This PDF file contains the front matter associated with SPIE Proceedings Volume 11699, including the Title Page, Copyright Information, and Table of Contents.

Quantum sources and receivers operating on-board satellites are an essential building block for global quantum networks. SpooQy-1 is a satellite developed at the Centre for Quantum Technologies, which has successfully demonstrated the operation of an entangled photon pair source on a resource-constrained CubeSat platform. This miniaturized and ruggedized photon pair source is being upgraded to be capable of space-to-ground quantum key distribution and long-range entanglement distribution. In this paper, we share results from SpooQy-1, discuss their relevance for the engineering challenges of a small satellite quantum node, and report on the development of the new light source.

Semiconductor quantum dots are prime candidates for quantum network applications such as quantum relays, but their typical emission wavelength, polarization qubit encoding scheme and low operating frequency are incompatible with existing technologies. Our work shows that InAs/InP quantum dots driven with GHz-clocked pulses, in combination with qubit transcoding interferometers, can bridge these gaps. The demonstrated teleportation of time-bin qubits in the telecom C band even when repetition rates exceed the inverse lifetime of the dot shows the potential for integrating such devices with long-distance quantum network technologies.

Quantum key distribution allows for a provably secure transmission of cryptographic keys over an optical channel. Encoded polarization states or time-bin degree of freedom have been used for successful demonstrations. However, photon losses in long fibers, slow single photon detectors, and detector dark counts significantly limit the overall bit rate. Improving key throughput and reducing the overhead of key reconciliation remain as major challenges. Methods which utilize multiple time bins allow for multiple key bits to be encoded in a single photon, thus increasing the fidelity of transmitted keys and decreasing the overhead of key reconciliation in real-world conditions. Previous implementations of these methods required that Alice and Bob share a time reference by sharing a dedicated classical channel used for synchronization. This work presents a technique that allows two parties to exchange time-bin encoded photons without the need for synchronized time references. Our technique uses a framing protocol which allows Alice to encode a time reference along with a key which is determined by Alice before transmission. Security can be achieved by monitoring the visibility of a pair of Franson interferometers, using decoy pulses and measuring the round trip time between Alice and Bob. The bit rate of this technique is limited only by the recovery time of the detector and the speed of the modulation electronics. We experimentally demonstrate a raw bit rate of 5Mb/s over an optical channel with 55dB of loss, which is competitive with current research. We also demonstrate absolute timing synchronization with an accuracy of 20ps.

CMOS-based integrated circuits are in most of the digital and wireless computing devices. Traditionally, CMOS is not considered a light emitting devices. For this reason, ULSI or ASIC circuits are in closed packages, functioning without any lights. Just like laser or LED, photonic CMOS transistors are light emitting devices. A phonic MOSFEST includes a laser or LED fabricated in the drain region, and a photonic sensor or avalanche photo diode (APD) in the well region. The MOSFET, laser, and photon sensor are manufactured as one integral device. When the MOSFET is on, both laser and APD are also on. Light emitted from the laser is absorbed by the APD, which triggers a large breakdown or light current flowing back into the MOSFET drain for much higher speed. When the MOSFET is off, the embedded laser and APD are also turned off. With novel designs of local interconnected nonlinear optical waveguides, and signal processing schemes, multiple-bandwidth optical computing may be realized.

The exponential growth of the internet is currently fulfilled by optical communication, but photonic communication channels are on the verge of a capacity crunch. We systematically study the use of bandwidth and energy of quantum-enhanced communication channels for classical information with different practical encodings. We introduce hybrid encoding protocols with a simultaneous coherent frequency and phase modulation and optimize them for the most advantageous quantum measurement at the receiver. We experimentally map the energy and bandwidth use for the optimization of practical resource-limited channels using a tabletop platform. We also report the initial progress on developing an integrated telecom testbed.

In recent years, we have seen an increase in computer attacks through our communication networks worldwide, whether due to cybersecurity systems’ vulnerability or their absence. This paper presents three quantum models to detect distributed denial of service attacks. We compare Quantum Support Vector Machines, hybrid QuantumClassical Neural Networks, and a two-circuit ensemble model running parallel on two quantum processing units. Our work demonstrates quantum models’ effectiveness in supporting current and future cybersecurity systems by obtaining performances close to 100%, being 96% the worst-case scenario. It compares our models’ performance in terms of accuracy and consumption of computational resources.

