High-Fidelity Indirect Readout of Trapped-Ion Hyperfine Qubits

Area of Science:

• Quantum Information Science
• Atomic Physics
• Quantum Computing

Background:

• Trapped ion qubits are promising for quantum computation.
• High-fidelity readout is essential for reliable quantum operations.
• Direct fluorescence detection can cause decoherence in spectator qubits.

Purpose of the Study:

• To develop and demonstrate a high-fidelity indirect readout protocol for trapped ion hyperfine qubits.
• To improve readout accuracy while minimizing decoherence of other qubits.

Main Methods:

• Utilizing laser-driven Raman transitions to map the state of a Beryllium-9 (Be+) qubit ion to a Magnesium-25 (Mg+) readout ion.
• Partitioning the Be+ ground-state hyperfine manifold into two subspaces for qubit state representation.
• Implementing a protocol robust to spontaneous photon scattering errors for enhanced fidelity.

Main Results:

• Demonstrated combined readout and back-action errors as low as 1.2e-4 and 0 for the two subspaces.
• Achieved these results with 68% confidence.
• Successfully avoided spectator qubit decoherence caused by stray resonant light.

Conclusions:

• The proposed indirect readout protocol offers high fidelity for trapped ion qubits.
• This method overcomes limitations of direct fluorescence detection, preserving spectator qubit coherence.
• The technique is a significant advancement for scalable quantum information processing with trapped ions.