Quantum Mechanics (IMAGE) University of Warsaw, Faculty of Physics Caption Photons can be so entangled that within quantum mechanics their states cannot be described without using complex numbers. Credit Source: QOT/jch Usage Restrictions the image may only be used with appropriate caption: Source: QOT/jch License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.