Quantum computing has the potential to reduce the computational cost required for quantum dynamics simulations. However, existing quantum algorithms for coupled electron-nuclear dynamics simulation either require fault-tolerant devices, or involve the Born-Oppenheimer (BO) approximation and pre-calculation of electronic states on classical computers. We present the first quantum simulation approach for molecular vibronic dynamics in a pre-BO framework with an analog mapping of nuclear degrees of freedom, i.e. without the separation of electrons and nuclei, by mapping the molecular Hamiltonian to a device with coupled qubits and bosonic modes. We perform a proof-of-principle emulation of our ansatz using a single-mode model system which represents vibronic dynamics of chemical systems, such as nonadiabatic charge transfer involving polarization of the medium, and propose an implementation of our approach on a trapped-ion device. We show that our approach has exponential savings in resource and computational costs compared to the equivalent classical algorithms. Furthermore, our approach has a much smaller resource and implementation scaling than the existing pre-BO quantum algorithms for chemical dynamics. The low cost of our approach will enable an exact treatment of electron-nuclear dynamics on near-term quantum devices.
We present a theoretical study of the time-dependent laser alignment of molecules taking into account the hyperfine coupling due to nuclear-quadrupole interactions. The coupling of nuclear spins to the overall angular momentum of molecules significantly influences their rotational dynamics. Here, we systematically analyze the impact of the nuclear-quadrupole coupling on the rotational dynamics of the linear $\text{I}_2$ and the asymmetric-top diiodobenzene molecule induced by external laser fields. We explore different regimes of pulse shapes and laser-pulse intensities and detail under which …
Pure, highly nuclear-spin-polarized molecules have only been produced with molecular beam-separation methods, with production rates up to ${\sim}3{\times}10^{12}$ s$^{-1}$. Here, we propose the production of spin-polarized molecular photofragments from the IR-excitation and photodissociation of molecular beams, with production rates approaching the tabletop-IR-laser photon fluxes of $10^{21}$ s$^{-1}$. We give details on the production of spin-polarized molecular hydrogen and water isotopes, from formaldehyde and formic acid beams, respectively. Macroscopic quantities of these molecules are im…
Except for ortho- and para-H2, very little is known about nuclear spin isomers (or spin modifications) of molecules. The main reason is the lack of practical enrichment techniques. Recently a few enrichment methods were developed, which opened up new possibilities in the field. These methods are briefly reviewed. Substantial progress in the field has been made by the introduction of Light-Induced Drift as a gas-phase separation tool. This is illustrated by extensive data on CH3F, which reveal that the gas-phase ortho-para conversion is governed by intramolecular mixing of the nuclear spin stat…
We present a general variational approach for computing the laser-induced rovibrational dynamics of molecules taking into account the hyperfine effects of the nuclear quadrupole coupling. The method combines the general variational approach TROVE, which provides accurate rovibrational hyperfine energies and wave functions for arbitrary molecules, with the variational method RichMol, designed for generalized simulations of the rovibrational dynamics in the presence of external electric fields. We investigate the effect of the nuclear quadrupole coupling on the short-pulse laser alignment of a p…
Streaking of photoelectrons has long been used for the temporal characterization of attosecond extreme ultraviolet pulses. When the time-resolved photoelectrons originate from a coherent superposition of electronic states, they carry an additional phase information, which can be retrieved by the streaking technique. In this contribution we extend the streaking formalism to include coupled electron and nuclear dynamics in molecules as well as initial coherences and demonstrate how it offers a novel tool to monitor non-adiabatic dynamics as it occurs in the vicinity of conical intersections and …
Nuclear spin levels play an important role in understanding magnetization dynamics and implementation and control of quantum bits in lanthanide-based single-molecule magnets. We investigate the hyperfine and nuclear quadrupole interactions for $^{161}$Dy and $^{163}$Dy nucleus in anionic DyPc$_2$ (Pc=phthalocyanine) single-molecule magnets, using multiconfigurational ab-initio methods (beyond density-functional theory) including spin-orbit interaction. The two isotopes of Dy are chosen because the others have zero nuclear spin. Both isotopes have the nuclear spin $I=5/2$, although the magnitud…
