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Chinese Physics B

Large-angle coherent atomic beam splitter via the bichromatic force

Chenyu Zu, Dong Wu, Binqi Chen, Yong Xia

Published Apr 3, 2026• 0 citations

Abstract

Abstract Atomic beam splitters are fundamental components of atom interferometers, with broad applications in high sensitivity metrology and integrated atom optics devices. In this work, we theoretically demonstrate coherent beam splitting of a metastable helium atomic beam using a pulsed bichromatic standing wave. Our key innovation is a fully self-consistent model coupling the optical Bloch equations - which include spontaneous emission via a Lindblad term - with the classical equations of atomic motion, enabling the simulation of real-time splitting dynamics. This allows us to simulate the real-time dynamics and identify optimal experimental parameters neglected in prior splitter studies. Crucially, we find that the optimal standing-wave phase difference is ϕ= 3π/4, not π/2, maximizing the distinction between the dynamical pathways for splitting the metastable helium beam (2 3 S 1 →3 3 P 2 transition). We propose and validate the use of optical pulses shorter than the spontaneous emission lifetime to suppress decoherence. Monte Carlo simulations predict a clean binary split with a tunable splitting angle to 56 mrad, corresponding to 56 ħk momentum transfer, and a splitting efficiency of 55 - 83% via detuning.

DOI: 10.1088/1674-1056/ae5b5e

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We demonstrate a coherent atomic beam splitter for metastable helium atoms, based on the diffraction of atomic matter waves from a blazed phase grating. The beam splitter is created by driving the two transitions of a three-level V system with differentially detuned standing light waves that have a relative spatial phase shift of pi/2. The light f ields create a potential that is approximately triangular as a function of position in the laser field. Splittings of 38 times the photon momentum have been observed.

Using a ``monochromatic'' (single-axial-velocity) and slow (250 m/s) beam of metastable helium atoms, we realize up to eighth-order Bragg scattering and obtain a splitting angle of 6 mrad at low laser power (3 mW). This corresponds to a truly macroscopic separation of 12 mm on the detector. For fifth-order scattering, we have observed several oscillations of the splitting ratio when varying the laser power (``Pendell\"osung oscillations''). The large splitting angle, the adjustable splitting ratio, and the cleanness of the split beams, with $200\ensuremath{-}\ensuremath{\mu}\mathrm{m}$ rms width each, make the beam splitter ideal for a large-enclosed-area atom interferometer.

We investigate schemes for the clean splitting of beams of three-level atoms using two standing-wave laser fields within an optical cavity. The proposed beam splitter is shown to work for atoms in the \ensuremath{\Lambda} ladder, and ssV configurations. For appropriate values of Rabi frequencies and detunings, we obtain a triangular type of potential for the atomic states of interest. As well as modeling the coherent evolution of the systems, we have used quantum Monte Carlo wave-function methods to model the effects of spontaneous emission on the resulting diffraction pattern, finding significant differences between the three configurations. We also investigate the limits of the Raman-Nath approximation for our systems, using the symmetric split-operator technique to include the effects of the kinetic term in the Hamiltonian. We also present the results of calculations in which the split output beams are recombined, demonstrating the expected interference for differently prepared input beams. In comparison with two-level beam splitters using a single standing wave, we obtain a superior splitting, while, in comparison with magneto-optical beam splitters, our system possesses the worthwhile practical advantages of experimental simplicity.

We have used a new technique to construct a clean, large-angle, coherent atomic beam splitter with an easily adjustable splitting angle. Helium atoms in the J=1 metastable state diffract from a far-detuned light field with ‘corkscrew’ polarization in the presence of a homogeneous magnetic field. Adiabatic transfer from magnetic energy to ‘transverse kinetic energy’ then allows symmetric diffraction of the incoming beam in a single, high diffraction order with a different value of M. The order is set by the value of the magnetic field. The result is a flexible, adjustable, large-angle, three-way atomic beam splitter for atom interferometry.

Bose–Einstein condensate (BEC)-based atom interferometry exploits low temperatures and long coherence lengths to facilitate high-precision measurements. Progress in atom interferometry promises improvements in navigational devices like gyroscopes and accelerometers, as well as applications in fundamental physics such as accurate determination of physical constants. Previous work demonstrates that beam splitters and mirrors for coherent manipulation of dilute BEC momentum in atom interferometers can be implemented with sequences of non-resonant standing-wave light pulses. While previous work focuses on the optimization of the optical pulses’ amplitude and duration to produce high-order momentum states with high fidelity, we explore how varying the shape of the optical pulses affects optimal beam-splitter performance, as well as the effect of pulse shape on the sensitivity of optimized parameters in achieving high fidelity in high-momentum states. In simulations of two-pulse beam splitters utilizing optimized square, triangle, and sinc-squared pulse shapes applied to dilute BECs, we, in some cases, reduce parameter sensitivity by an order of magnitude while maintaining fidelity.