arXiv subjects

Ruikang Liang

Publications and source records attributed to Ruikang Liang.

4 recordsLinked to original sources

arXiv2026

Exponential suppression of bit-flip errors in dissipative cat qubits

We study the infinite-dimensional Lindblad generator $L_ε=D[a^2-α^2]+εD[a]$, describing a dissipative cat qubit subject to single-photon loss. For sufficiently large $α$ and sufficiently small $ε>0$, we identify a two-dimensional spectral subspace near zero and establish an upper bound on the slow decay rate that decreases exponentially with $α^2$, uniformly in $ε$. This proves exponential suppression of bit-flip errors.

math-ph↗

arXiv2026

Enhancing the controllability of quantum systems via a static field

We provide a sufficient condition for the controllability of a bilinear closed quantum system steered by a static field and a time-varying field, based on the notion of weakly conically connected spectrum. More precisely, we show that if a controlled Hamiltonian with two inputs has a weakly conically connected spectrum, then, freezing one of the two inputs at almost every constant value, the obtained single-input system is controllable. The result is illustrated with two examples, enantio-selective excitation in a chiral molecule and the driven Jaynes-Cummings Hamiltonian.

math.OC↗

arXiv2025

An approach to control design for two-level quantum ensemble systems

Quantum ensemble systems arise in a variety of applications, including NMR spectroscopy and robust quantum control. While their theoretical properties have been extensively studied, relatively little attention has been given to the explicit construction of control inputs. In this paper, we address this gap by presenting a fully implementable control strategy for a one-parameter family of driftless two-level quantum systems. The proposed method is supported by rigorous analysis that guarantees accurate approximation of target distributions on SU(2). Convergence properties are established analytically, and numerical simulations are provided to demonstrate the effectiveness of the approach.

math.OC↗

arXiv2025

Ensemble control of n-level quantum systems with a scalar control

In this paper we discuss how a general bilinear finite-dimensional closed quantum system with dispersed parameters can be steered between eigenstates. We show that, under suitable conditions on the separation of spectral gaps and the boundedness of parameter dispersion, rotating wave and adiabatic approximations can be employed in cascade to achieve population inversion between arbitrary eigenstates. We propose an explicit control law and test numerically the sharpness of the conditions on several examples.

math.OC↗