TY - JOUR A1 - Zurita-Sánchez, Jorge R. A1 - Henkel, Carsten T1 - Lossy electrical transmission lines: Thermal fluctuations and quantization N2 - We present a theoretical framework for the analysis of the statistical properties of thermal fluctuations on a lossy transmission line. A quantization scheme of the electrical signals in the transmission line is formulated. We discuss two applications in detail. Noise spectra at finite temperature for voltage and current are shown to deviate significantly from the Johnson-Nyquist limit, and they depend on the position on the transmission line. We analyze the spontaneous emission, at low temperature, of a Rydberg atom and its resonant enhancement due to vacuum fluctuations in a capacitively coupled transmission line. The theory can also be applied to study the performance of microscale and nanoscale devices, including high-resolution sensors and quantum information processors Y1 - 2006 UR - http://pra.aps.org/pdf/PRA/v73/i6/e063825 U6 - https://doi.org/10.1103/Physreva.73.063825 SN - 1050-2947 ER - TY - JOUR A1 - Zurita-Sanchez, Jorge R. A1 - Henkel, Carsten T1 - Acoustic waves from mechanical impulses due to fluorescence resonant energy (Forster) transfer Blowing a whistle with light JF - epl : a letters journal exploring the frontiers of physics N2 - We present a momentum transfer mechanism mediated by electromagnetic fields that originates in a system of two nearby molecules: one excited (donor D*) and the other in ground state (acceptor A). An intermolecular force related to fluorescence resonant energy or Forster transfer (FRET) arises in the unstable D* A molecular system, which differs from the equilibrium van der Waals interaction. Due to the its finite lifetime, a mechanical impulse is imparted to the relative motion in the system. We analyze the FRET impulse when the molecules are embedded in free space and find that its magnitude can be much greater than the single recoil photon momentum, getting comparable with the thermal momentum (Maxwell-Boltzmann distribution) at room temperature. In addition, we propose that this FRET impulse can be exploited in the generation of acoustic waves inside a film containing layers of donor and acceptor molecules, when a picosecond laser pulse excites the donors. This acoustic transient is distinguishable from that produced by thermal stress due to laser absorption, and may therefore play a role in photoacoustic spectroscopy. The effect can be seen as exciting a vibrating system like a string or organ pipe with light; it may be used as an opto-mechanical transducer. Y1 - 2012 U6 - https://doi.org/10.1209/0295-5075/97/43002 SN - 0295-5075 VL - 97 IS - 4 PB - EDP Sciences CY - Mulhouse ER - TY - JOUR A1 - Zhang, Bo A1 - Henkel, Carsten T1 - Magnetic noise around metallic microstructures N2 - We compute the local spectrum of the magnetic field near a metallic microstructure at finite temperature. Our main focus is on deviations from a plane-layered geometry for which we review the main properties. Arbitrary geometries are handled with the help of numerical calculations based on surface integral equations. The magnetic noise shows a significant polarization anisotropy above flat wires with finite lateral width, in stark contrast to an infinitely wide wire. Within the limits of a two-dimensional setting, our results provide accurate estimates for loss and dephasing rates in so-called `atom chip traps' based on metallic wires. A simple approximation based on the incoherent summation of local current elements gives qualitative agreement with the numerics, but fails to describe current correlations among neighboring objects. Y1 - 2007 UR - http://dx.doi.org/10.1063/1.2800174 U6 - https://doi.org/10.1063/1.2800174 SN - 0021-8979 ER - TY - JOUR A1 - Zhang, B. A1 - Henkel, Carsten A1 - Haller, E. A1 - Wildermuth, S. A1 - Hofferberth, S. A1 - Kruger, P. A1 - Schmiedmayer, Jörg T1 - Relevance of sub-surface chip layers for the lifetime of magnetically trapped atoms N2 - We investigate the lifetime of magnetically trapped atoms above a planar, layered atom chip structure. Numerical calculations of the thermal magnetic noise spectrum are performed, based on the exact magnetic Green function and multi layer reflection coefficients. We have performed lifetime measurements where the center of a side guide trap is laterally shifted with respect to the current carrying wire using additional bias fields. Comparing the experiment to theory, we find a fair agreement and demonstrate that for a chip whose topmost layer is metallic, the magnetic noise depends essentially on the thickness of that layer, as long as the layers below have a, much smaller conductivity; essentially the same magnetic noise would be obtained with a metallic membrane suspended in vacuum. Based on our theory we give general scaling laws of how to reduce the effect of surface magnetic noise on the trapped atoms Y1 - 2005 ER - TY - JOUR A1 - Westbrook, N. A1 - Henkel, Carsten A1 - Westbrook, C. I. A1 - Landragin, A. A1 - Labeyrie, G. A1 - Cognet, L. A1 - Savalli, V. A1 - Horvath, G. A1 - Aspect, Alain A1 - Moelmer, Klaus A1 - Courtois, J.