Ponderomotive Optical Traps and Site-Selective Addressing for Rydberg-Atom Quantum Information Science

Ensembles of Rydberg atoms in laser traps serve as platforms for quantum simulation and neutral-atom quantum computing. Rydberg-atom quantum simulators offer a configurable, controllable and scalable approach to model low-temperature and many-body quantum systems, which are of interest in science and technology across the disciplines, including physics, engineering, chemistry and nuclear physics.

Such systems are often too complex to be modeled on a classical computer. By providing quantum modeling capability, Rydberg-atom quantum simulators/computers have the potential to drive societal change. Laser-trap arrays are a versatile platform to prepare and localize atoms in these devices.

However, laser beams are subject to pointing and intensity noise. The resultant random forces acting on the atoms cause motional decoherence, which in turn reduces simulator performance. To address this problem, the present project deals with research on Rydberg-atom laser traps that minimize motional decoherence and allow for in-trap quantum simulation by uninterrupted pinning of the atoms at locations where the laser intensity is near-zero, and by ensuring that all atomic quantum states experience the same trapping potential.

In this way, the detrimental effects of laser noise are minimized. The traps further enable site-selective quantum-state transitions in individual atoms at randomly accessed locations, as required in certain quantum simulations. The trapping methodology under investigation also promises progress in other fields of science, which include the measurement of atomic constants and the search for light axionic dark matter via microwave photon detection.

The project further benefits society through education of graduate students, outreach to the public, and connections with industry.

In the work, linear arrays of laser-cooled rubidium atoms are employed. The ponderomotive force that the trapping beams exert on the valence electron is used for both the trapping of the simulator atoms and for driving Rydberg-state transitions in them. The ac polarizability of Rb 5S1/2 and the Rydberg ponderomotive shift match at a “magic” wavelength of approximately 790.14 nm, which is accessed by narrow-band near-IR lasers.

The laser traps are formed by a linear, hollow cylindrical beam for radial confinement and an array of transverse beams. The traps have identical potentials for ground- and Rydberg-levels. The magic character of the traps minimizes motional decoherence and allows in-trap quantum simulation over a substantial fraction of the Rydberg-atom lifetime.

Ground- and Rydberg-state atoms are trapped at locations of minimal intensity, thus minimizing laser-noise-induced decoherence. The preparation of defect-free atom arrays follows, in part, established protocols. Photoionization only plays a minor role.

Transitions between Rydberg states are driven by microwave-modulated ponderomotive tweezer beams that are directed at selected trapping sites. The dynamic variables of the in-trap simulator include Rabi frequency, detuning, phase, and interaction strength. Interactions across trapping sites are afforded by strong dipolar couplings between nS1/2 and n’P1/2 states, which are conducive to fast simulators with interactions that can reach over several sites.

Readout methods involve Rydberg-atom ionization and state-selective fluorescence imaging. Optical Rydberg-atom circularization methods will be tested towards future applications, which may take advantage of long circular-state lifetimes and coherence times. The effort overall will lay foundations for ponderomotive Rydberg-atom quantum simulation and processing.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.