Abstract Matter-wave diffraction is an important and widely used method for manipulating atomic momentum states and for studying dynamical evolution in ultracold-atom physics. Here, we investigated momentum diffraction of ultracold 87 R b atoms using a short lattice pulse in the presence of a forced harmonic potential. The forced potential is achieved by combining a magnetic field gradient and a crossed-dipole trap. By tuning the gradient field strength and atomic evolution time in the trap, we found that populations of the forward and backward diffractive momentum components exhibit asymmetry relative to the original matter wave, a feature that has often been overlooked or deliberately avoided in previous studies. The factors that induce this asymmetric diffraction are identified and systematically analyzed, including the initial atomic velocity, the trap potential gradient, and the cooperative interactions among atomic spin-momentum modes. A transparent physical picture supported by analytical modeling is presented. This work can provide a better understanding of matter-wave diffraction in the presence of external fields and in complex or imperfect lattice configurations, thereby potentially advancing future research on ultracold atom interferometry and quantum simulation involving multiple spin-momentum modes.
Abstract Matter-wave diffraction is an important and widely used method for manipulating atomic momentum states and for studying dynamical evolution in ultracold-atom physics. Here, we investigated momentum diffraction of ultracold 87 R b atoms using a short lattice pulse in the presence of a forced harmonic potential. The forced potential is achieved by combining a magnetic field gradient and a crossed-dipole trap. By tuning the gradient field strength and atomic evolution time in the trap, we found that populations of the forward and backward diffractive momentum components exhibit asymmetry relative to the original matter wave, a feature that has often been overlooked or deliberately avoided in previous studies. The factors that induce this asymmetric diffraction are identified and systematically analyzed, including the initial atomic velocity, the trap potential gradient, and the cooperative interactions among atomic spin-momentum modes. A transparent physical picture supported by analytical modeling is presented. This work can provide a better understanding of matter-wave diffraction in the presence of external fields and in complex or imperfect lattice configurations, thereby potentially advancing future research on ultracold atom interferometry and quantum simulation involving multiple spin-momentum modes.
We have performed a principle-proof experiment of a magneto-optical diffraction (MOD) technique that requires no energy level splitting by a homogeneous magnetic field and a circularly polarized optical lattice, avoiding system errors in an interferometer based on the MOD. The principle for this MOD is that asynchronized switching of the quadrupole trap and the Ioffe trap in a quadrupole-Ioffe-configuration trap can generate a residual magnetic force to drive a Bose-Einstein condensate (BEC) to move. We have observed asymmetric atomic diffraction resulting from the asymmetric distribution of the Bloch eigenstates involved in the diffraction process when the condensate is driven by such a force, and matter-wave self-imaging due to coherent population oscillation of the dominantly occupied Bloch eigenstates. We have classified the mechanisms that lead to symmetric or asymmetric diffraction and found that our experiment presents a magnetic alternative to a moving optical lattice, with a great potential to achieve a very large momentum transfer ($>110\ensuremath{\hbar}k$) to a BEC using well-developed magnetic trapping techniques.
We have performed a principle-proof-experiment of a magneto-optical diffraction (MOD) technique that requires no energy level splitting by homogeneous magnetic field and a circularly polarized optical lattice, avoiding system errors in an interferometer based on the MOD. The principle for this new MOD is that asynchronized switching of quadrupole trap and Ioffe trap in a quadrupole-Ioffe-configuration trap can generate a residual magnetic force to drive a Bose-Einstein condensate (BEC) to move. We have observed asymmetric atomic diffraction resulting from the asymmetric distribution of the Bloch eigenstates involved in the diffraction process when the condensate is driven by such a force, and matter-wave self-imaging due to coherent population oscillation of the dominantly occupied Bloch eigenstates. We have classified the mechanisms that lead to symmetric or asymmetric diffraction, and found that our experiment presents a magnetic alternative to a moving optical lattice, with a great potential to achieve a very large momentum transfer (>110ℏk) to a BEC using well-developed magnetic trapping techniques.
