An important milestone toward the realization of a large-scale quantum computer and further demonstration of a new level of the quantum control of light were accomplished by a team of scientists at the University of California, Santa Barbara (UCSB), Zhejiang University of China and NEC Corp. of Japan. The researchers describe how they used a superconducting quantum integrated circuit to generate unique quantum states of light known as “NOON” states. Generated from microwave-frequency photons, the states were created and stored in two physically separated microwave storage cavities. They explain that quantum NOON states were created using one, two or three photons; all photons were located in one cavity, leaving the other cavity empty. This chip contains the superconducting integrated circuit used to generate NOON microwave states. Courtesy of Erik Lucero, UCSB. In this configuration, which is made possible by quantum mechanics, findings indicate that there is a 50 percent chance of seeing all the photons in one cavity and a 50 percent chance of not finding any. However, probing the cavity gently before looking inside it changes the quantum state, and the effect of probing can be detected even if the cavity is determined later to be empty. These findings were published in Physical Review Letters, Feb. 7, 2011 (doi: 10.1103/ PhysRevLett.106.060401). “It’s kind of like the states are ghostly twins or triplets,” said Haohua Wang, a postdoctoral fellow in physics at UCSB. “They are always together, but somehow you never know where they are. They also have a mysterious way of communicating, so they always seem to know what is going to happen.” The quantum integrated circuit, which includes superconducting quantum bits along with the microwave storage cavities, could eventually become part of a quantum computational architecture, the scientists concluded.