Trapping ultracold gases near cryogenic materials with rapid reconfigurability

Abstract

We demonstrate a novel atom chip trapping system that allows the placement and high-resolution imaging of ultracold atoms within microns from any 100 µm-thin, UHV-compatible material, while also allowing sample exchange with minimal experimental downtime. The sample is not connected to the atom chip, allowing rapid exchange without perturbing the atom chip or laser cooling apparatus. Exchange of the sample and retrapping of atoms has been performed within a week turnaround, limited only by chamber baking. Moreover, the decoupling of sample and atom chip provides the ability to independently tune the sample temperature and its position with respect to the trapped ultracold gas, which itself may remain in the focus of a high-resolution imaging system. As a first demonstration of this new system, we have confined a 700-nK cloud of 8 × 10 4 87 Rb atoms within 100 µm of a gold-mirrored 100-µm-thick silicon substrate. The substrate was cooled to 35 K without use of a heat shield, while the atom chip, 120 µm away, remained at room temperature. Atoms may be imaged and retrapped every 16 s, allowing rapid data collection.Ultracold gases trapped near cryogenic surfaces using atom chips 1 can serve as elements of hybrid quantum systems for quantum information processing, e.g., by coupling quantum gases to superconducting qubits 2 , or as sensitive, high-resolution, and wide-area probes of electronic current flow 3 , electric ac and patch fields 4 , and magnetic domain structure 5 and dynamics. Previous experiments have succeeded in trapping and imaging ultracold thermal and quantum gases of alkali atoms around carbon nanotubes 6 , near superconductors 7 at 4 K, microns from room-temperature gold wires 8 , and within a He dilution refrigerator 9 .

Sensing Magnetic Fields with a Giant Quantum Wave

“…The SQCRAMscope allows any approximately 1-cm 2 area, ≤150-μm-thin sample made of UHV-compatible material to be imaged from room temperature to cryogenic temperatures. We demonstrate here the functionality of the SQCRAMscope at room temperature and 35 K (see Appendix A) and believe operation down to approximately 4 K will soon be possible with the addition of a heat shield [10]. Lastly, we mention that because what the SQCRAMscope measures are nanotesla-strength, shortwavelength deviations in the mean field along the trap axis, the microscope is insensitive to much larger-up to hundreds of gauss-background or long-wavelength fluctuating fields along this axis.…”

“…See Ref. [10] for more details. We verify that the quasi-1D BEC located below the calibration wires is not fragmented by meandering currents in the atom chip's microwires at this far distance.…”

“…[10]. While the majority of the data shown here were taken at room temperature, we perform a magnetometry scan shown in Fig.…”

“…This drift is likely due to the slow settling of thermally contracting parts of the apparatus and can be mitigated by waiting longer before imaging. The temperature is measured with invacuum thermometers contacted to the cold head and calibrated to the temperature at the sample tip [10].…”

“…The BEC is confined in a high-aspect-ratio cigar-shaped trap formed using an atom-chip-based magnetic microtrap [9,10] (see Appendix A). This quasi-1D Bose gas lies within the quasicondensate regime because the transverse trap frequency ω ⊥ is 157× larger than the longitudinal trap frequency ω ∥ , the chemical potential μ is similar in magnitude to ω ⊥ , and the gas temperature is 2.6× lower than ω ⊥ .…”