Satellite-based optical quantum technologies represent a promising field for obtaining a worldwide quantum network. However, due to the limited size of satellites and the adverse conditions of a space environment, only compact and resistant devices can be used for this purpose. In this respect, we present for the first time the space qualification of integrated photonic circuits fabricated by Ultrafast Laser Writing. By inscribing different straight waveguides, directional couplers and Mach-Zehnder interferometer, and by exposing them to appropriate proton and gamma ray irradiations, we show that our integrated devices are suited for performing quantum experiments in a low Earth orbit.
Satellite-based optical quantum technologies represent a promising field for obtaining a worldwide quantum network. However, due to the limited size of satellites and the adverse conditions of a space environment, only compact and resistant devices can be used for this purpose. In this respect, we present for the first time the space qualification of integrated photonic circuits fabricated by Ultrafast Laser Writing. By inscribing different straight waveguides, directional couplers and Mach-Zehnder interferometer, and by exposing them to appropriate proton and gamma ray irradiations, we show that our integrated devices are suited for performing quantum experiments in a low Earth orbit.
We report photonic quantum circuits created using an ultrafast laser processing technique that is rapid, requires no lithographic mask and can be used to create three-dimensional networks of waveguide devices. We have characterized directional couplers--the key functional elements of photonic quantum circuits--and found that they perform as well as lithographically produced waveguide devices. We further demonstrate high-performance interferometers and an important multi-photon quantum interference phenomenon for the first time in integrated optics. This direct-write approach will enable the rapid development of sophisticated quantum optical circuits and their scaling into three-dimensions.
The emerging field of quantum technologies requires a range of photonic devices, many with demanding specifications. The area of quantum information processing requires scaling in order to increase the complexity of experiments, this has led researchers towards integrated photonic platforms. The key property of these single photon devices is low-loss operation and as a consequence glass and silica devices have been a dominant platform. Whereas atom chip sensors require stable compact systems for converting optical fibre modes to free space beams for atom trapping. In this talk I will present the photonic engineering undertaken at the University of Southampton to fabricate devices for the quantum technology community. The key fabrication approach is a direct UV writing technique, where a UV laser beam is used to define waveguides, splitters/couplers, Bragg gratings and 2D tilted gratings. The fabricated devices include cascaded arrays of Mach-Zehnder interferometers to preform photon-photon interactions, single photon sources via spontaneous four-wave mixing, integrated superconducting single photon detectors and 2D diffraction gratings. In addition to the inscription method I will describe the fabrication of the substrates required for the UV writing process which are generated via Flame Hydrolysis Deposition. I will discuss our most recent work on single photon linear optical networks constructed from a number of identical reconfigurable modules. The modules are characterised separately to produce an accurate model of the network and the cellular approach permits the replacement of modules that are deficient. Each module comprises of an array of 10 Mach-Zehnder interferometers with 40 thermo-optic phase shifters on each chip that control both the amplitude and phase of the optical modes. By concatenating modules any arbitrary N ×N unitary network can be realised. The channel waveguides are engineered to be mode matched to standard optical fibre producing excellent coupling efficiency. I will present our recent work in this area and other photonic devices for the field of quantum technology.
Photonics is a powerful framework for testing in experiments quantum information ideas, which promise significant advantages in computation, cryptography, measurement and simulation tasks. Linear optics is in principle sufficient to achieve universal quantum computation, but stability requirements become severe when experiments have to be implemented with bulk components. Integrated photonic circuits, on the contrary, due to their compact monolithic structure, easily overcome stability and size limitations of bench-top setups. Anyway, for quantum information applications, they have been operated so far only with fixed polarization states of the photons. On the other hand, many important quantum information processes and sources of entangled photon states are based on the polarization degree of freedom. In our work we demonstrate femtosecond laser fabrication of novel integrated components which are able to support and manipulate polarization entangled photons. The low birefringence and the unique possibility of engineering three-dimensional circuit layouts, allow femtosecond laser written waveguides to be eminently suited for quantum optics applications. In fact, this technology enables to realize polarization insensitive circuits which have been employed for entangled Bell state filtration and implementation of discrete quantum walk of entangled photons. Polarization sensitive devices can also be fabricated, such as partially polarizing directional couplers, which have enabled on-chip integration of quantum logic gates reaching high fidelity operation.
