Why did my entangled qubits decohere so fast?

hadamardhero

Decoherence wiped out the correlations before I could even finish the measurement sequence. I set up two qubits in an entangled state, waited a short delay with everything else looking stable, and the joint probabilities came out exactly like independent particles. The shielding and temperature controls checked out the same as before.

QMentor

hadamardhero, if the correlations vanished that fast despite stable readings, the qubits’ coherence time is probably shorter than the sequence allows. Measure T2 directly on the pair first to confirm the limit.

hadamardhero

Didn’t measure T2 on the pair itself. Singles looked fine, same as last runs.

algosurfer

hadamardhero, if the singles stay solid while the joint probabilities flatten out, the phase information is probably leaking faster than the populations, especially during that delay. I’d look first at whether the control pulses themselves are introducing any unintended coupling that only shows up in the entangled case. Does the platform you’re on show different coherence between the two qubits when they’re isolated versus paired?

hadamardhero

On this platform the measured coherence stays about the same for isolated runs versus paired ones. I didn’t see any extra drop when they were entangled.