Split-Evolution Quantum Phase Estimation Demonstrated on Quantinuum Hardware
Researchers have presented a hardware demonstration of split-evolution quantum phase estimation (SE-QPE), a modified quantum algorithm for simulating particle-conserving Hamiltonians, run on Quantinuum's H2-2 quantum computer. SE-QPE replaces controlled time evolution with CSWAP-based interference between two registers, reducing circuit depth and gate counts compared to canonical quantum phase estimation (QPE). The approach shows meaningful resource savings relevant to quantum chemistry simulations, particularly for complex molecules like FeMoco.
Split-evolution quantum phase estimation (SE-QPE) is a modification to the standard QPE algorithm designed for particle-conserving Hamiltonians, such as those encountered in quantum chemistry. Instead of using controlled time evolution, SE-QPE employs CSWAP-based interference between a target register and a reference register, which removes controlled-simulation overhead and allows parallel evolution on two registers, thereby reducing circuit depth per phase-kickback block. Crucially, unlike compute-uncompute substitutions, SE-QPE remains compatible with non-exact eigenstates, broadening its practical applicability. Resource analysis applied to Trotterized double-factorized chemistry Hamiltonians shows asymptotic reductions of approximately 33% in CX gate count, 25% in T gate count, and a depth ratio of 3/N for CX layers over canonical QPE across FeMoco active spaces. A hardware demonstration on the Quantinuum H2-2 device using a four-qubit ethylene model with up to 8 phase bits successfully resolved distinct energies and showed that auxiliary registers can serve as useful error detection filters. The authors note that combining SE-QPE and standard QPE implementations may be advantageous depending on the phase power regime. The paper was updated in version 2 to extend the hardware demonstration from 6 to 8 phase bits and expand resource-estimation details for FeMoco.
What's missing
The study is a preprint and has not yet undergone formal peer review. The hardware demonstration is limited to a small four-qubit model system (ethylene), and it remains an open question how SE-QPE will perform on larger, more chemically relevant active spaces at scale.
What different sources said
- arXiv physicsCenter
Split-Evolution Quantum Phase Estimation for Particle-Conserving Hamiltonians
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