The future global quantum internet will require high-performance matter-photon interfaces at scale. The highly demanding technological requirements indicate that the matter-photon interfaces currently under study all have potentially unworkable drawbacks, and there is a global race underway to identify the best possible new alternative. For overwhelming commercial and quantum reasons, silicon is the best possible host for such an interface. Silicon is not only the most developed integrated photonics and electronics platform by far, isotopically purified silicon-28 has also set records for quantum lifetimes at both cryogenic and room temperatures [1]. Despite this, the vast majority of research into photon-spin interfaces has notably focused on visible-wavelength colour centres in other materials. In this talk I will introduce a variety of silicon colour centres and discuss their properties in isotopically purified silicon-28. Some of these centres have zero-phonon optical transitions in the telecommunications bands [2], some have long-lived spins in their ground states [3], and some, including the newly rediscovered T centre, have both [4] and can be integrated into silicon photonics chips at scale [5].

[1] K. Saeedi, S. Simmons, J.Z. Salvail, et al. Science 342:830 (2013).
[2] C. Chartrand, L. Bergeron, K.J. Morse, et al. Phys. Rev. B 98:195201 (2018).
[3] K. Morse, R. Abraham, A. DeAbreu, et al. Science Advances 3:e1700930 (2017).
[4] L. Bergeron, C. Chartrand, A.T.K. Kurkjian, et al. PRXQuantum 1:020301 (2020).
[5] D. Higginbottom, A.T.K. Kurkjian, C. Chartrand et al. Nature 607:266 (2022).

Superconducting Nanowire-Single Photon Detectors (SNSPDs) have emerged as the highest-performing single-photon detectors, with detection efficiencies reaching 98%, maximum count rates over 1 Gcount/s, and the ability to distinguish between single-photon and multi-photon events. SNSPDs have enabled our group to demonstrate loophole-free tests of Bell’s inequality and device-independent randomness expansion. In this talk I will discuss a new scheme using SNSPDs for high-rate, high-fidelity entanglement distribution between remote nodes of a quantum network. The scheme uses a high-quality heralded entangled source and all-optical quantum repeaters. I will discuss requirements for the SNSPDs and strategies for achieving interferometric stability across the network. Both will be crucial for achieving high-fidelity entanglement distribution at high rates.

Superconducting nanowire single-photon detectors (SNSPDs) have become the gold standard for single photon detection at telecom wavelengths, and their high efficiency, high dynamic range, low timing jitter, and low dark count rates make them ideal for quantum applications. Many use cases benefit from arrays of SNSPDs, whether it’s to enable number resolution, to access higher maximum count rates, to cover larger active areas, or to provide imaging or spectroscopy capabilities. SNSPD array design typically involves a tradeoff between number of channels, active area, and timing properties. In this talk, I will discuss several applications of SNSPD arrays and describe how the applications’ different requirements affect the array and system-level design choices.

Superconducting single-photon detectors are a key technology for quantum information science, being of particular use for quantum key distribution and photonics-based quantum computing. However, the biasing, readout, and signal processing associated with the detector is typically handled by off-chip conventional semiconductor electronics. Increasingly, this solution is proving problematic: such electronics consume large amounts of power and are cumbersome to integrate on the same chip as the detectors. Superconducting classical electronics relying on Josephson junctions are an alternative, but require an integrated fabrication process, which adds complexity to the device. An alternative is to use the superconducting nanowires themselves, in the form of “cryotrons”, an alternative to Josephson junction superconducting switches first proposed in the 1950s, but recently experiencing renewed interest with scaling to the nanometer length scale. These technologies and applications of them to SNSPD readout and signal processing will be discussed.

We propose a new biasing concept for superconducting nanowire single photon detectors (SNSPD). It features the frequency-voltage relation of a Josephson junction to generate a bias supply with quantum precision. The quantum bias concept is characterized by a very low resistor and a frequency controlled noise-free quantum voltage source. In the first experiments, we intentionally slow down the time constant by using a very small bias resistor. We obtain an intrinsic time constant of about 100μs. Corresponding to this time constant, the generated current pulses for the Josephson junction through the SNSPD cause in time-average a constant bias current. The SNSPD as well as the Josephson junction are based on superconducting thin film technology and can be fabricated in general on the same substrate.

