This PDF file contains the front matter associated with SPIE Proceedings Volume 10733, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

On demand single photon emitters (SPEs) play a key role across a broad range of quantum technologies, including quantum computation, quantum simulation quantum metrology and quantum communications. In quantum networks and quantum key distribution protocols, where photons are employed as flying qubits, telecom wavelength operation is preferred due to the reduced fibre loss. However, despite the tremendous efforts to develop various triggered SPE platforms, a robust source of triggered SPEs operating at room temperature and the telecom wavelength is still missing. Here we report a triggered, optically stable, room temperature solid state SPE operating at telecom wavelengths. The emitters exhibit high photon purity (~ 5% multiphoton events) and a record-high brightness of ~ 1.5 MHz. The emission is attributed to localized defects in a gallium nitride (GaN) crystal. The high performance SPEs embedded in a technologically mature semiconductor are promising for on-chip quantum simulators and practical quantum communication technologies.

Color centres in diamond represent a very interesting system for realizing single photon emitters, even at room temperature, in particular are attracting an ever-growing interest in quantum optics, quantum information and quantum sensing, due to their appealing photo-physical properties combined with ease of access and manipulation in a solid state system characterized by high transparency and structural stability. Literally hundreds of optically active color centers can be created and controlled in the diamond matrix, to be employed either as bright and stable single-photon sources or individual spin systems with optical readout, with record performances even at room temperature. In concurrence with the remarkable results obtained at the state of the art on the exploitation of the unique properties of the negatively-charged nitrogen-vacancy complex (NV), new and appealing color centers are continuously being discovered and characterized. In the present contribution, the most recent results obtained by a collaboration among the Italian National Institutes of Metrologic Research (INRiM), the University of Torino and the Italian National Institutes of Nuclear Physics (INFN) will be overviewed and critically assessed in their future perspectives.

Ensembles of nitrogen-vacancy color centers in diamond hold promise for ultra-precise magnetometery, competing with superconducting quantum interference device detectors. Sensor and metrology applications for situations involving high sensitivity require efficient manipulation of the nitrogen-vacancy color centers electronic spins within large volume. Thus, the design of microwave antennas providing a uniform and strong microwave magnetic field over a relatively large volume is on a high demand. In this paper we report different antenna designs based on low loss high permittivity dielectric materials for coherent manipulation of a large ensemble of nitrogen-vacancy color centers in diamond. The operational principle of the proposed antennas is based on excitation of transverse electric (TE) or hybrid electromagnetic (HEM) modes of dielectric resonators. The first antenna design is based on TE₀₁ mode excited inside the resonator made on a ceramic with permittivity of 80. The uniformity of the microwave magnetic field generated by the antenna was verified by measurement of the optically detected magnetic resonance and Rabi frequency in a high-density ensemble of nitrogen-vacancy color centers placed in the center bore of the antenna. Rabi frequency of 10 MHz in a volume of 7 cubic millimeters with a standard deviation of less than 1% at 5 W pump power has been measured at the room temperature. This is enough to coherently excite all color centers in commercially available diamond plates at room temperature. The second antenna design is based on HEM_11δ mode excited in the ceramic resonator characterized by the permittivity of 235. The numerical simulations predict the Rabi frequency value of 34.85 MHz in a volume of 6 cubic millimeters with a standard deviation of less than 5% at 5 W pump power. The obtained result paves the way to improve the sensitivity of cutting-edge nitrogen-vacancy color centers based magnetometers by several orders of magnitude, practically reaching superconducting quantum interference device detectors level of sensitivity.

Boson sampling is considered as a strong candidate to demonstrate the “quantum advantage / supremacy” over classical computers. However, previous proof-of-principle experiments suffered from small photon number and low sampling rates owing to the inefficiencies of the single-photon sources and multi-port optical interferometers. In this talk, I will report two routes towards building Boson Sampling machines with many photons. In the first path, we developed SPDC two-photon source with simultaneously a collection efficiency of ~70% and an indistinguishability of ~91% between independent photons. With this, we demonstrate genuine entanglement of ten photons. Very recently, we managed to observe 12-photon entanglement using a novel SPDC source. Such a platform will provide enabling technologies for teleportation of multiple properties of photons and efficient scattershot boson sampling. In the second path, using a QD-micropillar, we produced single photons with high purity (>99%), near-unity indistinguishability for >1000 photons, and high extraction efficiency—all combined in a single device compatibly and simultaneously. We build 3-, 4-, and 5-bosonsampling machines which runs >24,000 times faster than all the previous experiments, and for the first time reaches a complexity about 100 times faster than the first electronic computer (ENIAC) and transistorized computer (TRADIC) in the human history. We are currently increasing the rate by optimizing the single-photon extraction efficiency to near unity, background-free resonance fluorescence, and using improved schemes such as boson sampling with photon loss, with the hope of achieving 20-photon boson sampling this year.

