Quantum Coherence in a Perylene-Based Metal–Organic Framework for Potential Solid-State Qubits
Chanchal Rani, Hochul Woo, Elizabeth Goodson, Juan S. Sandoval, Jonathan R. Palmer, Leila M. Foroughi, Adam J. Matzger, Michael R. Wasielewski, Theodore G. Goodson III
Metal-organic frameworks (MOFs) have emerged as promising candidates for quantum information and photonic applications due to their structural tunability and the potential to contain molecular qubits in architectures that support coherent light-matter interactions. In this study, we investigate the ultrafast coherent dynamics of a perylene-based MOF, UMCM-313, and its corresponding perylene-based organic linker crystal using time-resolved two-photon near-field scanning optical microscopy (NSOM). By tracking the electronic quantum coherence, we reveal coherent modes persisting up to several hundred femtoseconds (fs) at room temperature and extending to the picosecond regime (≈0.9-1 ps) at 173 K in the MOF, significantly longer than the coherence time observed in the organic linkers at the femtosecond scale. The enhanced electronic coherence of UMCM-313 is attributed to periodic chromophore separation and a reduced degree of homogeneous broadening. Because electron spin coherence can be several orders of magnitude longer than optical coherence, we further probed the spin coherence of photoexcited triplet states in UMCM-313 by using time-resolved and pulsed electron paramagnetic resonance (TREPR and pulse-EPR) spectroscopy. TREPR spectra reveal multiple triplet species within the framework, while pulse-EPR measurements yield a phase memory time of 237 ± 5 ns at 173 K. These results demonstrate that UMCM-313 supports both extended excitonic coherence and nanosecond spin coherence, underscoring the importance of periodic framework connectivity in sustaining phase-stable quantum states. The coexistence of electronic coherence and long-lived spin coherence highlights the potential of MOFs as hybrid platforms for quantum photonic and spintronic technologies capable of maintaining coherence under operationally accessible conditions.
Metal-organic frameworks (MOFs) have emerged as promising candidates for quantum information and photonic applications due to their structural tunability and the potential to contain molecular qubits in architectures that support coherent light-matter interactions. In this study, we investigate the ultrafast coherent dynamics of a perylene-based MOF, UMCM-313, and its corresponding perylene-based organic linker crystal using time-resolved two-photon near-field scanning optical microscopy (NSOM). By tracking the electronic quantum coherence, we reveal coherent modes persisting up to several hundred femtoseconds (fs) at room temperature and extending to the picosecond regime (≈0.9-1 ps) at 173 K in the MOF, significantly longer than the coherence time observed in the organic linkers at the femtosecond scale. The enhanced electronic coherence of UMCM-313 is attributed to periodic chromophore separation and a reduced degree of homogeneous broadening. Because electron spin coherence can be several orders of magnitude longer than optical coherence, we further probed the spin coherence of photoexcited triplet states in UMCM-313 by using time-resolved and pulsed electron paramagnetic resonance (TREPR and pulse-EPR) spectroscopy. TREPR spectra reveal multiple triplet species within the framework, while pulse-EPR measurements yield a phase memory time of 237 ± 5 ns at 173 K. These results demonstrate that UMCM-313 supports both extended excitonic coherence and nanosecond spin coherence, underscoring the importance of periodic framework connectivity in sustaining phase-stable quantum states. The coexistence of electronic coherence and long-lived spin coherence highlights the potential of MOFs as hybrid platforms for quantum photonic and spintronic technologies capable of maintaining coherence under operationally accessible conditions.
