Collective modes of a trapped ion-dipole system

We study a simple model consisting of an atomic ion and a polar molecule trapped in a single setup, taking into consideration their electrostatic interaction. We determine analytically their collective modes of excitation as a function of their masses, trapping frequencies, distance, and the molecule's electric dipole moment. We then discuss the application of these collective excitations to cool molecules, to entangle molecules and ions, and to realize two-qubit gates between them. We finally present a numerical analysis of the possibility of applying these tools to study magnetically ordered phases of two-dimensional arrays of polar molecules, a setup proposed to quantum-simulate some strongly-correlated models of condensed matter.Comment: v2: 13 pages, 8 figures (from 10 figure files). Matches published version in Appl. Phys. B, special issue "Wolfgang Paul 100

Measuring molecular electric dipoles using trapped atomic ions and ultrafast laser pulses

We study a hybrid quantum system composed of an ion and an electric dipole. We show how a trapped ion can be used to measure the small electric field generated by a classical dipole. We discuss the application of this scheme to measure the electric dipole moment of cold polar molecules, whose internal state can be controlled with ultrafast laser pulses, by trapping them in the vicinity of a trapped ion.Comment: 13 pages, 6 figures. Substantially modified version, with 4 new appendices; matches published versio

Superconducting circuit microwave photonics

ITAMP, Cambridge, MA, USA, June 29 - July 1, 2015; https://www.cfa.harvard.edu/itamp/LightMatterInteractionsinLowDimensions-schedule.htmlPeer Reviewe

Hybrid quantum magnetism in circuit-QED: from spin-photon waves to many-body spectroscopy

We introduce a model of quantum magnetism induced by the non-perturbative exchange of microwave photons between distant superconducting qubits. By interconnecting qubits and cavities, we obtain a spin-boson lattice model that exhibits a quantum phase transition where both qubits and cavities spontaneously polarise. We present a many-body ansatz that captures this phenomenon all the way, from a the perturbative dispersive regime where photons can be traced out, to the non-perturbative ultra-strong coupling regime where photons must be treated on the same footing as qubits. Our ansatz also reproduces the low-energy excitations, which are described by hybridised spin-photon quasiparticles, and can be probed spectroscopically from transmission experiments in circuit-QED, as shown by simulating a possible experiment by Matrix-Product-State methods.Comment: closer to published versio

Continuous matrix product states for coupled fields: Application to Luttinger Liquids and quantum simulators

A way of constructing continuous matrix product states (cMPS) for coupled fields is presented here. The cMPS is a variational \emph{ansatz} for the ground state of quantum field theories in one dimension. Our proposed scheme is based in the physical interpretation in which the cMPS class can be produced by means of a dissipative dynamic of a system interacting with a bath. We study the case of coupled bosonic fields. We test the method with previous DMRG results in coupled Lieb Liniger models. Besides, we discuss a novel application for characterizing the Luttinger liquid theory emerging in the low energy regime of these theories. Finally, we propose a circuit QED architecture as a quantum simulator for coupled fields.Comment: 10 pages, 5 figure

Quantum Ratchets for Quantum Communication with Optical Superlattices

We propose to use a quantum ratchet to transport quantum information in a chain of atoms trapped in an optical superlattice. The quantum ratchet is created by a continuous modulation of the optical superlattice which is periodic in time and in space. Though there is zero average force acting on the atoms, we show that indeed the ratchet effect permits atoms on even and odd sites to move along opposite directions. By loading the optical lattice with two-level bosonic atoms, this scheme permits to perfectly transport a qubit or entangled state imprinted in one or more atoms to any desired position in the lattice. From the quantum computation point of view, the transport is achieved by a smooth concatenation of perfect swap gates. We analyze setups with noninteracting and interacting particles and in the latter case we use the tools of optimal control to design optimal modulations. We also discuss the feasibility of this method in current experiments.Comment: Published version, 9 pages, 5 figure

Phase Stabilization of a Frequency Comb using Multipulse Quantum Interferometry

From the interaction between a frequency comb and an atomic qubit, we derive quantum protocols for the determination of the carrier-envelope offset phase, using the qubit coherence as a reference, and without the need of frequency doubling or an octave spanning comb. Compared with a trivial interference protocol, the multipulse protocol results in a polynomial enhancement of the sensitivity O(N^{-2}) with the number N of laser pulses involved. We present specializations of the protocols using optical or hyperfine qubits, Lambda-schemes and Raman transitions, and introduce methods where the reference is another phase-stable cw-laser or frequency comb