Component analysis of devices and technologies that will be integrated to produce space instruments is needed for future NASA missions. For quantum communications, there is a need for quantum memory, quantum repeaters, single photon emitter, and detectors. For quantum sensing, extremely low Size, Weight, and Power (SWaP) and self-calibrating electrometers, magnetometers, and thermometers are needed with nano-scale resolution. NASA Glenn's Q-SASP is developing quantum metrology capabilities in silicon carbide (SiC) to evaluate the energy structure, defect formation energy, band structure augmentation, generation/recombination rates, and limits of dipole-dipole coupling in non-metal implanted SiC devices. This work will discuss recent system developments, device developments, computational modeling, and spectroscopy results and analysis of defects created by non-metal implantations in SiC devices.

I will present a proposal for a modification to optical intensity interferometers that allows for sub-microarcsecond astrometry at angular separations as large as several arcseconds. The modification introduces an additional, adjustable path length into the optics, which creates a primary interference fringe for widely separated sources. Combined with recent technological advances in spectroscopy and ultrafast single-photon detection, this design could allow for unprecedented precision in angular resolution of stars. Promising applications include characterization of binary-orbits and stellar properties, exoplanet detection, and Galactic acceleration measurements.

To study the long-distance free-space quantum communication links, we simulated, designed, and built a well characterized atmospheric turbulence simulator (ATS) with the Fried parameter and scintillation index ranging from weak to strong turbulence regimes. The ATS was integrated with a non-turbulent path to conduct quantum interferometric experiments such as the heralded single photon g^2 (τ) measurement, and Hong-Ou-Mandel measurements are in progress. We observed that g^2 (0) for heralded photon increased to 1 with moderate turbulence. A significant effect of strong turbulence is expected on the biphoton HOM interference with one photon propagating through free space and the other through the ATS.

Precision synchronization is vital for long-distance quantum networking in which entanglement swapping between separate sources via an optical Bell state measurement requires temporal overlap of arriving photonic qubits. This challenge is particularly distinct in satellite-based entanglement distribution in which relative motion, channel effects, and propagation delay must be addressed. This work presents recent progress in achieving precision synchronization in a quantum networking testbed configured for a dual-uplink architecture in which photons from sources at two ground locations would interact at Bell-state measurement on a satellite. Results demonstrate sub-ps synchronization in cases of large Doppler arising from satellite motion.

Efficient transmission of optical beams from ground to space is important for free-space entanglement distribution in a dual-uplink architecture in which photons from entanglement sources at two ground locations interact in an optical Bell-state measurement implemented on a satellite. Efficient transmission requires large transmitting apertures to minimize diffraction losses and high-performance adaptive optics to overcome the effects of atmospheric turbulence. This paper presents analysis of the use of small beacon satellite(s) positioned ahead of the target satellite to reduce point-ahead ansisoplanatism error on the compensated uplink beams. Multiple configurations of the beacon(s), supporting two ground sites, are considered.

Real-time generation of quantum keys between satellite and ground nodes is essential for a scalable and global quantum network. We report the development of a QKD system that operate at gigahertz clock rate with multiplexed classical and quantum channels. This system is tested on a free-space link which is an emulation of the satellite to ground link with dynamic loss and random misalignments. With the assumption of a small satellite in low Earth orbit and a ground station with moderate aperture, we demonstrate the generation of >5 Mbits of quantum keys in a single emulated satellite pass.

Thermal atoms are an attractive platform for quantum information. A typical atomic vapor cell contains billions of identical quantum systems, an extremely large and easily accessible resource. However, harnessing this resource for quantum information is challenging due to the broad velocity distribution of thermal vapors. In this work we describe how we use atomic beams and velocity selection to observe atoms one-by-one, and to create a basic building block of a "bottom-up" approach to quantum information using thermal atoms.

