Selective Addressing of Coupled Qubits via Complex Frequency Zero Targeting

TL;DR

This paper presents a novel method using complex frequency pulses to selectively control coupled qubits in lossy quantum systems, effectively reducing crosstalk and overcoming limitations of traditional time-reversal based approaches.

Contribution

It introduces a robust CF pulse technique tailored for dissipative, coupled qubit systems, validated through theoretical modeling and realistic simulations.

Findings

CF pulses effectively excite target qubits with minimal crosstalk

Method outperforms conventional Gaussian pulses in selectivity

Validated on realistic Josephson junction-based transmon qubits

Abstract

Achieving precise, individual control over qubits within scalable quantum processors is critically hampered by parasitic couplings and spectral crowding, leading to detrimental crosstalk. While optimal absorption strategies based on time-reversal symmetry have shown promise for single emitters, their applicability is limited in realistic multi-qubit systems where realistic losses break time-reversal symmetry. This work introduces a robust approach using complex frequency (CF) pulses specifically tailored to the complex reflection zeros of the complete, coupled, and explicitly lossy qubit-waveguide system. This method circumvents the limitations of idealized time-reversal arguments by directly engaging with the dissipative system's true response characteristics. We first develop a theoretical framework for a system of three coupled two-level emitters, employing Heisenberg equations to derive the system's response and design appropriate CF pulses that inherently account for the system's dissipative nature. The efficacy and practicality of this approach are then validated through comprehensive transient simulations for a realistic model of three Josephson junction-based transmon qubits, explicitly including intrinsic qubit losses. Our results demonstrate that CF pulses can selectively excite a target qubit with significantly suppressed crosstalk to neighboring qubits, markedly outperforming conventional Gaussian pulses of comparable energy.