I present quantum nano-photonic devices based on nanophotonic resonators coupled to rare-earth-ions in crystals. The rare-earth ions exhibit long coherence times on optical transitions, which makes them suitable for optical quantum memories. We demonstrate a high-fidelity nanophotonic quantum memory based on a mesoscopic rare-earth ensemble coupled to a photonic crystal cavity. The nanocavity enables >95% spin polarization for efficient initialization of the atomic frequency comb memory, and time-bin-selective readout via enhanced optical Stark shift of the comb frequencies. Besides ensemble memories, single rare-earth-ions coupled to nano-resonators can be used as single optically addressable quantum bits where the quantum state is mapped on their Zeeman or hyperfine levels with long coherence time. Our solid-state nano-photonic quantum light-matter interfaces can be integrated with other chip-scale photon source and detector devices for multiplexed quantum and classical information processing at the nodes of quantum networks.

Single quantum emitters are an important resource for quantum photonics, constituting building blocks for single-photon sources, qubits, and deterministic quantum gates. Robust implementation of such functions, however, can only be achieved through systems that provide both strong light–matter interactions and a low-loss interface between emitter and probing optical fields. This presentation will discuss the development of quantum photonic integration platforms that allow the creation of photonic circuits incorporating single-emitter based functionality. The single emitter of choice is the self-assembled InAs quantum dot, which can be embedded inside a GaAs nanophotonic device. Such quantum dot containing nanophotonic structures can be designed to provide highly efficient coupling to an underlying waveguide-based photonic device based on transparent or nonlinear optical materials, such as Si3N4 and SiO2. The introduction of single quantum dot based devices as functional elements in quantum photonic circuits may enable significant scaling of on-chip photonic quantum information systems, in two complementary ways. First, by acting as chip-integrated on-demand, bright single-photon sources, these devices can significantly boost the photonic flux available for non-deterministic, linear-optics based quantum computation. Furthermore, single-emitters strongly coupled to on-chip cavities provide a path towards single-photon nonlinearities, which would enable deterministic quantum operations through cavity quantum electrodynamics within a quantum network formed by a photonic integrated circuit. New developments in heterogenous integration and hybrid, pick-and-place fabrication methods will be discussed in the talk.