Ultracold atoms in optical lattices provide a highly controllable environment for the clean experimental realization of various model Hamiltonians from condensed matter and statistical physics. For example, the two-component Bose-Hubbard model, which reduces to an anisotropic spin-1/2 Heisenberg model in a certain limit and thus allows for the study of quantum magnetism, can be implemented by using bosons with two different internal states that couple differently to an optical lattice potential. In this thesis, I present our first experiments with two-component hyperfine-state mixtures of ultracold 87Rb atoms in a state-dependent optical lattice, both in the strongly correlated regime and in the context of nonlinear atom optics. For the production of 87Rb Bose-Einstein condensates we have developed a moving-coil transporter apparatus featuring a magnetic TOP trap which serves as a 'phase-space funnel' to load a crossed optical dipole trap. The apparatus further incorporates a three-dimensional optical lattice setup with simultaneously usable hyperfine state-dependent and state-independent lattice beams of different spacing along the vertical axis. Internal state control is performed via rf and microwave Rabi pulses and Landau-Zener sweeps. As a first step towards studying strongly correlated two-component mixtures, we have realized a state-selective superfluid-to-Mott insulator transition, where one component enters the Mott insulator regime, while the other one stays superfluid. Using the state-dependent lattice we can tune the second component's properties from highly superfluid to strongly localized. At both extremes we find a reduction of the coherence of the primary component, i.e. a shift of the Mott transition to smaller values of the ratio U/t of interaction to tunneling. We ascribe this to a polaron-like dressing on the one hand, and a 'quantum emulsion' causing a disordered atomic background potential on the other hand. Further, we have observed and studied four-wave mixing of two-component matter waves. Using state-selective Kapitza-Dirac diffraction of a two-component BEC, we prepare seed and pump modes differing both in momentum and internal state. A novel collinear four-wave mixing process then populates the initially empty output modes. While this process can complicate studies of bosonic mixtures loaded into state-dependent optical lattices, it might prove useful for possible applications in quantum atom optics. | Ultracold atoms in optical lattices provide a highly controllable environment for the clean experimental realization of various model Hamiltonians from condensed matter and statistical physics. For example, the two-component Bose-Hubbard model, which reduces to an anisotropic spin-1/2 Heisenberg model in a certain limit and thus allows for the study of quantum magnetism, can be implemented by using bosons with two different internal states that couple differently to an optical lattice potential. In this thesis, I present our first experiments with two-component hyperfine-state mixtures of ultracold 87Rb atoms in a state-dependent optical lattice, both in the strongly correlated regime and in the context of nonlinear atom optics. For the production of 87Rb Bose-Einstein condensates we have developed a moving-coil transporter apparatus featuring a magnetic TOP trap which serves as a 'phase-space funnel' to load a crossed optical dipole trap. The apparatus further incorporates a three-dimensional optical lattice setup with simultaneously usable hyperfine state-dependent and state-independent lattice beams of different spacing along the vertical axis. Internal state control is performed via rf and microwave Rabi pulses and Landau-Zener sweeps. As a first step towards studying strongly correlated two-component mixtures, we have realized a state-selective superfluid-to-Mott insulator transition, where one component enters the Mott insulator regime, while the other one stays superfluid. Using the state-dependent lattice we can tune the second component's properties from highly superfluid to strongly localized. At both extremes we find a reduction of the coherence of the primary component, i.e. a shift of the Mott transition to smaller values of the ratio U/t of interaction to tunneling. We ascribe this to a polaron-like dressing on the one hand, and a 'quantum emulsion' causing a disordered atomic background potential on the other hand. Further, we have observed and studied four-wave mixing of two-component matter waves. Using state-selective Kapitza-Dirac diffraction of a two-component BEC, we prepare seed and pump modes differing both in momentum and internal state. A novel collinear four-wave mixing process then populates the initially empty output modes. While this process can complicate studies of bosonic mixtures loaded into state-dependent optical lattices, it might prove useful for possible applications in quantum atom optics. | 110 pages
Atom interferometers detect inertial effects with considerably larger sensitivity than that of traditional light wave interferometers. They uti- lize the relative small group velocity of coherent matter waves for more precise measurements, which is crucial for possible next-generation in- ertial navigation systems. In a hybrid optical dipole and magnetic trap system we generate Bose-Einstein condensates to be used as the source of matter waves for atom interferometry. We use tailored light pulse sequences to induce Kapitza-Dirac diffraction in the condensates, splitting them into multiple parts at discrete momentum orders. Nu- merical simulation and experimental realization is given for novel pulse sequences that splits ±4hk momentum orders.
Quantum gases in optical lattices allow for fundamental studies in atomic and condensed-matter physics and the exploration of novel effects. After a brief introduction to the fundamentals of quantum gas experiments in optical lattices, we discuss two recent experiments focusing on driven matter waves in a one-dimensional optical lattice. The first experiment uses a tilted bichromatic optical lattice to investigate the interplay of disorder and collisional interactions in the accelerated transport of a Bose-Einstein condensate. Here, a screening effect is observed, in which the interactions effectively cancel the damping of Bloch oscillations induced by a (quasi-)disordered potential. This effect can be understood through a modification of the underlying band structure by the interactions. The second experiment studies the dynamics of a weakly trapped condensate resonantly coupled to the orbitals of a strongly confining state-selective lattice. We observe momentum distributions that correspond to matter wave diffraction from a periodic structure; however, the diffractive dynamics remain strongly linked to the internal-state Rabi oscillations. In the regime investigated, which we call the nonadiabatic regime, no diffracting potential can be defined. We show how only for much stronger coupling, the internal and external dynamics decouple, transitioning from nonadiabatic diffraction to the well-studied Kapitza-Dirac diffraction. We further investigate prospects for realizing dissipative spin models in our ultracold atomic gas experiment. To this end, we develop and test in the laboratory several possible implementations of effective spins with differential coupling to a superfluid background and examine their viability for a realization of the spin-boson model. | 94 pages
Kapitza-Dirac scattering, the diffraction of matter waves from a standing light field, is widely utilized in ultracold gases, but its behavior in the strongly interacting regime is an open question. Here we develop a numerically-exact two-body description of Kapitza-Dirac scattering for two contact-interacting atoms in a one-dimensional harmonic trap subjected to a pulsed optical lattice, enabling us to obtain the numerically exact dynamics. We map how interaction strength, lattice depth, lattice wavenumber, and pulse duration reshape the diffraction pattern, leading to an interaction-dependent population redistribution in real and momentum-space. By comparing the exact dynamics to an impulsive sudden-approximation description, we delineate the parameter regimes where it remains accurate and those, notably at strong attraction and small lattice wavenumber, where it fails. Our results provide a controlled few-body benchmark for interacting Kapitza-Dirac scattering and quantitative guidance for Kapitza-Dirac-based probes of ultracold atomic systems.