A fast, low-loss optical switch would be a powerful tool for photonic quantum technologies, allowing the implementation of, for example, rapid quantum logic gates, loop memories, and improved heralded single photon sources. Integration into optical fibre promises an avenue to future scalability, but existing optical switches cannot achieve both high speed and high efficiency. Here I present two routes to fibre-integrated, low -loss and fast optical switching. The first uses the acousto-optic effect in a tapered fibre. We demonstrate that light in the tapered region of the fibre can be coupled between optical modes by an acoustic wave, which introduces a phase-shift. The second route is by a two-photon transition in rubidium vapour. A strong control field modulates the mode of a weak signal field. We demonstrate this effect with low loss (1dB) and on short timescales (100MHz) in bulk optics, and work towards a fibre-integrated vapour cell.

Photon-photon interaction is a crucial element in the development of quantum information science and engineering. We developed an InGaP quantum photonic platform with an extreme χ(2) nonlinearity combined with low optical losses in the near infrared wavelength range. Based on the InGaP quantum photonic platform, we realized direct photon-photon interactions via bulk optical nonlinearity, leading to exotic quantum correlations between photons, such as photon repulsion, attraction, and tunneling. This breakthrough opens up exciting possibilities for nonlinear quantum information processing in integrated photonic platforms. We also use the InGaP photonic devices for nonlinearity-enabled quantum networking, including sum-frequency generation enabled quantum teleportation of photons with different wavelengths.

We present recent results aiming to construct single photon sources, detectors and gates using the integration of hot Rubidium atoms and microring resonators (MRRs). We demonstrate strong coupling between an ensemble of ≈53 atoms interacting with a high-Q (>4x10^5) cavity mode, with a many-atom coupling strength g/2pi≈1 GHz and cooperativity C≈3.6 achieved. A peak single-atom cooperativity C0≈0.4 is inferred; to achieve higher cooperativity, we have developed defect mode photonic crystal ring resonators with a 10x reduction in mode volume compared to the MRR while maintaining Q>10^5. Finally, we will discuss theoretical results that support single photon operations using these devices.

This presentation focus on quantum transduction using rare-earth ions in solid state systems. We propose using magnetic materials with rare-earth dopants, harnessing the strong coupling between rare-earth spin transitions and magnons. We analyze this situation using a formalism similar to Ref. [PRL 113, 203601 (2014)]. We find that hosting rare-earth elements within a magnet dramatically speeds up the transduction rate by more than two orders of magnitude, which gives several key benefits: potentially higher efficiency as it is less affected by device internal losses, higher fidelity operations with the superconducting qubits, and reduced device constraints. Finally, we discuss several routes for implementing this type of quantum transducer.

In this work, we investigate non-optimized QKD links between arbitrary pairs of Alices and Bobs using off-the-shelf Toshiba QKD devices. Performance variation is observed when connecting unmatched Alices and Bobs, resulting in significantly lower average secret key rates compared to matched pairs. To address this, a novel algorithm is proposed to dynamically balance key consumption rates and optimize the weighted sum of key generation rates while considering system constraints. The evaluation highlights the potential for reducing the required number of QKD pairs from ~N^2 to ~N by utilizing a dynamically switched QKD network.

Intermodal quantum key distribution (IM-QKD) enables the integration of fiber networks and free-space channels, which are both necessary elements for the development of a global quantum network. IM-QKD permits to extend the reach of free-space links without trusting any additional node, but this requires to efficiently couple the freespace signal into a single-mode fiber (SMF). We present a preliminary point-to-point test conducted in a 620 m free-space channel, with the aim to be used in an intermodal QKD architecture switching between a fiber and a free-space link.

In this experiment, a commercial Quantum-Key-Distribution (QKD) system from Toshiba was integrated into a carrier-grade Fiber to the Home (FTTH) optical access network. The setup replicated real-life FTTH deployments with a 1:16 user GPON configuration. The QKD transmission occurred over a total of 4km consisting of two spitting stages. By optimizing transmission powers, a QKD link with 17 kbps Secure Key Rate (SKR) and 4.63% Quantum Bit Error Rate (QBER) was achieved, while maintaining 9 operational ONTs providing high-speed internet services. This successful demonstration showcases the feasibility of QKD over a GPON, enhancing access network security.

