Cristian Daniel Panda

Magneto-optical traps (MOTs) are a workhorse technology for neutral-atom quantum sensing, simulation, and computing. Here, we demonstrate a MOT optimized for inertial quantum sensing and precision metrology applications. Our MOT traps 4 × 108 cesium (Cs) atoms in a robust, modular system that achieves stable operation through two design features: (1) we use divergent cooling laser beams to reduce unwanted reflections, and (2) optical elements are mounted in a fiber-coupled, compact, and modular cage rigidly attached to the vacuum chamber. Following polarization-gradient cooling, the system produces atom samples with temperatures below 10 μK, similar to those achieved in conventional MOTs that use collimated laser beams. In addition, we observe the trapping of 2 × 107 Cs atoms in a non-conventional MOT geometry, where the cooling laser beams are diagonal to the principal axis of the quadrupole magnetic field.

Quantum inertial sensors test general relativity, measure fundamental constants, and probe dark matter and dark energy in the laboratory with outstanding accuracy. Their precision relies heavily on carefully choreographed quantum control of the atomic states with a collection of lasers, microwaves, and electric and magnetic fields. Making this technology available outside of the laboratory would unlock many applications, such as geophysics, geodesy, and inertial navigation. However, this requires an apparatus of reduced size, weight, and power use and increased robustness, modularity, and ease-of-use. Here, we describe the design and implementation of an in-vacuum electromagnet able to create the magnetic fields necessary for various quantum control operations, such as magneto-optical trapping or magnetic levitation to assist evaporative cooling. Placing the electromagnet inside the vacuum chamber has significant advantages, such as fast switching times that are not limited by induced current inside the vacuum chamber metal and reduced size, weight, and power usage. However, dissipating the heat produced typically requires complex designs that include bulky metal heatsinks or cooling using water or cryogens. Our design implements heatpipes in a compact, low-vibration, and robust apparatus, which uses a phase transition in the working fluid to achieve thermal conductivity that is more than 100 times larger than that of typical bulk metal. We show that the setup can conduct more than 50 W of thermal power in a configuration that provides ample optical access and is compatible with the ultrahigh vacuum requirements of atomic and molecular experiments.

Despite being the dominant force of nature on large scales, gravity remains relatively elusive to precision laboratory experiments. Atom interferometers are powerful tools for investigating, for example, Earth’s gravity¹, the gravitational constant², deviations from Newtonian gravity^3,4,5,6 and general relativity⁷. However, using atoms in free fall limits measurement time to a few seconds⁸, and much less when measuring interactions with a small source mass^2,5,6,9. Recently, interferometers with atoms suspended for 70 s in an optical-lattice mode filtered by an optical cavity have been demonstrated^{10,11,12,13,14}. However, the optical lattice must balance Earth’s gravity by applying forces that are a billionfold stronger than the putative signals, so even tiny imperfections may generate complex systematic effects. Thus, lattice interferometers have yet to be used for precision tests of gravity. Here we optimize the gravitational sensitivity of a lattice interferometer and use a system of signal inversions to suppress and quantify systematic effects. We measure the attraction of a miniature source mass to be a_mass = 33.3 ± 5.6_stat ± 2.7_syst nm s⁻², consistent with Newtonian gravity, ruling out ‘screened fifth force’ theories^3,15,16 over their natural parameter space. The overall accuracy of 6.2 nm s⁻² surpasses by more than a factor of four the best similar measurements with atoms in free fall^5,6. Improved atom cooling and tilt-noise suppression may further increase sensitivity for investigating forces at sub-millimetre ranges^17,18, compact gravimetry^19,20,21,22, measuring the gravitational Aharonov–Bohm effect^9,23 and the gravitational constant², and testing whether the gravitational field has quantum properties²⁴.

Atomic accelerometers and gravimeters are usually based on freely falling atoms in atomic fountains, which not only limits their size but also their robustness to environmental factors, such as tilts, magnetic fields, and vibrations. Such limitations have precluded their broad adoption in the field, for geophysics, geology, and inertial navigation. More recently, atom interferometers based on holding atoms in an optical lattice have been developed. Such gravimeters also suppress the influence of vibrations in the frequency range of ∼1 Hz and above by several orders of magnitude relative to conventional atomic gravimeters. Here, we show that such interferometers are robust to tilts of more than 8 mrad with respect to the vertical and can suppress the effect of even strong environmental magnetic fields and field gradients by using atoms in the F=3, 4 hyperfine ground states as co-magnetometers, potentially eliminating the need for shielding. We demonstrate gravimeter sensitivity of 0.7 mGal/Hz (1 mGal = 10 μm/s2) in a compact geometry where atoms only travel over millimeters of space.

In quantum metrology and quantum information processing, a coherent nonclassical state must be manipulated before unwanted interactions with the environment lead to decoherence. In atom interferometry, the nonclassical state is a spatial superposition, where each atom coexists in multiple locations as a collection of phase-coherent partial wavepackets. These states enable precise measurements in fundamental physics and inertial sensing. However, atom interferometers usually use atomic fountains, where the available interrogation time is limited to ~3 seconds (for 10 m fountains). Here, we analyze the theoretical and experimental limits to the coherence arising from collective dephasing of the atomic ensemble and realize atom interferometry with a spatial superposition state that is maintained for as long as 70 seconds. These gains in coherence may enable gravimetry measurements, searches for fifth forces, or fundamental probes into the non-classical nature of gravity.