Interference of atomic levels and superfluid-Mott insulator phase transitions in a two-component Bose-Einstein condensate

The superfluid-Mott insulator phase transition in a Bose-Einstein condensate of neutral atoms with doubly degenerate internal ground states in an optical lattice is theoretically investigated. The optical lattice is created by two counterpropagating linearly polarized laser beams with the angle theta between the polarization vectors (lin-angle-lin configuration). The phase diagram of the system and the critical values of the parameters are worked out. It is shown that the sign of the detuning plays an important role and that there is a strong suppression of the Mott transition in the case of blue detuning. Varying the laser intensity and/or the angle theta one can manipulate the Mott insulator to superfluid quantum phase transition as well as prepare the condensate in physically distinguishable "ferromagnetic" and "antiferromagnetic" superfluid states.     

Differential sum rule for the relaxation rate in the cuprates

Motivated by recent experiments by Basov et al., we study the differential sum rule for the effective scattering rate 1/tau(omega). We show that, in a dirty BCS superconductor, the area under 1/tau(omega) does not change between the normal and the superconducting states. For magnetically mediated pairing, a similar result holds between Tor=T(c), while, in the pseudogap phase, 1/tau(omega) is just suppressed compared to 1/tau(omega) in the normal state. We argue that this violation of the differential sum rule in the pseudogap phase is due to the absence of the feedback effects from the pairing.     

Bose-einstein condensation in quasi-2D trapped gases

We discuss Bose-Einstein condensation (BEC) in quasi-2D trapped gases and find that well below the transition temperature T(c) the equilibrium state is a true condensate, whereas at intermediate temperatures T相似文献   

Probing number squeezing of ultracold atoms across the superfluid-Mott insulator transition

The evolution of on-site number fluctuations of ultracold atoms in optical lattices is experimentally investigated by monitoring the suppression of spin-changing collisions across the superfluid-Mott insulator transition. For low atom numbers, corresponding to an average filling factor close to unity, large on-site number fluctuations are necessary for spin-changing collisions to occur. The continuous suppression of spin-changing collisions is thus direct evidence for the emergence of number-squeezed states. In the Mott insulator regime, we find that spin-changing collisions are suppressed until a threshold atom number, consistent with the number where a Mott plateau with doubly occupied sites is expected to form.     

New Josephson plasma modes in underdoped YBa2Cu3O6.6 induced by a parallel magnetic field

The c-axis reflectivity spectrum of underdoped YBa2Cu3O6.6 (YBCO) is measured below T(c)=59 K in parallel magnetic fields H parallel CuO2 up to 7 T. Upon application of a parallel field, a new peak appears at finite frequency in the optical conductivity at the expense of suppression of c-axis condensate weight. We conclude that the dramatic change originates from different Josephson coupling strengths between bilayers with and without Josephson vortices. We find that the 400 cm(-1) broad conductivity peak in YBCO gains the spectral weight under parallel magnetic field; this indicates that the condensate weight at omega=0 is distributed to this peak as well as to the new optical Josephson mode.     

Dynamical control of matter-wave tunneling in periodic potentials

We report on measurements of dynamical suppression of interwell tunneling of a Bose-Einstein condensate (BEC) in a strongly driven optical lattice. The strong driving is a sinusoidal shaking of the lattice corresponding to a time-varying linear potential, and the tunneling is measured by letting the BEC freely expand in the lattice. The measured tunneling rate is reduced and, for certain values of the shaking parameter, completely suppressed. Our results are in excellent agreement with theoretical predictions. Furthermore, we have verified that, in general, the strong shaking does not destroy the phase coherence of the BEC, opening up the possibility of realizing quantum phase transitions by using the shaking strength as the control parameter.     

Phase-fluctuating 3D Bose-Einstein condensates in elongated traps

We find that in very elongated 3D trapped Bose gases, even at temperatures far below the BEC transition temperature T(c), the equilibrium state will be a 3D condensate with fluctuating phase (quasicondensate). At sufficiently low temperatures the phase fluctuations are suppressed and the quasicondensate turns into a true condensate. The presence of the phase fluctuations allows for extending thermometry of Bose-condensed gases well below those established in current experiments.     

Vibrations and diverging length scales near the unjamming transition

We numerically study the vibrations of jammed packings of particles interacting with finite-range, repulsive potentials at zero temperature. As the packing fraction phi is lowered towards the onset of unjamming at phi(c), the density of vibrational states approaches a nonzero value in the limit of zero frequency. For phi >phi(c), there is a crossover frequency, omega* below which the density of states drops towards zero. This crossover frequency obeys power-law scaling with phi-phi(c). Characteristic length scales, determined from the dominant wave vector contributing to the eigenmode at omega*, diverge as power laws at the unjamming transition.     

