We investigate the finite-temperature properties of an ultracold atomic Fermi gas with spin population imbalance in a highly elongated harmonic trap. Previous studies at zero temperature showed that the gas stays in an exotic spatially inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superfluid state at the trap center; while moving to the edge, the system changes into either a nonpolarized Bardeen-Cooper-Schrieffer superfluid $(P<P_c)$ or a fully polarized normal gas $(P>P_c)$, depending on the smallness of the spin polarization $P$, relative to a critical value $P_c$. In this work, we show how these two phase-separation phases evolve with increasing temperature, and thereby construct a finite-temperature phase diagram. For typical interactions, we find that the exotic FFLO phase survives below one-tenth of Fermi degeneracy temperature, which seems to be accessible in the current experiment. The density profile, equation of state, and specific heat of the polarized system have been calculated and discussed in detail. Our results are useful for the ongoing experiment at Rice University on the search for FFLO states in quasi-one-dimensional polarized Fermi gases.

We consider rf spectroscopy of ultracold Fermi gases by exact simulations of the many-body state and the coherent dynamics in one dimension. Deviations from the linear response sum rule result are found to suppress the pairing contribution to the rf line shifts. We compare the coherent rotation and quasiparticle descriptions of rf spectroscopy which are analogous to NMR experiments in superfluid ${}^3\mathrm{He}$ and tunneling in solids, respectively. We suggest that rf spectroscopy in ultracold gases provides an interesting crossover between these descriptions that could be used for studying decoherence in quantum measurement, in the context of many-body quantum states.

We study procedures for the optimization of efficiency of light storage and retrieval based on the dynamic form of electromagnetically induced transparency in hot Rb vapor. We present a detailed analysis of two recently demonstrated optimization protocols: a time-reversal-based iteration procedure, which finds the optimal input signal pulse shape for any given control field, and a procedure based on the calculation of an optimal control field for any given signal pulse shape. We verify that the two procedures are mutually consistent and that they both independently achieve the maximum memory efficiency for any given optical depth. We observe good agreement with theoretical predictions for moderate optical depths $(<25)$, while at higher optical depths the experimental efficiency falls below the theoretically predicted values. We identify possible effects responsible for this reduction in memory efficiency.

The dissociative recombination of $\mathrm{B}\mathrm{H}_2{}^{+}$ has been studied at the storage ring CRYRING. The branching fraction analysis shows that dissociative recombination is dominated by the two-body $\mathrm{B}\mathrm{H}+\mathrm{H}$ channel constituting 56% of the total reactivity with the $\mathrm{B}+\mathrm{H}+\mathrm{H}$ and $\mathrm{B}+{\mathrm{H}}_2$ channels being 35 and 9%, respectively. Both the measured reaction rate and fragmentation behavior are different than for previously studied $X\mathrm{H}_2{}^{+}$ ions, which react both faster and predominantly dissociate through the full fragmentation channel. Explanations for such observations are discussed.

We present a general virial theorem for quantum particles with arbitrary zero-range or finite-range interactions in an arbitrary external potential. We deduce virial theorems for several situations relevant to trapped cold atoms: zero-range interactions with and without Efimov effect, hard spheres, narrow Feshbach resonances, and finite-range interactions. If the scattering length $a$ is varied adiabatically in a two-component Fermi gas, we find that the trapping potential energy as a function of $1∕a$ has an inflexion point at unitarity.

We reanalyzed our atom interferometer measurement of the electric polarizability of lithium, now accounting for the Sagnac effect due to the Earth’s rotation. The resulting correction to the polarizability is very small, but the visibility as a function of the applied phase shift is now better explained. The fact that the Sagnac and polarizability phase shifts are both proportional to $v^{-1}$, where $v$ is the atom velocity, suggests that a phase shift of the Sagnac type could be used as a counterphase to compensate for the electric polarizability phase shift. This exact compensation opens the way to higher-accuracy measurements of atomic polarizabilities, and we discuss how this can be done in practice and the final limitations of the proposed technique.

We show that it is possible to generate entanglement between two distant Bose-Einstein condensates by detection of Hanbury–Brown-Twiss-type correlations in photons Bragg scattered by the condensates. Upon coincident detection of two photons by two detectors, the projected joint state of two condensates is shown to be non-Gaussian. We verify the existence of entanglement by showing that the partially transposed state is negative. Further, we use the inequality in terms of higher-order moments to confirm entanglement. Our proposed scheme can be generalized for multiple condensates and also for spinor condensates with Bragg scattering of polarized light, with the latter capable of producing hyperentanglement.

We present a thorough analysis of single-atom detection using optical cavities. The large set of parameters that influence the signal-to-noise ratio for cavity detection is considered, with an emphasis on detunings, probe power, cavity finesse, and photon detection schemes. Real device operating restrictions for single photon counting modules and standard photodiodes are included in our discussion, with heterodyne detection emerging as the clearly favorable technique, particularly for detuned detection at high power.

Mode-exchange collisions occur in multimode Bose-Einstein condensates, in some cases, producing particle loss in the system. Nevertheless, little is known about mode-exchange collisions in the case when particles do not escape the trap. We show that these processes are relevant in quantum properties of the system such as the evolution of the relative population, the self-trapping effect, and the probability distribution of particles. Surprisingly, including mode-exchange terms in the model of the two-mode condensate allows for an exact analytical solution. Using this solution, we show that collisions favor the generation of entanglement between the modes of the condensate.

