Achieving dynamic manipulation and control of single molecules at high spatio-temporal resolution is pivotal for advancing atomic-scale computing and nanorobotics. However, this endeavour is critically challenged by complex nature of atomic and molecular interactions, high-dimensional characteristics of nanoscale systems, and scarcity of experimental data. Here, we present a toy model for controlling single-molecule diffusion by harnessing electrostatic forces arising from elementary surface charges within a lattice structure, mimicking embedded charges on a surface. We investigate the interplay between quantum mechanics and electrostatic interactions in single molecule diffusion processes using a combination of state-dependent diffusion equations and Green's functions. We find that surface charge density critically influences diffusion coefficients, exhibiting linear scaling akin to Coulombic forces. We achieve accurate predictions of experimental diffusion constants and extending the observed range to values reaching up to 6000 $μ\text{m}^2\text{ms}^{-1}$ and 80000 $μ\text{m}^2\text{ms}^{-1}$. The molecular trajectories predicted by our model bear resemblance to planetary motion, particularly in their gravity-assisted acceleration-like behaviour. It holds transformative implications for nanorobotics, motion control at the nanoscale, and computing applications, particularly in the areas of molecular and quantum computing where the trapping of atoms and molecules is essential. Beyond the state-of-the-art optical lattice and scanning tunnelling microscopy for atomic/molecular manipulation, our findings give unambiguous advantage of precise control over single-molecule dynamics through quantum manipulation at the angstrom scale.
Achieving dynamic manipulation and control of single molecules at high spatio-temporal resolution is pivotal for advancing atomic-scale computing and nanorobotics. However, this endeavour is critically challenged by complex nature of atomic and molecular interactions, high-dimensional characteristics of nanoscale systems, and scarcity of experimental data. Here, we present a toy model for controlling single-molecule diffusion by harnessing electrostatic forces arising from elementary surface charges within a lattice structure, mimicking embedded charges on a surface. We investigate the interplay between quantum mechanics and electrostatic interactions in single molecule diffusion processes using a combination of state-dependent diffusion equations and Green's functions. We find that surface charge density critically influences diffusion coefficients, exhibiting linear scaling akin to Coulombic forces. We achieve accurate predictions of experimental diffusion constants and extending the observed range to values reaching up to 6000 μm2ms−1 and 80000 μm2ms−1. The molecular trajectories predicted by our model bear resemblance to planetary motion, particularly in their gravity-assisted acceleration-like behaviour. It holds transformative implications for nanorobotics, motion control at the nanoscale, and computing applications, particularly in the areas of molecular and quantum computing where the trapping of atoms and molecules is essential. Beyond the state-of-the-art optical lattice and scanning tunnelling microscopy for atomic/molecular manipulation, our findings give unambiguous advantage of precise control over single-molecule dynamics through quantum manipulation at the angstrom scale.
This dissertation describes our experimental investigations of quantum transport and atomic motion control using optical potentials.The system we study consists of ultracold sodium atoms under the influence of light forces.First, we introduce the dynamics of neutral atoms in a periodic optical potential.The system resembles the textbook problem of an electron inside the crystalline lattice, and we review the main characteristics of the interaction for the atom optics case.In particular, atoms trapped in a lattice subject to large accelerations undergo Landau-Zener tunneling, process which makes the system unstable.The number of atoms trapped in the potential shows the characteristic exponential decay over time.However, deviations from this law are predicted by quantum mechanics.We use the experimental access to the non-exponential time to demonstrate the Quantum Zeno and Anti-Zeno effects.These effects show the influence of frequent observations on the decay rate of a quantum unstable system.The second part of the dissertation introduces a new system we plan to study, namely, the quantum interaction between sodium atoms in the ground ix state and a conductive surface.We are interested in the measurement of the Casimir-Polder potential with a precision of better than 1%.In order to do this, we have chosen to launch the atoms towards the surfaces at very small incident velocities (a few mm/s), and measure the influence of the interaction on the reflection probability.Atoms reflect from the purely attractive potential due to quantum reflection, an effect with no classical analogy.The experimental observation of quantum reflection requires atomic distributions with temperatures below 1 µK.For this purpose, we have produced and studied a Bose-Einstein condensate (BEC) with sodium atoms.The region where the BEC is created is separated spatially form the surfaces by a distance of 10 cm, vertically.In order to bring the atoms close to the surfaces prior to their launching, we have developed an optical elevator.The elevator uses a moving optical lattice in the regime where tunneling is negligible.Results of the macroscopic optical transport technique, and current progress towards a measurement of the Casimir-Polder interaction, are reported.
