This PDF file contains the front matter associated with SPIE Proceedings Volume 11091, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Combining state-of-the-art optimization and machine learning techniques with high speed electromagnetic solvers offers a new approach to “inverse” design and implement classical and quantum photonic circuits with superior properties, including robustness to errors in fabrication and environment, compact footprints, novel functionalities, and high efficiencies. We illustrate this with a number of demonstrated devices in silicon, diamond, and silicon carbide, including wavelength and polarization splitters and converters, power splitters, couplers, nonlinear optical isolators, on chip laser driven particle accelerators, and efficient quantum emitter-photon interfaces.

This talk explores distributed quantum information processing. In the recent years, the monolithic design of quantum computers has been investigated and huge efforts to realize such designs have been undertaken worldwide. By contrast, distributed quantum information processing relies on quantum signalling between quantum devices and systems. We begin by introducing the concept of distributed quantum information processing, detailing it's advantages and disadvantages. We further discuss the feasibility of quantum devices and systems to perform distributed quantum information processing, including recent developments using NV centers in diamond.

At the core of most quantum technologies, including quantum networks and quantum simulators, is the development of homogeneous, long lived qubits with excellent optical interfaces, and the development of high efficiency and robust optical interconnects for such qubits. To achieve this goal, we have been studying color centers in diamond (SiV, SnV) and silicon carbide (VSi in 4H SiC), in combination with novel fabrication techniques, and relying on the powerful and fast photonics inverse design approach that we have developed. Our inverse design approach offers a powerful tool to implement classical and quantum photonic circuits with superior properties, including robustness to errors in fabrication and temperature, compact footprints, novel functionalities, and high efficiencies. We illustrate this with a number of demonstrated devices in silicon, diamond, and silicon carbide.

Silicon-vacancy (SiV) color centers in diamond offer novel possibilities to probe light-matter interaction in nano-quantum optics and provide a scalable quantum system suitable for single-photon emission. However, their effective count-rate is still limited by non-radiative decay channels, radiation at wide angles and total internal reflection at the diamond interface. Recently optical antennas have been utilized in order to modify light-matter interaction at the nanoscale. Acting as resonators, they are able to increase the spontaneous emission rate of quantum emitters by several orders of magnitude in a broad spectral range. Because coupling a quantum emitter to a nano-antenna requires close proximity between the two systems, we implant Si ions on very thin diamond membranes that provide the required dimension for near-field interaction in a controlled manner and investigate the optical properties of SiV color centers in such diamond membranes. We consider gold nano-cones as nano-antennas, fabricated by focused electron beam induced deposition (EBID), followed by sputtering and focused ion beam (FIB) milling. The finite-difference time-domain (FDTD) calculations show that gold nano-cones can provide more than four orders of magnitude enhancement in the Purcell factor with an antenna efficiency (AE) of 80%.

Engineering solid state quantum systems is amongst grand challenges in realizing integrated quantum photonic circuitry. While several 3D systems (such as diamond, silicon carbide, zinc oxide) have been thoroughly studied, solid state emitters in two dimensional (2D) materials are still in their infancy. In this talk I will introduce hexagonal boron nitride (hBN) as a promising layered material that hosts ultra bright quantum emitters. I will present several avenues to engineer these emitters in large exfoliated sheets, multilayers and 2D monolayers using top down and bottom up approaches. I will also discuss potential atomistic structures of the defects supported by density functional theory. I will then highlight promising avenues to integrate the emitters with plasmonic and photonic cavities to achieve improved collection efficiency and Purcell enhancement. These are fundamental experiments to realize integrated quantum photonics with 2D materials. I will summarize by outlning challenges and promising directions in the field of quantum emitters and nanophotonics with 2D materials and other wide band gap materials.