Quantum computing aims at exploiting quantum phenomena to efficiently perform computations that are unfeasible even for the most powerful classical supercomputers. Among the promising technological approaches, photonic quantum computing offers the advantages of low decoherence, information processing with modest cryogenic requirements, and native integration with classical and quantum networks. To date, quantum computing demonstrations with light have implemented specific tasks with specialized hardware, notably Gaussian Boson Sampling which permitted quantum computational advantage to be reached. Here we report a first user-ready general-purpose quantum computing prototype based on single photons.

I give a pedagogical introduction to quantum error correction, making contact with classical error correction and modulation schemes.

We develop a hardware-efficient ansatz for variational optimization, derived from existing ansatze in the literature, that parametrizes subsets of all interactions in the Cost Hamiltonian in each layer. We treat gate orderings as a variational parameter and observe that doing so can provide significant performance boosts in experiments. We carried out experimental runs of a compilation-optimized implementation of fully-connected Sherrington-Kirkpatrick Hamiltonians on a 50-qubit linear-chain subsystem of Rigetti’s Aspen-M-3 transmon processor. Our results indicate that, for the best circuit designs tested, the average performance at optimized angles and gate orderings increases with circuit depth (using more parameters), despite the presence of a high level of noise. We report performance significantly better than using a random guess oracle for circuits involving up to ≃ 5, 000 two-qubit and ≃ 5, 000 one-qubit native gates. We additionally discuss various takeaways of our results toward more effective utilization of current and future quantum processors for optimization.

Strong magnetic interactions in ultracold quantum gases lead to self-organization of macroscopic patterns such as supersolid quantum droplets when the atoms confined in bulk. Microscopically the very same interactions facilitate quantum simulations of extended Hubbard models when these atoms are confined to a lattice. We theoretically investigate the phase diagram of strongly dipolar quantum gases confined in bulk and show that beyond the droplet regime honeycomb and labyrinthine states form, which are candidates for a new type of supersolid and superglass respectively. We also report on our progress building an experimental apparatus designed to capture dipolar atoms in bulk and transport them to a quantum gas microscope chamber where they populate an ultraviolet optical lattice. The narrow spacing of this lattice enables strong next-nearest neighbor interactions and requires the use of state-of-the art photonics, super-resolution techniques and precise magnetic field control for efficient readout of site populations.

We present numerical simulations of deep reinforcement learning on a measurement-based quantum processor--a time-multiplexed optical circuit sampled by photon-number-resolving detection--and find it generates squeezed cat states with an average success rate of 98%, far outperforming all other similar proposals. Since squeezed cat states are deterministic precursors to the Gottesman-Kitaev-Preskill bosonic error code, this is a key result for enabling fault tolerant photonic quantum computing.

We build a network source of indistinguishable photons, synchronized to an external clock, that could be used as scalable modular unit in an extended quantum network infrastructure. We characterize the indistinguishability and synchronization of this source. The Hong-Ou-Mandel dip shows near unity indistinguishability. Allan deviation analysis shows sub-picosecond jitter when locked to an external clock. The jitter figure is more than 10 times smaller than the pulse duration of 30ps. The source is compatible with many clock recovery systems, including the White Rabbit Precision Time Protocol (WR-PTP). This source enables scalable quantum protocols over multi-node, long-distance optical networks.