-Y. A1 - Phillips, W. D. A1 - Kaiser, Rolf A1 - Bagnato, V. T1 - New physics with evanescent wave atomic mirrors : the van der Waals force and atomic diffraction N2 - After a brief introduction to the field of atom optics and to atomic mirrors, we present experimental results obtained in our group during the last two years while studying the reflection of rubidium atoms by an evanescent wave. These involve the first measurement of the van der Waals force between an atom in its ground state and a dielectric wall, as well as the demonstration of a reflection grating for atoms at normal incidence. We also consider the influence of quantum reflection and tunnelling phenomena. Further studies using the atomic mirror as a probe of the van der Waals interaction, and of very small surface roughness are briefly discussed. Y1 - 1998 ER - TY - JOUR A1 - Schiefele, Jürgen A1 - Henkel, Carsten T1 - Casimir energy of a BEC : from moderate interactions to the ideal gas N2 - Considering the Casimir effect due to phononic excitations of a weakly interacting dilute Bose-Einstein condensate ( BEC), we derive a renormalized expression for the zero-temperature Casimir energy E-C of a BEC confined to a parallel plate geometry with periodic boundary conditions. Our expression is formally equivalent to the free energy of a bosonic field at finite temperature, with a nontrivial density of modes that we compute analytically. As a function of the interaction strength, E-C smoothly describes the transition from the weakly interacting Bogoliubov regime to the non- interacting ideal BEC. For the weakly interacting case, E-C reduces to leading order to the Casimir energy due to zero- point fluctuations of massless phonon modes. In the limit of an ideal Bose gas, our result correctly describes the Casimir energy going to zero. Y1 - 2009 UR - http://iopscience.iop.org/1751-8121/ U6 - https://doi.org/10.1088/1751-8113/42/4/045401 SN - 1751-8113 ER - TY - JOUR A1 - Schiefele, Juergen A1 - Henkel, Carsten T1 - Bosonic enhancement of spontaneous emission near an interface JF - Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics N2 - We show how the spontaneous emission rate of an excited two-level atom placed in a trapped Bose-Einstein condensate of ground-state atoms is enhanced by bosonic stimulation. This stimulation depends on the overlap of the excited matter-wave packet with the macroscopically occupied condensate wave function, and provides a probe of the spatial coherence of the Bose gas. The effect can be used to amplify the distance-dependent decay rate of an excited atom near an interface. KW - Bose-Einstein condensation KW - Correlation function KW - Bosonic stimulation KW - Superradiance KW - Spontaneous decay KW - Cavity-quantum electrodynamics Y1 - 2011 U6 - https://doi.org/10.1016/j.physleta.2010.11.058 SN - 0375-9601 VL - 375 IS - 3 SP - 680 EP - 684 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Rogobete, Lavinia A1 - Schniepp, H. A1 - Sandoghdar, Vahid A1 - Henkel, Carsten T1 - Spontaneous emission in nanoscopic dielectric particles Y1 - 2003 SN - 0030-3992 ER - TY - JOUR A1 - Rogobete, Lavinia A1 - Henkel, Carsten T1 - Spontaneous emission in a subwavelength environment characterized by boundary integral equations N2 - We discuss the impact of a dielectric nanoparticle on the fluorescence light from an emitter embedded in the particle. Numerical and analytical calculations predict a slower radiative decay compared to a bulk dielectric due to electrostatic screening. We assess the relevance of the nanoparticle shape and size and the position and orientation of the molecule. The numerical results are obtained from a rigorous solution of the Maxwell equations, formulated as boundary integral equations Y1 - 2004 ER - TY - JOUR A1 - Puhlmann, Dirk A1 - Henkel, Carsten A1 - Heuer, Axel A1 - Pieplow, Gregor A1 - Menzel, Ralf T1 - Characterization of a remote optical element with bi-photons JF - Physica scripta : an international journal for experimental and theoretical physics N2 - We present a simple setup that exploits the interference of entangled photon pairs. 'Signal' photons are sent through a Mach–Zehnder-like interferometer, while 'idlers' are detected in a variable polarization state. Two-photon interference (in coincidence detection) is observed with very high contrast and for significant time delays between signal and idler detection events. This is explained by quantum erasure of the polarization tag and a delayed choice protocol involving a non-local virtual polarizer. The phase of the two-photon fringes is scanned by varying the path length in the signal beam or by rotating a birefringent crystal in the idler beam. We exploit this to characterize one beam splitter of the signal photon interferometer (reflection and transmission amplitudes including losses), using only information about coincidences and control parameters in the idler path. This is possible because our bi-photon state saturates the Greenberger–Yelin–Englert inequality between contrast and predictability. KW - quantum optics KW - quantum eraser KW - entanglement KW - bi-photons Y1 - 2016 U6 - https://doi.org/10.1088/0031-8949/91/2/023006 SN - 0031-8949 SN - 1402-4896 VL - 91 SP - 113 EP - 114 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Pieplow, Gregor A1 - Henkel, Carsten T1 - Cherenkov friction on a neutral particle moving parallel to a dielectric JF - Journal of physics : Condensed matter N2 - We describe a simple mechanism of quantum friction for a particle moving parallel to a dielectric, based on a fully relativistic framework and the assumption of local equilibrium. The Cherenkov effect explains how the bare ground state becomes globally unstable and how fluctuations of the electromagnetic field and the particle's dipole are converted into pairs of excitations. Modeling the particle as a silver nano-sphere, we investigate the spectrum of the force and its velocity dependence. We find that the damping of the plasmon resonance in the silver particle has a relatively strong impact near the Cherenkov threshold velocity. We also present an expansion of the friction force near the threshold velocity for both damped and undamped particles. KW - quantum friction KW - quantum electrodynamics KW - Cherenkov radiation KW - transition radiation KW - fluctuation forces Y1 - 2015 U6 - https://doi.org/10.1088/0953-8984/27/21/214001 SN - 0953-8984 SN - 1361-648X VL - 27 IS - 21 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Pieplow, Gregor A1 - Henkel, Carsten T1 - Fully covariant radiation force on a polarizable particle JF - New journal of physics : the open-access journal for physics N2 - The electromagnetic force on a polarizable particle is calculated in a covariant framework. Local equilibrium temperatures for the electromagnetic field and the particle's dipole moment are assumed, using a relativistic formulation of the fluctuation-dissipation theorem. Two examples illustrate radiative friction forces: a particle moving through a homogeneous radiation background and above a planar interface. Previous results for arbitrary relative velocities are recovered in a compact way. Y1 - 2013 U6 - https://doi.org/10.1088/1367-2630/15/2/023027 SN - 1367-2630 VL - 15 IS - 4 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Perrin, Helene A1 - Colombe, Yves A1 - Mercier, Brigitte A1 - Lorent, Vincent A1 - Henkel, Carsten T1 - Diffuse reflection of a Bose-Einstein condensate from a rough evanescent wave mirror JF - Journal of physics : B, Atomic, molecular and optical physics N2 - We present experimental results showing the diffuse reflection of a Bose Einstein condensate from a rough mirror, consisting of a dielectric substrate supporting a blue-detuned evanescent wave. The scattering is anisotropic, more pronounced in the direction of the surface propagation of the evanescent wave. These results agree very well with theoretical predictions. Y1 - 2006 U6 - https://doi.org/10.1088/0953-4075/39/22/009 SN - 0953-4075 VL - 39 SP - 4649 EP - 4658 PB - IOP Publ. CY - Bristol ER - TY - JOUR A1 - Papke, Thomas A1 - Yadavalli, Nataraja Sekhar A1 - Henkel, Carsten A1 - Santer, Svetlana T1 - Mapping a plasmonic hologram with photosensitive polymer films: standing versus propagating waves JF - ACS applied materials & interfaces N2 - We use a photosensitive layer containing azobenzene moieties to map near-field intensity patterns in the vicinity of nanogrids fabricated within a thin silver layer. It is known that azobenzene containing films deform permanently during irradiation, following the pattern of the field intensity. The photosensitive material reacts only to stationary waves whose intensity patterns do not change in time. In this study, we have found a periodic deformation above the silver film outside the nanostructure, even if the latter consists of just one groove. This is in contradiction to the widely accepted viewpoint that propagating surface plasmon modes dominate outside nanogrids. We explain our observation based on an electromagnetic hologram formed by the constructive interference between a propagating surface plasmon wave and the incident light. This hologram contains a stationary intensity and polarization grating that even appears in the absence of the polymer layer. KW - propagating surface plasmons KW - nanostructured metal surface KW - azobenzene containing photosensitive material KW - surface relief grating Y1 - 2014 U6 - https://doi.org/10.1021/am503501y SN - 1944-8244 VL - 6 IS - 16 SP - 14174 EP - 14180 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Ostermeyer, Martin A1 - Korn, Dietmar A1 - Puhlmann, Dirk A1 - Henkel, Carsten A1 - Eisert, Jens T1 - Two-dimensional characterization of spatially entangled photon pairs N2 - We characterize the entanglement in position and momentum of photon pairs generated in type-II parametric down- conversion. Coincidence maps of the photon positions in the near-field and far-field planes are observed in two transverse dimensions using scanning fiber probes. We estimate the covariance matrix of an effective two-mode system and apply criteria for entanglement based on covariance matrices to certify space-momentum entanglement. The role