bistable-qubit-fpga

---
name: bistable-qubit-fpga
description: "Operating bistable qubits using FPGA-based 1-bit adaptive feedback control. Use when: mitigating TLS-induced dephasing errors in superconducting qubits, designing adaptive qubit control protocols, implementing real-time qubit frequency tracking, or stabilizing gate fidelities against discrete instabilities."
---

# Bistable Qubit FPGA Control Skill

Operating bistable qubits with FPGA-based adaptive feedback to mitigate two-level-system (TLS) defect-induced dephasing errors in solid-state quantum processors.

## Source

Paper: "Operating a bistable qubit" (arXiv: 2605.03187)
Category: quant-ph
Published: 2026-05

## Core Problem

Parasitic two-level-system (TLS) defects cause discrete, stochastic frequency shifts in superconducting qubits, making them bistable. This induces Ramsey beating and degrades gate fidelities over time.

## Key Technique: 1-Bit Feedback Protocol

### Principle
- Estimate the qubit's bistable frequency from a **single single-shot measurement**
- Reach the information limit set by the qubit's intrinsic entropy
- Deploy a classical FPGA controller for real-time adaptive correction

### Performance
- **Estimation bandwidth**: ~136 kHz
- **Error reduction**: 77%
- **Gate fidelity**: Stabilized over time with high fidelity

### Implementation Steps
1. **Single-shot measurement**: Perform one measurement to estimate current bistable state
2. **FPGA-based controller**: Use FPGA for real-time frequency estimation and correction
3. **Adaptive protocol**: Dynamically adjust control parameters based on estimated state
4. **Ramsey beating suppression**: Apply correction to suppress TLS-induced dephasing

## Applications
- Superconducting qubit operation with TLS defects
- Large-scale qubit array stabilization
- Real-time qubit frequency tracking
- Gate fidelity maintenance over time

## Key Insights
- Simple yet fundamentally efficient strategy for TLS-induced dephasing
- May enable operation of large future qubit arrays with discrete instabilities
- Reaches information-theoretic limit with minimal measurement overhead

## Activation Keywords
- bistable qubit, TLS defect, FPGA feedback, adaptive qubit control, dephasing mitigation, superconducting qubit stability, Ramsey beating suppression