  The Gottesman-Kitaev-Preskill (GKP) code was proposed in 2001 by Daniel
Gottesman, Alexei Kitaev, and John Preskill as a way to encode a qubit in an
oscillator. The GKP codewords are coherent superpositions of periodically
displaced squeezed vacuum states. Because of the challenge of merely preparing
the codewords, the GKP code was for a long time considered to be impractical.
However, the remarkable developments in quantum hardware and control technology
in the last two decades has made the GKP code a frontrunner in the race to
build practical, fault-tolerant bosonic quantum technology. In this
Perspective, we provide an overview of the GKP code with emphasis on its
implementation in the circuit-QED architecture and present our outlook on the
challenges and opportunities for scaling it up for hardware-efficient,
fault-tolerant quantum error correction.
