Photonic and Optomechanical Thermometry

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 re- liability 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 demon- strated, 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.This work was carried out under the 17FUN05 PhotOQuanT project, which has received funding from the EMPIR program, co-financed by the Participating States and the European Union’s Horizon 2020 research and innovation progra

Photonic and Thermal Modelling of Microrings in Silicon, Diamond and GaN for Temperature Sensing

© 2020 by the authors.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 Ith=α/β , α and β being the linear and quadratic absorption coefficients, respectively.Research funded by European Association of National Metrology Institutes (JRP f14 PhotOQuanT—17FUN05). This project has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme. The authors gratefully acknowledge support by the DFG research training group GrK1952/1 “Metrology for Complex Nanosystems”.Peer reviewe

Enhancement of the indistinguishability of single photon emitters coupled to photonic waveguides

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.Horizon 2020 Framework Programme (820423)

Perfect Photon Indistinguishability from a Set of Dissipative Quantum Emitters

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

Perfect Photon Indistinguishability from a Set of Dissipative Quantum Emitters

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.European Union’s Horizon 2020 research and innovation program under grant agreement No. 820423 (S2QUIP); CSIC Quantum Technology Platform PT-001y Agencia Estatal de Investigación (AEI) grant PID2019-106088RB-C31; European Metrology Programme for Innovation and Research: 20FUN05 SEQUME and CSIC Interdisciplinary Thematic Platform (PTI+): PTI-QTEP+

Micro-Kelvin Resolution at Room Temperature Using Nanomechanical Thermometry

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.This research is funded by the Spanish Ministry of Science under project MOMPs reference TEC2017-89765-R and the European Association of National Metrology Institutes (JRP f14 PhotOQuanT17FUN05). E.G.-S acknowledges financial support by the Spanish Ministry of Science under the project MicroBIOMS, reference PID2019-109765RA-I00. This project has received funding from the EMPIR program co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation program. The service from the Micro and Nanofabrication Laboratory (MiNa) and X-SEM Laboratory is funded by MCIU (CSIC13-4E-1794) and EU (FEDER, FSE)

Numerical Optimization of a Nanophotonic Cavity by Machine Learning for Near-Unity Photon Indistinguishability at Room Temperature

Room-temperature (RT), on-chip deterministic generation of indistinguishable photons coupled to photonic integrated circuits is key for quantum photonic applications. Nevertheless, high indistinguishability (I) at RT is difficult to obtain due to the intrinsic dephasing of most deterministic single-photon sources (SPS). Here, we present a numerical demonstration of the design and optimization of a hybrid slot-Bragg nanophotonic cavity that achieves a theoretical near-unity I and a high coupling efficiency (β) at RT for a variety of single-photon emitters. Our numerical simulations predict modal volumes in the order of 10(λ/2n), allowing for strong coupling of quantum photonic emitters that can be heterogeneously integrated. We show that high I and β should be possible by fine-tuning the quality factor (Q) depending on the intrinsic properties of the single-photon emitter. Furthermore, we perform a machine learning optimization based on the combination of a deep neural network and a genetic algorithm (GA) to further decrease the modal volume by almost 3 times while relaxing the tight dimensions of the slot width required for strong coupling. The optimized device has a slot width of 20 nm. The design requires fabrication resolution in the limit of the current state-of-the-art technology. Also, the condition for high I and β requires a positioning accuracy of the quantum emitter at the nanometer level. Although the proposal is not a scalable technology, it can be suitable for experimental demonstration of single-photon operation.ACKNOWLEDGMENTS The authors gratefully acknowledge financial support from the European Union’s Horizon 2020 research and innovation program under grant agreement no. 820423 (S2QUIP) and CSIC Quantum Technology Platform PT-001. J.M.L. acknowledges the Agencia Estatal de Investigación (AEI) grant PID2019-106088RB-C31

High precision integrated photonic thermometry enabled by a transfer printed diamond resonator on GaN waveguide chip

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

Photonic and Optomechanical Thermometry

International audienceTemperature 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