Integrated photonic circuits with many input and output modes are essential in applications ranging from conventional optical telecommunication networks, to the elaboration of photonic qubits in the integrated quantum information framework. In particular, the latter field has been object in the recent years of an increasing interest: the compactness and phase stability of integrated waveguide circuits are enabling experiments unconceivable with bulk-optics set-ups. Linear photonic devices for quantum information are based on quantum and classical interference effects: the desired circuit operation can be achieved only with tight fabrication control on both power repartition in splitting elements and phase retardance in the various paths. Here we report on a novel three-dimensional circuit architecture, made possible by the unique capabilities of femtosecond laser waveguide writing, which enables us to realize integrated multimode devices implementing arbitrary linear transformations. Networks of cascaded directional couplers can be built with independent control on the splitting ratios and the phase shifts in each branch. In detail, we show an arbitrarily designed 5×5 integrated interferometer: characterization with one- and two-photon experiments confirms the accuracy of our fabrication technique. We exploit the fabricated circuit to implement a small instance of the boson-sampling experiments with up to three photons, which is one of the most promising approaches to realize phenomena hard to simulate with classical computers. We will further show how, by studying classical and quantum interference in many random multimode circuits, we may gain deeper insight into the bosonic coalescence phenomenon.
Quantum simulators are getting to the level of real devices, constituted by a quantum system which can be controlled in its preparation, evolution and measurement and whose dynamics can implement that of the target quantum system we want to simulate. In this context, photonics quantum technologies are expected to play an instrumental role in the realization of controlled quantum systems capable, in their evolution, to simulate a given complex system. I will present some of the main results obtained in this field in our laboratory by using integrated waveguide optical circuits that represent the hardware of a quantum simulator. These systems are constituted by interferometer arrays of beam splitters and phase shifters fabricated on single integrated platforms by femtosecond laser writing technique and have the potential of speeding-up the evolution from lab systems to the next generation of quantum optical devices for real-world applications. Using the mobility of photons we are able to create arbitrary interconnections within these systems and to mimic the main features of quantum phenomena of increasing complexity.
Summary form only given. High-accuracy integrated photonic circuits are desired in many applications, ranging from telecommunications to sensing, especially where many optical modes or many wavelengths are involved. Particularly challenging are the requirements needed for quantum information applications [1], which have recently found in the integrated optics technology a quite unique and powerful platform [2]. In fact, quantum and classical interference effects are ubiquitously exploited in quantum photonic devices, thus requiring a tight fabrication control not only on the power splitting elements inside the circuit, but also on the phase induced by the various paths. Difficulties grow in case quantum simulation tasks [3] are addressed: the need to model other physical systems increases the circuit complexity and many elements need to be integrated without losing in precision.Femtosecond laser microfabrication has recently emerged as an ideal approach to fabricate integrated photonic circuits for quantum applications [4, 5]. *n the one hand it is appreciated for its low costs and fast-prototyping capabilities. *n the other hand, femtosecond laser written waveguides, due to their low birefringence, can support polarization-entangled two-photon states [5], which are useful to implement many quantum information protocols.In this work we demonstrate the capability of femtosecond laser writing technology to fabricate complex waveguide circuits, with tight phase control and polarization independent behaviour. Specifically, we manufacture optical circuits consisting of cascaded directional couplers, which implement discrete-time quantum walks of polarization entangled photon pairs. The scheme of a circuit realizing a four-steps quantum walk on an ordered one-dimensional lattice is shown in Fig. 1(a). To achieve a perfect polarization insensitive behaviour, directional couplers with an innovative three-dimensional geometry are employed (see the blow-up in Fig. 1(a)). In fact, waveguide birefringence causes a slight polarization dependence of the dimension and of the ellipticity of the guided mode, which may affect the coupling coefficients. We show that, by fabricating the two waveguides constituting the coupler on different planes, it is possible to find a condition in which the overlap integrals for differently polarized guided modes are equal, thus providing the desired polarization insensitivity in the coupling. In Fig. 1(b) the experimental two-photon correlations are reported, obtained by injecting polarization-entangled two-photon states with different symmetry, compared with the theoretical ones. This is equivalent to perform quantum walks of quantum particle pairs with bosonic or fermionic symmetry [6]. *ne can note the excellent agreement between the theory and the experiment, which testifies the accuracy of our fabrication process. We will also show how similar circuits, involving more optical modes and implementing arbitrary phase maps, enable to study quantum walks with disorder-induced effects and thus to observe phenomena such as Anderson localization.