Arrays of covalently bound organic molecules possess potential for light-harvesting and energy transfer applications due to the strong coherent dipole-dipole coupling between the transition dipole moments of the molecules involved. Here, we show that such molecular systems, based on perylene molecules, can be considered as arrays of qubits that are amenable for laser-driven quantum coherent control. The perylene monomers exhibit dephasing times four orders of magnitude longer than a typical gating time, thus allowing for the execution of a large number of gate operations on the subpicosecond timescale. Specifically, we demonstrate quantum logic gates and entanglement in bipartite (dimer) and tripartite (trimer) systems of perylene-based arrays. In dimers, naturally entangled states with a tailored degree of entanglement can be produced. The nonlocality of the molecular trimer entanglement is demonstrated by testing Mermin's (Bell-like) inequality violation.
Arrays of covalently bound organic molecules possess potential for light-harvesting and energy transfer applications due to the strong coherent dipole-dipole coupling between the transition dipole moments of the molecules involved. Here, we show that such molecular systems, based on perylene molecules, can be considered as arrays of qubits that are amenable for laser-driven quantum coherent control. The perylene monomers exhibit dephasing times four orders of magnitude longer than a typical gating time, thus allowing for the execution of a large number of gate operations on the subpicosecond timescale. Specifically, we demonstrate quantum logic gates and entanglement in bipartite (dimer) and tripartite (trimer) systems of perylene-based arrays. In dimers, naturally entangled states with a tailored degree of entanglement can be produced. The nonlocality of the molecular trimer entanglement is demonstrated by testing Mermin's (Bell-like) inequality violation.
Abstract Over the past few decades, the manipulation of organic molecules has become a central focus in theoretical and experimental physics. These molecules are foundational to many current technologies and hold potential for future advancements, such as quantum computers. They are particularly promising for light harvesting and energy transfer applications due to the strong dipole–dipole coupling between their transition dipole moments. However, there is still a limited understanding of when quantum resources in these systems remain relevant in the presence of high noise levels. In this paper, we investigate the effects of thermal noise on dimeric perylene-based arrays, focusing on quantum resources such as Bures entanglement, Hellinger coherence, EPR steering, and Bell inequality violation in Perylene-Bisimide. We analyze how equilibrium temperature, interaction strength, and molecular transitions impact the dynamics of quantum resources. Our results indicate that varying the molecules frequency transitions and tuning the dipole–dipole interaction strength can control quantum resources and the degree of Bell inequality violation. Additionally, we find that Hellinger coherence is more resistant against thermal noise than Bures entanglement and that Bell’s inequality is not violated at infinite temperatures. Furthermore, EPR steering demonstrates greater resilience to increasing temperatures compared to Bell inequality violation.
In this work, we explore the dynamics of quantum correlations, namely coherence, entanglement, and nonlocality associated with a Bell state, in a dimeric arrangement of organic PBI molecules, mediated by dipole-dipole interactions, under time-fractional dynamics. Within the framework of the time-fractional Schrödinger equation (TFSE) with Caputo fractional derivatives, we explore system dynamics for different values of the fractional order τ, transition energies, interaction strength, and purity p. We employ the relative entropy of coherence, logarithmic entanglement entropy and concurrence, and CHSH inequality to estimate system dynamics associated with coherence, entanglement, and nonlocality, respectively. These findings highlight the role of the fractional order τ in system dynamics, including memory effects and relaxation, and thereby bring together ideas from fractional calculus and quantum information theory perspectives and discuss methodologies to control and utilize these molecular quantum correlations.
Ultracold polar molecules possess a manifold of long-lived molecular rotational states, which can be coherently controlled using microwave fields and entangled by the long-range dipole-dipole interactions between molecules. The ability to control these features at the individual molecule level provides a rich toolbox with which to engineer quantum simulations of exotic materials or build a molecular quantum computer. Until recently, this level of single molecule control has eluded researchers due to the challenges inherent in taming the complex internal structure of molecules. In this thesis, we demonstrate full control over the internal quantum states and coherent interactions of individual NaCs molecules in optical tweezers. This platform is based on coherent assembly of ultracold Na and Cs atoms trapped and cooled in separate arrays, before being magnetoassociated at a Feshbach resonance to form weakly-bound molecules. Using high-resolution spectroscopy of electronically excited molecular states, we identify an efficient two-photon pathway to the rovibrational ground state of NaCs that we use to prepare an array of ground state molecules in tweezers. We demonstrate a "magic ellipticity'' technique to eliminate differential light shifts between two molecular rotational states and achieve coherence times of up to 250(40) ms for a superposition of those states. We then show that we can rearrange molecules in an array to eliminate defects and perform single-shot readout of multiple rotational states using controlled molecule dissociation and imaging of constituent atoms at high magnetic field. Finally, we coherently control the dipole-dipole interactions between two molecules, producing a Bell state with a fidelity of 94(3) % and demonstrating a universal entangling iSWAP gate for qubits encoded in molecular hyperfine states.
Ultrafast spectroscopy of molecular systems is fundamentally constrained by the Fourier uncertainty principle: high temporal resolution smears out electronic state signatures, while high spectral resolution obscures dynamic information. Here we overcome this limitation using time-resolved quantum ghost spectroscopy (tr-QGS) with entangled photon pairs, which enables independent control of temporal and spectral scales. We apply this approach to perylene bismide (PBI-1) trimers for energy transfer,by combining a quantum description of light-molecule interaction with time-dependent density matrix renormalization group (TD-DMRG) simulations. This explicitly includes five vibrational modes and nonadiabatic coupling between electronic states. Our simulations reveal that tr-QGS uniquely captures electronic coherence oscillating at 0.7 eV for >50 fs, a signature of nonadiabatic coupling that was obscured in conventional time-resolved fluorescence due to Fourier-limited broadening. Moreover, we observe a direct transfer from electronic to vibrational coherence at 200 fs, providing real-time visualization of vibronic relaxation pathways. The entangled photon correlation enables a sensitivity below the shot-noise limit and suppresses photobleaching artifacts that plague classical measurements. These results establish tr-QGS as a transformative tool for interrogating nonadiabatic dynamics in molecular aggregates, light-harvesting complexes, and photocatalysts, offering a route to reveal quantum coherence in chemistry with unprecedented time-energy precision.
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.
Polar molecules, with their rich internal structure, offer immense potential for fundamental physics, quantum technology, and controlled chemistry. However, their utilization is currently limited because of slow and imperfect state detection and weak dipolar interaction, limiting fast and large-scale entanglement generation. We propose and analyze a scheme for quantum logic control and measurement-based state preparation in a hybrid platform of polar molecules and neutral atoms. The method leverages fast, high-fidelity atom-molecule gates and high-fidelity atomic ancilla measurements to overcome the common challenges in molecule-only platforms, while preserving their diverse structural advantages. The proposed atom-molecule controlled-phase gate is based on resonant dipole-dipole exchange between a molecular rotational transition and an atomic Rydberg transition, rendering it three orders of magnitude faster than any direct molecule-molecule entangling gate. We further study several applications of our scheme including the preparation of molecular GHZ states for quantum enhanced precision measurements, the preparation of exotic molecular qudit states with topological order, and measurement-altered criticality. Our scheme is applicable to any polar molecule. It expands the paradigm of quantum logic control and paves the way to large-scale molecular entangled states. More generally, it highlights a concrete hybrid quantum system in which each qubit is utilized in an optimal way and where the measurement-based approach can yield a significant advantage in near-term devices.