Per Delsing and his team of physicists worked around this by using something called a superconducting quantum interference device, or SQUID. The SQUID, which is very sensitive to magnetic fields, acted as a mirror in the researchers' superconducting circuit. They passed a magnetic field through the SQUID, switching the field's direction a few billion times per second, which caused the SQUID to move back and forth at about 5 percent of the speed of light. Microwave photons were then observed. Consistent with the theory, the frequency of the released photons was about half the frequency of the mirror's wiggling.