UV-isomerisation in nematic elastomers as a route to photo-mechanical transducer

The macroscopic shape of liquid crystalline elastomers strongly depends on the order parameter of the mesogenic groups. This order can be manipulated if photoisomerisable groups, e.g. containing N=N bonds, are introduced into the material. We have explored the large photo-mechanical response of such an azobenzene-containing nematic elastomer at different temperatures, using force and optical birefringence measurements, and focusing on fundamental aspects of population dynamics and the related speed and repeatability of the response. The characteristic time of ``on'' and ``off'' regimes strongly depends on temperature, but is generally found to be very long. We were able to verify that the macroscopic relaxation of the elastomer is determined by the nematic order dynamics and not, for instance, by the polymer network relaxation.Comment: Latex (EPJE class) 12 figure

Dynamics of a pulsed continuous variable quantum memory

We study the transfer dynamics of non-classical fluctuations of light to the ground-state collective spin components of an atomic ensemble during a pulsed quantum memory sequence, and evaluate the relevant physical quantities to be measured in order to characterize such a quantum memory. We show in particular that the fluctuations stored into the atoms are emitted in temporal modes which are always different than those of the readout pulse, but which can nevertheless be retrieved efficiently using a suitable temporal mode-matching technique. We give a simple toy model - a cavity with variable transmission - which accounts for the behavior of the atomic quantum memory.Comment: 6 pages, 5 figure

Reorganization of a dense granular assembly: the `unjamming response function'

We investigate the mechanical properties of a static dense granular assembly in response to a local forcing. To this end, a small cyclic displacement is applied on a grain in the bulk of a 2D disordered packing under gravity and the displacement fields are monitored. We evidence a dominant long range radial response in the upper half part above the sollicitation and after a large number of cycles the response is `quasi-reversible' with a remanent dissipation field exhibiting long range streams and vortex-like symmetry.Comment: 5 pages, 5 figures, accepted version for publication in Phys. Rev.

Reversible Quantum Interface for Tunable Single-sideband Modulation

Using Electromagnetically Induced Transparency (EIT) in a Cesium vapor, we demonstrate experimentally that the quantum state of a light beam can be mapped into the long lived Zeeman coherences of an atomic ground state. Two non-commuting variables carried by light are simultaneously stored and subsequentely read-out, with no noise added. We compare the case where a tunable single sideband is stored independently of the other one to the case where the two symmetrical sidebands are stored using the same EIT transparency window.Comment: 4 pages, 6 figure

Dynamical Quantum Memories

We propose a dynamical approach to quantum memories using an oscillator-cavity model. This overcomes the known difficulties of achieving high quantum input-output fidelity with storage times long compared to the input signal duration. We use a generic model of the memory response, which is applicable to any linear storage medium ranging from a superconducting device to an atomic medium. The temporal switching or gating of the device may either be through a control field changing the coupling, or through a variable detuning approach, as in more recent quantum memory experiments. An exact calculation of the temporal memory response to an external input is carried out. This shows that there is a mode-matching criterion which determines the optimum input and output mode shape. This optimum pulse shape can be modified by changing the gate characteristics. In addition, there is a critical coupling between the atoms and the cavity that allows high fidelity in the presence of long storage times. The quantum fidelity is calculated both for the coherent state protocol, and for a completely arbitrary input state with a bounded total photon number. We show how a dynamical quantum memory can surpass the relevant classical memory bound, while retaining a relatively long storage time.Comment: 16 pages, 9 figure

Can optical squeezing be generated via polarization self-rotation in a thermal vapour cell?

The traversal of an elliptically polarized optical field through a thermal vapour cell can give rise to a rotation of its polarization axis. This process, known as polarization self-rotation (PSR), has been suggested as a mechanism for producing squeezed light at atomic transition wavelengths. In this paper, we show results of the characterization of PSR in isotopically enhanced Rubidium-87 cells, performed in two independent laboratories. We observed that, contrary to earlier work, the presence of atomic noise in the thermal vapour overwhelms the observation of squeezing. We present a theory that contains atomic noise terms and show that a null result in squeezing is consistent with this theory.Comment: 10 pages, 11 figures, submitted to PRA. Please email author for a PDF file if the article does not appear properl

Conditionnal squeezing of an atomic alignement

We investigate the possibility to perform a Quantum Non Demolition measurement of the collective alignment of an atomic ensemble in the case of a $F\geq 1$ spin. We compare the case of purely vectorial and purely tensorial Hamiltonians and show how to achieve conditional squeezing or entanglement of atomic alignment components.Comment: 7 pages, 2 figure

High quality anti-relaxation coating material for alkali atom vapor cells

We present an experimental investigation of alkali atom vapor cells coated with a high quality anti-relaxation coating material based on alkenes. The prepared cells with single compound alkene based coating showed the longest spin relaxation times which have been measured up to now with room temperature vapor cells. Suggestions are made that chemical binding of a cesium atom and an alkene molecule by attack to the C=C bond plays a crucial role in such improvement of anti-relaxation coating quality