We discuss a velocity selection technique for obtaining cold atoms, in which all atoms below a certain energy are spatially selected from the surrounding atom cloud. Velocity selection can in some cases be more efficient than other cooling techniques for the preparation of ultracold atom clouds in one dimension. With quantum mechanical and classical simulations and theory we present a scheme using a dipole force barrier to select the coldest atoms from a magnetically trapped atom cloud. The dipole and magnetic potentials create a local minimum which traps the coldest atoms. A unique advantage of this technique is the sharp cut-off in the velocity distribution of the sample of selected atoms. Such a non-thermal distribution should prove useful for a variety of experiments, including proposed studies of atomic tunneling and scattering from quantum potentials. We show that when the rms size of the atom cloud is smaller than the local minimum in which the selected atoms are trapped, the velocity selection technique can be more efficient in 1-D than some common techniques such as evaporative cooling. For example, one simulation shows nearly 6% of the atoms retained at a temperature 100 times lower than the starting condition.
We discuss a velocity selection technique for obtaining cold atoms, in which all atoms below a certain energy are spatially selected from the surrounding atom cloud. Velocity selection can in some cases be more efficient than other cooling techniques for the preparation of ultracold atom clouds in one dimension. With quantum mechanical and classical simulations and theory we present a scheme using a dipole force barrier to select the coldest atoms from a magnetically trapped atom cloud. The dipole and magnetic potentials create a local minimum which traps the coldest atoms. A unique advantage of this technique is the sharp cut-off in the velocity distribution of the sample of selected atoms. Such a non-thermal distribution should prove useful for a variety of experiments, including proposed studies of atomic tunneling and scattering from quantum potentials. We show that when the rms size of the atom cloud is smaller than the local minimum in which the selected atoms are trapped, the velocity selection technique can be more efficient in 1-D than some common techniques such as evaporative cooling. For example, one simulation shows nearly 6% of the atoms retained at a temperature 100 times lower than the starting condition.
We demonstrate a 1-D velocity selection technique which relies on combining magnetic and optical potentials. We have selected atom clouds with temperatures as low as 2.9% of the initial temperature, with an efficiency of 1%. The efficiency (percentage of atoms selected) of the technique can vary as slowly as the square root of the final temperature. In addition to selecting the coldest atoms from a cloud, this technique imparts a sharp cut-off in the velocity distribution. The cold selected atoms are confined in a small well, spatially separated from higher energy atoms. Such a non-thermal distribution may be useful for atom optics experiments, such as studies of atom tunneling.
In the last decades, experimental access to the quantum regime has been gained in a large variety of systems, including dilute ultracold gases, trapped ions, micromechanical oscillators, superconducting circuits, and many more.These systems allow for such exciting applications as quantum computing and communication, quantum metrology and quantum simulation.A physical system's quantum mechanical features can only be revealed by cooling it until the thermal excitations are negligible.To date, the coldest temperatures are reached with ultracold gases by a combination of laser cooling and evaporation, inherently producing individual ensembles.However, many applications can greatly benefit from a continuous source of ultracold atoms, for example sympathetic cooling of molecules or nanoscopic objects.Ideally, this cooling source operates without light, as most molecules have a rich internal structure and can absorb photons of many wavelengths.Another promising application of continuous sources of ultracold matter is atom interferometry.Such interferometers perform measurements of inertial forces, time and gravity.Currently, each cold sample is destroyed by its evaluation and the measurement is interrupted by the preparation of a new samples.Continuous sources can help to eliminate this restriction.So far, no dark and continuous sources exist in the microkelvin regime.This thesis presents the first preparation of such an ultracold atom cloud which is continuously replenished and protected from light.The continuously refilled reservoir is prepared by loading a magnetically guided atom beam into an elongated magnetic trapping potential.This static potential has an entrance barrier which allows atoms from a guided beam to enter the trap.Once in the trap, the atoms undergo collisions and redistribute their kinetic energy.Those gaining energy can escape again, but those losing energy are trapped.A steady state with 3.8 × 10 7 atoms atoms at a temperature of 102 µK is reached and maintained.The setup of the continuous loading scheme is described in this thesis.A key component is a mesoscopic atom chip which produces all magnetic fields for the continuous loading scheme.The initial atom source is a high-flux double magneto-optical trap system.An atomic beam is created out of the precooled atoms and guided to the static trap through a stray light protection allowing for a dark retrapping region.The cooling scheme does not rely on any specific atomic properties of the atoms and can thus be applied to a wide range of particles.The results offer exciting perspectives for an application as a continuous source of ultracold atoms, either as a coolant for sympathetic cooling or as a resource for metrology.
