Robust Geometric Quantum Computation with Time-Optimal Control

Dominique Sugny

Zhimin 治旻 Wang 王, Zhuang Ma, Xiangmin 祥敏 Yu 喻 +9 more

One of the key features required to realize fault-tolerant quantum computation is the robustness of quantum gates against errors. Since geometric quantum gate is naturally insensitivity to noise, it appears to be a promising routine to achieve high-fidelity, robust quantum gates. The implementation of geometric quantum gate however faces some troubles such as its complex interaction among multiple energy levels. Moreover, traditional geometric schemes usually take more time than equivalent dynamical ones. Here, we experimentally demonstrate a geometric gate scheme with the time-optimal control (TOC) technique in a superconducting quantum circuit. With a transmon qubit and operations restricted to two computational levels, we implement a set of geometric gates which exhibit better robustness features against control errors than the dynamical counterparts. The measured fidelities of TOC X gate and X/2 gate are 99.81% and 99.79% respectively. Our work shows a promising routine toward scalable fault-tolerant quantum computation.

Dominique Sugny, Bernard Bonnard A

The objective of this article is to present techniques of geometric time-optimal control developed to analyze the control of two-level dissipative quantum systems. Combined with numerical simulations they allow to compute the time-minimal control using a shooting method. The robustness with respect to initial conditions and dissipative parameters is also analyzed using a continuation method.

Zakaria Giunashvili

Shi-Liang Zhu, Paolo Zanardi A

Bao-Jie Liu, Xue‐Ke Song, Zheng‐Yuan Xue +2 more

Geometrical phases acquired in cyclic quantum evolutions can be utilized as natural resources for constructing robust logic gates for quantum information processing, which was originally proposed through adiabatic changes of the driving Hamiltonian. Practically, much efforts have been made to shorten the construction times of geometrical gates, known as non-adiabatic holonomic quantum computation (NHQC). However, previous NHQC gates require the driving Hamiltonian to satisfy a set of rather restrictive conditions, reducing the robustness of the resulting geometric gates against control errors. Here we show that non-adiabatic geometric gates can be constructed in an alternative way where the driving Hamiltonian can exhibit a high degree of flexibility for retaining the robustness of the geometric phases. Consequently, this approach makes it possible to incorporate most of the existing optimal control methods, such as dynamical decoupling, composite pulses, and shortcut to adiabaticity, into the construction of geometrical gates, to further address different types of errors. Furthermore, this extensible approach of geometric quantum computation can be applied to various physical platform such as superconducting qubits and nitrogen-vacancy (NV) centers. Specifically, we performed numerical simulation to show how the noise robustness in the recent experimental implementations [Phys. Rev. Lett. 119, 140503 (2017)] and [Nat. Photonics 11, 309 (2017)] of NHQC with NV centers can be significantly improved by our optimized NHQC approach. These results cover a large class of new techniques combing the noise robustness of both geometric phase and optimal control theory.