Quantum technologies play a pivotal role in driving transformative advancements across diverse fields, surpassing classical approaches and empowering us to address complex challenges more effectively; however, the need for ultra-low temperatures limits the use of these technologies to particular fields. This work comes to alleviate this problem. We present a way of phononic bandgap engineering using FEM by which the radiative mechanical energy dissipation of a nanomechanical oscillator can be significantly suppressed through coupling with a complementary oscillating mode of a defect of the surrounding phononic crystal (PnC). Applied to an optomechanically coupled nanobeam resonator in the megahertz regime, we find a mechanical quality factor improvement of up to four orders of magnitude compared to conventional PnC designs. As this method is based on geometrical optimization of the PnC and frequency matching of the resonator and defect mode, it is applicable to a wide range of resonator types and frequency ranges. Taking advantage of the, hereinafter referred to as, "regenerative coupling" in phononic crystals, the presented device is capable of reaching f × Q products exceeding 10E16 Hz with only two rows of PnC shield. Thus, stable quantum states with mechanical decoherence times up to 700 μs at room temperature can be obtained, offering new opportunities for the optimization of mechanical resonator performance and advancing the room temperature quantum field across diverse applications.

The development and optimization of photonic devices and various other nanostructure electromagnetic devices present a computationally intensive task. Much optimization relies on finite-difference time-domain or finite element analysis simulations, which can become very computationally demanding for finely detailed structures and dramatically reduce the available optimization space. In recent years, various inverse design machine learning (ML) techniques have been successfully applied to realize previously unexplored optimization spaces for photonic and quantum photonic devices. In this review, recent results using conventional optimization methods, such as the adjoint method and particle swarm, are examined along with ML optimization using convolutional neural networks, Bayesian optimizations with deep learning, and reinforcement learning in the context of new applications to photonics and quantum photonics.

When synthetic dyes are used to embellish the world, the wastewater holding these hazardous materials is wantonly released into the biosphere.Appropriate treatment for such effluents is thereby indispensable.In this context, the present study was conducted to fabricate an eco-friendly, cost-effective and new bismuth modified silicon nanowires (Bi@SiNWs)-based photocatalysts toward superior photocatalytic degradation of methylene blue (MB) dye under both UV and solar irradiations.SiNWs were synthesized by silver-assisted chemical etching while Bi nanoparticles were anchored onto the NWs via thermal evaporation.By assessing the morphology, elemental composition, structure and crystallinity characteristics, these Bi@SiNWs nanocomposites are systematically identified.Extensive investigations of blank SiNWs and Bi@SiNWs optical propertiesreflectance, transmittance, absorption coefficient, absorbance and optical band-gap -are presented.Near-perfect absorbance above 97%, over the visible wavelength region, has been achieved owing to the synergistic effect of Bi decoration on SiNWs.Accordingly, Bi@SiNWs showed remarkable photocatalytic ability for the degradation of MB up to 44% and 89% under UV and solar irradiation, respectively, only within 120 min.Repeated cycle runs revealed that the Bi@SiNWs composite photocatalyst exhibits strong reusability and photo-stability.Lastly, we will thoroughly provide the plausible mechanism for the photocatalytic degradation of MB over Bi@SiNWs.Our outcomes validate the potent role of Bi@SiNWs photocatalysts for effective environmental remediation.

An easy and low-cost way to fabricate monometallic Au nanoislands for plasmonic enhanced spectroscopy is presented. The method is based on direct thermal evaporation of Au on glass substrates to form nanoislands, with thicknesses between 2 and 15 nm, which are subsequently covered by a thin layer of silicon dioxide. We have used HR-SEM and AFM to characterize the nanoislands, and their optical transmission reveals strong plasmon resonances in the visible. The plasmonic performance of the fabricated substrates has been tested in fluorescence and Raman scattering measurements of two probe materials. Enhancement factors up to 1.8 and 9×104 are reported for confocal fluorescence and Raman microscopies, respectively, which are comparable to others obtained by more elaborated fabrication procedures.

Integrated optics is an exciting platform to achieve optical measurement of T in the micro and nanoscale with high accuracy and reliability. Nevertheless, silicon microrings are affected by two-photon absorption (TPA) that limits the sensitivity of the devices because of self-heating. Wide-bandgap materials can overcome this problem. In this talk I will present some examples of the use of GaN and diamond-based microdisks that surpass the limits of silicon-based microrings. Also, silicon nitride nanomembranes have been used to obtain high-temperature resolution down to 15 K at room T.

