Luca Guidoni

Double-lambda microscopic model for entangled light generation by four-wave-mixing

Motivated by recent experiments, we study four-wave-mixing in an atomic double-{Lambda} system driven by a far-detuned pump. Using the Heisenberg-Langevin formalism, and based on the microscopic properties of the medium, we calculate the classical and quantum properties of seed and conjugate beams beyond the linear amplifier approximation. A continuous-variable approach gives us access to relative-intensity noise spectra that can be directly compared with experiments. Restricting ourselves to the cold-atom regime, we predict the generation of quantum-correlated beams with a relative-intensity noise spectrum well below the standard quantum limit (down to -6 dB). Moreover, entanglement between seed and conjugate beams measured by an inseparability down to 0.25 is expected. This work opens the way to the generation of entangled beams by four-wave mixing in a cold-atom sample.

Electric field noise above surfaces: A model for heating rate scaling law in ion traps

Device miniaturization is a challenge that raises new issues because the scaling laws valid in the macroscopic range might fail, for instance due to the emergence of a new characteristic length. Even the simple case of the electricfield in the vicinity of a conductor surface can exhibit anomalous behavior caused by small inhomogeneities of the electric potential on the surface. These field fluctuations are crucial in the studies of short distance phenomena such as the measurement of the Casimir-Polder force, studies of non contact friction[1], gravitational forces and contact potentials. In a different context, recent success in quantum information experiment with trapped ions motivated the fabrication of micro-traps in order to fulfill the scalability requirement of a quantum computer. In such devices a set of micro-fabricated conducting electrodes generates an oscillating electric field that traps laser-cooled ions in a harmonic potential well, at a distance, d, of the surface. In this situation the presence of a fluctuating electric field affects the ion motion inducing a heating. This heating fixes a limit on the achievable fidelity of ion based quantum gates. One might try to account for this heating rate by considering typical electric noise sources in conductors, among which the most likely is Johnson noise. However, measured heating rates are orders of magnitude larger than the expected contribution of the Johnson noise. Moreover, Johnson noise would induce a heating rate that scales as d−2, whereas the observed one is partially consistent with a d−4 scaling, as would be expected from a random distribution of charges, leading to the notion of patch potentials[2]. However, this approach fails at small distances, where a d−1 scaling is observed[1]. Recent experiments[3] suggest that indeed the surface quality plays a dominant role in this anomalous heating.

Topologically decoherence-protected qubits with trapped ions

The authors introduced a new kind of Hamiltonian describing an infinite range coupling between particles placed on a square array with a large number of symmetries and describe its spectral properties. The authors also shows in particular that this Hamiltonian can be naturally realized using ions confined in a surface trap and that the induced protection is more effective than the one predicted for a short range Hamiltonian.

Trapping and cooling of Sr+ ions: strings and large clouds

This paper reports on trapping and laser cooling of singly ionized strontium ions in a linear Paul trap. We describe the loading technique based on two-photon absorption of femtosecond pulses at a wavelength of 431 nm and we compare this technique to electron-bombardment ionization. We perform Doppler cooling of the ions in the few-ions regime as well as in the case of large clouds. The analysis of the fluorescence spectra and direct imaging of the cloud allows us to identify the Coulomb-crystal regime. These experiments open the way to the use of a large cold trapped-ion cloud as a medium for quantum optics and quantum information experiments.

Feasibility of a quantum memory for continuous variables based on trapped ions: from generic criteria to practical implementation

We propose to use a large cloud of cold trapped ions as a medium for quantum optics and quantum information experiments. Contrary to most recent realizations of qubit manipulation based on a small number of trapped and cooled ions, we study the case of traps containing a macroscopic number of ions. We consider in particular the implementation of a quantum memory for quantum information stored in continuous variables and study the impact of the relevant physical parameters on the expected performances of the system.

Ultrafast gain dynamics of the green fluorescent protein

Abstract We investigated the excited state dynamics of the uv mutant of the green fluorescent protein (GFPuv) using spectrally resolved femtosecond pump–probe spectroscopy. The gain dynamics of GFPuv is characterized by a ‘slow’ picosecond mono-exponential growth contrary to the wild type (GFPwt) where ultrafast components have been previously reported. As GFPwt and GFPuv share the same chromophore, this difference can be attributed to an intrinsic improved homogeneity of the GFPuv sample. The study of a synthetic GFP chromophore allows us to confirm the key-role played by the interactions chromophore–proteic cage in GFP photophysics.

Isotope shifts of natural Sr+ measured by laser fluorescence in a sympathetically cooled Coulomb crystal

We measured by laser spectroscopy the isotope shifts between naturally occurring even isotopes of strontium ions for both the

Ultrafast excited-state dynamics of the green fluorescent protein

5s\phantom{\rule{0.16em}{0ex}}{\phantom{\rule{0.16em}{0ex}}}^{2}{S}_{1/2}\ensuremath{\rightarrow}5p\phantom{\rule{0.16em}{0ex}}{\phantom{\rule{0.16em}{0ex}}}^{2}{P}_{1/2}

Ion microtrap technology for quantum information and precision spectroscopy

(violet) and the

Precision measurement of the branching fractions of the5pP1/22state inSr+88with a single ion in a microfabricated surface trap

4d\phantom{\rule{0.16em}{0ex}}{\phantom{\rule{0.16em}{0ex}}}^{2}{D}_{3/2}\ensuremath{\rightarrow}5p\phantom{\rule{0.16em}{0ex}}{\phantom{\rule{0.16em}{0ex}}}^{2}{P}_{1/2}