H. B. van Linden van den Heuvell

Implementation of Quantum Search Algorithm using Classical Fourier Optics

We report on an experiment on Grovers quantum search algorithm showing that classical waves can search a N-item database as efficiently as quantum mechanics can. The transverse beam profile of a short laser pulse is processed iteratively as the pulse bounces back and forth between two mirrors. We directly observe the sought item being found in approximately square root[N] iterations, in the form of a growing intensity peak on this profile. Although the lack of quantum entanglement limits the size of our database, our results show that entanglement is neither necessary for the algorithm itself, nor for its efficiency.

Spatially resolved observation of dipole-dipole interaction between Rydberg atoms.

We have observed resonant energy transfer between cold Rydberg atoms in spatially separated cylinders. Resonant dipole-dipole coupling excites the 49s atoms in one cylinder to the 49p state while the 41d atoms in the second cylinder are transferred down to the 42p state. We have measured the production of the 49p state as a function of separation of the cylinders (0-80 microm) and the interaction time (0-25 micros). In addition, we measured the width of the electric field resonances. A full many-body quantum calculation reproduces the main features of the experiments.

Stability of standing matter waves in a trap

We discuss excited Bose-condensed states and find the criterion of dynamical stability of a kink-wise state, i.e., a standing matter wave with one nodal plane perpendicular to the axis of a cylindrical trap. The dynamical stability requires a strong radial confinement corresponding to the radial frequency larger than the mean-field interparticle interaction. We address the question of thermodynamic instability related to the presence of excitations with negative energy.

Spatially resolved excitation of Rydberg atoms and surface effects on an atom chip

We demonstrate spatially resolved, coherent excitation of Rydberg atoms on an atom chip. Electromagnetically induced transparency (EIT) is used to investigate the properties of the Rydberg atoms near the gold-coated chip surface. We measure distance-dependent shifts ({approx}10 MHz) of the Rydberg energy levels caused by a spatially inhomogeneous electric field. The measured field strength and distance dependence is in agreement with a simple model for the electric field produced by a localized patch of Rb adsorbates deposited on the chip surface during experiments. The EIT resonances remain narrow (<4 MHz) and the observed widths are independent of atom-surface distance down to {approx} 20 {mu}m, indicating relatively long lifetime of the Rydberg states. Our results open the way to studies of dipolar physics, collective excitations, quantum metrology, and quantum information processing involving interacting Rydberg excited atoms on atom chips.

Large interference effects of small chirp observed in two-photon absorption

Abstract It is shown that the populations of excited levels after a multi-photon excitation process are strongly influenced by the exact phase relations between the different frequency components within the excitation pulse (the ‘chirp’ of the pulse). This general effect, which can already show up dramatically if chirp has lengthened the pulse by only 10%, is experimentally demonstrated two systems: two-photon absorption in an atom and frequency-doubling in a nonlinear crystal.

Dissociation and autoionization of the lowest doubly excited state in H2

Abstract We report one-photon dissociation from the B 1Σu+ (ν′,J′) state of molecular hydrogen into an atom in the ground state and one in the 2s state. The excited atom is detected by means ofionization with an additional photon. In particular, dissociation into the 2s state is studied since in this way population of one unique doubly excited state, Q1 1Σg+ (2pσu)2, is monitored. Photoelectron energy spectra are recorded at wavelengths which are resonant with vibrational levels ν′ in the intermediate state ranging from 1 to 8. A decreasing dissociation intensity is observed with increasing vibrational quantum number ν′. To investigate the influence of rotation we excited several rotational levels in the B 1Σu+ (ν′=4) state. Strongly varying non-Franck-Condon behavior is observed as a function of the rotational quantum number.

Rydberg series in no excited by resonant MPI via the A 2Σ+ (υ′ = 1, J′) intermediate state

Abstract An investigation is reported of the rotationally selected υ = 1 Rydberg series ( n up to 43) of NO converging to the ionic ground state. Two-colour optical—optical double-resonance multiphoton processes (OODR MPI) via the A 2 Σ + (υ′=1) state excite the Rydberg states; the subsequent autoionizing decay to the υ + = 0 ionization channel is monitored through photoelectron energy analysis. The influence of the electron spectrometers magnetic field of 1 T is discussed. We present the assignment of three p series, nine f series, two s series and two d series; an additional series is observed but not assigned. The observed series converge to different rotational limits ranging from R + = 1 to R + = 5.

Observation of Stückelberg oscillations in dipole-dipole interactions

We have observed Stueckelberg oscillations in the dipole-dipole interaction between Rydberg atoms with an externally applied radio-frequency field. The oscillating rf field brings the interaction between cold Rydberg atoms in two separated volumes into resonance. We observe multiphoton transitions when varying the amplitude of the rf field and the static electric field offset. The angular momentum states we use show a quadratic Stark shift, which leads to a fundamentally different behavior than linearly shifting states. Both cases are studied theoretically using the Floquet approach and are compared. The amplitude of the sidebands, related to the interaction strength, is given by the Bessel function in the linearly shifting case and by the generalized Bessel function in the quadratically shifting case. The oscillatory behavior of both functions corresponds to Stueckelberg oscillations, an interference effect described by the semiclassical Landau-Zener-Stueckelberg model. The measurements prove coherent dipole-dipole interaction during at least 0.6 mus.

Cold trapped atoms detected with evanescent waves

Abstract:We demonstrate the in situ detection of cold 87Rb atoms near a dielectric surface using the absorption of a weak, resonant evanescent wave. We have used this technique in time of flight experiments determining the density of atoms falling on the surface. A quantitative understanding of the measured curve was obtained using a detailed calculation of the evanescent intensity distribution. We have also used it to detect atoms trapped near the surface in a standing-wave optical dipole potential. This trap was loaded by inelastic bouncing on a strong, repulsive evanescent potential. We estimate that we trap 1.5×104 atoms at a density 100 times higher than the falling atoms.

High-power femtosecond dye laser with tunable wavelength, pulse duration and chirp

Abstract We present a high-power femtosecond dye-laser system based on a CPM oscillator. The pulses have an energy up to 0.6 mJ and a variable pulse duration between 70 fs and 5 ps. The wavelength of the pulses is tunable throughout the visible, and the chirp of the pulses can be varied continuously.