Infrared and Thermal-Desorption Spectroscopy of H2 and D2 in Metal Organic Frameworks

In this thesis we provide an introduction to the use of Metal-Organic Frameworks (MOFs) for hydrogen storage and for the separation of hydrogen isotopologues, H2 and D2. MOFs are a class of materials comprised of `building-block’ metal-oxide clusters connected by organic ligands, which have the capacity to adsorb molecules such as hydrogen through weak, physisorptive mechanisms. We provide some background on the quantum mechanical structure of hydrogen isotopologues, the structure of a few state-of-the-art MOFs, the quantum mechanics of infrared spectroscopy, and the desorption dynamics of adsorbates generally. We provide a description of the experimental apparatus and procedure used in this work to acquire thermal desorption (TD) and simultaneous, in situ infrared (IR) spectra. Notably, this apparatus makes use of a pressure gauge to record TD spectra—to the best of the author’s knowledge, this is the first time such an apparatus has been created and shown to produce reproducible, physically-informative TD spectra. We demonstrate the potential of this novel spectroscopic technique on three MOFs, as we report their respective TDS and IR signatures. The agreement between our TDS and IR techniques is remarkable, as is the amount of information apparent in the TD spectra, and the agreement of our TD spectra with those in the literature. With our simple technique we are able to clearly distinguish the TD spectra of H2 and D2, allowing for the evaluation of MOFs with respect to their isotopologue separating ability. In addition to a proof of concept as to the proficiency of the experimental apparatus, this work presents two main findings: that the desorption of hydrogen isotopologues from MOFs does not follow the coverage-independent Polanyi-Wigner equation, and that stronger binding MOFs exhibit diminishing returns with respect to their ability to separate hydrogen isotopologues via temperature programming. As we argue on several occasions in this thesis, the TD spectra of hydrogen desorbing from the MOFs examined with our technique do not obey the coverage-independent Polanyi-Wigner equation. This is foremost demonstrated by the poor ab initio fits of our spectra to the equation. This result is also corroborated by the coverage dependence of the TD spectra of Co-MOF-74 (dobdc), however, and further by the ramp rate dependence of these spectra. In demonstrating this result, we advise against the use of the coverage-independent Polanyi-Wigner equation—and analysis techniques based off of it—when considering the desorption of hydrogen from MOFs. As these techniques have begun to feature prominently in the literature, this result proves exceedingly pertinent. We arrive at the latter conclusion by examining the MOFs reported on as a group, and examining the separation of H2 and D2 TD peaks as a function of MOF binding energy. We conclude through experimental as well as through computational techniques that the prospect of temperature-programmed separation through total desorption of H2 and total adsorption of D2 is exceedingly bleak. This surprising result rules out the most straightforward use of MOFs for hydrogen isotopologue separation, what we name Zero Point Energy Separation (ZPES) at a single site. As the field surrounding MOFs tacitly assumes this as a promising possibility, again this result proves exceedingly pertinent. The prospect of more imaginative uses of MOFs for temperature-programmed isotopologue separation remains open, as does the possibility of isotopologue separation through other mechanisms involving MOFs

Variance-Based Sensitivity Analysis of Λ\Lambda-type Quantum Memory

The storage and retrieval of photonic quantum states, quantum memory, is a key resource for a wide range of quantum applications. Here we investigate the sensitivity of $\Lambda$-type quantum memory to experimental fluctuations and drift. We use a variance-based approach, focusing on the effects of fluctuations and drift on memory efficiency. We consider shot-to-shot fluctuations of the memory parameters, and separately we consider longer timescale drift of the control field parameters. We find the parameters that a quantum memory is most sensitive to depend on the quantum memory protocol being employed, where the observed sensitivity agrees with physical interpretation of the protocols. We also present a general framework that is applicable to other figures of merit beyond memory efficiency. These results have practical ramifications for quantum memory experiments.Comment: 8 pages, 6 figures, submitted to PR

Broadband Quantum Memory in Atomic Ensembles

Broadband quantum memory is critical to enabling the operation of emerging photonic quantum technology at high speeds. Here we review a central challenge to achieving broadband quantum memory in atomic ensembles -- what we call the 'linewidth-bandwidth mismatch' problem -- and the relative merits of various memory protocols and hardware used for accomplishing this task. We also review the theory underlying atomic ensemble quantum memory and its extensions to optimizing memory efficiency and characterizing memory sensitivity. Finally, we examine the state-of-the-art performance of broadband atomic ensemble quantum memories with respect to three key metrics: efficiency, memory lifetime, and noise.Comment: 40 pages, 11 figures, submitted to Advances in AMO Physic

High-efficiency, high-speed, and low-noise photonic quantum memory

We present a demonstration of simultaneous high-efficiency, high-speed, and low-noise operation of a photonic quantum memory. By leveraging controllable collisional dephasing in a neutral barium atomic vapor, we demonstrate a significant improvement in memory efficiency and bandwidth over existing techniques. We achieve greater than 95% storage efficiency and 26% total efficiency of 880 GHz bandwidth photons, with $\mathcal{O}(10^{-5})$ noise photons per retrieved pulse. These ultrabroad bandwidths enable rapid quantum information processing and contribute to the development of practical quantum memories with potential applications in quantum communication, computation, and networking

Infrared and Thermal-Desorption Spectroscopy of Hydrogen in Metal-Organic Frameworks

A body of research has recently formed around the study of hydrogen adsorption in Metal-Organic Frameworks (MOFs), specifically with regard to using these materials as quantum sieves for the separation of molecular deuterium (D2 ) from molecular hydrogen (H2 ). This work presents a custom apparatus for in situ Infrared (IR) and Thermal-Desorption Spectroscopy (TDS) of H2 and D2 adsorbed into MOFs, an analysis of spectroscopic results, and a close examination of current theoretical models for hydrogen-MOF TDS through computational techniques. Ultimately we conclude that the prevailing model for hydrogen-MOF desorption is unphysical, and, while there is still some industrial benefit to molecular separation with stronger binding MOFs, we present the surprising conclusion that stronger binding MOFs exhibit diminishing returns with respect to their H2 –D2 separation factor. This conclusion is supported by theoretical as well as empirical evidence