A broad effort is currently underway to develop quantum computers that can outperform classical counterparts for certain computational or simulation tasks. Suppressing errors is one of the central challenges for useful quantum computing, requiring quantum error correction for large-scale processing. However, the overhead in the realization of error-corrected “logical” qubits, where information is encoded across many physical qubits for redundancy, poses significant challenges to large-scale logical quantum computing. In this talk, we will discuss the recent advances involving programmable, coherent manipulation of quantum systems based on neutral atom arrays excited into Rydberg states, allowing the control over several hundred qubits in two dimensions. Optical control techniques are central to this approach. In particular, we use this platform to explore quantum algorithms with encoded logical qubits and quantum error correction techniques. Using this logical processor with various types of error-correcting codes, we demonstrate that we can improve logical two-qubit gates by increasing code size, outperform physical qubit fidelities, create logical GHZ states, and perform computationally complex scrambling circuits using 48 logical qubits and hundreds of logical gates. These results herald the advent of early error-corrected quantum computation, enabling new applications and inspiring a shift in addressing both the challenges and opportunities that lay ahead.

Neuromorphic (brain-inspired) photonics leverages photonic chips to accelerate neural networks, offering high-speed and energy efficient solutions for use in datacom, autonomous vehicles, or other time sensitive applications. However, the limited size of photonic neural networks limits the complexity of solvable tasks. A natural candidate to provide increased complexity is quantum computing and its exponential speedup capabilities. Specifically, we explore photonic continuous variable (CV) quantum computation. Combining classical networks with trainable CV quantum circuits yields hybrid networks that provide significant trainability and accuracy improvements. On a classification task, hybrid networks achieve the same accuracy as fully classical networks that are twice the size. When noise is applied to the network parameters, the hybrid and classical networks maximize accuracy below the expected on-chip noise level. These results demonstrate that hybrid networks can achieve increased performance with smaller network sizes, providing a promising route to scalable neuromorphic photonic processing.

With recent developments in the field of quantum computing and cryptography, establishing quantum networks would allow for the implementation of post-quantum cryptographic protocols, distributed quantum computing, and quantum sensor networks. Though, quantum networks require the use of quantum repeaters to preserve the transmitted quantum information over long distances. This work focuses on the implementations of quantum frequency conversion which is used to ensure the signal is of a suitable frequency for transmission between the different optical components in the system.

The Quantum Internet will readily transfer quantum bits between users near and far and over multiple different channels, and could be used for secure communications, distributed quantum computing and metrological applications. Satellite to ground quantum links are a crucial technology, as they will allow large distances and reaching locations with little infrastructure. I will give an overview of the upcoming Canadian quantum communication satellite mission QEYSSat, and discuss recent advances in the generation and distribution of free-space quantum information using novel techniques including time-bin and reference frame independent protocols.

We present a satellite-compatible reconfigurable quantum network architecture. During the satellite-pass the network adopts a point-to-multipoint topology where all the users communicate with the satellite, whereas outside of a satellite pass, the signal is rerouted to form a fully-connected network between the ground users. Exploiting multiplexing techniques, we show simulation results that indicate that this scheme can be used to enhance the secure key rate and to connect a multitude of users on the ground with minimal hardware requirements.

Quantum sources that produce entangled photon pairs are crucial and indispensable components in quantum applications. Entangled photon sources based on nonlinear crystals or waveguides require bulky free-space optics and precision alignment. In contrast, fiber-based entangled photon sources, where entangled photon pairs are directly generated in an optical fiber, make quantum technologies less costly, more practical and accessible, as well as compatible with telecom fiber network infrastructure. In this talk, we review the development of fiber-based entangled and hyper-entangled photon pair sources based on the periodically-poled silica fiber (PPSF). We demonstrate practical and high quality entanglement sources at room temperature, compact and alignment free. The technology has now been commercialized. My talk will reveal the key technological advantages of using PPSF as a nonlinear material for complex quantum state generation, including entangled, hyper-entangled, and hypo-entangled state generation. I will also briefly discuss the applications of polarization-frequency hyper-entanglement and characterization of high-dimensional entanglement systems, including deriving entanglement witnesses using machine learning.

