Decoherence-free creation of atom-atom entanglement in cavity via fractional adiabatic passage

We propose a robust and decoherence insensitive scheme to generate controllable entangled states of two three-level atoms interacting with an optical cavity and a laser beam. Losses due to atomic spontaneous transitions and to cavity decay are efficiently suppressed by employing fractional adiabatic passage and appropriately designed atom-field couplings. In this scheme the two atoms traverse the cavity-mode and the laser beam in opposite directions as opposed to other entanglement schemes in which the atoms are required to have fixed locations inside a cavity. We also show that the coherence of a traveling atom can be transferred to the other one without populating the cavity-mode.Comment: 4 pages, 5 figures, Submitted to Phys. Re

Non-locality of the energy density for all single-photon states

The non-locality of single-photon states has been analyzed from several different but interrelared perspectives. In this article, we propose a demonstration based on the electromagnetic energy density observable and on the anti-local property of the frequency operator $\Omega=c(-\Delta)^{1/2}$. The present proof is based on the standard quantization of the electromagnetic field, which can be formulated equivalently in the momentum representations or in the position representations of Landau-Peierls and of Bia{\l}ynicki-Birula. Our proof extends to all single-photon states the results of Bia{\l}ynicki-Birula, that were formulated for two particular classes of states, involving either a uniform localization [I. Bia{\l}ynicki-Birula, Phys. Rev. Lett. {\bf80} 5247 (1998)], or alternatively, states that are electrically or magnetically localized, as defined in [I. Bia{\l}ynicki-Birula, Z. Bia{\l}ynicka-Birula, Phys.Rev. A {\bf79} 032112 (2009)]. Our approach is formulated in terms of Knight's definition of strict localization, based on the comparison of single-photon states expectation values of local observables with that of the vacuum

Temporal spying and concealing process in fibre-optic data transmission systems through polarization bypass

International audienceRecent research has been focused on the ability to manipulate a light beam in such a way to hide, namely to cloak, an event over a finite time or localization in space. The main idea is to create a hole or a gap in the spatial or time domain so as to allow for an object or data to be kept hidden for a while and then to be restored. By enlarging the field of applications of this concept to telecommunications, researchers have recently reported the possibility to hide transmitted data in an optical fibre. Here we report the first experimental demonstration of perpetual temporal spying and blinding process of optical data in fibre-optic transmission line based on polarization bypass. We successfully characterize the performance of our system by alternatively copying and then concealing 100% of a 10-Gbit s-1 transmitted signal.

All-optical regeneration of polarization of a 40-Gbit/s return-to-zero telecommunication signal

10We report all-optical regeneration of the state of polarization of a 40 Gbit∕s return-to-zero telecommunication signal. The device discussed here consists of a 6.2-km-long nonzero dispersion-shifted fiber, with low polarization mode dispersion, pumped from the output end by a backward propagating wave coming from either an external continuous source or a reflection of the signal. An initially scrambled signal acquires a degree of polarization close to 100% toward the polarization generator output. All-optical regeneration is confirmed by means of polarization and bit-error-rate measurements as well as real-time observation of the eye diagrams. We show that the physical mechanism underlying the observed four-wave-mixing-based polarization attraction phenomenon can be described in terms of the geometric approach developed for the study of Hamiltonian singularities.openopenJ. Fatome; D. Sugny; S. Pitois; P. Morin; M. Guasoni; A. Picozzi; H. R. Jauslin; C. Finot; G. Millot; S. WabnitzJ., Fatome; D., Sugny; S., Pitois; P., Morin; Guasoni, Massimiliano; A., Picozzi; H. R., Jauslin; C., Finot; G., Millot; Wabnitz, Stefa

Isomorphism between the Bialynicki-Birula and the Landau-Peierls Fock space quantization of the electromagnetic field in position representation

We first present a summary of the quantization of the electromagnetic field in position space representation, using two main approaches: the Landau-Peierls approach in the Coulomb gauge and the Bialynicki-Birula approach, based on the Riemann-Silberstein vector. We describe both in a framework that starts with a classical Hamiltonian structure and builds the quantum model in a bosonic Fock space by a precisely defined principle of correspondence. We show that the two approches are completly equivalent. This is formulated by showing that there is a unitary map between the Fock spaces that makes them isomorphic. Since all the physically measurable quantities can be expressed in terms of scalar products, this implies that the two quantizations lead to exactly the same physical properties. We show furthemore that the isomorphism is preserved in the time evolutions. To show the equivalence, we use the concepts of helicity and frequency operators. The combination of these two operators provides a formulation that allows one to make the link between these two methods of quantization in a precise way. We also show that the construction in the Bialynicki-Birula quantization that avoids the presence of negative eigenvalues in the Hamiltonian, in analogy with the one for the Dirac equation for electrons and positrons, can be performed through an alternative choice of the canonical variables for Maxwell's equations

Non-local property of single-photon states: Illustration with spontaneously emitted photon from a Hydrogen atom

