[Homemade Quantum Computer NMRQCP] Sending Tiny Signals to the PC!

*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.

So far, I've been working on the hardware (circuit) construction, but this time I will talk about the test where I finally capture the analog signals picked up by that circuit into a PC and analyze them using software (Python)!

Sending Tiny Signals to the PC! Introducing a High-Resolution Sound Card

The tiny analog signals picked up by the homemade receiver coil cannot be handled by a PC as they are, so they need to be passed through an ADC (A/D Converter) for digital processing.

To avoid missing the delicate messages from the quantum world, this time I adopted a "96KHz / 24-bit Hi-Fi USB External Sound Card" to perform high-resolution sampling.

The connection method is simple: the output from the analog circuit is passed through a "general-purpose shielded BNC cable," and using a "BNC to 3.5mm mono plug adapter," it is connected to the microphone input (or line input) of this sound card.

Creating a "Real-time FFT Analyzer" in Python

Once the hardware is connected, the next step is creating a Python script to read these audio waveforms.

I wrote a program that acquires the data stream from the sound card using the audio input library "PyAudio," calculates the Fast Fourier Transform (FFT) at regular intervals using "NumPy," and plots it on a graph using "Matplotlib."

# Execute FFT (Fast Fourier Transform)
# Apply a window function (Hamming window) to reduce noise at both ends
window = np.hamming(CHUNK)
fft_data = np.abs(np.fft.rfft(audio_data * window))

This is just a part of the code, but it includes techniques like applying a process called a "Hamming window" to reduce noise at both ends of the waveform.

Experimental Results and the Appearance of an Unexpected "Formidable Enemy"

Here is the result of actually running the circuit and executing the program!

A graph was successfully plotted on the screen as the "EFNMR Real-time FFT Analyzer"! I was able to confirm that the system, which can analyze the amplitude for each frequency (Frequency) on the PC side, is functioning properly. The signal acquisition itself is a huge success.

However, if you look closely at the graph, peaks in the low-frequency band, which seem to be environmental noise, have become visible. The system might be too excellent, as I found that it reacts keenly even to human voices and slight noises.

"Silence" seems to be absolutely essential for quantum computer experiments. From now on, it looks like I will need to take measures like conducting experiments in a quiet, empty room.

Finally, the hardware and software are connected, and the project has taken a massive step forward!

• 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!