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| Publications of John E. Thomas :chronological alphabetical combined listing:%% Papers Published @article{fds248493, Author = {Joseph, JA and Thomas, JE and Kulkarni, M and Abanov, AG}, Title = {Observation of shock waves in a strongly interacting Fermi gas.}, Journal = {Physical review letters}, Volume = {106}, Number = {15}, Pages = {150401}, Year = {2011}, Month = {April}, url = {http://www.ncbi.nlm.nih.gov/pubmed/21568532}, Abstract = {We study collisions between two strongly interacting atomic Fermi gas clouds. We observe exotic nonlinear hydrodynamic behavior, distinguished by the formation of a very sharp and stable density peak as the clouds collide and subsequent evolution into a boxlike shape. We model the nonlinear dynamics of these collisions by using quasi-1D hydrodynamic equations. Our simulations of the time-dependent density profiles agree very well with the data and provide clear evidence of shock wave formation in this universal quantum hydrodynamic system.}, Doi = {10.1103/physrevlett.106.150401}, Key = {fds248493} } @article{fds248492, Author = {Cao, C and Elliott, E and Joseph, J and Wu, H and Petricka, J and Schäfer, T and Thomas, JE}, Title = {Universal quantum viscosity in a unitary Fermi gas.}, Journal = {Science (New York, N.Y.)}, Volume = {331}, Number = {6013}, Pages = {58-61}, Year = {2011}, Month = {January}, url = {http://www.ncbi.nlm.nih.gov/pubmed/21148347}, Abstract = {A Fermi gas of atoms with resonant interactions is predicted to obey universal hydrodynamics, in which the shear viscosity and other transport coefficients are universal functions of the density and temperature. At low temperatures, the viscosity has a universal quantum scale ħ n, where n is the density and ħ is Planck's constant h divided by 2π, whereas at high temperatures the natural scale is p(T)(3)/ħ(2), where p(T) is the thermal momentum. We used breathing mode damping to measure the shear viscosity at low temperature. At high temperature T, we used anisotropic expansion of the cloud to find the viscosity, which exhibits precise T(3/2) scaling. In both experiments, universal hydrodynamic equations including friction and heating were used to extract the viscosity. We estimate the ratio of the shear viscosity to the entropy density and compare it with that of a perfect fluid.}, Doi = {10.1126/science.1195219}, Key = {fds248492} } @article{fds183756, Author = {J.E. Thomas}, Title = {The nearly perfect Fermi gas}, Journal = {Physics Today}, Series = {May 2010}, Pages = {34-37}, Year = {2010}, Month = {May}, Key = {fds183756} } @article{fds248495, Author = {Thomas, JE}, Title = {Is an ultra-cold strongly interacting Fermi gas a perfect fluid}, Journal = {Nucl. Phys. A}, Volume = {830}, Pages = {635}, Year = {2009}, Month = {October}, Key = {fds248495} } @article{fds248496, Author = {Du, X and Zhang, Y and Petricka, J and Thomas, JE}, Title = {Controlling spin current in a trapped Fermi gas.}, Journal = {Physical review letters}, Volume = {103}, Number = {1}, Pages = {010401}, Year = {2009}, Month = {July}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/19659125}, Abstract = {We study fundamental features of spin current in a very weakly interacting Fermi gas of 6Li. By creating a spin current and then reversing its flow, we demonstrate control of the spin current. This reversal is predicted by a spin vector evolution equation in energy representation, which shows how the spin and energy of individual atoms become correlated in the nearly undamped regime of the experiments. The theory provides a simple physical description of the spin current and explains both the large amplitude and the slow temporal evolution of the data. Our results have applications in studying and controlling fundamental spin interactions and spin currents in ultracold gases.}, Doi = {10.1103/physrevlett.103.010401}, Key = {fds248496} } @article{fds248497, Author = {Du, X and Zhang, Y and Thomas, JE}, Title = {Inelastic collisions of a Fermi gas in the BEC-BCS crossover.}, Journal = {Physical review letters}, Volume = {102}, Number = {25}, Pages = {250402}, Year = {2009}, Month = {June}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/19659058}, Abstract = {We measure inelastic three-body and two-body collisional decay rates for a two-component Fermi gas of 6Li, which are highly suppressed by the Pauli exclusion principle. Our measurements are made in the BEC-BCS crossover regime, near the two-body collisional (Feshbach) resonance. At high temperature (energy) the data show a dominant three-body decay process, which is studied as a function of bias magnetic field. At low energy, the data show a coexistence of two-body and three-body decay processes near and below the Feshbach resonance. Below resonance, the observed two-body inelastic decay can arise from molecule-atom and molecule-molecule collisions. We suggest that at and above resonance, an effective two-body decay rate arises from collisions between atoms and correlated (Cooper) pairs that can exist at sufficiently low temperature.}, Doi = {10.1103/physrevlett.102.250402}, Key = {fds248497} } @article{fds248494, Author = {Luo, L and Thomas, JE}, Title = {Thermodynamic measurements in strongly interacting Fermi gas}, Journal = {Journal of Low Temperature Physics}, Volume = {154}, Number = {1-2}, Pages = {1-29}, Publisher = {Springer Nature}, Year = {2009}, Month = {January}, ISSN = {0022-2291}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000261606000001&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Abstract = {Strongly interacting Fermi gases provide a clean and controllable laboratory system for modeling strong interparticle interactions between fermions in nature, from high temperature superconductors to neutron matter and quark-gluon plasmas. Model-independent thermodynamic measurements, which do not require theoretical models for calibrations, are very important for exploring this important system experimentally, as they enable direct tests of predictions based