Currently, the mainstream method for realizing quantum computers is called the gate method, which is being developed in various countries around the world. As the number of qubits increases, the wiring becomes more complicated, and the technical limit to the scale is being reached.

　On the other hand, our researchers focused on a one-way quantum calculation method that is different from the gate method.In this method, a large number of qubits are first placed in a entangled state (cluster state), and each qubit is measured according to the desired quantum calculation to perform quantum calculation.In other words, if we can prepare a "two-dimensional cluster state" in which qubits are connected in a mesh pattern by superimposing all quantum calculation patterns, then it is relatively easy to measure each qubit, and any quantum calculation can be performed. It can be done, but it has not been realized.

　Under these circumstances, we have succeeded in generating a two-dimensional cluster state using our unique time domain multiplex technology.In this method, light emitted continuously from one quantum light source is separated in time, and each separated pulse of light is treated as a qubit, so that large-scale quantum entanglement is treated as a small number of optics. It can be generated by the element.We also theoretically devised a method for efficient calculation using the two-dimensional cluster state generated by this system, and found that quantum calculation with 2 inputs and 2 calculation steps is feasible. ..Furthermore, in principle, this size can be increased as much as possible.

　This result has achieved the generation of a two-dimensional cluster state that has not been realized for about 20 years since the advocacy of one-way quantum computation, and is expected to bring about a major change in the field of quantum computers.

Paper information:[Science] Generation of time-domain-multiplexed 2-dimensional cluster state