Strain-mediated coupling in a quantum dot-mechanical oscillator hybrid system.

Recent progress in nanotechnology has allowed the fabrication of new hybrid systems in which a single two-level system is coupled to a mechanical nanoresonator. In such systems the quantum nature of a macroscopic degree of freedom can be revealed and manipulated. This opens up appealing perspectives for quantum information technologies, and for the exploration of the quantum-classical boundary. Here we present the experimental realization of a monolithic solid-state hybrid system governed by material strain: a quantum dot is embedded within a nanowire that features discrete mechanical resonances corresponding to flexural vibration modes. Mechanical vibrations result in a time-varying strain field that modulates the quantum dot transition energy. This approach simultaneously offers a large light-extraction efficiency and a large exciton-phonon coupling strength g0. By means of optical and mechanical spectroscopy, we find that g0/2 π is nearly as large as the mechanical frequency, a criterion that defines the ultrastrong coupling regime.

Realization of a superconducting atom chip.

We have trapped rubidium atoms in the magnetic field produced by a superconducting atom chip operated at liquid helium temperatures. Up to 8.2x10(5) atoms are held in a Ioffe-Pritchard trap at a distance of 440 microm from the chip surface, with a temperature of 40 microK. The trap lifetime reaches 115 s at low atomic densities. These results open the way to the exploration of atom-surface interactions and coherent atomic transport in a superconducting environment, whose properties are radically different from normal metals at room temperature.

Nondestructive Rydberg atom counting with mesoscopic fields in a cavity.

We present an efficient, state-selective, nondemolition atom-counting procedure based on the dispersive interaction of a sample of circular Rydberg atoms with a mesoscopic field contained in a high-quality superconducting cavity. The state-dependent atomic index of refraction, proportional to the atom number, shifts the classical field phase. A homodyne procedure translates the information from the phase to the intensity. The final field intensity is readout by a mesoscopic atomic sample. This method opens promising routes for quantum information processing and nonclassical state generation with Rydberg atoms.

Rabi oscillations revival induced by time reversal: a test of mesoscopic quantum coherence.

Using an echo technique proposed by Morigi et al., we have time-reversed the atom-field interaction in a cavity quantum electrodynamics experiment. The collapse of the atomic Rabi oscillation in a coherent field is reversed, resulting in an induced revival signal. The amplitude of this "echo" is sensitive to nonunitary decoherence processes. Its observation demonstrates the existence of a mesoscopic quantum superposition of field states in the cavity between the collapse and the revival times.

Coherence-preserving trap architecture for long-term control of giant Ryberg atoms.

We present a way to trap a single Rydberg atom, make it long-lived, and preserve an internal coherence over time scales reaching into the minute range. We propose to trap using carefully designed electric fields, to inhibit the spontaneous emission in a nonresonant conducting structure, and to maintain the internal coherence through a tailoring of the atomic energies using an external microwave field. We thoroughly identify and account for many causes of imperfection in order to verify at each step the realism of our proposal.

Entanglement of a mesoscopic field with an atom induced by photon graininess in a cavity.

We observe that a mesoscopic field made of several tens of microwave photons exhibits quantum features when interacting with a single Rydberg atom in a high-Q cavity. The field is split into two components whose phases differ by an angle inversely proportional to the square root of the average photon number. The field and the atomic dipole are phase entangled. These manifestations of photon graininess vanish at the classical limit. This experiment opens the way to studies of large quantum state superpositions at the quantum-classical boundary.

Antagonistic effects of T-Ag and VP16 reveal a role for RNA pol II elongation on alternative splicing.

Here we investigate the promoter control of alternative splicing by studying two transcriptional activators on templates under replicating conditions. SV40 large T-antigen (T-Ag) activates template replication only 2-fold but transcription 25-fold. T-Ag-mediated replication, reported to inhibit RNA polymerase II elongation, provokes a 10- to 30-fold increase in the inclusion of the fibronectin EDI exon into mature mRNA. The T-Ag effect is exon specific, occurs in cis and depends strictly on DNA replication and not on cell transformation. VP16, an activator of transcriptional initiation and elongation, has a similar effect on transcription but the opposite effect on splicing: EDI inclusion is inhibited by 35-fold. VP16 completely reverts the T-Ag effect, but a VP16 mutant with reduced elongation ability provokes only partial reversion. Both T-Ag and VP16 promote conspicuous co-localization of mRNA with nuclear speckles that contain the SR protein SF2/ASF, a positive regulator of EDI inclusion. Therefore, we conclude that co-localization of transcripts and speckles is not sufficient to stimulate EDI inclusion.

