Bell inequality violation in gate-defined quantum dots.

Area of Science:

• Quantum Information Science
• Solid-State Physics
• Quantum Computing

Background:

• Quantum computers utilize entanglement for enhanced computational power.
• Verifying non-classical correlations (entanglement) in spin qubits is crucial but challenging.
• Previous efforts faced difficulties in simultaneously achieving high concurrence and readout fidelities.

Purpose of the Study:

• To demonstrate the violation of Bell's inequality in a silicon quantum dot system.
• To achieve high-fidelity quantum operations and measurements for spin qubits.
• To prove genuine quantum entanglement in a scalable qubit platform.

Main Methods:

• Utilized heralded initialization and gate set tomography (GST) for calibration.
• Achieved over 99% fidelity for the full 2-qubit gate set, including state preparation and measurement (SPAM).
• Employed direct parity readout for Bell inequality violation measurement.

Main Results:

• Demonstrated a Bell state fidelity of 97.17% without readout error correction.
• Violated Bell's inequality with a Bell signal (S) of 2.731.
• Exceeded the classical limit even at 1.1 K and with entanglement lifetimes up to 100 μs.

Conclusions:

• Violation of Bell's inequality in silicon quantum dots confirms quantum entanglement.
• This achievement is a significant milestone towards realizing quantum advantage.
• The demonstrated high fidelities pave the way for robust quantum computation in silicon.