Researchers have uncovered a new technique to create and manipulate pairs of particle-like excitations in organic semiconductors that carry non-classical spin information across space, much like the entangled photon pairs in the famous Einstein-Podolsky-Roden “paradox”.
‘Unlike semiconductors, such as silicon, electrons confined in one-dimensional organic polymers do not behave as quasi-independent particles: each electron’s quantum state depends on the position, motion, and spin of all the others, which can create correlations between them with seemingly odd, action-at-a-distance properties known as quantum entanglement’ said former Winton Advanced Research Fellow Dr Alex Chin (now at the CNRS & Sorbonne Université, Paris).
The uniquely quantum phenomenon of entanglement is a critical resource for powering quantum technologies but is notoriously difficult to generate, maintain, and measure in organic nanostructures. ‘One of major problems for organic wires is that the entangled particles created from light are bound together by very strong forces, and this essentially prevents their non-local quantum properties from being seen or exploited’, continues Chin. ‘Worse still, in such close proximity exciton pairs have a strong tendency to annihilate each other, so – in order to be useful – they need to be separated within a few hundred femtoseconds after their formation’. Chin and colleagues in Paris, Cornell University and the group of Akshay Rao’s (lead author Raj Pandya; Winton Cohort 2016) have found an elegant solution to this problem, applying a sequence of ultrashort laser pulses to create and separate pairs of entangled particles – known as excitons – along the back-bones of conjugated polymers like those found in many flexible optoelectronic devices. Surprisingly, the team also found that their technique could generate entangled excitons in materials fabricated from bio-pigments, such as the carotenoids found in the shells of crustaceans. These findings have just been reported in the journal Chem.
The results not only provide a surprising experimental scheme for future studies of quantum non-locality in solid-state organics, they also open up exciting links between molecular quantum information, thermodynamics, and enhanced energy harvesting in processes such as singlet-exciton fission. Indeed, this last process (singlet fission) has recently been shown to provide many of the physical ingredients needed for quantum communications and computing (see https://www.nature.com/articles/s41598-020-75459-x).
The Cambridge and Paris researchers are currently trying to utilise and control the motion of these entangled particles in room temperature devices.