Hybrid Architectures for Quantum Repeaters

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Towards the goal of achieving a global internet network based on quantum communications, or quantum internet, quantum repeaters will enable quantum communications over arbitrarily long distances. Quantum repeaters extend the communication range by using only short-range quantum channels through amplification or entanglement swapping to distribute entanglement between distant end nodes. The principle of operation of a hybrid quantum repeater is based on, first, the transfer of quantum information stored in polarization encoded photonic qubits (ideal for travelling long distances) to solid state spin qubits (ideal for storing and processing information) and second, creating entanglement between spin qubits to establish the communication channel. Employing hybrid quantum repeaters instead of all-optical approaches offers numerous advantages including (i) robust heralding of the incoming photons by charge detection in the electronic circuit, (ii) longer qubit coherence times for storing and processing quantum information and (iii) theoretical up to 100% efficiency of the entanglement protocol to establish the quantum channel. Quantum dot circuits based on optically active materials, such as GaAs, bilayer graphene, and 2D transition metal dichalcogenides (TMDs), are a necessary component of the hybrid quantum repeater to achieve coherent photon-to-spin conversion due to their direct band gap character. The project will run on three main fronts in parallel. First, it will focus on the design of GaAs quantum dot circuits to efficiently create and confine spins from photo-generated electron-hole pairs. Second we will develop and implement Bell state measurement protocols for spin qubits in quantum dots, which will allow the entanglement of two different spins by projecting them onto one of the four Bell states. The main advantage of this idea compared to photonic qubits, is that in principle a failed Bell state measurement doesn't collapse the wave function and another measurement can be attempted until it succeeds. Finally, we will also investigate novel 2D materials for the realization of quantum dot circuits. The choice of materials include bilayer graphene, molybdenum disulfide (MoS2) and tungsten diselenide (WSe2). These optically active materials have only very recently started to be investigated for the implementation of electrostatically defined quantum dots. NSERC support to this project will benefit the scientific community by adding a novel information transfer approach in quantum technologies as well as by better understanding the material and device requirements to implement it. Additionally, with the advancement of quantum communications the Canadian telecommunication industry, and society in general, will have a world leading advantage in the quest for long range quantum communication.