Single photon sources (SPS) based on semiconductor quantum dot (QD) platforms are restricted to low temperature (T) operation due to the presence of strong dephasing processes. Although the integration of QD in optical cavities provides an enhancement of its emission properties, the technical requirements for maintaining high indistinguishability (I) at high T are still beyond the state of the art. Recently, new theoretical approaches have shown promising results by implementing two-dipole-coupled-emitter systems. Here, we propose a platform based on an optimized five-dipole-coupled-emitter system coupled to a cavity which enables perfect I at high T. Within our scheme the realization of perfect I single photon emission with dissipative QDs is possible using well established photonic platforms. For the optimization procedure we have developed a novel machine-learning approach which provides a significant computational-time reduction for high demanding optimization algorithms. Our strategy opens up interesting possibilities for the optimization of different photonic structures for quantum information applications, such as the reduction of quantum decoherence in clusters of coupled two-level quantum systems.

In this paper, we report a novel design of bismuth nanoparticle-passivated silicon nanowire (Bi@SiNW) heterojunction composites for high diode performances and improved effective carrier lifetime and absorption properties. High-density vertically aligned SiNWs were fabricated using a simple and cost-effective silver-assisted chemical etching method. Bi nanoparticles (BiNPs) were then anchored in these nanowires by a straightforward thermal evaporation technique. The systematic study of the morphology, elemental composition, structure, and crystallinity provided evidence for the synergistic effect between SiNWs and BiNPs. Bi@SiNWs exhibited an eight-fold enhancement of the first-order Raman scattering compared to bare silicon. Current–voltage characteristics highlighted that bismuth treatment dramatically improved the rectifying behavior and diode parameters for Bi-passivated devices over Bi-free devices. Significantly, Bi wire-filling effectively increased the minority carrier lifetime and consequently reduced the surface recombination velocity, further indicating the benign role of Bi as a surface passivation coating. Furthermore, the near-perfect absorption property of up to 97% was achieved. The findings showed that a judicious amount of Bi coating is required. In this study the reasons behind the superior improvement in Bi@SiNW’s overall properties were elucidated thoroughly. Thus, Bi@SiNW heterojunction nanocomposites could be introduced as a promising and versatile candidate for nanoelectronics, photovoltaics and optoelectronics.

We find the optimal configuration for maximum photon indistinguishability ( I ) in the case of a five-emitter system coupled to a cavity using a machine-learning optimization procedure which provides the optimal position of each emitter. (This work was published in Nanomaterials MDPI [ 1 ]).

Temperature is one of the most relevant physical quantities that affects almost all processes in nature. However, the realization of accurate temperature standards using current temperature references, like the triple point of water, is difficult due to the requirements on material purity and stability of the environment. In addition, in harsh environments, current temperature sensors with electrical readout, like platinum resistors, are difficult to implement, urging the development of optical temperature sensors. In 2018, the European consortium Photoquant, consisting of metrological institutes and academic partners, started investigating new temperature standards for self-calibrated, embedded optomechanical sensor applications, as well as optimised high resolution and high reliability photonic sensors, to measure temperature at the nano and meso-scales and as a possible replacement for the standard platinum resistant thermometers. This article presents an overview of the results obtained with sensor prototypes that exploit photonic and optomechanical techniques for sensing temperatures over a large temperature range (5 K to 300 K). Different concepts are demonstrated, including ring resonators, ladder-like resonators and suspended membrane optomechanical thermometers, highlighting initial performance and challenges, like self-heating that need to be overcome to realize photonic and optomechanical thermometry applications.

We present an analytical model for the dynamical self-heating effect in air-cladded optical microring resonators (ORRs). The spatially and time resolved temperature field is calculated by integrating the corresponding boundary value problem of the heat equation. It turns out that the self-heating amplitude is approximately proportional to the total absorbed power and anti-proportional to the thermal conductivity of the cladding material. Further, two-photon absorption plays a major role in the heating process, even for moderate input powers, due to the strong light confinement. Heating times are determined to be in the microsecond range and may limit the response time of ORR devices. The explicit formulas for the temperature fields allow a much faster determination of heating properties compared to elaborate finite element simulations. Thus, our model is predestinated for scanning large parameter spaces. We present such an analytical model for the self-heating effect in ORRs. For this purpose, we solve the heat equation on the ORRs geometrical domain. The heat source is caused by two effects, linear absorption from defect states and quadratic two-photon absorption (TPA). Due to the strong light confinement on resonance, very high light intensities are reachable in the resonator ring and the TPA might become a dominant heat source even for low excitation powers. We utilize insulating Neumann boundary conditions to calculate the temperature increase in the substrate region as a convolution between heat source and the corresponding Greens function. The temperature field in the ring structure is calculated by solving the corresponding eigenvalue problem that arises from a separation ansatz. The result is discussed in terms of maximum self-heating, response time and power dependence for ORRs with very high Q-factors of over 100 000. Finally, we compare the analytical calculations of the self-heating effect with finite element computations.