Onset and saturation of ion heating by odd-parity rotating magnetic fields in a field-reversed configuration

Heating of figure-8 orbit ions by odd-parity rotating magnetic fields (RMF(O)) applied to an elongated field-reversed configuration (FRC) is investigated. The largest energy gain occurs at resonances (s congruent to omega(R)/omega) of the RMF(O) frequency, omega(R), with the figure-8 orbital frequency, omega, and is proportional to s2 for s-even resonances and to s for s-odd resonances. The threshold for the transition from regular to stochastic orbits explains both the onset and saturation of heating. The FRC magnetic geometry lowers the threshold for heating below that in the tokamak by an order of magnitude.     

Quantum suppression of microwave ionization of Rydberg atoms at high scaled frequency

Microwave ionization of Rydberg atoms is well described as the onset of classical chaos when the microwave frequency omega is less than the Kepler frequency 1/n(3). However, when omega>1/n(3), i.e., at high scaled frequency Omega=omegan(3)>1, classical ionization is predicted to be suppressed by quantum interference, an analogue to Anderson localization in a solid. Using 17.55 GHz microwave fields we have observed the ionization of Sr Rydberg atoms in the regime 1相似文献   

Kinetic arrest of the first-order to R3c Pbnm phase transition in supercooled La(x)MnO(3+δ) (x = 1 and 0.9)

We report the occurrence of kinetic arrest of the first-order phase transition from R3c to Pbnm in supercooled La(x)MnO(3±δ) (x = 1 and 0.9, i.e. δ > 0.125). Structural studies have been done, employing low temperature transmission electron microscopy (LT-TEM) and low temperature x-ray diffraction (LT-XRD) techniques. No phase transformation was observed even in La(x)MnO(3±δ) aged for ~12 h at 98 K. The evidence of the occurrence of kinetic arrest was realized at low temperatures through in situ electron beam triggered nucleation and perpetual devitrification of the R3c phase into a Pbnm phase. It was clearly evidenced that the R3c structure of La(x)MnO(3±δ), below its ferromagnetic transition temperature, is metastable and prone to be transformed to a Pbnm orthorhombic structure following initiation by an electron beam trigger. The electron beam transformed Pbnm phase was found to transform back to the R3c phase through a first-order phase transition occurring close to the ferromagnetic to paramagnetic transition (T(c)) during heating. The glass-like kinetics of the arrested R3c phase has been investigated through resistance relaxation measurements, showing a decreasing logarithmic rate of decay of the arrested R3c phase towards the stable Pbnm phase with decreasing temperature, down to 5 K. On the basis of the correlations observed in the resistance-versus-temperature, magnetization-versus-temperature, magnetization-versus-field, resistance relaxation and LT-XRD measurements, the occurrence of kinetic arrest has been attributed to the suppression of Jahn-Teller distortion by double exchange across the insulator-metal transition.     

Characterization of Electronic Spectra of Rhodium Monohydride and Monodeuteride

Emission spectra of two new electronic transitions of Pb(2) have been measured with a Fourier transform spectrometer in the 5200-8500 cm(-1) range. The emissions were observed from the afterglow of a microwave discharge in a mixture of Pb(x) vapor with hydrogen and argon carrier gas. By comparison with the results of ab initio calculations, the spectra are assigned to transitions from the lowest 1(g) and 1(u) states to the X(1)0(+)(g) ground state. The X(2)1(g) --> X(1)0(+)(g) transition between the fine-structure components of the X(3)Sigma(-)(g) ground state must be magnetic dipole in nature and thus is the first purely magnetic dipole fine-structure transition observed in the optical region. The 1(u) state is mostly a component of the low-lying inverted A(3)Pi(u) state and so is denoted A(2)1(u). Vibrational analyses have yielded the following electronic energies and vibrational constants for (208)Pb(2) (in cm(-1)): X(1)0(+)(g): omega(e) = 110.20(2), omega(e)x(e) = 0.341(2); X(2)1(g): T(e) = 5304.9(1), omega(e) = 120.57(7), omega(e)x(e) = 0.254(14); A(2)1(u): T(e) = 7817.5(2), omega(e) = 126.45(6), omega(e)x(e) = 0.399(11), where the numbers in parentheses are the standard deviations of the parameters. Copyright 2000 Academic Press.     

Microsecond time-scale dynamics from relaxation in the rotating frame: experiments using spin lock with alternating phase

A spin lock comprised of radiofrequency pulses with alternating phase, (x) (-x)(x) (-x) , is proposed as a new technique to probe microsecond time-scale dynamics. A series of R1rho measurements using different pulse duration tp allows one to determine exchange rate, kex, the product p(a)p(b)(Delta omega(ab))2 involving populations of the exchanging species, p(a) and p(b), together with chemical shift difference, (Delta omega(ab)), and the strength of the spin-lock field, B1. The interpretation is based on simple analytical expression for R1rho derived on the basis of Redfield theory. The application of the method is demonstrated for partially deuterated molecule of cyclohexane undergoing chair-to-chair interconversion at -9 degrees C.     

