Abstract
Electron spins in silicon quantum dots are promising qubits due to their long coherence times, scalable fabrication, and potential for all-electrical control. However, charge noise in the host semiconductor presents a major obstacle to achieving high-fidelity single- and two-qubit gates in these devices. In this work, we measure the charge-noise spectrum of a Si/SiGe singlet-triplet qubit over nearly 12 decades in frequency using a combination of methods, including dynamically-decoupled exchange oscillations with up to 512 π pulses during the qubit evolution. The charge noise is colored across the entire frequency range of our measurements, although the spectral exponent changes with frequency. Moreover, the charge-noise spectrum inferred from conductance measurements of a proximal sensor quantum dot agrees with that inferred from coherent oscillations of the singlet-triplet qubit, suggesting that simple transport measurements can accurately characterize the charge noise over a wide frequency range in Si/SiGe quantum dots.
Highlights
Electron spins in silicon quantum dots are promising qubits due to their long coherence times, scalable fabrication, and potential for all-electrical control
Despite their long coherence times, which lead to highfidelity single-1–3 and two-qubit gates[4,5,6,7], electron spins in Si/SiGe quantum dots suffer from charge noise
Most single- and two-qubit gates rely on manipulating electrons by precisely controlling their local electrostatic potentials, which typically result from voltages applied to gate electrodes, but are affected by charge fluctuations in the environment
Summary
Dynamically-decoupled exchange oscillations in S-T0 qubits, which are useful for measuring high-frequency charge noise[14], usually involve applying X gates to refocus exchange oscillations. When VT = 0, we find that the minimum value of exchange coupling in our device is between 0.5 and 2.1 MHz, and we are not able to achieve ΔBz ≫ J To circumvent this problem, we generate a Hadamard gate H by tuning ε such that. These measurements provide a more detailed picture of the lowfrequency noise than the estimations made from the dephasing of exchange oscillations discussed above These measurements indicate that the noise is not described by a single spectral exponent across the relevant frequency range. We perform exchange-based CPMG measurements using the S-T0 qubit by refocusing exchange oscillations with 1 ≤ nπ ≤ 512 composite X gates spaced by a time interval tint during the evolution. A detailed description of the analysis of all CPMG measurements, including spin-echo measurements, is given in
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