RESUMEN
Atomic sensing is, at large, based on measuring energy differences. Specifically, magnetometry is typically performed by using a superposition of two quantum states, the energy difference of which depends linearly on the magnetic field due to the Zeeman effect. The magnetic field is then evaluated from repeated measurements of the accumulated dynamic phase between the two Zeeman states. Here we show that atomic clock states, with an energy separation that is independent of the magnetic field, can nevertheless acquire a phase that is magnetic field dependent. We experimentally demonstrate this on an ensemble of optically trapped ^{87}Rb atoms. Finally, we use this effect to propose a magnetic field sensing method for static and time-dependent magnetic fields and analyze its sensitivity, showing it essentially allows for high-sensitivity magnetometery.
RESUMEN
Ultracold atom-ion mixtures are gaining increasing interest due to their potential applications in ultracold and state-controlled chemistry, quantum computing, and many-body physics. Here, we studied the dynamics of a single ground-state cooled ion during few, to many, Langevin (spiraling) collisions with ultracold atoms. We measured the ion's energy distribution and observed a clear deviation from the Maxwell-Boltzmann distribution, characterized by an exponential tail, to a power-law distribution best described by a Tsallis function. Unlike previous experiments, the energy scale of atom-ion interactions is not determined by either the atomic cloud temperature or the ion's trap residual excess-micromotion energy. Instead, it is determined by the force the atom exerts on the ion during a collision which is then amplified by the trap dynamics. This effect is intrinsic to ion Paul traps and sets the lower bound of atom-ion steady-state interaction energy in these systems. Despite the fact that our system is eventually driven out of the ultracold regime, we are capable of studying quantum effects by limiting the interaction to the first collision when the ion is initialized in the ground state of the trap.
RESUMEN
The non-crystallographic phase problem arises in numerous scientific and technological fields. An important application is coherent diffractive imaging. Recent advances in X-ray free-electron lasers allow capturing of the diffraction pattern from a single nanoparticle before it disintegrates, in so-called 'diffraction before destruction' experiments. Presently, the phase is reconstructed by iterative algorithms, imposing a non-convex computational challenge, or by Fourier holography, requiring a well-characterized reference field. Here we present a convex scheme for single-shot phase retrieval for two (or more) sufficiently separated objects, demonstrated in two dimensions. In our approach, the objects serve as unknown references to one another, reducing the phase problem to a solvable set of linear equations. We establish our method numerically and experimentally in the optical domain and demonstrate a proof-of-principle single-shot coherent diffractive imaging using X-ray free-electron lasers pulses. Our scheme alleviates several limitations of current methods, offering a new pathway towards direct reconstruction of complex objects.
RESUMEN
We report on the measurement of the contribution of the magnetic-dipole hyperfine interaction to the tensor polarizaility of the electronic ground state in ^{87}Rb. This contribution was isolated by measuring the differential shift of the clock transition frequency in ^{87}Rb atoms that were optically trapped in the focus of an intense CO_{2} laser beam. By comparing to previous tensor polarizability measurements in ^{87}Rb, the contribution of the interaction with the nuclear electric-quadrupole moment was isolated as well. Our measurement will enable better estimation of blackbody shifts in Rb atomic clocks. The methods reported here are applicable for future spectroscopic studies of atoms and molecules under strong quasistatic fields.