Nanophotonic traps for cold atoms typically have trap volumes that are orders of magnitude smaller than, e.g., free-space optical tweezers. This makes efficient loading of these traps challenging, thereby limiting the total number of atoms coupled to the nanophotonic waveguide. Here, we demonstrate that Λ -enhanced gray-molasses ( Λ GM ) can substantially increase the number of trapped atoms in a nanofiber-based cold-atom setup. Specifically, we observe a sixfold increase in the number of loaded atoms compared to conventional red-detuned polarization-gradient cooling. Despite the unusually small depth of our optical trap of only 24 μ K , we load about 4000 individual cesium atoms, achieving optical depths exceeding 140 and reaching the collisional blockade regime over a length of approximately 1 mm. After loading, we perform efficient electromagnetically induced transparency (EIT)-assisted cooling that is found to increase the trap storage time to 400(9) ms. This is a fivefold improvement over the passive storage time. Remarkably, we observe that EIT-cooling also works with two co-propagating nanofiber-guided light fields and requires only a few hundred picowatts of optical power. Our results provide an efficient method to boost both the number of loaded atoms and the storage time of nanophotonic atom traps.
Nanophotonic traps for cold atoms typically have trap volumes that are orders of magnitude smaller than, e.g., free-space optical tweezers. This makes efficient loading of these traps challenging, thereby limiting the total number of atoms coupled to the nanophotonic waveguide. Here, we demonstrate that Λ -enhanced gray-molasses ( Λ GM ) can substantially increase the number of trapped atoms in a nanofiber-based cold-atom setup. Specifically, we observe a sixfold increase in the number of loaded atoms compared to conventional red-detuned polarization-gradient cooling. Despite the unusually small depth of our optical trap of only 24 μ K , we load about 4000 individual cesium atoms, achieving optical depths exceeding 140 and reaching the collisional blockade regime over a length of approximately 1 mm. After loading, we perform efficient electromagnetically induced transparency (EIT)-assisted cooling that is found to increase the trap storage time to 400(9) ms. This is a fivefold improvement over the passive storage time. Remarkably, we observe that EIT-cooling also works with two co-propagating nanofiber-guided light fields and requires only a few hundred picowatts of optical power. Our results provide an efficient method to boost both the number of loaded atoms and the storage time of nanophotonic atom traps.
Λ-enhanced gray-molasses loading and EIT cooling of neutral atoms in nanophotonic traps
Nanophotonic traps for cold atoms typically have trap volumes that are orders of magnitude smaller than, e.g., free-space optical tweezers. This makes efficient loading of these traps challenging, thereby limiting the total number of atoms coupled to the nanophotonic waveguide. Here, we demonstrate that Λ-enhanced gray-molasses (ΛGM) can substantially increase the number of trapped atoms in a nanofiber-based cold-atom setup. Specifically, we observe a six-fold increase in the number of loaded atoms compared to conventional red-detuned polarization gradient cooling. Despite the unusually small depth of our optical trap of only 24 μK, we load about 4000 individual Cesium atoms, achieving optical depths exceeding 140 and reaching the collisional blockade regime over a length of approximately 1 mm. After loading, we perform efficient EIT-assisted cooling that is found to increase the trap storage time to 400(9) ms. This is a 5-fold improvement over the passive storage time. Remarkably, EIT-cooling also works with two co-propagating nanofiber-guided light fields and requiries only about a few hundred picowatt of optical power. Our results provide an efficient method to boost both the number of loaded atoms and the storage time of nanophotonic atom traps.
We present a low-cost implementation of lambda-enhanced gray molasses cooling in a nonstandard beam geometry and with an inexpensive laser locking setup that only provides limited coherence of the Raman laser beams. In contrast to the established use of resource-intensive phase-locking methods, our laser system uses two independent lasers, frequency- locked to a spectral feature produced by an electromagnetically induced transparency (EIT) resonance. We show that this approach achieves sufficient coherence to enable effective gray molasses cooling without the need for costly GHz electronics, significantly reducing the complexity and cost of experimental setups and represents a step toward more accessible cold atom technologies. Furthermore, the cooling remains efficient even with a nonoptimal beam geometry, typical of cold-atoms quantum computing platforms based on optical tweezers. A wave-function Monte Carlo analysis supports the experimental findings, offering insight into the cooling dynamics of this unconventional scheme.
