# Light-Activated Qubit Coupling in a Vanadyl Porphyrin Trimer

## TL;DR

This paper introduces a molecular system where light can control quantum interactions, enabling potential quantum computing applications.

## Contribution

The novel contribution is a light-activated molecular system that enables ultrafast and controllable qubit coupling.

## Key findings

- Photoexcitation induces a spin-quintet state within subpicosecond timescales.
- Long-lived spin polarization is observed even at room temperature.
- The system demonstrates optically controlled spin interactions in molecules.

## Abstract

Molecules provide a modular and chemically tunable platform
for
quantum information science. In recent years, significant advances
have been made in enabling optical spin initialization, coherent control,
and both optical and electrical readout of molecular qubits. Yet,
a central challenge remains: realizing scalable architectures through
the controlled and ultrafast activation of interqubit interactions.
Here, we present a molecular system composed of two vanadyl porphyrin
qubits bridged by a free-base porphyrin chromophore, where the qubits
are magnetically independent in the ground state but become coupled
upon photoexcitation. Femtosecond transient absorption and time-resolved
electron paramagnetic resonance experiments, supported by DFT calculations
and spectral simulations, reveal that photoexcitation induces the
formation of a spin-quintet state within subpicosecond time scales.
Notably, long-lived spin polarization persists up to room temperature.
Theoretical modeling offers design principles for harnessing this
mechanism in future applications. These results provide a proof of
concept for optically controlled spin interactions in molecules, paving
the way for light-activated molecular quantum gates.