Single-molecule sensitivity of nuclear magnetic resonance (NMR) and angstrom resolution of magnetic resonance imaging (MRI) are the highest challenges in magnetic microscopy. Recent development in dynamical-decoupling- (DD) enhanced diamond quantum sensing has enabled single-nucleus NMR and nanoscale NMR. Similar to conventional NMR and MRI, current DD-based quantum sensing utilizes the frequency fingerprints of target nuclear spins. The frequency fingerprints by their nature cannot resolve different nuclear spins that have the same noise frequency or differentiate different types of correlati…
Electronic decoherence processes in molecules and materials are usually thought and modeled via schemes for the system-bath evolution in which the bath is treated either implicitly or approximately. Here we present computations of the electronic decoherence dynamics of a model many-body molecular system described by the Su-Schreefer-Heeger Hamiltonian with Hubbard electron-electron interactions using an exact method in which both electronic and nuclear degrees of freedom are taken into account explicitly and fully quantum mechanically. To represent the electron-nuclear Hamiltonian in matrix fo…
An array of planar Penning traps, holding single electrons, can realize an artificial molecule suitable for NMR-like quantum information processing. The effective spin-spin coupling is accomplished by applying a magnetic field gradient, combined to the Coulomb interaction acting between the charged particles. The system lends itself to scalability, since the same substrate can easily accommodate an arbitrary number of traps. Moreover, the coupling strength is tunable and under experimental control. Our theoretical predictions take into account a realistic setting, within the reach of current t…
Coherence, the stability of the relative phase between quantum states, lies at the heart of quantum mechanics. Applications such as precision measurement, interferometry, and quantum computation are enabled by physical systems that have quantum states with robust coherence. With the creation of molecular ensembles at sub-$μ$K temperatures, diatomic molecules have become a novel system under full quantum control. Here, we report on the observation of stable coherence between a pair of nuclear spin states of ultracold fermionic NaK molecules in the singlet rovibrational ground state. Employing m…
We demonstrate the extension of coherence between all four two-electron spin ground states of an InAs quantum dot molecule (QDM) via non-local suppression of nuclear spin fluctuations in both constituent quantum dots (QDs), while optically addressing only the upper QD transitions. Long coherence times are revealed through dark-state spectroscopy as resulting from nuclear spin locking mediated by the exchange interaction between the QDs. Lineshape analysis provides the first measurement of the quieting of the Overhauser field distribution correlating with reduced nuclear spin fluctuations.
A single-molecule magnet placed in a magnetic field perpendicular to its anisotropy axis can be truncated to an effective two-level system, with easily tunable energy splitting. The quantum coherence of the molecular spin is largely determined by the dynamics of the surrounding nuclear spin bath. Here we report the measurement of the nuclear spin--lattice relaxation in a single crystal of the single-molecule magnet Mn$_{12}$-ac, at $T \approx 30$ mK in perpendicular fields $B_{\perp}$ up to 9 T. Although the molecular spin is in its ground state, we observe an increase of the nuclear relaxatio…
We show that two-particle interferences can be used to probe the nuclear motion in a doubly-excited hydrogen molecule. The dissociation of molecular hydrogen by electron impact involves several decay channels, associated to different molecular rotational states, which produce quantum interferences in the detection of the atomic fragments. Thanks to the correlations between the angular momentum and vibrational states of the molecule, the fragments arising from each dissociation channel carry out a phase-shift which is a signature of the molecule rotation. These phase-shifts, which cannot be obs…
Nuclear magnetic resonance (NMR) has enormous applications. Two-dimensional NMR is an essential technique to characterize correlations between nuclei and, hence, molecule structures. Towards the ultimate goal of single-molecule NMR, dynamical-decoupling- (DD) enhanced diamond quantum sensing enables the detection of single nuclear spins and nanoscale NMR. However, there is still the lack of a standard method in DD-based quantum sensing to characterize correlations between nuclear spins in single molecules. Here we present a scheme of two-dimensional DD-based quantum sensing, as a universal met…
