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High-fidelity control and entanglement of Rydberg atom qubits (1806.04682v1)

Published 12 Jun 2018 in quant-ph, cond-mat.quant-gas, and physics.atom-ph

Abstract: Individual neutral atoms excited to Rydberg states are a promising platform for quantum simulation and quantum information processing. However, experimental progress to date has been limited by short coherence times and relatively low gate fidelities associated with such Rydberg excitations. We report progress towards high-fidelity quantum control of Rydberg atom qubits. Enabled by a reduction in laser phase noise, our approach yields a significant improvement in coherence properties of individual qubits. We further show that this high-fidelity control extends to the multi-particle case by preparing a two-atom entangled state with a fidelity exceeding 0.97(3), and extending its lifetime with a two-atom dynamical decoupling protocol. These advances open up new prospects for scalable quantum simulation and quantum computation with neutral atoms.

Citations (307)

Summary

  • The paper demonstrates a robust method for high-fidelity qubit control and two-qubit entanglement, reaching over 0.97 fidelity.
  • It employs advanced laser noise suppression techniques to extend single-atom Rabi oscillation coherence to 27 microseconds.
  • The work leverages the Rydberg blockade mechanism to entangle Rubidium-87 atoms, offering potential for scalable quantum processors.

Overview of High-Fidelity Control and Entanglement of Rydberg Atom Qubits

The research paper titled "High-fidelity control and entanglement of Rydberg atom qubits" reports significant advancements in the manipulation of Rydberg atom qubits for quantum information processing. The work presents a detailed experimental setup aimed at achieving high-fidelity quantum control, a critical challenge for quantum simulations and computations.

Key Contributions and Findings

The researchers tackle the pervasive issues of short coherence times and low gate fidelities in Rydberg atom implementations. By addressing laser phase noise through a meticulous setup involving frequency-stabilized lasers, they achieve marked improvements in single-atom coherence. A notable outcome is the preparation of a two-atom entangled state with a fidelity exceeding 0.97, demonstrating the method's efficacy in multi-particle systems.

Several technical improvements are highlighted:

  • Laser Noise Reduction: The paper employs a combination of high-fidelity laser locking techniques to suppress phase noise, a known limiter of coherence in Rydberg atom setups. This involves spectral filtering with an ultra-low expansion reference cavity and utilizing injection-locking schemes.
  • Single Atom Coherence: Long-lived Rabi oscillations were recorded with coherence times extending up to 27 microseconds. This was achieved through a functional setup optimized for minimizing sensitivity to Doppler shifts and scattering from intermediate states.
  • Multi-Particle Entanglement: Moving beyond single-qubit fidelity, the team demonstrates their approach's robustness by entangling two atoms with significant fidelity improvement through a dynamical decoupling protocol that substantially extends the lifetime of the entangled state.

Detailed Methodology

The experimental approach includes cooling individual Rubidium-87 atoms and arranging them into an optical tweezer array. These atoms are then coherently coupled to Rydberg states using dual-color laser systems. Techniques such as resonance Rabi oscillation monitoring and Ramsey experiments validate improvements in coherence due to implemented noise reduction methods.

An important theoretical construct employed is the Rydberg blockade mechanism, which facilitates the coupling of atoms into a symmetric entangled state while restricting doubly excited states. The blockade's efficacy is demonstrated through experimentally obtained oscillation patterns in the two-atom system, where the fit frequencies correspond closely with theoretical predictions.

Impact and Future Directions

The enhancements in fidelity and control reported imply promising prospects for scalable quantum simulation and computation. The work offers a viable path towards higher-fidelity gate operations in quantum processors built from neutral atom arrays. Future implications can be drawn in terms of increasing the complexity of quantum simulations that can be accurately realized using these techniques.

Ongoing research will likely focus on extending these protocols to larger atomic arrays, reducing decoherence factors further, and improving overall system stability. Developments in this domain could significantly contribute to establishing neutral Rydberg atoms as a cornerstone for robust quantum computing architectures.