Synthetic Elucidation of Design Principles for Molecular Qubits

Nathanael P. Kazmierczak, Kaitlin M. Luedecke, Elisabeth T. Gallmeier +1 more

Paramagnetic molecules offer unique advantages for quantum information science owing to their spatial compactness, synthetic tunability, room-temperature quantum coherence, and potential for optical state initialization and readout. However, current optically addressable molecular qubits are hampered by rapid spin-lattice relaxation (T1) even at sub-liquid nitrogen temperatures. Here we use temperature- and orientation-dependent pulsed electron paramagnetic resonance (EPR) to elucidate the negative sign of the ground-state zero-field splitting (ZFS) and assign T1 anisotropy to specific degrees of freedom in an optically addressable S = 1 Cr(IV) molecular qubit. The anisotropy displays a distinct sin2(2θ) functional form that is not observed in S = ½ Cu(II) or V(IV) microwave addressable molecular qubits. The Cr(IV) T1 anisotropy is ascribed to couplings between electron spins and rotational motion in low-energy acoustic or pseudo-acoustic phonons. Our findings suggest that rotational degrees of freedom should be suppressed to maximize the coherence temperature of optically addressable qubits.

Garima Chanana

S. Higashijima, Yusaku I. Kurokawa, Yoshishige Tsuchiya +3 more

Ali Abu-Nada

Abstract In this article, the hydrogen molecular ground-state energies using our algorithm based on quantum variational principle are calculated. They are calculated through a simulator since the system of the present study (i.e., the hydrogen molecule) is relatively small and hence the ground-state energies for this molecule are efficiently classically simulable using a simulator. Complete details of this algorithm are elucidated. For this, a full description on the fermions–qubits and the molecular Hamiltonian–qubit Hamiltonian transformations, is given. The authors search for qubit system parameters ( θ 0 {\theta }_{0} and θ 1 {\theta }_{1} ) that yield the minimum energies for the system and also study the ground state energies as a function of the molecular bond length. Proposed circuit is humble and does not include many parameters compared with that of Kandala et al., the authors control only two parameters ( θ 0 {\theta }_{0} and θ 1 {\theta }_{1} ).

SHUNRI ODA

Alicia B Magann, Matthew Grace, HERSCHEL A. RABITZ +1 more

Optimally-shaped electromagnetic fields have the capacity to coherently control the dynamics of quantum systems and thus offer a promising means for controlling molecular transformations relevant to chemical, biological, and materials applications.Currently, advances in this area are hindered by the prohibitive cost of the quantum dynamics simulations needed to explore the principles and possibilities of molecular control.However, the emergence of nascent quantum-computing devices suggests that efficient simulations of quantum dynamics may be on the horizon.In this article, we study how quantum computers could be employed to design optimally-shaped fields to control molecular systems.We introduce a hybrid algorithm that utilizes a quantum computer for simulating the field-induced quantum dynamics of a molecular system in polynomial time, in combination with a classical optimization approach for updating the field.Qubit encoding methods relevant for molecular control problems are described, and procedures for simulating the quantum dynamics and obtaining the simulation results are discussed.Numerical illustrations are then presented that explicitly treat paradigmatic vibrational and rotational control problems, and also consider how optimally-shaped fields could be used to elucidate the mechanisms of energy transfer in light-harvesting complexes.Resource estimates, as well as a numerical assessment of the impact of hardware noise and the prospects of near-term hardware implementations, are provided for the latter task.