23 August 2018 IQ Communication
Coherent spin–photon coupling using a resonant exchange qubit

Udson Cabral Mendes contributes to a publication in Nature

Many researchers in the field of quantum science and technology are driven by the prospect of making a substantial contribution to the development of quantum computers. Sharing this motivation, Udson Cabral Mendes, a postdoctoral fellow at the Institut quantique (IQ), investigates ways for spin quantum bits and photons to interact strongly in a quantum chip.

Spin quantum bits are a compelling option to form the building blocks of quantum computers. Indeed, their long coherence time and small physical size make them an attractive alternative for solid-state quantum computation. However, connecting different spin quantum bits across the quantum chip remains a major challenge. A first step toward addressing this issue was reported in both Science and Nature publications to which Udson is a co-author.

In an international effort, Udson and Pr Alexandre Blais combined their theoretical expertise with experimental teams from QuTech and ETH-Zurich to demonstrate, in proof-of-principle experiments, how to transfer the information encoded in a spin quantum bit to a microwave photon in a superconducting resonator. “While the idea behind both Science and Nature papers is the same, the physics of the photon-spin quantum bit coupling, devices and material used in the experiments are very different” explains Udson.

Science: Strong spin-photon coupling in silicon

In the experiment performed by the QuTech group led by Pr Lieven Vandersypen, the spin quantum bit is formed in a silicon material by confining a single electron spin in two quantum boxes – also known as double quantum dots. Using a clever trick with magnetic fields first proposed by Pr Michel Pioro-Ladrière from IQ and his team, the researchers were able to couple the electron spin to the electric field of the photon.

Nature: Coherent spin-photon coupling using a resonant exchange qubit

As for the experiment with the ETH-Zurich led by Prs Andreas Wallraff, Klaus Ensslin et Thomas Ihn, the spin quantum bit is comprised of gallium arsenide material, in which three electron spins are trapped in three quantum boxes forming a so-called resonant exchange qubit. In this device, the coupling between photon and the spin quantum bit is a result of a spin-to-charge conversion process mediated by exchange interaction.

“In future quantum computers, microwave photons could be used to transmit quantum information among spin qubits separated by a centimeter or even more in a complex chip.” adds Pr Blais.

Udson will pursue his postdoctoral fellowship at IQ until 2019 where there will be more such exciting opportunities to contribute to the development of quantum technologies.

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