75 research outputs found
Observation of Stueckelberg 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 multi-photon 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 semi-classical Landau-Zener-Stueckelberg model. The
measurements prove coherent dipole-dipole interaction during at least 0.6
micro-seconds
Designs of magnetic atom-trap lattices for quantum simulation experiments
We have designed and realized magnetic trapping geometries for ultracold
atoms based on permanent magnetic films. Magnetic chip based experiments give a
high level of control over trap barriers and geometric boundaries in a compact
experimental setup. These structures can be used to study quantum spin physics
in a wide range of energies and length scales. By introducing defects into a
triangular lattice, kagome and hexagonal lattice structures can be created.
Rectangular lattices and (quasi-)one-dimensional structures such as ladders and
diamond chain trapping potentials have also been created. Quantum spin models
can be studied in all these geometries with Rydberg atoms, which allow for
controlled interactions over several micrometers. We also present some
nonperiodic geometries where the length scales of the traps are varied over a
wide range. These tapered structures offer another way to transport large
numbers of atoms adiabatically into subwavelength traps and back.Comment: 9 pages, 10 figure
High-Precision Measurement of Rydberg State Hyperfine Splitting in a Room-Temperature Vapour Cell
We present direct measurements of the hyperfine splitting of Rydberg states
in rubidium 87 using Electromagnetically Induced Transparency (EIT)
spectroscopy in a room-temperature vapour cell. With this method, and in spite
of Doppler-broadening, line-widths of 3.7 MHz FWHM, i.e. significantly below
the intermediate state natural linewidth are reached. This allows resolving
hyperfine splittings for Rydberg s-states with n=20...24. With this method we
are able to determine Rydberg state hyperfine splittings with an accuracy of
approximately 100 kHz. Ultimately our method allows accuracies of order 5 kHz
to be reached. Furthermore we present a direct measurement of
hyperfine-resolved Rydberg state Stark-shifts. These results will be of great
value for future experiments relying on excellent knowledge of Rydberg-state
energies an
Cold trapped atoms detected with evanescent waves
We demonstrate the in situ detection of cold 87 Rb 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 x 10 4 atoms at a density 100 times higher than the falling atoms.Comment: 5 pages, 3 figure
Radio-frequency driven dipole-dipole interactions in spatially separated volumes
Radio-frequency (rf) fields in the MHz range are used to induce resonant
energy transfer between cold Rydberg atoms in spatially separated volumes.
After laser preparation of the Rydberg atoms, 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. The energy exchanged
between the atoms in this process is 33 GHz. An external rf-field brings this
energy transfer into resonance. The strength of the interaction has been
investigated as a function of amplitude (0-1 V/cm) and frequency (1-30 MHz) of
the rf-field and as a function of a static field offset. Multi-photon
transitions up to fifth order as well as selection rules prohibiting the
process at certain fields have been observed. The width of the resonances has
been reduced compared to earlier results by switching off external magnetic
fields of the magneto-optical trap, making sub-MHz spectroscopy possible. All
features are well reproduced by theoretical calculations taking the strong
ac-Stark shift due to the rf-field into account
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 (~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 ~20 \mum,
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
Characterization of a high-power tapered semiconductor amplifier system
We have characterized a semiconductor amplifier laser system which provides up to 200mW output after a single-mode optical fiber at 780nm wavelength. The system is based on a tapered semiconductor gain element, which amplifies the output of a narrow-linewidth diode laser. Gain and saturation are discussed as a function of operating temperature and injection current. The spectral properties of the amplifier are investigated with a grating spectrometer. Amplified spontaneous emission (ASE) causes a spectral background with a width of 4nm FWHM. The ASE background was suppressed to below our detection limit by a proper choice of operating current and temperature, and by sending the light through a single-mode optical fiber. The final ASE spectral density was less than 0.1nW/MHz, i.e. less than 0.2 % of the optical power. Related to an optical transition linewidth of MHz for rubidium, this gives a background suppression of better than -82dB. An indication of the beam quality is provided by the fiber coupling efficiency up to 59 %. The application of the amplifier system as a laser source for atom optical experiments is discussed
Characterizing the local vectorial electric field near an atom chip using Rydberg state spectroscopy
We use the sensitive response to electric fields of Rydberg atoms to
characterize all three vector components of the local electric field close to
an atom-chip surface. We measured Stark-Zeeman maps of and Rydberg
states using an elongated cloud of ultracold Rubidium atoms ( K)
trapped magnetically m from the chip surface. The spectroscopy of
states yields a calibration for the generated local electric field at the
position of the atoms. The values for different components of the field are
extracted from the more complex response of states to the combined electric
and magnetic fields. From the analysis we find residual fields in the two
uncompensated directions of V/cm and V/cm
respectively. This method also allows us to extract a value for the relevant
field gradient along the long axis of the cloud. The manipulation of electric
fields and the magnetic trapping are both done using on-chip wires, making this
setup a promising candidate to observe Rydberg-mediated interactions on a chip.Comment: 8 pages, 5 figure
- …