Creating a large angle coherent atomic beamsplitter without a magnetic field

Many atom interferometer applications would benefit from large angle atomic beamsplitters with narrow distributions. The interaction between a magnetic field and two standing wave laser fields can provide such a beamsplitter. Unfortunately, the required magnetic fields are undesirable in many interferometer applications, and few atomic systems have a suitable transition. We show that a similar beamsplitter for a three level atomic system can be obtained in the absence of a magnetic field as long as the excitation fields interacting with the two transitions are standing waves with a differential detuning. This technique could be used on transitions other than J = 1 to J′ = 1. Consider a three state system in the basis |a〉, |e〉, |b〉, where the field with rabi frequency Ω_a(Ω_b) interacts only with the transition from |a〉 → |e〉(|b〉 → |e〉). For Ω_a = Ω_b, and φ = π/2, the eigenenergies of H as a function of z are shown in Fig. 1. For states which approach |a〉 and |b〉 when |Ω| → 0, the potentials are given by ± (Δ/2 + |sin(kz)|). In contrast, the state which approaches |e〉 when |Ω| → 0, has a nearly triangular potential. Figure 2 shows the theoretical momentum distribution for scattering of a mono-energetic atomic beam where all atoms are in |e〉 initially and the interaction time is t = (7.5)(2π)/Δ. The narrowness of these peaks even at large values of the momentum splitting are the most important feature of this technique. The vertical lines in Fig. 3 show preliminary experimental results for an effusive He beam using the J = 1 to J′ = 1 subsystem of the 2S₁³ to 2³P₁ transition in He, excited by a σ₊ polarized standing wave and a σ _- polarized standing wave. In the experiment the initial populations were evenly distributed among the three ground states and the transverse momentum distribution was ± ℏk.