Conditional phase shifts using trapped atoms

We describe a scheme for producing conditional nonlinear phase shifts on two-photon optical fields using an interaction with one or more ancilla two-level atomic systems. The conditional field state transformations are induced by using high efficiency fluorescence shelving measurements on the atomic ancilla. The scheme can be nearly deterministic and is of obvious benefit for quantum information applications

Entangling a nanomechanical resonator with a microwave field

We show how the coherent oscillations of a nanomechanical resonator can be entangled with a microwave cavity in the form of a superconducting coplanar resonator. Dissipation is included and realistic values for experimental parameters are estimated.Comment: submitted to J. Mod. Op

Relational time for systems of oscillators

Using an elementary example based on two simple harmonic oscillators, we show how a relational time may be defined that leads to an approximate Schrodinger dynamics for subsystems, with corrections leading to an intrinsic decoherence in the energy eigenstates of the subsystem.Comment: Contribution to the Int. J. of Quant. Info. issue dedicated to the memory of Asher Pere

Development of a Miniature Electrostatic Accelerometer /MESA/ for low g applications Summary report

Design, fabrication, and testing of miniature digital electrostatic accelerometer for low gravity measurements in spac

Fast and robust two-qubit gates for scalable ion trap quantum computing

We propose a new concept for a two-qubit gate operating on a pair of trapped ions based on laser coherent control techniques. The gate is insensitive to the temperature of the ions, works also outside the Lamb-Dicke regime, requires no individual addressing by lasers, and can be orders of magnitude faster than the trap period

Quantum computation with optical coherent states

We show that quantum computation circuits using coherent states as the logical qubits can be constructed from simple linear networks, conditional photon measurements and "small" coherent superposition resource states

Heuristic for estimation of multiqubit genuine multipartite entanglement

For every N-qubit density matrix written in the computational basis, an associated "X-density matrix" can be obtained by vanishing all entries out of the main- and anti-diagonals. It is very simple to compute the genuine multipartite (GM) concurrence of this associated N-qubit X-state, which, moreover, lower bounds the GM-concurrence of the original (non-X) state. In this paper, we rely on these facts to introduce and benchmark a heuristic for estimating the GM-concurrence of an arbitrary multiqubit mixed state. By explicitly considering two classes of mixed states, we illustrate that our estimates are usually very close to the standard lower bound on the GM-concurrence, being significantly easier to compute. In addition, while evaluating the performance of our proposed heuristic, we provide the first characterization of GM-entanglement in the steady states of the driven Dicke model at zero temperature.Comment: 19 pages, 5 figure

Effects of damping on the quantum limits to optical phase shifts in Kerr nonlinear media

It was recently shown [Phys. Rev. A 45, 1919 (1992)] that the phase shift induced by a control beam on a signal in cross Kerr modulation is limited by the quantum nature of the control. We show that dissipation rapidly restores the classical phase shift