Recent advances in nanofabrication technology now enable unprecedented control over 2D heterostructures, in which single- or few-atom thick materials with synergetic opto-electronic properties can be combined to develop next-generation devices [1,2]. Precise control of light can be achieved at the interface between 2D metal and dielectric layers, where surface plasmon polaritons strongly confine electromagnetic energy. Here we reveal quantum and finite-size effects in hybrid systems consisting of graphene and few-atomic-layer noble metals, based on a quantum description that captures the electronic band structure of these materials. We also examine the case where a dielectric such hexagonal Boron Nitride (hBN) is placed between graphene and the metal film. Specifically, we simulate the graphene and metal within the random-phase approximation, incorporating in the metal phenomenological information on the main characteristics of the conduction electronic band structure, such as surface states, electron spill out, and a directional band gap associated with bulk atomic-layer corrugation [3]. These phenomena are found to play an important role in the metal screening of the plasmonic fields, determining the extent to which they propagate in the graphene layer. Remarkably, we find that a monoatomic metal layer is capable of pushing graphene plasmons toward the intraband transition region, rendering them acoustic, while the addition of more metal layers only produces minor changes in the dispersion but strongly affects the lifetime. We further find that a quantum approach is required to correctly account for the sizable Landau damping associated with single-particle excitations in the metal. We anticipate that these results will aid in the design of future platforms for extreme light-matter interaction of the nanoscale. References [1] D. N. Basov, M. M. Fogler and F. J. García de Abajo, Polaritons in van derWaals Materials. Science 354, aag1992 (2016). [2] D. Alcaraz Iranzo, S. Nanot, E. J. C. Dias, I. Epstein, C. Peng, D. K. Efetov, M. B. Lundeberg, R. Parret, J. Osmond, J. Y. Hong et al., Probing the ultimate plasmon confinement limits with a van der Waals heterostructure. Science 360, 291–295 (2018). [3] E. V. Chulkov, V. M. Silkin and P. M. Echenique, Surface science 437, 330-352 (1999) Acknowledgements This work has been supported in part by the Spanish MINECO (MAT2017-88492-R and SEV2015-0522), ERC (Advanced Grant 789104-eNANO), the Catalan CERCA Program, and Fundació Privada Cellex. A.R.E. acknowledges a grant cofounded by the Generalitat de Catalunya and the European Social Fund FEDER

The concentration of light on extreme-subwavelength scales provided by plasmons in conducting media enables strong extrinsic light-matter interactions required for optical sensing [1], quantum photonic [2], and nonlinear optical [3] technologies. While significant research has been devoted to the interaction of atoms and molecules with the enhanced linear optical fields generated by plasmonic nanostructures and their ability to enhance spontaneous emission from quantum emitters, light-matter coupling of the near fields produced by nonlinear optical processes in hybrid systems remains relatively unexplored [4]. Here we propose to utilize near fields generated by the plasmon-assisted nonlinear optical response of nanostructured graphene to resonantly couple the 2D layer with proximal quantum emitters operating in the near infrared [5]. Although graphene plasmon resonances are typically limited to the infrared and terahertz frequencies, below those of long-lived optical excitations in robust solid-state quantum light sources and many biologically interesting molecules, we show that electrically tuning the third harmonic of a localized plasmon in a graphene nanoisland to resonate with an electronic excitation in a few-level atomic system can enable graphene plasmon-mediated energy transfer and coherent control of quantum states. In the present scheme, emitter and plasmon resonances are nondegenerate, circumventing strong enhancement of spontaneous emission that arises in the linear coupling scheme. The combination of an intrinsically large nonlinear response and intense in-plane electric field enhancement associated with localized electrically-tunable plasmons renders graphene an ideal material platform for nonlinear near field coupling [5], although this principle could be straightforwardly applied to other plasmonic materials, opening a wide range of applications in sensing and quantum nano-optics. [1] J. N. Anker, W. P. Hall, O. Lyandres, N. C. Shah, J. Zhao, and R. P. Van Duyne, Nat. Mater. 7, 442 (2008). [2] M. S. Tame, K. R. McEnery, Ş. K. Özdemir, J. Lee, S. A. Maier, and M. S. Kim, Nat. Phys. 9, 329 (2013). [3] M. Kauranen and A. V. Zayats, Nat. Photon. 6, 737 (2012). [4] B. Metzger, M. Hentschel, and H. Giessen, Nano Lett. 17, 1931 (2017). [5] J. D. Cox and F. J. García de Abajo, Phys. Rev. Lett. 121, 257403 (2018).

