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 NMR quantum computa- tion experiments, spin{1/2 nuclei, such as113Cd, 199Hg,125Te and 77Se could leverage the prospective scalable quantum computer architectures, enabling many and heteronu- clear qubits for NMR quantum information processing (QIP) implementations. A com- putational 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 in ve MRE complexes were examined using spin{orbit zeroth order regular approxi- mation (ZORA) and four{component relativistic methods. In particular the influence. of diferent conformers, basis sets, functionals and methods to treat the relativistic effects as well as solvent effects were studied. The diferences in the chemical shifts and spin{spin coupling constants between diferent low energy conformers of the stud- ied complexes were found to be very small. The TZ2P basis set was found to be the optimum choice for the studied chemical shifts, while TZ2P{J basis set was the best for couplings studied in this work. PBE0 exchange-correlation functional exhibited the best performance for studied MRE complexes. The addition of the solvent effects has not improved on the gas phase results in comparison to experiment, with the exception of the phosphorus chemical shift. The use of MRE complexes as qubit molecules for NMR QIP could face the challenges on single qubit control and multiqubit operations. They present chemical shifts appropriately dispersed, allowing the qubit addressability and exceptional large spin{spin couplings, which could reduce the time of quantum gate operations and likely preserving the coherence.