Quantum computer and quantum computation method

A quantum computer comprising:

• a plurality of optical systems arranged in series each of the plurality of optical systems comprising:
• a first half-wave plate which receives a light beam;
• a first polarizing beam splitter which receives a light beam passing through the first half-wave plate;
• a first switching mirror which reflects or transmits a first light beam transmitted by the first polarizing beam splitter;
• a first photodetector which detects the first light beam transmitted by the first switching mirror;
• a first polarization rotator which receives the first light beam reflected by the first switching mirror;
• an optical cavity which receives the first light beam passing through the first polarization rotator and contains an atom;
• a second switching mirror which reflects or transmits a second light beam reflected by the first polarizing beam splitter;
• a second photodetector which detects the second light beam transmitted by the second switching mirror;
• a second polarization rotator which receives the second light beam reflected by the second switching mirror;
• and
• a high reflection mirror which receives the second light beam passing through the second polarization rotator and reflects the received light beam in a direction opposite to an incident direction of the received light beam, the first polarization beam splitter outputting a third light beam received from the first switching mirror or the second switching mirror to adjacent one of the optical systems;
• a plurality of third switching mirrors each provided between adjacent two optical systems, each of the third switching mirrors reflecting or transmitting a light beam output from one of the two optical systems;
• a plurality of light sources each providing the light beam to the corresponding optical system;
• and
• a measurement system which measures polarization of an incoming light beam, the measurement system comprising:
• a second half-wave plate which receives the incoming light beam output from the last-stage optical system, the last-stage optical system arranged at an down end of the plurality of optical systems:
• a second polarizing beam splitter which receives the incoming light beam passing through the second half-wave plate;
• and
• a pair of third and fourth photodetectors, the third photodetector detecting the incoming light beam reflected by the second polarizing beam splitter, the fourth photodetector detecting the incoming light beam transmitted by the second polarizing beam splitter.