Measuring The Gravitational Field with an Atomic Ruler

This thesis presents the experimental and theoretical studies of the survival resonances in a dissipative atom-optics system, and their applications. We demonstrate this resonant phenomenon by using an alternative approach to the standard atom-optics $\delta$-kicked rotor (AODKR), where we add spatially periodic dissipation or loss to each pulse. The system evolution is therefore non-unitary. We first investigate the emergence of the survival resonances by exposing a cloud of laser-cooled Rubidium-85 atoms to standing-wave light pulses. The frequency of the light is tuned close to an open atomic transition. Scattering of the light from the standing wave leads the atoms to decay into a dark state that is far-off-resonance to both the standing-wave light and the subsequent detection light. Once the atoms go to the dark state, they are considered to be lost. The atom number is thereby {\it not} a conserved quantity. Consequently, a meaningful dynamic observable is the survival probability of the atoms. Varying the pulse interval reveals a series of resonant peaks at integer multiples of half the Talbot time. These peaks are deemed survival resonances and are a matter-wave interferometric phenomenon. The appearance of the peaks can be conceptually understood through the matter-wave Talbot-Lau effect. For a complete understanding, we build a model to simulate the system which captures the dynamics well. In addition to acting as an optical mask that modulates the wave functions' amplitude, the still present optical dipole force of the standing wave imprints a phase pattern to the atomic wave functions. This gives rise to a micro-lensing effect that increases the peak survival dramatically. Using such an effect can help to enhance the incisiveness of the resonances, which might find applications in precision measurements. The width of survival resonance peaks narrows faster than expected from the Fourier-limit when the pulse number is changed. The standard AODKR displays a similar sub-Fourier behavior. This thesis also demonstrates two applications of using survival resonances. The temporally pulsed spatially periodic dissipation is used for preparing well-defined initial conditions. Feeding back lost atoms gives a non-thermal atomic state that enhances subsequent survival resonance measurements. This can find its application in the state preparation in atom interferometry. To show the feasibility of using survival resonances in an atom interferometer, we construct a proof-of-concept atomic gravimeter. With a vertically arranged standing-wave light beam, we perform an interferometric measurement of the gravitational acceleration $g$ utilizing the survival resonances. Gravity removes the survival resonances, but they re-emerge when the standing wave co-moves with the free-falling atomic cloud. To study the performance of this technique and find a good parameter combination, we carry out a series of simulations and experiments. We measure $g$ with a precision of 5 ppm using a drop distance of less than 1 mm. The sensitivity improves with the square of the drop time, which indicates we can reach a precision of the $\mu$-Gal regime with a drop distance of 10 cm. The simple implementation makes this technique an attractive candidate for a low cost and compact atomic gravimeter

Dark-state sideband cooling in an atomic ensemble

We utilize the dark state in a {\Lambda}-type three-level system to cool an ensemble of 85Rb atoms in an optical lattice [Morigi et al., Phys. Rev. Lett. 85, 4458 (2000)]. The common suppression of the carrier transition of atoms with different vibrational frequencies allows them to reach a subrecoil temperature of 100 nK after being released from the optical lattice. A nearly zero vibrational quantum number is determined from the time-of-flight measurements and adiabatic expansion process. The features of sideband cooling are examined in various parameter spaces. Our results show that dark-state sideband cooling is a simple and compelling method for preparing a large ensemble of atoms into their vibrational ground state of a harmonic potential and can be generalized to different species of atoms and molecules for studying ultracold physics that demands recoil temperature and below

Measuring the local gravitational field using survival resonances in a dissipatively driven atom-optics system

We do a proof-of-principle demonstration of an atomic gravimeter based on survival resonances of dissipatively driven atoms. Exposing laser-cooled atoms to a sequence of near-resonant standing-wave light pulses reveals survival resonances when the standing-wave interference pattern accelerates. The resonant accelerations determine the local gravitational acceleration and we achieve a precision of 5 ppm with a drop distance less than 1 mm. The incisiveness of the resonances scales with the square of the drop time. Present results indicate that an appropriately designed atomic gravimeter based on survival resonances might be able to reach a precision of 1μGal with a 10-cm-high fountain. The relatively simple experimental construction of this technique may be of interest for a compact absolute atomic gravimeter

Observation of collective atomic recoil motion in a momentum-squeezed, ultra-cold, degenerate fermion gas

