Scanning Cryogenic Magnetometry with a Bose-Einstein Condensate

Sabrina R. Leslie, James Higbie, Mukund Vengalattore +2 more

József Fortágh, Andreas Günther

Microscopic imaging of local magnetic fields provides a window into the organizing principles of complex and technologically relevant condensed-matter materials.However, a wide variety of intriguing strongly correlated and topologically nontrivial materials exhibit poorly understood phenomena outside the detection capability of state-of-the-art high-sensitivity high-resolution scanning probe magnetometers.We introduce a quantum-noise-limited scanning probe magnetometer that can operate from room-to-cryogenic temperatures with unprecedented dc-field sensitivity and micron-scale resolution.The Scanning Quantum Cryogenic Atom Microscope (SQCRAMscope) employs a magnetically levitated atomic Bose-Einstein condensate (BEC), thereby providing immunity to conductive and blackbody radiative heating.The SQCRAMscope has a field sensitivity of 1.4 nT per resolution-limited point (approximately 2 μm) or 6 nT= ffiffiffiffiffiffi Hz p per point at its duty cycle.Compared to point-by-point sensors, the long length of the BEC provides a naturally parallel measurement, allowing one to measure nearly 100 points with an effective field sensitivity of 600 pT= ffiffiffiffiffiffi Hz p for each point during the same time as a point-by-point scanner measures these points sequentially.Moreover, it has a noise floor of 300 pT and provides nearly 2 orders of magnitude improvement in magnetic flux sensitivity (down to 10 -6 Φ 0 = ffiffiffiffiffiffi Hz p ) over previous atomic probe magnetometers capable of scanning near samples.These capabilities are carefully benchmarked by imaging magnetic fields arising from microfabricated wire patterns in a system where samples may be scanned, cryogenically cooled, and easily exchanged.We anticipate the SQCRAMscope will provide charge-transport images at temperatures from room temperature to 4 K in unconventional superconductors and topologically nontrivial materials.

Richard Turner, Matthew Naides, Ruby A. Lai +2 more

Fan Yang, Stephen Taylor, Stephen D. Edkins +3 more

The SQCRAMscope is a recently realized Scanning Quantum CRyogenic Atom Microscope that utilizes an atomic Bose-Einstein condensate to measure magnetic fields emanating from solid-state samples. The quantum sensor does so with unprecedented DC sensitivity at micron resolution from room-to-cryogenic temperatures. An additional advantage of the SQCRAMscope is the preservation of optical access to the sample: Magnetometry imaging of, e.g., electron transport may be performed in concert with other imaging techniques. This multimodal imaging capability can be brought to bear with great effect in the study of nematicity in iron-pnictide high-temperature superconductors, where the relationship between electronic and structural symmetry-breaking resulting in a nematic phase is under debate. Here, we combine the SQCRAMscope with an in situ microscope that measures optical birefringence near the surface. This enables simultaneous and spatially resolved detection of both bulk and near-surface manifestations of nematicity via transport and structural deformation channels, respectively. By performing the first local measurement of emergent resistivity anisotropy in iron pnictides, we observe sharp, nearly concurrent transport and structural transitions. More broadly, these measurements demonstrate the SQCRAMscope's ability to reveal important insights into the physics of complex quantum materials.

K. Toyoda, Yoshiro Takahashi, T. Yabuzaki

Jessica Butcher

Since the first Bose-Einstein Condensate (BEC) was demonstrated in a dilute atomic gas [1], rotating BECs have been of interest to researchers due to their quantized circulation. We propose a new method of creating controlled vortices in a BEC. Atoms are held in the focus of a scanning beam that rapidly scans to produce a time-averaged potential [2]. We have made theoretical calculations to measure the heating caused by a scanning beam trap and to find the regime where a scanning beam produces a time-averaged potential. The scanning beam splits the BEC into four parts then imprints a relative phase on each part such that, when the parts recombine, a vortex forms. We have simulated such a system using the Gross-Pitaevskii equation and have demonstrated the laser scanning pattern using a two-dimensional acousto-optic modulator (AOM). The optics for the scanning beam trap have been designed and the experimental trap dimensions are used in our simulations. To carry out the experimental part of this project, we are currently building and testing an all-optical BEC apparatus: we have made a magneto-optical trap (MOT) which cools the 87Rb atomsto 30uK. We are currently setting up an optical dipole trap to perform the final stages of cooling.