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Dynamical decoupling (DD) is normally ineffective when applied to DC measurement. In its straightforward implementation, DD nulls out DC signal as well while suppressing noise. This work proposes a phase relay method that is capable of continuously interrogating the DC signal over many DD cycles. We illustrate its efficacy when applied to the measurement of a weak DC magnetic field with an atomic spinor Bose–Einstein condensate. Sensitivities approaching standard quantum limit or Heisenberg limit are potentially realizable for a coherent spin state or a squeezed spin state of 10000 atoms, respectively, while ambient laboratory level noise is suppressed by DD. Our work offers a practical approach to mitigate the limitations of DD to DC measurement and would find other applications for resorting coherence in quantum sensing and quantum information processing research. [ABSTRACT FROM AUTHOR]

A unified and empirically adequate microscopic theory of novel pseudogap phenomena and Bose-liquid superconductivity and superfluidity in high- T c cuprates and other systems is developed based on the original ideas of the pseudogap state and unusual superconducting/superfluid states of matter. This theory establishes the following laws: (i) the high- T c cuprates and other systems with low Fermi energies ε F ∼ ε A (where ε A is the energy of the attractive interaction between fermionic quasiparticles) are bosonic superconductors and superfluids exhibiting pseudogap behavior above the superconducting/superfluid transition temperature T c and a λ -like phase transition at T c , (ii) the pseudogap state and bosonic Cooper pairs in such systems (with ε F ≲ 2 ε A and Bardeen–Cooper–Schrieffer (BCS)-like gap Δ F ≳ 0.17 ε F ) are formed above T c , (iii) only a minority of preformed bosons condenses into a Bose superfluid at T c and (iv) only the systems with ε F > > ε A > > Δ F become BCS-type conventional or topological fermionic superconductors and superfluids. A modified BCS-like model describes the precursor Cooper pairing of fermionic quasiparticles and the formation of bosonic Cooper pairs above T c . The criteria for the bosonization of Cooper pairs and fermion–boson transitions are formulated. The mean-field theory describing new laws of condensation of attracting bosons into Bose superfluids below T c is presented. The proposed microscopic theory explains all the emerging pseudogap behaviors and unusual superconducting/superfluid states and properties of high- T c materials and other systems. In high- T c cuprates, the unconventional electron–phonon interactions and polaronic effects give rise to in-gap states, Fermi-surface reconstruction, two distinct pseudogaps and unusual normal-state properties, a quantum critical point and crossover from BCS superconductivity to Bose-liquid superconductivity. The theory of three-dimensional (3D) and two-dimensional (2D) Bose superfluids describes fairly well the novel superconducting states (i.e., the so-called A and B phases below T c and an extended A phase and related vortex-like state above T c ) and properties of high- T c cuprates (e.g., λ -like transition at T c , first-order phase transition at lower temperatures and other unusual features) in accordance with the experimental data. The reasons for suppression and enhancement of superconductivity by disorders in high- T c cuprates are discussed. Strongly enhanced 2D Bose-liquid superconductivity emerging within a 3D cuprate superconductor (with the highest bulk T c ) persists up to room temperature in multi-lamellar blocks and at grain boundaries and interfaces. Most enhanced 3D Bose-liquid superconductivity can emerge at room temperature in high- T c hydrides under high pressures. Superconducting/superfluid states and properties of heavy-fermion and organic compounds, ruthenate (Sr 2 RuO 4) and possibly high- T c hydrides, quantum liquids ( 3 He and 4 He ) and atomic Fermi gases are also well explained by the proposed theory of Bose superfluids. Finally, new criteria and principles of unconventional superconductivity and superfluidity are formulated. [ABSTRACT FROM AUTHOR]

This work is a theoretical study of the excitons relaxation dynamics in cuprous oxide at ultra-low temperatures and within a potential trap. Exciton–phonon collisions and exciton–exciton collisions have been included as relaxation processes. Special attention is given to the thermal distribution, cooling process and the condensation of the exciton gas with high number of excitons. It has been done by solving the Boltzmann equation numerically, using MATLAB. In this work, the relaxation behaviour has been analysed for the temperatures between 0.1 and 3 K. It has been found that for the temperatures above 0.1 K the local effective temperatures are coming down to the bath temperatures, i.e. the excitons reach the local equilibrium with the lattice, but for 0.1 K it does not happen. For 3 K, the global distributions do not change at all with time, but for 0.1 K this change is significant. Maybe this thermal loss of excitons for 0.1 K is related to the Bose–Einstein condensation of excitons. Interestingly, for the temperature of 0.1 K the condensate has been formed with sufficiently high number of excitons, for the times larger than 300 ns. Also, the results have been compared with the other theoretical results. [ABSTRACT FROM AUTHOR]

