arXiv subjects

Joseph H. Thywissen

Publications and source records attributed to Joseph H. Thywissen.

24 records · Page 2Linked to original sources

arXiv2009

Response to comment by Tin-Lun Ho on "Itinerant Ferromagnetism in a Strongly Interacting Fermi Gas of Ultracold Atoms", Science 325, 1521 (2009)

Ho claims in his comment that our experiment is direct evidence that itinerant ferromagnetism does not exist in ultracold Fermi gases. This claim is incorrect and based on an invalid estimate of relaxation times and an erroneous interpretation of the detectability of ferromagnetic domains. We point out that the experimental evidence is consistent with the existence of ferromagnetism, but further experiments are needed to distinguish a ferromagnetic ground state from a non-magnetic ground state with ferromagnetic correlations.

cond-mat.quant-gas↗

arXiv2009

Itinerant Ferromagnetism in a Fermi Gas of Ultracold Atoms

Can a gas of spin-up and spin-down fermions become ferromagnetic due to repulsive interactions? This question which has not yet found a definitive theoretical answer was addressed in an experiment with an ultracold two-component Fermi gas. The observation of non-monotonic behavior of lifetime, kinetic energy, and size for increasing repulsive interactions provides strong evidence for a phase transition to a ferromagnetic state. It implies that itinerant ferromagnetism of delocalized fermions is possible without lattice and band structure and validates the most basic model for ferromagnetism introduced by Stoner.

cond-mat.quant-gas↗

arXiv2004

Using magnetic chip traps to study Tonks-Girardeau quantum gases

We discuss the use of microfabricated magnetic traps, or "chip traps," to study quasi-one-dimensional quantum gases. In particular, we discuss the feasibility of studying the Tonks-Girardeau limit, in which the gas is strongly interacting. We review the scaling of the oscillation frequencies of a chip trap, and show that it seems feasible to attain a Tonks-Girardeau parameter as large as 200. The primary difficulty of this approach is detection, since the strongly interacting limit occurs for low densities. We propose a way to "freeze" the distribution, and then measure it with a single-atom detector. This method can also be applied to optical dipole traps.

cond-mat.soft↗

arXiv2004

Exponentially Localized Magnetic Fields for Single-Spin Quantum Logic Gates

An infinite array of parallel current-carrying wires is known, from the field of neutral particle optics, to produce an exponentially localized magnetic field when the current direction is antiparallel in adjacent wires. We show that a finite array of several tens of superconducting Nb nanowires can produce a peak magnetic field of 10mT that decays by a factor of 10^4 over a length scale of 500nm. Such an array is readily manufacturable with current technology, and is compatible with both semiconductor and superconducting quantum computer architectures. A series of such arrays can be used to individually address single single-spin or flux qubits spaced as little as 100nm apart, and can lead to quantum logic gate times of 5ns.

cond-mat.mes-hall↗

arXiv2004

Observation of deviations from ideal gas thermodynamics in a trapped Bose-Einstein condensed gas

We have investigated experimentally the finite-temperature properties of a Bose-Einstein condensed cloud of $^{87}$Rb atoms in a harmonic trap. Focusing primarily on condensed fraction and expansion energy, we measure unambiguous deviations from ideal-gas thermodynamics, and obtain good agreement with a Hartree-Fock description of the mixed cloud. Our results offer for the first time clear evidence of the mutual interaction between the condensed and thermal components. To probe the low-temperature region unaccessible to the usual time-of-flight technique, we use coherent Bragg scattering as a filtering technique for the condensate. This allows us to separate spatially the condensed and normal components in time of flight, and to measure reliably temperatures as low as $0.2 T_{\rm c}^0$ and thermal fractions as low as 10%.Finally, we observe evidence for the limitations of the usual image analysis procedure, pointing out to the need for a more elaborate model of the expansion of the mixed cloud.

cond-mat.other↗

arXiv2003

The critical temperature of a trapped, weakly interacting Bose gas

We report on measurements of the critical temperature of a harmonically trapped, weakly interacting Bose gas as a function of atom number. Our results exclude ideal-gas behavior by more than two standard deviations, and agree quantitatively with mean-field theory. At our level of sensitivity, we find no additional shift due to critical fluctuations. In the course of this measurement, the onset of hydrodynamic expansion in the thermal component has been observed. Our thermometry method takes this feature into account.

cond-mat↗