impurity atoms

A big part of the burgeoning science of quantum computation is reliably storing and processing information in the form of quantum bits, or qubits.  One of the obstacles to this goal is the difficulty of preserving the fragile quantum condition of qubits against unwanted outside influence even as the qubits interact among themselves in a programmatic way. 
Spin qubits are one of the most promising candidates for the purpose.  Besides being charged, electrons possess spin, a kind of magnetic axis that can only assume specific quantized values.  An atom with a single unpaired electron can serve as a qubit if that electron can be tickled into residing in both of two allowed quantum states (usually called spin up and down) at the same time.  Likewise, a carefully contrived small puddle of electrons known as a quantum dot can also serve as a qubit.  The dot’s spin consists of the aggregate spin of the small number of electrons (two, three, four, etc.) residing in the dot.  In this way the dot acts as a sort of artificial atom.
JQI scientists, publishing in Physical Review Letters, show how both of these qubit types — atomic spins and quantum dot spins — can be combined into a workable quantum system.  According to Jacob Taylor, the leader of the JQI work, their suggestion for a new qubit interaction protocol uses the dot’s spin to turn on what is essentially a chemical reaction between two atomic spins which sit as much as 50 or 100 nm apart.   In the proposed scheme, the atoms designated for qubit duty are phosphorus impurities sitting in a silicon crystal.