diff --git a/cirq-core/cirq/experiments/t1_decay_experiment.py b/cirq-core/cirq/experiments/t1_decay_experiment.py
index 01af366d1f4..a8ee85e70b5 100644
--- a/cirq-core/cirq/experiments/t1_decay_experiment.py
+++ b/cirq-core/cirq/experiments/t1_decay_experiment.py
@@ -137,9 +137,8 @@ def exp_decay(x, t1, a, b):
 
         # Fit to exponential decay to find the t1 constant
         try:
-            popt, _ = optimize.curve_fit(exp_decay, xs, probs, p0=[t1_guess, 1.0, 0.0])
-            self.popt = popt
-            t1 = popt[0]
+            self.popt, _ = optimize.curve_fit(exp_decay, xs, probs, p0=[t1_guess, 1.0, 0.0])
+            t1 = self.popt[0]
             return t1
         except RuntimeError:
             warnings.warn("Optimal parameters could not be found for curve fit", RuntimeWarning)