Employing Forbidden Transitions as Qubits in a Nuclear Spin-Free Chromium Complex

The
implementation of quantum computation (QC) would revolutionize
scientific fields ranging from encryption to quantum simulation. One
intuitive candidate for the smallest unit of a quantum computer, a
qubit, is electronic spin. A prominent proposal for QC relies on high-spin
magnetic molecules, where multiple transitions between the many MS levels are employed as qubits.
Yet, over a decade after the original notion, the exploitation of
multiple transitions within a single manifold for QC remains unrealized
in these high-spin species due to the challenge of accessing forbidden
transitions. To create a proof-of-concept system, we synthesized the
novel nuclear spin-free complex [Cr­(C3S5)3]3– with precisely tuned zero-field splitting
parameters that create two spectroscopically addressable transitions,
with one being a forbidden transition. Pulsed electron paramagnetic
resonance (EPR) measurements enabled the investigation of the coherent
lifetimes (T2) and quantum control (Rabi
oscillations) for two transitions, one allowed and one forbidden,
within the S = 3/2 spin manifold.
This investigation represents a step forward in the development of
high-spin species as a pathway to scalable QC systems within magnetic
molecules.