This PDF file contains the front matter associated with SPIE Proceedings Volume 11806, including the Title Page, Copyright information, and Table of Contents.

Photonic spin density (PSD) in the near-field gives rise to exotic phenomena such as photonic skyrmions, optical spin-momentum locking and unidirectional topological edge waves. Experimental investigation of these phenomena requires a nanoscale probe that directly interacts with PSD. Here, we propose and demonstrate that the nitrogen-vacancy (NV) center in diamond can be used as a quantum sensor for detecting the spinning nature of photons. This room temperature magnetometer can measure the local polarization of light in ultra-subwavelength volumes through photon-spin-induced virtual transitions. The direct detection of light's spin density at the nanoscale using NV centers in diamond opens a new frontier for studying exotic phases of photons as well as future on-chip applications.

Classical Hong-Ou-Mandel (HOM) effect – two-particle interference on a lossless beamsplitter, reveals the fundamental difference between bosonic and fermionic particles. As a result of such interference, pairs of bosons coalesce while pairs of fermions anti-coalesce. Here we report an observation of the anti-HOM effect where bosons anti-coalesce and fermions show coalescent-like behavior when interfere on a lossy beamsplitter. By exploiting two-photon entangled states, we provide an experimental demonstration of the anti-HOM effect for both bosonic and fermionic spatial wavefunctions of the photons. This fundamental phenomenon may enrich quantum information and metrology protocols where states of entangled photons are dynamically converted.

We describe the operation of a free-space confocal optical microscope operated in a dilution refrigerator. The microscope is installed on a cold insertable probe to enable fast sample exchange while the refrigerator is held at low temperatures. A vector magnet provides a 6 T field normal to the sample and 1 T fields at arbitrary angles. A variety of optical microscopies and spectroscopies, including photoluminescence, Raman, magneto-optical Kerr effect, and spin relaxometry measurements are described, and some of the challenges associated with performing these measurements at milliKelvin temperatures are explored.

Nanocativies enable a wide range of weak and strong light-matter coupling phenomena at the single molecule level. In this talk, I will explore classical and quantum optical effects behind strong plasmon-molecule interactions, with particular focus on two different topics. First, I will treat the quantization of the electromagnetic fields in both purely metallic and hybrid metallo-dielectric nanostructures. Secondly, I will explore the impact of molecular vibrations in the so-called plasmonic Purcell effect.

Multi-photon split states, where each photon is in a different input mode, represent an essential resource for various quantum applications. Accordingly, characterisation of such states is important from the fundamental and practical perspectives. We propose a segmented coupled waveguide array as a new form of compact low-loss quantum circuit and apply it for the scalable multi-photon split state tomography with optimized performance and no need of reconfigurability. We develop an optimization algorithm to design the array with minimally necessary number of waveguides and smallest sensitivity to noise in the tomography. Such a novel platform can enable fast, scalable, and fully integrated quantum systems.

The integration of nano-scale quantum emitters with nano-photonic circuits is a prerequisite for a broad range of quantum technologies, benefitting quantum communication, quantum sensing or quantum information processing. However, the assembly of single emitters with high positioning accuracy in large-scale arrays and their efficient interfacing with photonic quantum channels constitutes a major challenge. Here, we show how single colloidal core-shell quantum dots (CQDs) are embedded in photonic integrated circuits that allow for individual excitation and photoluminescence collection. By utilizing finite-difference time-domain simulations, we design nanophotonic interfaces with high coupling efficiencies between CQDs and single-mode optical waveguides. Here, we utilize a tantalum pentoxide (Ta2O5) on insulator nanophotonic platform that enables integrated optics experiments at the single-photon level due to low intrinsic material fluorescence and low-loss waveguiding. We employ a PMMA thin film for patterning hundreds of nanoscale apertures that are precisely aligned to prefabricated nanophotonic devices and transfer a solution of CdSeTe/ZnS CQDs diluted in decane into the apertures. The CQDs are positioned with 50 nm accuracy with respect to optical waveguides. Highly efficient 3D fiber-chip interfaces produced from a polymer in direct laser writing allow us to characterize the CQDwaveguide coupling and assess the spectral characteristics of the collected photoluminescence. Moreover, we record the second order autocorrelation function g2(τ) of the photoluminescence signal, which shows photon antibunching indicative of individual quantum emitters. Addressing individual CQDs via independent waveguide channels and a reproducible integration approach that extends to larger numbers of devices provides a novel perspective for realizing quantum technology with solution-processible single-photon emitters.

