In this talk, I will discuss several schemes for all-optical quantum information processing that have been developed to overcome formidable limitations of the well-known approaches based on single-photon qubits and continuous-variable states.
Quantum teleportation, a transfer protocol of quantum states, is the essence of many sophisticated quantum information protocols. There have been two complementary approaches to optical quantum teleportation: discrete variables (DVs) and continuous variables (CVs). However, both approaches have pros and cons. Here we take a “hybrid” approach to overcome the current limitations: CV quantum teleportation of DVs. This approach enabled the first realization of deterministic quantum teleportation of photonic qubits without post-selection. We also applied the hybrid scheme to several experiments, including entanglement swapping between DVs and CVs, conditional CV teleportation of single photons, and CV teleportation of qutrits. We are now aiming at universal, scalable, and fault-tolerant quantum computing based on these hybrid technologies.
Continuous-variable quantum information processing with optical field quadrature amplitudes is advantageous in deterministic creation of Gaussian entanglement. On the other hand, non-Gaussian state preparation and operation are currently limited, but heralding schemes potentially overcome this difficulty. Here, we summarize our recent progress in continuous-variable quantum optical experiments. In particular, we have recently succeeded in creation of ultra-large-scale cluster-type entanglement with full inseparability, multiplexed in the time domain; storage and on-demand release of heralded single-photon states, which is applied to synchronization of two heralded single-photon states; real-time quadrature measurements regarding non-Gaussian single-photon states with exponentially rising wavepackets; squeezing with relatively broader bandwidth by using triangle optical parametric oscillator.
Entangled continuous variable (CV) Gaussian states with different wavelengths plays a central role in recent CV-based approaches to quantum network, quantum information processing and quantum metrology. Typically, experiments demonstrating CV entanglement exploit the optical parametric frequency down conversion. Due to the probabilistic nature of photon pair generation, the entanglement involving the post-selection of photonic qubits is limited to at most three colors. Here We theoretically present a scheme for the deterministic generation of entanglement among bright multicolor CV Gaussian states from an optomechanical system using existing experimental technologies. In our scheme an optical frequency comb is input into an optomechanical resonator and then the amplified optomechanical coupling makes multipartite entanglement among them. Our scheme overcomes the limitation of usable frequency of entangled CVs in frequency conversion process. It can be extended to generate multipartite entanglement between orthogonal modes with a single frequency or between microwave and optical CVs, or even among a microwave frequency comb. This optomechanical device can be integrated on a chip.