It is now widely accepted that a future quantum internet will be developed supporting a wide variety of applications. The efficiency (and even viability) of such a internet will be highly dependent on how we move information around it. We discuss various routing options and show these impose quite different constraints on the fundamental building blocks of those networks. Introducing the concepts of quantum multiplexing and quantum network aggregation we show how communication maybe possible between two users on that network even when there are insufficient resources to allow such information to be transmitted over individual routes.

Quantum networks are poised to enable large-scale secure communication, distributed quantum computing and simulation by means of shared entangled states over the nodes of the network. The Nitrogen-Vacancy (NV) centre in diamond is a promising candidate to act as node of such a quantum network, with long-lived multiple qubits and an optical interface for entanglement. We present updates on our effort towards the realisation of such a network.

Quantum networks enable a broad range of practical and fundamental applications. Experimental realization of such networks is hampered by many challenges, one of them being a lack of an efficient interface between stationary and flying qubits working at room temperature. We demonstrate an interface between ensembles of the nitrogen-vacancy centers in diamond and photons with wavelengths near 1550 nm. Photons are coupled to spins via local dynamical stress produced by optomechanical driving of a diamond microdisk. Our approach does not involve intrinsic optical transitions and can be easily adapted to many other colour centers.

Quantum computing architectures where atom-laser interactions form the basis of qubit manipulation, such as trapped ion and Rydberg systems, are leading the progress towards universal quantum computation. M Squared is developing many of the advanced laser systems that are underpinning this progress, including systems that are designed to implement quantum logic gates with optical and hyperfine qubits with high fidelity. High power systems that are enabling the scaling of qubit numbers are also being developed. These systems are described, along with an account of how the requirements of lasers for quantum computing experiments are expected to evolve in the future.

Ion traps are one approach to represent Qubits in future quantum computer architectures. Nevertheless, progress has to be made to scale ion trap setups for multiple ions and qubit scaling. Next to the ion trap architecture itself the manipulation of the ion’s state and their readout by means of a laser and fluorescence detection optics are key architectural building blocks. A setup dedicated to the optical addressing of each individual ion in the trap will be described, consisting of micro-optics for diffraction limited focusing of the laser beam onto the ion and a miniaturized actuation mechanism for the micron scale movement of the focus with the ion, where the electrical feedback signal stems from the detection unit. The setup’s design with an initial layout for up to 10 ions in parallel can further be scaled towards ca. 50 ions in parallel at least. Publisher’s Note: The manuscript PDF, originally published on 5 March 2021, was withdrawn on 12 March 2021 per author request.

A central goal in photonic quantum information processing is the ability to perform high-fidelity logic gates between multiple optical qubits. Here, we present our recent theoretical work on using optical nonlinearities to implement controlled-phase gates between two optical qubits. Our approach is based on using dynamically coupled cavities to convert photons travelling in a waveguide into highly confined cavity modes. This conversion enables very strong interactions between photons in quasi-monochromatic modes, which enables high fidelity gates. We will discuss gate protocols based on second- and third order nonlinear materials as well as interactions with two-level emitters.

Trapped-ion quantum computers have demonstrated high-performance gate operations in registers of about ten qubits. However, scaling up and parallelizing quantum computations with long 1D ion strings is an outstanding challenge due to the global nature of the motional modes of the ions which mediate qubit-qubit couplings. We devise methods to implement scalable and parallel entangling gates by using engineered localized phonon modes. We propose to tailor these modes by tuning the local potential of individual ions with programmable optical tweezers. Localized modes of small subsets of qubits enable to perform entangling gates on these subsets in parallel.

We show that 1D array of nonlinear evanescently-coupled waveguides could be used as a quasi 2D lattice via a synthetic frequency dimension induced by nonlinear coupling. We demonstrate the analogy of this platform to a multi-level atom interacting with light for classical and quantum photonic states. Using this framework, we adapt well-known coherent processes from atomic optics, such as electromagnetically induced transparency and stimulated Raman adiabatic passage to design novel photonic devices. Owing to demonstrated ultra-low noise of sum-frequency generation in lithium niobate, our devices are particularly useful for quantum information applications: quantum memory and quantum transduction.

