Averaging gate approximation error and performance of Unitary Coupled Cluster ansatz in Pre-FTQC Era
arXiv:2301.04150 · doi:10.22331/q-2025-07-21-1800
Abstract
Fault-tolerant quantum computation (FTQC) is essential to implement quantum algorithms in a noise-resilient way, and thus to enjoy advantages of quantum computers even with presence of noise. In FTQC, a quantum circuit is decomposed into universal gates that can be fault-tolerantly implemented, for example, Clifford+T gates. Here, T gate is usually regarded as an essential resource for quantum computation because its action cannot be simulated efficiently on classical computers and it is experimentally difficult to implement fault-tolerantly. Practically, it is highly likely that only a limited number of T gates are available in the near future. Pre-FTQC era, due to the constraint on available resources, it is vital to precisely estimate the decomposition error of a whole circuit. In this paper, we propose that the Clifford+T decomposition error for a given quantum circuit containing a large number of quantum gates can be modeled as the depolarizing noise by averaging the decomposition error for each quantum gate in the circuit, and our model provides more accurate error estimation than the naive estimation. We exemplify this by taking unitary coupled-cluster (UCC) ansatz used in the applications of quantum computers to quantum chemistry as an example. We theoretically evaluate the approximation error of UCC ansatz when decomposed into Clifford+T gates, and the numerical simulation for a wide variety of molecules verified that our model well explains the total decomposition error of the ansatz. Our results enable the precise and efficient usage of quantum resources in the early-stage applications of quantum computers and fuel further research towards what quantum computation can achieve in the upcoming future.
28 pages, (5+22) figures, v3: published version
References in corpus (12)
- Supplementary information for "Quantum supremacy using a programmable superconducting processor"
- Quantum computational advantage using photons
- Strong quantum computational advantage using a superconducting quantum processor
- Quantum Error Mitigation
- Phase-Programmable Gaussian Boson Sampling Using Stimulated Squeezed Light
- Early Fault-Tolerant Quantum Computing
- Even shorter quantum circuit for phase estimation on early fault-tolerant quantum computers with applications to ground-state energy estimation
- Hunting for quantum-classical crossover in condensed matter problems
- Partially Fault-tolerant Quantum Computing Architecture with Error-corrected Clifford Gates and Space-time Efficient Analog Rotations
- On proving the robustness of algorithms for early fault-tolerant quantum computers
- Probabilistic unitary synthesis with optimal accuracy
- Classical variational optimization of PREPARE circuit for quantum phase estimation of quantum chemistry Hamiltonians