Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session A31: Addressing Molecular Magnetic Qubits (QIS1)Focus
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Sponsoring Units: DCP GMAG Chair: Evelyn Goldfield, National Science Foundation Room: BCEC 203 |
Monday, March 4, 2019 8:00AM - 8:36AM |
A31.00001: TBD Invited Speaker: Alan Aspuru-Guzik NA |
Monday, March 4, 2019 8:36AM - 8:48AM |
A31.00002: First-principles studies of spin-electric coupling in frustrated triangular single molecule magnet qubits Fhokrul Islam, Carlo Canali, Mark Pederson The efficient manipulation of the quantum states of single-molecule magnets (SMMs) by an electric field is highly desirable for using SMMs in molecular spintronics and quantum information processing. Frustrated triangular SMMs with antiferromagnetic exchange, such as Cu3, are characterized by a doubly degenerate S=1/2 ground-state with opposite chirality. It has been proposed theoretically [1] and later verified by ab-initio calculations [2] that the lack of inversion symmetry in these triangular SMMs allows an external electric field to couple these two chiral spin states, even in the absence of spin-orbit interaction. The existence of such spin-electric coupling (SEC) has been observed only very recently in an experiment with a single crystal Fe3 SMM [3]. In this talk, following this recent development, we consider the Fe3 molecule and compare its SEC strength with the one of other triangular SMMs (Cu3, V3 and V15), discussing their advantages and disadvantages. |
Monday, March 4, 2019 8:48AM - 9:00AM |
A31.00003: Spin frustration, zero-field splittings, and Jahn-Teller effects in trinuclear copper SMMs: Insights from spin-flip calculations Pavel Pokhilko, Anna Krylov SMMs (single-molecule magnets) are molecules with several unpaired electrons that can be prepared in high-spin states and retain their magnetization for some time. From methodological point of view, SMMs are strongly correlated systems that require specially designed ab initio methods. In our group, we use spin-flip approach (SF). Starting from the highest spin state (usually triplet or quartet), SF treats in a balanced way lower-spin configurations, which is crucial for qualitatively correct description of SMMs. I will present the SF results for copper di- and triradicals. One of the systems has a spin-frustrated trinuclear copper structural motif. Natural orbital analysis indicates that the two lowest doublets and the quartet have purely covalent character thus validating Heisenberg-Dirac-van-Vleck model Hamiltonian. PBE50, a recommended functional from previous benchmarks, matches an experimental estimate for Jahn-Teller splitting of the doublets states – 19 cm-1. A large zero-field splitting, previously explained through Dzyaloshinskii-Moriya interaction, originating from spin-orbit coupling (SOC). Validation of this idea will be done using our new SOC code withing EOM-CC framework. Additional confirmation comes from El-Sayed rules, predicting a relative magnitude of SOC. |
Monday, March 4, 2019 9:00AM - 9:12AM |
A31.00004: Generalized Hartree-Fock with Non-perturbative Treatment of Strong Magnetic Field: Application to Molecular Spin Phase Transition Xiaosong Li In this work, we present a framework of ab initio variational approach |
Monday, March 4, 2019 9:12AM - 9:48AM |
A31.00005: Molecular Magnets for Information and Sensing Applications: Response to Fields and Nuclear Spins Invited Speaker: Kyungwha Park Recent advances have allowed the experimental realizations of quantum bits and quantum gates by using molecular magnets as active elements, as well as the experimental implementation of quantum algorithms within them. In particular, lanthanide-based molecular magnets are promising for such applications because of strong spin-orbit interaction, compatible molecular geometry to devices, and tunability of coupling between electron and nuclear spins via electric field. So far, there is a lack of ab-initio studies of such coupling and tuning corresponding magnetic properties for lanthanide-based molecular magnets. Nearly degenerate f-orbitals and strongly localized f-electrons suggest importance of calculations beyond density-functional theory. Here we investigate how magnetic properties of monometallic terbium-based molecular magnets are influenced by electric field and coupling to nuclear spin, using multireference quantum chemistry methods including scalar relativistic effects and spin-orbit interaction. We present effects of chemical environment and electric field on such coupling and magnetic anisotropy. |
Monday, March 4, 2019 9:48AM - 10:00AM |
A31.00006: Implementing high fidelity single and entangling two-qubit gates in multi-level systems Khadijeh Najafi, Sophia Economou, Edwin Barnes A recent experiment introduced a novel multi-level nuclear spin (3/2) of single molecule magnet TbPc2 as qubit or qudit. Due to the strong coupling of the nuclear spin to the electric field, this system exhibits simultaneously long coherence times and fast controllability. One of the important questions to address is how well one can implement quantum gates in these systems. By using a combination of analytically solvable two level dynamics and the Suzuki-Trotter product formula, we design z-rotations of high fidelity. We also investigate the implementation of two-qubit entangling gates mediated by a superconducting transmission line resonator coupling two TbPc2 qudits. |
