A violation of the so-called Bell inequality represents a strong proof of the ability to create and control quantum states of a pair of quantum bits with no classical analogues. Andrea Morello and co-workers have now demonstrated a violation of Bell’s inequality in a pair of qubits in silicon, encoded in the electron spin and the nuclear spin associated with a single phosphorus donor embedded in a nanoelectronic device. The cover image is an artist’s impression of visual fragments mapped spatially from data directly extracted from the measurement of the quantum state of the phosphorus atom. It expresses the creation of entangled qubits that lie at the heart of quantum computation.

Letter p242; News & Views p216 IMAGE: PAUL THOMAS (UNSW), IN COLLABORATION WITH K. RAXWORTHY (CURTIN UNIV.), A. MORELLO AND J. P. DEHOLLAIN (UNSW) COVER DESIGN: BETHANY VUKOMANOVIC