Session S06: Quantum Information Processing with Rydberg Atoms

Live

We present recent results demonstrating a controlled-NOT gate based on electromagnetically induced transparency (EIT), originally proposed by M\"{u}ller \emph{et al.}. The scheme relies on the strong long-range interactions between Rydberg atoms which, through Rydberg blockade, facilitates conditional transfer between target atomic qubits dependent on the initial state of a control atom. We have achieved a gate fidelity $F \geq 0.82$ and have demonstrated Bell state entanglement by measuring parity oscillations. This method has the potential to be scaled to multiple qubits gates without a change in pulse area providing a route to create useful entangled states for high-precision measurements beyond the standard quantum limit without error correction.   

Live

We present recent results on high-fidelity entanglement and detection of strontium Rydberg atoms in tweezer arrays. Two-electron atoms such as strontium offer several advantages for Rydberg physics, such as the ability to rapidly auto-ionize the Rydberg electron. We implement such a scheme and demonstrate significantly increased Rydberg state detection fidelities compared to previous work relying on trapping losses. Building off recent work on atomic-array optical clocks, we use strontium's clock state as a metastable ground state from which single-photon Rydberg excitation with fast Rabi frequency is easily accessible. We observe high-fidelity and long-lived blockade oscillations and present a lower bound argument for entanglement fidelity measured without local spin-addressing. Finally, we discuss ongoing efforts into quantum simulation, quantum gates, and entanglement-enhanced clocks.   

Live

Due to their long-range nature, dipole-dipole interactions in polar molecules and Rydberg atoms provide a versatile tool that can provide dramatic speedups in a variety of quantum computation protocols. In this talk, I will discuss how by dressing multiple Rydberg states, asymmetric blockade can be achieved via dipole-dipole interactions. I will then show how the resultant asymmetric blockade can be used to engineer multi-qubit control gates in which there are multiple control qubits and multiple target qubits.   

Live

Development of neutral-atom qubit platforms has progressed at a breakneck pace over the past several years, including improvements to quantum non-demolition readout fidelity, control over Rydberg interactions, and spatial manipulation of large atom arrays. However, many prior demonstrations of gates with neutral atoms have used global addressing of the atom array, which forces gate operations to be serialized. We present a method for single-qubit gates in strontium that affords single-site addressability as well as amplitude, phase, and frequency control for each qubit. Additionally, our approach capitalizes on the long coherence times of nuclear-spin states and leverages RF techniques developed by the superconducting josephson-junction community. We aim to scale this gate to large qubit arrays in a parallelizable, hardware-efficient manner.   

Live

Neutral atoms trapped in focused light arrays have emerged as a leading contender to serve as a high-fidelity, scalable platform for quantum computing, as they can be individually interrogated with high precision using focused lasers; entangled via Rydberg interaction; and routinely trapped in the hundreds to thousands using optical lattices or tweezer arrays. Alkaline earth atoms in particular benefit from a complex level structure which allows for rapid doppler cooling to microkelvin temperatures, and possess long-lived metastable states which can be used for shelving. Prior work on trapping strontium in optical tweezers has focused on the bosonic isotope $^{\mathrm{88}}$Sr, whose zero-spin nucleus leads to simplified cooling schemes, but which allows for coherent transitions only in the optical regime. The complex nuclear structure of $^{\mathrm{87}}$Sr, however, opens up additional degrees of freedom which can be explored for quantum information processing. We discuss our recent progress toward trapping, cooling, and imaging both isotopes in reconfigurable arrays of optical tweezers, and discuss the path toward large numbers of qubits prepared and read out with the high fidelities necessary for implementing realistic QC algorithms.   

Not Participating

There is a great interest for Rydberg-atom programmable quantum simulators because of their advantages in scalability and arbitrary control of individual interactions via Rydberg states [1]. Here we report, three-dimensional quantum systems are constucted with rubidium single atoms arranged by 250 holographic optical tweezers and entangled through Rydberg-state excitation. Their quantum dynamics are successfully observed for various symmetric structures and analyzed with Lindblad master equations for coherent and dissipative many-body system behaviors [2]. Their scaling behavior in the intermediate-scale quantum simulation regime of N$=$50-100 are to be presented. [1] A. Browaeys and T. Lahaye, “Many-body physics with individually controlled Rydberg atoms,” Nature Physics (2020). \underline {https://doi.org/10.1038/s41567-019-0733-z} [2] W. Lee, et al. "Coherent and dissipative dynamics of entangled few-body systems of Rydberg atoms," Physical Review A 99, 043404 (2019).~   

On Demand

Adiabatic evolutions of a multi-qubit system to the many-body ground states of a targeted Hamiltonian allow various tasks for quantum information processing. However, the very nature of energy gap closing near critical points requires slow ramps of control parameters, while dephasing due to experimental imperfections limits coherence time, making it hard to get the targeted states adiabatically. Shortcuts to adiabaticity [1] could resolve this problem by speeding up the adiabatic evolutions, but require nonlocal interactions that are hard to implement in currently available quantum simulators. In this work, we adopt a recently proposed scheme utilizing discrete changes of a control parameter [2] to achieve the many-body ground states of our Rydberg-atom quantum simulator [3], adiabatically despite zero energy gaps along the evolution pathways. We have observed that the scheme not only works for atoms all within blockade radius, which are effectively described as a two-level system, but also improves the final ordered state probability of 1D atom chains simulating Ising quantum magnets. [1] A. del Campo, and K. Sengupta, Eur. Phys. J. Spec. Top. 224, 189 (2015). [2] K. Xu et al., Sci. Adv. 5, eaax3800 (2019). [3] H. Kim et al., Phys. Rev. Lett. 120, 180502 (2018).   

Rydberg atoms excited to entangled superpositions states in a chain of atoms

Proposed is a quantum control methodology to create entangled states of two typical classes, the W and the Greenberg-Horne-Zeilinger (GHZ) for an arbitrary chain of atoms. Excitation to the Rydberg state is obtained through two-photon adiabatic passage using overlapping chirped pulses and co-action of the Rabi frequency, one-photon detuning, and the strength of the Rydberg-Rydberg interactions. Generation of the W and GHZ in a triatomic chain is performed via a control scheme derived from analysis of the field interaction Hamiltonian in order to find resonance times between the energy states and the pulse. By engineering desirable avoided crossings of energy bare states by manipulating chirp conditions we arrive at predetermined superposition states at the end of the pulse duration. Control conditions differ for creation of the GHZ and W state and are addressed as obstacles to scalability of the system.   

Development of a performant simulations framework for modeling realistic gate operations in neutral atom quantum computers

Individually addressable neutral atoms, trapped in holographically defined optical tweezers, provide access to coherent, controllable quantum objects that possess a rich and complex Hilbert space. Furthermore, interactions between nearby atoms can be activated to create many-body entangled states. Such a collection of controllable interacting atoms can be a superb platform for studies in quantum information processing. Given the complexity of the system it is imperative that theory and numerical simulations be used to develop and verify proposed control schemes; full numerical simulations can be difficult to construct given the complicated atomic structure, and are time-consuming to perform especially when dissipation is included. We present a simulations framework, written in the Julia programming language, that leverages several features of the language including metaprogramming and native parallelization to study and prescribe coherent control of 87Sr. We use this framework to concisely build and efficiently simulate pulse sequences that effect single qubit and two-qubit entangling gates, demonstrating high fidelity gates using experimentally accessible control parameters.