Coherent Quantum Oscillations in a Silicon Charge Qubit

TL;DR

This paper demonstrates and characterizes fast quantum oscillations in a silicon charge qubit, revealing decoherence mechanisms and showing that echo sequences can extend coherence times.

Contribution

It provides experimental evidence of coherent charge oscillations in silicon qubits and analyzes the impact of charge noise on decoherence, with techniques to mitigate it.

Findings

Measured T2* times range from 127ps to 2.1ns.

Charge-echo sequences extend T2* from 127ps to 760ps.

Decoherence is primarily caused by detuning noise.

Abstract

Fast quantum oscillations of a charge qubit in a double quantum dot fabricated in a Si/SiGe heterostructure are demonstrated and characterized experimentally. The measured inhomogeneous dephasing time T2* ranges from 127ps to ~2.1ns; it depends substantially on how the energy difference of the two qubit states varies with external voltages, consistent with a decoherence process that is dominated by detuning noise(charge noise that changes the asymmetry of the qubit's double-well potential). In the regime with the shortest T2*, applying a charge-echo pulse sequence increases the measured inhomogeneous decoherence time from 127ps to 760ps, demonstrating that low-frequency noise processes are an important dephasing mechanism.