ARLINGTON, Va. -- AFRL-sponsored research ongoing at the Massachusetts Institute of Technology (MIT) is accelerating the development of quantum computers. Quantum computing helps the Air Force pursue important capabilities in cryptoanalysis, or "code breaking"; microwave electronics; and materials science. The lab-funded researchers, teamed across the Lincoln Laboratory and the Research Laboratory for Electronics at MIT, developed what they call "amplitude spectroscopy." This technology analyzes an atom's response to different electromagnetic radiation amplitudes at a fixed frequency in order to extract the atom's energy-level structure (spectroscopy) over a broad bandwidth.

The researchers demonstrated amplitude spectroscopy using superconducting artificial atom structures consisting of two superconductors linked by a nonconductive barrier. When the atoms cool to ultralow temperatures via dilution refrigeration followed by microwave-induced cooling (similar to laser cooling for atoms), they exhibit energy levels akin to a natural atom or molecule.

The fabrication of such structures is unique and requires special tools. Whereas most researchers use ultrathin aluminum film to create artificial atoms, the MIT team uses niobium, leveraging a semiconductor-based, multilayer fabrication process that uses optical lithography and chemical-mechanical planarization. One of the key accomplishments of the MIT work is the newfound capacity to fabricate the deep-submicron Josephson junctions necessary for realizing artificial atoms.

As the researchers learn more about these superconducting structures, they will continue to apply this knowledge in furthering quantum computing technology--both for present-day development needs and future possibilities. Meanwhile, scientists can use artificial atoms as the "quantum bits"(i.e., qubits) of quantum computing technology--a challenging, long-term focus area that drives near-term innovations. AFRL has funded several of this same team's successes, which include Mach-Zehnder interferometry in a strongly driven superconducting qubit, microwave-induced cooling of a superconducting qubit; and amplitude spectroscopy of a solid-state artificial atom.