[Homemade Quantum Computer NMRQCP] System Integration! But Standing in the Way is "Debug Hell"

*Original Japanese version is available here.

 Hello! I'm a KOSEN student taking on the challenge of developing a quantum computer using a homemade Earth's Field NMR (EFNMR) system.

This time, I'm sharing the story of the "system integration test," where I brought together all the parts I've built individually so far. I thought it was finally complete, but I ended up receiving a harsh baptism into hardware development...

System Integration! But Standing in the Way is "Debug Hell"

I conducted an integration test of the entire system by combining the homemade "1600-turn sensor coil," "MOSFET drive circuit," and "op-amp receiver circuit" inside an aluminum case, and capturing the signal to a PC via a StarTech USB sound card.

I triumphantly turned on the power, but absolutely no signal came into the PC. I checked over and over, wondering if it was a wiring mistake or microphone permission settings... After grueling debugging work, the cause turned out to be something incredibly basic: the "9V rectangular Panasonic alkaline battery" powering the op-amp was completely empty.

"Oh, it was just a dead battery!" I felt relieved knowing the cause, but the real tragedy struck right after this.

A Fatal Polarity Mistake. A Plume of Smoke Rises

I rushed out to buy a new battery and, in my eagerness to see the waveform as quickly as possible, hastily reconnected the wiring the moment I got back.

To my horror, I connected the positive and negative terminals (polarity) in reverse. Smoke billowed from the heart of the system—the ultra-low distortion, ultra-low noise op-amp (AD797BRZ)—and it short-circuited. The expensive component I had painstakingly micro-soldered was ruined in an instant, and I literally held my head in despair.

Fortunately, I had a spare op-amp and was able to start the recovery work immediately, but I swore to myself that from now on, I will always double-check everything when applying current to ensure this never happens again.

Signal Detection on the OS, and a New Wall in Python

After pulling myself together, I restored the circuit and restarted the system. Finally, I succeeded in detecting the signal input from the microphone (the waveform accompanying the energization) on the OS side!

"Yes! Now I can see the quantum waveform!" I thought, and ran the Python script (efnmr_monitor.py) I wrote to perform real-time FFT analysis.

However, the graph that appeared on the screen didn't reflect any waveform; it remained completely flat.

Just when I thought I had overcome the hardware wall, a new wall appeared: software configuration. The road to a quantum computer is definitely not straightforward, but next time I plan to solve this device ID problem and finally capture a real "waveform"!

• Daily experiment notes and code: Available on my GitHub repository (nmr-qc-project)
  
• Real-time development scenes and oscilloscope waveforms: Posting on X (formerly Twitter)
  

If you are wondering things like "Will it really work?" or "How do you generate waveforms?", please bookmark this blog and follow me on X!