Monday, March 4, 2019 10:00AM - 10:12AM |
A31.00007: Multireference ab initio studies of magnetic properties of TbPc2-type single-molecule magnets in different charge states Ryan Pederson, Aleksander Wysocki, Nicholas Mayhall, Kyungwha Park Lanthanide-based single-molecule magnets (SMMs) can have exceptionally large magnetic anisotropy due to interplay between the ligand crystal field and spin-orbit interaction. Among them, TbPc2 SMM was shown to be promising for quantum information science applications. Although a variety of TbPc2-type SMMs were synthesized in neutral and charged states under different chemical environment, there are no systematic theoretical studies of magnetic properties of such SMMs yet. Almost degenerate 4f orbitals demand multireference quantum chemistry calculations for the magnetic properties. Here, we investigate electronic structure and magnetic properties of TbPc2 and TbPcNc SMMs as a function of oxidation state, ligand type and distortion of molecular geometry, using first-principles relativistic multireference methods including spin-orbit interaction. By applying effective pseudospin Hamiltonian to the lowest multiplet, we examine how these chemical factors affect several important energy scales, such as tunnel splitting, exchange coupling between the Tb magnetic moment and the ligand spin, zero-field splitting, and magnetic anisotropy barrier. |
Monday, March 4, 2019 10:12AM - 10:24AM |
A31.00008: Towards magnetic resonance imaging of a single molecule. Alexei Bylinskii, Ziwei Qiu, Jeremy Amdur, Lei Sun, Dominik Bucher, Oren Ben Dor, David Glenn, Nithya Arunkumar, Elana Urbach, Tamara Sumarac, Bo Dwyer, Ronald L Walsworth, Danna Freedman, Mikhail Lukin, Hongkun Park While magnetic resonance is an established tool for applications ranging from molecular structure determination to quantum computing, it typically requires large ensembles of molecules to detect the weak magnetic signals. In order to push magnetic resonance spectroscopy and control to the single-molecule limit, we magnetically couple spin-carrying metal-organic complexes to the electron spin of an individual nitrogen-vacancy (NV) defect in diamond, which can be optically initialized and read out. The electron spin on the coordinated metal acts as a reporter of the nuclear spin positions on the complex or a target of interest attached to it, promising to extend electron paramagnetic resonance spectroscopy (EPR) to the limit of single-molecule magnetic resonance imaging (MRI). In addition, the complex can be coherently controlled via the NV center and act as a molecular qubit, which can be assembled into desired quantum spin network architectures via chemical linking. |
Monday, March 4, 2019 10:24AM - 10:36AM |
A31.00009: Magnetic Anisotropy of a Tri-anionic Complex Der-you Kao, Shawn Domagal-Goldman The trivalent chromium tri-oxalate complex, {Cr+3[(C2O4) -2]3}-3 is known to exist as a tri-anion in water. Such systems are difficult to describe with standard DFT due to the fact the HOMO level of the complex solute is pushed to higher energies than the LUMO levels of the H2O solvent. The mismatch in the solute/solvent Fermi-levels causes charge transfer from the tri-anion to the water as shown in earlier work. However, the spin of the solute complex is not affected by the unphysical charge transfer. The generalized gradient approximation gives a magnetic anisotropy for the isolated and solvated tri-anion Cr+3[(C2O4) -2]3}-3 (H2O)24 of 0.83 and 0.82 Kelvin respectively. These values of magnetic anisotropy agree with 0.89 Kelvin (0.619 cm-1), which is derived from measurement [1], and imply that the oxalates lose electrons. In this paper results on the electronic and magnetic structure of the tri-anionic complex in water are presented with and without a self-interaction corrected method as a function of cluster size. |
Monday, March 4, 2019 10:36AM - 10:48AM |
A31.00010: NSF Quantum Leap Big Idea Evelyn Goldfield We are in the midst of the second quantum revolution which aims to exploit quantum phenomena such as superposition, entanglement, interference to enable major advances in quantum sensing, quantum communication, quantum computation and quantum simulation. These advances require a broad inter-disciplinary effort which includes physical scientists (including chemical physicists and chemists of all types), computer scientists, mathematicians and engineers. The NSF's Quantum Leap (QL) Big Idea draws from all these disciplines to engage in a transformative, high-risk-high reward enterprise to address fundamental questions such as how to prepare and manipulate complex or dynamic quantum states; how to control material-light interactions to create new quantum phenomena; how to design and engineer systems that use quantum effects to their fullest extent. In this talk, I will focus on opportunities for those engaged in chemical and molecular science to engage in NSF QL related initiatives. |
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