Measurement induced entanglement and quantum computation with atoms in optical cavities

We propose a method to prepare entangled states and implement quantum computation with atoms in optical cavities. The internal state of the atoms are entangled by a measurement of the phase of light transmitted through the cavity. By repeated measurements an entangled state is created with certainty, and this entanglement can be used to implement gates on qubits which are stored in different internal degrees of freedom of the atoms. This method, based on measurement induced dynamics, has a higher fidelity than schemes making use of controlled unitary dynamics.Comment: 4 pages including 2 figures. v2+3: minor change

Spin-Orbit Mediated Control of Spin Qubits

We propose to use the spin-orbit interaction as a means to control electron spins in quantum dots, enabling both single qubit and two qubit operations. Very fast single qubit operations may be achieved by temporarily displacing the electrons. For two qubit operations the coupling mechanism is based on a combination of the spin-orbit coupling and the mutual long-ranged Coulomb interaction. Compared to existing schemes using the exchange coupling, the spin-orbit induced coupling is less sensitive to random electrical fluctuations in the electrodes defining the quantum dots.Comment: 4 pages, 3 figures; minor changes - final version as published in Phys. Rev. Let

Spin-orbit induced spin-qubit control in nanowires

We elaborate on a number of issues concerning our recent proposal for spin-qubit manipulation in nanowires using the spin-orbit coupling. We discuss the experimental status and describe in further detail the scheme for single-qubit rotations. We present a derivation of the effective two-qubit coupling which can be extended to higher orders in the Coulomb interaction. The analytic expression for the coupling strength is shown to agree with numerics.Comment: 5 pages, 3 figures, Contribution to ICN+T2006, Basel, Switzerland, July-August, 200

Fractional quantum Hall states of atoms in optical Lattices

We describe a method to create fractional quantum Hall states of atoms confined in optical lattices. We show that the dynamics of the atoms in the lattice is analogous to the motion of a charged particle in a magnetic field if an oscillating quadrupole potential is applied together with a periodic modulation of the tunneling between lattice sites. We demonstrate that in a suitable parameter regime the ground state in the lattice is of the fractional quantum Hall type and we show how these states can be reached by melting a Mott insulator state in a super lattice potential. Finally we discuss techniques to observe these strongly correlated states.Comment: 4+epsilon pages including 3 figures. V2: Changes in the presentatio

Spin-Photon Entangling Diode

We propose a semiconductor device that can electrically generate entangled electron spin-photon states, providing a building block for entanglement of distant spins. The device consists of a p-i-n diode structure that incorporates a coupled double quantum dot. We show that electronic control of the diode bias and local gating allow for the generation of single photons that are entangled with a robust quantum memory based on the electron spins. Practical performance of this approach to controlled spin-photon entanglement is analyzed.Comment: 4 pages, 2 figures; figures update

A Hybrid Long-Distance Entanglement Distribution Protocol

We propose a hybrid (continuous-discrete variable) quantum repeater protocol for distribution of entanglement over long distances. Starting from entangled states created by means of single-photon detection, we show how entangled coherent state superpositions, also known as `Schr\"odinger cat states', can be generated by means of homodyne detection of light. We show that near-deterministic entanglement swapping with such states is possible using only linear optics and homodyne detectors, and we evaluate the performance of our protocol combining these elements.Comment: 4 pages, 3 figure

A useful reparameterisation to obtain samples from conditional inverse Wishart distributions

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