Recent theoretical and experimental advances have led to better understanding and control of simple molecules, bringing them to the forefront of quantum science. Diatomic polar molecules, with their vibrational and rotational degrees of freedom and electric dipole moment, are excellent candidates for a scalable qubit, probes of beyond-Standard Model physics, and quantum simulation of topological and chiral many-body systems. These applications call for high-phase space density (PSD) of molecules in a single quantum state. To date, the highest molecular PSD is achieved by coherently associating degenerate quantum gases of atoms into molecules. However, this requires fine-tuning of experimental parameters to maximize spatial overlap of the atomic density distributions while minimizing three-body recombination of the atoms.\nIn this thesis, we propose a bottom-up solution to gain single particle control of ultracold molecules for the first time. We use optical tweezers to deterministically assemble a single NaCs molecule in a single quantum state from a pair of Na and Cs atoms. Added benefits of using optical tweezers include: tight confinement of isolated atoms enabling cooling of Na and Cs to their quantum ground state of motion in less than 100~ms, and dynamic reconfigurability of optical tweezer arrays which will allow scaling up to defect-free arrays of single molecules. In the process, we realize a conceptually simple platform for studying atomic collisions and molecular spectra which derives its strength from the ability to gather "before" and "after" images of single atoms.
Molecules, with their rich spectrum of internal states as well as strong and tunable dipolar interactions, are promising candidates for a broad range of experiments including quantum information, quantum chemistry, precision measurement and probing physics beyond the Standard Model, and quantum simulation of interacting many-body systems. At the same time, the complexity that made them attractive also poses a significant challenge to achieve a high level of quantum control that is required in many of their potential applications. Multiple approaches are being pursued for full quantum control of molecules including association of atomic gases and direct cooling of molecules, yet it remains challenging to control molecules at single particle level due to the difficulty in tuning the atom-atom interaction and laser cooling of molecules. In this thesis, we achieved full control on a single weakly bound ground state molecule created by coherent optical association from single atoms. We first discuss the trapping and imaging of the atoms in the optical tweezer and the cooling into a single quantum state in order to achieve the quantum control of atoms. Combining this control with the resolution and flexibility of tweezers. we developed a versatile platform to study interactions between single atoms and properties of single molecules, using precise optical spectroscopy on pairs of atoms in the tweezer. Based on these studies, we proposed a promising pathway for coherent all-optical creation of molecules and experimentally demonstrated full control on the molecule including all degrees of freedom.
Quantum phenomena are typically observable at length and time scales smaller than those of our everyday experience, often involving individual particles or excitations. The past few decades have seen a revolution in the ability to structure matter at the nanoscale, and experiments at the single particle level have become commonplace. This has opened wide new avenues for exploring and harnessing quantum mechanical effects in condensed matter. These quantum phenomena, in turn, have the potential to revolutionize the way we communicate, compute and probe the nanoscale world. Here, we review developments in key areas of quantum research in light of the nanotechnologies that enable them, with a view to what the future holds. Materials and devices with nanoscale features are used for quantum metrology and sensing, as building blocks for quantum computing, and as sources and detectors for quantum communication. They enable explorations of quantum behaviour and unconventional states in nano- and opto-mechanical systems, low-dimensional systems, molecular devices, nano-plasmonics, quantum electrodynamics, scanning tunnelling microscopy, and more. This rapidly expanding intersection of nanotechnology and quantum science/technology is mutually beneficial to both fields, laying claim to some of the most exciting scientific leaps of the last decade, with more on the horizon.
Since the invention of the scanning tunnelling microscope (STM) in the early 1980s atomic level microscopy has taken on a new dimension. The STM and the atomic force microscope (AFM) have become key instruments in the study of phenomena in the smallest dimensions ranging from magnetism in ultra-thin films, through the understanding of how atoms and molecules organise themselves, to insights into the propagation of electron waves. A good understanding of these issues will facilitate the manufacture of components or devices that are a few atomic dimensions in size and this will have far-reaching implications in fields ranging from medicine through to consumer electronics. As early as the 1970s, the scientific community was discussing the possibility of embedding a few molecules, or even a single molecule, between electrodes to perform the basic switching function. This is now possible in the case of individual components but key challenges lie with the economic commercial fabrication of whole devices. A key challenge lies in determining whether such quantum computers will work and how quantum effects can be used to perform variety of previously unsuspected and potentially useful schemes of information processing.
The dynamics of an electronic wavefunction often have non-trivial consequences on its spatial distribution, for example, during tunnelling or chemical bond formation. Yet, revealing spatio-temporal coupling requires ultrafast videography at the intrinsic size of electronic wavefunctions, at the so-called space-time limit. Here we experimentally access the intrinsic quantum motion of individual electrons at the space-time limit while they are tunnelling through an energy barrier, using atomic-scale lightwave-driven scanning tunnelling microscopy with attosecond time resolution. While modulating the tunnelling barrier with two time-delayed near-infrared pulses forming phase-controlled single-cycle waveforms, isolated electron tunnelling transients shorter than 1 fs are identified. The measured spatial extension depends on the interplay of multi-photon and field-driven dynamics, as confirmed by full quantum simulations. We experimentally localize the attosecond-confined tunnelling wave packet on the angstrom scale and use it to map a single copper adatom on a silver surface. This fusion of attosecond science with atomic-scale scanning tunnelling microscopy makes it possible to study wavefunction dynamics inside atoms, molecules and solids.