Despite recent surge of interest in semiconducting perovskite nanocrystals as the new type of quantum dots exhibiting superior optical properties compared to many existing quantum dot systems, precise control of quantum confinement and dimensionality has been challenging. We developed a strategy that controls the quantum confinement in colloidal CsPbX3 quantum dots very precisely resulting in the exciton emission nearly free from the heterogeneous broadening in an ensemble of quantum dots at room temperature. Built upon the exquisite control of quantum confinement achieved in this system, we uncovered an unusual exciton property in strongly confined CsPbX3 quantum dots. For instance, the confinement of exciton in the same space as the photo-generated polaron activated the parity-forbidden exciton transition via symmetry breaking, which illustrates the unique nonlinear optical behavior that results from the strong electron-phonon coupling in perovskite quantum dots. We also developed a procedure to introduce the magnetic dopants, such as Mn2+, into the lattice of CsPbI3 quantum dots, where one can potentially create exciton magnetic polaron, i.e., creating optically induced ferromagnetic state. From the comparison of the temperature-dependent shift of the exciton transition energy and lifetime of the emission in both doped and undoped CsPbI3 quantum dots, we investigated the conditions under which the exciton magnetic polaron can be created in magnetically doped perovskite quantum dots. The results from this study demonstrate the potential of the perovskite quantum dots with precisely controlled quantum confinement and magnetic doping as the single photon emitter or carrier of the quantum information applicable for future quantum information processing applications.

An ensemble of emitters can behave differently from its individual constituents when it interacts coherently via common vacuum light modes. One example of a many-body collective coupling is so-called superfluorescent coupling, where the excited emitters are initially fully uncorrelated and coherence is established through spontaneously triggered correlations from quantum fluctuations. Subsequently, the coupled emitters emit a strong superfluorescent pulse. Since this phenomenon requires low inhomogeneity and a fine balance of interactions between the resonant emitters and their decoupling from the environment, superfluorescence has only been observed in a limited number of systems, such as certain atomic and molecular gases and a few solid-state systems. Here, we investigate densely packed arrays of fully inorganic cesium lead halide perovskite quantum dots[1], known as superlattices. These quantum dots obtain exceptional optical properties such as an lowest bright triplet state with an ultrafast radiative decay that is 1000x faster compared to other conventional nanocrystals at cryogenic temperatures[2]. The resulting high oscillator strength and a long exciton dephasing time[3] are key ingredients for strong light-matter interactions. In a solvent-drying-induced assembly process, perovskite quantum dots form densely packed cuboidal superlattices that show key signatures of superfluorescence[4]. We observe a more than twenty-fold accelerated radiative decay with dynamically red-shifted emission, extension of the first-order coherence time by more than a factor of four, photon bunching and an intensity-dependent time delay after which the photon burst is emitted. Also, at high excitation density, the superfluorescent decay exhibits a Burnham-Chiao ringing behavior, reflecting the coherent Rabi-type interaction.

Core/shell colloidal semiconductor nanocrystals are very efficient room temperature single photon emitters. In particular, in asymmetric core/shell nanoparticles (dots-in rods) with a spherical CdSe core surrounded by a rod-like CdS shell, blinking effects, multi-excitonic emission and polarization of the emitted photons can be independently controlled by tuning the shell dimensions [1]. This allows an unprecedented capability in radiative channels engineering, making dot-in-rods “state of the art” blinking-free sources of polarized single photons on-demand. In this talk I will discuss our recent results and the different strategies we are pursuing to develop hybrid photonic devices by coupling single nanocrystals with photonic structures such as deep parabolic mirrors [2], liquid crystals [3], semiconductor nanowires [4] and tapered nanofibers. In particular the deposition of a single emitter on a nanofiber and the observation of single photon statistics through the guided mode of the fiber will be reported. Finally I will show how this hybrid system is a very promising playground for novel chiral optics experiments, including a spin-orbit coupling effect for light [5]. [1] F. Pisanello, G. Leménager, L. Martiradonna, L. Carbone, S. Vezzoli, P. Desfonds, P.D. Cozzoli, J.P. Hermier, E. Giacobino, R. Cingolani, M. DeVittorio & A. Bramati, Non-blinking single photon generation with anisotropic colloidal nanocrystals : toward Room-temperature efficient colloidal quantum sources, Advanced Materials, 25, 1974 (2013) [2] V. Salakhutdinov, M. Sondermann, L. Carbone, E. Giacobino, A. Bramati, G. Leuchs, Optical trapping of nanoparticles by full solid-angle focusing , Optica, 3, 1181 (2016) [3] L. Pelliser, M. Manceau, C. Lethiec, D. Coursault, S. Vezzoli, G. Leménager, L. Coolen, M. DeVittorio, F. Pisanello, L. Carbone, A. Maître, A. Bramati, E. Lacaze, Alignement of Rod-Shaped Single Photon Emitters driven by Line Defects in Liquid Crystals, Adv. Funct. Mat. 25, 1719 (2015) [4] W. Geng, M. Manceau, N. Rahbany, V. Sallet, M. De Vittorio, L. Carbone, Q. Glorieux, A. Bramati, C. Couteau, Localised excitation of a single photon source by a nanowaveguide, Scientific Reports 6, 19721 (2016) [5] M. Joos, C. Ding, V. Loo, G. Blanquer, E. Giacobino, A. Bramati, V. Krachmalnikoff and Q. Glorieux, Polarization Control of Linear Dipole radiation using an Optical Nanofiber, Phys. Rev. Applied, 9, 064035 (2018)