Today’s quantum technology relies on the realization of large-scale non-classical systems in practical formats to enable quantum-accelerated computing, secure communications and enhanced sensing. Optical on-chip quantum frequency combs, characterized by many equidistantly spaced frequency modes, allow the storage of large amounts of quantum information and together with control mechanisms can provide practical large-scale quantum systems. In this contribution, we present recent advances on the controlled generation and use of quantum frequency combs for information processing. First, we demonstrate an electrically-pumped laser-integrated quantum light source of two- and high-dimensional maximally entangled photons. We exploit a hybrid InP-SiN approach which allows to include a filter, a gain section and a parametric photon pair source in a single system. Second, we demonstrate the generation of high-dimensional bi-photon quantum frequency combs with tunable entropies by exploiting a novel excitation technique and spectral filtering. Using this, we reveal unidirectional bosonic quantum walks, asymmetric energy transfer, and directional entanglement transport.

We present a turn-key portable picosecond fiber laser for efficient quantum dot excitation to generate single photons. The laser combines a mode-hop-free tunability in the regions 770-980 nm and 1150-1500 nm with a high pulse-to-pulse coherence of 98%. A high single photon purity and indistinguishability were demonstrated. An excellent long-term power stability with a standard deviation of less than 0.3% and wavelength stability of better than 5 pm were achieved. The laser enables excitation of different semiconductor quantum dots and excitation schemes, essential for versatile easy-to-use single-photon sources based on quantum dots for research applications and commercial quantum computing.

We demonstrate a source of polarisation-entangled photons that produces pairs of entangled photons at a rate of 1.25 gigahertz. Our system is enabled by Periodically Poled Lithium Niobate waveguides that produce degenerate photon-pairs with a centre wavelength of 1560 nm and a 0.1 nm bandwidth. We measured the degree of entanglement and obtained a CHSH parameter of 2.73. From measurements of polarisation discrimination in a BB84 protocol with two mutually unbiased bases, we obtained a measurement fidelity of 98% and estimated the maximum secure key rate to be 0.633 gigabits per second.

We present an experiment where a reconfigurable photonic processor fabricated in glass by femtosecond laser micromachining is used for the generation of four-photons GHZ entangled states, with high efficiency and fidelity. The chip is used in synergy with a bright and quasi-deterministic source of single photons based on semiconductor quantum dot. The very efficient interfacing of these two platforms is ensured by the excellent connectivity between glass photonic circuits and standard optical fibers. In addition, in order to benchmark the quality of the generated states, this processor is used to implement a quantum secret sharing protocol on chip.

Trapped-ion qubits have been advantageous in quantum information processing due to their long coherence times and high-fidelity state preparation, logic gate operation, and readout. In recent years, we have fabricated chips with electrodes – for generating the electric field for trapping ions – and photonic waveguides and grating out-couplers – for delivering light to the ions. The integrated photonics can potentially lower the laser power requirement and lead to faster gates; however, there are challenges that need to be overcome for the platform to be beneficial. Here, we demonstrate single and two qubit gates with Sr+ trapped ion qubits, driven by delivering light to the ions both via free space and integrated photonics. We show that robust quantum logic is within reach using the integrated photonic platform, and the approaches we are taking in mitigating current challenges.

The continued evolution of quantum technologies requires heterogenous material platforms for packaging, scalability, integration, and multiplexing. Here, we demonstrate direct bonding of single-crystal diamond membranes, a proven host of coherent qubits for networking and sensing, to a wide variety of materials including fused silica, sapphire, thermal oxide, and lithium niobate. We realize bonded films with thickness as low as 10 nanometers. TEM imaging reveals sub-nm interface regions between crystalline diamond and sapphire. We demonstrate compatibility with quantum photonics by realizing several varieties of integrated nanophotonic cavities with quality factors exceeding 20000. Additionally, the membranes allow us to significantly improve the coherence and microwave addressability of tin vacancy qubits, allowing us to achieve a coherent spin-photon interface at 4 Kelvin. The bonded diamond membranes and coherent qubits therein can be readily integrated into fully packaged quantum networking nodes.

