Tin as a nuclear spin qubit in silicon*

Nuclear spin qubits in silicon are renowned for long coherence times and superb control fidelity, as demonstrated by donor-based systems such as implanted phosphorous.  Isoelectronic species are an intriguing alternative to donors.  Having no strong confining potential, a nuclear spin qubit can interact with an electron through a hyperfine interaction that is fully controlled by electrodes of gate-defined quantum dots (QDs).  Such electrostatic control can be used to shuttle electrons from one nuclear spin qubit to another with relative ease to mediate entanglement between distant nuclear spins.  In this talk we will discuss the potential of isoelectronic nuclear spins qubits, with an emphasis on tin [PRX Quantum 3, 040320 (2022)]. Our density-functional-theory calculations indicate an enhanced hyperfine interaction in tin relative to other isoelectronic candidates resulting in promising qubit performance.  A hyperfine-induced electron-nuclear controlled-phase (e-n-CPhase) gate operation in the tin system is predicted to be exceptionally resilient to charge or voltage noise and diabatic spin flips are suppressed with a modest magnetic field.  The only other significant source of anticipated e-n-CPhase error is from extraneous nuclear spins which may be mitigated through enrichment (to eliminate nuclear spins) and/or compensation (by tracking the slow drift in nuclear spin noise).  We predict the effectiveness of combining these mitigation strategies by calculating spin-cluster correlation expansions.  Comparing our model with experiments at 800 ppm ²⁹Si bolsters confidence in our predictions.  In addition, our experimental effort to demonstrate this unique qubit technology is ramping up, confirming the viability of tin implantation and demonstrating coherent electron shuttling.  These results lay the groundwork for realizing the promise of a QD-coupled tin qubit platform.