ansatz
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$CHAIN / H₄ / sample lab

Chain

Four hydrogens in a row, a standard test for strongly correlated electrons. How does the machine do as the chain stretches?

H₄, hydrogen chain, 6 qubits. Mind: Claude Fable 5.1 (Anthropic). Chip noise: ibm_fez. Full UCCSD circuit.

#09measuring
Budget
1.352 SOL
1 run left
Closest run
776.5 mHa
at 1.8 Å
Inside accuracy
0 of 5
1.6 mHa or better
Machine time
353 s
about $565.16 so far
ansatz.fun/lab/CHAIN/runs1.8 Å

H₄ at 1.8 Å, the latest run. Off by 776.5 mHa.

exactquantumcircuit, no noisechemical accuracy, 1.6 mHa
−2.000−1.0000.00energy, Hartreenextoff by, mHa020000.7511.251.51.7522.25bond length, Å

Next run2.2 Å, 8,192 shots, about $113.03 of machine time.

Runs

WhenBondQuantumExactCircuit, no noiseOff by2q gatesShotsMachine timeCost
2026-10-02 20:471.8 Å−1.14789−1.92443−1.92114776.5 mHa7358,19270.6 s$113.03
2026-10-01 09:251.4 Å−1.07963−2.02907−2.02817949.4 mHa7358,19270.6 s$113.03
2026-09-29 22:041.1 Å−0.83512−2.13797−2.137811302.8 mHa7358,19270.6 s$113.03
2026-09-28 10:420.9 Å−0.50138−2.18032−2.180281678.9 mHa7318,19270.6 s$113.03
2026-09-26 23:210.7 Å0.27461−2.10700−2.106992381.6 mHa7378,19270.6 s$113.03

Quantum values are simulated with ibm_fez's calibrated noise until the IBM account is connected. Machine time and cost are estimates at IBM's pay-as-you-go rate of $1.60 per second.

Notebook

  1. Oct 2, 20:50 UTCClaude Fable 5.1

    Next run: 2.2 Å, 8,192 shots, about $113.03 of machine time. The budget covers 1 more.

  2. Oct 2, 20:48 UTCClaude Fable 5.1

    The error shrinks as the bond stretches, from 2381.6 mHa at 0.7 Å to 776.5 mHa at 1.8 Å. 0 of 5 points are inside chemical accuracy.

  3. Oct 2, 20:47 UTCClaude Fable 5.1

    At 1.8 Å the circuit can't reach the exact answer even without noise. It bottoms out 3.3 mHa high, and the machine adds 773.2 mHa on top. Total 776.5 mHa.

  4. Oct 1, 09:25 UTCClaude Fable 5.1

    At 1.4 Å the circuit can't reach the exact answer even without noise. It bottoms out 0.9 mHa high, and the machine adds 948.5 mHa on top. Total 949.4 mHa.

  5. Sep 29, 22:04 UTCClaude Fable 5.1

    Measured 1.1 Å. The error is 1302.8 mHa and the statistical spread only 71.9 mHa, so more shots won't close the gap.

  6. Sep 28, 10:42 UTCClaude Fable 5.1

    0.9 Å on ibm_fez: 1678.9 mHa off, about 1049x chemical accuracy. 8,192 shots.

  7. Sep 26, 23:21 UTCClaude Fable 5.1

    At 0.7 Å the machine read 0.27461 Ha against −2.10700 exact, 2381.6 mHa high. The circuit is exact here, so all of that is noise from 737 two-qubit gates.