Theory and Experimental Demonstration of Quantum Invariant Filtering

TL;DR

This paper introduces Quantum Invariant Filtering (QIF), a novel method for designing quantum control protocols directly in the frequency domain to achieve precise spectral filtering on qubits, demonstrated experimentally with high fidelity.

Contribution

The paper develops a new framework, QIF, that maps desired spectral responses into feasible Hamiltonian modulations, enabling advanced quantum control and sensing.

Findings

High-fidelity spectral filtering on a nitrogen-vacancy center

Suppression of noise and coherence preservation for milliseconds

Robustness to 50% drive-amplitude errors

Abstract

Quantum control protocols are typically devised in the time domain, leaving their spectral behavior to emerge only a posteriori. Here, we invert this paradigm. Starting from a target frequency-domain filter, we employ the dynamical-invariant framework to derive the continuous driving fields that enact the chosen spectral response on a qubit. This approach, Quantum Invariant Filtering (QIF), maps arbitrary finite-impulse responses, including multi-band and phase-sensitive profiles, into experimentally feasible Hamiltonian modulations. Implemented on a single nitrogen-vacancy center in diamond, the method realizes the prescribed passbands with high fidelity, suppresses noise, and preserves coherence for milliseconds, two orders of magnitude longer than Carr-Purcell-Meiboom-Gill sequences, while remaining robust to 50% drive-amplitude errors. Our results establish QIF as a broadly applicable framework for enhanced quantum control and sensing across diverse physical platforms, including superconducting qubits, trapped ions, and nuclear magnetic resonance systems.