We consider theoretically static and dynamic properties of vortex formation in trapped Bose-Einstein condensates in synthetic magnetic field and compare the results created by rotating frame method. As the first step, we discuss the ground state properties and show that the number of vortices and rotational frequency is a linear relation. We further deduce the analytical results and find it qualitatively agrees with numerical solutions. In addition, we explore the vortex dynamics, focusing on the difference between the two rotational methods. Numerical results indicate that synthetic magnetic field is more difficult to add a large angular momentum. However, this issue can be effectively improved by increasing the contact interaction. [ABSTRACT FROM AUTHOR]

We suggest to subject anharmonically trapped Bose-Einstein condensates to sinusoidal forcing with a smooth, slowly changing envelope, and to measure the coherence of the system after such pulses. In a series of measurements with successively increased maximum forcing strength, one then expects an adiabatic return of the condensate to its initial state as long as the pulses remain sufficiently weak. In contrast, once the maximum driving amplitude exceeds a certain critical value there should be a drastic loss of coherence, reflecting significant heating induced by the pulse. This predicted experimental signature is traced to the loss of an effective adiabatic invariant, and to the ensuing breakdown of adiabatic motion of the system's Floquet state when the many-body dynamics become chaotic. Our scenario is illustrated with the help of a two-site model of a forced bosonic Josephson junction, but should also hold for other, experimentally accessible configurations. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Physics is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We present here our experimental results on transfer of laser-cooled atom cloud to a quadrupole magnetic trap. We show that by choosing appropriately the ratio of potential energy in magnetic trap to kinetic energy of cloud in molasses, we can obtain the maximum phase-space density in the magnetic trap. These results guide us to choose the value of current to be switched in the quadrupole coils used for magnetic trapping for a given temperature of the cloud after molasses. This study is also useful to set the initial phase-space density of the cloud before evaporative cooling. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Physics is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

One possible way to produce ultra-cold, high-phase-space-density quantum gases of molecules in the rovibronic ground state is given by molecule association from quantum-degenerate atomic gases on a Feshbach resonance and subsequent coherent optical multi-photon transfer into the rovibronic ground state. In ultra-cold samples of Cs2 molecules, we observe two-photon dark resonances that connect the intermediate rovibrational level | v=73, J=2〉 with the rovibrational ground state | v=0, J=0〉 of the singlet X1 Σ ground-state potential. For precise dark resonance spectroscopy we exploit the fact that it is possible to efficiently populate the level | v=73, J=2〉 by two-photon transfer from the dissociation threshold with the stimulated Raman adiabatic passage (STIRAP) technique. We find that at least one of the two-photon resonances is sufficiently strong to allow future implementation of coherent STIRAP transfer of a molecular quantum gas to the rovibrational ground state | v=0, J=0〉. [ABSTRACT FROM AUTHOR]

The stochastic Gross-Pitaevskii equation represents a versatile approach for studying the dynamics of trapped degenerate ultracold Bose gases in the presence of large phase and density fluctuations. Following a brief review of the original formulation of Stoof, which highlights the benefits of this approach and its relation to alternative theories, we present selected applications for the dynamics of effectively one-dimensional systems, and briefly discuss the generalization to two-dimensional systems, highlighting certain potential pitfalls in their numerical implementations. [ABSTRACT FROM AUTHOR]

This article reviews recent progresses in ultracold quantum gases, and it includes three subjects which are the Fermi gases across a Feshbach resonance, quantum gases in the optical lattices and the fast rotating quantum gases. In this article, we discuss many basic physics pictures and concepts in quantum gases, for examples, the resonant interaction, universality and condensation in the lowest Landau level; we introduce fundamental theoretical tools for studying these systems, such as mean-field theory for BEC-BCS crossover and for the boson Hubbard model; also, we emphasize the important unsolved problems in the forefront of this field, for instance, the temperature effect in optical lattices. [ABSTRACT FROM AUTHOR]