on the best current non-perturbative many-body theories. At Duke University, we use all-optical methods to produce a strongly interacting Fermi gas of spin-1/2-up and spin-1/2-down 6Li atoms that is magnetically tuned near a collisional (Feshbach) resonance. We conduct a series of measurements on the thermodynamic properties of this unique quantum gas, including the energy E, entropy S, and sound velocity c. Our model-independent measurements of E and S enable a precision study of the finite temperature thermodynamics. The E (S ) data are directly compared to several recent predictions. The temperature in both the superfluid and normal fluid regime is obtained from the fundamental thermodynamic relation T = ∂E/∂S by parameterizing the E(S) data using two different power laws that are joined with continuous E and T at a certain entropy S c, where the fit is optimized. We observe a significant change in the scaling of E with S above and below S c. Taking the fitted value of S c as an estimate of the critical entropy for a superfluid-normal fluid phase transition in the strongly interacting Fermi gas, we estimate the critical parameters. Our E (S) data are also used to experimentally calibrate the endpoint temperatures obtained for adiabatic sweeps of the magnetic field between the ideal and strongly interacting regimes. This enables the first experimental calibration of the temperature scale used in experiments on fermionic pair condensation, where the ideal Fermi gas temperature is measured before sweeping the magnetic field to the strongly interacting regime. Our calibration shows that the ideal gas temperature measured for the onset of pair condensation corresponds closely to the critical temperature T c estimated in the strongly interacting regime from the fits to our E(S) data. We also calibrate the empirical temperature employed in studies of the heat capacity and obtain nearly the same T c. We determine the ground state energy by three different methods, using sound velocity measurements, by extrapolating E (S) to S = 0 and by measuring the ratio of the cloud sizes in the strongly and weakly interacting regimes. The results are in very good agreement with recent predictions. Finally, using universal thermodynamic relations, we estimate the chemical potential and heat capacity of the trapped gas from the E(S) data. © Springer Science+Business Media, LLC 2008.}, Doi = {10.1007/s10909-008-9850-2}, Key = {fds248494} } @article{fds248499, Author = {Du, X and Luo, L and Clancy, B and Thomas, JE}, Title = {Observation of anomalous spin segregation in a trapped Fermi gas.}, Journal = {Physical review letters}, Volume = {101}, Number = {15}, Pages = {150401}, Year = {2008}, Month = {October}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/18999574}, Abstract = {We report the observation of spin segregation, i.e., time-dependent separation of the spin density profiles of two spin states, in a trapped, coherently prepared Fermi gas of 6Li with a magnetically tunable scattering length a12 close to zero. For |a12| approximately = 5 bohr, as the cloud profiles evolve, the measured difference in the densities at the cloud center increases in 200 ms from 0 to approximately = 60% of the initial mean density and changes sign with a12. The data are in disagreement in both amplitude and temporal evolution with a spin-wave theory for a Fermi gas. In contrast, for a Bose gas, an analogous theory has successfully described previous observations of spin segregation. The observed segregated atomic density profiles are far from equilibrium, yet they persist for approximately = 5 s, long compared to the axial trapping period of 6.9 ms. We find the zero crossing in a12=0, where spin segregation ceases, at 527.5+/-0.2 G.}, Doi = {10.1103/physrevlett.101.150401}, Key = {fds248499} } @article{fds248498, Author = {Thomas, JE}, Title = {Energy measurement and virial theorem for confined universal Fermi gases}, Journal = {Physical Review A - Atomic, Molecular, and Optical Physics}, Volume = {78}, Number = {1}, Pages = {013630}, Publisher = {American Physical Society (APS)}, Year = {2008}, Month = {July}, ISSN = {1050-2947}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000258180300186&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Abstract = {Optically trapped two-component Fermi gases near a broad Feshbach resonance exhibit universal thermodynamics, where the properties of the gas are independent of the details of the two-body scattering interactions. We show that the measured cloud profiles of both species determine the total energy of universal gases for any trapping potential U and any spin mixture, without assuming either the local density approximation or harmonic confinement. A global proof of the virial theorem yields the total energy of the gas at all temperatures in the scale-invariant form E= ?U/ , where ? is an arbitrary energy scale in terms of which all length and energy scales that appear in the confining potential are written. This result enables model-independent energy measurement in any trap by observing only the cloud profiles, and provides a consistency check for many-body calculations in the universal regime. © 2008 The American Physical Society.}, Doi = {10.1103/PhysRevA.78.013630}, Key = {fds248498} } @article{fds248500, Author = {Turlapov, A and Kinast, J and Clancy, B and Luo, L and Joseph, J and Thomas, JE}, Title = {Is a gas of strongly interacting atomic fermions a nearly perfect fluid?