Ramsey and Hahn Echo coherence measurements on IBM Quantum hardware (preparing for CPMG)

PennyLane Help
1

Hello everyone,

I’m an independent learner working with PennyLane and Qiskit on IBM Quantum hardware, and I’d appreciate some technical feedback on a small coherence characterization study I’ve completed.

What I’ve implemented so far:

  • Ramsey interferometry on a single superconducting qubit

  • ⟨Z⟩ oscillations vs phase and Ramsey fringe visibility

  • Contrast decay extraction and exponential fit yielding T₂* ≈ 2.25 μs

  • Hahn Echo sequence (π refocusing pulse)

  • Echo decay analysis yielding T₂ ≈ 37 μs, showing strong refocusing of low-frequency noise

All analysis was done using linear least-squares and log-linear fitting (no SciPy).

Goal / next step:

I’d like to extend this work to a CPMG experiment (multiple π pulses) to:

  • Study T₂ as a function of pulse number

  • Probe the noise spectrum more systematically

  • Compare CPMG performance to Hahn Echo on current IBM hardware

Questions for the community:

  1. Does the Hahn Echo implementation and analysis approach look reasonable?

  2. Are there practical limits on π-pulse counts for CPMG on IBM backends?

  3. Any best practices for timing symmetry and delay handling (dt)?

  4. Would comparing with backend-reported T₂ values be meaningful?

Thank you very much for your time and for maintaining such a helpful forum.

I’m happy to share code snippets or plots if useful.

Best regards,

Arshad

(Self-learner)

ramsey
hahn-echo
decoherence
T2
quantum-hardware
ibm-quantum

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2

Hi @ARSHAD ,

Welcome to the Forum!

This looks quite specific to IBM technology. I’m not sure that someone here will be able to provide detailed feedback on your exact questions. Let’s hope that someone can indeed provide an answer!

As a more general guide, we have PennyLane functionality for pulse programming (qml.pulse) and we have a few demos on pulse programming. These demos use other technologies (not IBM hardware) but you may find the answers you’re looking for in there.

I hope this helps!