Coordination between transcription and pre-mRNA processing.

A large body of work has proved that transcription by RNA polymerase II and pre-mRNA processing are coordinated events within the cell nucleus. Capping, splicing and polyadenylation occur while transcription proceeds, suggesting that RNA polymerase II plays a role in the regulation of these events. The presence and degree of phosphorylation of the carboxy-terminal domain of RNA polymerase II large subunit is important for functioning of the capping enzymes, the assembly of spliceosomes and the binding of the cleavage/polyadenylation complex. Nuclear architecture and gene promoter structure have also been shown to play key roles in coupling between transcription and splicing.

A complementarity experiment with an interferometer at the quantum-classical boundary.

To illustrate the quantum mechanical principle of complementarity, Bohr described an interferometer with a microscopic slit that records the particle's path. Recoil of the quantum slit causes it to become entangled with the particle, resulting in a kind of Einstein-Podolsky-Rosen pair. As the motion of the slit can be observed, the ambiguity of the particle's trajectory is lifted, suppressing interference effects. In contrast, the state of a sufficiently massive slit does not depend on the particle's path; hence, interference fringes are visible. Although many experiments illustrating various aspects of complementarity have been proposed and realized, none has addressed the quantum-classical limit in the design of the interferometer. Here we report an experimental investigation of complementarity using an interferometer in which the properties of one of the beam-splitting elements can be tuned continuously from being effectively microscopic to macroscopic. Following a recent proposal, we use an atomic double-pulse Ramsey interferometer, in which microwave pulses act as beam-splitters for the quantum states of the atoms. One of the pulses is a coherent field stored in a cavity, comprising a small, adjustable mean photon number. The visibility of the interference fringes in the final atomic state probability increases with this photon number, illustrating the quantum to classical transition.

Step-by-step engineered multiparticle entanglement

After quantum particles have interacted, they generally remain in an entangled state and are correlated at a distance by quantum-mechanical links that can be used to transmit and process information in nonclassical ways. This implies programmable sequences of operations to generate and analyze the entanglement of complex systems. We have demonstrated such a procedure for two atoms and a single-photon cavity mode, engineering and analyzing a three-particle entangled state by a succession of controlled steps that address the particles individually. This entangling procedure can, in principle, operate on larger numbers of particles, opening new perspectives for fundamental tests of quantum theory.

Interaction between the (-170) CRE and the (-150) CCAAT box is necessaryfor efficient activation of the fibronectin gene promoter by cAMP and ATF-2.

The fibronectin promoter contains an ATF/cyclic AMP (cAMP) response element (CRE) site two helical turns upstream of a CCAAT site with which it interacts. We investigated the effects of mutating these (-170) CRE and(-150) CCAAT elements on the promoter activity regulated by three different modulators previously known to act through CRE: ATF-2, cAMP and E1a. While the cooperation seems to play no role in E1a action, integrity of the (-150) CCAAT is necessary for ATF-2 and cAMP efficient activation in a cell-specific manner. These results show that the CRE and CCAAT elements function as a 'composite element' and establish a cell-specific function for CRE-CCAAT synergy.

Slow molecule detection or Ramsey fringes in two-photon spectroscopy: which is better for high resolution spectroscopy and metrology ?

The CO2 laser locked onto a saturated absorption resonance of OsO4 provides a secondary frequency standard in the 10 mm region, with an accuracy of 50 Hz to 1 kHz. For averaging times less than 100 s its stability performance is better than the Hydrogen maser. This paper deals with the present attempt to increase this performance by using a two-photon molecular resonance as a reference. We begin with some preliminary and promising results on a two-photon line of SF6 leading to characteristics similar to those obtained with a saturation line of OsO4 . Then two alternative methods to increase the resolution are presented : optical detection of slow molecules and a new development of the well-known Ramsey fringes. Metrological features are analyzed for both methods.