Gray molasses cooling of 39K atoms in optical tweezers
Robust cooling and nondestructive imaging are prerequisites for many emerging applications of neutral atoms trapped in optical tweezers, such as their use in quantum information science and analog quantum simulation. The tasks of cooling and imaging can be challenged, however, by the presence of large trap-induced shifts of their respective optical transitions. Here, we explore a system of 39K atoms trapped in a near-detuned (780 nm) optical tweezer, which leads to relatively minor differential (ground vs. excited state) Stark shifts. We demonstrate that simple and robust loading, cooling, and imaging can be achieved through a combined addressing of the D1 and D2 transitions. While imaging on the D2 transition, we can simultaneously apply Λ-enhanced gray molasses (GM) on the D1 transition, preserving low backgrounds for single-atom imaging through spectral filtering. Using D1 cooling during and after trap loading, we demonstrate enhanced loading efficiencies as well as cooling to low temperatures. These results suggest a simple and robust path for loading and cooling large arrays of potassium atoms in optical tweezers through the use of resource-efficient near-detuned optical tweezers and GM cooling.
Abstract Interfacing trapped neutral atoms with light propagating in nanophotonic waveguides enables efficient and long-range photon-mediated atom–atom interactions. Here we demonstrate a hybrid nanophotonic trap for cold neutral atoms, which leverages surface forces for attraction and blue-detuned evanescent light for repulsion. We attribute the attractive potential to a combination of the Casimir–Polder interaction and electrostatic attraction due to charges on the waveguide surface. Despite the shallow depth of the trap, we load atoms into it via adiabatic transfer from a conventional two-colour dipole trap with an efficiency of 96(5)%. Notably, the hybrid trap supports a long atomic storage time of 140(9) ms. Moreover, it exhibits a Ramsey coherence time T2∗ T 2 * = 17.8(7) ms and spin-echo coherence time T2′ T 2 ′ = 44.7(2.5) ms, which greatly exceed previously reported values. Our results pave the way for further explorations of atom–surface interactions at the nanoscale and illustrate the potential of harnessing surface forces to enhance storage and coherence times for atoms coupled to nanophotonic waveguides. This advance offers new opportunities for neutral-atom quantum technologies.
Λ-Enhanced Gray Molasses Cooling of 85Rb Atoms in Tweezers Using the D2 Line
We demonstrate the implementation of Λ-enhanced gray molasses cooling on the D2 line of 85Rb atoms in an optical tweezer array. This technique yields lower atomic temperatures of 4.0(2) μK compared to red-detuned polarization gradient cooling, and consequently extends the T2∗ coherence time of the hyperfine clock qubit by a factor of 1.5. The method is alignment-free and can be readily implemented on laser beams used for magneto-optical trapping, as it only requires frequency and phase modulation control. Our experimental observations are corroborated by a numerical model based on a semi-classical force approach extended to a four-level system, including two hyperfine states of the upper manifold that are 120 MHz apart.
Robust cooling and nondestructive imaging are prerequisites for many emerging applications of neutral atoms trapped in optical tweezers, such as their use in quantum information science and analog quantum simulation.The tasks of cooling and imaging can be challenged, however, by the presence of large trap-induced shifts of their respective optical transitions.Here, we explore a system of 39 K atoms trapped in a near-detuned (780 nm) optical tweezer, which leads to relatively minor differential (ground versus excited state) Stark shifts.We demonstrate that simple and robust loading, cooling, and imaging can be achieved through combined addressing of the D 1 and D 2 transitions.While imaging on the D 2 transition, we can simultaneously apply -enhanced gray molasses (GM) on the D 1 transition, preserving low backgrounds for single-atom imaging through spectral filtering.Using D 1 cooling during and after trap loading, we demonstrate enhanced loading efficiencies as well as cooling to low temperatures.These results suggest a simple and robust path for loading and cooling large arrays of potassium atoms in optical tweezers through the use of resource-efficient near-detuned optical tweezers and GM cooling.