Ultrasensitive pulsed, balanced homodyne detector: application to time-domain quantum measurements

A pulsed, balanced homodyne detector has been developed for precise measurement of the electric field quadratures of pulsed optical quantum states. A high level of common mode suppression (>85 dB) and low electronic noise (730 electrons per pulse) provide a signal-to-noise ratio of 14 dB for measurement of the quantum noise of individual pulses. Measurements at repetition rates as high as 1 MHz are possible. As a test, quantum tomography of the coherent state was performed, and the Wigner function and the density matrix were reconstructed with 99.5% fidelity. The detection system can be used for ultrarsensitive balanced detection in cw mode, e.g., for weak absorption measurements.     

Phase diagram of superfluid 3He in 99.3% porosity aerogel

We report on continuous-wave NMR measurements of the energy gaps of the A-like and B-like superfluid phases of 3He at 28.4 mT confined to a 99.3% porosity silica aerogel. The gaps are suppressed by the presence of the aerogel in a temperature-independent manner, but the suppression is considerably stronger than expected from the suppression of T(c). We then use our measurements to calculate the free energy ratio between the A-like and B-like phases. The equilibrium AB transition temperature, derived from where this ratio reaches unity, is consistent with previous measurements of the initial displacement of the pinned AB interface on warming. On this basis, we present for the first time the equilibrium phase diagram of the A-like and B-like phases of superfluid 3He in aerogel.     

Magneto-oscillations due to electron-electron interactions in the ac conductivity of a two-dimensional electron gas

Electron-electron interactions give rise to the correction, deltasigma(int)(omega), to the ac magnetoconductivity, sigma(omega), of a clean 2D electron gas that is periodic in omega_(c)(-1), where omega_(c) is the cyclotron frequency. Unlike conventional harmonics of the cyclotron resonance, which are periodic with omega, this correction is periodic with omega(3/2). Oscillations in deltasigma(int)(omega) develop at low magnetic fields, omega_(c)相似文献   

Suppression of superconductivity in granular metals

We investigate the suppression of the superconducting transition temperature due to Coulomb repulsion in granular metallic systems at large tunneling conductance between the grains, g(T)>1. We find the correction to the superconducting transition temperature for 3D granular samples and films. We demonstrate that, depending on the parameters of superconducting grains, the corresponding granular samples can be divided into two groups: (i). the granular samples that belong to the first group may have only insulating or superconducting states at zero temperature depending on the bare intergranular tunneling conductance g(T), while (ii). the granular samples that belong to the second group in addition have an intermediate metallic phase where superconductivity is suppressed while the effects of the Coulomb blockade are not yet strong.     

Bound states of the Josephson degrees of freedom and trap oscillations

It is shown that the interaction of the Josephson degrees of freedom with states of condensate motion can produce their equilibrium bound states. As a result of the appearance of these states, first, the tunneling splitting is significantly increased in double-well trapped condensates. Second, the bound states can realize an absolute minimum of the thermodynamic energy for a sufficiently strong interaction. Transition to the new ground state is a second-order phase transition. The existence of the bound state leads to an equilibrium distortion of the condensate shape. This implies that the Josephson states can be detected by observing the change in the condensate shape.     

Bichromatic microwave photoresistance of a two-dimensional electron system

We explore experimentally bichromatic (frequencies omega(1) and omega(2)) photoresistance of a two-dimensional electron system in the regimes of microwave-induced resistance oscillations and zero-resistance states. We find bichromatic resistance to be well described by a superposition of omega(1) and omega(2) and components, provided that both monochromatic resistances are positive. This relation holds even when the oscillation amplitudes are small and one could expect additive contributions from monochromatic photoresistances. In contrast, whenever a zero-resistance state is formed by one of the frequencies, such superposition relation breaks down and the bichromatic resistance is strongly suppressed.     

Excitations of one-dimensional Bose-Einstein condensates in a random potential

We examine bosons hopping on a one-dimensional lattice in the presence of a random potential at zero temperature. Bogoliubov excitations of the Bose-Einstein condensate formed under such conditions are localized, with the localization length diverging at low frequency as l(omega) approximately 1/omega(alpha). We show that the well-known result alpha=2 applies only for sufficiently weak random potential. As the random potential is increased beyond a certain strength, alpha starts decreasing. At a critical strength of the potential, when the system of bosons is at the transition from a superfluid to an insulator, alpha=1. This result is relevant for understanding the behavior of the atomic Bose-Einstein condensates in the presence of random potential, and of the disordered Josephson junction arrays.