The energy levels of an optically active quantum system can be shifted via the AC Stark effect by applying a strong, far-detuned laser. In addition to achieving a spin-selective AC Stark shift larger than 20 GHz, we observe a small Overhauser shift of approximately 1 GHz in a single negatively charged InGaAs quantum dot. We attribute this small shift to dynamic nuclear polarization via electron spin pumping induced by the high power, although far-detuned AC Stark laser. Low power scans reveal two regimes: high power where the frequency shift is linear in AC Stark laser power, and low power where the behavior is non-linear. Linewidth analysis provides a method to quantify the effect of the AC Stark laser on the nuclear spin environment, which in turn affects the quantum dot transitions.

Optical sensors have applications in a range of settings, from measuring mechanical vibrations in manufacturing processes to biometrics in security devices and the detection of proteins and viruses in biomedical research. Many sensing approaches exist and plasmonic systems in particular have been studied extensively due to their ability to confine light below the diffraction limit, which greatly enhances their sensitivity compared to conventional approaches. Recently, various quantum techniques have been discovered that can outperform classical sensing ones and provide sensitivity beyond the shot-noise limit. The use of these quantum techniques in plasmonics for improving sensing performance is currently being explored. We study the performance of a plasmonic sensor that exploits the quantum nature of light and its highly confined field. We consider specialized quantum states and by comparison we show how each can provide improved sensitivity beyond the shot-noise limit.

Quantum sensors take advantage of the inherent sensitivity of quantum systems to external environment perturbations to precisely measure target signals. The same interaction with the environment, however, limits the device sensitivity by reducing the coherence of the quantum states. Quantum control can play a crucial role in improving the sensor performance. We explore quantum control tools to improve the performance of a NitrogenVacancy (NV) center as a single-qubit sensor of ultra-weak magnetic fields in noisy environments. We present a method to obtain a precise spectroscopic characterization of the NV environment, instrumental to design robust sensing strategies with improved noise protection. Then, we exploit optimal quantum control based on a set of numerical methods to optimize the temporal dependence of the sensor driving field adapted to quantum sensing purposes, and prove its advantage to achieve best compromises between signal acquisition and noise cancellation.

The Aharonov-Bohm effect – where electron-interference fringe positions are shifted based on the presence of a non-local magnetic field – has not yet been utilised to its full potential in quantum device design. In this paper, we show that the de Broglie wavelength of the electron is changed locally by its interaction with the magnetic vector potential. The vector potential thus acts as a quantum “phase plate”, changing the phase difference between interfering electron wavefunctions in a non-dispersive, gauge-invariant manner. This model is then shown to be applicable to the design and optimisation of phase-dependent quantum devices such as superconducting quantum interference devices (SQUIDs), quantum sensors, and so on.

Ensembles of atoms or other quantum emitters are envisioned to be an important component of quantum applications, ranging from quantum memories for light to photon-photon gates to metrology. It has historically been an outstanding challenge to exactly solve for the quantum dynamics of an optical field as it propagates through and interacts with an ensemble. The standard axiomatic approach is to use the one-dimensional Maxwell-Bloch equations, which assume that excited atoms emit independently into unwanted directions. This ignores the wave interference of the emitted light, which depends on correlations between the atoms. Here, we discuss an alternative theoretical approach, which accounts for interference and the precise atomic positions. In this formalism, an interacting quantum spin model describes the dynamics of the atomic internal degrees of freedom under multiple photon scattering, while the field properties can subsequently be re-constructed from the spin correlations. Using this model, we then show how interference can be exploited as an extremely powerful resource to suppress the unwanted emission of light and the subsequent loss of information into undesirable directions. The effects of interference are particularly prominent in ordered arrays of emitters. For example, it can be shown that an array acts as a perfectly lossless waveguide for light, in direct analogy to a conventional photonic crystal waveguide. By exploiting this concept, we derive a novel protocol for a quantum memory for light, whose error probability as a function of optical depth scales exponentially better than previously known bounds.

