One step closer to quantum computing
In conventional computers, data are rendered as bits that are always in one of two states: 0 and 1. A quantum bit, also called qubit, can exist in both these states at once, a condition known as superposition. This quantum 'weirdness' allows many calculations to be performed in parallel. Making qubits 'talk' to each other, and thereby create a logic gate, has proven to be a daunting task. However, two-qubit gates on many pairs of atoms in parallel are reaching fruition, thanks to the repeating pattern of optical lattices and the long coherence times of neutral atoms arranged in such systems. A team of scientists working on the EU-funded project NODOS (Non-adiabatic quantum dynamics in novel optical superlattices) have developed a technique to implement a two-qubit gate on a selected pair of atoms. The solution proposed involves the use of superlattices. Optical lattices for ultracold atoms are implemented by superimposed counter-propagating laser beams. NODOS researchers developed an optical superlattice structure, consisting of two optical lattices with similar periodicities, to confine rubidium (Rb) atoms. With this array of ultracold Rb atoms, a two-qubit gate on a selected pair of neighbouring atoms could be realised by exploiting spin-exchange interactions. To achieve such a gate required the merging of two atoms in the same lattice site so that their wave functions overlap. Specifically, by controlling the relative frequency and intensity of the optical superlattice, the researchers propose to merge pairs of interacting atoms into a single lattice site. Such a two-qubit gate could swap qubits in less than a millisecond with an error probability lower than 10-3. Furthermore, the optical superlattice architecture induces a hyperfine position shift, several orders of magnitude smaller than the laser wavelength, also enabling the realisation of single-qubit gates. The NODOS project results have been detailed in a publication in the renowned journal Physical Review A. With the basic building blocks for a quantum computer now identified and the experimental apparatus set up, the research team can start building a functioning quantum computer.
Keywords
Quantum computing, qubit, logic gates, optical lattices, ultracold atoms, spin-exchange
