Dark Spin-Cat States as Biased Qubits.

Area of Science:

• Quantum Computing
• Atomic Physics
• Quantum Information Science

Background:

• Atomic qubits are crucial for quantum computation.
• Current atomic qubit implementations face challenges with noise and error rates.
• Developing robust and universally implementable qubits is a key research goal.

Purpose of the Study:

• To present a novel biased atomic qubit design, the "dark spin cat."
• To demonstrate the qubit's noise resilience and biased error characteristics.
• To explore the implementation of quantum gates using this qubit architecture.

Main Methods:

• Encoding a qubit in ground state Zeeman levels of atoms as a "spin cat."
• Coupling ground and excited state spin manifolds using light.
• Analyzing the properties of dark states immune to spontaneous emission and light coupling.
• Investigating qubit stabilization under strong Rabi drive for large ground state manifold sizes (F_g).

Main Results:

• Identification of two dark states in the ground state manifold, forming the "dark spin cat."
• Autonomous stabilization of the dark spin cat against common noise sources.
• Demonstration of a significantly biased qubit noise profile.
• Exponential decrease in bit-flip error rate with increasing F_g relative to dephasing rate.

Conclusions:

• The dark spin cat offers a robust and universally implementable atomic qubit.
• The qubit exhibits inherent noise bias, favoring reduced bit-flip errors.
• Bias-preserving single-qubit and entangling gates can be implemented, as shown on a Rydberg tweezer platform.