Quantum entanglement, correlations between multiple systems that cannot be described by classical physics, is a key to realization of large-scale quantum computation . Since the early 2000s, many researches and approaches have been taken to realize large-scale quantum entanglement. However, the largest record was quantum entanglement between 14 parties, generated using ion trap system . In optical systems, quantum entanglement can be easily generated by interfering non-classical lights called squeezed light . Despite this simplicity, conventional method in optical system requires larger setup as the number of entangled parties increases and the experimental demonstrations were limited to generation of nine-partite entanglement . In most physical system, not limited to optical system, large-scale generation of quantum entanglement has remained a challenging task and a huge obstacle toward realization of quantum computing.
In 2011, however, a solution to this obstacle was proposed ; Dr. Nicolas Menicucci from RMIT University proposed a time-domain multiplexing method. This method allows generation of large-scale quantum entanglement on optical system without having to increase the size of experimental setup. Although this proposal was a theoretical breakthrough that shows the possibility of feasible large-scale quantum entanglement generation, experimental demonstration was not achieved due to technological difficulties.
In 2013, our group, based on the above proposal, developed necessary technologies and demonstrated generation of large-scale quantum entanglements, overcoming the limitation in their size for the first time . By applying time-domain multiplexing method, we can consider a continuous-wave squeezed light as multiple, independent, and temporally localized wave packets of squeezed lights and generate large-scale entanglement using only two squeezed-light sources. To generate such a large-scale quantum entanglement, we first generate multiple disjointed two-mode entanglements by interfering two squeezed-light wave packets, then, we delay one of the wave packet and interfere them with wave packets before and after. This results in an entanglement consists of multiple squeezed light wave packets that are entangled with temporally adjacent wave packets.
Also, in the process of making time-domain multiplexed entanglement, we also developed many technology such as a low-loss optical delay line. As the result, we generated quantum entanglement consists of more than 16,000 parties, 1,000 times more than that of the previous research. By further improve the stability of our system, in principle, it is possible to generate large-scale quantum entanglement without limitations on the number of the entangled parties.
Moreover, this particular entanglement we generated can be combined with quantum teleportation to realize time-domain multiplexed quantum computer. By using time-domain multiplexing, not only that we can realize large-scale quantum entanglement, but we can also realize teleportation-based quantum computer in a scalable fashion. As a next step, we are now pursuing realization of large-scale quantum computer based on the experimental system we developed for generation of time-domain multiplexed large-scale quantum entanglement.
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