Enhancing NMR Quantum Computation by Exploring Heavy Metal Complexes as Multiqubit Systems: A Theoretical Investigation

Abstract

Assembled together with the most common qubits used in nuclear resonance magnetic (NMR) quantum computation experiments, spin-1/2 nuclei, such as 113 Cd, 199 Hg, 125 Te, and 77 Se, could leverage the prospective scalable quantum computer architectures, enabling many and heteronuclear qubits for NMR quantum information processing (QIP) implementations. A computational design strategy for prescreening recently synthesized complexes of cadmium, mercury, tellurium, selenium, and phosphorus (called MRE complexes) as suitable qubit molecules for NMR QIP is reported. Chemical shifts and spin−spin coupling constants (SSCCs) in five MRE complexes were examined using the spin−orbit zeroth order regular approximation (ZORA) at the density functional theory level and the four-component relativistic Dirac−Kohn−Sham approach. In particular, the influence of different conformers, basis sets, exchange−correlation functionals, and methods to treat the relativistic as well as solvent effects were studied. The differences in the chemical shifts and SSCCs between different low energy conformers of the studied complexes were found to be very small. The TZ2P basis set was found to be the optimum choice for the studied chemical shifts, while the TZ2P-J basis set was the best for the couplings studied in this work. The PBE0 exchange−correlation functional exhibited the best performance for the studied MRE complexes. The addition of solvent effects has not improved on the gas phase results in comparison to the experiment, with the exception of the phosphorus chemical shift. The use of MRE complexes as qubit molecules for NMR QIP could face the challenges in single qubit control and multiqubit operations. They exhibit chemical shifts appropriately dispersed, allowing qubit addressability and exceptionally large spin−spin couplings, which could reduce the time of quantum gate operations and likely preserve the coherence.

Extending NMR Quantum Computation Systems by Employing Compounds with Several Heavy Metals as Qubits

“…In this work, we aimed to go a step further in relation to the use of heavy metals ( 113 Cd, 199 Hg, 77 Se, and 125 Te) as qubits. Supported by the findings of our last mentioned work [20], the use of heavy metals combined with the most frequently used qubits ( 1 H, 13 C, 19 F, 29 Si, and 31 P) can boost the emergent scalable heteronuclear spin system in NMR-QIP. An NMR computer can be programmed electronically analogously to a quantum computer, but also, it can be implemented at room pressure and temperature using macroscopic liquid samples [21].…”

“…Along the same lines, our latest work [20] focused on heteronuclear systems with heavy metals such as 113 Cd, 199 Hg, 77 Se, and 125 Te as qubits for NMR-QIP. We examined the NMR parameters of metal complexes with phosphine chalcogenide ligands (called MRE) using spin-orbit ZORA and four-component relativistic methods.…”

Synthesis and structural characterization of Zn2+, Cd2+ and Hg2+ complexes with tripyrrolidinophosphine chalcogenides

“…However, the coordination chemistry of cyclic amino analogues of the type (R2N)3PE (R2N = piperidine, pyrrolidine, morpholine, etc.) is still much less studied [16][17][18][19].…”

Recent Innovations in Solid-State and Molecular Qubits for Quantum Information Applications

“…Najafi et al study superconducting resonators as a means of achieving coupling between single-molecule magnet qubits, which is necessary for the implementation of quantum logic gates . Similarly, Lino et al study a coupling strategy for nuclear-spin qubits by placing NMR-active nuclei in close proximity to each other within a single molecule or in a dimer . Kung et al describe a spintronic qubit in which circularly polarized light excites different electron transitions depending on the polarization direction .…”

“…12 Similarly, Lino et al study a coupling strategy for nuclear-spin qubits by placing NMR-active nuclei in close proximity to each other within a single molecule or in a dimer. 13 Kung et al describe a spintronic qubit in which circularly polarized light excites different electron transitions depending on the polarization direction. 14 Lee and colleagues report a new tunnel barrier material for a transmon qubit that operates by measuring the voltage across a superconductor junction to enable novel quantum circuit elements.…”