Kavli Affiliate: Birgitta Whaley
| First 5 Authors: Oskar Leimkuhler, K. Birgitta Whaley, , ,
| Summary:
We introduce a hybrid quantum-classical eigenvalue solver that constructs a
wavefunction ansatz from a linear combination of matrix product states in
rotated orbital bases, enabling the characterization of chemical ground states
that are not subject to the constraint of a one-dimensional area law of
entanglement. The energy is converged via a gradient-free generalized sweep
algorithm based on quantum subspace diagonalization, with a potentially
exponential speedup in the off-diagonal matrix element contractions upon
translation into shallow quantum circuits of linear depth in the number of
qubits. Chemical accuracy is attained in numerical experiments for both a
stretched water molecule and an octahedral arrangement of hydrogen atoms,
achieving substantially better correlation energies compared to a unitary
coupled-cluster benchmark, with orders of magnitude reductions in quantum
resource estimates and a surprisingly high tolerance to shot noise. This
proof-of-concept study suggests a promising new avenue for scaling up
simulations of strongly correlated chemical systems on near-term quantum
hardware.
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