We demonstrate clear collective atomic recoil motion in a dilute, momentum-squeezed, ultra-cold degenerate fermion gas by circumventing the effects of Pauli blocking. Although gain from bosonic stimulation is necessarily absent because the quantum gas obeys Fermi-Dirac statistics, collective atomic recoil motion from the underlying wave-mixing process is clearly visible. With a single pump pulse of the proper polarization, we observe two mutually-perpendicular wave-mixing processes occurring simultaneously. Our experiments also indicate that the red-blue pump detuning asymmetry observed with Bose-Einstein condensates does not occur with fermions

Survival resonances in an atom-optics system driven by temporally and spatially periodic dissipation

We investigate laser-cooled atoms periodically driven by pulsed standing waves of light tuned close to an open atomic transition. This nonunitary system displays survival resonances for certain driving frequencies. The survival resonances emerge as a result of the matter-wave Talbot-Lau effect, similar to the Talbot effect causing quantum resonances in the atom optics δ-kicked rotor. Since the Talbot-Lau effect occurs for incoherent waves, the survival resonances can be observed using thermal atoms. A microlensing effect can enhance the height and incisiveness of the resonances. This may find applications in precision measurements

Measuring The Gravitational Field with an Atomic Ruler

This thesis presents the experimental and theoretical studies of the survival resonances in a dissipative atom-optics system, and their applications. We demonstrate this resonant phenomenon by using an alternative approach to the standard atom-optics $\delta$-kicked rotor (AODKR), where we add spatially periodic dissipation or loss to each pulse. The system evolution is therefore non-unitary. We first investigate the emergence of the survival resonances by exposing a cloud of laser-cooled Rubidium-85 atoms to standing-wave light pulses. The frequency of the light is tuned close to an open atomic transition. Scattering of the light from the standing wave leads the atoms to decay into a dark state that is far-off-resonance to both the standing-wave light and the subsequent detection light. Once the atoms go to the dark state, they are considered to be lost. The atom number is thereby {\it not} a conserved quantity. Consequently, a meaningful dynamic observable is the survival probability of the atoms. Varying the pulse interval reveals a series of resonant peaks at integer multiples of half the Talbot time. These peaks are deemed survival resonances and are a matter-wave interferometric phenomenon. The appearance of the peaks can be conceptually understood through the matter-wave Talbot-Lau effect. For a complete understanding, we build a model to simulate the system which captures the dynamics well. In addition to acting as an optical mask that modulates the wave functions' amplitude, the still present optical dipole force of the standing wave imprints a phase pattern to the atomic wave functions. This gives rise to a micro-lensing effect that increases the peak survival dramatically. Using such an effect can help to enhance the incisiveness of the resonances, which might find applications in precision measurements. The width of survival resonance peaks narrows faster than expected from the Fourier-limit when the pulse number is changed. The standard AODKR displays a similar sub-Fourier behavior. This thesis also demonstrates two applications of using survival resonances. The temporally pulsed spatially periodic dissipation is used for preparing well-defined initial conditions. Feeding back lost atoms gives a non-thermal atomic state that enhances subsequent survival resonance measurements. This can find its application in the state preparation in atom interferometry. To show the feasibility of using survival resonances in an atom interferometer, we construct a proof-of-concept atomic gravimeter. With a vertically arranged standing-wave light beam, we perform an interferometric measurement of the gravitational acceleration $g$ utilizing the survival resonances. Gravity removes the survival resonances, but they re-emerge when the standing wave co-moves with the free-falling atomic cloud. To study the performance of this technique and find a good parameter combination, we carry out a series of simulations and experiments. We measure $g$ with a precision of 5 ppm using a drop distance of less than 1 mm. The sensitivity improves with the square of the drop time, which indicates we can reach a precision of the $\mu$-Gal regime with a drop distance of 10 cm. The simple implementation makes this technique an attractive candidate for a low cost and compact atomic gravimeter

Review on the Application and Development of Biochar in Ironmaking Production

In recent years, the concept of green, low-carbon and clean energy consumption has been deeply rooted in the hearts of the people, and countries have actively advocated the use of new energy. In the face of problems such as resource shortage and environmental pollution, we began to explore the use of new fuels instead of coal for production. Biomass resources have the characteristics of being renewable and carbon neutral and having large output. As an energy utilization, it is helpful to promote the transformation of the energy structure in various countries. Applying it to ironmaking production is not only conducive to energy conservation and emission reduction in the ironmaking process but also can achieve efficient utilization of crop waste. By introducing the source and main preparation methods of biochar, this paper expounds the main links and advantages of biochar in the ironmaking process and puts forward the direction of biochar in ironmaking in the future