microcavity. (D) Electric field distribution of the 1st (left), 2nd (middle), and 3rd (right) mode of the optimized metacavity.
Sensing capabilities of the microcavity and metacavity sensors. (A) Left: Variation of transmittance spectra with respect to DBR pair number change from 5 to 11. Right: Zoom in view of the 2nd mode. (B) Variation of the Q‐factor (blue region), the transmittance intensity (yellow), and FoMBulk (red) with respect to DBR pair number change from 5 to 11. The key parameters of metacavity, together with the illustration of the adsorbate layer (thickness: t) deposited inside the metacavity sensing surface are presented on the left side of the chart. (C) Simulated surface FoM variations of the microcavity sensors with respect to structural parameters (Lcav, a, h, and d) when surface adsorbate layer was varied from 0 to 120 nm. (D) Resonance wavelength shift of the 1st (top), 2nd (middle), and 3rd (bottom) modes of the optimized metacavity (red lines) and bare microcavity (blue lines) with a 100‐nm Al2O3 thin film deposited on the sensing surface.
Fabrication and characterization of the metacavity and bare microcavity sensors. (A) Overview of the metacavity fabrication steps: (i, ii) DBR deposition on a sapphire substrate; (iii) transfer of a large‐scale AAO template; (iv) formation of the metasurface and subsequent (v) mask removal; (vi) SiO2 layer deposition; (vii) Cu tag deposition; and (viii) Cu─Cu bonding. (B) Top: photographs of the bare microcavity (left) and metacavity (right). Bottom: schematic of the microfluidic channel for sample injection. (C) SEM images of the cross section of the cavity (left) and the metasurface (right and top inset image), alongside the AAO template (bottom inset image). (D) Simulation (blue) and experimental (red) normalized transmission spectra of the optimized metacavity and a zoom‐in of the three modes. (E) Experimental Q‐factor variations of the three modes of the optimized metacavity and bare microcavity sensors.
Sensing capabilities of the metacavity and bare microcavity sensors. (A) Normalized transmittance spectra of one of the metacavities with cavity been filled with DI and different concentrations of aqueous ethanol solutions (5–30 vol%) sequentially. (B) Simulation and experimental resonance wavelength shift results of the metacavity with RI change. (C) Experimental Q‐factor, SBulk (left), and FoMBulk (right) of recent photonic resonator refractometric sensors. (D) Simulation and experimental resonance wavelength shift results of the bare microcavity (blue) and metacavity (red) as a function of Al2O3 thin film thickness. (E) Transmittance spectra of one of the metacavities with inner surface deposited with different thicknesses of Al2O3 thin film.
Sensing capabilities of the microcavity and metacavity sensors. (A) Biosensing procedure: (i and ii) cSP protein binding on the bare sensor surface; (iii) oriented functionalization of mAb on the sensing surface; (iv) sensor washing and spectra measurement; (v) pseudovirus sample loading; and (vi) sensor washing and spectra measurement. (B) Normalized experimental transmittance spectra of one of the metacavity sensors in response to different virus concentrations. (C) Normalized simulation transmittance spectra as a function of RI (n, k) change. (D) Normalized experimental transmittance spectra of one of the bare microcavity sensors in response to different virus concentrations. (E) Experimental Q‐factor changes in the metacavity (red) and bare microcavity (blue) sensors in response to different virus concentrations. (F) Experimental resonance wavelength shifts in the metacavity (red) and bare microcavity (blue) in response to different virus concentrations. The electric field distribution change with the variation in simulated RI values is also presented.
High Quality–Factor All–Dielectric Metacavity for Label–Free Biosensing

November 2024

·

168 Reads

High sensitivity and high quality‐factor are crucial for achieving outstanding sensing performance in photonic biosensors. However, strong optical field confinement and high light–biomolecule interactions on photonic surfaces are usually contradictory and challenging to satisfy simultaneously. Here, a distinctive configuration for addressing this issue is reported: embedding a nanophotonic metasurface inside a micro vertical cavity as a meta‐channel (metacavity) biosensor. The analyte solution serves as the cavity medium, thereby maximizing the light–analyte interaction. Simulation validation is conducted to optimize the metacavity with high structural robustness and remarkable optical and sensing properties. Large‐scale low‐cost metacavity biosensors are realized by combining anodic aluminum oxide template technique and wafer bonding. Experimentally, the metacavity biosensor demonstrates a notable quality‐factor (maximum 4140) and high bulk refractometric sensitivity (450 nm RIU⁻¹), resulting in an unprecedented figure‐of‐merit (1670 RIU⁻¹). Moreover, the metacavity biosensor achieves high surface sensitivity, together with a detection‐limit of 119 viral copies mL⁻¹ for label‐free severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) pseudovirus sensing, revealing remarkable performance in both bulk and surface sensing.