We discuss a new proof of the non-locality of single-photons using a concrete physical observable such as the local energy density. As an illustration of this non-locality, we compute the mean value of the local energy observable for the spontaneous emission from a Hydrogen atom. We find that, in the subspace of single-photon states, the mean value of the local energy density observable is non-zero everywhere and decreases as a power of the distance

Information quantique par passage adiabatique (portes quantiques et décohérence)

La première partie de cette thèse est consacrée à l'élaboration théorique de processus adiabatiques permettant l'implémentation de portes logiques quantiques, les constituants élémentaires des ordinateurs quantiques, par l'interaction de champs laser impulsionnels avec des atomes. L'utilisation de techniques adiabatiques permet des implémentations robustes, i.e. insensibles aux fluctuations des paramètres expérimentaux. Les processus décrits dans cette thèse ne nécessitent que le contrôle précis des polarisations et des phases relatives des champs lasers. Ces processus permettent l'implémentation d'un ensemble universel de portes quantiques, autorisant l'implémentation de toute autre porte quantique par combinaisons. La seconde partie de cette thèse concerne les effets de la décohérence par déphasage sur le passage adiabatique. La formule de probabilité de transition d'un système à deux niveaux tenant compte de ces effets décohérents est établie. Cette formule est valable dans les différents régimes, diabatique et adiabatique, et permet d'établir les paramètres de trajectoires elliptiques optimisant le transfert de population.The first part of this thesis is about adiabatic quantum processes designed for the implementation of quantum logic gates, the elementary components of quantum computers, by the interaction of pulsed laser fields with atoms. The adiabatic methods allow robust processes, i.e. which are not sensitive to the fluctuations of experimental parameters. The processes described in this thesis only require accurate control of the polarisations and the relative static phases of the laser fields. These processes allow the implementation of a universal set of quantum gates, which make possible the implementation of all the other quantum gates by combinations. The second part of this thesis concerns the effects of dephasing decoherence in adiabatic passage. The transition probability formula of a two level system with dephasing is established. This formula is valid in all regimes, from diabatic to adiabatic, and can be used to derive the parameters of elliptic trajectories that optimise the population transfer.DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF

Contrôle optimal de la dynamique dissipative de systèmes quantiques

DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF

Pas de titre en français

Dans ce travail, nous établissons et testons la technique de passage adiabatique parallèle (PAP) qui optimise le passage adiabatique en sélectionnant un trajet spécifique qui permet une dynamique rapide tout en préservant la robustesse standard de la technique adiabatique. L'intuition de PAP est basée sur le fait que l'on s'attend à une probabilité de transition nonadiabatique allant vers zéro par analyse Landau-Zener lorsque la courbure relative des deux énergies propres tend vers zéro. Dans ce travail nous testons la robustesse de cette technique et nous montrons sa supériorité par rapport à une dynamique avec un chirp linéaire traditionnel et des impulsions gaussiennes. Nous montrons son extension sur les transitions multiphotons dans les systèmes quantiques multiniveaux, où l'effet Stark joue un rôle important. Nous avons déterminé une forme optimale d'impulsion dans laquelle les décalages des niveaux sont simultanément compensés par la phase programmé de l'impulsion du laser. Ensuite, est présentée la technique de passage adiabatique parallèle local. Cela correspond à une dynamique où la valeur propre de l'état peuplé est parallèle à la plus proche au cours du temps. Nous développons l'idée de transfert de population par passage adiabatique de l'état fondamental à une superposition d'états. Le transfert est exécuté par des impulsions femtosecondes mises en forme dans le domaine spectral. Les états excités sont déplacés de façon dynamique en raison de la présence de composants non-résonnants des canaux différents. Nous montrons que ce décalage Stark peut être compensé par un autre champ ou par une mise en forme spécifique des impulsions appropriées.In this work we establish and test the technique of parallel adiabatic passage (PLAP) thatoptimizes the adiabatic passage in the sense that it selects specific paths that allow a fastadiabatic dynamics while preserving the standard robustness of adiabatic techniques. Theintuition of PLAP is based on the fact that the use of eigenvalues that are parallel for alltimes is expected to lead to a small nonadiabatic transition probability from Landau-Zeneranalysis for two-state approximations. In this work we test the robustness of this techniqueand show its superiority to the traditional linearly chirped dynamics with Gaussian pulses. Weshow its extension for two-photon and three-photon transitions on multilevel quantum systems,where the Stark shift plays an important role in a strong field regime. We have determined anoptimal pulse shaping in which the static and dynamic energy level shifts are simultaneouslycompensated by a programmed phase of a laser field. Next the local parallel adiabatic passagetechnique is presented. This corresponds to a dynamics where the eigenvalue of the populatedstate is parallel to the closest one at all times.We extend the idea of population transfer by adiabatic passage from the ground state toa superposition of states. The transfer is executed with spectrally shaped femtosecond laserpulses. The excited states are dynamically shifted in energy due to the presence of nonresonantcomponents of different channels. We show that this Stark shift can be compensated by anotherfield or by shaping appropriately the pulses.DIJON-BU Doc.électronique (212319901) / SudocSudocFranceF