}, Journal = {Journal of Low Temperature Physics}, Volume = {150}, Number = {3-4}, Pages = {567-576}, Publisher = {Springer Nature}, Year = {2008}, Month = {February}, ISSN = {0022-2291}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000252469100066&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Abstract = {We use all-optical methods to produce a highly-degenerate Fermi gas of spin-1/2 6Li atoms. A magnetic field tunes the gas near a collisional (Feshbach) resonance, producing strong interactions between spin-up and spin-down atoms. We have measured properties of a breathing mode over a wide range of temperatures. As the temperature is increased from below the superfluid transition to above, the frequency of the mode is always close to the hydrodynamic value, while the damping rate increases. A complete explanation of both the frequency and the damping rate in the normal collisional regime has not been achieved. Our measurements of the damping rate as a function of the energy of the gas are used to estimate an upper bound on the viscosity. Using our new measurements of the entropy of the gas, we estimate the ratio of the shear viscosity to the entropy density and compare the result with a recent string theory conjecture for the minimum viscosity of a perfect quantum fluid. © Springer Science+Business Media, LLC 2007.}, Doi = {10.1007/s10909-007-9589-1}, Key = {fds248500} } @article{fds248502, Author = {Clancy, B and Luo, L and Thomas, JE}, Title = {Observation of nearly perfect irrotational flow in normal and superfluid strongly interacting Fermi gases.}, Journal = {Physical review letters}, Volume = {99}, Number = {14}, Pages = {140401}, Year = {2007}, Month = {October}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/17930648}, Abstract = {We study the hydrodynamic expansion of a rotating strongly interacting Fermi gas by releasing a cigar-shaped cloud with a known angular momentum from an optical trap. As the aspect ratio of the expanding cloud approaches unity, the angular velocity increases, indicating quenching of the moment of inertia I to as low as 0.05 of the rigid body value I(rig). Remarkably, we observe this behavior in both the superfluid and collisional normal fluid regimes, which obey nearly identical zero-viscosity irrotational hydrodynamics. We attribute irrotational flow in the normal fluid to a decay of the rotational part of the stream velocity during expansion, which occurs when the shear viscosity is negligible. Using conservation of angular momentum, we directly observe a fundamental result of irrotational hydrodynamics, I/I(rig) = delta2, where delta is the deformation parameter of the cloud.}, Doi = {10.1103/physrevlett.99.140401}, Key = {fds248502} } @article{fds248503, Author = {Joseph, J and Clancy, B and Luo, L and Kinast, J and Turlapov, A and Thomas, JE}, Title = {Measurement of sound velocity in a fermi gas near a feshbach resonance}, Journal = {Physical Review Letters}, Volume = {98}, Number = {17}, Pages = {170401}, Publisher = {American Physical Society (APS)}, Year = {2007}, Month = {April}, ISSN = {0031-9007}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000246803900001&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Abstract = {Sound waves are excited in an optically trapped degenerate Fermi gas of spin-up and spin-down atoms with magnetically tunable interactions. Measurements are made throughout the crossover region, from a weakly interacting Fermi gas through the resonant Fermi superfluid regime to a Bose condensate of dimer molecules. The measured sound velocities test theories of hydrodynamic wave propagation and predictions of the equation of state. At resonance, the sound velocity exhibits universal scaling with the Fermi velocity, to within 1.8% over a factor of 30 in density. © 2007 The American Physical Society.}, Doi = {10.1103/PhysRevLett.98.170401}, Key = {fds248503} } @article{fds248504, Author = {Luo, L and Clancy, B and Joseph, J and Kinast, J and Thomas, JE}, Title = {Measurement of the entropy and critical temperature of a strongly interacting Fermi gas.}, Journal = {Physical review letters}, Volume = {98}, Number = {8}, Pages = {080402}, Year = {2007}, Month = {February}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/17359072}, Abstract = {We report a model-independent measurement of the entropy, energy, and critical temperature of a degenerate, strongly interacting Fermi gas of atoms. The total energy is determined from the mean square cloud size in the strongly interacting regime, where the gas exhibits universal behavior. The entropy is measured by sweeping a bias magnetic field to adiabatically tune the gas from the strongly interacting regime to a weakly interacting regime, where the entropy is known from the cloud size after the sweep. The dependence of the entropy on the total energy quantitatively tests predictions of the finite-temperature thermodynamics.}, Doi = {10.1103/physrevlett.98.080402}, Key = {fds248504} } @article{fds248506, Author = {Luo, L and Clancy, B and Joseph, J and Kinast, J and Turlapov, A and Thomas, JE}, Title = {Evaporative cooling of unitary Fermi gas mixtures in optical traps}, Journal = {New Journal of Physics}, Volume = {8}, Number = {9}, Pages = {213-213}, Publisher = {IOP Publishing}, Year = {2006}, Month = {September}, ISSN = {1367-2630}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000240807500003&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Abstract = {We measure the scaling laws for the number of atoms and the cloud size as a function of trap depth for evaporative cooling of a unitary Fermi gas in an optical trap. A unitary Fermi gas comprises a trapped mixture of atoms in two hyperfine states which is tuned to a collisional (Feshbach) resonance using a bias magnetic field. Near resonance, the zero energy s-wave scattering length diverges, and the s-wave scattering cross-section is limited by unitarity to be 4π/k2, where k is the relative wavevector of the colliding particles. In this case, the collision cross-section for evaporation scales inversely with the trap depth, enabling runaway evaporation under certain conditions. We demonstrate high evaporation efficiency, which is achieved by maintaining a high ratio ηof trap depth to thermal energy as the trap depth is lowered. We derive and demonstrate a trap lowering curve which maintains η constant for a unitary gas. This evaporation curve yields a quantum degenerate sample from a classical gas in a fraction of a second, with only a factor of three loss in atom number. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.