In this talk, we establish chip-based integrated silicon nitride photonics as a platform for experiments on the interactions between free electrons and light. Placing the fibre-coupled microresonators in a transmission electron microscope, we observe a quantised loss of energy for electrons passing the waveguide in an aloof geometry and inelastically scattering off the initially empty cavity modes while generating photons. Coincidence measurements performed on both particles reveal the common origin of these correlated electron-photon pairs, while post-selection allows for enhanced imaging of the resonator’s optical modes and promises applications as a high-fidelity heralded photon Fock state source.

Neutral atomic gases provide fantastic opportunities for studying and controlling quantum phenomena, ranging from many-body physics to quantum computers. In our research, we use the well-known interactions between cold gases and electromagnetic radiation to harness various quantum degrees of freedom. Quantum memories, used for storing and manipulating photonic signals, will be a key component in quantum communications systems, especially in realizing critical quantum repeater infrastructure. Cold atoms have significant potential as high performance spin-wave quantum memories, due to the long storage times associated with low temperature and slow thermal diffusion. In our work, we demonstrate two memory protocols in ultracold (sometimes Bose-condensed) atoms, which hold the potential for high-performance light storage: the Autler-Townes splitting (ATS) and superradiant approaches. These methods provide a path towards practical implementations in both ground- and satellite-based quantum communications systems, and we are working on both increasing performance and developing practical implementations.

In this talk, I will present the latest results in superconducting single-photon detectors. Superconducting wires have remarkable sensitivity to single-photons and are a reliable and high-performance technology with significant impact on the quantum information research community. However, increasingly applications as diverse as detection of high-energy particles and searches for dark matter are being pursued. Finally, research on these nanowires has permitted their use for basic electronics circuits such as comparators, shift registers, and counters. We will review these and other topics surrounding the development of nanowire single-photon detectors.

Here we show that incorporating broadband metamaterial perfect absorbers into a photodetector’s active area can improve device efficiency and speed. We show an optical absorption of 93% across the spectral region where commercially available Si and InGaAs detectors have poor efficiencies. Combining the metamaterial perfect absorber with an avalanche photodiode layer stack, we aim to realize a high efficiency portable single photon avalanche diode with high timing resolution ideal for quantum ranging, quantum communication, and medical imaging applications.

Gyroscopes find wide applications in everyday life from navigation and inertial sensing to rotation sensors in hand-held devices and automobiles. Current devices, based on either atomic or solid-state systems, typically impose a choice between long-time stability and high sensitivity in a miniaturized system. Thanks to their optical properties, nuclear spins associated with NV centers in diamond have been proposed to overcome this challenge. While optical polarization improves these devices' sensitivities, further improvement is needed. Here, we propose a gyroscope protocol based on a two-spin system that includes a spin intrinsically tied to the host material, while the other spin is effectively in an inertial frame. The rotation rate is then extracted by measuring the relative rotation angle between the two spins starting from their population states, which are robust against spin dephasing. Importantly, the relative rotation rate between the two spins is enhanced by their hyperfine coupling by more than an order of magnitude, further boosting the achievable sensitivity. The ultimate sensitivity of the gyroscope is limited by the lifetime of the spin system and is compatible with a broad dynamic range, even in the presence of magnetic noises or control errors due to initialization and qubit manipulations. Our result enables precise measurement of slow rotations and exploration of fundamental physics.

Prior to the development of MRI, NMR diffraction (NMRd) was proposed as a method to investigate the structure of crystalline materials. When realized on the atomic scale, NMRd would be a powerful tool for studying materials structure, combining the spectroscopic capabilities of NMR with spatial encoding at condensed matter's fundamental length-scale. In this talk, I will present a nanoMRI platform for achieving angstrom-scale NMRd measurements.