We demonstrate a hybrid photonic thermometer, integrating two wide-bandgap materials (diamond and GaN) by transfer printing. Temperature errors as low as 9.2 mK are reported – a nearly fivefold improvement over current state of the art.

Ultrahigh sensitivity temperature measurement is becoming increasingly relevant for different scientific and technological fields from fundamental physics to high-precision engineering applications. Here, we demonstrate the use of a nanomechanical resonator—free standing silicon nitride membranes with thicknesses in the nanoscale—for room temperature thermometry reaching an unprecedented resolution of 15 μK. These devices were characterized by using an interferometric system at high vacuum, where there are only two possible mechanisms for heat transfer: thermal conductivity and radiation. While the expected behavior should be to decrease the frequency of the mechanical resonance due to the thermoelastic effect, we observe that the nanomechanical response can be both positive and negative depending on the thermal flux: a heat point source always shifts the mechanical resonance to lower frequencies, while a distributed heat source shifts the resonance to higher frequencies.

We demonstrate a dual-material integrated photonic thermometer, fabricated by high accuracy micro-transfer printing. A freestanding diamond micro-disk resonator is printed in close proximity to a gallium nitride on a sapphire racetrack resonator, and respective loaded Q factors of 9.1 × 104 and 2.9 × 104 are measured. We show that by using two independent wide-bandgap materials, tracking the thermally induced shifts in multiple resonances, and using optimized curve fitting tools the measurement error can be reduced to 9.2 mK. Finally, for the GaN, in a continuous acquisition measurement we record an improvement in minimum Allan variance, occurring at an averaging time four times greater than a comparative silicon device, indicating better performance over longer time scales.

One of the main steps towards large-scale quantum photonics consists of the integration of single photon sources (SPS) with photonic integrated circuits (PICs). For that purpose, the PICs should offer an efficient light coupling and a high preservation of the indistinguishability of photons. Therefore, optimization of the indistinguishability through waveguide design is especially relevant. In this work we have developed an analytical model that uses the Green's Dyadic of a 3D unbounded rectangular waveguide to calculate the coupling and the indistinguishability of an ideal point-source quantum emitter coupled to a photonic waveguide depending on its orientation and position. The model has been numerically evaluated through finite-difference time-domain (FDTD) simulations showing consistent results. The maximum coupling is achieved when the emitter is embedded in the center of the waveguide but somewhat surprisingly the maximum indistinguishability appears when the emitter is placed at the edge of the waveguide where the electric field is stronger due to the surface discontinuity.

In this work, vertically aligned silicon nanowires (SiNWs) with relatively high crystallinity have been fabricated through a facile, reliable, and cost-effective metal assisted chemical etching method. After introducing an itemized elucidation of the fabrication process, the effect of varying etching time on morphological, structural, optical, and electrical properties of SiNWs was analysed. The NWs length increased with increasing etching time, whereas the wires filling ratio decreased. The broadband photoluminescence (PL) emission was originated from self-generated silicon nanocrystallites (SiNCs) and their size were derived through an analytical model. FTIR spectroscopy confirms that the PL deterioration for extended time is owing to the restriction of excitation volume and therefore reduction of effective light-emitting crystallites. These SiNWs are very effective in reducing the reflectance to 9-15% in comparison with Si wafer. I-V characteristics revealed that the rectifying behaviour and the diode parameters calculated from conventional thermionic emission and Cheung's model depend on the geometry of SiNWs. We deduce that judicious control of etching time or otherwise SiNWs' length is the key to ensure better optical and electrical properties of SiNWs. Our findings demonstrate that shorter SiNWs are much more optically and electrically active which is auspicious for the use in optoelectronic devices and solar cells applications.

