Hybrid quantum logic and a test of Bell's inequality using two different atomic isotopes

Area of Science:

• Quantum Mechanics
• Quantum Information Processing
• Atomic Physics

Background:

• Entanglement is a fundamental quantum property crucial for quantum information processing (QIP).
• Previous experiments generated entangled states using identical particles or heralded methods.
• Hybrid entanglement with non-identical particles remained a significant challenge.

Purpose of the Study:

• To deterministically generate and characterize a hybrid entangled state of two trapped-ion qubits with different isotopes.
• To perform a Bell's inequality test on this novel entangled state.
• To demonstrate the potential of mixed-species quantum logic for quantum computing.

Main Methods:

• Utilized a deterministic, laser-driven two-qubit quantum logic gate.
• Employed trapped ions of two different calcium isotopes, (40)Ca(+) and (43)Ca(+).
• Performed full quantum state tomography and tested the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality.

Main Results:

• Achieved a maximally entangled hybrid state of (40)Ca(+) and (43)Ca(+) qubits with 99.8% fidelity.
• Violated the CHSH Bell inequality by 15 standard deviations, closing the detection loophole.
• Demonstrated the feasibility of mixed-species quantum logic in trapped ions.

Conclusions:

• Mixed-species quantum logic is a powerful technique for building trapped-ion quantum computers.
• The developed entangling gate mechanism can be applied to different atomic elements, reducing errors.
• This approach is essential for achieving fault-tolerant quantum error correction and general-purpose quantum computing.