Photonics integration is a key technology for realizing large-scale photonic quantum information processing. We demonstrate state-of-art reconfigurable photonic processors based on low-loss silicon nitride waveguide networks. We present the science behind such a processor, which consists of a large mesh of integrated reconfigurable Mach Zehnder interferometers. In this talk, we will present the newest results of the current generation of our programmable quantum photonic processors obtained by classical as well as quantum optical characterization. Furthermore, we show the challenges of scaling up quantum photonic processors and the range of potential applications of large-scale quantum information processing those will enable.

Titanium in-diffused waveguides in lithium niobate is a promising integration platform for building devices for quantum communication, due to its low-loss propagation, high-efficiency coupling to telecom fiber, high second order nonlinearity and electro-optic coefficient. Over recent years we have been investigating the integration of superconducting nanowire single photon detectors (SNSPDs) in this platform, together with the Integrated Quantum Optics group at Paderborn University and colleagues at NIST Boulder. I will report on the proof-of-principle demonstrations of functional devices, as well as discuss our progress to improve the efficiency and yield of on-chip detectors.

Superconducting nanowires and nanostrips have been used extensively in single-photon detection and have recently demonstrated the capability for photon-number resolution. These devices can also find use for microwave analog and digital superconducting electronics for purposes such as signal processing and multiplexing, and potentially for applications to readout of superconductive quantum computing. This talk will discuss novel electronics and photodetection devices based on superconducting nanowires.

Nuclear spins in diamond are promising for their use as qubits in quantum computers and quantum networks, and for simulating many-body physics phenomena. Building on recent results [1,2], we combine precise knowledge of the nuclear spin environment with dynamic nuclear polarization techniques and selective readout protocols to extend control over more nuclear spin qubits within a large interacting cluster. These techniques open the door to the quantum simulation of complex many-body physics phenomena using nuclear spins in diamond. [1] – M. H. Abobeih et al. Nature, 576, 411–415 (2019) [2] – C. E. Bradley et al. Phys. Rev. X 9, 031045 (2019).

Quantum internet will enable a number of revolutionary applications, such as distributed quantum computing, large scale quantum communication and cooperative operation of atomic clocks. Cold atomic ensembles are a very promising approach for quantum internet, featuring long coherence time and collectively enhanced interaction with single photons. The current central theme in this direction is to improve the performance of fundamental building blocks and to construct small-scale networks which go beyond state of the art. In this talk, I will present our experimental works in this direction, such as the improvement of single-node performance with cavity enhancement, optical lattice, and Rydberg nonlinearity. I will also talk about the extension of atom-atom entanglement distance via quantum frequency conversion, and the establishment of entanglement among three quantum nodes via three-photon interference etc.

Optical quantum networks for distributing entanglement between quantum machines will enable distributed quantum computing, secure communications and new sensing methods. These networks will contain quantum transducers for connecting computing qubits to travelling optical photon qubits, and quantum repeater links for distributing entanglement at long distances. In this talk I present implementations of quantum hardware for repeaters and transducers using nano-photonics and rare-earth ions, like ytterbium and erbium, exhibiting highly coherent optical and spin transitions in a solid-state environment. In particular, i discuss optically addressable single quantum bits with single shot readout based on ytterbium 171 atoms, and on-chip storage and processing of photons using erbium ensembles coupled to silicon photonics.

I will describe my group's work on designing architectures for the quantum internet, with a close eye on the potential for near-term demonstrations. In particular I will discuss approaches based on rare-earth ions (individual and ensembles), quantum dots, and defects in diamond.

Semiconductor quantum dots are excellent emitters of single photons. Often, the same mode is used to resonantly excite a QD and to collect the emitted single-photons, requiring cross polarization to separate out scattered laser light. This reduces the source brightness to ≤50%, and potentially eliminates their use in some quantum applications. We demonstrate a resonant-excitation approach to creating single photons that is free of any filtering whatsoever. This integrated device allows us to resonantly excite single quantum-dot states in several cavities in the plane of the device using connected cavity-waveguides, while the cavity-enhanced single-photon fluorescence is directed vertically (off-chip) in a Gaussian mode.

