Abstract
We isolate a novel four-wave mixing process, enabled by **coherent** **population** **trapping** (CPT), leading to efﬁcient phase sensitive ampliﬁcation. This process is permitted by the exploitation of two
transitions starting from the same twofold degenerate ground state. One of the transitions is used for CPT, deﬁning bright and dark states from which ultra intense four-wave mixing is obtained via the other transition. This leads to the measurement of a strong phase sensitive gain even for low optical densities and out-of-resonance excitation. The enhancement of four-wave mixing is interpreted in the framework of the dark-state polariton formalism.

Show more
10 Read more

Dual-frequency VECSELfor atomic clocks using **coherent** **population** **trapping**
P. Dumont 1 , J.-M. Danet 2 , D. Holleville 2 , S. Guerandel 2 , G. Baili 3 , L. Morvan 3 , G. Pillet 3 ,
D. Dolfi 3 , G. Beaudoin 4 , I. Sagnes 4 , P. Georges 1 , G. Lucas-Leclin 1

Meas. 49, 1313 (2000).
[2] T. Zanon et al, “High Contrast Ramsey Fringes with **Coherent**-**Population**-**Trapping** Pulses in a Double Lambda Atomic System” Phys.
Rev. Lett. 94, 193002, (2005).
[3] G. Baili, L. Morvan, M. Alouini, D. Dolfi, F. Bretenaker, I. Sagnes and A. Garnache, “Experimental demonstration of a tunable dual- frequency semiconductor laser free of relaxation oscillations”, Opt. Lett. 34, 3421 (2009).

PACS 37.10.De – Atom cooling methods
PACS 37.10.Vz – Mechanical effects of light on atoms, molecules, and ions
Abstract. - An experimental investigation is made of sub-recoil cooling by velocity selective **coherent** **population** **trapping** in a two-level system in Sr. The experiment is carried out using the narrow linewidth intercombination line at 689 nm. Here, the ratio between the recoil shift and the linewidth is as high as 0.64. We show that, on top of a broader momentum profile, subrecoil features develop, whose amplitude is strongly dependent on the detuning from resonance. We attribute this structure to a velocity selective **coherent** **population** **trapping** mechanism. We also show that the **population** **trapping** phenomenon leads to complex momentum profiles in the case of highly saturated transitions, displaying a multitude of subrecoil features at integer multiples of the recoil momentum.

Show more
We investigate the effect of **coherent** **population** **trapping** (CPT) in an atom inter- ferometer gravimeter based on the use of stimulated Raman transitions. We find that CPT leads to significant phase shifts, of order of a few mrad, which may compromise the accuracy of inertial measurements. We show that this effect is rejected by the k-reversal technique, which consists in averaging inertial measurements performed with two opposite orientations of the Raman wavevector k, provided that internal states at the input of the interferometer are kept identical for both configurations. PACS 37.25.+k; 37.10.Vz; 03.75.Dg; 42.60.By

Show more
13 Read more

Stringent conditions on the phase relation of multiple photons are a prerequisite for novel pro- tocols of high-resolution **coherent** spectroscopy. In a recent experiment we have implemented an
interrogation process of a Ca +
-ion cloud based on three-photon **coherent** **population** **trapping**, with the potential to serve as a frequency reference in the THz-range. This high-resolution interroga- tion has been made possible by phase-locking both laser sources for cooling and repumping of the trapped ions to a clock laser at 729 nm by means of an optical frequency comb. The clock laser, a titanium-sapphire laser built in our lab locked onto two high-finesse cavities reaches a linewidth of

Show more
Both existing and future tests of fundamental physics with atom interferometry and high-precision inertial sens- ing technology demand critical investigations of light-based systematic error sources (e.g., [7]). Analyses of stimulated Raman transitions in the open literature commonly neglect the effects of spontaneous emission, or treat it solely as a source of decoherence (e.g., [8]). An additional consequence of spontaneous emission is **coherent** **population** **trapping** (CPT), or the transfer of atomic **population** to a decoupled (dark) superposition state. CPT has been extensively analyzed and observed experimentally in three-level () atomic systems with Raman resonances excited by bichromatic laser fields [9–11]. Since the discovery of the effect, it has been exploited for precision measurement applications including chip-scale atomic clocks [12] and atomic magnetometry [13], in which narrow rf resonances are achieved in steady-state laser opera- tion. However, possible residual non-steady-state CPT effects in atom interferometry with stimulated Raman transitions have not been discussed in the literature. This work addresses

