Based on feedback control techniques and our realization of nearly complete transferring cold cesium (Cs) atoms from a magneto-optical trap (MOT) to a far-off-resonance microscopic optical tweezer, we investigated the possibility for nearly deterministic loading of a single Cs atom in a MOT and in a microscopic optical tweezer. We combined feedback controls on the gradient of the MOT quadrupole magnetic field (QMF) and on blue-detuned light-assisted collisions (LAC) of confined cold atoms in the tweezer. Using active feedback on QMF of the MOT, we have achieved ~ 98% of probability of single atom loading in a MOT. In a microscopic optical tweezer, by combining the feedback controls on the QMF and the LAC, we finally achieved ~ 95.2% of probability of single atom loading in the tweezer. This two-path feedback control scheme may be extended to load a small-size 2D tweezer array with exact single atom trapped in each site simultaneously. This is very important and promising to implement an addressable multiple-qubit system for demonstrating quantum register and quantum processor.
We investigate the use of light assisted collisions for the deterministic preparation of individual atoms in a microtrap. Blue detuned light is used in order to ensure that only one of the collision partners is lost from the trap. We obtain a 91% loading efficiency of single 85 Rb atoms. This can be achieved within a total preparation time of 542 ms. A numerical model of the process quantitatively agrees with the experiment giving an in-depth understanding of the dynamics of the process and allowing us to identify the factors that still limit the loading efficiency. The fast loading time in combination with the high efficiency may be sufficient for loading quantum registers at the size required for competitive quantum computing.
Continuously replenished optical tweezer arrays will unlock unlimited-depth quantum circuits with neutral atom qubits. A key bottleneck limiting the cycle time of these systems is removing atoms from tweezers initially loaded with more than one atom. In the conventional technique of light-assisted collisions, slow collisional dynamics limit the timescale for removing excess atoms to several milliseconds. Here, we propose and demonstrate a scheme for selectively removing one atom at a time from multiply occupied tweezers on a microsecond timescale, using intra-tweezer Rydberg blockade and autoionization. We demonstrate the protocol in
171Yb in two complementary regimes. With two-photon Rydberg excitation from the ground state, we reduce multi-atom probability to 1% in 64.8
μs, while retaining single atoms in 58.2(2)% of the tweezers, which is comparable to the filling fraction achieved with light-assisted collisions under the same experimental conditions, but over two orders of magnitude faster. With single-photon excitation from the metastable state
3P0, reduced single-atom loss enables a higher filling fraction of 74.8(3)%, at the cost of additional temporal overhead to prepare the atoms in
3P0. The final filling fraction is limited by an unexplained two-body loss mechanism, which, if solved, could enable fast, quasi-deterministic loading.
A single atom in a magneto–optical trap (MOT) with trap size (hundreds of micrometers) can be transferred into an optical microscopic tweezer with a probability of ~ 100%. The ability to transfer a single atom into two traps back and forth allows us to study the loading process. The loading probability is found to be insensitive to the geometric overlap of the MOT and the tweezer. It is therefore possible to perform simultaneously loading of a single atom into all sites of the tweezer array for many qubits. In particular, we present a simulation of the one-dimensional and two-dimensional arrays of an optical microscopic tweezer. We find the same qualitative behavior for all of the trap parameters.
Continuously replenished optical tweezer arrays will unlock unlimited-depth quantum circuits with neutral atom qubits. A key bottleneck limiting the cycle time of these systems is removing atoms from tweezers initially loaded with more than one atom. In the conventional technique of light-assisted collisions, slow collisional dynamics limit the timescale for removing excess atoms to several milliseconds. Here, we propose and demonstrate a scheme for selectively removing one atom at a time from multiply occupied tweezers on a microsecond timescale, using intra-tweezer Rydberg blockade and autoionization. We demonstrate the protocol in Yb 171 in two complementary regimes. With two-photon Rydberg excitation from the ground state, we reduce the multi-atom probability to 1% in 64.8 μ s , while retaining single atoms in 58.2 ( 2 ) % of the tweezers, which is comparable to the filling fraction achieved with light-assisted collisions under the same experimental conditions, but over two orders of magnitude faster. With single-photon excitation from the metastable state P 0 3 , reduced single-atom loss enables a higher filling fraction of 74.8 ( 3 ) % , at the cost of additional temporal overhead to prepare the atoms in P 0 3 . The final filling fraction is limited by an unexplained two-body loss mechanism, which, if solved, could enable fast, quasi-deterministic loading.
The realization of large-scale fully controllable quantum systems is an exciting frontier in modern physical science. We use atom-by-atom assembly to implement a platform for the deterministic preparation of regular one-dimensional arrays of individually controlled cold atoms. In our approach, a measurement and feedback procedure eliminates the entropy associated with probabilistic trap occupation and results in defect-free arrays of more than 50 atoms in less than 400 milliseconds. The technique is based on fast, real-time control of 100 optical tweezers, which we use to arrange atoms in desired geometric patterns and to maintain these configurations by replacing lost atoms with surplus atoms from a reservoir. This bottom-up approach may enable controlled engineering of scalable many-body systems for quantum information processing, quantum simulations, and precision measurements.