Spin-Polarized Molecular Triplet States as Qubits: Phosphorus Hyperfine Coupling in the Triplet State of Benzoisophosphinoline

Abstract

Advances in quantum information science (QIS) require the development of new molecular materials to serve as microwave addressable qubits that can be read out optically. Laser photoexcitation of organic π-conjugated molecules often results in spinpolarized phosphorescent triplet states that can be readily observed and manipulated using time-resolved electron paramagnetic resonance (EPR) techniques. Photoexcitation of Nmesityl-1,8-naphthalimide (M-NMI) and its phosphorus analogues, 2-mesitylbenzoisophosphinoline (M-BIPD) and 2-mesitylbenzoisophosphinoline oxide (M-BIPDO) results in ultrafast spin−orbit charge-transfer intersystem crossing to form the corresponding phosphorescent triplet states M-3 *NMI, M-3 *BIPD and M-3 *BIPDO. The ultrafast triplet formation dynamics, phosphorescence, and spin-polarized EPR spectra of these triplet states were examined. The most promising qubit candidate, M-3 *BIPD, was examined using pulse-EPR to measure its spin relaxation times, and pulse electron−nuclear double resonance spectroscopy to perform a two-qubit CNOT gate using the phosphorus nuclear spin.

Quantum chemical sensing using molecular triplet qubits in a flexible metal–organic framework

“…The control of MOF orientation is expected to enable more advanced quantum sensing by sophisticated qubit manipulation. Triplets can also be detected optically by phosphorescence and delayed fluorescence, leading to highly sensitive sensing and, ultimately, to single molecule quantum sensing 27,46 . The triplet-MOF complex will provide an ultra-sensitive and highly selective quantum sensing platform that will have impact in a wide range of fields such as analytical chemistry, life sciences, and medicine.…”

“…Except for a few pioneering examples [27][28][29][30] , photoexcited triplets are largely unexplored in the context of qubits. Photoexcited triplet states have the advantage that anisotropic spin-orbit coupling (SOC) allows temperature-independent sublevel selective intersystem crossing (ISC) from the photoexcited singlet state, creating highly polarized electronic states, even at room temperature [32][33][34][35] (Fig.…”

“…Unlike defect-based systems, molecular qubits [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] are uniform in structure and can be precisely controlled. Furthermore, their small size allows them to closely approach the target analyte.…”

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

“…7,8 Christensen et al also present a novel qubit found in the spin-polarized triplet state of benzoisophosphinoline, characterized by the hyperfine coupling of phosphorus. 9 By controlling the chemical environment, Xu et al study the anisotropic behavior of a single-molecule magnet within an oriented single crystal, 10 and Garcia-Garibay and colleagues embed paramagnetic organic spin centers within a metal−organic framework. 11 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.…”

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

“…These systems employ molecules with unpaired electrons that can be characterized by electron paramagnetic resonance (EPR) and measured for quantum information by optical means, such as photoluminescence. Freedman and colleagues introduce a new single-molecule magnet qubit based on a Ni 2+ complex, a concept that is further explored by Wasielewski, Han, Sherwin, Awschalom, and Freedman using a V 3+ system. , Christensen et al also present a novel qubit found in the spin-polarized triplet state of benzoisophosphinoline, characterized by the hyperfine coupling of phosphorus . By controlling the chemical environment, Xu et al study the anisotropic behavior of a single-molecule magnet within an oriented single crystal, and Garcia-Garibay and colleagues embed paramagnetic organic spin centers within a metal–organic framework .…”