New superconducting metamaterial traps quantum light

Conventional computers store information in a bit, a fundamental unit of logic that can take a value of 0 or 1. Quantum computers rely on quantum bits, also known as a "qubits," as their fundamental building blocks. Bits in traditional computers encode a single value, either a 0 or a 1. The state of a qubit, by contrast, can simultaneously have a value of both 0 and 1. This peculiar property, a consequence of the fundamental laws of quantum physics, results in the dramatic complexity in quantum systems. 

Quantum computing is a nascent and rapidly developing field that promises to use this complexity to solve problems that are difficult to tackle with conventional computers. A key challenge for quantum computing, however, is that it requires making large numbers of qubits work together—which is difficult to accomplish while avoiding interactions with the outside environment that would rob the qubits of their quantum properties.

New research from the lab of Oskar Painter, John G Braun Professor of Applied Physics and Physics in the Division of Engineering and Applied Science, explores the use of superconducting metamaterials to overcome this challenge.

Metamaterials are specially engineered by combining multiple component materials at a scale smaller than the wavelength of light, giving them the ability to manipulate how particles of light, or photons, behave. Metamaterials can be used to reflect, turn, or focus beams of light in nearly any desired manner. A metamaterial can also create a frequency band where the propagation of photons becomes entirely forbidden, a so-called "photonic bandgap."

The Caltech team used a photonic bandgap to trap microwave photons in a superconducting quantum circuit, creating a promising technology for building future quantum computers.

"In principle, this is a scalable and flexible substrate on which to build complex circuits for interconnecting certain types of qubits," says Painter, leader of the group that conducted the research, which was published in Nature Communications on September 12. "Not only can one play with the spatial arrangement of the connectivity between qubits, but one can also design the connectivity to occur only at certain desired frequencies."