The interaction of macroscopic mechanical object with electron charge and spin plays a vital role in today’s information technology and fundamental studies of the quantum-classical boundary. Recently emerged valleytronics encodes information to the valley degree-of-freedom and promises exciting applications in communication and computation. Exploring the interplay between the valley physics and macroscopic mechanics will bring new perspectives for valley information processing and exploration of the quantum-classical boundary. Recently discovered two-dimensional (2D) transition metal dichalcogenides (TMDs) provide an appealing platform to explore valley-mechanical interaction. Their honeycomb lattice supports two valleys (namely K and K’) and thus forms a spin-like binary system called valley-pseudospin. The broken inversion symmetry together with the strong spin-orbit coupling give rise to a unique optical selection rule, which provides a powerful tool for optical generation and manipulation of the valley. On the other hand, nano-mechanical systems made of 2D materials have shown high mechanical strength, high quality-factor, and extraordinary mass and force sensitivities. Their extremely small mass also leads to large quantum zero-point motion and thus facilitates its use in quantum system. Because of the broken inversion symmetry in monolayer TMDs, electrons in the K and K’ valleys possess total magnetic moments that are equal in magnitude but opposite in sign. When a magnetic field gradient is applied perpendicular to the monolayer, it experiences a net force whose direction depends on which valley is populated and therefore allows transduction of the valley information (K or K’) into the mechanical motion (upward or downward displacement). We fabricate the valley-resonators by dry-transferring an exfoliated monolayer MoS2 onto pre-patterned square hole structures, which are conformally coated with a film of high permeability permalloy (Ni/Fe). Under an external magnetic field, the permalloy film distorts the field and generates a strong local magnetic field gradient. For an applied magnetic field of 26 mT, the magnetic field gradient in the central region of the suspended MoS2 reaches ~4000 T/m. The monolayer nature of the MoS2 membrane is confirmed by Raman and photoluminescence (PL) spectroscopy. A PL scan across the sample shows that the emission from the suspended regions is much stronger than that from the metal substrate, which confirms that the membrane is freestanding. The square structure has a lateral dimension of 5.2 × 5.2 um^2 and the resonator has an effective mass of 21 fg. The mechanical resonance frequency is ~35.7 MHz and the quality factor is 22,000 at 30 K. We observe the valley-mechanical actuation of the monolayer MoS2 at low temperature. We detect the resonator motion by an optical interferometric scheme using a probe laser (654 nm) and excite the K and K’ valleys alternatingly by modulating the polarization of the pump laser (633 nm) between left- and right-circular (LCP and RCP) while keeping the optical intensity constant. This exerts an oscillating push-pull force to drive the resonator. The measured displacement of the resonator shows a clear Lorentzian response. Meanwhile, a linearly-polarized pump light shows no driving effect because it equally populates both valleys and thus results in zero net force. The mechanical displacement shows an opposite phase when the pump laser polarization is switched to opposite helicity, which confirms that the excitation of carriers at different valleys exerts opposite forces onto the monolayer. In the measurement, the polarization modulation frequency is close to the mechanical resonance (~35.7 MHz) which is much slower than the decay of the valley carriers, whose timescale is in the range of picoseconds to a few nanoseconds. Therefore, the valley carrier population adiabatically follows the polarization modulation. The probe light is kept linearly-polarized throughout the measurement to eliminate its effect on the net valley population. Utilizing the fact that the direction of the force depends on which valley is populated, we demonstrate transduction of the valley information into the mechanical state of the nano-resonator. We examine the mechanical quadratures of the device when it is resonantly driven by opposite valley population. Two distinct mechanical states of opposite phase are clearly resolved within the measurement uncertainty and the confidence level of differentiating the two states is close to 100%. This result demonstrates that the valley information of the monolayer is unambiguously transferred into the mechanical states. In conclusion, our experiment demonstrates direct transduction of valley information to mechanical states of a MoS2 monolayer resonator. The valley-mechanical interaction lays the foundation for a new class of valley-controlled mechanical devices. It also facilitates hybridization of valley pseudospin with other quantum information carriers such as two-level qubits and microwave photons.

The advent of quantum optics and quantum information processing goes hand in hand with the search for adequate active and passive components operating on the single-photon level at telecommunication wavelengths. Among a variety of approaches, a hybrid arrangement of integrated single-photon sources, reconfigurable photonic circuitry, and detectors on a single chip is particularly promising with respect to complexity, compactness, reproducibility, stability, and ease of fabrication. While a multitude of detection technologies are currently investigated, waveguide-integrated superconducting nanowire single-photon detectors stand out due to their near-unity detection efficiencies at outstanding timing accuracy and speed. Here, by exploiting the concept of critical coupling, we present the integration of a short nanowire into a two-dimensional double heterostructure photonic crystal cavity to realize an integrated single-photon detector with excellent performance metric. The complete detector characterization reveals on-chip detection efficiencies of almost 70% at telecom wavelengths, recovery times of 480 ps, and vanishingly low dark count rates. Compared to photonic crystal nanobeam cavities, our overhauled design approach reduces outscattering losses and can readily be combined with single-photon emitters integrated into on-chip cavities. Our silicon photonics approach paves the way for the implementation of compact on-chip detector arrays and time-multiplexed single-detector schemes.