An outstanding challenge in quantum networking is interfacing both classical and quantum technologies. A future quantum network will require one to effectively interface disparate qubit for entanglement distribution applications. In addition, the quantum network will also need to be seamlessly integrated with a classical network to realize the quantum protocols. This talk will highlight recent results toward interfacing integrated photonic qubits, trapped ions, and superconducting qubits and will present progress toward constructing a classical network infrastructure and initial results on operating the classical and quantum network in unison.

The quest to engineer quantum computers of a useful scope faces many challenges that will require continued investigation of the physics underlying the devices. In this talk, I focus on trapped ion quantum computing. I discuss several recent advances my research group has contributed regarding optical control of Ba+ ions for quantum information processing, including multi-level qudit control and novel all-optical loading techniques, and provide a brief outlook on how photonic technologies can enable further progress in this field.

To study long-distance free-space quantum communication links, the Air Force Institute of Technology (AFIT) simulated, designed, built, and characterized an atmospheric turbulence simulator (ATS) with the Fried parameter ranging from 0≤ D⁄r_0 <18.2. The ATS was integrated with a non-turbulent path to conduct quantum interferometric experiments such as the heralded single photon g^2 (τ), and the two-photon Hong-Ou-Mandel (HOM) measurement. We observed that g^2 (0) increased to 1 and that the visibility of the HOM dip significantly decreased in moderate turbulence . Additionally, we tested the reconstruction of polarized-entangled photonic states in various turbulence regimes, and as expected, turbulence weakly affected the reconstruction of the polarization states. This presentation details the experimental setup, results, and analysis of those experiments.

Temporal encodings of quantum information are prevalent in applications because of their suitability for long-distance quantum communication and their compatibility with optical fiber communication networks. Perhaps the simplest temporal encoding is time-bin encoding, i. e. in superpositions of two (or more) temporally separated optical pulses. Early attempts at generating time-bin entanglement from single quantum emitters was not able to avoid the problem of re-excitation or was converted probabilistically from polarization entangled photon pairs from a quantum dot. Direct generation requires a metastable level to carry the coherence and avoid double pair emission into the desired time bins. In order to use dark exciton states as metastable states we have worked on their efficient creation and coherent control in the presence of in-plane magnetic fields. Much of this is based on our recent work on advanced excitation schemes using chirped pulses. With chirped pulses we are now able to deterministically populate a dark exciton state and to transfer this population to the biexciton, which can then emit a photon pair.

Highly entangled photon sources play a crucial role in advancing the capabilities of quantum networks. In this context, we introduce an advanced scheme aimed at improving entanglement of photons emitted from quantum dots based on the framework proposed by Fognini et al. (2018). We propose a setup with reduced physical footprint which employs one electro-optic modulator strategically to enhance entanglement, mitigating the detrimental effects of fine structure splitting (FSS) observed in quantum dots that contribute to the degradation of entanglement.

We discuss the exciting regime of "dynamical resonance florescence," which adds significant modification and fundamental control to the usual CW resonance florescence schemes such as the Mollow triplet, when using coherent pulses whose time duration is shorter than the inverse decay time of the emitter (quantum dot or two level system). We present two examples, including (i) semiconductor quantum dot cavity systems, where we also show recent experiments and simulations side by side, and (ii) waveguide QED systems excited with single photon Fock states. We describe how the usual emission spectrum and intensity outputs are dynamically modified with short pulse excitation, and also demonstrate how single photon nonlinearies are uniquely accessed in this regime. These short-pulsed emission regimes with dynamic driving of two-level emitters allow for the generation of a variety of exotic quantum states of light.