Quantum nanophotonics interfacing optical photons with coherent atomic spins have the potential to revolutionize secure communications, ultra-scale sensing, distributed quantum computing, and enhanced metrology, but currently lack scalable material and device platform necessary for building robust quantum light-matter interfaces. The trivalent rare-earth ion such as erbium (Er3+) is a promising candidate for quantum interfaces because of its narrow optical transition as well as a long spin coherence time. Here, we present an epitaxial Er3+:Y2O3 on silicon platform for scalable quantum light-matter interconnect, enabling efficient spin-photon interfaces based on individual rare-earth qubits and quantum transduction via ensembles of ions.

Topological insulators (TIs) are a distinctive class of materials, which are insulating in the bulk but support topologically protected conducting surface states. Since their discovery, most work on these materials has focused on their electronic properties, whilst their interaction with electromagnetic fields has largely been untouched. In small topological insulator nanoparticles (TINPs) the dispersion relation of the topological surface states is no longer continuous but discretized. This system forms a type of topological quantum dot. By studying the optical transition properties between the states of the topological quantum dot we explore their use as a lasing system. The optical properties of the particle can be tuned by varying particle size, light frequency, and light polarization, providing a toolbox for quantum optics and quantum information technologies.

Recent progress in the development of direct band gap GeSn is exploited to investigate the optical injection and coherent control of spin currents in this group IV semiconductor. The analysis of these properties could provide essential information for future innovative optical photon-to-spin conversion interfaces, long-sought after for entanglement distribution. A 30-band k•p model is used to evaluate the electronic properties in the material for a relatively wide range of energies, and a linear tetrahedron method is employed for the Brillouin zone integrations. Carrier, spin, current, and spin current injection rates are calculated for a bichromatic field of frequencies ω and 2ω.

Building quantum networks requires efficient coupling of solid-state quantum emitters to photonic devices. Tinvacancy center (SnV) has attracted much interest for having long spin coherence times at temperatures above 1 K. Employing SnV as an optically addressable qubit requires integration with photonic structures to both route the emitted photons and enhance the light-matter interaction. We present incorporation of high-quality SnV centers with narrow linewidths in suspended diamond waveguides. Furthermore, we fabricate photonic crystal cavities in diamond with embedded SnV centers. We observe strong intensity enhancement of the photon emission when the cavity is resonant with the color center. Time-resolved photoluminescence measurements confirm that this effect is due to radiative Purcell enhancement of the spontaneous emission. Finally, we demonstrate Stark tuning of transition frequency of SnV centers, essential for multiemitter applications. These results are a significant step toward color-center-based quantum information processing applications without the need for dilution refrigerators.

In this talk we show how time-resolved Raman spectroscopy can be combined with Time Correlated Single Photon Counting (TCSPC) to create and evidence entanglement between light and a collective molecular vibration (i.e. an optical phonon) [3]. We further show that the correlations are strong enough to violate the Bell Inequality, which provides the most stringent test for entanglement. We measure the decay of these hybrid photon-phonon Bell correlations with sub-picosecond time-resolution and find that they survive over several hundred oscillations at ambient conditions.

The transport of quantum states without loss of "coherence" is extremely important for realizing quantum information systems. Quantum effects have been demonstrated in exotic systems, such as cold atoms suspended in magnetic fields, but these systems are extremely challenging to realise. In this work we will translate this work into the chemical domain, using thin films of "J-aggregates". These J-aggregates are quantum many-body systems characterized by the sharing of excitonic states over two or more molecules. This novel organic quantum soft-matter platform can confine the light at the nanoscale taking the advantages of supramolecular chemistry to design properties on demand.

The deterministic integration of quantum emitters into on-chip photonic elements is crucial for the implementation of scalable on-chip quantum circuits. Here, we report on the deterministic integration of single quantum dots (QD) into tapered multimode interference beam splitters using in-situ electron beam lithography (EBL). We demonstrate the functionality of the deterministic QD-waveguide structures by µPL spectroscopy and by studying the photon cross-correlation between the two MMI output ports. The latter confirms single-photon emission and on-chip splitting associated with g(2)(0) << 0.5. Moreover, the deterministic integration of QDs enables the demonstration and controlled study of chiral light-matter effects and directional emission in QD-WGs, and the realization of low-loss heterogenous QD-WG systems with excellent quantum optical properties.

