Microwave ac Zeeman force for ultracold atoms

Abstract

We measure the AC Zeeman force on an ultracold gas of 87 Rb due to a microwave magnetic field targeted to the 6.8 GHz hyperfine splitting of these atoms. An atom chip produces a microwave near-field with a strong amplitude gradient, and we observe a force over three times the strength of gravity. Our measurements are consistent with a simple 2-level theory for the AC Zeeman effect and demonstrate its resonant, bipolar, and spin-dependent nature. We observe that the dressed atom eigenstates gradually mix over time and have mapped out this behavior as a function of magnetic field and detuning. We demonstrate the practical spin-selectivity of the force by pushing or pulling a specific spin state while leaving other spin states unmoved.

Microwave trap for atoms and molecules

“…Figure 5(b) shows the ratio Ω z /Ω x , which is independent of the power as we would expect. The mean ratio is 3.33 (6), consistent with the predicted value of 3.28.…”

“…Such a trap was developed specifically for ultracold Cs [3], but it used the magnetic dipole interaction at a frequency almost resonant with the groundstate hyperfine transition, so was specific to that particular atom. More recently, a similar species-specific microwave-induced force has been used to generate spindependent potentials on atom chips, where strong gradients can be produced in the near-field of coplanar waveguides and resonators [4][5][6]. By contrast, ours is a very general trap that uses the electric dipole interaction far from any resonance.…”

Regulating spin reversal in dipolar systems by the quadratic Zeeman effect

“…The physics of the alternating current quadratic Zeeman effect [22,[70][71][72][73] is similar to the alternating current Stark effect [74][75][76][77]. Let us consider a system of atoms enumerated by j = 1, 2, .…”

“…If the nucleus of an atom has a nonzero spin, then there exists hyperfine structure. And even if there is no the latter, when the nuclear spin is zero, there always exists the spin structure of energy levels, as soon as an atom contains electrons [22][23][24][25][26][27][28][70][71][72][73]. Since all atoms have electrons, their energy levels depend on the presence of external magnetic fields, including alternating fields.…”

Microwave Atom Chip Design

“…DC Zeeman potentials are spin-dependent and modify the energy of all spins in a proportional manner; optical dipole potentials can be engineered to include a spindependence but at the cost of significant spontaneous emission heating [6]. Fortunately, the AC Zeeman (ACZ) effect, based on microwave hyperfine transitions, offers a clear mechanism for spin-specific control of atoms [7]. However, strong microwave gradients on length scales much shorter than the wavelength are needed for trapping, so microwave near fields generated by atom chip currents must be employed.…”