Single photons and quantum interference between indistinguishable pairs of photons are promising resources in the ongoing development of quantum information technologies. On-demand generation of such photons on a photonic integrated circuit (PIC) is desirable as it can allow for stable operation and device scalability alongside other requisite components. Solid-state two-level emitters—in particular, epitaxial semiconductor quantum dots—have demonstrated to be a good source of single photons, though efficient integration onto PICs remains a challenge. Hybrid integration of such dots into on-chip photonic circuitry can provide a basis for testing practical implementations of quantum communication devices. In this talk, I will discuss NRC's InP-based nanowire quantum dots and our work integrating these onto silicon nitride integrated photonics. The cryogenic environment poses challenges in the operation of key components such as optical phase shifters, tunable filters, and on-chip detectors. With this in mind, I will review our progress and near-term plans for realizing on-chip quantum information processing. Also examined is our recent work developing nanowire sources that emit in telecom O or C bands—a key requirement for practical long distance quantum communications—and coherent control schemes for optical pumping.

The preparation of quantum-dot qubits in the excited state is an integral part of the performance of an on-demand single photon source. Recent excitation schemes strategically use pulses that avoid spectral overlap with the qubit emission for easier differentiation between the pump and signal. In this work, we look at the robustness of two such pumping schemes, (i) a dichromatic pulse, and (ii) a notch-filtered adiabatic rapid passage (NARP) approach, in the presence of phonon coupling. We find that due to large instantaneous pulse strengths, the dichromatic pulse suffers from phonon-induced pure dephasing and can have up to 50% worse performance as a single photon source. On the other hand, the NARP approach is more robust against the phonon coupling due to a weaker and smoother pulse profile.

The development of photonic-based quantum information technologies depends on the availability of devices that consistently, and with high efficiency, deterministically emit identical single photons. Furthermore, a key requirement for the implementation of fiber-based quantum secured communication protocols demands that these sources be compatible with optical fiber networks operating in the low-loss telecom C-band (λ ~ 1550 nm). Semiconductor quantum dot emitters offer on-demand operation at high rates and can be incorporated into photonic structures that allow for high efficiency collection. Through composition engineering of InAs_(x)P_(1-x) dot-in-a-rod (DROD) nanowire quantum dot structures we have previously demonstrated single photon emission from wavelengths of up to the telecom O-band. Here we show how the DROD structure can be modified to shift emission wavelength to the telecom C-band with single-photon purities of g(2)(0) = 0.062. Through further optimization of these structures, we aim to dramatically increase source brightness with the long-term goal of developing scalable and efficient C-band emitting site-selected single-photon sources.

Typical schemes for generating correlated states of light require a highly nonlinear medium that is strongly coupled to an optical mode. However, unavoidable dissipative processes, which cause photon loss and blur nonlinear quantum effects, often impede such methods. In this talk, I will report on our experimental implementation of the opposite approach. Using a strongly dissipative, weakly coupled medium, we generate and study strongly correlated states of light. Specifically, we study the transmission of resonant light through an ensemble of non-interacting atoms that weakly couple to a guided optical mode. Dissipation removes uncorrelated photons while preferentially transmitting highly correlated photons, created through collectively enhanced nonlinear interactions. As a result, the transmitted light constitutes a strongly correlated many-body state of light, revealed in the second-order correlation function. The latter exhibits strong antibunching or bunching, depending on the optical depth of the atomic ensemble. The demonstrated mechanism opens a new avenue for generating nonclassical states of light and for exploring correlations of photons in non-equilibrium systems using a mix of nonlinear and dissipative processes.

