Quantum Computing with Cs Atom Qubits

Entanglement is an essential feature of quantum mechanics. For instance, if two identical particles can each be in either state A or B, they can be in an entangled state AA+BB, which means that the particles are in a superposition of both being in A or both being in B, but never one in A and the other in B. These highly non-classical states are central to the working of quantum computers. To date, proto-quantum computers have been made with up to 14 quantum bits (qubits), but their outputs can be readily reproduced with classical computers. As entangled states become increasingly complex they can no longer be modeled on classical computers. A quantum computer with more than 50 qubits could solve certain kinds of problems that are otherwise unsolvable. Quantum computing is being pursued using several different types of qubits, including ions, superconducting Josephson junctions, quantum dots, photons, nitrogen vacancy centers in diamonds, and neutral atoms. Each candidate qubit has its strengths and weakness. Neutral atoms trapped in optical lattices can be well-isolated from their environment, so they have relatively long coherence times, an essential qubit feature. Trapping them with light presents a relatively straightforward path to scalability well beyond 50 qubits. Still, there has been less work on trapped neutral atoms than on most other qubit candidates. The work proposed here is directed toward developing neutral atoms for quantum computation. Experimental techniques needed for a neutral atom quantum computer will be developed. Previously atoms in a 5 micron spaced 3D optical lattice have been trapped and cooled, with an atom at half the sites. Using accurate site occupancy maps and the ability to address individual sites within a 5×5×5 site volume, a procedure to arbitrarily sort the atoms within that volume will be executed. For instance, perfectly occupied 3×3×3 cubes and 5×5 planes will be created. Since the atoms can be cooled to near their vibrational ground state after sorting, the sorting procedure can be checked and small errors corrected if need be, giving an ideal starting point for a quantum computation. A new technique for measuring the internal states of a neutral atom qubit without atom loss by coherently splitting atoms based on their internal states, and then locking them in place with a shorter length scale optical lattice will be demonstrated. They can then be reliably detected in this new lattice, where their location encodes their initial internal state. A new type of single qubit microwave gate where atoms do not need to leave their storage basis will be demonstrated, which promises exceptionally high fidelity. Also work will continue to demonstrate two-qubit Rydberg gates, taking advantage of the low temperature of the atoms and the associated excellent localization. After all these techniques are developed, the system will allow for the implementation of ~3000 gates on 25 atoms before any atom loss is expected. This would constitute a sufficient proof of principle of scalability in neutral atom systems to stimulate further work in error correction and scaling in these systems.