An international team of physicists and chemists, including scientists from the Institute of Molecular Science of the University of Valencia (ICMol), has developed a new strategy to improve the performance of quantum bits (qubits) for quantum computation: they are making these nanomagnets invisible to magnetic field noise, so the qubits behave as in a clean environment. The result, published in Nature, is another step towards one of the holy grails of modern applied Physics: the creation of quantum computers.
Compared to current computers and devices, based on transistors which process information bits in the binary form of 0s and 1s, quantum computers would bring about an exponential increase in speed when performing certain computational tasks. The huge power of qubits - the quantum analogue of the bit in computing - may end up leaving the current machines behind and revolutionizing both fundamental and applied fields, for example computational chemistry and secure telecommunications.
These advances seem possible in the atomic and subatomic world, where the physical laws governing the behaviour of these quantum objects are very different from those of the 'classical' world where we live in. In particular magnetic molecules may play the role of minimal pieces with a built-in function, to be integrated into a more complex physical setup.
However, the development of these cutting-edge devices is extremely difficult to achieve because the quantum effects which they rely on are very fragile and sensitive to the environment. Indeed, magnetic noise is the major problem faced by quantum computing based on magnetic qubits. Qubits have to communicate with each other in an environment which, if too noisy, prevents an efficient quantum information storage and processing. Alas, up to now, the same strategies that reduce this noise also impede the necessary interaction between qubits, a major hurdle.
The recent achievement precisely consists in designing magnetic molecules that become invisible when interacting with a magnetic field. That is, they are able to communicate with each other without being affected by the magnetic noise generated by both the environment and the magnetic interactions generated between them when approaching. In this sense, they are analogous to metamaterials - materials invisible to light.
To achieve this kind of invisibility, they applied the same kind of processes used by Atomic Clocks: procedures which are known as Atomic Clocks Transitions. In these transitions the resonance frequency between two atomic states (or here, molecular states) is kept constant and insensitive to external perturbations, such as those produced by a magnetic field.
This is one more step essential step to continue advancing in the design of more robust magnetic qubits. In the short term, it will improve communication between them allowing to process quantum information more efficiently. In the longer term, it will enable to build quantum computers that use this kind of magnetic molecules as essential components.
For more information, please read:
Enhancing coherence in molecular spin qubits via atomic clock transitions, original article on Nature.
Making molecular-spin qubits more robust, outreach piece on Physics Today, where several independent experts in the field put this research in perspective.