The study of waveguide-QED systems, where a continuum of quantum field modes is coupled to qubits or two-level systems, has improved our ability to manipulate quantum light-matter interactions on chip. In the typical theoretical approaches to waveguide QED, there are a few necessary approximations, e.g., considering the system in the weak excitation regime, or treating the waveguide as a bath. However, these inherent approximations can break down with short pulse excitation. Here, we investigate the few-photon quantum nonlinear response of chiral qubits, when excited with one and two-photon Fock states. Our theory uses a numerically exact approach, based on Matrix Product States, avoiding the limitations of the usual waveguide-QED approximations. Using a chiral-emitter waveguide system, we show explicitly the breakdown of the weak excitation approximation, and study the single and two-photon nonlinear responses. We demonstrate the impact on the qubit population, and discuss how the phase change can be examined from the photon quantum correlation functions, seeing a radical departure from scattering theory solutions.

Semiconductor quantum dots (QDs) are a type of solid-state quantum emitter that can act as a near-ideal quantum light-matter interface when integrated with high-quality nanophotonic systems. Though QDs have typically been used to create state-of-the-art, on-demand single photon sources, here we widen the perspective on QDs, showing how to design quantum photonic integrated circuits based on both linear and nonlinear QD phase shifters. Specifically, we find that linear QD phase shifters can be used to realize cryogenically-compatible, fast, low-loss, and high-fidelity reconfigurable linear circuits. When paired with QDs that mediate interactions between photonic qubits, generating nonlinear phase shifts, deterministic quantum photonic logic gates can be achieved. Thus, our work paves the way for the realization of on-chip, cryogenically-compatible linear and nonlinear quantum photonic circuits, including quantum photonic neural networks, which can form the foundation for scalable and efficient quantum photonic technologies.

We introduce a theory to model spontaneous emission rates and the Purcell factor for linear gain media, including coupled loss and gain cavity systems. We demonstrate why the usual Fermi's golden rule fails and show the impact of a non-local gain term. We show how to model such effects with a standard Maxwell calculation, which also exploits the power of quasinormal modes. As an application of the theory, we show how one can use gain compensation to improve the Purcell factors of gold-dimer plasmon modes by over one million fold.

Optically active spin defects in diamond have proven to be a promising resource for the implementation of quantum information processing. Their long-term implementation requires the application of microwave and optical coherent control schemes to single, low noise defects coupled to diamond nanophotonic devices with near-unity interfacing efficiencies to the underlying photonic integrated circuits. Such systems will enable the generation of multi-qubit entangled states — the core resource for the implementation of long-distance quantum communication and quantum networking. In this presentation I will introduce our most recent efforts in applying photonic integrated quantum systems towards scalable quantum information processing.

The NV centre in diamond has a long history in advancing quantum photonics technologies. Large-scale applications requires compatibility with integrated photonics for routing, with microelectronics integration equivalently important to realise control. Research to date has concentrated on microwires on diamond or in-house metallisation. In this work, we demonstrate integration of NV in nanodiamonds with silicon microelectronics. A key merit here is exploiting multi-layer metallisation for vector control and routing driving signals. We employ a 0.13um CMOS technology with seven metallic layers: the top layer for static magnetic fields with microwave control in the layer below, across 50μm spaced unit cells. Alignment markers enable lithographic positioning of nanodiamonds with associated NVs. We coherently control a positioned NV using the silicon structure and observe fifty times less power is required compared to an external antenna. The prototype paves the way for integrating solid-state quantum systems with sophisticated microelectronics, leveraging proximal silicon logic.

I will deliver an overview and progress of Xanadu’s photonic quantum computing architecture and the role that photonic chip integration plays in enabling its implementation.

