## 초록

제 1형의 매개하향변환에서 발생하는 광자쌍과 Hong-Ou-Mandel 간섭계를 이용하여 4 가지 형태의 Bell 상태를 선택적으로 발생시키고, 두 검출기 앞에 설치한 두 편광자의 각도를 조합하여 측정한 동시계수로부터 Bell 부등식의 위배여부를 분석하였다. $S$의 평균값은 $|{\Psi^{+}\rangle}$상태에서 2.50121,${{|{\Psi^{-}}}\rangle}$ 상태에서 2.50172, ${{|{\Phi^{+}}}\rangle}$상태에서 2.54365, ${{|{\Phi^{-}}}\rangle}$상태에서 2.47830을 얻었다. 이는 숨은변수이론에 근거한 S의 최대값인 2를 초과하는 것으로서, 평균 초과량은 표준편차의 7.48배에 해당하며, Bell 부등식이 위배되는 것을 확인하였다.

Bell's inequality is analyzed in the Bell states produced by a Hong-Ou-Mandel interferometer by placing 2 HWPS and 2 QWPS at both outputs. Average S values of 2.50121, 2.50172, 2.54365, 2.47830 are obtained in the four Bell states ${{|{\Psi^{+}}}\rangle}$, ${{|{\Psi^{-}}}\rangle}$, ${{|{\Phi^{+}}}\rangle}$, ${{|{\Phi^{-}}}\rangle}$ , respectively, from the coincidence measurement in the type-I down-conversion. The results show that the S values are clealy above the upper bound, 2, of the Bell inequality based on the local hidden-variable theory. Bell's inequality is violated by about 7.48 standard deviations on average in all cases.

Bell's inequality is analyzed in the Bell states produced by a Hong-Ou-Mandel interferometer by placing 2 HWPS and 2 QWPS at both outputs. Average S values of 2.50121, 2.50172, 2.54365, 2.47830 are obtained in the four Bell states ${{|{\Psi^{+}}}\rangle}$, ${{|{\Psi^{-}}}\rangle}$, ${{|{\Phi^{+}}}\rangle}$, ${{|{\Phi^{-}}}\rangle}$ , respectively, from the coincidence measurement in the type-I down-conversion. The results show that the S values are clealy above the upper bound, 2, of the Bell inequality based on the local hidden-variable theory. Bell's inequality is violated by about 7.48 standard deviations on average in all cases.

## 키워드

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Bell-inequality, Bell-states, HOM interferometer, polarization-entangled