Show more
∆C = ωC − ωD 5/2 S 1/2 with ωP 1/2 S 1/2 , ωP 1/2 D 3/2 and
ωD 5/2 S 1/2 the atomic transition frequencies. Like fur-
ther explained in [15], the dressed laser-coupled subsys- tem {(S 1/2, nB, nR, nC), (D5/2, nB, nR, nC − 1)} can be diagonalised at the lowest order of the perturbation and the new eigenstates {|Si, |Qi} are then a **coherent** super- position of the two uncoupled states. {|Si, |Qi} are both coupled to the |P i state (P 1/2, nB − 1, n R, nC ) through the strong dipole transition excited by the 397 nm laser, but with a very different strength, depending on the de- tuning ∆C and the Rabi frequency ΩC, which control the proportion of the two uncoupled states in the new eigenstates. Including |Di = (D 3 /2 , nB − 1, nR + 1, nC), the subsystem {|Qi, |P i, |Di}, coupled by the two dipole transitions forms a Λ-scheme where the two feet are sta- ble or metastable. This scheme is the paradigm of the configurations giving rise to a **coherent** **population** trap- ping in a dark state when the two (meta)stable states are degenerated in the dressed state picture [1]. Because the

Show more
Intrinsic limits for the Q-factor in a microcavity are given either by its radiative losses due to imperfect light confinement or by the residual absorption of the consti- tuting material. Therefore, the manufacturing of high-Q resonators requires high purity materials [10], complex technological processes to reduce fabrication imperfec- tions [11] and careful design to avoid radiative losses [12, 13]. It is possible to compensate for optical losses by using a gain material within the microcavity [14–16]. Another way to increase the Q-factor consists in insert- ing a highly dispersive material inside the microcavity [17]. In this case, the photon lifetime is increased by a factor proportional to the group index of the dispersive material [18, 19]. This technique has already been pro- posed and experimentally demonstrated in atomic sys- tems embedded in macroscopic ring cavities using coher- ent effects such as **coherent** **population** **trapping** or elec- tromagnetically induced transparency (EIT) [18–23]. In those configurations, a powerful pump beam induces a steep dispersion centered at the signal frequency, tuned to the cavity resonance. In this context, it has also been

Show more
12 Read more

The contactless confinement (Fig. 1.A-B) of Jurkat cells (T lymphocytes) in a paramagnetic medium was successfully achieved above NdFeB micro-magnets (Fig 1.C). Experiments were made with an extremely low concentration of contrast agent (GdDO3A) (C=5-10mM - δχ ~ 4-3 µSI). Cytotoxicity testing (Live/Dead cell viability assays) shows that such low concentrations have no impact on cell viability. However, after a few dozens of minutes diamagnetic **trapping** is lost and the cells sediment on the edge of the magnets. Such a phenomenon could be explained by the internalisation of the paramagnetic salt by endocytosis [4]. This study opens broad and attractive alternatives for contactless cell arraying and sorting based on their size, magnetic susceptibility and endocytosis capabilities. Such methods are being investigated further, and could be applied for sorting cancer, stem and blood cells.