A relaxation method is employed to study a rotating dense Bose-Einstein condensate beyond the Thomas-Fermi approximation. We use a slave-boson model to describe the strongly interacting condensate and derive a generalized nonlinear Schrödinger equation with a kinetic term for the rotating condensate. In comparison with previous calculations, based on the Thomas-Fermi approximation, significant improvements are found in regions where the condensate in a trap potential is not smooth. The critical angular velocity of the vortex formation is higher than in the Thomas-Fermi prediction.

We address nonlinear signal switching between two low-index defect channels induced in periodic optical lattices. In contrast to conventional directional couplers, where the guiding mechanism is total internal reflection or refraction, in such a Bragg-type coupler, the guidance is of a photonic–band-gap origin. The coupling length in the low-index coupler is controlled by the lattice parameters and by the channel spacing. In the nonlinear regime the Bragg-type coupler behaves as an all-optical switch, exhibiting a remarkable difference of switching power for focusing versus defocusing nonlinearity.

It is numerically shown that the Petermann excess noise factor diverges to infinity at an exceptional point (EP) found near an avoided resonance crossing in a stadium-shaped dielectric microcavity. Square-root singularity of eigenvalue at the EP is explicitly demonstrated in two-dimensional parameter space spanned by refractive index and deformation parameter. The results imply that mode-mode interaction makes the Petermann factor large.

We report the observation of a delayed all-optical routing using an ultraslow-light phenomenon in a defected solid medium. Unlike simultaneously enhanced slow-light-based four-wave mixing processes, the present observation demonstrates on-demand delayed all-optical routing via the direct retrieval of atomic coherence strongly coupled with the slow light.

We experimentally and theoretically study the broadening of paramagnetic resonance lines by transverse magnetic field gradients when a perturbative description is inadequate. The experiments are performed with an evanescent wave magnetometer using an octadecyltrichlorosilane-coated glass cell containing ${}^{87}\text{R}\text{b}$ and ${\text{N}}_2$ buffer gas. We find that the transverse broadening of the resonance line is inversely proportional to the square root of the holding field. We also provide a quantitative theoretical explanation of the experimental results.

We discuss double ionization of atoms in strong laser pulses using a reduced dimensionality model. Following the insight obtained from an analysis of the classical mechanics of the process, we confine each electron to move along the lines that point towards the two-particle Stark saddle in the presence of a field. The resulting effective two-dimensional model is similar to the aligned electron model, but it enables correlated escape of electrons with equal momenta, as observed experimentally. The time-dependent solution of the Schrödinger equation allows us to discuss in detail the time dynamics of the ionization process, the formation of electronic wave packets, and the development of the momentum distribution of the outgoing electrons. In particular, we are able to identify the rescattering process, simultaneous direct double ionization during the same field cycle, as well as other double ionization processes. We also use the model to study the phase dependence of the ionization process.

We explore the pairing properties of the one-dimensional attractive Hubbard model in the presence of finite spin polarization. The correlation exponents for the most important fluctuations are determined as a function of the density and the polarization. We find that in a system with spin population imbalance, Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-type pairing at wave vector $Q=\mid k_{F,\uparrow }-k_{F,\downarrow }\mid$ is always dominant and there is no Chandrasekhar-Clogston limit. We then investigate the case of weakly coupled one-dimensional (1D) systems and determine the region of stability of the 1D FFLO phase. This picture is corroborated by density-matrix-renormalization-group simulations of the spatial noise correlations in uniform and trapped systems, unambiguously revealing the presence of fermion pairs with nonzero momentum $Q$. This opens up an interesting possibility for experimental studies of FFLO states.

A method is proposed and considered theoretically for using phase-sensitive amplification as the intensity-discrimination (saturable absorption) element in a laser cavity to generate stable and robust mode-locking. The phase-sensitive amplifier acts as a phase filter for selecting the specific intensity-dependent phase rotation of the mode-locked pulse that locks the phase to the amplifier pump phase. The nonlinear phase rotation is analogous to the nonlinear polarization rotation which is used with passive polarizers for mode-locking. It is demonstrated that the phase-sensitive amplification mechanism can indeed result in stable mode-locking. An average cavity model explicitly calculates the stability of the mode-locked pulses.

We investigate the influence of atomic transit time $\tau$ on the laser linewidth by the quantum Langevin approach. With comparing the bandwidths of cavity mode $\kappa$, atomic polarization ${\gamma }_{ab}$, and atomic transit broadening ${\tau }^{-1}$, we study the laser linewidth in different limits. We also discuss the spectrum of fluctuations of output field and the influence of pumping statistics on the output field.The influence of atomic transit time $\tau$ on laser field has not been carefully discussed before, to our knowledge. In particular, a laser operating in the region of ${\gamma }_{ab}⪡{\tau }^{-1}⪡\kappa ∕2$ appears not to have been analyzed in previous laser theories. Our work could be a useful complementarity to laser theory. It is also an important theoretical foundation for the recently proposed active optical atomic clock based on bad-cavity laser mechanism.