Electronic Spin Qubit Candidates Arrayed within Layered Two-Dimensional Polymers

Abstract

Molecular electronic spin qubits are promising candidates for quantum information science applications because they can be reliably produced and engineered via chemical design. Embedding electronic spin qubits within two-dimensional polymers (2DPs) offers the possibility to systematically engineer inter-qubit interactions while maintaining long coherence times, both of which are prerequisites to their technological utility. Here, we introduce electronic spin qubits into a diamagnetic 2DP by n-doping naphthalene diimide subunits with varying amounts of CoCp 2 and analyze their spin densities by quantitative electronic paramagnetic resonance spectroscopy. Low spin densities (e.g., 6.0 × 10 12 spins mm −3 ) enable lengthy spin−lattice (T 1 ) and spin−spin relaxation (T 2 ) times across a range of temperatures, ranging from T 1 values of 164 ms at 10 K to 30.2 μs at 296 K and T 2 values of 2.36 μs at 10 K to 0.49 μs at 296 K for the lowest spin density sample examined. Higher spin densities and temperatures were both found to diminish T 1 times, which we attribute to detrimental cross-relaxation from spin− spin dipolar interactions and spin−phonon coupling, respectively. Higher spin densities decreased T 2 times and modulated the T 2 temperature dependence. We attribute these differences to the competition between hyperfine and dipolar interactions for electron spin decoherence, with the dominant interaction transitioning from the former to the latter as spin density and temperature increase. Overall, this investigation demonstrates that dispersing electronic spin qubits within layered 2DPs enables chemical control of their inter-qubit interactions and spin decoherence times.

Crystalline Arrays of Copper Porphyrin Qubits Based on Ion-Paired Frameworks

“…We attribute this trend to the decreasing spin density per unit cell (0.196, 0.162, and 0.142 spins nm –3 , respectively) and the increasing Cu 2+ nearest-neighbor distance (10.6, 17.7, 19.9 Å, respectively) from 5 to 7 to 4 . We conclude that the reduced spin density leads to weaker dipolar coupling between nearby qubits and yields longer T m , as has previously been found in qubits embedded within MOFs and 2DPs. ,, …”

“…We conclude that the reduced spin density leads to weaker dipolar coupling between nearby qubits and yields longer T m , as has previously been found in qubits embedded within MOFs and 2DPs. 1,17,19 Hyperfine coupling of the qubits to nearby 1 H nuclear spins also contributes to decoherence. Fourier analysis of the Rabi oscillations (Figures 5C and S2) collected at 5 K at the g ∥ and g ⊥ transitions revealed a peak at 12.4 and 14.1 MHz, respectively.…”

“…Quantum information science (QIS) takes advantage of materials that can obtain a quantum superposition state, which is of interest for quantum computing, quantum cryptography, and quantum sensing. − These efforts rely on the development of the quantum bit, or qubit, , and numerous qubit candidates have been studied, including trapped ions, quantum dots, and nitrogen-vacancy centers in diamond. − Molecules with unpaired electrons can also function as qubits and have the potential of being designed and tuned using synthetic and physical chemical principles. ,− Furthermore, it is now increasingly possible to design solid-state molecular assemblies to order qubits into extended arrays with emergent properties. Several types of supramolecular assemblies can incorporate molecular spins, including metal–organic frameworks (MOFs) ,− or two-dimensional polymers (2DPs) . The promise of these approaches is to tune qubit coupling, and especially their spin–lattice ( T 1 ) and spin–spin ( T m ) relaxation times …”

“…Several types of supramolecular assemblies can incorporate molecular spins, including metal−organic frameworks (MOFs) 1,15−18 or two-dimensional polymers (2DPs). 19 The promise of these approaches is to tune qubit coupling, and especially their spin−lattice (T 1 ) and spin−spin (T m ) relaxation times. 14 Framework materials are promising candidates for organizing qubits into periodic arrays.…”

Spin-Polarized Radicals with Extremely Long Spin-Lattice Relaxation Time at Room Temperature in a Metal-Organic Framework

“…T1 of polarized spins have been evaluated in various molecular materials and although those with long T1 at cryogenic temperatures have been observed, 18 T1 near room temperature is often only a few or tens of micro-seconds. 19 The development of molecular materials exhibiting ESP with a longer T1 at room temperature will be the key to expanding the scope of future molecular quantum technology.…”