The performance of superconducting qubits has improved by several orders of magnitude in the past decade. These circuits benefit from the robustness of superconductivity and the Josephson effect, and at present they have not encountered any fundamental physical limits. However, building an error-corrected information processor with many such qubits will require solving specific architecture problems that constitute a new field of research. For the first time, physicists will have to master quantum error correction to design and operate complex active systems that are dissipative in nature, yet remain coherent indefinitely. We offer a view on some directions for the field and speculate on its future.
“John Bell’s discovery that entanglement had experimentally testable consequences opened a new experimental field in which the boundaries of validity of quantum mechanics would be explored as far as current technology would permit. One new direction was proposed at the beginning of the 80’s by Tony Leggett (recipient of the 2003 Nobel Prize in Physics): test the application of quantum mechanics to collective electrical variables of radio-frequency circuits, like macroscopic currents and voltages. In circuits that are purely linear, like an inductance-capacitance (LC) harmonic oscillator, the difference between classical and quantum behavior is very subtle and is hard to observe if one does not introduce a non-linear element…”