ATOMIC PHYSICS 17: XVII International Conference on Atomic Physics; ICAP 2000
551(2001); http://dx.doi.org/10.1063/1.1354337View Description Hide Description
This paper reviews recent progress on microwave clocks using laser cooled neutral atoms. With an ultra-stable cryogenic sapphire oscillator as interrogation oscillator, a cesium fountain operates at the quantum projection noise limit. With detected atoms, the relative frequency stability δν/ν is where τ is the integration time in seconds. This stability is comparable to that of hydrogen masers. At the measured stability reaches Equally important is the accuracy of the frequency standard since is the primary reference for the definition of the time unit, the second. The accuracy of our cesium fountain FO1 is presently currently the best reported value.
A fountain has also been constructed and the ground-state hyperfine energy has been compared to the Cs primary standard with a relative accuracy of Comparing the hyperfine energies of atoms with different atomic numbers Z, one can search for possible variations of the fine structure constant with time. Measurements of the ratio spread over an interval of 24 months indicate no change at a level of placing a new upper limit for The second attractive feature of fountains is the smallness of the frequency shift induced by the mean field interaction between atoms. This shift is found to be at least ∼50 times below that of cesium.
Finally, the interest of the microgravity of space for cold atom experiments is out-lined. A space mission, ACES, carrying ultra-stable clocks, is presented. ACES has been selected by the European Space Agency to fly on the International Space Station in 2004.
551(2001); http://dx.doi.org/10.1063/1.1354338View Description Hide Description
We review our progress in a measurement of Using an atom interferometer method based on adiabatic transfer between atomic states, we measure the recoil velocity of cesium due to the scattering of a photon. Our current statistical uncertainty is on the order of 3 parts per billion in This paper will summarize our current status in dealing with the systematic effects of this measurement.
551(2001); http://dx.doi.org/10.1063/1.1354339View Description Hide Description
Optical frequency metrology plays an important role for the determination of the Rydberg constant and offers an alternative way to determine the fine structure constant α. We have developed a new technique for measuring optical frequencies using femtosecond light pulses culminating in the single laser optical frequency synthesizer. This new technique greatly simplifies the task of measuring optical frequencies.
551(2001); http://dx.doi.org/10.1063/1.1354340View Description Hide Description
Using a Penning trap single ion mass spectrometer, we have measured the atomic masses of 13 isotopes, many important for fundamental metrology and fundamental constants. The accuracy of the measurements, is typically two orders of magnitude better than previously accepted values. A wide variety of self consistency checks greatly reduces the possibility of unknown systematic errors.
As part of a program to determine the Molar Planck constant and the fine structure constant α, we measured the masses of and Our high accuracy atomic mass measurements can be combined with values of from atom interferometry measurements and accurate wavelength measurements for different atoms to give several independent determinations of and α. This route to α through the atomic mass of the proton the electron to proton mass ratio and the Rydberg constant is based on simple physics. It can potentially achieve the several ppb accuracy needed to test the QED determination of α extracted from measurements of the electron g factor.
551(2001); http://dx.doi.org/10.1063/1.1354341View Description Hide Description
Theories unifying gravity and other interactions predict spatial and temporal variation of physical “constants” in the Universe. Comparison of quasar absorption line spectra with laboratory spectra provide the best probe for variability of the fine structure constant, over cosmological time-scales. We have demonstrated  that high sensitivity to the variation of α can be obtained from a comparison of the spectra of heavy and light atoms and have obtained an order of magnitude gain in precision over previous methods . Our new constraints  on α come from simultaneous fitting of numerous absorption lines of the following species: Mg I, Mg II, AlII, AlIII, SiII, CrII, FeII, Ni II and Zn II. The results are based on an analysis of 49 absorption systems covering cosmological time starting from about 10% of the age of the Universe after Big Bang (the redshift parameters cover ). The data contain statistical evidence for a smaller α at earlier epochs at the 4.3σ level. We briefly discuss possible systematic errors and numerous tests done to estimate and reduce these errors. Careful searches have so far not revealed any spurious effect that can explain the observations.