When atoms are optically coupled to a one dimensional waveguide, they can interact through macroscopic distances. The retardation effects inherent to field propagation and the associated delay in information backflow between the atoms result in a departure from the familiar Markovian dynamics. We study the case of two two level atoms coupled along a waveguide. One remarkable feature of the dynamics in this regime is the formation of long-lived bound states in the continuum (BIC),³⁰ that refer to a hybrid diatomic molecule bound together by propagating modes of a field. In particular, we study the probability of reaching such a bound states of the system starting in an initially anti-symmetric state of the emitters.

In this work we do a brief analysis of some widespread technologies for imaging science and security, while we also propose new techniques to exceed their standard classical limits by using quantum illumination and quantum detection, and exploiting special quantum modulation phenomena.

We introduce a first-order quantum-phase-transition model, which exhibits giant sensitivity χ∝N2 at the critical point. Exploiting this effect, we propose a quantum critical detector (QCD) to amplify weak input signals. The time-dynamic QCD functions by triggering a first-order dynamical quantum phase transition in a system of spins with long-range interactions coupled to a bosonic mode. We numerically demonstrate features of the dynamical quantum phase transition, which leads to a time-dependent quantum gain. We also show the linear scaling with the spin number N in both the quantum gain and the corresponding signal-to-quantum noise ratio of this QCD. Our QCD can be a resource for metrology, weak signal amplification, and single photon detection.

The core of optical quantum information science is to use photonic quibits to encode, communicate, manipulate, and measure information, while single-photon efficient emitters (SPED) are one of the key devices to detect photonic qubits. Today, many SPED materials platforms, device architectures, and device performance are being actively explored.1 However, the fundamental study of ultrafast photophysics in situ devices remains a challenge. Another major challenge is current SPED devices rely on traditional semiconductor device physics. To break current device limitations, quantum materials including nanocrystal semiconductors and 2D semiconductors, may lead to novel device physics due to their unique ultrafast photophysics phenomena such as phonon bottleneck effect, multiple exciton interaction, and phase transition ultrafast locking. However, these phenomena are not fully understood. Therefore, in this talk we use a unique ultrafast photocurrent spectroscopy of sub-20 ps time resolution to study the in situ next generation SPED, which is on the platform of solution-processed PbS nanocrystals and 2D black phosphorus. We study the ultrafast photocurrent under various conditions such as temperature (80K to 450 K), laser flux, and electrical field dependence (up to 105 V/cm). We address the ultrafast photophysics dynamics including carrier photogeneration, recombination, transport, and trapping.2-4 References 1. R. H. Hadfield, “single-photon detectors for optical quantum information applications” Nat. Photonics, 3, 696 (2009) 2. J. Gao, et. al. “Carrier Transport Dynamics in High Speed BlackPhosphorus Photodetectors” ACS Photonics, 5, 1412 (2018) 3. J. Gao, et. al. “Solution-Processed, High-Speed, and High-Quantum-Efficiency Quantum Dot Infrared Photodetectors” ACS Photonics, 3, 1217 (2016) 4. J. Gao, et. al. “Solution-Processed single-photon efficient detectors” under preparation.

We apply concepts from machine learning to design topological one-dimensional systems. We also use tensorflow and related tools for designing quantum gates for multilevel qdits with random and unknown media. We report on experiments concerning the realization of a large-scale Ising machine and the use of an optical neural network for detecting cancer morphodynamics in in-vitro tumor models.