On-chip heralded single photon sources are of key importance in the development of chip-scale devices exploiting the quantum properties of light. Single photon states can be produced as single photons heralded from correlated photon pairs generated through spontaneous four wave mixing. On-chip heralded single photon sources based on spontaneous four wave mixing have been already demonstrated. However, the heralded and herald photons are usually generated with wavelengths very close to the pump one, limiting the pump rejection efficiency and the application to the mid infrared. Moreover, the common sources of heralded photons based on spontaneous four wave mixing require spectral post filtering to achieve high purity, limiting the brightness and the integration of these sources. A solution to these problems can be provided by intermodal four wave mixing. In this work, we demonstrate the generation of photon pairs through intermodal four wave mixing in silicon waveguides, measuring the coincidences between the idler at 1.281 μm and the signal at 1.952 μm. We then discuss the application of intermodal four wave mixing to on-chip heralded single photon sources.

The performance of single photon sources based on single quantum dot emitters coupled to microcavities is analyzed with respect to different conditions of polarization. Electro-optic tuning is shown as a method to tune microcavities with distributed Bragg reflector mirrors into polarization degeneracy. Typically, for large cavity polarization splitting, excitation in the linearly polarized cavity modes is the only viable method for resonantly driving a single photon source. However, polarization degenerate cavities allow for arbitrary polarization conditions. A semi-classical model is used to analyze the performance of single photon sources under different polarization conditions. Further, the effect of residual cavity polarization splitting is analyzed under pulsed excitation.

Back in 2002, Toshiba released its pioneer Quantum LED design. [1] It opened a route for electrically driven quantum light sources adapted to different spectral ranges and environments. However, several constraints of the design, like the lack of a built-in wavelength tuning mechanism, or how to surpass the large sheet resistance in nanophotonic structures, remained unsolved. Just recently, completely new approaches appeared adding new functionalities to the original design. [2,4] We will present our own design. It is based on a vertical multijunction heterostructure where quantum light emission and tuning into photonic crystal cavities might become possible, for the first time, without constraints. [2] The device comprises of two separated electrical injection and electrical tuning regions in a bi-polar transistor configuration. The connection between them is purely optical and thus, it naturally avoids the sheet resistance problems that plague other approximations, especially when applied to nanophotonic devices. The first fabricated devices show single photon emission with g2(0)<0.1 at injection currents as low as 100 mA/cm2 and fully linear conversion between electrical power and single photon flux. References: [1]Z.Yuan et al Electrically Driven Single-Photon Source. Science 2002, 295, 102. [2]B. Alén et al “Tunable monolithic quantum light source and quantum circuit thereof” Patent pending EP/17382061.4, PCT/EP2018/052960. Date: Feb 8th 2017 [3]J. P.Murray et al “Electrically Driven and Electrically Tunable Quantum Light Sources”. Appl. Phys. Lett. 2017, 110 (7), 071102. [4]P.Munnelly et al “Electrically Tunable Single-Photon Source Triggered by a Monolithically Integrated Quantum Dot Microlaser”. ACS Photonics 2017, 4 (4), 790–794.

To facilitate the implementation of large scale photonic quantum walks, we have developed a polymer waveguide platform capable of robust, polarization insensitive single mode guiding over a broad range of visible and nearinfrared wavelengths. These devices have considerable elasticity, which we exploit to enable tuning of optical behaviour by precise mechanical deformations. In this work, we investigate pairs of beamsplitters arranged as interferometers. These systems demonstrate stable operation over a wide range of phases and reflectivities. We discuss device performance, and present an outlook on flexible polymer chips supporting large, reconfigurable optical circuits.

The efficient generation, coherent control, manipulation and measurement of quantum states of light and matter is at the core of quantum technologies. Hybrid quantum systems, where one combines the best parts of multiple individual quantum systems together without their weaknesses, are now seen as a way to engineer composite quantum systems with the properties one requires. This would in principle allow one to probe new physical regimes. However, the issue until recently has been that hybridization has not resulted in systems with superior properties. Recently however we [Nature Photonics 11, 3639 (2016)] have shown an increased coherence times in hybrid system is of composed nitrogen-vacancy centers strongly coupled to a superconducting microwave resonator. This demonstration has enabled this kind of hybrid system to enter the regime where quantum nonlinearities are present. We discuss several types of nonlinearity effects that can be naturally explored (bistability and superradiance). Our work paves the way for the creation of spin squeezed states, novel metamaterials, long-lived quantum multimode memories and solid-state microwave frequency combs. Further in the longer term it may enable the exploration of many-body phenomena in new cavity quantum electrodynamics experiments.

