[논문 리뷰] Room-temperature quantum sensing with photoexcited triplet electrons in organic crystals

Harpreet Singh, Noella D’Souza외 7명|arXiv (Cornell University)|2024. 02. 21.

Organic and Molecular Conductors Research인용 수 6

한 줄 요약

본 논문은 pentacene-doped p-terphenyl crystals에서 photoexcited spin-triplet electrons를 이용한 실온 양자 센싱을 시연하고, high-contrast 및 coherent control을 갖춘 optically detected magnetic resonance (ODMR)을 달성했으며, 긴 코히런스 시간을 초래하는 pulsed schemes를 포함합니다.

ABSTRACT

Quantum sensors have notably advanced high-sensitivity magnetic field detection. Here, we report quantum sensors constructed from polarized spin-triplet electrons in photoexcited organic chromophores, specifically focusing on pentacene-doped para-terphenyl (${\approx}$0.1%). We demonstrate essential quantum sensing properties at room temperature: electronic optical polarization and state-dependent fluorescence contrast, by leveraging differential pumping and relaxation rates between triplet and ground states. We measure high optically detected magnetic resonance (ODMR) contrast ${\approx}16.8\%$ of the triplet states at room temperature, along with long coherence times under spin echo and CPMG sequences, $T_2{=}2.7μ$s and $T_2^{DD}{=}18.4μ$s respectively, limited only by the triplet lifetimes. The material offers several advantages for quantum sensing, including the ability to grow large ($cm$-scale) crystals at low cost, the absence of paramagnetic impurities, and the diamagnetism of electronic states used for sensing when not optically illuminated. Utilizing pentacene as a representative of a broader class of spin triplet-polarizable organic molecules, this study highlights new potential for quantum sensing in chemical systems.

연구 동기 및 목표

• Demonstrate optical initialization and readout of photoexcited triplet spins in organic crystals at room temperature.
• Show high-contrast ODMR and coherent microwave control of triplet sublevels.
• Quantify coherence times (T2, T2DD) and relaxation (T1) in the pentacene-doped p-terphenyl system.
• Assess practical advantages of organic-crystal q-sensors for scalable, low-cost quantum sensing.

제안 방법

• Use pentacene doped into para-terphenyl crystals as a model system for triplet-based quantum sensing.
• Implement optical pumping to polarize triplet sublevels via differential intersystem crossing rates.
• Probe spin transitions with optically detected magnetic resonance (ODMR) at room temperature.
• Employ both continuous-wave and pulsed optical excitation to enhance ODMR contrast.
• Characterize coherence with Rabi, Ramsey, Hahn echo, and Carr-Purcell-Meiboom-Gill (CPMG) sequences.
• Extract sensitivity estimates from measured slope, photon counts, and readout windows.

Fig. 1: System and Principle. (A) Crystal structure of pentacene molecule doped in p -terphenyl. Primitive lattice vectors are marked $\hat{\textbf{a}}$ , $\hat{\textbf{b}}$ , and $\hat{\textbf{c}}$ , with lattice parameters: $a{=}8.2$ Å, $b{=}5.6$ Å, $c{=}13.6$ Å [ 26 ] . Molecular axis are marked

실험 결과

연구 질문

• RQ1 Can room-temperature quantum sensing be achieved with photoexcited triplet electrons in organic crystals?
• RQ2 What ODMR contrast and coherence times are attainable in pentacene-doped p-terphenyl at room temperature?
• RQ3 How do pulsed optical initialization and dynamical decoupling affect ODMR contrast and spin coherence in this system?
• RQ4 What practical advantages do organic-crystal q-sensors offer for scalable, low-cost magnetic sensing compared to inorganic defect centers?

주요 결과

• ODMR contrast up to 16.8% for the Txy transition under pulsed illumination.
• Rabi oscillations observed at 12.9 MHz demonstrating coherent control.
• T2 = 2.7 μs from Hahn echo measurements.
• T2DD = 18.4 μs with a 148 ns CPMG train.
• T1 = 22.9 μs for triplet-ground relaxation.
• Under bias B0 = 2.5 mT, DC sensitivities of 327 nT/√Hz (Txy) and 257 nT/√Hz (Txz) were achieved (volume-normalized: 24 μT μm3/2/√Hz and 19.5 μT μm3/2/√Hz, respectively).
• Pulse-laser initialization yields higher ODMR contrast (up to 16.8%) than cw illumination, with potential for further gains.

Fig. 2: ODMR of the photoexcited triplet. (A) ODMR spectrum at zero-field measured using cw-illumination protocol ( Inset (i)) at 0.6 W MW power. Data reveals three triplet transitions at 108, 1340, and 1448 MHz; linewidth $\ell{=}7$ MHz. $T_{yz}$ transition contrast is inverted in sign. (B) Linewid