Researchers Observe Spin Electric Transitions, Paving Way for Quantum Computing Advancements

Researchers from various international institutes have made a significant breakthrough in quantum computing by observing spin electric transitions in a molecular exchange qubit, specifically in a molecular spin triangle Fe3. This is the first experimental evidence of such transitions in polynuclear complexes. The team used low-temperature magnetic far IR spectroscopy for the experiment and introduced the concept of a generalized exchange qubit. This research could potentially lead to the development of more efficient and powerful quantum computers in the future.

What are Spin Electric Transitions in Molecular Exchange Qubits?

A team of researchers from Laboratoire National des Champs Magnétiques Intenses, Paul Scherrer Institute, Institut de Chimie de Strasbourg, and Centro S3 CNR Istituto di Nanoscienze have made a significant breakthrough in the field of quantum computing. They have observed spin electric transitions in a molecular exchange qubit, specifically in a molecular spin triangle Fe3. This is the first experimental evidence of such transitions in polynuclear complexes.

The team used low-temperature magnetic far IR spectroscopy to perform the experiment. The co-presence of electric and magnetic dipole transitions allowed them to estimate the spin electric coupling. They also introduced the concept of a generalized exchange qubit, which applies to a wide class of molecular spin triangles and includes the scalar chirality and the partial spin sum qubits as special cases.

How are Electron Spins Manipulated?

Traditionally, the manipulation of electron spin magnetization is achieved with resonant spectroscopy techniques such as Electron Paramagnetic Resonance (EPR). These techniques drive the system via the magnetic field component of the radiation. However, multispin systems offer the possibility of going beyond this paradigm of encoding qubits in decoherence-free subspaces and of performing the manipulation by electrical means.

Polynuclear magnetic molecules represent a wide class of highly engineerable multispin systems. Spin triangles, among the first and best explored polynuclear magnetic molecules, have known a renewed interest in the last years due to their possible use for the implementation of the spin chirality qubit. Such encoding would allow the qubit manipulation by localized and rapidly oscillating electric fields.

What are the Challenges in Observing Spin Electric Transitions?

The actual observation of spin electric transitions in polyatomic magnetic molecules has so far remained elusive. The challenge is two-fold and includes at a general level the identification of molecules with a sizable magneto-electric (ME) coupling and more specifically a fortunate correspondence between the energies of the electrically addressable transitions within the molecule and the frequency range of the experimental technique.

Techniques utilizing resonators such as EPR are constrained to fixed frequencies and cannot be tuned at will to the excitation energies of different molecules. Moreover, they are optimized to expose the sample to only the B1 component of the incipient radiation. On the other hand, broadband techniques that are based on coplanar waveguides combined with microwave signal generators are constrained to frequencies below 100 GHz and are capable of addressing only a few examples of spin triangles with very weak interactions.

How was the Experiment Conducted?

The molecule selected for this demonstration is one for which ME coupling has been experimentally observed through EPR spectroscopy. In particular, it was shown by two of the authors that static electric fields of the order of 107 V/m modify the intensity of the continuous wave EPR spectra of the Fe3 complex. Using pulsed EPR spectroscopy, they have shown that pulsed electric fields can dynamically drive the magnetizations, a result that represents a significant step towards the electrical control of the spin.

The Fe3 molecule also allows one to address the second challenge mentioned above. In this respect, one needs molecules whose relevant transitions, for example, the doublet-doublet energy gaps, fall in an experimentally accessible spectral region. According to their previous investigations, the doublet-doublet gap of Fe3 should approximately be 50-55 cm-1, i.e., within the THz gap.

What are the Implications of this Research?

The researchers used MFIR spectroscopy to obtain the first observation of spin electric transitions in polynuclear molecular complexes and provide an estimate of the ME coupling. Moreover, they showed that the Fe3 complex implements a generalized qubit amenable to electrical control and characterized by a hybrid degree of freedom.

This research represents a significant step towards the electrical control of the spin, which is a crucial aspect of quantum computing. The findings could potentially lead to the development of more efficient and powerful quantum computers in the future.