Theory of hole spin qubits in silicon and germanium quantum dots

Rövid cím: 
Theory of hole spin qubits in quantum dots
2023. 04. 21. 10:15
BME building F, seminar room of the Dept. of Theoretical Physics
Stefano Bosco (Basel)

Hole spin qubits in silicon and germanium quantum dots are promising platforms for large-scale quantum computers because of their large intrinsic spin-orbit interaction, which permits efficient and ultrafast all-electric qubit control without additional components.

I will present schemes to engineer this interaction in different architectures, e.g. in the squeezed Ge quantum dots proposed in [1], aiming to optimize quantum information processing. A large spin-orbit interaction mediates a strong coupling between hole spins and microwave photons. Hole spin-photon coupling is not only strong but is also electrically tunable and can be engineered to be longitudinal [2], where the microwave field couples to the phase of the spin. This type of coupling enables exact protocols for fast and high-fidelity two-qubit gates that could even work at high temperatures.

On the other hand, the spin-orbit interaction also couples the spin to charge noise, causing the qubit to decohere. To overcome this issue, I will discuss qubit designs that enable sweet spots where charge noise can be completely removed [3]. These sweet spots appear in hole spin qubits encoded in silicon fin field-effect transistors, devices commonly used in the modern semiconductor industry. In these qubits, the noise caused by hyperfine interactions with nuclear spins -another leading source of decoherence in spin qubits- is also strongly suppressed, greatly enhancing their coherence, and reducing the need for expensive isotopically purified materials [4].

Moreover, the large spin-orbit interaction in hole quantum dots enables phenomena that are out of reach in competing architectures. For example, in these systems the exchange interactions between nearby spins can be highly anisotropic, even at zero magnetic fields, opening the way to novel protocols to enhance the speed and fidelity of two-qubit gates in future quantum processors. 


[1] Bosco et al (2021) PRB 104

[2] Bosco et al (2022) PRL 129

[3] Bosco Hetenyi Loss (2021) PRX Quantum 2

[4] Bosco and Loss (2021) PRL 127