}, Doi = {10.1088/1367-2630/8/9/213}, Key = {fds248506} } @article{fds248505, Author = {Thomas, JE}, Title = {Ultracold Fermi gas on a chip}, Journal = {Nature Physics}, Volume = {2}, Number = {6}, Pages = {377-378}, Publisher = {Springer Science and Business Media LLC}, Year = {2006}, Month = {June}, ISSN = {1745-2473}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000238529600017&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Doi = {10.1038/nphys326}, Key = {fds248505} } @article{fds52329, Author = {J. E. Thomas and J. Joseph and B. Clancy and L. Luo and J. Kinast and A. Turlapov}, Title = {Optical trapping and fundamental studies of atomic Fermi gases}, Volume = {6326}, Pages = {632602}, Booktitle = {Proceedings of the SPIE}, Year = {2006}, Key = {fds52329} } @article{fds52299, Author = {J. E. Thomas and J. Kinast and A. Turlapov}, Title = {Universal thermodynamics of a strongly interacting Fermi gas}, Volume = {850}, Pages = {69-76}, Booktitle = {AIP Conference Proceedings}, Publisher = {AIP}, Editor = {Y. Takano and S. P. Hershfield and S. O. Hill and P. J. Hirshfeld and A. M. Goldman}, Year = {2006}, Key = {fds52299} } @article{fds248501, Author = {Thomas, JE}, Title = {Optically-trapped Fermi gases}, Journal = {Habitation}, Volume = {10}, Pages = {242}, Year = {2006}, Key = {fds248501} } @article{fds248508, Author = {Kinast, J and Turlapov, A and Thomas, JE}, Title = {Optically trapped Fermi gases model strong interactions in nature}, Journal = {Optics and Photonics News}, Volume = {16}, Number = {12 SPEC. ISS.}, Pages = {21}, Publisher = {The Optical Society}, Year = {2005}, Month = {December}, url = {http://dx.doi.org/10.1364/OPN.16.12.000021}, Abstract = {Strongly interacting Fermi gases are produced in an optical trap, by using a magnetic field to tune them to a collisional resonance. In this regime, the gas exhibits remarkable properties, such as highly anisotropic expansion, universal thermodynamics, and high-temperature superfluidity. An amazing similarity between the elliptic flow observed in experiments at RHIC and the anisotropic expansion of an ultracold, strongly interacting Fermi gas of 6Li atoms at temperatures 20 orders of magnitude colder was also noticed. These fermi gases permit studies of hydrodynamic flow over a wide range of temperatures, including both superfluid and strongly collisional regimes.}, Doi = {10.1364/OPN.16.12.000021}, Key = {fds248508} } @article{fds248507, Author = {Lu, ZH and Thomas, JE and Bali, S}, Title = {Observation of phase-sensitive temporal correlations in the resonance fluorescence from two-level atoms.}, Journal = {Optics letters}, Volume = {30}, Number = {18}, Pages = {2478-2480}, Year = {2005}, Month = {September}, ISSN = {0146-9592}, url = {http://www.ncbi.nlm.nih.gov/pubmed/16196358}, Abstract = {We have made what we believe is the first observation of phase-dependent temporal correlations in the fluorescent field emitted by coherently driven two-level atoms in free space. We measured the temporal fluctuations of the fluorescent field when the resonant driving field was in phase and out of phase with the local-oscillator field.}, Doi = {10.1364/ol.30.002478}, Key = {fds248507} } @article{fds248509, Author = {Reil, F and Thomas, JE}, Title = {Observation of phase conjugation of light arising from enhanced backscattering in a random medium.}, Journal = {Physical review letters}, Volume = {95}, Number = {14}, Pages = {143903}, Year = {2005}, Month = {September}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/16241655}, Abstract = {We measure the fundamental phase conjugation of a light field arising from enhanced backscattering in a multiple scattering medium. The measurements employ a two-window, time-resolved heterodyne method to suppress specularly reflected light and to determine the transverse Wigner function of the field, yielding joint amplitude and phase information. Using this method, a light field backscattered from an aqueous suspension of polystyrene spheres is found to reverse curvature relative to that of the incident field.}, Doi = {10.1103/physrevlett.95.143903}, Key = {fds248509} } @article{fds248512, Author = {Thomas, JE and Kinast, J and Turlapov, A}, Title = {Virial theorem and universality in a unitary fermi gas.}, Journal = {Physical review letters}, Volume = {95}, Number = {12}, Pages = {120402}, Year = {2005}, Month = {September}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/16197054}, Abstract = {Unitary Fermi gases, where the scattering length is large compared to the interparticle spacing, can have universal properties, which are independent of the details of the interparticle interactions when the range of the scattering potential is negligible. We prepare an optically trapped, unitary Fermi gas of 6Li, tuned just above the center of a broad Feshbach resonance. In agreement with the universal hypothesis, we observe that this strongly interacting many-body system obeys the virial theorem for an ideal gas over a wide range of temperatures. Based on this result, we suggest a simple volume thermometry method for unitary gases. We also show that the observed breathing mode frequency, which is close to the unitary hydrodynamic value over a wide range of temperature, is consistent with a universal hydrodynamic gas with nearly isentropic dynamics.}, Doi = {10.1103/physrevlett.95.120402}, Key = {fds248512} } @article{fds248511, Author = {Kinast, J and Turlapov, A and Thomas, JE}, Title = {Damping of a unitary Fermi gas.}, Journal = {Physical review letters}, Volume = {94}, Number = {17}, Pages = {170404}, Year = {2005}, Month = {May}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/15904273}, Abstract = {We measure the temperature dependence of the radial breathing mode in an optically trapped, unitary Fermi gas of 6Li, just above the center of a broad Feshbach resonance. The damping rate reveals a clear change in behavior which we interpret as arising from a superfluid transition. We suggest pair breaking as a mechanism for an increase in the damping rate which occurs at temperatures well above the transition. In contrast to the damping, the frequency varies smoothly and remains close to the unitary hydrodynamic value. At low temperature T, the damping depends on the atom number only through the reduced temperature, and extrapolates to 0 at T = 0.