# Quantum bath control with nuclear spin state selectivity via pulse-adjusted dynamical decoupling

## TL;DR

This paper introduces a novel approach to dynamical decoupling in quantum systems by intentionally adjusting pulse errors, enabling nuclear spin state selectivity and efficient quantum bath polarization.

## Contribution

It demonstrates that deliberate pulse deviations in dynamical decoupling can achieve nuclear state selectivity and enhance quantum bath control, a departure from traditional error minimization.

## Key findings

- Achieved nuclear spin state selectivity using pulse-adjusted dynamical decoupling.
- Enabled efficient polarization transfer to the $^{13}$C quantum bath.
- Demonstrated the generality of the physical mechanism for quantum control applications.

## Abstract

Dynamical decoupling (DD) is a powerful method for controlling arbitrary open quantum systems. In quantum spin control, DD generally involves a sequence of timed spin flips ($\pi$ rotations) arranged to average out or selectively enhance coupling to the environment. Experimentally, errors in the spin flips are inevitably introduced, motivating efforts to optimise error-robust DD. Here we invert this paradigm: by introducing particular control "errors" in standard DD, namely a small constant deviation from perfect $\pi$ rotations (pulse adjustments), we show we obtain protocols that retain the advantages of DD while introducing the capabilities of quantum state readout and polarisation transfer. We exploit this nuclear quantum state selectivity on an ensemble of nitrogen-vacancy centres in diamond to efficiently polarise the $^{13}$C quantum bath. The underlying physical mechanism is generic and paves the way to systematic engineering of pulse-adjusted protocols with nuclear state selectivity for quantum control applications.