Photon pairs generated in spontaneous parametric downconversion exhibit a strong correlation in time, which has been used to synchronize spatially separated clocks in the past in quantum key distribution implementations to a high accuracy. A symmetric version of this scheme can be used to allow for an absolute clock synchronization, and the entanglement properties of photons generated in spontaneous down conversion allows to strengthen the authenticity of the received signals through entanglement witnesses. Aspects of this time synchronization technique with respect to use in optical fibers and remaining vulnerabilities are discussed. [1] C. Ho, A. Lamas-Linares, and C. Kurtsiefer: Clock synchronization by remote detection of correlated photon pairs, New Journal of Physics 11, 045011 (2009). [2] J. Lee, L. Shen, A. Cerè, J. Troupe, A. Lamas-Linares, C. Kurtsiefer: Symmetrical clock synchronization with time-correlated photon pairs, Appl. Phys. Lett. 114, 101102 (2019).

We investigate coherent perfect absorption (CPA) of squeezed coherent states of light by an absorbing beam splitter. First we derive the absorption coefficients for quantum coherence and for intensity, which generally differ. Secondly, we present the remarkable properties of a CPA-gate: two identical but otherwise arbitrary incoming squeezed coherent states can be completely stripped off their coherence, producing a pure entangled squeezed vacuum state at the output. Importantly, this output state of light is not entangled with the absorbing beam splitter by which it was produced. This makes the CPA gate potentially interesting for continuous-variable quantum state preparation.

SWAP gate is an essential element of nearest neighbor qubit networks which carry out quantum information processing tasks. The customary way of applying the SWAP gate consists of consecutive probabilistic operations which requires considerable resources. We propose the theoretical design of a structure constructed from linear optical elements on-chip, which applies the SWAP gate deterministically. Using reconfigurable elements, the structure can apply either the SWAP or instead the identity gate. Utilizing components frequently employed in the design and physical implementation of photonic networks on-chip, the structure can be implemented on various platforms. With its compact structure requiring no detectors or ancilla qubits, our design substantially reduces the required resources for the implementation of the SWAP gate.

Quantum key distribution protocols (QKD) identify eavesdroppers on quantum channel based on laws of quantum mechanics. In the original BB84 protocol, unauthorized measurements on qubits are discovered after Alice and Bob sacrifice some random resulting key bits as a test and find out a mismatch rate. Decoy state protocol alerts photon number splitting attack when the decoy multiphoton pulses deliberately positioned by Alice are registered abnormally higher at Bob’s detectors than the single photon pulses are. E91 protocol is the first QKD protocol that ever brought about entangled atoms. Based on Bell’s theorem, a probability coefficient is constrained within a fixed range under the circumstances of interception. While in practice, bit error rate (BER) is not necessarily associated with vicious eavesdropping. Detection inefficiency, transmission loss, imperfect entanglement sources and many other factors contribute as false alarms. Error correction is an essential post-processing procedure to tolerate implementation limits, yet secure the accuracy of the transmitted key. Quantifying third party contaminations also helps setting an optimal BER threshold to decide if one should abandon all previous communications. In this work, we summarize major causes of bit error in various practical QKD protocols mentioned above and study whether error correction models, such as low-density parity-check code (LDPC), perform accordingly to different kinds of errors.

Integrating semiconductor quantum dots (QDs) in planar photonic devices such as waveguides and photonic crystals, provides an excellent approach to develop on-chip quantum photonic circuits with deterministic photon-emitter interfaces [1]. To further scale up this technology, a key requirement is to develop reconfigurable circuitry that can be operated at a speed compatible with the emitter coherence time (0.1–1 μs) without adding excessive loss or emitter decoherence. The existing routing mechanisms, based on thermo-optic and electro-optic effects, do not meet these demands as they are either too slow or require very large footprints, limiting both scalability and efficiency. In this work, we demonstrate a different approach to on-chip routing by using nano-opto-electro-mechanical devices integrated with single-photon sources, i.e., InAs QDs in GaAs [2]. Unlike refractive-index-tuning methods, such opto-electro-mechanical interaction can be very strong at the nanoscale and, most importantly, material-independent [3], thus offering the advantage of a much smaller attainable device footprint, lower insertion loss, and faster switching speed. We report a gap-variable directional coupler whose splitting ratio is controlled mechanically via capacitive actuators, allowing us to perform disturbance-free routing of single photons emitted by embedded QDs with extinction ratios >20 dB and nW-level power consumption. Taking advantage of the reduced device footprint (<30 μm2) and the small dimension involved, we demonstrate sub-microsecond switching time (~370 ns) and a total insertion loss of 0.67 dB/switch. Such low loss and overall device performance are key to implementing networks of controllable quantum gates and schemes for on-chip photon de-multiplexing [4]. REFERENCES: [1] P. Lodahl, S. Mahmoodian, and S. Stobbe, “Interfacing single photons and single quantum dots with photonic nanostructures” Rev. Mod. Phys. 87, 347 (2015). [2] C. Papon et al. “Nanomechanical single-photon routing” arXiv preprint arXiv:1811.10962 (2018). [3] L. Midolo, A. Schliesser, and A. Fiore, “Nano-opto-electro-mechanical systems” Nat. Nanotechnol. 13(1), 11 (2018). [4] H. Wang et al. “Toward scalable boson sampling with photon loss” Phys. Rev. Lett., 120(23), 230502 (2018).

