Until recently, quantum photonic architecture comprised of large-scale (bulk) optical elements, leading to severe limitations in miniaturization, scalability and stability. The development of the first integrated quantum optical circuitry removes this bottleneck and allows realization of quantum optical schemes whose greatly increased capacity for circuit complexity is crucial to the progress of experimental quantum information science and the development of practical quantum technologies.Integrated quantum photonic circuits within Silica-on-Silicon waveguide chips were simulated, designed and tested. Hundreds of devices have been fabricated with the core components found to be robust and highly repeatable. Amongst these demonstrations, all the basic components required for quantum information applications are shown. The first integrated quantum metrology experiments are demonstrated by beating the standard quantum limit with twoand four-photon entangled states while providing the first re-configurable integrated quantum circuit capable of adaptively controlling levels of non-classical interference of photons. The tested integrated devices show no limitations to obtain high quality performances. It is reported near-unity visibility of two-photon non-classical interference and a Controlled-NOT gate that could in principle work in the fault tolerant regime.It is demonstrated the realization of a compiled version of Shors quantum factoring algorithm on an integrated waveguide chip. This demonstration serves as an illustration to the importance of using integrated optics for quantum optical experiments.

Integrated quantum photonics is a promising approach for future practical and large-scale quantum information processing technologies, with the prospect of on-chip generation, manipulation and measurement of complex quantum states of light. The gallium arsenide (GaAs) material system is a promising technology platform, and has already successfully demonstrated key components including waveguide integrated single-photon sources and integrated single-photon detectors. However, quantum circuits capable of manipulating quantum states of light have so far not been investigated in this material system. Here, we report GaAs photonic circuits for the manipulation of single-photon and two-photon states. Two-photon quantum interference with a visibility of 94.9±1.3% was observed in GaAs directional couplers. Classical and quantum interference fringes with visibilities of 98.6±1.3% and 84.4±1.5% respectively were demonstrated in Mach-Zehnder interferometers exploiting the electro-optic Pockels effect. This work paves the way for a fully integrated quantum technology platform based on the GaAs material system.

We demonstrate fast polarization and path control of photons at 1550 nm in lithium niobate waveguide devices using the electro-optic effect. We show heralded single photon state engineering, quantum interference, fast state preparation of two entangled photons, and feedback control of quantum interference. These results point the way to a single platform that will enable the integration of nonlinear single photon sources and fast reconfigurable circuits for future photonic quantum information science and technology.

We demonstrate a client-server quantum key distribution (QKD) scheme. Large resources such as laser and detectors are situated at the server side, which is accessible via telecom fiber to a client requiring only an on-chip polarization rotator, which may be integrated into a handheld device. The detrimental effects of unstable fiber birefringence are overcome by employing the reference-frame-independent QKD protocol for polarization qubits in polarization maintaining fiber, where standard QKD protocols fail, as we show for comparison. This opens the way for quantum enhanced secure communications between companies and members of the general public equipped with handheld mobile devices, via telecom-fiber tethering.

The spectacular success of silicon-based photonic integrated circuits (PICs) in the past decade naturally begs the question of whether similar fabrication procedures can be applied to other material platforms with more desirable optical properties. In this work, we demonstrate the individual passive components (grating couplers, waveguides, multi-mode interferometers and ring resonators) necessary for building large scale integrated circuits in suspended gallium arsenide (GaAs). Implementing PICs in suspended GaAs is a viable route towards achieving optimal system performance in areas with stringent device constraints like energy efficient transceivers for exascale systems, integrated electro-optic comb lasers, integrated quantum photonics, cryogenic photonics and electromechanical guided wave acousto-optics.The scale, complexity and performance of silicon photonic integrated circuits (PICs) has revolutionized optical communications in the past decade 1 . Perhaps the most surprising aspect of this revolution is the fact that silicon does not possess many desirable optical properties (apart from a high refractive index) and the silicon photonics revolution was primarily driven by the availability of a foundry fabrication infrastructure, courtesy of the microelectronics industry, that could be applied to optics 2-4 . Over the past two decades, a wide variety of component designs have been optimized and their fabrication process perfected for silicon 5 and it is hard to foresee a similar investment of resources in any other material platform. On the other hand, there are a number of application areas in which silicon's lack of desirable optical properties proves a severe limitation to achieving system performance. These limitations include the absence of a direct bandgap, lack of a χ (2) nonlinearity to build fast electro-optic devices and zero piezoelectric response which makes it challenging to design acousto-optic devices. As a representative example, one of the key challenges facing transceivers for exascale systems 6 is avoiding the ∼ 3 dB penalty for coupling light from the III-V laser die to the silicon PIC. Electro-optic frequency comb 7 based coherent communication systems 8 will also benefit greatly from monolithic integration of lasers and modulators. On the quantum photonics side, one of the outstanding problems facing linear optic implementations of quantum computing is implementing feed-forward routines on a chip 9 , which requires (monolithically) interfacing fast, low loss modulators with efficient single photon detectors. Despite the outstanding performance improvements of carrier based depletion modulators, electro-optic modulators present the only near-term solution that can satisfy both the bandwidth (∼ 40 GHz) and loss requirements (< 3 dB) necessary for scalability 10 . Other application areas where alternative material platforms are worth exploring are: cryogenic photonic circuits for interfacing superconducting digital circuits with the outside world 11 and integrated acousto-optics, which re...