Hiring Institution
Centre of Nanoscience and Nanotechnology (C2N) – Centre National de la Recherche Scientifique (CNRS)

PhD-Awarding Institutions
Université Paris Saclay (UPSaclay)
RMIT University (RMIT)

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Option 1

Quantum optics at the single photon level in thin film lithium niobate waveguides

The generation and the manipulation of quantum states of light is a fundamental issue for quantum information. Among these states, twin-photon states whose quantum entanglement and quantum superposition allowed exciting and breakthrough demonstrations in the field of quantum information. Over the last years, a new platform for the generation of twin-photon states has emerged. It is based on thin film lithium niobate on insulator (LNOI), a material widely used by the quantum and nonlinear community for its large nonlinear coefficients. On this platform, lithium niobate thickness is below 1 µm and the advances in nanotechnology fabrications allow reduced-size waveguides in which optical modes with cross sections less than 1 µm₂ can propagate. On this new platform, we can design sophisticated integrated circuits, compatible with telecom band, to generate nonclassical states of light and manipulate their quantum properties with high efficiencies due the high nonlinearities obtained thanks to the tight optical confinement. The nanofabrication of the waveguides on this LNOI platform is done at RMIT University.

The thesis project objective is to explore the generation and manipulation of quantum states on this new platform at the single photon level. The quantum states will be generated through spontaneous parametric generation, where a pump photon at 780 nm is converted into twin photons at 1560 nm, called “signal” and “idler”. The aim is to demonstrate the quantum entanglement of the generated twin photons and use this remarkable property for entanglement swapping, where two independent photons generated in separate waveguides become entangled after a Bell-like quantum measurement. The required architecture of the LNOI waveguides will be designed and fabricated during the project and an experimental setup dedicated to the quantum demonstrations will be set. For the demonstration, two independent periodically poled LNOI waveguides will be fabricated on a same chip to generated twin photons. The LNOI chip will as well include a tunable integrated beam-splitter to mix the two “signal” modes for the Bell-State projection and measurement. Extra building blocks will be added to root, select, and shape the different optical modes.

The project will be performed in collaboration between the primary institutions C2N and RMIT and associated collaboration with Adelaide, gathering their expertise in nonlinear and quantum optics, nanophotonic and LNOI nanotechnology.

Option 2

Multi-mode quantum entanglement on thin film lithium niobate platform

Quantum entanglement is a remarkable resource for several quantum information protocols such as quantum key generation and distribution or quantum teleportation. So far, this resource has been implemented using twin-photons with mostly a limitation to two-mode entanglement.

Over the last years, a new platform for the generation of twin-photon states has emerged. It is based on thin film lithium niobate on insulator (LNOI), a material widely used by the quantum and nonlinear community for its large nonlinear coefficients. On this platform, lithium niobate thickness is below 1 µm and the advances in nanotechnology fabrication allows reduced-size waveguides in which optical modes with cross sections less than 1 µm₂ can propagate.

The thesis project aims to explore the multi-mode entanglement generation on LNOI platform, in an array of coupled periodically poled waveguides. When pumped at 780 nm, twin-photons at degeneracy (1560 nm) are generated in a single fundamental mode propagating in the waveguide. When the waveguides are close enough to each other, the fundamental mode can couple evanescently to the adjacent waveguides. Both nonlinear interaction and linear coupling create the multi-mode entanglement between the fundamental modes at the output of the waveguides array.

During the PhD, we will explore a simple case of two-coupled waveguides and then an array of 3 and 5 waveguides and potentially more complex multi-mode structures. We will investigate continuous variables (CV) multimode entanglement. In this regime, the quantum fluctuations of the quadratures of the fundamental modes are entangled, offering a new powerful resource for quantum information protocols. Moreover, the engineering of the optical excitation in each waveguide allows to reach various entanglement graphs, it means the entanglement relation between the different optical fundamental modes.

The project will be performed in collaboration between the primary institutions C2N and RMIT and associated collaboration with Adelaide, gathering their expertise in nonlinear and quantum optics, nanophotonic and LNOI nanotechnology.

Option 3

Non-Gaussian quantum states generation on thin film lithium niobate platform

Quantum information tasks based on Gaussian statistics can be efficiently simulated by classical computational resources. To highlight the quantum advantages of these tasks, the involvement of non-Gaussian states is crucial. In optics, the optical modes that are involved in quantum information processing have Gaussian statistics, meaning that the quantum fluctuations of their fields exhibit a Gaussian distribution.

The PhD project will explore the non-Gaussian states generation on Lithium Niobate On Insulator (LNOI) platform, combining nonlinear interaction and single photon detection. Indeed, a simple architecture to generate a non-Gaussian state is to remove a single photon from a squeezed vacuum state. On LNOI platform this achievement requires a periodically poled LN waveguide to generated squeezed vacuum, followed by a 99:1 integrated beam-splitter. When a single photon is detected on the 1%-output channel, the quantum state on the other output is non-Gaussian. During the PhD studies, we will first study this simple case, before proposing a design on LNOI platform to generated entangled non Gaussian optical states. The design will be based on several PPLN waveguides followed by an array of linear waveguides. Additional devices will also be added on the LNOI chip to shape the single photon state for a high detection efficient and
quantum projection.

The project will be performed in collaboration between the primary institutions C2N and RMIT and associated collaboration with Adelaide, gathering their expertise in nonlinear and quantum optics, nanophotonic and LNOI nanotechnology.

Kamel Bencheikh
Dist. Prof. Arnan Mitchell

Nonlinear optics, Quantum Optics, Integrated photonics