}, Doi = {10.1103/physrevlett.94.170404}, Key = {fds248511} } @article{fds248510, Author = {Kinast, J and Turlapov, A and Thomas, JE and Chen, Q and Stajic, J and Levin, K}, Title = {Heat capacity of a strongly interacting Fermi gas.}, Journal = {Science (New York, N.Y.)}, Volume = {307}, Number = {5713}, Pages = {1296-1299}, Year = {2005}, Month = {February}, url = {http://www.ncbi.nlm.nih.gov/pubmed/15681340}, Abstract = {We have measured the heat capacity of an optically trapped, strongly interacting Fermi gas of atoms. A precise addition of energy to the gas is followed by single-parameter thermometry, which determines the empirical temperature parameter of the gas cloud. Our measurements reveal a clear transition in the heat capacity. The energy and the spatial profile of the gas are computed using a theory of the crossover from Fermi to Bose superfluids at finite temperatures. The theory calibrates the empirical temperature parameter, yields excellent agreement with the data, and predicts the onset of superfluidity at the observed transition point.}, Doi = {10.1126/science.1109220}, Key = {fds248510} } @article{fds248515, Author = {Kinast, J and Turlapov, A and Thomas, JE}, Title = {Breakdown of hydrodynamics in the radial breathing mode of a strongly interacting Fermi gas}, Journal = {Physical Review A - Atomic, Molecular, and Optical Physics}, Volume = {70}, Number = {5 A}, Pages = {051401(R)}, Publisher = {American Physical Society (APS)}, Year = {2004}, Month = {November}, ISSN = {1050-2947}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000225479000008&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Abstract = {The magnetic-field dependence of the frequency and damping time for the radial breathing mode of an optically trapped Fermi gas of 6Li atoms near a Feshbach resonance was investigated. For fields near 1080 G, a breakdown of hydrodynamic behavior was observed, which was manifested by a sharp increase in frequency and damping rate. It was observed that when the Feshbach molecular state in the singlet potential has a higher energy than the two-particle Fermi energy, the system becomes BCS-like. The results show that at higher fields near 925 G, the frequency decreased, and an abrupt frequency increased at a field of 1080 G, accompanied by rapid damping.}, Doi = {10.1103/PhysRevA.70.051401}, Key = {fds248515} } @article{fds248516, Author = {Kinast, J and Hemmer, SL and Gehm, ME and Turlapov, A and Thomas, JE}, Title = {Evidence for superfluidity in a resonantly interacting Fermi gas.}, Journal = {Physical review letters}, Volume = {92}, Number = {15}, Pages = {150402}, Year = {2004}, Month = {April}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/15169270}, Abstract = {We observe collective oscillations of a trapped, degenerate Fermi gas of 6Li atoms at a magnetic field just above a Feshbach resonance, where the two-body physics does not support a bound state. The gas exhibits a radial breathing mode at a frequency of 2837(05) Hz, in excellent agreement with the frequency of nu(H) identical with sqrt[10nu(x)nu(y)/3]=2830(20) Hz predicted for a hydrodynamic Fermi gas with unitarity-limited interactions. The measured damping times and frequencies are inconsistent with predictions for both the collisionless mean field regime and for collisional hydrodynamics. These observations provide the first evidence for superfluid hydrodynamics in a resonantly interacting Fermi gas.}, Doi = {10.1103/physrevlett.92.150402}, Key = {fds248516} } @article{fds248514, Author = {Lee, KF and Thomas, JE}, Title = {Entanglement with classical fields}, Journal = {Physical Review A - Atomic, Molecular, and Optical Physics}, Volume = {69}, Number = {5 A}, Pages = {052311}, Publisher = {American Physical Society (APS)}, Year = {2004}, Month = {January}, ISSN = {1050-2947}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000221813700049&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Abstract = {A simple classical-field optical heterodyne method which employs postselection to reproduce the polarization correlations of four-particle entangled state was experimentally analyzed. A heuristic argument relating this method to the measurement of multiple quantum fields by correlated homodyne detection was given. The polarization correlations of the 32 elements in the truth table from the quantum mechanical Greenberger-Horne-Zeilinger experiments on the violation of local realism were reproduced. A form of classical entanglement swapping in a four-particle basis was also demonstrated.}, Doi = {10.1103/PhysRevA.69.052311}, Key = {fds248514} } @article{fds248513, Author = {Thomas, J and Gehm, M}, Title = {Optically Trapped Fermi Gases}, Journal = {American Scientist}, Volume = {92}, Number = {3}, Pages = {238-238}, Publisher = {Sigma Xi}, Year = {2004}, ISSN = {0003-0996}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000220792000020&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Doi = {10.1511/2004.47.930}, Key = {fds248513} } @article{fds303754, Author = {Gehm, ME and Hemmer, SL and O’Hara, KM and Thomas, JE}, Title = {Unitarity-limited elastic collision rate in a harmonically trapped Fermi gas}, Journal = {Physical Review A - Atomic, Molecular, and Optical Physics}, Volume = {68}, Number = {1}, Pages = {4}, Publisher = {American Physical Society (APS)}, Year = {2003}, Month = {January}, url = {http://arxiv.org/abs/cond-mat/0304633v1}, Abstract = {We derive the elastic collision rate for a harmonically trapped Fermi gas in the extreme unitarity limit where the s-wave scattering cross section is [Formula Presented] with [Formula Presented] the relative momentum. The collision rate is given in the form [Formula Presented]—the product of a universal collision rate [Formula Presented] and a dimensionless function of the ratio of the temperature T to the Fermi temperature [Formula Presented] We find that I has a peak value of [Formula Presented] at [Formula Presented] [Formula Presented] for [Formula Presented] and [Formula Presented] for [Formula Presented] We estimate the collision rate for recent experiments on a strongly-interacting degenerate Fermi gas of atoms. © 2003 The American Physical Society.