Optical quantum memories enable long-distance quantum information distribution, which is critical for establishing the global quantum Internet. Rare-earth qubits are promising candidates due to their spin-optical interfaces with excellent spin coherence and optical properties. When doped into inorganic solids, they display relatively long excited-state lifetimes and, in turn, low storage efficiencies, which are difficult to optimize via material design. Metal–organic frameworks (MOFs) allow fine-tuning of spin coherence and excited-state lifetimes through rational design of coordination environments, thereby offering alternative platforms to host rare-earth qubits. By incorporating Nd 3+ and Yb 3+ into an oxalate-based MOF, we develop frameworks that exhibit spin decoherence time exceeding 5 μs at 3.4 K, near-infrared and/or telecommunication-band photoluminescence, and excited-state lifetimes up to 150 μs. These materials hold promise with long storage times and high storage efficiencies. Spin dynamics analysis reveals design principles to further improve coherence, promoting the development of rare-earth MOFs for quantum information science.
The study of dephasing time in a material by using time-resolved two-photon near-field scanning optical microscope (NSOM) with classical light has been of great interest due to its many applications. If a material shows longer coherence time between molecules and excitation pulse,it can contain information about the material for a longer time. On the contrary, the use of quantum light for studying the molecular structure has also been of great interest in many applications. In this study, a correlation between quantum coherence of the material and the probability of absorbing classical and quantum light has been shown. The dephasing time in rhodamine-B (Rh-B) chromophores doped in polystyrene nanospheres (PS-Rh) and bare Rh-B chromophores has been observed using time-resolved two-photon NSOM at room temperature. It has been observed that the quantum coherence on a single PS bead doped with Rh-B chromophores has a longer lifetime compared to the bare Rh-B chromophores. A possible reason for longer coherence time in PS-Rh nanospheres could be the isolation of Rh-B chromophores inside the PS nanospheres, which removes the heterogeneity and local environment effects and increases the interference between the laser pulse and superposition state. The interaction of these PS-Rh nanospheres and Rh-B chromophores with classical and entangled light has also been investigated using classical and entangled two-photon absorption spectroscopies, and the cross-sections have been calculated. It was observed that doped PS-Rh nanospheres show higher nonlinear optical properties than the Rh-B chromophores. In this study, it has been shown that, in addition to the transition dipole moment and detuning energy, classical and entangled two-photon cross-sections are also being affected by the quantum coherence.
Long spin coherence times of carriers are essential for implementing quantum technologies using semiconductor devices for which, however, a possible obstacle is spin relaxation. For the spin dynamics, decisive features are the band structure, crystal symmetry, and quantum confinement. Perovskite semiconductors recently have come into focus of studies of their spin states, notivated by efficient optical access and potentially long-living coherence. Here, we report an electron spin coherence time T2 of the order of 1 ms, measured for a bulk FA0.95Cs0.05PbI3 lead halide perovskite crystal. Using periodic laser pulses, we synchronize the electron spin Larmor precession about an external magnetic field in an inhomogeneous ensemble, the effect known as spin mode locking. It appears as a decay of the optically created ensemble spin polarization within the dephasing time T2∗ of up to 20 ns and its revival during the spin coherence time T2 reaching the millisecond range. This exceptionally long spin coherence time in a bulk crystal is complemented by millisecond-long longitudinal spin relaxation times T1 for electrons and holes, measured by optically-detected magnetic resonance. These long-lasting spin dynamics highlight perovskites as promising platform for the quantum devices with all-optical control.
Dense rare-earth spin ensembles in solids offer strong collective light-matter coupling for scalable quantum technologies but are typically incompatible with long coherence times due to strong dipolar interactions. Here we challenge this paradigm by showing long-lived coherence in such systems. In a stoichiometric EuCl_{3}·6H_{2}O crystal, we achieve hyperfine coherence times T_{2}^{CPMG} of up to 15 s at 4 K, extending the zero-field value T_{2} of 1.28 ms by more than four orders of magnitude using dynamical decoupling at a zero-first-order Zeeman (ZEFOZ) transition. Homogeneous linewidth measurements reveal a substantial suppression of resonant Eu^{3+}-Eu^{3+} spin interactions introduced by the full concentration near the ZEFOZ point. Coherence remains resilient to strong local perturbations, with a 32 ms coherence time for Eu^{3+} ions adjacent to Er^{3+} dopants. These results establish stoichiometric rare-earth crystals as a promising platform for quantum memories and spin-photon interfaces, demonstrating that intrinsically high optical depth and long-lived spin coherence can coexist in a fully concentrated ensemble.