Qubit analog with polariton superfluid in an annular trap

October 2024

·

34 Reads

·

6 Citations

Science Advances

We report on the experimental realization and characterization of a qubit analog with semiconductor exciton-polaritons. In our system, a polaritonic condensate is confined by a spatially patterned pump laser in an annular trap that supports energy-degenerate vortex states of the polariton superfluid. Using temporal interference measurements, we observe coherent oscillations between a pair of counter-circulating vortex states coupled by elastic scattering of polaritons off the laser-imprinted potential. The qubit basis states correspond to the symmetric and antisymmetric superpositions of the two vortex states. By engineering the potential, we tune the coupling and coherent oscillations between the two circulating current states, control the energies of the qubit basis states, and initialize the qubit in the desired state. The dynamics of the system is accurately reproduced by our theoretical two-state model, and we discuss potential avenues to implement quantum gates and algorithms with polaritonic qubits analogous to quantum computation with standard qubits.




Figure 1. Vortex-superposition polaritonic qubit. A pump laser creates a Mexican hat-shaped potential for the polaritonic condensate (b). The potential supports two energy-degenerate counter-propagating polariton modes |⟲⟩ , |⟳⟩ (a, c), which are coupled with rate Ω by small defects or ellipticity of the trapping potential. The resulting superpositions (|⟲⟩ ± |⟳⟩)/ √ 2 of the two vortex modes form vertically and horizontally oriented two-lobe eigenmodes (d,f) that represent the qubit basis states |0, 1⟩ energy-split by ∓Ω (e). Another pair of states (|⟲⟩ ± i |⟳⟩)/ √ 2 with diagonally oriented lobes (g,i) represents the third axis of the Bloch sphere (h) for the continuum of states of the system. In panels (a, c, d, f, g, i) the shading is proportional to the amplitude of the polaritonic condensate and the color encodes its phase varying from 0 to 2π.
Figure 2. Polariton condensate in an annular trap. a. Integrated photoluminescence spectrum of polaritons vs the pumping strength P, with inset illustrating the schematics of the measurement. Slightly above the condensation threshold P = 1.2P th (dashed vertical line), the polaritons condense to the vortex states with orbital angular momenta l = ±1 having the same energy. b. Polariton condensate intensity (profile height) and spatially-resolved degree of circular polarization (color) for σ − (top) or σ + (bottom) polarized pump laser. The circularly polarized pump generates polariton condensate with the same spatially-uniform polarization. c. Polariton condensate photoluminescence (red) for increasing (from left to right) ratios of the horizontal and vertical axes of the elliptic profile of the pump laser (blue).
Figure 3. Interferometric measurement of the system dynamics. Time-averaged spatial interferograms of the polaritonic condensate at four different delay times τ = −0.18, −0.08, 0, 0.08 ns between the signal beam and the reference taken at ρ 0 ≃ ρ c and θ 0 ≃ π/4, as obtained from the experimental measurements (a) and theoretical model (b). The condensate amplitude extracted from the interferometric images and magnified view of the center of interferograms reveal the presence or absence of singularity (fork-shaped interference fringes) associated with the vortex states (small panels e, f, g, h). The polariton wavefunction ψ exhibits continuous Rabi oscillations with frequency Ω between the two vortex states |⟲⟩ and |⟳⟩, quantified by vorticities | ⟨ψ| ⟲, ⟳⟩ | 2 . Introducing a potential barrier that enhances the scattering between the vortex states increases the oscillation frequency (lower panel in c). On the Bloch sphere, the dynamics of the system corresponds to the spin precession in the zy plane slightly biased towards x direction (ground state |0⟩) (d).
Superfluid Polaritonic Qubit in an Annular Trap

August 2023

·

309 Reads

We report on the experimental realization and characterization of an exciton-polariton qubit prototype. In our system, a Bose-Einstein condensate of semiconductor exciton-polaritons is confined by a spatially-patterned pump laser in an annular trap that supports energy-degenerate circulating currents of the polariton superfluid. Using non-invasive temporal interference measurements, we observe coherent oscillations between a pair of counter-circulating superfluid vortex states of the polaritons coupled by elastic scattering off the laser-imprinted potential. The qubit basis states correspond to the symmetric and antisymmetric superpositions of the two vortex states forming orthogonal double-lobe spatial wavefunctions. By engineering the potential, we tune the coupling and coherent oscillations between the two circulating current states, control the energies of the qubit basis states and thereby initialize the qubit in the desired state. The dynamics of the system is accurately reproduced by our theoretical two-state model, and we discuss potential avenues to achieve complete control over our polaritonic qubit and implement controllable interactions and quantum gates between such qubits.


Persistent Room-Temperature Valley Polarization in Graphite-filtered WS2 Monolayer

March 2023

·

54 Reads

·

4 Citations

Transition metal dichalcogenide (TMD) monolayers (1L) in the 2H-phase are two-dimensional semiconductors with two valleys in their band structure that can be selectively populated using circularly polarized light. The choice of the substrate for monolayer TMDs is an essential factor for the optoelectronic properties and for achieving a high degree of valley polarization at room temperature (RT). In this work, we investigate the room-temperature valley polarization of monolayer WS2 on different substrates. A degree of polarization of photoluminescence (PL) in excess of 27% is found from neutral excitons in 1L-WS2 on graphite at room temperature, under resonant excitation. Using chemical doping through photochlorination we modulate the polarization of the neutral exciton emission from 27% to 38% for 1L-WS2/graphite. We show that the valley polarization strongly depends on the interplay between doping and the choice of the supporting layer of TMDs. Time-resolved PL measurements, corroborated by a rate equation model accounting for the bright exciton population in the presence of a dark exciton reservoir support our findings. These results suggest a pathway towards engineering valley polarization and exciton lifetimes in TMDs, by controlling the carrier density and/or the dielectric environment at ambient conditions.