}, Doi = {10.1103/PhysRevA.68.011603}, Key = {fds303754} } @article{fds303755, Author = {Gehm, ME and Hemmer, SL and Granade, SR and O’Hara, KM and Thomas, JE}, Title = {Mechanical stability of a strongly interacting Fermi gas of atoms}, Journal = {Physical Review A - Atomic, Molecular, and Optical Physics}, Volume = {68}, Number = {1}, Pages = {4}, Publisher = {American Physical Society (APS)}, Year = {2003}, Month = {January}, url = {http://arxiv.org/abs/cond-mat/0212499v2}, Abstract = {A strongly attractive, two-component Fermi gas of atoms exhibits universal behavior and should be mechanically stable as a consequence of the quantum-mechanical requirement of unitarity. This requirement limits the maximum attractive force to a value smaller than that of the outward Fermi pressure. To experimentally demonstrate this stability, we use all-optical methods to produce a highly degenerate, two-component gas of [Formula Presented] atoms in an applied magnetic field near a Feshbach resonance, where strong interactions are observed. We find that gas is stable at densities far exceeding that predicted previously for the onset of mechanical instability. Further, we provide a temperature-corrected measurement of an important, universal, many-body parameter, which determines the stability—the mean-field contribution to the chemical potential in units of the local Fermi energy. © 2003 The American Physical Society.}, Doi = {10.1103/PhysRevA.68.011401}, Key = {fds303755} } @article{fds248517, Author = {Thomas, JE and Hemmer, SL and Kinast, J and Turlapov, A and Gehm, ME and O'Hara, KM}, Title = {Dynamics of a highly-degenerate, strongly-interacting Fermi gas of atoms}, Journal = {Journal of Low Temperature Physics}, Volume = {104}, Number = {1-2}, Pages = {655-664}, Publisher = {World Scientific}, Year = {2003}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000229968900021&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Abstract = {We use all-optical methods to produce a highly-degenerate, Fermi gas of 6 Li atoms near a Feshbach resonance, where strong interactions are predicted. In this regime, the zero-energy scattering length is larger than the interparticle spacing, and both the mean field energy and the collision rate take on universal forms as a consequence of unitarity and many-body interactions. Our experiments study universal hydrodynamic expansion of the gas and universal mean field interactions. By measuring the cloud radii of the trapped gas, we determine a universal parameter for strongly interacting two-component Fermi systems, the ratio of the mean field energy to the kinetic energy. © 2004 Plenum Publishing Corporation.}, Doi = {10.1023/b:jolt.0000012624.69815.77}, Key = {fds248517} } @article{fds248538, Author = {O'Hara, KM and Hemmer, SL and Gehm, ME and Granade, SR and Thomas, JE}, Title = {Observation of a strongly interacting degenerate Fermi gas of atoms.}, Journal = {Science (New York, N.Y.)}, Volume = {298}, Number = {5601}, Pages = {2179-2182}, Year = {2002}, Month = {December}, url = {http://www.ncbi.nlm.nih.gov/pubmed/12424386}, Abstract = {We report on the observation of a highly degenerate, strongly interacting Fermi gas of atoms. Fermionic lithium-6 atoms in an optical trap are evaporatively cooled to degeneracy using a magnetic field to induce strong, resonant interactions. Upon abruptly releasing the cloud from the trap, the gas is observed to expand rapidly in the transverse direction while remaining nearly stationary in the axial direction. We interpret the expansion dynamics in terms of collisionless superfluid and collisional hydrodynamics. For the data taken at the longest evaporation times, we find that collisional hydrodynamics does not provide a satisfactory explanation, whereas superfluidity is plausible.}, Doi = {10.1126/science.1079107}, Key = {fds248538} } @article{fds248537, Author = {Lee, KF and Thomas, JE}, Title = {Experimental simulation of two-particle quantum entanglement using classical fields.}, Journal = {Physical review letters}, Volume = {88}, Number = {9}, Pages = {097902}, Year = {2002}, Month = {March}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/11864055}, Abstract = {We experimentally demonstrate simulation of two entangled quantum bits using classical fields of two frequencies and two polarizations. Multiplication of optical heterodyne beat signals from two spatially separated regions simulates coincidence detection of two particles. The product signal so obtained contains several frequency components, one of which can be selected by bandpass frequency filtering. The bandpassed signal contains two indistinguishable, interfering contributions, permitting simulation of four polarization-entangled Bell-like states. These classical field methods may be useful in small scale simulations of quantum logic operations that require multiparticle entanglement without collapse.}, Doi = {10.1103/physrevlett.88.097902}, Key = {fds248537} } @article{fds248539, Author = {Granade, SR and Gehm, ME and O'Hara, KM and Thomas, JE}, Title = {All-optical production of a degenerate Fermi gas.}, Journal = {Physical review letters}, Volume = {88}, Number = {12}, Pages = {120405}, Year = {2002}, Month = {March}, ISSN = {0031-9007}, url = {http://www.ncbi.nlm.nih.gov/pubmed/11909435}, Abstract = {We achieve degeneracy in a mixture of the two lowest hyperfine states of 6Li by direct evaporation in a CO2 laser trap, yielding the first all optically produced degenerate Fermi gas. More than 10(5) atoms are confined at temperatures below 4 microK at full trap depth, where the Fermi temperature for each state is 8 microK. This degenerate two-component mixture is ideal for exploring mechanisms of superconductivity ranging from Cooper pairing to Bose-Einstein condensation of strongly bound pairs.