Gate-reflectometry dispersive readout and coherent control of a spin qubit in silicon

Abstract

Silicon spin qubits have emerged as a promising path to large-scale quantum processors. In this prospect, the development of scalable qubit readout schemes involving a minimal device overhead is a compelling step. Here we report the implementation of gate-coupled rf reflectometry for the dispersive readout of a fully functional spin qubit device. We use a p-type double-gate transistor made using industry-standard silicon technology. The first gate confines a hole quantum dot encoding the spin qubit, the second one a helper dot enabling readout. The qubit state is measured through the phase response of a lumped-element resonator to spin-selective interdot tunneling. The demonstrated qubit readout scheme requires no coupling to a Fermi reservoir, thereby offering a compact and potentially scalable solution whose operation may be extended above 1 K.

Operation of a silicon quantum processor unit cell above one kelvin

“…Here we demonstrate operation of a scalable silicon quantum processor unit cell, comprising two qubits confined to quantum dots (QDs) at ∼1.5 Kelvin. We achieve this by isolating the QDs from the electron reservoir, initialising and reading the qubits solely via tunnelling of electrons between the two QDs [7][8][9]. We coherently control the qubits using electrically-driven spin resonance (EDSR) [10,11] in isotopically enriched silicon 28 Si [12], attaining single-qubit gate fidelities of 98.6% and coherence time T * 2 = 2 µs during 'hot' operation, comparable to those of spin qubits in natural silicon at millikelvin temperatures [13][14][15][16].…”

Optimal dispersive readout of a spin qubit with a microwave resonator

“…This is due to the corrections to the dispersive shift appearing in Eq. (18). In the absence of these corrections, any reduction in the spin-photon coupling g s leads to a simultaneous reduction of the readout contrast and of the relaxation rate.…”

“…The effect of the corrections to the dispersive shift appearing in Eq. (18) are discussed separately in Sec. IV F.…”

“…We now relax this assumption to include all terms in Eq. (18). The optimization landscape for the SNR and measurement rate beyond the assumption χ s ≈ g 2 s /∆ is shown in Fig.…”

“…The expression for χ s corresponds to the one given in Eq. (18). In the case where the transition term is offresonant with all possible transitions between eigenstates of H 0 , the dispersive Hamiltonian may be projected into the molecular ground state |− to obtain an effective dispersive spin Hamiltonian (to an irrelevant additive constant):…”