An ultrastrong coupling (USC) between photons and qubits 10 times larger than ever seen may open the door to a domain of physics and applications deemed unattainable until recently. Researchers at the University of Waterloo's Institute for Quantum Computing (IQC) are investigating light-matter interactions in quantum optics. For their research, they fabricated aluminum circuits and then cooled them in dilution refrigerators to one percent of a degree above absolute zero, making the circuits superconducting and able to carry a current without resistance or loss of energy. These superconducting circuits/qubits obey the laws of quantum mechanics and behave as artificial atoms. Researchers then applied a small magnetic field through a coil inside the dilution refrigerator and sent photons using microwave pulses into the superconducting circuit. By measuring photon transmissions, they were able to define the resonance of the qubit by the reflection of the photons off the qubit. This illustration shows a qubit attached to a waveguide where light in the form of microwaves enters and exits. Courtesy of the University of Waterloo. IQC researcher and postdoctoral student Pol Forn-Diaz said the team measured a range of frequencies broader than the qubit. “This means there is a very strong interaction between the qubit and the photons,” said Forn-Diaz. “It is so strong that the qubit is seeing most of the photons that propagate in the circuit, which is a distinctive signature of ultrastrong coupling in an open system.” The IQC team's research coupled with their circuit could potentially act as a quantum simulator propelling even more research and study of quantum systems in nature. The research was published in Nature Physics (doi:10.1038/nphys3905).