Enhancing the ODMR Signal of Organic Molecular Qubits

• URL: http://arxiv.org/abs/2409.19249v2
• Date: Tue, 1 Oct 2024 18:37:49 GMT
• Title: Enhancing the ODMR Signal of Organic Molecular Qubits
• Authors: Yong Rui Poh, Joel Yuen-Zhou,
• Abstract summary: In quantum information science and sensing, electron spins are often purified into a specific polarisation through an optical-spin interface. Diamond-NV centres and transition metals are both excellent platforms for these so-called colour centres. In our earlier attempt at designing such organic high-spin $pi$-diradicals, we proposed to spin-polarise by shelving triplet $M_S=pm1$ populations as singlets.
• Score: 0.0
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: In the fields of quantum information science and sensing, electron spins are often purified into a specific polarisation through an optical-spin interface, a process known as optically-detected magnetic resonance (ODMR). Diamond-NV centres and transition metals are both excellent platforms for these so-called colour centres, while metal-free molecular analogues are also gaining popularity for their extended polarisation lifetimes, milder environmental impacts, and reduced costs. In our earlier attempt at designing such organic high-spin $\pi$-diradicals, we proposed to spin-polarise by shelving triplet $M_{S}=\pm1$ populations as singlets. This was recently verified by experiments albeit with low ODMR contrasts of <1% at temperatures above 5 K. In this work, we propose to improve the ODMR signal by moving singlet populations back into the triplet $M_{S}=0$ sublevel, designing a true carbon-based molecular analogue to the NV centre. To achieve both spin channels in $\pi$-diradicals, we leverage on weaker spin-orbit couplings beyond the nearest-neighbour approximation, made possible by careful control of orbital nodal structures and group-theoretical considerations. These analyses are further confirmed by ab initio calculations of a realistic trityl-based radical dimer. Microkinetic analyses point towards high ODMR contrasts of around 30% under experimentally-feasible conditions, a stark improvement from previous works. Finally, in our quest towards ground-state optically-addressable molecular spin qubits, we exemplify how our symmetry-based design avoids Zeeman-induced singlet-triplet mixings during electron paramagnetic resonance (EPR) experiments, setting the scene for realising electron spin qubit gates.

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