Among different solid-state emitters of quantum light, epitaxial GaAs quantum dots (QDs) have recently emerged as nearly-ideal sources of triggered polarization entangled photon pairs [1]. This property, combined with the strongly suppressed probability of multiphoton emission under resonant excitation [2] has allowed the implementation of quantum teleportation using photons subsequently emitted by a single QD [3]. In this talk I will discuss the peculiar properties of GaAs QDs [4,5], their performance as emitters of both single and entangled photons, as well as possible methods to engineer their light emission characteristics [1,4] to meet the demanding requirements imposed by photonic quantum technologies. [1] D. Huber et al. Phys. Rev. Lett. 121, 033902 (2018). [2] L. Schweickert et al. Appl. Phys. Lett. 112, 093106 (2018). [3] M. Reindl et al. Science Adv. (2018). [4] X. Yuan et al. Nat. Comm. 9, 3058 (2018). [5] M. Reindl et al. https://arxiv.org/abs/1901.11251.

Coherent quantum devices play a central role in quantum science and engineering. Rare-earth ions such as erbium in solids feature numerous 4f- intra-shell transitions that are effectively shielded from their crystalline surroundings by closed outer shells, allowing for long spin coherence times and narrow optical transitions. Recent ensemble experiments have established the rare-earth doped crystals as the leading materials for optical quantum memories. However, the development of large-scale quantum devices based on rare-earth doped materials has remained a challenge. Here we describe a scalable quantum photonic platform based on epitaxially grown oxide thin films doped with trivalent ions on silicon substrates. The platform builds upon the recent developments of high quality epitaxial rare-earth doped oxides on silicon, and highlights the integration of quantum coherent materials with existing silicon technologies for ultimate device scalability. The proposed device platform builds upon our capability to epitaxially grow high quality, near-lattice-matched Y2O3 thin films on silicon. The epitaxial thin film is of high structural quality and offers several distinct advantages: (1) significantly less optical loss and better quantum emitter coherence; (2) atomic precision placement of rare-earth emitters (via delta doping) with respect to the photonic mode for controllable ion-photon coupling; (3) scalable top-down device fabrication using standard lithography and etching techniques; (4) heterogeneous integration with silicon takes full advantage of existing silicon photonics technologies for routing, tuning, and modulation of the quantum emission from rare-earth ions.

We theoretically study the Dirac fermion dynamics in a graphene monolayer in the presence of an applied ultrafast laser pulse. The pulse has the duration of a few femtoseconds and the amplitude of 0.1 - 0.5 V/Å. The waveform of the pulse is described by Hermit Gaussian polynomials with varying carrier-envelope phase. We show that the ultrafast dynamics of Dirac fermions strongly depends on the carrier-envelope phase and the frequency of the applied pulse. The ultrafast pulse generates an electric current which results in a finite transferred charge. The ultrafast field-driven current and the corresponding net transferred charge depend on the waveform of the applied pulse. Our results pave the way for the development of ultrafast information processing in the terahertz domain.

Metamaterials are presented as a suitable platform to implement controllable constructive and destructive quantum interference. We investigate general lossy asymmetric and unbalanced 2x2 networks to realize nonclassical multiphoton interference effects. A design roadmap for achieving maximum programmability while setting a limit on the minimum value of quantum interference baseline counts is also reported. Specifically, we explore the capabilities of metasurfaces (2D alternates for metamaterials), by engineering the local interaction of light and matter at the subwavelength scale for realizing quantum interference, and conclude that metamaterials are a versatile platform for experiments on the foundations of quantum mechanics such as quantum coalescence effects.