Quantum technologies such encryption, communication, computing, imaging, and metrology are active areas of research and development. A successful commercialization of these endeavors depends on availability of reliable, efficient, and cost-effective hardware in the form of single photon sources and photodetectors capable of photon number resolution. An ideal single photon source produces deterministically and efficiently indistinguishable photons, one (or two) at a time, at a desired rate and propagating in a chosen direction. Somewhat surprisingly, an attenuated laser does not meet all of these criteria, therefore, alternative sources need to be developed. A few decades of research yielded several sources that, although still not ideal, perform better than an attenuated laser. This presentation is a tutorial on these sources. It begins with a discussion why single photon sources are needed using examples from quantum encryption and imaging, and why an attenuated laser will not suffice. After reviewing physical characteristics of an ideal source, an in-depth and objective discussion of the major sources follows, in particular those based on spontaneous parametric down conversion, four wave mixing, quantum dot, color center, isolated system, and ensemble. The presentation ends with a brief discussion of generating entangled photon pairs and their use in quantum communication and imaging.

T centers in silicon could serve as efficient quantum memories based on spin-photon interface. But these emitters have long excited state lifetimes and are therefore dim. We demonstrate high-efficiency single photon emission from the zero-phonon line of a single T center using a nanobeam. The tapered nanobeam features coupling efficiency of 71% into a lensed fiber, enabling an order of magnitude improvement in photon count rates as compared to previously reported values. Consequently, we demonstrate single photon emission from the zero-phonon line, representing the coherent emission from the T center. Our result is an important step towards CMOS-integrated spin-photon interfaces.

Solid-state single and entangled photon emitters linked coherently over long distances with optical fibers enable a new generation of quantum-based communications networks. Currently, epitaxial semiconductor quantum dots (QDs) pave the way as a scalable approach for fabricating deterministic non-classical light sources that can be integrated with other photonic or electronic components in miniaturized form. Here, we present a new quantum material system based on GaSb QDs formed by filling droplet-etched nanoholes [1,2], a technique which has been previously used for the state-of-the-art single- and entangled-photon sources in the GaAs-based materials emitting at wavelengths shorter than 800 nm [3-6]. We show that while the GaSb QDs exhibit high homogeneity and small fine structure splitting similarly to their GaAs counterparts, they also enable single-photon emission in the 3rd telecom window [7] with prospects for extending towards 2µm. These properties make them ideal candidates for quantum photonic applications requiring compatibility with Si-photonics and fiber-based telecom. [1] J. Hilska et al. Cryst. Growth Des. 21 1917−1923, 2021 [2] A. Chellu et al. APL Materials 9, pp

Quantum information science and technology (QIST) harnesses a burgeoning class of photonic devices, enabling the manipulation of quantum states in both light and matter for superior performance compared to classical technologies. While early-stage demonstrations in various areas of QIST have predominantly employed bulk-optic components, the imperative for integrated photonic devices becomes evident in the quest for scalability. This transition is crucial for substantial reductions in SWaP-C (Size, Weight, Power, and Cost) and is seen as essential for achieving the quantum advantage. This paper provides an overview of the evolution of classical and quantum light sources from bulk-optics to mini-bulk-optics to integrated photonics, examining their potential for scalable QIST deployments. While these components can greatly advance quantum computing, communication, sensing, and metrology, they also have readily shown promise in numerous classical technologies such as optical processors, LIDAR, and optical communications. This indicates the mutual dependence of QIST and integrated photonics for growth and fruition.

Below-threshold signal-idler quantum Kerr combs are the most explored quantum Kerr state to-date, both for fundamental study and application in quantum technologies. However, after the first onset of optical parametric oscillation, the connectivity of the below-threshold modes grows in complexity as modes which were once purely populated with spontaneous photons develop comparatively strong mean fields which drive correlations themselves. In this talk, I will describe numeric and experimental study of this second class of states, with a focus on quantum correlations and quadrature squeezing as tools for understanding classical nonlinear optics.

