Josip Kukucka

Exceptional properties such as long coherence times [1], fault tolerant single [2] and two-qubit fidelities [3,4,5,6], fast and high fidelity state read-out [7, 8, 9], together with CMOS integration capabilities [10] set spin-qubits amongst the top players in the race towards the quantum computer.

Currently, those exceptional characteristics are scattered among different spin-qubit platforms. This is where Ge kicks in. Firstly, a large spin-orbit coupling allows fast and fully electrical spin state manipulation [11, 12, 13]. Secondly, holes couple only weakly to nuclear spins. Finally, the small effective mass and the low disorder in this material reduces the fabrication complexity [14]. Recent experiments have demonstrated high-quality qubits operating in depletion mode [15], two-qubit gates [16] and a four-qubit quantum processor [17].

Here, we show our results on a singlet-triplet qubit in planar Ge. Exploiting the large and tunable out-of- plane g-factors allow X-rotation frequency of up to 600 MHz, and a quality factor exceeding 200 at a magnetic field of only 10 mT.

The reported results not only compete with state of the art spin qubits but pave also the way for on-chip co- integration with superconducting technology. Furthermore, the electrical tunability of g-factors might offer an in-situ solution for the standing problem of non-uniform spin-qubit transition frequencies, qubit addressability and crosstalk protection in dense spin-qubit arrays.

References

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[2]  Y.C.Yang et al, npj Quantum Information, 5 (2019)
[3]  A.R.Mills et al, Science Advances, 14 (2022)
[4]  X.Xue et al, Nature, 601 (2022) 343-347
[5]  A.Noiri et al, Nature, 601 (2022) 338-342
[6]  M.T.Madzik et al, Nature, 601 (2022) 348-353
[7]  G.A.Oakes et al, arxiv:2203.06608 (2022)
[8]  E.J.Connors and J.J.Nelson et al, Phys.Rev.Applied, 13 (2020) 024019
[9]  D.J.Niegemann et al, arXiv:2207.10523v1 (2022)
[10]  R.Maurand et al, Nature Communications, 7 (2016) 13575
[11]  H. Watzinger and J.Kukucka et al, Nature Communications, 9 (2018) 3092
[12]  F.N.M.Froning and L.C.Camenzind et al, Nature Nanotechnology, 16 (2021) 308-312
[13]  K.Wang and G.Xu et al, Nature Communications, 13 (2022) 206
[14]  G.Scappucci et al, Nature Reviews Materials, 6 (2021) 926-943
[15]  D.Jirovec et al, Nature Materials, 20 (2021) 1106-1112
[16]  N.W.Hendrickx and D.P.Franke et al, Nature, 577 (2020) 487-491
[17]  N.W.Hendrickx et al, Nature, 591 (2021) 580-585