551(2001); http://dx.doi.org/10.1063/1.1354342View Description Hide Description
551(2001); http://dx.doi.org/10.1063/1.1354343View Description Hide Description
Quantum jumps between Fock states of a one-electron oscillator reveal the quantum limit of a cyclotron accelerator. The states live for seconds when spontaneous emission is inhibited by 140 within a cylindrical Penning trap cavity. Averaged over hours the oscillator is in thermal equilibrium with black-body photons in the cavity. At 80 mK, quantum jumps occur only when resonant microwave photons are introduced into the cavity, opening a route to improved measurements of the magnetic moments of the electron and positron. The temperature demonstrated is about 60 times lower than the 4.2 K temperature at which charged elementary particles were previously stored. Implications for the production of cold antihydrogen are discussed.
551(2001); http://dx.doi.org/10.1063/1.1354344View Description Hide Description
The linear Stark effect on a single molecule allows us to sweep its frequency through resonance with a fixed laser frequency by applying a sinusoidal RF voltage on two electrodes. If the conditions of adiabatic following are fulfilled, we can prepare the excited molecular state with near certainty. Spontaneous emission from this state gives rise to a single photon. With our current experimental conditions, up to 75% of the sweeps lead to the emission of a single photon. Since the adiabatic passage is done on command, the molecule performs as a high rate source of triggered photons. The experimental results are in quantitative agreement with quantum Monte Carlo simulations.
551(2001); http://dx.doi.org/10.1063/1.1354345View Description Hide Description
Ground state cooling and coherent manipulation of ions in an rf-(Paul) trap is the prerequisite for quantum information experiments with trapped ions. With resolved sideband cooling on the optical quadrupole transition we have cooled one and two ions to the ground state of vibration with up to 99.9% probability. With a novel cooling scheme utilizing electromagnetically induced transparency on the manifold we have achieved simultaneous ground state cooling of two motional sidebands 1.7 MHz apart. Starting from the motional ground state we have demonstrated coherent quantum state manipulation on the quadrupole transition at 729 nm. Up to 30 Rabi oscillations within 1.4 ms have been observed in the motional ground state and in the Fock state. In the linear quadrupole rf-trap with 700 kHz trap frequency along the symmetry axis (2 MHz in radial direction) the minimum ion spacing is more than 5 μm for up to 4 ions. We are able to cool two ions to the ground state in the trap and individually address the ions with laser pulses through a special optical addressing channel.
551(2001); http://dx.doi.org/10.1063/1.1354346View Description Hide Description
We have performed multiparticle entanglement experiments with circular Rydberg atoms crossing one at a time a high Q superconducting microwave cavity. Two-level atoms and a zero or one photon field stored in the cavity act as qubits carrying quantum information. Controlled qubit entanglement is produced by the quantum Rabi oscillation coupling the atom to the cavity field. Qubit state superpositions are produced and analyzed by classical microwave pulses before and after the atom cross the high Q cavity, using a Ramsey interferometer arrangement. We have demonstrated the coherent operation of a quantum phase gate and used it to perform for the first time a quantum nondestructive measurement of a single photon. Combining this gate with quantum Rabi oscillations of various durations, we have entangled step by step three subsystems—two atom and one field mode—by a controlled succession of one and two qubit operations. Once some limitations of our experiment are overcome, it will be generalized to larger number of particles, opening the way to the study of even more complex entangled states.
551(2001); http://dx.doi.org/10.1063/1.1354347View Description Hide Description
We consider experimental issues relevant to quantum computing, and discuss the best way to achieve the essential requirements of reliable quantum memory and gate operations. Nuclear spins in trapped ions or atoms are a very promising candidate for the qubits. We estimate the parameters required to couple atoms using light via cavity QED in order to achieve quantum gates. We briefly comment on recent improvements to the Cirac-Zoller method for coupling trapped ions via their vibrational degree of freedom. Error processes result in a trade-off between quantum gate speed and failure probability. A useful quantum computer does appear to be feasible using a combination of ion trap and optical methods. The best understood method to stabilize a large computer relies on quantum error correction. The essential ideas of this are discussed, and recent estimates of the noise requirements in a quantum computing device are given.