Ultrafast pulses allow observation of molecular dynamics with femtosecond time resolution through pump probe experiments. However, averaging over an ensemble of molecules tends to wash out phase sensitive information, necessary to probe quantum effects, due to the intrinsic inhomogeneity in molecular conformations, orientations and interactions that lead to unique potential energy landscapes for each molecule. It is therefore important to go beyond the ensemble average when looking at quantum dynamics of organic systems at room temperature, and resolve the behaviour of specific molecules on an individual basis. In this thesis, we show the creation, manipulation and observation of ultrafast coherent effects in single molecules at room temperature, and resolve a certain measure of environmental influence on the specific dynamics of each molecule. Moreover, we apply this insight to investigate a functional light harvesting biosystem, and lay the basis for a technique that has the time and space resolution required to observe these systems in vivo. In chapter 1, we introduce the concepts and techniques the research in this thesis is built on. In chapter 2, we treat the possibility of controlling ultrafast pulses at the high-NA diffraction limit, and come to conclusions about the procedure to follow there that hold for all pulse-shaping experiments. We show in proof of principle experiments that we can control the ultrafast characteristics of optical pulses in nanometric excitation volumes. In chapters 3 and 4 we report the creation, detection and control of ultrafast quantum dynamics in single organic molecules at room temperature. We show that manipulation of superposition states is possible in these systems within a coherence dephasing time of ~50 fs. This leads to the first observation of rabi-oscillations in room temperature single molecules, to ultrafast operation of an organic qubit, and to the creation of non-stationary superposition states (vibrational wavepackets). We probe the influence of the local environment on the composition and dynamics of these wavepackets and show we can optimize the state preparation protocol for each individual molecule in its own nanoenvironment, leading to high fidelity coherent control. In these chapters we lay out the proof of principle work of detecting the quantumdynamics of a complex system in interaction with its environment at room temperature. In chapter 5 we discuss application of these techniques to the investigation of long lived coherence in photosynthetic systems. We show that electronic coherence between different rings of the LH2 system persists to time scales of 100s of femtoseconds at room temperature. Moreover we show that the energy transfer pathways in LH2 adapt to environmentally induced changes in the molecule and that the nature of the transfer remains coherent for each pathway, providing strong evidence that coherent energy transfer is the optimum process for energy transfer in photosynthesis. Finally, in chapter 6 we take the technical development one step further and report on the creation of a framework based on plasmonic antennas that allows for control of the amplitude-phase characteristics in nanometric sized hotspot fields. We show for the first time that the ultrafast characteristics of plasmonic hotspots can directly be engineered through design of the plasmonic system and experimentally demonstrate two much-anticipated examples: a sub-diffraction resolution phase shaper and an ultrafast plasmonic switch for pump probe experiments. The results presented in this thesis form the first creation and observation of ultrafast coherent dynamics in individual molecular systems at room temperature. This is a necessary step to be able to do true quantum tomography in complex systems, resolve the influence of the environment on molecular dynamics, and investigate the physics that determines evolutionary optimization and functionality in biomolecules.
Artificial atom-like systems are a promising candidate for next generation quantum processing. Among them, dark excitons exhibit one of the longest lifetimes at high temperatures. Here, we demonstrate coherent control of dark excitonic states in metal-organic chalcogenolates (MOChas) by using an ultrafast pulse shaper at room temperature. These dark exciton states are optically accessed via two-photon absorption and directly read out with a four-wave mixing process. The system is described by a non-perturbative, two-photon Hamiltonian based on well-known atomic physics and applied to a three level system comprised of two dark excitons. Empirical and theoretical state specific optical access is shown via a simple optical pulse shape. The developed Hamiltonian-based description is a first step towards a quantum processing platform using three-level systems and two photon transitions, one example being dark excitons in the MOCha silver benzeneselenolate (mithrene). Simple conditions for gate operations are laid out and described.