Quantum computers have the potential to perform tasks exponentially faster than classical computers. Key to this speedup is the massive parallelism and entanglement arising from the superposition of states in quantum bits, or qubits. But the requisite quantum coherence is very fragile, and can be lost through interactions with the environment or other noise sources (see the article by John Preskill in Physics Today, Physics Today 0031-9228 52 6 1999 24 https://doi.org/10.1063/1.882692 June 1999, page 24 ).
Therein lies the challenge of building a real quantum computer: Qubits must be sufficiently isolated from the environment so that they can maintain their coherence throughout the computation. But they must also be sufficiently coupled to the outside world to allow controlled state preparation, manipulation, and measurement.
Much of the experimental attention has been focused on qubit implementations involving nuclear magnetic resonance or trapped ions. Superconducting circuits, long a dark horse in...
