Room-Temperature Quantum Coherence and Rabi Oscillations in Vanadyl Phthalocyanine: Toward Multifunctional Molecular Spin Qubits

Abstract

Here we report the investigation of the magnetic relaxation and the quantum coherence of vanadyl phthalocyanine, VOPc, a multifunctional and easy-processable potential molecular spin qubit. VOPc in its pure form (1) and its crystalline dispersions in the isostructural diamagnetic host TiOPc in different stoichiometric ratios, namely VOPc:TiOPc 1:10 (2) and 1:1000 (3), were investigated via a multitechnique approach based on the combination of alternate current (AC) susceptometry, continuous wave, and pulsed electron paramagnetic resonance (EPR) spectroscopy. AC susceptibility measurements revealed a linear increase of the relaxation rate with temperature up to 20 K, as expected for a direct mechanism, but τ remains slow over a very wide range of applied static field values (up to ∼5 T). Pulsed EPR spectroscopy experiments on 3 revealed quantum coherence up to room temperature with T(m) ∼1 μs at 300 K, representing the highest value obtained to date for molecular electronic spin qubits. Rabi oscillations are observed in this nuclear spin-active environment ((1)H and (14)N nuclei) at room temperature also for 2, indicating an outstanding robustness of the quantum coherence in this molecular semiconductor exploitable in spintronic devices.

Molecular Spins in the Context of Quantum Technologies

“…Since, for typical pulsed ESR setups, the time to manipulate an electron spin is about 10 ns, both T 1 and T 2 need to be much longer in order to observe coherent spin oscillations and, possibly to perform some error corrections. As a matter of facts, Rabi oscillations at room temperature have been recently reported in VOPc [17]. These results represent an important milestone for molecular magnetism.…”

The Rise of Single-Ion Magnets as Spin Qubits

“…Moreover, a pronounced crystal size dependence of the relaxation time was observed in complexes 6-8. Another mononuclear V(IV) based spin qubits with short V=O bond (1.58 Å) is the complex VOPc 9 (Pc = Phthalocyanine) (Figure 4a) [31,48]. Together with its d 1 electron configuration, this molecule makes a perfect two level system for spin qubit.…”

Electronic Structures, and Optical and Magnetic Properties of Quadruple-Decker Phthalocyanines

“…For instance, single-molecule magnets using copper phthalocyanine [1], nitrogen, and phosphorous atom in fullerene cages, such as N@C 60 [2], and P@C 60 , endohedral metallofullerene, such as Sc 3 N@C 80 [3], Sc 3-x YN@C 80 (CF 3 ) n [4,5], Gd x Sc 3-x N@C 80 [6], HoSc 2 N@C 80 [7], LnSc 2 N@C 80 [8], (Sc 3 N@C 80 ) 2 dimmer [9], scandium oxide endohedral metallofullerenes Sc 4 O 2 @C 80 (CF 3 ) n , Sc 4 O 2 @C 80 [10,11], and endohedral metallofullerene encapsulated within single-walled-carbon nanotube (SWCNTs) as peapods [12][13][14], were applied for controlling the magnetic interaction with entanglement of quantum spin in the spinlattice relaxation process. Experimental verification of spintronics, and nuclear magnetic resonance (NMR) quantum computers using single nitrogen vacancy defects in the center of diamonds [15], perfluorobutadienyl iron complex [16], nitrogen endohedral fullerenes, vanadium phthalocyanines [17], and single-molecule magnets [18,19] were performed for analyzing spin dynamics, Rabi oscillation, and entanglement of nuclear spin as quantum bits in quantum algorithm calculation. The Rabi oscillation at room temperatures was detected in a solid state molecular system using vanadium phthalocyanine mixed with the isostructural diamagnetic host complex using titanyl-phthalocyanine in a molar ratio of 1:1000 [17][18][19].…”

“…Experimental verification of spintronics, and nuclear magnetic resonance (NMR) quantum computers using single nitrogen vacancy defects in the center of diamonds [15], perfluorobutadienyl iron complex [16], nitrogen endohedral fullerenes, vanadium phthalocyanines [17], and single-molecule magnets [18,19] were performed for analyzing spin dynamics, Rabi oscillation, and entanglement of nuclear spin as quantum bits in quantum algorithm calculation. The Rabi oscillation at room temperatures was detected in a solid state molecular system using vanadium phthalocyanine mixed with the isostructural diamagnetic host complex using titanyl-phthalocyanine in a molar ratio of 1:1000 [17][18][19].…”