Correlated motion of two atoms trapped in a single mode cavity field

We study the motion of two atoms trapped at distant positions in the field of a driven standing wave high-Q optical resonator. Even without any direct atom-atom interaction the atoms are coupled through their position dependent influence on the intracavity field. For sufficiently good trapping and low cavity losses the atomic motion becomes significantly correlated and the two particles oscillate in their wells preferentially with a 90 degrees relative phase shift. The onset of correlations seriously limits cavity cooling efficiency, raising the achievable temperature to the Doppler limit. The physical origin of the correlation can be traced back to a cavity mediated cross-friction, i.e. a friction force on one particle depending on the velocity of the second particle. Choosing appropriate operating conditions allows for engineering these long range correlations. In addition this cross-friction effect can provide a basis for sympathetic cooling of distant trapped clouds.Comment: 10 pages, 9 figures, accepted for publication in Phys. Rev. A. Minor grammatical changes to previous versio

HPV 16 Strukturproteine als Vehikel zur Immunisierung

Bestimmte Typen der humanpathogenen Papillomviren (HPV), z.B. HPV 16, sind ursächlich an der Entstehung von Gebärmutterhalskrebs und seinen Vorläuferläsionen beteiligt. Unter natürlichen Bedingungen erfolgt die Infektion mit HPV in undifferenzierten Epithelzellen des Stratum basale. Jedoch können infektiöse Papillomviren und durch Expression des Hauptstrukturproteins L1 hergestellte virus-ähnliche Partikel (virus-like particles, VLPs), aber auch das „minor“ Strukturprotein L2, an eine Vielzahl von Zellen binden und von diesen aufgenommen werden. Diese Eigenschaft sollte für eine DNA-Immunisierung genutzt werden in der Annahme, daß eine Induktion der Immunantwort effizienter sei, wenn ein Shuttle zum Eintritt der Nukleinsäure in Zellen eingesetzt wird. So könnte eine erhöhte Proteinexpresession in den getroffenen Zellen stattfinden. Die Freisetzung größerer Antigenmengen aus infizierten Zellen wie Muskel- oder Epithelzellen könnte vermehrt zu „cross-priming“ professioneller Antigen-präsentierender Zellen führen und dadurch oder durch direkte Infektion von Zellen des Immunsystems wie Dendritischen Zellen (DCs) die Präsentation des Antigens erhöhen. In dieser Arbeit sollte untersucht werden, ob die Strukturproteine L1 und L2 des HPV Typs 16 diese Aufgabe erfüllen können. Zu diesem Zweck sollten drei verschiedene Vehikelpräparationen mit Ovalbumin als Reportergen hergestellt und getestet werden: (i) Pseudovirionen, bei denen die für das Antigen kodierende Reporter-DNA in HPV 16-VLPs verpackt ist, (ii) VLPs, an die das Reportergen von außen chemisch gebunden ist und (iii) ein Peptid von HPV 16 L2, an das das Reportergen gebunden vorliegt. Durch Dis- und Reassembly, bei dem in vitro DNA in VLPs verpackt wird, konnten Pseudovirionen hergestellt werden. Auch die Kopplung des Reportergens an VLPs war erfolgreich. Allein die Bindung zwischen dem HPV 16 L2-Peptid und dem Reportergen konnte nicht nachgewiesen werden. Trotzdem wurden alle Präparationen im Mausmodell auf ihre Immunogenität getestet. Die eingesetzte DNA-Menge pro Maus wurde als Standard gesetzt, um die Effizienz der verschiedenen Vehikelpräparationen vergleichen zu können. In einer intramuskulär (i.m.) durchgeführten DNA-Titration konnte festgestellt werden, daß eine Menge von mindestens 10 µg DNA benötigt wird, um eine meßbare zelluläre Immunantwort zu induzieren. Da die Vehikelpräparationen jedoch das maximale Volumen von 0,05 ml überschritten, das in einer i.m.-Injektion pro Maus eingesetzt werden kann, wurde außerdem die subkutane (s.c.) Route getestet. Bei dieser Applikationsart reichte sogar eine Menge von 100 µg DNA nicht aus, um eine meßbare Immunantwort hervor zu rufen. In der vergleichenden Immunisierung der Shuttle-Vektoren mit nackter DNA erhielt jede Maus über das Vehikel 3 µg DNA, eine Menge, die sich in der i.m. Titration als gerade nicht mehr immunogen erwies. Ein möglicher adjuvanter Effekt der VLPs bei einer Immunisierung mit Ovalbumin war vorher experimentell ausgeschlossen worden. So sollte getestet werden, ob durch Vehikel eingeschleuste DNA immunogener ist als nackte DNA. Eine Zunahme der Immunantwort im Vergleich zu nackter DNA konnte jedoch nicht festgestellt werden. Somit konnte die Hypothese, daß Vehikelpräparationen bestehend aus HPV 16-Strukturproteinen und für Ovalbumin kodierender DNA immunogener sind als nackte DNA, in dieser Arbeit nicht bestätigt werden