There has been rapidly growing interest in hybrid quantum devices involving a solid-state spin and a macroscopic mechanical oscillator. In such a hybrid device, phonons can both control and readout the spin systems as well as transduce quantum information between remote and even disparate quantum elements in a solid-state quantum network. In this talk, I present an all-diamond approach where a nitrogen vacancy (NV) center defect spin is embedded in a diamond nano optomechanical resonator. This system combines the excellent mechanical and optical qualities of diamond with the robust quantum coherence of the NV center. I will present initial experimental results on the coupling of spin, mechanical, and optical degrees of freedom that show the potential to realize a variety of novel, quantum-enabled tasks including scalable quantum communication protocols and spin squeezing.

Securing information has been a concern for more than 4,000 years, but in the times in which we are connecting every single aspect of our businesses and lives, developing secure products and infrastructures has become a global priority. Remarkably, quantum technologies bring unique possibilities for the cryptographic world. In this talk, we will describe recent efforts on the development of a highly integrated quantum entropy source, a key component to generate unpredictable cryptographic keys in any connected device. In particular, we will present the integration of two quantum entropy sources, one in Silicon Photonics and the other in Indium Phosphide. The devices are based on the accelerated phase diffusion process observed in pulsed semiconductor lasers, a macroscopic quantum effect resulting from microscopic spontaneous emission events. Both chip implementations enable Gb/s generation rates in form factors below 2mm x 5mm in indium Phosphide and 0.5mm x 1mm in Silicon Photonics. Our results show progress towards the industrialization of quantum devices using standard semiconductor production lines and processes.

Quantum physics can provide sources of randomness that can be certified as being uncorrelated to any outside process or variable, i.e. sources of private randomness, based on a violation of a Bell inequality. Initial experimental realizations of such sources of certified randomness are based on atomic or atomic-like systems, but suffer from impractically low generation rates for most applications. High efficiency infrared photodetectors and photon pair sources permitted experimental demonstrations of loophole free violation of the Bell inequality using photons. The random bit generation rate for these setups was on the order of tens per second, where the main limitation is the fixed repetition rate of the photon pair source combined with the small violation observed. In our experiment, we close the detection loophole with a system efficiency over 82%. The source of entangled photon pairs is based on continuously pumped spontaneous parametric down conversion. We estimate a collection efficiency of ≈90% into single mode fibers and detect photons with a transition edge sensors. Detection events are time-tagged and organized into time bins, for which we consider four possible outcomes: one or more detections at Alice’s side, one or more detections at Bob’s side, one or more detections at both Alice’s and Bob’s, and no detection in either channel. These events eventually lead to a CHSH-type Bell inequality that is violated for a range of time bin widths. With such an arrangement, we reach asymptotic device-indepentnet random bit generation rates on the order of 1000 bits per second.

The progressive development of quantum technologies in many areas, ranging from investigation on foundamentals of quantum of mechanics to quantum information and computation, has increased the interest on those problems that can exhibit a quantum advantage. The Boson Sampling problem is a clear example where traditional computers fail in the task of sampling from the distribution of n indistinguishable photons after a propagation in a m-mode optical interferometer. In this context, in the absence of classical algorithms able to simulate efficiently multi-photon interference, the validation of Boson Sampling is still an open problem. Here we investigate a novel approach to Boson Sampling validation based on statistical properties of correlation functions. In particular we discuss its feasibility in actual proof-of-principle experiments. Furthermore we provide an extensive study of the physical resources required to validate experiments, investigating also the role of bosonic bunching in high-dimensional applications. Our investigation confirms the goodness of the validation protocol, paving the way to use this toolbox for the validation of Boson Sampling devices.

We experimentally demonstrate an optical quantum random number generator with real-time randomness extraction to directly output Gaussian distributed random numbers by measuring the vacuum fluctuation of quantum state. A tight randomness estimation and a Gaussian extractor are proposed to eliminate the influence of side information introduced by the imperfect devices in practical system. The generation of Gaussian distributed quantum random numbers can simply the procedure and reduce the calculation error by optimizing the procedure that transforms uniform distributed random numbers into Gaussian distributed random numbers. And the calculated Gaussian distributed random numbers can be utilized to transformed into random numbers with unique distributions.