Liquid crystals offer several advantages as solvents for molecules used for nuclear magnetic resonance quantum computing (NMRQC). The dipolar coupling between nuclear spins manifest in the NMR spectra of molecules oriented by a liquid crystal permits a significant increase in clock frequency, while short spin-lattice relaxation times permit fast recycling of algorithms, and save time in calibration and signal-enhancement experiments. Furthermore, the use of liquid crystal solvents offers scalability in the form of an expanded library of spin-bearing molecules suitable for NMRQC. These ideas ar…
Dynamic nuclear polarization (DNP) of molecules in a solution at room temperature has potential to revolutionize nuclear magnetic resonance spectroscopy and imaging. The prevalent methods for achieving DNP in solutions are typically most effective in the regime of small interaction correlation times between the electron and nuclear spins, limiting the size of accessible molecules. To solve this limitation, we design a mechanism for DNP in the liquid phase that is applicable for large interaction correlation times. Importantly, while this mechanism makes use of a resonance condition similar to …
Ultracold molecules undergo "sticky collisions" that result in loss even for chemically nonreactive molecules. Sticking times can be enhanced by orders of magnitude by interactions that lead to non-conservation of nuclear spin or total angular momentum. We present a quantitative theory of the required strength of such symmetry-breaking interactions based on classical simulation of collision complexes. We find static electric fields as small as $10$~V/cm can lead to non-conservation of angular momentum, while we find nuclear spin is conserved during collisions. We also compute loss of collision…
Lanthanide-based single-ion magnetic molecules can have large magnetic hyperfine interactions as well as large magnetic anisotropy. Recent experimental studies reported tunability of these properties by changes of chemical environments or by application of external stimuli for device applications. In order to provide insight onto the origin and mechanism of such tunability, here we investigate the magnetic hyperfine and nuclear quadrupole interactions for $^{159}$Tb nucleus in TbPc$_2$ (Pc=phthalocyanine) single-molecule magnets using multireference ab-initio methods including spin-orbit inter…
Molecular spin qubits with long spin coherence time as well as non-invasive operation methods on such qubits are in high demand. It was shown that both molecular electronic and nuclear spin levels can be used as qubits. In solid state systems with dopants, an electric field was shown to effectively change the spacing between the nuclear spin qubit levels when the electron spin density is high at the nucleus of the dopant. Inspired by such solid-state systems, we propose that divalent lanthanide (Ln) complexes with an unusual electronic configuration of Ln$^{2+}$ have a strong interaction betwe…
Intramolecular nuclear dynamics in intermolecular Coulombic electron capture
University of Tübingen（蒂宾根大学）；Institute of Physical and Theoretical Chemistry, University of Tübingen（蒂宾根大学物理与理论化学研究所）；Center for Light-Matter Interaction, Sensors and Analytics (LISA+), University of Tübingen（蒂宾根大学光-物质相互作用、传感器与分析中心）
We propose a method to measure the hyperfine vectors between a nitrogen-vacancy (NV) center and an environment of interacting nuclear spins. Our protocol enables the generation of tunable electron-nuclear coupling Hamiltonians while suppressing unwanted inter-nuclear interactions. In this manner, each nucleus can be addressed and controlled individually thereby permitting the reconstruction of the individual hyperfine vectors. With this ability the 3D-structure of spin ensembles and spins in bio-molecules can be identified without the necessity of varying the direction of applied magnetic fiel…
The possibility that quantum processing with nuclear spins might be operative in the brain is proposed and then explored. Phosphorus is identified as the unique biological element with a nuclear spin that can serve as a qubit for such putative quantum processing - a neural qubit - while the phosphate ion is the only possible qubit-transporter. We identify the "Posner molecule", $\text{Ca}_9 (\text{PO}_4)_6$, as the unique molecule that can protect the neural qubits on very long times and thereby serve as a (working) quantum-memory. A central requirement for quantum-processing is quantum entang…