Fast quantum logic gates with trapped ions interacting with external laser and quantized cavity field beyond the Lamb-Dicke regime

A scheme to implement quantum logic gates by manipulating trapped ions through interaction with monochromatic external laser field and quantized cavity field, beyond the Lamb-Dicke regime, is presented. Characteristic times, for implementing ionic state transitions using non-resont laser pulse or quantized cavity field, shows a sharp decline for large Lamb-Dicke parameter value of $\eta_{L}=\eta_{c}=0.2$, and is seen to decrease further with increase in number of initial state vibrational quanta $m$.Comment: Revised version, One major correction, 6 pages, Two table

Optical decay from a Fabry-Perot cavity faster than the decay time

The dynamical response of an optical Fabry-Perot cavity is investigated experimentally. We observe oscillations in the transmitted and reflected light intensity if the frequency of the incoupled light field is rapidly changed. In addition, the decay of a cavity-stored light field is accelerated if the phase and intensity of the incoupled light are switched in an appropriate way. The theoretical model by M. J. Lawrence em et al, JOSA B 16, 523 (1999) agrees with our observations.Comment: submitted to Josa

Collective effects in the dynamics of driven atoms in a high-Q resonator

We study the quantum dynamics of N coherently driven two-level atoms coupled to an optical resonator. In the strong coupling regime the cavity field generated by atomic scattering interferes destructively with the pump on the atoms. This suppresses atomic excitation and even for strong driving fields prevents atomic saturation, while the stationary intracavity field amplitude is almost independent of the atom number. The magnitude of the interference effect depends on the detuning between laser and cavity field and on the relative atomic positions and is strongest for a wavelength spaced lattice of atoms placed at the antinodes of the cavity mode. In this case three dimensional intensity minima are created in the vicinity of each atom. In this regime spontaneous emission is suppressed and the dominant loss channel is cavity decay. Even for a cavity linewidth larger than the atomic natural width, one regains strong interference through the cooperative action of a sufficiently large number of atoms. These results give a new key to understand recent experiments on collective cavity cooling and may allow to implement fast tailored atom-atom interactions as well as nonperturbative particle detection with very small energy transfer.Comment: 12 pages, 13 figures, significantly extended version, slightly different from the published on

Ground state cooling in a bad cavity

We study the mechanical effects of light on an atom trapped in a harmonic potential when an atomic dipole transition is driven by a laser and it is strongly coupled to a mode of an optical resonator. We investigate the cooling dynamics in the bad cavity limit, focussing on the case in which the effective transition linewidth is smaller than the trap frequency, hence when sideband cooling could be implemented. We show that quantum correlations between the mechanical actions of laser and cavity field can lead to an enhancement of the cooling efficiency with respect to sideband cooling. Such interference effects are found when the resonator losses prevail over spontaneous decay and over the rates of the coherent processes characterizing the dynamics.Comment: 6 pages, 5 figures; J. Mod. Opt. (2007