Gaussian operations are vital tools for constructing various continuous-variable quantum protocols. As advanced quantum research advances towards larger and more complex scalable quantum networks, implementing multimode Gaussian operations (e.g., multimode squeezing/entangling operations) becomes essential. Not only for examining the unknown multimode Gaussian operation, but also for controlling the multimode Gaussian operation, characterization of multimode Gaussian operation is required. However, the previous works have been limited to investigate multimode linear operation. In this work, we experimentally characterize complete information of multimode Gaussian processes, which go beyond the linear operation by including multimode squeezing and entangling operation. Any multimode Gaussian processes can be described with transfer matrix T and noise matrix N. With the new method of using coherent and vacuum probe, the transfer matrix T and the noise matrix N was obtained. Characterizing the noise matrix N enables us to determine the noise during the process. Our method can be further used in many quantum protocols, especially for quantum information processing.

This work will describe methodologies founded on time-frequency correlation also offer inspiration for classical target detection protocols with significantly higher source power, thereby extending the detection range. Remarkably, classical correlated probe-reference light, despite appearing random and chaotic, can reconstruct sub-Hz level single-frequency SFG output. In contrast, uncorrelated noise light doesn't undergo SFG and is entirely rejected. Consequently, background noise can be effectively distinguished, leading to a rejection capability exceeding 100dB, while the SFG process achieves nearly 100% efficiency in converting true probe photons.

Tomorrows future quantum-internet will need to support a wide range of operations including those arising from quantum-communication, distributed quantum computation and quantum remote sensing tasks. Such applications require the transmission of quantum information across the network where channel losses are a serious problem. Here we introduce the concept of quantum multiplexing to reduce the severity of this issue where multiple-qubits of information are encoded onto each transmitted photon. We will show how one not only saves on the number of photons needed but also on the physical resources required within the network nodes. We will discuss the implementations of quantum multiplexing in various networking applications.

Here we present the experimental distribution of four-dimensional entangled qudits between integrated photonic devices. Qudits offer advantages over qubits such as higher information capacity, and improved noise robustness. Integrated photonics allows for the reliable preparation and manipulation of large-scale entangled quantum states on a single device, with outstanding phase stability. However, reliable transmission of these states between devices, integrated or otherwise, has been a challenge, mainly due to the difficulty of maintaining phase stability between multiple optical channels. We implement an active phase stabilisation algorithm, utilising the same circuitry as for the quantum states, enabling stable distribution of qudits.

The use of trivalent erbium, typically embedded in solid state, has widespread adoption as a dopant in telecommunications devices. and shows promise for on-chip nanolasers and spin-based quantum memories for quantum communication. In particular, its natural telecom C-band optical transition and spin-photon interface make it ideal for integration into existing optical fiber networks without the need for frequency conversion. Here, we present Er-doped titanium dioxide thin film growth on silicon substrates using a foundry-scalable atomic layer deposition process with a wide range of doping control over the Er concentration for integrated photonics applications. Finally, we coupled Er ensembles with high quality factor Si nanophotonic cavities and demonstrate a large Purcell enhancement (about 300) of their optical lifetime. Our findings demonstrate a low-temperature, non-destructive, and substrate-independent process for integrating Er-doped materials with silicon photonics, which can be widely applied in integrated photonics industry and in developing on-chip quantum memories.

Multi-institutional quantum networks that connect nodes at a metropolitan scale are being developed. Those networks face limitations due to the need for synchronous, real-time communication of classical information alongside with quantum channels. Using the same fiber simultaneously for classical and quantum traffic is beneficial but requires additional consideration. Unexpectedly, blending classical and quantum traffic can enhance classical data transmission with quantum features, such as unambiguous security. Additionally, classical information capacity can be dramatically improved by reusing quantum-networking hardware. I will discuss communicating with faint light, significantly weaker than that used for conventional classical communication, yet significantly stronger than that used for quantum communication and quantum key distribution.

Time-entanglement is a promising resource for the implementation of quantum communications over standard fiber networks. In particular, photonic qudits can enhance the performance of quantum communication, including quantum key distribution, in terms of noise robustness, quantum information content, distance reach, as well as security and secret key rates. However, time-entangled photonic qudits are not ready yet to be fully exploited for quantum communications in fiber networks that are fully compatible with standard telecommunication architecture. Here, we demonstrate the implementation of telecommunication-compatible quantum communications based on picosecond-spaced time-entangled qudits. To this end, we make use of an integrated photonic chip comprising a cascade of programmable interferometers and a spiral waveguide. We use entangled qudits to implement high-speed quantum key distribution, chip-to-chip entanglement distribution, and quantum state propagation over 60 km of standard fiber. Our results show the potential of time-entangled qudits for high-speed quantum communications in telecommunication-compatible architecture.

