QEncode Benchmark
Back to leaderboard

H2

/jordan wigner/uccsd tapered
Certified
Beats CCSD(T)
cc-pvdz

H2_ccpvdz_JW_UCCSD_v4_tapered__sha256_93a0f8a8604d9aed

VQE Gap

1.0478e-9 Ha

CASCI ref

-1.131287 Ha

Qubits (tapered)

1

CCSD(T) corr.

-3.459e-2 Ha

Molecule / Problem

NameH2
Basis setcc-pvdz
GeometryH 0.0 0.0 0.0; H 0.0 0.0 0.735
Charge0
Spin0
Active electrons2
Active orbitals2
Orbital optimizationHF

Encoding / Circuit

Qubit mappingjordan-wigner
Ansatz typeuccsd_tapered
Ansatz reps (HEA)1
TaperingZ2 symmetry — 3 symmetries removed
Qubits (original)4
Qubits (tapered)1
Num parameters1
Circuit depth2
2Q gates0
Non-Clifford gates1
T gates (FT estimate)12 (ε = 0.001)

T-gate count is the resource-relevant cost of a fault-tolerant implementation. It is an estimate from the non-Clifford rotations in the pre-transpilation circuit, assuming standard rotation synthesis to precision ε — not a compiled count for a specific device.

Note on UCCSD circuit metrics

UCCSD uses exponential Pauli operators (exp(iθH)) that are symbolic before compilation. Circuit depth and 2-qubit gate counts are not reported here — they depend on the target hardware and transpiler.

Energy Results

HF energy-1.1286227699 Ha
MP2 energy-1.1549489623 Ha
CCSD energy-1.1632095636 Ha
CCSD(T) energy-1.1632095636 Ha
CASCI ground state-1.1312865113 Ha
VQE best energy-1.1312865102 Ha
|VQE − CASCI| gap1.047818e-9 Ha
CCSD(T) correlation-3.458679e-2 Ha

Optimizer / Run Config

AlgorithmCOBYLA
Multistart runs1
Max iterations500
Total func evals20
Num parameters1
Backenddefault.qubit

Provenance / Reproducibility

Entry IDH2_ccpvdz_JW_UCCSD_v4_tapered__sha256_93a0f8a8604d9aed
Schema version4.0.0
Created (UTC)2026-07-15T13:22:26.427398+00:00
SHA-256 hash93a0f8a8604d9aed42d897a6982b4814a535d05728d82234119f2ebfbb00fce7
Python3.11.15
PySCF2.6.2
PennyLane0.45.0
OpenFermion1.6.1
NumPy2.2.6
SciPy1.13.1

Reproduce this result

# Clone repo and install pinned environment

git clone https://github.com/qencode-benchmark/qencode-benchmark

cd qencode-benchmark

pip install -r requirements-v4.txt

# Run this entry

python scripts/generate_entry_v4.py \

--molecule H2 \

--mapping jordan_wigner \

--ansatz-type uccsd \

--multistart 1 \

--max-iter 500 \

--out-dir releases/v4/db