Paramagnetic molecules offer unique advantages for quantum information science owing to their spatial compactness, synthetic tunability, room-temperature quantum coherence, and potential for optical state initialization and readout. However, current optically addressable molecular qubits are hampered by rapid spin-lattice relaxation (T1) even at sub-liquid nitrogen temperatures. Here we use temperature- and orientation-dependent pulsed electron paramagnetic resonance (EPR) to elucidate the negative sign of the ground-state zero-field splitting (ZFS) and assign T1 anisotropy to specific degrees of freedom in an optically addressable S = 1 Cr(IV) molecular qubit. The anisotropy displays a distinct sin2(2θ) functional form that is not observed in S = ½ Cu(II) or V(IV) microwave addressable molecular qubits. The Cr(IV) T1 anisotropy is ascribed to couplings between electron spins and rotational motion in low-energy acoustic or pseudo-acoustic phonons. Our findings suggest that rotational degrees of freedom should be suppressed to maximize the coherence temperature of optically addressable qubits.Paramagnetic molecules offer unique advantages for quantum information science owing to their spatial compactness, synthetic tunability, room-temperature quantum coherence, and potential for optical state initialization and readout. However, current optically addressable molecular qubits are hampered by rapid spin-lattice relaxation (T1) even at sub-liquid nitrogen temperatures. Here we use temperature- and orientation-dependent pulsed electron paramagnetic resonance (EPR) to elucidate the negative sign of the ground-state zero-field splitting (ZFS) and assign T1 anisotropy to specific degrees of freedom in an optically addressable S = 1 Cr(IV) molecular qubit. The anisotropy displays a distinct sin2(2θ) functional form that is not observed in S = ½ Cu(II) or V(IV) microwave addressable molecular qubits. The Cr(IV) T1 anisotropy is ascribed to couplings between electron spins and rotational motion in low-energy acoustic or pseudo-acoustic phonons. Our findings suggest that rotational degrees of freedom should be suppressed to maximize the coherence temperature of optically addressable qubits.

The Journal of Physical Chemistry LettersAug 21, 202330 citations

Coherence and Quantum Optics VI

Joseph H. Eberly, L. Mandeļ, E. Wolf

Springer eBooksJan 1, 1989160 citations

Coherence and Quantum Optics IX

Michael Berry

Jun 13, 200713 citations

Coherent Optical Memory Based on a Laser-Written On-Chip Waveguide

Tian-Xiang Zhu, Chao Liu, Liang Zheng +3 more

Quantum memory is the core device for the construction of large-scale quantum networks. For scalable and convenient practical applications, integrated optical memories, especially on-chip optical memories, are crucial requirements because they can be easily integrated with other on-chip devices. Here, we report the coherent optical memory based on a type-IV waveguide fabricated on the surface of a rare-earth ion-doped crystal (i.e., $\mathrm{E}{\mathrm{u}}^{3+}$ : ${\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$ ). The properties of the optical transition (${}^{7}{\mathrm{F}}_{0}\ensuremath{\rightarrow}{}^{5}{\mathrm{D}}_{0}$) of the ${\mathrm{Eu}}^{3+}$ ions inside the surface waveguide are well preserved compared to those of the bulk crystal. Spin-wave atomic frequency comb storage is demonstrated inside the type-IV waveguide. The reliability of this device is confirmed by the high interference visibility of $97\ifmmode\pm\else\textpm\fi{}1\mathrm{%}$ between the retrieval pulse and the reference pulse. The developed on-chip optical memory paves the way towards integrated quantum nodes.Quantum memory is the core device for the construction of large-scale quantum networks. For scalable and convenient practical applications, integrated optical memories, especially on-chip optical memories, are crucial requirements because they can be easily integrated with other on-chip devices. Here, we report the coherent optical memory based on a type-IV waveguide fabricated on the surface of a rare-earth ion-doped crystal (i.e., $\mathrm{E}{\mathrm{u}}^{3+}$:${\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$). The properties of the optical transition (${}^{7}{\mathrm{F}}_{0}\ensuremath{\rightarrow}{}^{5}{\mathrm{D}}_{0}$) of the ${\mathrm{Eu}}^{3+}$ ions inside the surface waveguide are well preserved compared to those of the bulk crystal. Spin-wave atomic frequency comb storage is demonstrated inside the type-IV waveguide. The reliability of this device is confirmed by the high interference visibility of $97\ifmmode\pm\else\textpm\fi{}1\mathrm{%}$ between the retrieval pulse and the reference pulse. The developed on-chip optical memory paves the way towards integrated quantum nodes.

arXiv:2008.12901Physical Review AppliedNov 30, 202024 citations

\mathrm{E}{\mathrm{u}}^{3+}

{\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}

). The properties of the optical transition (${}^{7}{\mathrm{F}}_{0}\ensuremath{\rightarrow}{}^{5}{\mathrm{D}}_{0}$) of the

{\mathrm{Eu}}^{3+}

ions inside the surface waveguide are well preserved compared to those of the bulk crystal. Spin-wave atomic frequency comb storage is demonstrated inside the type-IV waveguide. The reliability of this device is confirmed by the high interference visibility of $97\ifmmode\pm\else\textpm\fi{}1\mathrm{%}$ between the retrieval pulse and the reference pulse. The developed on-chip optical memory paves the way towards integrated quantum nodes.