Electrically-driven single-photon sources (SPSs) are required for the scalable quantum technologies. Color centers in diamond emerged as attractive candidates for room-temperature SPSs. SiV centers are especially attractive due to their outstanding emission properties. However, although electroluminescence from SiV centers has been demonstrated, the single-photon electroluminescence (SPEL) from a single center has not been achieved due to the low SPEL rate. Here, we explain why the SPEL rate in recent experiments was low to be resolved and design a diamond p-i-n diode with a SiV center and show how to achieve an SPEL rate of more than 900000 photons/s.

We experimentally demonstrate spectral manipulation of heralded single photons by electro-optic temporal phase modulation employing complex, Fresnel-like wide-band electronic waveforms. We show spectral compression of classical telecom light enhancing its maximal intensity by over 80, by compressing its full-width at half maximum (FWHM) bandwidth from 0.856 nm down to 3.1 pm (383 MHz), thus achieving a compression factor of over 270. We show a compression gain by increasing the aperture of a Fresnel time lens (temporal waveform duration). We demonstrate a similar compression on a single-photon level from ~1.5 nm (~190 GHz) down to the sub-2GHz regime. Our findings should significantly improve the performance of future quantum information processors based on hybrid quantum networks.

The capability to engineer and characterize high dimensional states has become a crucial request in the quantum information field. The quantum walk dynamics proved to be a suitable resource for developing general quantumstate engineering protocols. Here, we experimentally verified the flexibility of an engineering protocol based on a one-dimensional quantum walk in the Orbital Angular Momentum (OAM). Although this degree of freedom has found several applications in the quantum information field, extract the information stored in them appears to be difficult. Therefore, we employ machine learning protocols to classify and characterize particularly structured beams endowed with a not uniform distribution of the polarization on the transverse plane. Moreover, we prove that by modeling the engineering process through a refined model it is possible to improve the performances of measurement techniques such as holographic projection and machine-learning based classification. These results represent a further investigation in the manipulation and detection of OAM modes coupling the photonics platforms with machine-learning protocols.

The tripartite W state exhibits maximal entanglement between three parties, represented as 1/sqrt(3)(|001>+|010>+|100>), and has interesting applications for quantum communication, fundamental tests of quantum mechanics, and in quantum sensing and quantum computing. We experimentally demonstrate the generation of a three-photon discrete-energy-entangled W state in optical fiber. The source relies on multiphoton-pair generation via spontaneous four-wave mixing, and post-selection. By taking advantage of constraints imposed by the SFWM process, post-selection, and the properties of the W state, we verify the state produced by this source without resorting to frequency conversion.

This Conference Presentation, “Efficiently quantifying entanglement in high-dimensional quantum photonic systems,” was recorded for the Photonics West 2021 Digital Forum.

This Conference Presentation, “Polarization-entaglement distribution in fiber-optic channels,” was recorded for the Photonics West 2021 Digital Forum.

We realize quantum computational advantage in a Gaussian Boson Sampling (GBS) experiment. We inject 25 two mode squeezed states into a 100-mode ultralow-loss interferometer with full connectivity and random matrix. We rule out thermal states, distinguishable photons, and uniform distribution hypotheses. This GBS machine can sample 14 orders of magnitude faster than classical supercomputer.

The study of open quantum systems, quantum thermodynamics and quantum many-body spin physics in realistic solid-state platforms, has been a long-standing goal in quantum and condensed-matter physics. In this talk I will address these topics through the platform of nitrogen-vacancy (NV) spins in diamond, in the context of purification (or cooling) of a spin bath as a quantum resource and for enhanced metrology. I will first describe a general theoretical framework we developed for Hamiltonian engineering in an interacting spin system [1]. I will then extend this framework to coupling of the spin ensemble to a spin bath, including both coherent and dissipative dynamics [2]. Using these tools I will present a scheme for efficient purification of the spin bath, surpassing the current state-of-the-art and providing a path toward applications in quantum technologies, such as enhanced MRI sensing.