Switching off microcavity polariton condensate near the exceptional point

January 2021

·

152 Reads

·

1 Citation

Gain and loss modulation are ubiquitous in nature. An exceptional point arises when both the eigenvectors and eigenvalues coalesce, which in a physical system can be achieved by engineering the gain and loss coefficients, leading to a wide variety of counter-intuitive phenomena. In this work we demonstrate the existence of an exceptional point in an exciton polariton condensate in a double-well potential. Remarkably, near the exceptional point, the polariton condensate localized in one potential well can be switched off by an additional optical excitation in the other well with very low (far below threshold) laser power which surprisingly induces additional loss into the system. Increasing the power of the additional laser leads to a situation in which gain dominates in both wells again, such that the polaritons re-condense with almost the same density in the two potential wells. Our results offer a simple way to optically manipulate the polariton lasing process in a double-well potential structure. Extending such configuration to complex potential well lattices offers exciting prospects to explore high-order exceptional points and non-Hermitian topological photonics in a non-equilibrium many-body system.


Citations (6)


... 12 Recently, polaritonic qubits have been generated for the realization of quantum gates and algorithms, analogous to quantum computation with standard qubits. 13,14 Flexibly creating and manipulating exciton polaritonic states with specific energy and momentum is crucial for applications in photonics and quantum technologies. 15,16 The tunable momentum of polaritons introduces more allowed scattering processes in reciprocal space, in which polaritons can participate, facilitating the directional control of radiation and other scattering processes. ...

Reference:

Guiding polaritonic energy and momentum through two-dimensional Bravais lattices
Qubit analog with polariton superfluid in an annular trap

Science Advances

... 15 and 24) In addition, this process assists in sustaining large degrees of VP at room temperature. 25 Finally, after following a quality assessment procedure, incorporating lPL, and reflectance experiments, the complete heterostructure is encapsulated in poly-methyl methacrylate (PMMA, Microchem) and transferred on top of an elastic substrate with a cruciform shape (see detailed methodology in the supplementary material, Sec. A, Fig. S1). ...

Persistent Room-Temperature Valley Polarization in Graphite-filtered WS2 Monolayer

... The selection of examples is designed to illustrate the capabilities of PHOENIX and to cover various variations of the equations implemented as well as a number of different variants, types, and possibilities of post-processing that can be performed. Applications include extensions of our previous research [36,37,38,39,40] covering the fields of topology, non-Hermitian physics, nonlinear physics, and quantum-state tomography based on Monte Carlo simulations with quantum noise. This relatively broad spectrum of examples is intended to help the easy and widespread use of PHOENIX and its adaptation to other interesting scenarios. ...

Switching Off a Microcavity Polariton Condensate near the Exceptional Point
  • Citing Article
  • June 2022

ACS Photonics

... Surface charge transfer-based doping [11], substitutional doping [12], interstitial doping [13], and vacancy-based doping [14] are the main post-growth doping mechanisms for 2D-TMDs [15]. Based on these mechanisms, there are several reported doping techniques such as chemical treatment [13], ion implantation [16], plasma doping [17], thermal annealing [18], electron beam irradiation [19], and ultraviolet-ozone (UV-O3) treatment [20], which aim to achieve n-and/or p-type doping. Due to the high sensitivity of 2D materials' properties, the main challenge in post-growth doping is to maintain their superb optoelectrical properties for device applications, while controlling the doping concentration with consistency. ...

Impact of thermal annealing in forming gas on the optical and electrical properties of MoS2 monolayer

... Thus, polariton condensation is necessarily accompanied by the formation of an incoherent uncondensed excitonic reservoir [8]. Such a reservoir can also manifest itself indirectly in experiments via its repulsive interactions with polaritons [19][20][21][22], allowing the creation of on-demand trapping potentials by spatially selective laser excitation [23][24][25][26][27]. ...

Polariton Condensate Trapping by Parametric Pair Scattering

... A polariton dyad represents a pair of polariton condensates excited by localized optical beams in a plane of a microcavity, separated by a distance d from each other, see Fig. 1c-e. Excitation is performed in the nonresonant regime, where the energy of an excitation beam is considerably (tens of meV) higher than the polariton energy 41,42 . Such a pump creates a reservoir of incoherent high-energy excitons (see Fig. 1c), which in turn feeds the polariton condensate. ...

Persistent Currents in Half-Moon Polariton Condensates
  • Citing Article
  • April 2020

ACS Photonics