Quantum networks are now starting to appear around the world, but most of these are focused solely on optical fiber channels. Just as our classical communications are based on a hybrid wired and wireless communication infrastructure, so too will an eventual quantum network depend on both fiber and free-space links. The latter will allow communications to fixed structures (the 'last mile' problem) as well as a variety of mobile platforms, e.g., cars, drones, and satellites. Here we will discuss our current efforts to develop and deploy the relevant quantum technologies.

A quantum internet is regarded as the holy grail of quantum information processing, enabling the deployment of a broad range of quantum technologies/protocols on a global scale. However, a quantum version of the current Internet Protocol (to make a network of networks) is missing, despite the necessity to control large-scale self-organizing quantum networks. In this talk, we present a practical recipe to give entangled bits (ebits) efficiently to arbitrary two points in a given quantum network with arbitrary topology, by networking its subnetworks with minimum cost. This recipe forms the basis of designing and controlling a global-scale quantum internet.

Quantum correlation is critical in quantum information applications, and numerous inequalities have been established to quantify the non-classical correlations such as the Bell nonlocality and quantum steering. We introduce an experimental method to map full-domain correlation for nonlocality and quantum steering in the Clauser-Horne-Shimony-Holt scenarios. This approach accounts for detection imperfections and simplifies interpretations, answering fundamental questions about nonlocality and quantum steering. Additionally, we illustrate its utility in calibrating an entanglement-based quantum key distribution protocol with arbitrary bipartite states. Our correlation maps offer a direct, straightforward contribution to quantum information applications.

Quantum repeaters are crucial for extending the limits of fiber-based quantum communication. We focus on quantum-dot molecules (QDMs) as spin-photon interfaces and a promising platform for this technology. Using a fully quantum-mechanical master-equation formalism, we simulate protocol sequences considering the semiconductor material properties of QDMs [Schall et al., Adv. Quant. Technol. 4.6, 2100002 (2021)] and time-dependent electric fields for gate operations. Our findings indicate that typical QDMs, with currently attainable switching speeds, operate near the adiabatic regime, enabling high-fidelity gate operations. Our approach enables the estimation of transfer rates and predicts fabrication parameters for semiconductor QMDs.

Spin qubits in silicon carbide (SiC) are promising systems for scalable applications in quantum computing and communication thanks to the wafer-scale availability and CMOS compatible fabrication technologies. Among these, silicon vacancies (VSi) in 4H-SiC stand out due to demonstrated high-fidelity multi-qubit gates and preserved spin-optical properties when integrated into nanophotonic waveguides and resonators. In this work, we combine study of the intrinsic spin dynamics and nanofabrication engineering efforts for advancing VSi spin qubits in SiC towards scalable integrated quantum photonics. We infer all the relevant decay rates for estimation of minimum required Purcell factor for strong emitter-cavity coupling. With direct tapered waveguide-to-fiber coupling in cryogenic environment, we show the efficient extraction of light from the system. We also report latest progress on SiC-based Fabry Perót cavities which potentially offer a compact full scalable solution.

Quantum communication technologies are starting to develop into a rising industry branch of their own. The associated light sources and detectors/sensorics mostly require cryogenic cooling. In order to scale up this new industry and make it accessible for commercial use, new compact, autonomous, and low power cryogenics are a vital key condition. We have developed a revolutionary compressor technology together with high-performance cryogenic cooling systems, that operate on low power consumption, without the use of cooling water, and in a quantum industry compatible 19” rack format. We will show how this enables critical building blocks of photonic based quantum computing and communication technologies such as single photon sources & single photon detectors to be made truly scaleable outside of laboratories. First use cases together with detailed performance data will be reviewed.