The capability of generating two intense, femtosecond x-ray pulses with controlled time delay opens the possibility of performing time-resolved experiments for x-ray induced phenomena. We have applied this capability to study the photoinduced dynamics in diatomic molecules. In molecules composed of low-Z elements, \textit{K}-shell ionization creates a core-hole state in which the main decay mode is an Auger process involving two electrons in the valence shell. After Auger decay, the nuclear wavepackets of the transient two-valence-hole states continue evolving on the femtosecond timescale, lea…
Nuclear magnetic resonance (NMR) is a powerful method for determining the structure of molecules and proteins. While conventional NMR requires averaging over large ensembles, recent progress with single-spin quantum sensors has created the prospect of magnetic imaging of individual molecules. As an initial step towards this goal, isolated nuclear spins and spin pairs have been mapped. However, large clusters of interacting spins - such as found in molecules - result in highly complex spectra. Imaging these complex systems is an outstanding challenge due to the required high spectral resolution…
The Posner molecule (calcium phosphate trimer), has been hypothesized to function as a biological quantum information processor due to its supposedly long-lived entangled $^{31}$P nuclear spin states. This hypothesis was challenged by our recent finding that the molecule lacks a well-defined rotational axis of symmetry -- an essential assumption in the proposal for Posner-mediated neural processing -- and exists as an asymmetric dynamical ensemble. Following up, we investigate here the spin dynamics of the molecule's entangled $^{31}$P nuclear spins within the asymmetric ensemble. Our simulati…
Reported in this paper is the impact of the fluctuations of the geometry of the nano-meter gas containers in the medium on the NMR line shape of the gas inside of the nano-containers. We calculate exactly the NMR line shape of the gas of spin-1/2 carrying molecules for two typical dynamics of the nano-container volume and the orientation with respect to the external magnetic field: (i) for a Gaussian stochastic dynamics, and (ii) for the regular harmonic vibrations. For the Gaussian ensemble of static disordered containers having an infinite correlation time, $τ_{\sf c} \to \infty $, the overa…
The detection of a nuclear spin in an individual molecule represents a key challenge in physics and biology whose solution has been pursued for many years. The small magnetic moment of a single nucleus and the unavoidable environmental noise present the key obstacles for its realization. Here, we demonstrate theoretically that a single nitrogen-vacancy (NV) center in diamond can be used to construct a nano-scale single molecule spectrometer that is capable of detecting the position and spin state of a single nucleus and can determine the distance and alignment of a nuclear or electron spin pai…
Molecular nanostructures may constitute the fabric of future quantum technologies, if their degrees of freedom can be fully harnessed. Ideally one might use nuclear spins as low-decoherence qubits and optical excitations for fast controllable interactions. Here, we present a method for entangling two nuclear spins through their mutual coupling to a transient optically-excited electron spin, and investigate its feasibility through density functional theory and experiments on a test molecule. From our calculations we identify the specific molecular properties that permit high entangling power ga…
Single-molecule nuclear magnetic resonance (NMR) is a crown-jewel challenge in the field of magnetic resonance spectroscopy and has important applications in chemical analysis and in quantum computing. Recently, it becomes possible to tackle this grand challenge thanks to experimental advances in preserving quantum coherence of nitrogen-vacancy (NV) center spins in diamond as a sensitive probe and theoretical proposals on atomic-scale magnetometry via dynamical decoupling control. Through decoherence measurement of NV centers under dynamical decoupling control, sensing of single $^{13}\textbf{…
Efficient polarization of organic molecules is of extraordinary relevance when performing nuclear magnetic resonance (NMR) and imaging. Commercially available routes to dynamical nuclear polarization (DNP) work at extremely low-temperatures, thus bringing the molecules out of their ambient thermal conditions and relying on the solidification of organic samples. In this work we investigate polarization transfer from optically-pumped nitrogen vacancy centers in diamond to external molecules at room temperature. This polarization transfer is described by both an extensive analytical analysis and …