}, Doi = {10.1103/physrevlett.88.120405}, Key = {fds248539} } @article{fds303757, Author = {O’Hara, KM and Hemmer, SL and Granade, SR and Gehm, ME and Thomas, JE and Venturi, V and Tiesinga, E and Williams, CJ}, Title = {Measurement of the zero crossing in a Feshbach resonance of fermionic [Formula Presented]}, Journal = {Physical Review A - Atomic, Molecular, and Optical Physics}, Volume = {66}, Number = {4}, Pages = {4}, Publisher = {American Physical Society (APS)}, Year = {2002}, Month = {January}, url = {http://arxiv.org/abs/cond-mat/0207717v1}, Abstract = {We measure a zero crossing in the scattering length of a mixture of the two lowest hyperfine states of [Formula Presented] To locate the zero crossing, we monitor the decrease in temperature and atom number arising from evaporation in a [Formula Presented] laser trap as a function of magnetic field B. The temperature decrease and atom loss are minimized for [Formula Presented] consistent with no evaporation. We also present preliminary calculations using potentials that have been constrained by the measured zero crossing and locate a broad Feshbach resonance at [Formula Presented] in agreement with previous theoretical predictions. In addition, our theoretical model predicts a second and much narrower Feshbach resonance near 55 mT. 5555 2002 The American Physical Society.}, Doi = {10.1103/PhysRevA.66.041401}, Key = {fds303757} } @article{fds4968, Author = {F. Reil and J. E. Thomas}, Title = {Time-resolved, two-window measurement of Wigner functions for coherent backscatter from a turbid medium}, Journal = {Proc. SPIE}, Volume = {4705}, Pages = {22-29}, Booktitle = {Saratov Fall Meeting 2001: Coherent Optics of Ordered and Random Media II}, Editor = {Dmitry A. Zimnyakov}, Year = {2002}, Key = {fds4968} } @article{fds4969, Author = {S. R. Granade and M. E. Gehm and K. M. O’Hara and J.E. Thomas}, Title = {Preparation of a degenerate, two-component Fermi gas by evaporation in a single beam optical trap}, Volume = {74}, Series = {Postconference Edition}, Pages = {169-170}, Booktitle = {OSA Trends in Optics and Photonics (TOPS) Quantum Electronics and Laser Science Conference (QELS 2002), OSA Technical Digest}, Publisher = {Optical Society of America, Washington, D.C.}, Year = {2002}, Key = {fds4969} } @article{fds4971, Author = {J. E. Thomas and S. R. Granade and M. E. Gehm and M.-S. Chang and K. M. O’Hara}, Title = {Optical trapping of a two-component Fermi gas}, Pages = {46-54}, Booktitle = {Proceedings of the XV International Conference on Laser Spectroscopy}, Publisher = {World Scientific, New Jersey}, Editor = {S. Chu and V. Vuletic and A. J. Kerman and C. Chin}, Year = {2002}, Key = {fds4971} } @article{fds4963, Author = {K. M. O’Hara and S. R. Granade and M. E. Gehm and M.-S. Chang and J. E. Thomas}, Title = {Modeling the evaporative cooling of fermionic atoms in an optical trap}, Journal = {OSA Trends in Optics and Photonics (TOPS)}, Volume = {57}, Series = {Postconference Edition}, Pages = {253}, Booktitle = {Quantum Electronics and Laser Science Conference (QELS 2001), Technical Digest}, Publisher = {Optical Society of America, Washington, DC,}, Year = {2001}, Key = {fds4963} } @article{fds4964, Author = {M. E. Gehm and S. R. Granade and M.-S. Chang and K. M. O’Hara and J.E. Thomas}, Title = {Optically trapped Fermi gas}, Volume = {57}, Series = {Postconference Edition}, Pages = {253-254}, Booktitle = {OSA Trends in Optics and Photonics Quantum Electronics and Laser Science Conference}, Publisher = {Optical Society of America, Washington, DC}, Year = {2001}, Key = {fds4964} } @article{fds4965, Author = {K. F. Lee and F. Reil and J.E. Thomas}, Title = {Classical-wave analogs of quantum measurement}, Volume = {57}, Series = {Postconference Edition}, Pages = {62-63}, Booktitle = {OSA Trends in Optics and Photonics (TOPS) Quantum Electronics and Laser Science Conference (QELS 2001), Technical Digest}, Publisher = {Optical Society of America, Washington, D.C.}, Year = {2001}, Key = {fds4965} } @article{fds4966, Author = {F. Reil and K. F. Lee and J.E. Thomas}, Title = {Two-window heterodyne methods for measurement of optical coherence in multiple scattering media}, Volume = {57}, Series = {Postconference edition}, Pages = {145-146}, Booktitle = {OSA Trends in Optics and Photonics (TOPS) Quantum Electronics and Laser Science Conference (QELS 2001), Technical Digest}, Publisher = {Optical Society of America, Washington, DC}, Year = {2001}, Key = {fds4966} } @article{fds248518, Author = {O’Hara, KM and Thomas, JE}, Title = {Standing room only at the quantum scale}, Journal = {Science}, Volume = {291}, Number = {5513}, Pages = {2556}, Year = {2001}, url = {http://dx.doi.org/10.1126/science.1060025}, Doi = {10.1126/science.1060025}, Key = {fds248518} } @article{fds248519, Author = {O’Hara, KM and Gehm, ME and Granade, SR and Thomas, JE}, Title = {Scaling laws for evaporative cooling in time-dependent optical traps}, Journal = {Phys. Rev. A}, Volume = {64}, Number = {5}, Pages = {051403(R)}, Publisher = {American Physical Society (APS)}, Year = {2001}, ISSN = {1050-2947}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000172074200006&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Abstract = {We derive scaling laws for the number of atoms, collision rate, and phase-space density as a function of trap depth for evaporative cooling in an adiabadically lowered optical trap. The results are in excellent agreement with a Boltzmann equation model and show that very large increases in phase-space density can be obtained without excessive slowing of the evaporation rate. Predictions are in reasonable agreement with a recent experiment that achieves Bose-Einstein condensation by evaporation in an optical trap. We also discuss evaporation of fermionic mixtures and explain why Pauli blocking does not strongly inhibit cooling. © 2001 The American Physical Society.