This talk presents recent experimental demonstrations that use integrated nanophotonic processors for various quantum computations such as quantum machine learning and in particular reinforcement learning, where agents interact with environments by exchanging signals via a communication channel. We show that this exchange allows boosting the learning of the agent. Another experiment underlines the feasibility of such photonic integrated processors for a homomorphically-encrypted quantum walk computation. This secure quantum computation exploits path- and polarization as degrees-of-freedom for encrypting the input and output of the photonic processor. As last demonstration I will present counter-intuitive quantum communication tasks that are linked to the Zeno effect. As outlook I will discuss technological challenges for the scale up of photonic quantum computers, and our group’s current work for addressing some of those.

As applications in fields like security or medicine require sensitive schemes in order to detect IR photons, an interesting strategy consists in converting weak IR signals into the optical domain where detectors with single photon sensitivity are readily available. We introduce here a novel platform for ultra-sensitive conversion and detection of far and mid-infrared signals, inspired by cavity optomechanics. The conversion process, relying on the intrinsic ability of specific molecular vibrations to interact both with optical and IR fields, is optimized through the use of doubly resonant nano-antennas. Our study demonstrates noise levels improving on state of the art for IR detectors operating at room temperature and opens the path to single IR photon detection devices.

Epsilon-near-zero (ENZ) materials also defined as near zero permittivity materials have attracted much attention for their peculiar physical features. In this work, we study analytically and numerically the emission decay rate of a hybrid system combining a vertical dipolar emitter in the presence of ENZ spherical Nano-particle. We examine the asymptotic behavior of the fluorescence decay rate in the near field of the ENZ spherical nanoparticle. We demonstrate the competition between the radiative and non-radiative channels. Our results show that a fundamental understanding of multiple contributions is critical to control the fluorescence decay rate in its molecular environment.

Superconducting Nanowire Single photon Detectors (SNSPDs) offer unparalleled performance for IR photon counting, combining close to unity quantum efficiency, low intrinsic noise and ultrafast timing jitter. The ability of SNSPDs to count photons in mid-IR band up to 7 um wavelength opens up new possibilities in quantum optics, laser ranging, free space Quantum Key Distribution (QKD) and astronomy. Here we report on development of mid-IR SNSPDs including device design, fabrication, optimisation of superconducting materials and characterisation. We present a characterisation setup covering 1.5 - 4.2 um spectral region based on tuneable optical parametric oscillator with picosecond long pulses. We then demonstrate the viability of mid infrared SNSPDs for a variety of applications and report the results from single photon light detection and ranging (LIDAR) experiment with 2.3 um photons. This work paves the way for future app in free space QKD, deep space communication and astronomy.

Photonics is a sophisticated platform for the development of novel quantum technologies, from quantum processors to distributed quantum communication. Most linear optical architectures focus on encoding qubits into photons using, for example, polarization or a dual-rail approach. However, encoding higher-dimensional systems - qudits - can in principle provide improved information capacity and noise tolerance in communication, and lower error thresholds in fault-tolerant quantum computation. Here we present new schemes for generating high-dimensional photonic entanglement and discuss how to build cluster states for universal high-dimensional quantum computation.

Two-photon states emitted from spontaneous parametric downconversion (SPDC) can exhibit quantum correlations in various degrees of freedom. On the other hand, plasmonic nanostructures show enhanced transmission thanks to the conversion of light into surface plasmon polaritons. It has been shown previously that polarization, time-energy and orbital angular momentum entanglement are preserved in such structures. The fact that surface plasmons are collective charge density waves, consisting of billions of electrons makes this observation remarkable. Here we show that spatial entanglement is also preserved by characterizing it after the photons interacted with gold nanopillar arrays. The detection is realized with novel single photon avalanche diode (SPAD) arrays with high spatial and temporal resolution. By measuring the spatial correlations of the photon in the near- and far-fields, we can characterize the state with respect to spatial entanglement with and without the nano-structure.

As the field of artificial intelligence is pushed forward, the question arises of how fast autonomous machines can learn. Within artificial intelligence, an important paradigm is reinforcement learning, where agents - learning entities capable of decision making - interact with the world they are placed in, called an environment. Thanks to these interactions, agents receive feedback from the environment and thus progressively adjust their behaviour to accomplish a given goal. An important question in reinforcement learning is how fast agents can learn to fulfill their tasks. To answer this question we consider a novel reinforcement learning framework where quantum mechanics is used. In particular, we quantize the agent and the environment and grant them the possibility to also interact quantum-mechanically, that is, by using a quantum channel for their communication. We demonstrate that this feature enables a speed-up in the agent's learning process, and we further show that combining this scenario with classical communication enables the evaluation of such an improvement. This learning protocol is implemented on an integrated re-programmable photonic platform interfaced with photons at telecommunication wavelengths. Thanks to the full tunability of the device, this platform proves the best candidate for the implementation of learning protocols, where a continuous update of the learning process is required.

