Quantum device and method of controlling quantum device

A method of controlling a quantum device, wherein the quantum device comprises:

• a plurality of quantum bit elements each including a diamond crystal layer and a color center, the diamond crystal layer having a central portion and extending portions connected to the central portion and extending in 2n directions (n is an integer of 2 or more) from the central portion, the color center being formed in the central portion;
• an input optical waveguide that is connected to each of n ends of the extending portions and transmits light introduced into the color center;
• an output optical waveguide that is connected to each of n ends of the extending portions and transmits a photon emitted from the color center;
• and
• a branching element connected to the output optical waveguide of a first quantum bit element of the plurality of quantum bit elements and the output optical waveguide of a second quantum bit element of the plurality of quantum bit elements;
• the method of controlling a quantum device, comprising:
• introducing light into the first quantum bit element and the second quantum bit element;
• and
• causing a first photon emitted from the first quantum bit element and a second photon emitted from the second quantum bit element to form quantum entanglement in the branching element.