Biomedical subjects

David E Pritchard

Publications and source records attributed to David E Pritchard.

9 recordsLinked to original sources

PubMed2006

Imaging the Mott insulator shells by using atomic clock shifts.

Microwave spectroscopy was used to probe the superfluid-Mott insulator transition of a Bose-Einstein condensate in a three-dimensional optical lattice. By using density-dependent transition frequency shifts, we were able to spectroscopically distinguish sites with different occupation numbers and to directly image sites with occupation numbers from one to five, revealing the shell structure of the Mott insulator phase. We used this spectroscopy to determine the onsite interaction and lifetime for individual shells.

Journal Article↗

PubMed2006

Parametric amplification of scattered atom pairs.

We have observed parametric generation and amplification of ultracold atom pairs. A 87Rb Bose-Einstein condensate was loaded into a one-dimensional optical lattice with quasimomentum k0 and spontaneously scattered into two final states with quasimomenta k1 and k2 . Furthermore, when a seed of atoms was first created with quasimomentum k1 we observed parametric amplification of scattered atoms pairs in states k1 and k2 when the phase-matching condition was fulfilled. This process is analogous to optical parametric generation and amplification of photons and could be used to efficiently create entangled pairs of atoms. Furthermore, these results explain the dynamic instability of condensates in moving lattices observed in recent experiments.

Journal Article↗

PubMed2005

World Year of Physics: a direct test of E=mc2.

One of the most striking predictions of Einstein's special theory of relativity is also perhaps the best known formula in all of science: E=mc(2). If this equation were found to be even slightly incorrect, the impact would be enormous--given the degree to which special relativity is woven into the theoretical fabric of modern physics and into everyday applications such as global positioning systems. Here we test this mass-energy relationship directly by combining very accurate measurements of atomic-mass difference, Delta(m), and of gamma-ray wavelengths to determine E, the nuclear binding energy, for isotopes of silicon and sulphur. Einstein's relationship is separately confirmed in two tests, which yield a combined result of 1-Delta(mc2)/E=(-1.4+/-4.4)x10(-7), indicating that it holds to a level of at least 0.00004%. To our knowledge, this is the most precise direct test of the famous equation yet described.

Journal Article↗

PubMed2005

Photon recoil momentum in dispersive media.

A systematic shift of the photon recoil momentum due to the index of refraction of a dilute gas of atoms has been observed. The recoil frequency was determined with a two-pulse light grating interferometer using near-resonant laser light. The results show that the recoil momentum of atoms caused by the absorption of a photon is n variant Planck's k, where n is the index of refraction of the gas and k is the vacuum wave vector of the photon. This systematic effect must be accounted for in high-precision atom interferometry with light gratings.

Journal Article↗

PubMed2004

Cyclotron frequency shifts arising from polarization forces.

The cyclotron frequency of a charged particle in a uniform magnetic field B is related to its mass m and charge q by the relationship omega(c) = qB/m. This simple relationship forms the basis for sensitive mass comparisons using ion cyclotron resonance mass spectroscopy, with applications ranging from the identification of biomolecules and the study of chemical reaction rates to determinations of the fine structure constant of atomic spectra. Here we report the observation of a deviation from the cyclotron frequency relationship for polarizable particles: in high-accuracy measurements of a single CO+ ion, a dipole induced in the orbiting ion shifts the measured cyclotron frequency. We use this cyclotron frequency shift to measure non-destructively the quantum state of the CO+ ion. The effect also provides a means to determine to a few per cent the body-frame dipole moment of CO+, thus establishing a method for measuring dipole moments of molecular ions for which few comparably accurate measurements exist. The general perturbation that we describe here affects the most precise mass comparisons attainable today, with applications including direct tests of Einstein's mass-energy relationship and charge-parity-time reversal symmetry, and possibly the weighing of chemical bonds.

Journal Article↗

PubMed2004

Dispersion compensation for atom interferometry.

A new technique for maintaining high contrast in an atom interferometer is used to measure large de Broglie wave phase shifts. Dependence of an interaction induced phase on the atoms' velocity is compensated by applying an engineered counterphase. The counterphase is equivalent to a rotation, is precisely determined by a frequency, and can be used to measure phase shifts due to interactions of unknown strength. Phase shifts of 150 rad (5 times larger than previously possible) have now been measured in an atom beam interferometer, and we suggest that this technique can enable comparisons of atomic polarizability with precision of one part in 10,000.

Journal Article↗

PubMed2003

An ion balance for ultra-high-precision atomic mass measurements.

We have developed the analog of a double-pan balance for determining the masses of single molecular ions from the ratio of their two cyclotron frequencies. By confining two different ions on the same magnetron orbit in a Penning trap, we balance out many sources of noise and error (such as fluctuations of the magnetic field). To minimize the systematic error associated with the Coulomb interaction between the two ions, they are kept about 1 millimeter apart from each other, resulting in fractional uncertainty below 1 x 10(-11). Such precision opens the door to numerous applications of mass spectrometry, including metrology, fundamental physics, and weighing chemical bonds.

Journal Article↗

PubMed2003

The onset of matter-wave amplification in a superradiant Bose-Einstein condensate.

The interaction of short and strong laser pulses with an atomic Bose-Einstein condensate is found to generate patterns of recoiling atoms that are different from those seen in previous light-scattering experiments. This phenomenon can only be explained by optical stimulation, showing that the previous description of superradiance as atomic stimulation is incomplete and that matter-wave amplification in Bose-Einstein condensates is suppressed at short times. Our experiments clarify the nature of bosonic stimulation in the four-wave mixing of light and atoms.

Journal Article↗

PubMed2002

Glory oscillations in the index of refraction for matter waves.

We have measured the index of refraction for sodium de Broglie waves in gases of Ar, Kr, Xe, and N2 over a wide range of sodium velocities. We observe glory oscillations--a velocity-dependent oscillation in the forward scattering amplitude. An atom interferometer was used to observe glory oscillations in the phase shift caused by the collision, which are larger than glory oscillations observed in the cross section. The glory oscillations depend sensitively on the shape of the interatomic potential, allowing us to discriminate among various predictions for these potentials, none of which completely agrees with our measurements.

Journal Article↗