The spins of electrons or their vacancies (holes) are promising candidates for encoding quantum information because they can be isolated in silicon quantum dots using technology compatible with industrial microelectronics processes.
Unlike electron spins, hole spins can be manipulated by an electric field. They actually show a strong “spin-orbit interaction”, which means that the displacement of a hole induced by an electric field is coupled to the state of the spin via the “spin-orbit interaction”. Researchers at Irig have for the first time succeeded in using this effect to coherently couple a hole spin in silicon to a microwave photon.
Vibrations and hole spin resonance at the same frequency
How did you do it? “In the channel of a silicon transistor manufactured at CEA-Leti, we enclosed a hole between two gates at a very low temperature (T = 10 mK) and then connected the end of a superconducting microwave resonator to one of the two gates. When a photon is trapped in the resonator, it induces electric field fluctuations that are delivered directly to the gate of the transistor, causing the hole in the transistor channel to oscillate. works when the frequency of these oscillations is exactly the same as the resonant frequency of the spin of the hole,” explains Cécile Xinquing Yu, PhD student at Irig.
Coherently coupling a microwave photon and a hole spin qubit in silicon: Irig researchers have succeeded. This result paves the way to remote two-spin entanglement using a microwave photon as the mediator of the quantum interaction. This could be beneficial for the realization of quantum processors based on silicon spin qubits. In fact, in this configuration, the photon is absorbed to change the spin from the ↓ state to the ↑ state, and then re-emitted by changing the spin of the hole from the ↑ state to the ↓ state, and so on. The rate of this “absorption/emission” is directly related to the strength of the coupling between the spin and the photon.
By varying the orientation of the magnetic field, the researchers tracked this absorption/emission rate. The results obtained clearly show, compared to a theoretical model, that the spin and the photon are entangled thanks to the spin-orbit interaction. Note that the strongest coupling observed converts the photon into a spin excitation in less than three nanoseconds! “These results therefore show that hole spin qubits and microwave photons trapped in silicon transistors can talk to each other very quickly, much faster than their coherence time,” says Romain Maurand, physicist at Irig. This makes it possible to exchange a photon between multiple spins to achieve long-range spin-spin entanglement, which could be beneficial for the fabrication of quantum processors based on silicon spin qubits.
references
Yu CX, Zihlmann S, Abadillo-Uriel JC, Michal VP, Rambal N, Niebojewski H, Bedecarrats T, Vinet M, Dumur E, Filippone M, Bertrand B, De Franceschi S, Niquet YM, and Maurand R
Strong coupling between a photon and a hole spin in silicon.
Nature Nanotechnology, 2023.