Implementation of Quantum Level Addressability and Geometric Phase Manipulation in Aligned Endohedral Fullerene Qudits

Abstract

Endohedral nitrogen fullerenes have been proposed as building blocks for quantum information processing due to their long spin coherence time. However, addressability of the individual electron spin levels in such a multiplet system of 4S3/2 has never been achieved because of the molecular isotropy and transition degeneracy among the Zeeman levels. Herein, by molecular engineering, we lifted the degeneracy by zero‐field splitting effects and made the multiple transitions addressable by a liquid‐crystal‐assisted method. The endohedral nitrogen fullerene derivatives with rigid addends of spiro structure and large aspect ratios of regioselective bis‐addition improve the ordering of the spin ensemble. These samples empower endohedral‐fullerene‐based qudits, in which the transitions between the 4 electron spin levels were respectively addressed and coherently manipulated. The quantum geometric phase manipulation, which has long been proposed for the advantages in error tolerance and gating speed, was implemented in a pure electron spin system using molecules for the first time.

Molecular One‐ and Two‐Qubit Systems with Very Long Coherence Times

“…Molecules could solve some of such limitations since they possess properties that make them potentially very interesting for quantum applications: i) Their physicochemical properties are extensively tunable by chemical synthetic means, [ 6 ] ii) they are highly monodisperse with sizes at the nanoscale or even lower, iii) their production is scalable, iv) they possess intrinsically non‐harmonic energy spectra allowing preparation of multiple‐state coherences, [ 7 ] and v) they can be arranged in highly ordered 2D and 3D arrays, [ 8,9 ] allowing the exploitation of the dipolar interaction to implement more‐qubit operations. The quintessential figure of merit for any qubit implementation in quantum computing is the ratio of coherence time (the time available to complete a quantum algorithm) to the single gate operation time.…”

“…[ 11,24 ] In fact, hydrogen‐less N@C 60 displays very long coherence times, and has been studied in detail at the single‐qubit level. [ 7,25 ] However, the preparation of pure material is exceedingly tedious, [ 26 ] functionalization is challenging, and indeed potential two‐qubit systems based on bis‐N@C 60 ‐compounds have not been synthesized in significant quantities, as far as we are aware. [ 27 ] Persistent neutral organic radicals such as substituted triarylmethyl or 2,2,6,6‐tetramethylpiperidinyloxyl (TEMPO), on the other hand, have been extensively investigated for their use in site‐directed spin labeling, which allows determining distances in biological systems in physiologically relevant conditions or even in intact cells.…”

Spin-Electric Coupling with Anisotropy-Induced Vanishment and Enhancement in Molecular Ferroelectrics

“…Considering the strong axial anisotropy (| D | ≫ E ), in the high field limit, eq can be further simplified by replacing the D ̿ tensor with the effective ZFS parameter D eff as where D eff = (3cos 2 β D⃗ , B⃗ 0 – 1)| D |/2, β D⃗ , B⃗ 0 is the polar angle of the D ̿ tensor with respect to the magnetic field, and Ŝ z is the spin operator in the magnetic field direction.…”

“…Considering the strong axial anisotropy (|D| ≫ E), in the high field limit, eq 5 can be further simplified by replacing the D̿ tensor with the effective ZFS parameter D eff 49 as…”

Single-Molecule Fullerenes: Current Stage and Perspective

“…Third, new principles and applications based on the properties of fullerenes should be explored. In recent years, a large number of endohedral fullerenes encapsulating magnetic atoms have been studied as single-molecule magnets. − The fullerene cage can significantly reduce the relaxation processes associated with environmental fluctuations, and the carbonaceous elemental composition can effectively preserve spin coherence due to the zero nuclear spin of 12 C, leading to the emergence of quantum states with long spin coherence. − In combination with single-molecule devices, these fullerenes hold promise for a variety of quantum spin applications, including quantum computing, , atomic clock, and quantum metrology and sensing. , The atoms/clusters encapsulated in the carbon cages are good samples to study the unusual valence states, confined interactions and motions. − The atoms/clusters encapsulated in the carbon cages are good samples to study the unusual valence states, as well as confined interactions and motions. − These will greatly expand the application prospects of fullerenes and single-molecule devices.…”