Show more
light 670
In the previous section, we reported results for which the photoacoustic effect was used as feedback mechanism for optical wavefront shaping of **coherent** light. In this sec- tion, we now illustrate how photoacousting imaging may directly benefit from effects based on the coherence of light, such as speckle illumination or optical wavefront shaping. Generally speaking, the ultimate objective of photoacous- tic imaging is to quantitatively reconstruct the distribu- tion of optical absorption, described via the absorption coefficient µ a (r). This objective has usually been pursued

Show more
22 Read more

E c is the coincidence energy, i.e., the energy of the most
stable coincidence configuration with respect to the stable self-trapped one. The coincidence energy E c plays the role
of an activation energy for the hopping process of the polaron. The hopping rate for the small polaron hopping is thus ∝e −E c /k B T , but the energy in this Arrhenius term, to be paid by thermal agitation, is related to the motions of the surrounding atoms, not to the motion of the electronic charge itself. According to the typical tunneling probability in the coincidence configuration, compared to the time scale of the coincidence, the transfer can be adiabatic (i.e., the electronic charge has the time to tunnel), nonadiabatic (i.e., the electronic charge has not the time to tunnel, so that many occurrences of the coincidence are necessary before a jump occurs), or lie in-between. In an adiabatic hopping, the charge is progressively transferred from the initial to the final site, together with the self-**trapping** distortion [ 4 ].

Show more
14 Read more

challenging to integrate in cache-**coherent** systems without affecting the consistency model, as remote updates and cacheable reads and writes follow different paths through the memory hierarchy [69].
Note that Coup’s advantages come at the cost of a more restricted set of operations: Coup only works with commutative updates, while RMOs support non-commutative operations, such as fetch-and-add and compare-and-swap. Also, Coup significantly outperforms RMOs only if data is reused (i.e., updated or read multiple times before switching between read- and update-only modes). This is often the case in real applications (chapter 4).

Show more
57 Read more

L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB. NRC Publicat[r]

37 Read more

Axiom 1 says that, if all the individuals of a **population** exhibit all their achieve- ments above the threshold (i.e., if x ≥ 1), this **population** is not poor. Conversely, if x << 1, Axiom 2 implies that the **population** is poor. Ambiguity remains only when- ever some individuals exhibit some achievements above the threshold, and others, not. Our last axiom deals with such ambiguous cases. Suppose that a **population**, x, is not poor. Take λ > 0 and consider the auxiliary **population** given by x λ . Axiom 4 says that this new **population** should not be considered as poor neither. Clearly, if x 1/z ≥ 1 (resp. x1/z < 1), then (x λ 1/z) ≥ 1 (resp. < 1), so that the

Show more
18 Read more

Mots clés : partage de coûts, additivité, ordre aléatoire
ABSTRACT
We reconsider the discrete version of the axiomatic cost-sharing model. We propose a condition of (informational) coherence requiring that not all informational refinements of a given problem be solved differently from the original problem. We prove that strictly **coherent** linear cost-sharing rules must be simple random-order rules.

22 Read more

Second, we model the impact of trap connectivity on H diffusion by deriving Oriani's formula in the framework of random walks and introducing the mean escape frequency from the vacancy. The First Passage Time Analysis from Puchala [29] , applied to the basin composed of the states where H occupies the interstitial sites of the vacancy ( Appendix ), enables a rigorous calculation of the escape frequency with the real connectivity in between the various sites involved. The limitations of Oriani's formula are determined. They have two physical origins. First there is not an exact compensation between the various activation energies involved, namely: the bulk diffusion activation energy, the exit activation energy and the segregation energy. In the case of Ni, this enhances diffusion with respect to Oriani's formula (i.e. the **trapping** efﬁciency is lower than predicted by Oriani) below room temperature and at high trap concentration. Second, the trap connectivity is at the origin of a geometric factor which scales like the square of the characteristic length of the network of traps connected by low barriers. It has a weak inﬂuence for a point defect but can be important for larger defects, like intragranular precipitates, if they provide long, fast, diffusion paths. The method exposed in the Appendix gives the tools for establishing traps efﬁciency quantitatively, which can be useful for designing microstructures optimized for resisting to H damage.

Show more
As explained in the following, our theory shows that the main relaxation mechanism for the trapped quasiparticle states is their excitation into the extended continuum states above the s[r]

12 Read more

The optimal segmentation of a mesh animation (dynamic mesh or unconstrained mesh sequence) into rigid components can be guessed when the motion is known.. This is, for instance, the case[r]

21 Read more