Magneto-optical trapping of bosonic and fermionic neon isotopes and their mixtures: isotope shift of the ^3P_2 to ^3D_3 transition and hyperfine constants of the ^3D_3 state of Ne-21

We have magneto-optically trapped all three stable neon isotopes, including the rare Ne-21, and all two-isotope combinations. The atoms are prepared in the metastable ^3P_2 state and manipulated via laser interaction on the ^3P_2 to ^3D_3} transition at 640.2nm. These cold (T = 1mK) and environmentally decoupled atom samples present ideal objects for precision measurements and the investigation of interactions between cold and ultracold metastable atoms. In this work, we present accurate measurements of the isotope shift of the ^3P_2 to ^3D_3 transition and the hyperfine interaction constants of the ^3D_3 state of Ne-21. The determined isotope shifts are (1625.9\pm0.15)MHz for Ne-20 to Ne-22, (855.7\pm1.0)MHz for Ne-20 to Ne-21, and (770.3\pm1.0)MHz for Ne-21 to Ne-22. The obtained magnetic dipole and electric quadrupole hyperfine interaction constants are A(^3D_3)= (-142.4\pm0.2)MHz and B(^3D_3)=(-107.7\pm1.1)MHz, respectively. All measurements give a reduction of uncertainty by about one order of magnitude over previous measurements

Active laser frequency stabilization using neutral praseodymium (Pr)

We present a new possibility for the active frequency stabilization of a laser using transitions in neutral praseodymium. Because of its five outer electrons, this element shows a high density of energy levels leading to an extremely line-rich excitation spectrum with more than 25000 known spectral lines ranging from the UV to the infrared. We demonstrate the active frequency stabilization of a diode laser on several praseodymium lines between 1105 and 1123 nm. The excitation signals were recorded in a hollow cathode lamp and observed via laser-induced fluorescence. These signals are strong enough to lock the diode laser onto most of the lines by using standard laser locking techniques. In this way, the frequency drifts of the unlocked laser of more than 30 MHz/h were eliminated and the laser frequency stabilized to within 1.4(1) MHz for averaging times >0.2 s. Frequency quadrupling the stabilized diode laser can produce frequency-stable UV-light in the range from 276 to 281 nm. In particular, using a strong hyperfine component of the praseodymium excitation line E = 16 502.616_7/2 cm^-1 -> E' = 25 442.742_9/2 cm^-1 at lambda = 1118.5397(4) nm makes it possible - after frequency quadruplication - to produce laser radiation at lambda/4 = 279.6349(1) nm, which can be used to excite the D2 line in Mg^+.Comment: 10 pages, 14 figure

Polariton Analysis of a Four-Level Atom Strongly Coupled to a Cavity Mode

We present a complete analytical solution for a single four-level atom strongly coupled to a cavity field mode and driven by external coherent laser fields. The four-level atomic system consists of a three-level subsystem in an EIT configuration, plus an additional atomic level; this system has been predicted to exhibit a photon blockade effect. The solution is presented in terms of polaritons. An effective Hamiltonian obtained by this procedure is analyzed from the viewpoint of an effective two-level system, and the dynamic Stark splitting of dressed states is discussed. The fluorescence spectrum of light exiting the cavity mode is analyzed and relevant transitions identified.Comment: 12 pages, 9 figure

Cavity QED and quantum information processing with "hot" trapped atoms

We propose a method to implement cavity QED and quantum information processing in high-Q cavities with a single trapped but non-localized atom. The system is beyond the Lamb-Dick limit due to the atomic thermal motion. Our method is based on adiabatic passages, which make the relevant dynamics insensitive to the randomness of the atom position with an appropriate interaction configuration. The validity of this method is demonstrated from both approximate analytical calculations and exact numerical simulations. We also discuss various applications of this method based on the current experimental technology.Comment: 14 pages, 8 figures, Revte