Distributed quantum processing over local optical networks is a route to fault-tolerant quantum computing at scale and practical quantum advantage. The performance of modular, networked quantum technologies will, however, be contingent upon the quality of their light-matter interconnects. Silicon colour centres offer optically-coupled spin qubit registers as the basis for quantum networks and distributed quantum computing. Silicon is an ideal platform for commercial quantum technologies: it unites advanced photonics and the microelectronics industry, as well as hosting long-lived spin qubits. The silicon T centre was recently discovered to combine direct telecommunications-band photonic emission, long-coherence electron and nuclear spins [1,2], and proven integration into industry-standard, CMOS-compatible, silicon-on-insulator (SOI) photonic chips at scale. In this talk I present recent advances networking T centres with nanophotonics. We enhance the optical emission rate by an order of magnitude with integrated nanocavities to create coherent optical interfaces. We determine the T centre’s hyperfine spin qubit coupling and introduce schemes for operating each T centre as a deterministic four-qubit spin register. T centre devices producing spin-entangled photons can make immediate use of integrated silicon photonic networks boasting low-loss active components, efficient coupling to standard telecommunications fibres, and efficient on-chip photon detectors. These elements may be assembled to create an on-chip spin-photon quantum processor that interfaces with optical fibres for long-range communication over the quantum internet.

Recently, fluorescent point defects in silicon have been explored as promising candidates for single photon sources, which may pave the way towards the integration of quantum photonic devices with existing silicon-based electronic platforms. However, the current processes for creating such defects are complex, and commonly require one or two implantation steps. In this work, we have demonstrated implantation-free methods for obtaining G and W-centers in commercial silicon-on-insulator substrates using femtosecond laser annealing. We also demonstrate an enhancement of the color centers’ optical properties by coupling them with photonic structures. For example, we have shown an improvement in emission directivity for G centers by embedding them into silicon Mie resonators fabricated by dewetting, achieving an extraction efficiency exceeding 60% with standard numerical apertures. We will also address the control of emission polarization by embedding color centers in photonic crystals.

Photonic graph states serve as promising resources in various measurement-based quantum computation and communication protocols, such as quantum repeaters. However, their realization with linear optics poses challenges due to the absence of deterministic photon-entangling gates in such platforms. A potential solution involves leveraging quantum emitters, such as quantum dots or NV centers, to establish entanglement and subsequently transfer it to the emitted photons. The design of a quantum circuit that implements the generation of a graph state within such a framework is highly non-trivial nonetheless. Here, we introduce a generation circuit optimization approach that leverages the concept of local equivalency of graphs and employs graph theoretical correlations to explore alternative, cost-effective circuits. Obtaining a 50% reduction in the use of 2-qubit gates for preparing repeater graph states highlights the potential efficacy of our method.

Inelastic electron-light scattering is a powerful tool for investigating optical properties on the nanoscale in an ultrafast transmission electron microscope. Combining electron microscopy with integrated photonics, the requirement of pulsed laser and electron sources can be overcome. In this talk, we demonstrate the spatial and spectral characterization of the intracavity field of a photonic chip-based, high-Q silicon nitride microresonator utilizing free electron-light interaction. By combining optical and electron spectroscopies, we moreover probe the emergence of various nonlinear intracavity states. This novel combination of nonlinear integrated photonics and electron microscopy promises new schemes in electron beam manipulation as well as electron-based probing of optical microresonator states.

An on-demand source of bright entangled photon pairs is desirable for quantum key distribution (QKD) and quantum repeaters. The leading candidate to generate entangled photon pairs is based on spontaneous parametric down-conversion (SPDC) in a non-linear crystal. However, a fundamental trade-off exists between entanglement fidelity and efficiency in SPDC sources due to multiphoton emission at high brightness, which limits the pair extraction efficiency to 0.1% when operating at near-unity fidelity. Quantum dots in photonic nanostructures can in principle overcome this trade-off; however, the quantum dots that have achieved an en- entanglement fidelity on par with an SPDC source (99%) have poor pair extraction efficiency of 0.01%. Here, we show a measured peak concurrence of 95.3% ± 0.5% and pair extraction efficiency of 0.65% from an InAsP quantum dot in an InP photonic nanowire waveguide. Additionally, we show that an oscillating two-photon Bell state generated by a semiconductor quantum dot can establish a secure key for peer-to-peer QKD while using all generated photon pairs. Using our time-resolved QKD scheme alleviates the need to remove the exciton fine structure splitting.