We present a full analysis of the optical and quantum properties of highly efficient perovskite nanocubes with increased photostability. These emitters exhibit reduced blinking together with a strong photon antibunching. Moreover, we achieved the coupling of a single perovskite nanocube with a tapered optical nanofiber, a step toward a compact integrated single photon source.

Silicon photonics based on CMOS technology is a very attractive platform to build compact, low-cost and scalable quantum photonics integrated circuits addressing the requirements of quantum key distribution protocols. We show record low propagation losses below 0.5 dB/cm and below 0.05 dB/cm for silicon and silicon nitride waveguides respectively. We will present our results on integrated components such as hybrid III-V on silicon lasers for weak coherent pulse generation, high-quality microresonators for entangled photon pair generation and we will show our recent developments on high crystalline quality NbN thin films with improved critical temperature for waveguide-integrated superconducting single photon detectors.

We report a single photon detector based on NbTiN microbridges, suitable for operation within telecommunication wavelengths. We observed an excellent signal-to-noise ratio of the readout signal while the corresponding jitter contributed by electrical noise was measured to be less than 10 ps. Routing the current through a parallel electrical connection to set the microbridge back to the superconducting state after photon absorption enabled us to overcome the hysteresis of the state transition. Our approach combines facile fabrication of fast microscale detectors with efficient current redistribution mechanism, enabling prospective applications in quantum photonics which requires accurate estimation of photon arrival events.

Characterizing the temporal response function of single-photon detectors (SPDs) is essential for quantum communication protocols and time-resolved measurements. Typically, this characterization is obtained from the arrival time statistics of photons from a pulsed laser. In this work, we present an alternative approach using time-correlated photon pairs generated in spontaneous parametric down-conversion (SPDC). We demonstrate a continuous wavelength-tunability from 526 nm to 661 nm for one photon of the pair, and 1050 nm to 1760 nm for the other photon a range comparable to existing pulsed-laser systems. With this source, we characterized single-photon avalanche detectors sensitive to the two distinct wavelength bands, one based on Silicon, the other based on Indium Gallium Arsenide.

Herein, we investigated the performance of a Si waveguide-integrated superconducting nanowire single-photon detector (SNSPD) with an arrayed waveguide grating (AWG) comprising SiN/SiON. The system detection efficiency of SNSPD with AWG was unchanged whether the AWG is at a room or cryogenic temperature because the insertion loss was unchanged while the passband shifts 1.7-nm lower at cryogenic temperature. On the other hand, the dark count rate of the SNSPD with AWG decreased by approximately 20 dB when the AWG was at cryogenic temperature. The AWG at the cryogenic temperature functioned as a cold optical bandpass filter, which suppressed the dark count rate due to the background room-temperature blackbody radiation through fiber optics. The noise equivalent power (NEP) of the SNSPD with AWG improved from 4.8 × 10^-17 W/Hz^-1/2 for the room-temperature AWG to 2.2 × 10^-18 W/Hz^-1/2 for the cryogenic-temperature AWG. Results demonstrated that the integration of photonic circuits with SNSPD at the cryogenic temperature benefited not only scalability but also performance.

Single photon sources (quantum emitters) are a key building block for emerging quantum technologies. Especially attractive for quantum photonic circuitry is the prospect of integrating such sources with conventional photonic structures such as resonators and waveguides. In this talk, we will first present our work on realizing single photon emitters (SPEs) in hexagonal boron nitride (hBN), a van der Waals material, via strain engineering. Following this we will discuss the coupling of such SPEs to silicon nitride microdisk resonators and to plasmonic surface lattice resonances. Prospects of realizing electrically driven SPEs using few layer hBN placed in van der Waals heterostructures will also be discussed.

We consider the effective potential in a linear Paul trap with an asymmetrical power supply system. Only the DC voltage component is applied to the one pair of rod electrodes, and only the AC component is applied to the other pair. We propose an analytical description of the effective potential for an asymmetrical power supply scheme. Mathematical simulation shows the effective potential splitting along the axis of the trap. To confirm the proposed description, we perform an experimental localization of starch microparticles with an asymmetrical power supply system. The charged microparticles localization area splitting into two spatially separated areas along the trap axis is shown.