The famous thought-experiment of Schrödinger, where he imagined a cat to be dead and alive at the same time, represents the paradoxical behavior of quantum systems. While microscopic objects can be in a superposition of states, what we call quantum coherence, macroscopic objects cannot. The frontier between these two worlds is given by the interaction of the object with its noisy environment.
A main challenge in quantum physics hence lies in achieving coherent control of a quantum system through cleverly engineering coupling schemes without degrading its coherence properties. Such quantum systems, also called
qubits, find increasing interest for quantum computing and quantum simulation.
A promising candidate for these applications is spins trapped in
quantum dots*. However, as spin-spin interactions are short-range, the construction of large quantum processors with spin qubits is limited and hence a long-range interaction is sought for. By using a system that amplifies electromagnetic microwaves (a superconducting resonator), the coupling of spin qubits to microwave photons will allow such long-range spin-spin interaction in the future. To achieve this, the delocalization of a spin in a double quantum dot ('flopping mode' (FM) qubits), which confers a sizeable electric dipole to the spin, is essential in order to realize strong spin-photon coupling. However, current implementations of this system have so far shown reduced performances.
This study presents a novel hole-based flopping mode (FM) spin qubit in a silicon nanowire coupled to a niobium nitride microwave resonator. Two unprecedented discoveries for this system have been made. First, the achievement of high quantum performances, and second, the identification of its main limiting factor - noise in the electromagnetic environment.
This promising finding calls for a mitigation of this well understood noise source, regularly tackled by improving the electromagnetic environment.
With the limit on quantum properties identified, spin-photon coupling can be implemented without tradeoff. This places the hole spin flopping-mode qubit as a promising tool to leverage light-matter interaction, such as entangling distant spins, or fast spin state measurement.
"flopping mode" spin qubit
*: a delocalized spin qubit between two quantum dots with a large electric dipole.
hole*: absence of an electron in a semiconductor.
quantum dots*: artificial atoms where single electrons or holes are trapped.
Tutelles UMR : CEA, UGA, Grenoble INP - UGA.
Fundings : European Union’s Horizon 2020 research and innovation programme, National Strategy France 2030, spin–photon PEPR chair, Spanish Ministry of Science, innovation and Universities.
Collaborations : Université Grenoble Alpes (UGA), CEA, IRIG-MEM-L_Sim, Grenoble, France.
Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas, Madrid 28049, Spain.
Université Grenoble Alpes (UGA), CEA, LETI, Minatec Campus, Grenoble, France.