Molecular spin qudits for quantum algorithms

Abstract

Presently, one of the most ambitious technological goals is the development of devices working under the laws of quantum mechanics. One prominent target is the quantum computer, which would allow the processing of information at quantum level for purposes not achievable with even the most powerful computer resources. The large-scale implementation of quantum information would be a game changer for current technology, because it would allow unprecedented parallelised computation and secure encryption based on the principles of quantum superposition and entanglement. Currently, there are several physical platforms racing to achieve the level of performance required for the quantum hardware to step into the realm of practical quantum information applications. Several materials have been proposed to fulfil this task, ranging from quantum dots, Bose-Einstein condensates, spin impurities, superconducting circuits, molecules, amongst others. Magnetic molecules are among the list of promising building blocks, due to (i) their intrinsic monodispersity, (ii) discrete energy levels (iii) the possibility of chemical quantum state engineering, and (iv) their multilevel characteristics that lead to Qudits, where the dimension of the Hilbert space is d > 2. Herein we review how a molecular nuclear spin qudit, (d = 4), known as TbPc, gathers all the necessary requirements to perform as a molecular hardware platform with a first generation of molecular devices enabling even quantum algorithm operations.

Synthetic Hilbert Space Engineering of Molecular Qudits: Isotopologue Chemistry

“…[30] The 159 TbPc 2 molecule is built up from an atomic core of a metal ion surrounded by a shell of organic material (Figure 3). [30] The 159 TbPc 2 molecule is built up from an atomic core of a metal ion surrounded by a shell of organic material (Figure 3).…”

“…[34] Magnetic studies showed slow relaxation leading to the observation of hysteresis loops; the tetranuclear cage being an SMM. [30] Copyright 2018, the Royal Society of Chemistry. c) Hysteresis loop showing quantum tunneling (QTM) events associated to the nuclear spins.…”

“…In our own work, we could show that the 159 TbPc 2 -SMM complex fulfills all criteria to act as qudit. [30] The 159 TbPc 2 molecule is built up from an atomic core of a metal ion surrounded by a shell of organic material (Figure 3). At low temperatures, the lanthanide-based spin behaves as simple, few-level system sufficiently decoupled from the environment allowing for long decoherence times, thereby making them ideal candidates for the implementation of qudits.…”

“…c) Hysteresis loop showing quantum tunneling (QTM) events associated to the nuclear spins. Panels a-c reproduced with permission [30]. Copyright 2018, the Royal Society of Chemistry.…”

Scalable quantum computing with qudits on a graph

“…Therefore, the reduction of the number of operations that are required for the realization of multi-qubit gates remains a crucial problem.One of possible ways to reduce the number of required operations is to use additional degrees of freedom of quantum systems. This idea has stimulated an extended activity [20,21] in theoretical [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] and experimental studies [39][40][41][42][43][44][45][46] of quantum computing models with qudits, which are d-dimensional (d > 2) quantum systems. In particular, qudits can be used for substituting ancillas [30,[37][38][39], which allows the reduction of the required number of interactions between information carriers for the realization of multi-qubit gates.…”