A Lens to Focus Quantum Spins

A future quantum computer might use photonic qubits to move information around, but the qubits need to be transferred to a stationary medium such as atoms to perform computations. Given the weakness of the light-matter interaction, the transfer often requires a large ensemble of atoms, which can collectively take on a single photonic qubit. However, standard quantum logic operations are impractical with large ensembles and work best with one atom per qubit. Now a team of theorists has proposed techniques to focus a quantum state spread over many atoms down to nearly a single atom. These techniques could allow multiple photonic qubits to be transferred into a quantum memory made of single-qubit atoms.