A key requirement for the development of highly efficient silicon nanowires (SiNWs) for use in various kinds of cutting-edge applications is the outstanding passivation of their surfaces. In this vein, we report on a superior passivation of a SiNWs surface by bismuth nano-coating (BiNC) for the first time. A metal-assisted chemical etching technique was used to produce the SiNW arrays, while the BiNCs were anchored on the NWs through thermal evaporation. The systematic studies by Scanning Electron Microscopy (SEM), energy dispersive X-ray spectra (EDX), and Fourier Transform Infra-Red (FTIR) spectroscopies highlight the successful decoration of SiNWs by BiNC. The photoluminescence (PL) emission properties of the samples were studied in the visible and near-infrared (NIR) spectral range. Interestingly, nine-fold visible PL enhancement and NIR broadband emission were recorded for the Bi-modified SiNWs. To our best knowledge, this is the first observation of NIR luminescence from Bi-coated SiNWs (Bi@SiNWs), and thus sheds light on a new family of Bi-doped materials operating in the NIR and covering the important telecommunication wavelengths. Excellent anti-reflectance abilities of ~10% and 8% are observed for pure SiNWs and Bi@SiNWs, respectively, as compared to the Si wafer (50–90%). A large decrease in the recombination activities is also obtained from Bi@SiNWs heterostructures. The reasons behind the superior improvement of the Bi@SiNWs performance are discussed in detail. The findings demonstrate the effectiveness of Bi as a novel surface passivation coating, where Bi@SiNWs heterostructures are very promising and multifunctional for photovoltaics, optoelectronics, and telecommunications.

Staying in control of delicate processes in the evermore emerging field of micro, nano and quantum-technologies requires suitable devices to measure temperature and temperature flows with high thermal and spatial resolution. In this work, we design optical microring resonators (ORRs) made of different materials (silicon, diamond and gallium nitride) and simulate their temperature behavior using several finite-element methods. We predict the resonance frequencies of the designed devices and their temperature-induced shift (16.8 pm K-1 for diamond, 68.2 pm K-1 for silicon and 30.4 pm K-1 for GaN). In addition, the influence of two-photon-absorption (TPA) and the associated self-heating on the accuracy of the temperature measurement is analysed. The results show that owing to the absence of intrinsic TPA-processes self-heating at resonance is less critical in diamond and GaN than in silicon, with the threshold intensity I th = α / β , α and β being the linear and quadratic absorption coefficients, respectively.

Coupled photonic crystal microcavities have been considered when exploring platforms for quantum photonic effects like quantum-optical Josephson interferometers, single photon emitters and coupled-cavity single-photon emitters and many others. Arrays of photonic cavities are relevant structures for developing large-scale photonic integrated circuits, single mode coupled-cavity lasers and for investigating basic quantum electrodynamics phenomena due to the photon hopping between interacting nanoresonators. In this work we have measured the emission of two L7 microcavities when their separation is varied. We have found optical coupled modes more clearly defined at specific cavity separations. Finally, we have simulated the optical mode distribution of the coupled system using the GME method, finding a good agreement between experiment and theory.

We investigated the fabrication of large-area (cm2) nanostructured glasses for solar cell modules with hydrophobic and hydrophilic properties using soft lithography and colloidal lithography. Both of these techniques entail low-cost and ease of nanofabrication. We explored the use of simple 1D and 2D nanopatterns (nanowires and nanocones) and the effect of introducing disorder in the nanostructures. We observed an increase in the transmitted light for ordered nanostructures with a maximum value of 99% for wavelengths >600 nm when ordered nanocones are fabricated on the two sides of the solar glass. They produced an increment in the efficiency of the packaged solar cell with respect to the glass without nanostructures. On the one hand, the wettability properties showed that the ordering of the nanostructures improved the hydrophobicity of the solar glasses and increased their self-cleaning capacity. On the other hand, the disordered nanostructures improved the hydrophilic properties of solar glasses, increasing their anti-fogging capacity. The results show that by selecting the appropriate nanopattern, the wettability properties (hydrophobic or hydrophilic) can be easily improved without decreasing the efficiency of the solar cell underneath.

Protein detection by optical measurement can be obtained through absorption measurements using wavelengths in the range between 270 and 280 nm. Efficient light sources or optical filters in this wavelength range can avoid the use of spectral measurement for detection [1]. A study about the relationship between the reflectivity in the near UV and the vertical aspect ratio was performed for gratings fabricated using low-cost soft lithography which allows for easy replication of wide-area nanopatterns [2]. The reflectivity was measured at 45° in the UV-visible for samples fabricated in silicon and aluminum. A well-defined reflection peak in the range 270 – 280 nm was found in the reflectivity spectrum with features changing depending on the depth of the gratings. Moreover, wetting properties of the gratings were also investigated using contact angle measurements with water droplets, obtaining hydrophobic or hydrophilic gratings depending on the period and depth of the etching.