Perspective on hybrid quantum information processing: a method for large-scale quantum information processing

There are two encoding schemes for quantum information processing (QIP). One is called qubit encoding which corresponds to ‘digital’ encoding, precisely speaking, quantum information is encoded as a superposition of two orthogonal states. The other is called continuous-variable (CV) encoding which corresponds to ‘analog’ encoding, precisely speaking, quantum information is encoded in a wave function with a continuous basis or in amplitude and phase of wave. In some sense, qubit encoding corresponds to a particle picture of quantum mechanics and the CV one corresponds to a wave picture. Both have advantages and disadvantages and grew separately. There are two models of QIP for both encoding schemes. One is the quantum circuit model, where a quantum circuit consists of quantum gates which process input quantum states. The other is the measurement-based model or one-way QIP, where a large-scale entangled state called a cluster state is initially prepared and then we make a measurement and feedforward depending on the desired operations.