551(2001); http://dx.doi.org/10.1063/1.1354348View Description Hide Description
Entangled states are a crucial component in quantum computers, and are of great interest in their own right, highlighting the inherent nonlocality of quantum mechanics. As part of the drive toward larger entangled states for quantum computing, we have engineered the most complex entangled state so far in a collection of four trapped atomic ions. Notably, we employ a technique which is readily scalable to much larger numbers of atoms. Limits to the current experiment and plans to circumvent these limitations are presented.
551(2001); http://dx.doi.org/10.1063/1.1354349View Description Hide Description
The paper describes two types of nonlinear optical processes which are based on electromagnetically induced transparency. These are: (1) Collinear generation of FM-like Raman sidebands and (2) a type of pondermotive light scattering which is inherent to the interaction of slow light with cold atoms. Connections to other areas of EIT-based nonlinear optics are also described.
551(2001); http://dx.doi.org/10.1063/1.1354350View Description Hide Description
We describe several novel experimental effects resulting from optical coherences in multilevel atoms driven with coherent laser fields. Four configurations were explored using Rb vapor cells: lambda dark-line resonances, single beam double-lambda oscillations, and cascade two-photon transitions in co- and counter-propagating geometries. Experiments were performed with high spectral-resolution using low-power diode lasers sources and optically thick cells. Two of the most striking effects we observed are: (1) a self-oscillation that occurs at 3.0 GHz on the hyperfine frequency when a single laser field pumps the atoms, and (2) a coherent blue-beam emission that we observe in the co-propagating cascade two-photon case. These phenomena lead to complex lineshapes, and the effects sometimes dominate the well-known 3-level coherence effects. Additional higher-order mixing or cascaded interferences are apparent in all four experimental configurations. Many of these can be viewed as multi-wave mixing enhanced by optical coherences around closed-loop paths of atomic energy levels. The effects are particularly strong when four-photon closed-loop paths with resonant energy levels are possible, as in, the double-lambda system or as a four-wave mixing “box.”
551(2001); http://dx.doi.org/10.1063/1.1354351View Description Hide Description
The muon g-2 experiment at the Brookhaven National Laboratory is described, including its motivation, goal and present status. The latest result based on 1998 data is where the error is primarily statistical. This value agrees with the present theoretical value. Data obtained thus far and now being analyzed should have a statistical error of about 0.5 ppm.
551(2001); http://dx.doi.org/10.1063/1.1354353View Description Hide Description
In this talk I discuss the relevance of atomic physics in understanding some important questions about elementary particle physics. A particular attention is devoted to atomic parity violation measurements which seem to suggest new physics beyond the Standard Model. Atomic physics might also be relevant in discovering possible violations of the CPT symmetry.
551(2001); http://dx.doi.org/10.1063/1.1354354View Description Hide Description
We report on the measurement of the g-factor of the electron bound in an atomic ion. A single hydrogenic ion is stored in a Penning trap. The electronic spin state of the ion is monitored via the continuous Stern-Gerlach effect in a quantum non-demolition measurement. Quantum jumps between the two spin states (spin up and spin down) are induced by a microwave field at the spin precession frequency of the bound electron. The g-factor of the bound electron is obtained by varying the microwave frequency and counting the number of spin flips for a fixed time interval. Applications of the continuous Stern-Gerlach effect include high-accuracy tests of bound-state quantum electrodynamics (QED), the measurement of the atomic mass of the electron, the determination of the fine structure constant α, and the measurement of nuclear g-factors.
551(2001); http://dx.doi.org/10.1063/1.1354355View Description Hide Description
This paper discusses measurements of the Lamb shift in hydrogenic ions and how they have been used to test quantum electrodynamics. There is a discussion of the validity of renormalisation and also a consideration of Lamb shift measurements for hydrogenic ions of medium Z elements, with a description of a novel experiment on slow ions and a discussion of what the results of this experiment should tell us.