of higher- order spatial modes for observing spatial entanglement between the two photons is discussed. Y1 - 2009 UR - http://www.informaworld.com/openurl?genre=journal&issn=0950-0340 U6 - https://doi.org/10.1080/09500340903359962 SN - 0950-0340 ER - TY - JOUR A1 - Nemati, Somayyeh A1 - Henkel, Carsten A1 - Anders, Janet T1 - Coupling function from bath density of states JF - epl : a letters journal exploring the frontiers of physics N2 - Modelling of an open quantum system requires knowledge of parameters that specify how it couples to its environment. However, beyond relaxation rates, realistic parameters for specific environments and materials are rarely known. Here we present a method of inferring the coupling between a generic system and its bosonic (e.g., phononic) environment from the experimentally measurable density of states (DOS). With it we confirm that the DOS of the well-known Debye model for three-dimensional solids is physically equivalent to choosing an Ohmic bath. We further match a real phonon DOS to a series of Lorentzian coupling functions, allowing us to determine coupling parameters for gold, yttrium iron garnet (YIG) and iron as examples. The results illustrate how to obtain material-specific dynamical properties, such as memory kernels. The proposed method opens the door to more accurate modelling of relaxation dynamics, for example for phonon-dominated spin damping in magnetic materials. Y1 - 2022 U6 - https://doi.org/10.1209/0295-5075/ac7b42 SN - 0295-5075 SN - 1286-4854 VL - 139 IS - 3 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Negretti, Antonio A1 - Henkel, Carsten T1 - Enhanced phase sensitivity and soliton formation in an integrated BEC interferometer N2 - We study the dynamics of Bose-Einstein condensates in time-dependent microtraps for the purpose of understanding the influence of the mean field interaction on the performance of interferometers. We identify conditions where the nonlinearity due to atom interactions increases the sensitivity of interferometers to a phase shift. This feature is connected with the adiabatic generation of a dark soliton. We analyse the robustness of this phenomenon with respect to thermal fluctuations, due to excited near fields in an electromagnetic surface trap Y1 - 2004 UR - http://ej.iop.org/links/q85/PfG7mUoiRHJEqjWjKfr+iQ/b4_23_l02.pdf SN - 0953-4075 ER - TY - JOUR A1 - Müller, Matthias M. A1 - Haakh, Harald R. A1 - Calarco, Tommaso A1 - Koch, Christiane P. A1 - Henkel, Carsten T1 - Prospects for fast Rydberg gates on an atom chip JF - Quantum information processing N2 - Atom chips are a promising candidate for a scalable architecture for quantum information processing provided a universal set of gates can be implemented with high fidelity. The difficult part in achieving universality is the entangling two-qubit gate. We consider a Rydberg phase gate for two atoms trapped on a chip and employ optimal control theory to find the shortest gate that still yields a reasonable gate error. Our parameters correspond to a situation where the Rydberg blockade regime is not yet reached. We discuss the role of spontaneous emission and the effect of noise from the chip surface on the atoms in the Rydberg state. KW - Optimal control KW - Phase gate KW - Rydberg atoms KW - Cavity quantum electrodynamics Y1 - 2011 U6 - https://doi.org/10.1007/s11128-011-0296-0 SN - 1570-0755 VL - 10 IS - 6 SP - 771 EP - 792 PB - Springer CY - New York ER - TY - JOUR A1 - Mkrtchian, Vanik E. A1 - Henkel, Carsten T1 - Green function solution of generalised boundary value problems JF - Physics Letters A N2 - We construct an expression for the Green function of a differential operator satisfying nonlocal, homogeneous boundary conditions starting from the fundamental solution of the differential operator. This also provides the solution to the boundary value problem of an inhomogeneous partial differential equation with inhomogeneous, nonlocal boundary conditions. The construction applies for a broad class of linear partial differential equations and linear boundary conditions. KW - Boundary value problem KW - Green function Y1 - 2020 U6 - https://doi.org/10.1016/j.physleta.2020.126573 SN - 0375-9601 SN - 1873-2429 SN - 0031-9163 VL - 384 IS - 23 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Mkrtchian, Vanik E. A1 - Henkel, Carsten T1 - On non-equilibrium photon distributions in the Casimir effect JF - Annalen der Physik N2 - The electromagnetic field in a typical geometry of the Casimir effect is described in the Schwinger-Keldysh formalism. The main result is the photon distribution function (Keldysh Green function) in any stationary state of the field. A two-plate geometry with a sliding interface in local equilibrium is studied in detail, and full agreement with the results of Rytov fluctuation electrodynamics is found. KW - Casimir effect KW - van der Waals interaction KW - quantum friction KW - nonequilibrium electrodynamics of nanosystems Y1 - 2014 U6 - https://doi.org/10.1002/andp.201300135 SN - 0003-3804 SN - 1521-3889 VL - 526 IS - 1-2 SP - 87 EP - 101 PB - Wiley-VCH CY - Weinheim ER -