}, Doi = {10.1103/PhysRevA.64.051403}, Key = {fds248519} } @article{fds248520, Author = {O’Hara, KM and Granade, SR and Gehm, ME and Thomas, JE}, Title = {Loading Dynamics of CO2 Laser Traps}, Journal = {Phys. Rev. A}, Volume = {63}, Number = {4}, Pages = {043403}, Year = {2001}, ISSN = {1050-2947}, url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000168095300076&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=47d3190e77e5a3a53558812f597b0b92}, Abstract = {We present a simple Fokker-Planck model for the evolution of the number of atoms and the spatial distribution in a CO2 laser trap which is loaded from a magneto-optical trap (MOT). Deep CO2 laser traps can achieve very high densities, but reach equilibrium slowly compared to shallow traps. Equilibrium times range from milliseconds for shallow traps to seconds in traps which are deep compared to the thermal energy. A universal function for the maximum number of trapped atoms is given, assuming that the optical dipole trap reaches thermal equilibrium with the MOT. ©2001 The American Physical Society.}, Doi = {10.1103/PhysRevA.63.043403}, Key = {fds248520} } @article{fds248521, Author = {O'Hara, KM and Gehm, ME and Granade, SR and Bali, S and Thomas, JE}, Title = {Stable, strongly attractive, two-state mixture of lithium fermions in an optical trap}, Journal = {Physical review letters}, Volume = {85}, Number = {10}, Pages = {2092-2095}, Year = {2000}, Month = {September}, url = {http://www.ncbi.nlm.nih.gov/pubmed/10970470}, Abstract = {We use an all-optical trap to confine a strongly attractive two-state mixture of lithium fermions. By measuring the rate of evaporation from the trap, we determine the effective elastic scattering cross section 4pia(2) to show that the magnitude of the scattering length |a| is very large, in agreement with predictions. We show that the mixture is stable against inelastic decay provided that a small bias magnetic field is applied. For this system, the s-wave interaction is widely tunable at low magnetic field, and can be turned on and off rapidly via a Raman pi pulse. Hence, this mixture is well suited for fundamental studies of an interacting Fermi gas.}, Doi = {10.1103/physrevlett.85.2092}, Key = {fds248521} } @article{fds4954, Author = {A. Wax and F. Reil and K. F. Lee and S. Bali and J. E. Thomas}, Title = {Time-resolved optical phase space distributions for coherent backscatter}, Journal = {Proc. SPIE}, Volume = {4001}, Pages = {130-134}, Booktitle = {Saratov Fall Meeting ‘99: Optical Technologies in Biophysics and Medicine}, Editor = {Valery V. Tuchin and Dmitry A Zimnyakov and Alexander B. Pravdin}, Year = {2000}, Key = {fds4954} } @article{fds4959, Author = {J. E. Thomas and F. Reil and K. F. Lee and A. Wax and S. Bali}, Title = {Wigner Phase Space Distributions and Coherence Tomography}, Journal = {to appear in Proc. SPIE}, Volume = {3914}, Year = {2000}, Key = {fds4959} } @article{fds4960, Author = {J. E. Thomas and F. Reil and K. F Lee and A. Wax and S. Bali}, Title = {Wigner Phase Space Distributions and Coherence Tomography}, Journal = {Proc. SPIE}, Volume = {3927}, Pages = {147-155}, Booktitle = {Optical Pulse and Beam Propagation II}, Editor = {Yehuda B Band}, Year = {2000}, Key = {fds4960} } @article{fds248522, Author = {Wax, A and Bali, S and Thomas, JE}, Title = {Path-length-resolved optical phase space distributions for enhanced backscatter}, Journal = {Phys. Rev. Lett.}, Volume = {85}, Pages = {66}, Year = {2000}, Key = {fds248522} } @article{fds248524, Author = {Lee, KF and Reil, F and Bali, S and Wax, A and Thomas, JE}, Title = {Heterodyne measurement of Wigner distributions for classical optical fields.}, Journal = {Optics letters}, Volume = {24}, Number = {19}, Pages = {1370-1372}, Year = {1999}, Month = {October}, ISSN = {0146-9592}, url = {http://dx.doi.org/10.1364/ol.24.001370}, Abstract = {We demonstrate a two-window heterodyne method for measuring the x-p cross correlation, ??(*)(x)? (p)?, of an optical field ? for transverse position x and transverse momentum p. This scheme permits independent control of the x and p resolution. A simple linear transform of the x-p correlation function yields the Wigner phase-space distribution. This technique is useful for both coherent and low-coherence light sources and may permit new biological imaging techniques based on transverse coherence measurement with time gating. We point out an interesting analogy between x-p correlation measurements for classical-wave and quantum fields.}, Doi = {10.1364/ol.24.001370}, Key = {fds248524} } @article{fds248526, Author = {Wax, A and Bali, S and Thomas, JE}, Title = {Optical phase-space distributions for low-coherence light.}, Journal = {Optics letters}, Volume = {24}, Number = {17}, Pages = {1188-1190}, Year = {1999}, Month = {September}, ISSN = {0146-9592}, url = {http://dx.doi.org/10.1364/ol.24.001188}, Abstract = {Using a novel heterodyne technique, we measure optical phase-space distributions in momentum and position for low-coherence light. Quantitative information is obtained simultaneously about the longitudinal and the transverse coherence properties as well as the wave-front curvature of the light field. This method can be used to monitor these optical parameters directly for signal fields scattered from samples of interest, for tomographic imaging.}, Doi = {10.1364/ol.24.001188}, Key = {fds248526} } @article{fds4946, Author = {A. Wax and J. E. Thomas}, Title = {Measurement of Smoothed Wigner Phase Space Distributions for Low-Coherence Light in Multiple Scattering Media}, Journal = {Proc. SPIE}, Volume = {3598}, Pages = {2}, Booktitle = {Coherence Domain Optical Methods in Biomedical Science and Clinical Applications III}, Editor = {Valery V. Tuchin and Joseph A. Izatt}, Year = {1999}, Month = {January}, Key = {fds4946} } @article{fds303756, Author = {O’hara, KM and Granade, SR and Gehm, ME and Savard, TA and Bali, S and Freed, C and Thomas, JE}, Title = {Ultrastable CO | |
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