Quantum computing implementations with neutral particles

We review quantum information processing with cold neutral particles, that is, atoms or polar molecules. First, we analyze the best suited degrees of freedom of these particles for storing quantum information, and then we discuss both single- and two-qubit gate implementations. We focus our discussion mainly on collisional quantum gates, which are best suited for atom-chip-like devices, as well as on gate proposals conceived for optical lattices. Additionally, we analyze schemes both for cold atoms confined in optical cavities and hybrid approaches to entanglement generation, and we show how optimal control theory might be a powerful tool to enhance the speed up of the gate operations as well as to achieve high fidelities required for fault tolerant quantum computation.Comment: 19 pages, 12 figures; From the issue entitled "Special Issue on Neutral Particles

Quantum gates driven by microwave pulses in hyperfine levels of ultracold heteronuclear dimers

We theoretically investigated the implementation of universal quantum gates in hyperfine levels of ultracold heteronuclear polar molecules in their lowest rotational manifolds. Quantum bits are manipulated by microwave pulses, taking advantage of the strong state mixing generated by the hyperfine interactions. Gate operations are either driven by a sequence of Gaussian pulses or by a pulse shaped by optimal control theory. Alkaline molecules of experimental interest are considered. We show that high fidelity gates can be driven by microsecond pulses. The richness of the energy structure and the state mixing offer promising perspectives for the manipulation of a large number of qubits

Implementing Quantum Gates and Algorithms in Ultracold Polar Molecules

We numerically investigate the implementation of small quantum algorithms, an arithmetic adder and the Grover search algorithm, in registers of ultracold polar molecules trapped in a lattice by concatenating intramolecular and intermolecular gates. The molecular states are modulated by the exposition to static electric and magnetic fields different for each molecule. The examples are carried out in a two-molecule case. Qubits are encoded either in rovibrational or in hyperfine states, and intermolecular gates involve states of neighboring molecules. Here we use pi pulses (i.e. laser pulses such that the integral of the product of the transition dipole moment and their envelope is equal to pi, thus ensuring a total population inversion between two states) and pulses designed by optimal control theory adapted to a multi-target problem to drive unitary transformations between the qubit states.info:eu-repo/semantics/publishe