Notch filtering the nuclear environment of a spin qubit

Abstract

Electron spins in gate-defined quantum dots provide a promising platform for quantum computation. In particular, spin-based quantum computing in gallium arsenide takes advantage of the high quality of semiconducting materials, reliability in fabricating arrays of quantum dots and accurate qubit operations. However, the effective magnetic noise arising from the hyperfine interaction with uncontrolled nuclear spins in the host lattice constitutes a major source of decoherence. Low-frequency nuclear noise, responsible for fast (10 ns) inhomogeneous dephasing, can be removed by echo techniques. High-frequency nuclear noise, recently studied via echo revivals, occurs in narrow-frequency bands related to differences in Larmor precession of the three isotopes Ga,Ga and As (refs 15,16,17). Here, we show that both low- and high-frequency nuclear noise can be filtered by appropriate dynamical decoupling sequences, resulting in a substantial enhancement of spin qubit coherence times. Using nuclear notch filtering, we demonstrate a spin coherence time (T) of 0.87 ms, five orders of magnitude longer than typical exchange gate times, and exceeding the longest coherence times reported to date in Si/SiGe gate-defined quantum dots.

Spectrum of the Nuclear Environment for GaAs Spin Qubits

“…For comparison with results presented in Ref. [6] we extrapolate this frequency dependence to 667 kHz. Using the extrapolated value we estimate the CPMG decay time in an experiment in which τ is fixed but n is varied, T CPMG 2 = π 2 /4S (1/2τ ).…”

Nonlinear and dot-dependent Zeeman splitting in GaAs/AlGaAs quantum dot arrays

“…The spin of an electron confined in a semiconductor quantum dot realizes an addressable and readable two-level system (qubit) with long coherence time [4,5]. Spin-orbit coupling (SOC) plays a major role in semiconductor-based devices, and understanding its details is important for the operation of spin qubits in these systems.…”

Logical Qubit in a Linear Array of Semiconductor Quantum Dots

“…There are inevitably large numbers of nuclear spins in III-V systems, requiring more reliance on dynamical decoupling. Encouragingly, dynamically decoupled coherence times approaching milliseconds appear to be feasible [37], although a fully hyperfine-compensating modification to our control scheme would require additional design in this case. Finally, our scheme could be adapted to the problem of substitutional donors coupled to SiMOS-like dots or spin-shuttling channels, in which case, its implementation would resemble the schemes indicated in Refs.…”

“…Experiments with multiple coupled qubits have demonstrated proof-of-principle computations and preliminary steps towards a logical qubit. The field of quantum-processing technology includes photons [17,22], trapped ions [14,15,23], superconducting qubits [18,19,25,[28][29][30], and spins in diamond [24,26], gallium arsenide [20,[32][33][34][35][36][37][38], and silicon [27,[39][40][41][42][43][44][45][46][47]. However, there are unique advantages to a silicon quantum processor, and the potential for high-fidelity control of longlived spin qubits motivates this proposal.…”