Singlet-Only Always-On Gapless Exchange Qubits with Baseband Control.

Area of Science:

• Quantum computing
• Spintronics
• Solid-state physics

Background:

• Conventional exchange-only qubits face challenges with magnetic field gradients and nuclear environments.
• Leakage and coherent errors limit the performance of current spin qubit architectures.

Purpose of the Study:

• To propose and analyze a novel spin qubit, the singlet-only always-on gapless exchange (SAGE) qubit.
• To demonstrate the SAGE qubit's resilience against magnetic field gradient noise and leakage errors.
• To evaluate the performance of SAGE qubits for single- and two-qubit gate operations.

Main Methods:

• Encoding a single qubit in the spins of four electrons.
• Utilizing always-on exchange interactions to create a protected qubit subspace.
• Simulating qubit dynamics under realistic noise models, including magnetic gradient and charge noise.

Main Results:

• The SAGE qubit subspace is protected from coherent errors induced by local magnetic field gradients.
• Leakage out of the computational subspace is energetically suppressed due to continuous exchange interactions.
• Coherence times improve by an order of magnitude, and single-qubit gate infidelities decrease significantly compared to conventional exchange-only qubits under dominant magnetic gradient noise.
• Two-qubit gates are achieved with a single interqubit exchange pulse, featuring simplified sequences and comparable durations to existing methods.

Conclusions:

• The SAGE qubit offers a promising advancement for robust quantum information processing.
• Its inherent protection mechanisms and simplified gate operations pave the way for more scalable and reliable quantum computers.
• The SAGE qubit architecture demonstrates superior performance in realistic noise environments dominated by magnetic gradients.