A Shift On A Chip

摘要

The Lamb shift, a minute change in certain energy levels of quantum systems that was first measured in atomic hydrogen some 60 years ago, has now been observed in a solid-state superconducting system. The emission and absorption of light by atoms can be significantly affected by their environment. For many years, physicists have studied how atoms behave in cavities that confine light and restrict the frequencies with which the atoms interact. Cavity quantum electrodynamics (cavity QED) experiments, which examine how light and matter interact in a cavity, can be designed such that an atom is well described as a two-state system (or 'qubit') interacting with a single light frequency in a nearly lossless cavity. It has been observed, for instance, that the frequency of the light emitted (or absorbed) in an atomic transition can be altered by a cavity. More recently, similar effects have been observed in circuit QED, in which pieces of solid-state superconducting systems acting as qubits are embedded in on-chip circuits that are, in effect, one-dimensional cavities. Writing in Science, Fragner et al. now report experiments in which one of the most studied effects of QED in atomic physics - the Lamb shift - has been measured in circuit QED (Fig. 1).