Fast, Accurate, and Realizable Two-Qubit Entangling Gates by Quantum Interference in Detuned Rabi Cycles of Rydberg Atoms

Xiao-Feng Shi

Phys. Rev. Applied 11, 044035 (2019) – Published 11 April 2019

Ultracold neutral atoms offer a promising route toward scalable quantum computing—a route that is unfortunately hindered by Doppler dephasing, a major stumbling block that spoils the fidelity of entangling gates. This study uses a theory based on quantum interference to show that it is possible to significantly suppress Doppler dephasing, allowing a high-fidelity entangling gate even with present-day technology. The interference-induced entanglement described here not only lays a foundation for such neutral-atom gates, but also sheds light on quantum information science involving other physical systems.

Accurate Quantum Logic Gates by Spin Echo in Rydberg Atoms

Xiao-Feng Shi

Phys. Rev. Applied 10, 034006 (2018) – Published 5 September 2018

Implementation of accurate quantum gates based on Rydberg interactions is required for scalable quantum computing with ultracold neutral atoms, but has been held back by the difficulty of realizing high-fidelity two-qubit Rydberg gates. This study proposes an easily realizable controlled-Z gate of high intrinsic fidelity, based on spin echo in Rydberg atoms. The ability to attain an accurate entangling Rydberg gate, with neither pulse shaping nor atomic vibrational-ground-state cooling, makes ultracold atoms promising for large-scale quantum computing.

Deutsch, Toffoli, and cnot Gates via Rydberg Blockade of Neutral Atoms

Xiao-Feng Shi

Phys. Rev. Applied 9, 051001 (2018) – Published 22 May 2018

Using only Deutsch gates, one could construct a quantum circuit to accomplish any feasible quantum computation, but unfortunately a working Deutsch gate has remained out of reach, due to lack of a protocol. This study proposes an easily realizable Deutsch-gate protocol, based on the blockade interactions in e.g. neutral Rydberg atoms. This protocol can be extended to realize the CNOT gate, as well as the Toffoli gate, which can be used in quantum error correction. Given the very broad applicability of these gates, this result is a significant advance in quantum information science.

Rydberg Quantum Gates Free from Blockade Error

Xiao-Feng Shi

Phys. Rev. Applied 7, 064017 (2017) – Published 12 June 2017

Rapid, accurate quantum gates are needed for an efficient quantum computer. Among the various physical platforms for logic gates, neutral atoms excited to high-lying states have met with much attention, but have been fundamentally limited by the gate protocol based on the well-known “blocking” method. Using a Rydberg interaction to tailor a generalized Rabi oscillation frequency, this study presents a class of exceedingly rapid and accurate two-bit quantum-gate protocols, with implications for quantum control across a wide range of platforms featuring two-body interactions.