Most cold atoms experiments in microgravity platforms or in Space are achieved using atom chips, leading to limitations in terms of optical access and inhomogeneous magnetic fields. Optical dipole traps do not have these drawbacks but have difficulties producing atomic samples with a large number of atoms at ultra low temperature in the absence of gravity. Here, we report on an efficient evaporative cooling in two-crossed laser beams during parabolic flights. Time-averaged potentials combine the advantages of large capture volume and trap compression, increasing the initial phase space density and collision rate to favor the evaporative process. With this technique we demonstrate the production of an ultra cold gas of 2.5×104 rubidium atoms at a temperature below 100 nK in less than 4 seconds. Our experiment paves the way for the development of quantum sensors applied to fundamental physics and geodesy as well as the study of ultracold atomic physics in Space.
Abstract Most cold atoms experiments in microgravity platforms or in space are achieved using atom chips, constrained by limited optical access and inhomogeneous magnetic fields. Despite their higher power consumption, optical dipole traps are interesting alternatives because they do not have these drawbacks. Nevertherless, producing samples with a large number of ultracold atoms in a dipole trap, in the absence of gravity, has remained challenging so far. Here, we report on an efficient evaporative cooling in two-crossed laser beams during parabolic flights. Time-averaged potentials combine the advantages of large capture volume and trap compression, increasing the initial phase space density and collision rate to favor the evaporative process. With this technique we demonstrate the production of an ultra cold gas of 2.3 × 10 4 rubidium atoms at a temperature below 100 nK in less than 4 seconds. Our experiment paves the way for the development of quantum sensors applied to fundamental physics and geodesy as well as the study of ultracold atomic physics in space.
We present a cooling method for a cold Fermi gas by parametrically driving atomic motions in a crossed-beam optical dipole trap (ODT). Our method employs the anharmonicity of the ODT, in which the hotter atoms at the edge of the trap feel the anharmonic components of the trapping potential, while the colder atoms in the center of the trap feel the harmonic one. By modulating the trap depth with frequencies that are resonant with the anharmonic components, we selectively excite the hotter atoms out of the trap while keeping the colder atoms in the trap, generating parametric cooling. This experimental protocol starts with a magneto-optical trap (MOT) that is loaded by a Zeeman slower. The precooled atoms in the MOT are then transferred to an ODT, and a bias magnetic field is applied to create an interacting Fermi gas. We then lower the trapping potential to prepare a cold Fermi gas near the degenerate temperature. After that, we sweep the magnetic field to the noninteracting regime of the Fermi gas, in which the parametric cooling can be manifested by modulating the intensity of the optical trapping beams. We find that the parametric cooling effect strongly depends on the modulation frequencies and amplitudes. With the optimized frequency and amplitude, we measure the dependence of the cloud energy on the modulation time. We observe that the cloud energy is changed in an anisotropic way, where the energy of the axial direction is significantly reduced by parametric driving. The cooling effect is limited to the axial direction because the dominant anharmonicity of the crossed-beam ODT is along the axial direction. Finally, we propose to extend this protocol for the trapping potentials of large anharmonicity in all directions, which provides a promising scheme for cooling quantum gases using external driving.
We present a cooling method for a cold Fermi gas by parametrically driving atomic motions in a crossed-beam optical dipole trap (ODT). Our method employs the anharmonicity of the ODT, in which the hotter atoms at the edge of the trap feel the anharmonic components of the trapping potential, while the colder atoms in the center of the trap feel the harmonic one. By modulating the trap depth with frequencies that are resonant with the anharmonic components, we selectively excite the hotter atoms out of the trap while keeping the colder atoms in the trap, generating parametric cooling. This experimental protocol starts with a magneto-optical trap (MOT) that is loaded by a Zeeman slower. The precooled atoms in the MOT are then transferred to an ODT, and a bias magnetic field is applied to create an interacting Fermi gas. We then lower the trapping potential to prepare a cold Fermi gas near the degenerate temperature. After that, we sweep the magnetic field to the noninteracting regime of the Fermi gas, in which the parametric cooling can be manifested by modulating the intensity of the optical trapping beams. We find that the parametric cooling effect strongly depends on the modulation frequencies and amplitudes. With the optimized frequency and amplitude, we measure the dependence of the cloud energy on the modulation time. We observe that the cloud energy is changed in an anisotropic way, where the energy of the axial direction is significantly reduced by parametric driving. The cooling effect is limited to the axial direction because the dominant anharmonicity of the crossed-beam ODT is along the axial direction. Finally, we propose to extend this protocol for the trapping potentials of large anharmonicity in all directions, which provides a promising scheme for cooling quantum gases using external driving.